1 acpi= [HW,ACPI,X86,ARM64,RISCV64] 2 Advanced Configuration and Power Interface 3 Format: { force | on | off | strict | noirq | rsdt | 4 copy_dsdt } 5 force -- enable ACPI if default was off 6 on -- enable ACPI but allow fallback to DT [arm64,riscv64] 7 off -- disable ACPI if default was on 8 noirq -- do not use ACPI for IRQ routing 9 strict -- Be less tolerant of platforms that are not 10 strictly ACPI specification compliant. 11 rsdt -- prefer RSDT over (default) XSDT 12 copy_dsdt -- copy DSDT to memory 13 For ARM64 and RISCV64, ONLY "acpi=off", "acpi=on" or 14 "acpi=force" are available 15 16 See also Documentation/power/runtime_pm.rst, pci=noacpi 17 18 acpi_apic_instance= [ACPI, IOAPIC] 19 Format: <int> 20 2: use 2nd APIC table, if available 21 1,0: use 1st APIC table 22 default: 0 23 24 acpi_backlight= [HW,ACPI] 25 { vendor | video | native | none } 26 If set to vendor, prefer vendor-specific driver 27 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 28 of the ACPI video.ko driver. 29 If set to video, use the ACPI video.ko driver. 30 If set to native, use the device's native backlight mode. 31 If set to none, disable the ACPI backlight interface. 32 33 acpi_force_32bit_fadt_addr 34 force FADT to use 32 bit addresses rather than the 35 64 bit X_* addresses. Some firmware have broken 64 36 bit addresses for force ACPI ignore these and use 37 the older legacy 32 bit addresses. 38 39 acpica_no_return_repair [HW, ACPI] 40 Disable AML predefined validation mechanism 41 This mechanism can repair the evaluation result to make 42 the return objects more ACPI specification compliant. 43 This option is useful for developers to identify the 44 root cause of an AML interpreter issue when the issue 45 has something to do with the repair mechanism. 46 47 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 48 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 49 Format: <int> 50 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 51 debug output. Bits in debug_layer correspond to a 52 _COMPONENT in an ACPI source file, e.g., 53 #define _COMPONENT ACPI_EVENTS 54 Bits in debug_level correspond to a level in 55 ACPI_DEBUG_PRINT statements, e.g., 56 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 57 The debug_level mask defaults to "info". See 58 Documentation/firmware-guide/acpi/debug.rst for more information about 59 debug layers and levels. 60 61 Enable processor driver info messages: 62 acpi.debug_layer=0x20000000 63 Enable AML "Debug" output, i.e., stores to the Debug 64 object while interpreting AML: 65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 66 Enable all messages related to ACPI hardware: 67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 68 69 Some values produce so much output that the system is 70 unusable. The "log_buf_len" parameter may be useful 71 if you need to capture more output. 72 73 acpi_enforce_resources= [ACPI] 74 { strict | lax | no } 75 Check for resource conflicts between native drivers 76 and ACPI OperationRegions (SystemIO and SystemMemory 77 only). IO ports and memory declared in ACPI might be 78 used by the ACPI subsystem in arbitrary AML code and 79 can interfere with legacy drivers. 80 strict (default): access to resources claimed by ACPI 81 is denied; legacy drivers trying to access reserved 82 resources will fail to bind to device using them. 83 lax: access to resources claimed by ACPI is allowed; 84 legacy drivers trying to access reserved resources 85 will bind successfully but a warning message is logged. 86 no: ACPI OperationRegions are not marked as reserved, 87 no further checks are performed. 88 89 acpi_force_table_verification [HW,ACPI] 90 Enable table checksum verification during early stage. 91 By default, this is disabled due to x86 early mapping 92 size limitation. 93 94 acpi_irq_balance [HW,ACPI] 95 ACPI will balance active IRQs 96 default in APIC mode 97 98 acpi_irq_nobalance [HW,ACPI] 99 ACPI will not move active IRQs (default) 100 default in PIC mode 101 102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 103 Format: <irq>,<irq>... 104 105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 106 use by PCI 107 Format: <irq>,<irq>... 108 109 acpi_mask_gpe= [HW,ACPI] 110 Due to the existence of _Lxx/_Exx, some GPEs triggered 111 by unsupported hardware/firmware features can result in 112 GPE floodings that cannot be automatically disabled by 113 the GPE dispatcher. 114 This facility can be used to prevent such uncontrolled 115 GPE floodings. 116 Format: <byte> or <bitmap-list> 117 118 acpi_no_auto_serialize [HW,ACPI] 119 Disable auto-serialization of AML methods 120 AML control methods that contain the opcodes to create 121 named objects will be marked as "Serialized" by the 122 auto-serialization feature. 123 This feature is enabled by default. 124 This option allows to turn off the feature. 125 126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 127 kernels. 128 129 acpi_no_static_ssdt [HW,ACPI] 130 Disable installation of static SSDTs at early boot time 131 By default, SSDTs contained in the RSDT/XSDT will be 132 installed automatically and they will appear under 133 /sys/firmware/acpi/tables. 134 This option turns off this feature. 135 Note that specifying this option does not affect 136 dynamic table installation which will install SSDT 137 tables to /sys/firmware/acpi/tables/dynamic. 138 139 acpi_no_watchdog [HW,ACPI,WDT] 140 Ignore the ACPI-based watchdog interface (WDAT) and let 141 a native driver control the watchdog device instead. 142 143 acpi_rsdp= [ACPI,EFI,KEXEC] 144 Pass the RSDP address to the kernel, mostly used 145 on machines running EFI runtime service to boot the 146 second kernel for kdump. 147 148 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 149 Format: To spoof as Windows 98: ="Microsoft Windows" 150 151 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 152 of 2 which is mandated by ACPI 6) as the supported ACPI 153 specification revision (when using this switch, it may 154 be necessary to carry out a cold reboot _twice_ in a 155 row to make it take effect on the platform firmware). 156 157 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 158 acpi_osi="string1" # add string1 159 acpi_osi="!string2" # remove string2 160 acpi_osi=!* # remove all strings 161 acpi_osi=! # disable all built-in OS vendor 162 strings 163 acpi_osi=!! # enable all built-in OS vendor 164 strings 165 acpi_osi= # disable all strings 166 167 'acpi_osi=!' can be used in combination with single or 168 multiple 'acpi_osi="string1"' to support specific OS 169 vendor string(s). Note that such command can only 170 affect the default state of the OS vendor strings, thus 171 it cannot affect the default state of the feature group 172 strings and the current state of the OS vendor strings, 173 specifying it multiple times through kernel command line 174 is meaningless. This command is useful when one do not 175 care about the state of the feature group strings which 176 should be controlled by the OSPM. 177 Examples: 178 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 179 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 180 can make '_OSI("Windows 2000")' TRUE. 181 182 'acpi_osi=' cannot be used in combination with other 183 'acpi_osi=' command lines, the _OSI method will not 184 exist in the ACPI namespace. NOTE that such command can 185 only affect the _OSI support state, thus specifying it 186 multiple times through kernel command line is also 187 meaningless. 188 Examples: 189 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 190 FALSE. 191 192 'acpi_osi=!*' can be used in combination with single or 193 multiple 'acpi_osi="string1"' to support specific 194 string(s). Note that such command can affect the 195 current state of both the OS vendor strings and the 196 feature group strings, thus specifying it multiple times 197 through kernel command line is meaningful. But it may 198 still not able to affect the final state of a string if 199 there are quirks related to this string. This command 200 is useful when one want to control the state of the 201 feature group strings to debug BIOS issues related to 202 the OSPM features. 203 Examples: 204 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 205 '_OSI("Module Device")' FALSE. 206 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 207 '_OSI("Module Device")' TRUE. 208 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 209 equivalent to 210 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 211 and 212 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 213 they all will make '_OSI("Windows 2000")' TRUE. 214 215 acpi_pm_good [X86] 216 Override the pmtimer bug detection: force the kernel 217 to assume that this machine's pmtimer latches its value 218 and always returns good values. 219 220 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 221 Format: { level | edge | high | low } 222 223 acpi_skip_timer_override [HW,ACPI] 224 Recognize and ignore IRQ0/pin2 Interrupt Override. 225 For broken nForce2 BIOS resulting in XT-PIC timer. 226 227 acpi_sleep= [HW,ACPI] Sleep options 228 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig, 229 s4_nohwsig, old_ordering, nonvs, 230 sci_force_enable, nobl } 231 See Documentation/power/video.rst for information on 232 s3_bios and s3_mode. 233 s3_beep is for debugging; it makes the PC's speaker beep 234 as soon as the kernel's real-mode entry point is called. 235 s4_hwsig causes the kernel to check the ACPI hardware 236 signature during resume from hibernation, and gracefully 237 refuse to resume if it has changed. This complies with 238 the ACPI specification but not with reality, since 239 Windows does not do this and many laptops do change it 240 on docking. So the default behaviour is to allow resume 241 and simply warn when the signature changes, unless the 242 s4_hwsig option is enabled. 243 s4_nohwsig prevents ACPI hardware signature from being 244 used (or even warned about) during resume. 245 old_ordering causes the ACPI 1.0 ordering of the _PTS 246 control method, with respect to putting devices into 247 low power states, to be enforced (the ACPI 2.0 ordering 248 of _PTS is used by default). 249 nonvs prevents the kernel from saving/restoring the 250 ACPI NVS memory during suspend/hibernation and resume. 251 sci_force_enable causes the kernel to set SCI_EN directly 252 on resume from S1/S3 (which is against the ACPI spec, 253 but some broken systems don't work without it). 254 nobl causes the internal blacklist of systems known to 255 behave incorrectly in some ways with respect to system 256 suspend and resume to be ignored (use wisely). 257 258 acpi_use_timer_override [HW,ACPI] 259 Use timer override. For some broken Nvidia NF5 boards 260 that require a timer override, but don't have HPET 261 262 add_efi_memmap [EFI; X86] Include EFI memory map in 263 kernel's map of available physical RAM. 264 265 agp= [AGP] 266 { off | try_unsupported } 267 off: disable AGP support 268 try_unsupported: try to drive unsupported chipsets 269 (may crash computer or cause data corruption) 270 271 ALSA [HW,ALSA] 272 See Documentation/sound/alsa-configuration.rst 273 274 alignment= [KNL,ARM] 275 Allow the default userspace alignment fault handler 276 behaviour to be specified. Bit 0 enables warnings, 277 bit 1 enables fixups, and bit 2 sends a segfault. 278 279 align_va_addr= [X86-64] 280 Align virtual addresses by clearing slice [14:12] when 281 allocating a VMA at process creation time. This option 282 gives you up to 3% performance improvement on AMD F15h 283 machines (where it is enabled by default) for a 284 CPU-intensive style benchmark, and it can vary highly in 285 a microbenchmark depending on workload and compiler. 286 287 32: only for 32-bit processes 288 64: only for 64-bit processes 289 on: enable for both 32- and 64-bit processes 290 off: disable for both 32- and 64-bit processes 291 292 alloc_snapshot [FTRACE] 293 Allocate the ftrace snapshot buffer on boot up when the 294 main buffer is allocated. This is handy if debugging 295 and you need to use tracing_snapshot() on boot up, and 296 do not want to use tracing_snapshot_alloc() as it needs 297 to be done where GFP_KERNEL allocations are allowed. 298 299 allow_mismatched_32bit_el0 [ARM64] 300 Allow execve() of 32-bit applications and setting of the 301 PER_LINUX32 personality on systems where only a strict 302 subset of the CPUs support 32-bit EL0. When this 303 parameter is present, the set of CPUs supporting 32-bit 304 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0 305 and hot-unplug operations may be restricted. 306 307 See Documentation/arch/arm64/asymmetric-32bit.rst for more 308 information. 309 310 amd_iommu= [HW,X86-64] 311 Pass parameters to the AMD IOMMU driver in the system. 312 Possible values are: 313 fullflush - Deprecated, equivalent to iommu.strict=1 314 off - do not initialize any AMD IOMMU found in 315 the system 316 force_isolation - Force device isolation for all 317 devices. The IOMMU driver is not 318 allowed anymore to lift isolation 319 requirements as needed. This option 320 does not override iommu=pt 321 force_enable - Force enable the IOMMU on platforms known 322 to be buggy with IOMMU enabled. Use this 323 option with care. 324 pgtbl_v1 - Use v1 page table for DMA-API (Default). 325 pgtbl_v2 - Use v2 page table for DMA-API. 326 irtcachedis - Disable Interrupt Remapping Table (IRT) caching. 327 328 amd_iommu_dump= [HW,X86-64] 329 Enable AMD IOMMU driver option to dump the ACPI table 330 for AMD IOMMU. With this option enabled, AMD IOMMU 331 driver will print ACPI tables for AMD IOMMU during 332 IOMMU initialization. 333 334 amd_iommu_intr= [HW,X86-64] 335 Specifies one of the following AMD IOMMU interrupt 336 remapping modes: 337 legacy - Use legacy interrupt remapping mode. 338 vapic - Use virtual APIC mode, which allows IOMMU 339 to inject interrupts directly into guest. 340 This mode requires kvm-amd.avic=1. 341 (Default when IOMMU HW support is present.) 342 343 amd_pstate= [X86] 344 disable 345 Do not enable amd_pstate as the default 346 scaling driver for the supported processors 347 passive 348 Use amd_pstate with passive mode as a scaling driver. 349 In this mode autonomous selection is disabled. 350 Driver requests a desired performance level and platform 351 tries to match the same performance level if it is 352 satisfied by guaranteed performance level. 353 active 354 Use amd_pstate_epp driver instance as the scaling driver, 355 driver provides a hint to the hardware if software wants 356 to bias toward performance (0x0) or energy efficiency (0xff) 357 to the CPPC firmware. then CPPC power algorithm will 358 calculate the runtime workload and adjust the realtime cores 359 frequency. 360 guided 361 Activate guided autonomous mode. Driver requests minimum and 362 maximum performance level and the platform autonomously 363 selects a performance level in this range and appropriate 364 to the current workload. 365 366 amijoy.map= [HW,JOY] Amiga joystick support 367 Map of devices attached to JOY0DAT and JOY1DAT 368 Format: <a>,<b> 369 See also Documentation/input/joydev/joystick.rst 370 371 analog.map= [HW,JOY] Analog joystick and gamepad support 372 Specifies type or capabilities of an analog joystick 373 connected to one of 16 gameports 374 Format: <type1>,<type2>,..<type16> 375 376 apc= [HW,SPARC] 377 Power management functions (SPARCstation-4/5 + deriv.) 378 Format: noidle 379 Disable APC CPU standby support. SPARCstation-Fox does 380 not play well with APC CPU idle - disable it if you have 381 APC and your system crashes randomly. 382 383 apic= [APIC,X86] Advanced Programmable Interrupt Controller 384 Change the output verbosity while booting 385 Format: { quiet (default) | verbose | debug } 386 Change the amount of debugging information output 387 when initialising the APIC and IO-APIC components. 388 For X86-32, this can also be used to specify an APIC 389 driver name. 390 Format: apic=driver_name 391 Examples: apic=bigsmp 392 393 apic_extnmi= [APIC,X86] External NMI delivery setting 394 Format: { bsp (default) | all | none } 395 bsp: External NMI is delivered only to CPU 0 396 all: External NMIs are broadcast to all CPUs as a 397 backup of CPU 0 398 none: External NMI is masked for all CPUs. This is 399 useful so that a dump capture kernel won't be 400 shot down by NMI 401 402 autoconf= [IPV6] 403 See Documentation/networking/ipv6.rst. 404 405 apm= [APM] Advanced Power Management 406 See header of arch/x86/kernel/apm_32.c. 407 408 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 409 Format: { "0" | "1" } 410 See security/apparmor/Kconfig help text 411 0 -- disable. 412 1 -- enable. 413 Default value is set via kernel config option. 414 415 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 416 Format: <io>,<irq>,<nodeID> 417 418 arm64.nobti [ARM64] Unconditionally disable Branch Target 419 Identification support 420 421 arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory 422 Set instructions support 423 424 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension 425 support 426 427 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication 428 support 429 430 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix 431 Extension support 432 433 arm64.nosve [ARM64] Unconditionally disable Scalable Vector 434 Extension support 435 436 ataflop= [HW,M68k] 437 438 atarimouse= [HW,MOUSE] Atari Mouse 439 440 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 441 EzKey and similar keyboards 442 443 atkbd.reset= [HW] Reset keyboard during initialization 444 445 atkbd.set= [HW] Select keyboard code set 446 Format: <int> (2 = AT (default), 3 = PS/2) 447 448 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 449 keyboards 450 451 atkbd.softraw= [HW] Choose between synthetic and real raw mode 452 Format: <bool> (0 = real, 1 = synthetic (default)) 453 454 atkbd.softrepeat= [HW] 455 Use software keyboard repeat 456 457 audit= [KNL] Enable the audit sub-system 458 Format: { "0" | "1" | "off" | "on" } 459 0 | off - kernel audit is disabled and can not be 460 enabled until the next reboot 461 unset - kernel audit is initialized but disabled and 462 will be fully enabled by the userspace auditd. 463 1 | on - kernel audit is initialized and partially 464 enabled, storing at most audit_backlog_limit 465 messages in RAM until it is fully enabled by the 466 userspace auditd. 467 Default: unset 468 469 audit_backlog_limit= [KNL] Set the audit queue size limit. 470 Format: <int> (must be >=0) 471 Default: 64 472 473 bau= [X86_UV] Enable the BAU on SGI UV. The default 474 behavior is to disable the BAU (i.e. bau=0). 475 Format: { "0" | "1" } 476 0 - Disable the BAU. 477 1 - Enable the BAU. 478 unset - Disable the BAU. 479 480 baycom_epp= [HW,AX25] 481 Format: <io>,<mode> 482 483 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 484 Format: <io>,<mode> 485 See header of drivers/net/hamradio/baycom_par.c. 486 487 baycom_ser_fdx= [HW,AX25] 488 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 489 Format: <io>,<irq>,<mode>[,<baud>] 490 See header of drivers/net/hamradio/baycom_ser_fdx.c. 491 492 baycom_ser_hdx= [HW,AX25] 493 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 494 Format: <io>,<irq>,<mode> 495 See header of drivers/net/hamradio/baycom_ser_hdx.c. 496 497 bert_disable [ACPI] 498 Disable BERT OS support on buggy BIOSes. 499 500 bgrt_disable [ACPI][X86] 501 Disable BGRT to avoid flickering OEM logo. 502 503 blkdevparts= Manual partition parsing of block device(s) for 504 embedded devices based on command line input. 505 See Documentation/block/cmdline-partition.rst 506 507 boot_delay= Milliseconds to delay each printk during boot. 508 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled, 509 and you may also have to specify "lpj=". Boot_delay 510 values larger than 10 seconds (10000) are assumed 511 erroneous and ignored. 512 Format: integer 513 514 bootconfig [KNL] 515 Extended command line options can be added to an initrd 516 and this will cause the kernel to look for it. 517 518 See Documentation/admin-guide/bootconfig.rst 519 520 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 521 bttv.radio= Most important insmod options are available as 522 kernel args too. 523 bttv.pll= See Documentation/admin-guide/media/bttv.rst 524 bttv.tuner= 525 526 bulk_remove=off [PPC] This parameter disables the use of the pSeries 527 firmware feature for flushing multiple hpte entries 528 at a time. 529 530 c101= [NET] Moxa C101 synchronous serial card 531 532 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 533 Sometimes CPU hardware bugs make them report the cache 534 size incorrectly. The kernel will attempt work arounds 535 to fix known problems, but for some CPUs it is not 536 possible to determine what the correct size should be. 537 This option provides an override for these situations. 538 539 carrier_timeout= 540 [NET] Specifies amount of time (in seconds) that 541 the kernel should wait for a network carrier. By default 542 it waits 120 seconds. 543 544 ca_keys= [KEYS] This parameter identifies a specific key(s) on 545 the system trusted keyring to be used for certificate 546 trust validation. 547 format: { id:<keyid> | builtin } 548 549 cca= [MIPS] Override the kernel pages' cache coherency 550 algorithm. Accepted values range from 0 to 7 551 inclusive. See arch/mips/include/asm/pgtable-bits.h 552 for platform specific values (SB1, Loongson3 and 553 others). 554 555 ccw_timeout_log [S390] 556 See Documentation/arch/s390/common_io.rst for details. 557 558 cgroup_disable= [KNL] Disable a particular controller or optional feature 559 Format: {name of the controller(s) or feature(s) to disable} 560 The effects of cgroup_disable=foo are: 561 - foo isn't auto-mounted if you mount all cgroups in 562 a single hierarchy 563 - foo isn't visible as an individually mountable 564 subsystem 565 - if foo is an optional feature then the feature is 566 disabled and corresponding cgroup files are not 567 created 568 {Currently only "memory" controller deal with this and 569 cut the overhead, others just disable the usage. So 570 only cgroup_disable=memory is actually worthy} 571 Specifying "pressure" disables per-cgroup pressure 572 stall information accounting feature 573 574 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 575 Format: { { controller | "all" | "named" } 576 [,{ controller | "all" | "named" }...] } 577 Like cgroup_disable, but only applies to cgroup v1; 578 the blacklisted controllers remain available in cgroup2. 579 "all" blacklists all controllers and "named" disables 580 named mounts. Specifying both "all" and "named" disables 581 all v1 hierarchies. 582 583 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 584 Format: <string> 585 nosocket -- Disable socket memory accounting. 586 nokmem -- Disable kernel memory accounting. 587 nobpf -- Disable BPF memory accounting. 588 589 checkreqprot= [SELINUX] Set initial checkreqprot flag value. 590 Format: { "0" | "1" } 591 See security/selinux/Kconfig help text. 592 0 -- check protection applied by kernel (includes 593 any implied execute protection). 594 1 -- check protection requested by application. 595 Default value is set via a kernel config option. 596 Value can be changed at runtime via 597 /sys/fs/selinux/checkreqprot. 598 Setting checkreqprot to 1 is deprecated. 599 600 cio_ignore= [S390] 601 See Documentation/arch/s390/common_io.rst for details. 602 603 clearcpuid=X[,X...] [X86] 604 Disable CPUID feature X for the kernel. See 605 arch/x86/include/asm/cpufeatures.h for the valid bit 606 numbers X. Note the Linux-specific bits are not necessarily 607 stable over kernel options, but the vendor-specific 608 ones should be. 609 X can also be a string as appearing in the flags: line 610 in /proc/cpuinfo which does not have the above 611 instability issue. However, not all features have names 612 in /proc/cpuinfo. 613 Note that using this option will taint your kernel. 614 Also note that user programs calling CPUID directly 615 or using the feature without checking anything 616 will still see it. This just prevents it from 617 being used by the kernel or shown in /proc/cpuinfo. 618 Also note the kernel might malfunction if you disable 619 some critical bits. 620 621 clk_ignore_unused 622 [CLK] 623 Prevents the clock framework from automatically gating 624 clocks that have not been explicitly enabled by a Linux 625 device driver but are enabled in hardware at reset or 626 by the bootloader/firmware. Note that this does not 627 force such clocks to be always-on nor does it reserve 628 those clocks in any way. This parameter is useful for 629 debug and development, but should not be needed on a 630 platform with proper driver support. For more 631 information, see Documentation/driver-api/clk.rst. 632 633 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 634 [Deprecated] 635 Forces specified clocksource (if available) to be used 636 when calculating gettimeofday(). If specified 637 clocksource is not available, it defaults to PIT. 638 Format: { pit | tsc | cyclone | pmtmr } 639 640 clocksource= Override the default clocksource 641 Format: <string> 642 Override the default clocksource and use the clocksource 643 with the name specified. 644 Some clocksource names to choose from, depending on 645 the platform: 646 [all] jiffies (this is the base, fallback clocksource) 647 [ACPI] acpi_pm 648 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 649 pxa_timer,timer3,32k_counter,timer0_1 650 [X86-32] pit,hpet,tsc; 651 scx200_hrt on Geode; cyclone on IBM x440 652 [MIPS] MIPS 653 [PARISC] cr16 654 [S390] tod 655 [SH] SuperH 656 [SPARC64] tick 657 [X86-64] hpet,tsc 658 659 clocksource.arm_arch_timer.evtstrm= 660 [ARM,ARM64] 661 Format: <bool> 662 Enable/disable the eventstream feature of the ARM 663 architected timer so that code using WFE-based polling 664 loops can be debugged more effectively on production 665 systems. 666 667 clocksource.verify_n_cpus= [KNL] 668 Limit the number of CPUs checked for clocksources 669 marked with CLOCK_SOURCE_VERIFY_PERCPU that 670 are marked unstable due to excessive skew. 671 A negative value says to check all CPUs, while 672 zero says not to check any. Values larger than 673 nr_cpu_ids are silently truncated to nr_cpu_ids. 674 The actual CPUs are chosen randomly, with 675 no replacement if the same CPU is chosen twice. 676 677 clocksource-wdtest.holdoff= [KNL] 678 Set the time in seconds that the clocksource 679 watchdog test waits before commencing its tests. 680 Defaults to zero when built as a module and to 681 10 seconds when built into the kernel. 682 683 cma=nn[MG]@[start[MG][-end[MG]]] 684 [KNL,CMA] 685 Sets the size of kernel global memory area for 686 contiguous memory allocations and optionally the 687 placement constraint by the physical address range of 688 memory allocations. A value of 0 disables CMA 689 altogether. For more information, see 690 kernel/dma/contiguous.c 691 692 cma_pernuma=nn[MG] 693 [KNL,CMA] 694 Sets the size of kernel per-numa memory area for 695 contiguous memory allocations. A value of 0 disables 696 per-numa CMA altogether. And If this option is not 697 specified, the default value is 0. 698 With per-numa CMA enabled, DMA users on node nid will 699 first try to allocate buffer from the pernuma area 700 which is located in node nid, if the allocation fails, 701 they will fallback to the global default memory area. 702 703 numa_cma=<node>:nn[MG][,<node>:nn[MG]] 704 [KNL,CMA] 705 Sets the size of kernel numa memory area for 706 contiguous memory allocations. It will reserve CMA 707 area for the specified node. 708 709 With numa CMA enabled, DMA users on node nid will 710 first try to allocate buffer from the numa area 711 which is located in node nid, if the allocation fails, 712 they will fallback to the global default memory area. 713 714 cmo_free_hint= [PPC] Format: { yes | no } 715 Specify whether pages are marked as being inactive 716 when they are freed. This is used in CMO environments 717 to determine OS memory pressure for page stealing by 718 a hypervisor. 719 Default: yes 720 721 coherent_pool=nn[KMG] [ARM,KNL] 722 Sets the size of memory pool for coherent, atomic dma 723 allocations, by default set to 256K. 724 725 com20020= [HW,NET] ARCnet - COM20020 chipset 726 Format: 727 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 728 729 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 730 Format: <io>[,<irq>] 731 732 com90xx= [HW,NET] 733 ARCnet - COM90xx chipset (memory-mapped buffers) 734 Format: <io>[,<irq>[,<memstart>]] 735 736 condev= [HW,S390] console device 737 conmode= 738 739 con3215_drop= [S390] 3215 console drop mode. 740 Format: y|n|Y|N|1|0 741 When set to true, drop data on the 3215 console when 742 the console buffer is full. In this case the 743 operator using a 3270 terminal emulator (for example 744 x3270) does not have to enter the clear key for the 745 console output to advance and the kernel to continue. 746 This leads to a much faster boot time when a 3270 747 terminal emulator is active. If no 3270 terminal 748 emulator is used, this parameter has no effect. 749 750 console= [KNL] Output console device and options. 751 752 tty<n> Use the virtual console device <n>. 753 754 ttyS<n>[,options] 755 ttyUSB0[,options] 756 Use the specified serial port. The options are of 757 the form "bbbbpnf", where "bbbb" is the baud rate, 758 "p" is parity ("n", "o", or "e"), "n" is number of 759 bits, and "f" is flow control ("r" for RTS or 760 omit it). Default is "9600n8". 761 762 See Documentation/admin-guide/serial-console.rst for more 763 information. See 764 Documentation/networking/netconsole.rst for an 765 alternative. 766 767 uart[8250],io,<addr>[,options] 768 uart[8250],mmio,<addr>[,options] 769 uart[8250],mmio16,<addr>[,options] 770 uart[8250],mmio32,<addr>[,options] 771 uart[8250],0x<addr>[,options] 772 Start an early, polled-mode console on the 8250/16550 773 UART at the specified I/O port or MMIO address, 774 switching to the matching ttyS device later. 775 MMIO inter-register address stride is either 8-bit 776 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 777 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 778 to be equivalent to 'mmio'. 'options' are specified in 779 the same format described for ttyS above; if unspecified, 780 the h/w is not re-initialized. 781 782 hvc<n> Use the hypervisor console device <n>. This is for 783 both Xen and PowerPC hypervisors. 784 785 { null | "" } 786 Use to disable console output, i.e., to have kernel 787 console messages discarded. 788 This must be the only console= parameter used on the 789 kernel command line. 790 791 If the device connected to the port is not a TTY but a braille 792 device, prepend "brl," before the device type, for instance 793 console=brl,ttyS0 794 For now, only VisioBraille is supported. 795 796 console_msg_format= 797 [KNL] Change console messages format 798 default 799 By default we print messages on consoles in 800 "[time stamp] text\n" format (time stamp may not be 801 printed, depending on CONFIG_PRINTK_TIME or 802 `printk_time' param). 803 syslog 804 Switch to syslog format: "<%u>[time stamp] text\n" 805 IOW, each message will have a facility and loglevel 806 prefix. The format is similar to one used by syslog() 807 syscall, or to executing "dmesg -S --raw" or to reading 808 from /proc/kmsg. 809 810 consoleblank= [KNL] The console blank (screen saver) timeout in 811 seconds. A value of 0 disables the blank timer. 812 Defaults to 0. 813 814 coredump_filter= 815 [KNL] Change the default value for 816 /proc/<pid>/coredump_filter. 817 See also Documentation/filesystems/proc.rst. 818 819 coresight_cpu_debug.enable 820 [ARM,ARM64] 821 Format: <bool> 822 Enable/disable the CPU sampling based debugging. 823 0: default value, disable debugging 824 1: enable debugging at boot time 825 826 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 827 Format: 828 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 829 830 cpuidle.off=1 [CPU_IDLE] 831 disable the cpuidle sub-system 832 833 cpuidle.governor= 834 [CPU_IDLE] Name of the cpuidle governor to use. 835 836 cpufreq.off=1 [CPU_FREQ] 837 disable the cpufreq sub-system 838 839 cpufreq.default_governor= 840 [CPU_FREQ] Name of the default cpufreq governor or 841 policy to use. This governor must be registered in the 842 kernel before the cpufreq driver probes. 843 844 cpu_init_udelay=N 845 [X86] Delay for N microsec between assert and de-assert 846 of APIC INIT to start processors. This delay occurs 847 on every CPU online, such as boot, and resume from suspend. 848 Default: 10000 849 850 cpuhp.parallel= 851 [SMP] Enable/disable parallel bringup of secondary CPUs 852 Format: <bool> 853 Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise 854 the parameter has no effect. 855 856 crash_kexec_post_notifiers 857 Run kdump after running panic-notifiers and dumping 858 kmsg. This only for the users who doubt kdump always 859 succeeds in any situation. 860 Note that this also increases risks of kdump failure, 861 because some panic notifiers can make the crashed 862 kernel more unstable. 863 864 crashkernel=size[KMG][@offset[KMG]] 865 [KNL] Using kexec, Linux can switch to a 'crash kernel' 866 upon panic. This parameter reserves the physical 867 memory region [offset, offset + size] for that kernel 868 image. If '@offset' is omitted, then a suitable offset 869 is selected automatically. 870 [KNL, X86-64, ARM64, RISCV] Select a region under 4G first, and 871 fall back to reserve region above 4G when '@offset' 872 hasn't been specified. 873 See Documentation/admin-guide/kdump/kdump.rst for further details. 874 875 crashkernel=range1:size1[,range2:size2,...][@offset] 876 [KNL] Same as above, but depends on the memory 877 in the running system. The syntax of range is 878 start-[end] where start and end are both 879 a memory unit (amount[KMG]). See also 880 Documentation/admin-guide/kdump/kdump.rst for an example. 881 882 crashkernel=size[KMG],high 883 [KNL, X86-64, ARM64, RISCV] range could be above 4G. 884 Allow kernel to allocate physical memory region from top, 885 so could be above 4G if system have more than 4G ram 886 installed. Otherwise memory region will be allocated 887 below 4G, if available. 888 It will be ignored if crashkernel=X is specified. 889 crashkernel=size[KMG],low 890 [KNL, X86-64, ARM64, RISCV] range under 4G. When crashkernel=X,high 891 is passed, kernel could allocate physical memory region 892 above 4G, that cause second kernel crash on system 893 that require some amount of low memory, e.g. swiotlb 894 requires at least 64M+32K low memory, also enough extra 895 low memory is needed to make sure DMA buffers for 32-bit 896 devices won't run out. Kernel would try to allocate 897 default size of memory below 4G automatically. The default 898 size is platform dependent. 899 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB) 900 --> arm64: 128MiB 901 --> riscv: 128MiB 902 This one lets the user specify own low range under 4G 903 for second kernel instead. 904 0: to disable low allocation. 905 It will be ignored when crashkernel=X,high is not used 906 or memory reserved is below 4G. 907 908 cryptomgr.notests 909 [KNL] Disable crypto self-tests 910 911 cs89x0_dma= [HW,NET] 912 Format: <dma> 913 914 cs89x0_media= [HW,NET] 915 Format: { rj45 | aui | bnc } 916 917 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU 918 function call handling. When switched on, 919 additional debug data is printed to the console 920 in case a hanging CPU is detected, and that 921 CPU is pinged again in order to try to resolve 922 the hang situation. The default value of this 923 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT 924 Kconfig option. 925 926 dasd= [HW,NET] 927 See header of drivers/s390/block/dasd_devmap.c. 928 929 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 930 (one device per port) 931 Format: <port#>,<type> 932 See also Documentation/input/devices/joystick-parport.rst 933 934 debug [KNL] Enable kernel debugging (events log level). 935 936 debug_boot_weak_hash 937 [KNL] Enable printing [hashed] pointers early in the 938 boot sequence. If enabled, we use a weak hash instead 939 of siphash to hash pointers. Use this option if you are 940 seeing instances of '(___ptrval___)') and need to see a 941 value (hashed pointer) instead. Cryptographically 942 insecure, please do not use on production kernels. 943 944 debug_locks_verbose= 945 [KNL] verbose locking self-tests 946 Format: <int> 947 Print debugging info while doing the locking API 948 self-tests. 949 Bitmask for the various LOCKTYPE_ tests. Defaults to 0 950 (no extra messages), setting it to -1 (all bits set) 951 will print _a_lot_ more information - normally only 952 useful to lockdep developers. 953 954 debug_objects [KNL] Enable object debugging 955 956 debug_guardpage_minorder= 957 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 958 parameter allows control of the order of pages that will 959 be intentionally kept free (and hence protected) by the 960 buddy allocator. Bigger value increase the probability 961 of catching random memory corruption, but reduce the 962 amount of memory for normal system use. The maximum 963 possible value is MAX_ORDER/2. Setting this parameter 964 to 1 or 2 should be enough to identify most random 965 memory corruption problems caused by bugs in kernel or 966 driver code when a CPU writes to (or reads from) a 967 random memory location. Note that there exists a class 968 of memory corruptions problems caused by buggy H/W or 969 F/W or by drivers badly programming DMA (basically when 970 memory is written at bus level and the CPU MMU is 971 bypassed) which are not detectable by 972 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 973 tracking down these problems. 974 975 debug_pagealloc= 976 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 977 enables the feature at boot time. By default, it is 978 disabled and the system will work mostly the same as a 979 kernel built without CONFIG_DEBUG_PAGEALLOC. 980 Note: to get most of debug_pagealloc error reports, it's 981 useful to also enable the page_owner functionality. 982 on: enable the feature 983 984 debugfs= [KNL] This parameter enables what is exposed to userspace 985 and debugfs internal clients. 986 Format: { on, no-mount, off } 987 on: All functions are enabled. 988 no-mount: 989 Filesystem is not registered but kernel clients can 990 access APIs and a crashkernel can be used to read 991 its content. There is nothing to mount. 992 off: Filesystem is not registered and clients 993 get a -EPERM as result when trying to register files 994 or directories within debugfs. 995 This is equivalent of the runtime functionality if 996 debugfs was not enabled in the kernel at all. 997 Default value is set in build-time with a kernel configuration. 998 999 debugpat [X86] Enable PAT debugging 1000 1001 default_hugepagesz= 1002 [HW] The size of the default HugeTLB page. This is 1003 the size represented by the legacy /proc/ hugepages 1004 APIs. In addition, this is the default hugetlb size 1005 used for shmget(), mmap() and mounting hugetlbfs 1006 filesystems. If not specified, defaults to the 1007 architecture's default huge page size. Huge page 1008 sizes are architecture dependent. See also 1009 Documentation/admin-guide/mm/hugetlbpage.rst. 1010 Format: size[KMG] 1011 1012 deferred_probe_timeout= 1013 [KNL] Debugging option to set a timeout in seconds for 1014 deferred probe to give up waiting on dependencies to 1015 probe. Only specific dependencies (subsystems or 1016 drivers) that have opted in will be ignored. A timeout 1017 of 0 will timeout at the end of initcalls. If the time 1018 out hasn't expired, it'll be restarted by each 1019 successful driver registration. This option will also 1020 dump out devices still on the deferred probe list after 1021 retrying. 1022 1023 delayacct [KNL] Enable per-task delay accounting 1024 1025 dell_smm_hwmon.ignore_dmi= 1026 [HW] Continue probing hardware even if DMI data 1027 indicates that the driver is running on unsupported 1028 hardware. 1029 1030 dell_smm_hwmon.force= 1031 [HW] Activate driver even if SMM BIOS signature does 1032 not match list of supported models and enable otherwise 1033 blacklisted features. 1034 1035 dell_smm_hwmon.power_status= 1036 [HW] Report power status in /proc/i8k 1037 (disabled by default). 1038 1039 dell_smm_hwmon.restricted= 1040 [HW] Allow controlling fans only if SYS_ADMIN 1041 capability is set. 1042 1043 dell_smm_hwmon.fan_mult= 1044 [HW] Factor to multiply fan speed with. 1045 1046 dell_smm_hwmon.fan_max= 1047 [HW] Maximum configurable fan speed. 1048 1049 dfltcc= [HW,S390] 1050 Format: { on | off | def_only | inf_only | always } 1051 on: s390 zlib hardware support for compression on 1052 level 1 and decompression (default) 1053 off: No s390 zlib hardware support 1054 def_only: s390 zlib hardware support for deflate 1055 only (compression on level 1) 1056 inf_only: s390 zlib hardware support for inflate 1057 only (decompression) 1058 always: Same as 'on' but ignores the selected compression 1059 level always using hardware support (used for debugging) 1060 1061 dhash_entries= [KNL] 1062 Set number of hash buckets for dentry cache. 1063 1064 disable_1tb_segments [PPC] 1065 Disables the use of 1TB hash page table segments. This 1066 causes the kernel to fall back to 256MB segments which 1067 can be useful when debugging issues that require an SLB 1068 miss to occur. 1069 1070 disable= [IPV6] 1071 See Documentation/networking/ipv6.rst. 1072 1073 disable_radix [PPC] 1074 Disable RADIX MMU mode on POWER9 1075 1076 disable_tlbie [PPC] 1077 Disable TLBIE instruction. Currently does not work 1078 with KVM, with HASH MMU, or with coherent accelerators. 1079 1080 disable_cpu_apicid= [X86,APIC,SMP] 1081 Format: <int> 1082 The number of initial APIC ID for the 1083 corresponding CPU to be disabled at boot, 1084 mostly used for the kdump 2nd kernel to 1085 disable BSP to wake up multiple CPUs without 1086 causing system reset or hang due to sending 1087 INIT from AP to BSP. 1088 1089 disable_ddw [PPC/PSERIES] 1090 Disable Dynamic DMA Window support. Use this 1091 to workaround buggy firmware. 1092 1093 disable_ipv6= [IPV6] 1094 See Documentation/networking/ipv6.rst. 1095 1096 disable_mtrr_cleanup [X86] 1097 The kernel tries to adjust MTRR layout from continuous 1098 to discrete, to make X server driver able to add WB 1099 entry later. This parameter disables that. 1100 1101 disable_mtrr_trim [X86, Intel and AMD only] 1102 By default the kernel will trim any uncacheable 1103 memory out of your available memory pool based on 1104 MTRR settings. This parameter disables that behavior, 1105 possibly causing your machine to run very slowly. 1106 1107 disable_timer_pin_1 [X86] 1108 Disable PIN 1 of APIC timer 1109 Can be useful to work around chipset bugs. 1110 1111 dis_ucode_ldr [X86] Disable the microcode loader. 1112 1113 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 1114 this option disables the debugging code at boot. 1115 1116 dma_debug_entries=<number> 1117 This option allows to tune the number of preallocated 1118 entries for DMA-API debugging code. One entry is 1119 required per DMA-API allocation. Use this if the 1120 DMA-API debugging code disables itself because the 1121 architectural default is too low. 1122 1123 dma_debug_driver=<driver_name> 1124 With this option the DMA-API debugging driver 1125 filter feature can be enabled at boot time. Just 1126 pass the driver to filter for as the parameter. 1127 The filter can be disabled or changed to another 1128 driver later using sysfs. 1129 1130 reg_file_data_sampling= 1131 [X86] Controls mitigation for Register File Data 1132 Sampling (RFDS) vulnerability. RFDS is a CPU 1133 vulnerability which may allow userspace to infer 1134 kernel data values previously stored in floating point 1135 registers, vector registers, or integer registers. 1136 RFDS only affects Intel Atom processors. 1137 1138 on: Turns ON the mitigation. 1139 off: Turns OFF the mitigation. 1140 1141 This parameter overrides the compile time default set 1142 by CONFIG_MITIGATION_RFDS. Mitigation cannot be 1143 disabled when other VERW based mitigations (like MDS) 1144 are enabled. In order to disable RFDS mitigation all 1145 VERW based mitigations need to be disabled. 1146 1147 For details see: 1148 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst 1149 1150 driver_async_probe= [KNL] 1151 List of driver names to be probed asynchronously. * 1152 matches with all driver names. If * is specified, the 1153 rest of the listed driver names are those that will NOT 1154 match the *. 1155 Format: <driver_name1>,<driver_name2>... 1156 1157 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 1158 Broken monitors, graphic adapters, KVMs and EDIDless 1159 panels may send no or incorrect EDID data sets. 1160 This parameter allows to specify an EDID data sets 1161 in the /lib/firmware directory that are used instead. 1162 Generic built-in EDID data sets are used, if one of 1163 edid/1024x768.bin, edid/1280x1024.bin, 1164 edid/1680x1050.bin, or edid/1920x1080.bin is given 1165 and no file with the same name exists. Details and 1166 instructions how to build your own EDID data are 1167 available in Documentation/admin-guide/edid.rst. An EDID 1168 data set will only be used for a particular connector, 1169 if its name and a colon are prepended to the EDID 1170 name. Each connector may use a unique EDID data 1171 set by separating the files with a comma. An EDID 1172 data set with no connector name will be used for 1173 any connectors not explicitly specified. 1174 1175 dscc4.setup= [NET] 1176 1177 dt_cpu_ftrs= [PPC] 1178 Format: {"off" | "known"} 1179 Control how the dt_cpu_ftrs device-tree binding is 1180 used for CPU feature discovery and setup (if it 1181 exists). 1182 off: Do not use it, fall back to legacy cpu table. 1183 known: Do not pass through unknown features to guests 1184 or userspace, only those that the kernel is aware of. 1185 1186 dump_apple_properties [X86] 1187 Dump name and content of EFI device properties on 1188 x86 Macs. Useful for driver authors to determine 1189 what data is available or for reverse-engineering. 1190 1191 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1192 <module>.dyndbg[="val"] 1193 Enable debug messages at boot time. See 1194 Documentation/admin-guide/dynamic-debug-howto.rst 1195 for details. 1196 1197 early_ioremap_debug [KNL] 1198 Enable debug messages in early_ioremap support. This 1199 is useful for tracking down temporary early mappings 1200 which are not unmapped. 1201 1202 earlycon= [KNL] Output early console device and options. 1203 1204 When used with no options, the early console is 1205 determined by stdout-path property in device tree's 1206 chosen node or the ACPI SPCR table if supported by 1207 the platform. 1208 1209 cdns,<addr>[,options] 1210 Start an early, polled-mode console on a Cadence 1211 (xuartps) serial port at the specified address. Only 1212 supported option is baud rate. If baud rate is not 1213 specified, the serial port must already be setup and 1214 configured. 1215 1216 uart[8250],io,<addr>[,options[,uartclk]] 1217 uart[8250],mmio,<addr>[,options[,uartclk]] 1218 uart[8250],mmio32,<addr>[,options[,uartclk]] 1219 uart[8250],mmio32be,<addr>[,options[,uartclk]] 1220 uart[8250],0x<addr>[,options] 1221 Start an early, polled-mode console on the 8250/16550 1222 UART at the specified I/O port or MMIO address. 1223 MMIO inter-register address stride is either 8-bit 1224 (mmio) or 32-bit (mmio32 or mmio32be). 1225 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1226 to be equivalent to 'mmio'. 'options' are specified 1227 in the same format described for "console=ttyS<n>"; if 1228 unspecified, the h/w is not initialized. 'uartclk' is 1229 the uart clock frequency; if unspecified, it is set 1230 to 'BASE_BAUD' * 16. 1231 1232 pl011,<addr> 1233 pl011,mmio32,<addr> 1234 Start an early, polled-mode console on a pl011 serial 1235 port at the specified address. The pl011 serial port 1236 must already be setup and configured. Options are not 1237 yet supported. If 'mmio32' is specified, then only 1238 the driver will use only 32-bit accessors to read/write 1239 the device registers. 1240 1241 liteuart,<addr> 1242 Start an early console on a litex serial port at the 1243 specified address. The serial port must already be 1244 setup and configured. Options are not yet supported. 1245 1246 meson,<addr> 1247 Start an early, polled-mode console on a meson serial 1248 port at the specified address. The serial port must 1249 already be setup and configured. Options are not yet 1250 supported. 1251 1252 msm_serial,<addr> 1253 Start an early, polled-mode console on an msm serial 1254 port at the specified address. The serial port 1255 must already be setup and configured. Options are not 1256 yet supported. 1257 1258 msm_serial_dm,<addr> 1259 Start an early, polled-mode console on an msm serial 1260 dm port at the specified address. The serial port 1261 must already be setup and configured. Options are not 1262 yet supported. 1263 1264 owl,<addr> 1265 Start an early, polled-mode console on a serial port 1266 of an Actions Semi SoC, such as S500 or S900, at the 1267 specified address. The serial port must already be 1268 setup and configured. Options are not yet supported. 1269 1270 rda,<addr> 1271 Start an early, polled-mode console on a serial port 1272 of an RDA Micro SoC, such as RDA8810PL, at the 1273 specified address. The serial port must already be 1274 setup and configured. Options are not yet supported. 1275 1276 sbi 1277 Use RISC-V SBI (Supervisor Binary Interface) for early 1278 console. 1279 1280 smh Use ARM semihosting calls for early console. 1281 1282 s3c2410,<addr> 1283 s3c2412,<addr> 1284 s3c2440,<addr> 1285 s3c6400,<addr> 1286 s5pv210,<addr> 1287 exynos4210,<addr> 1288 Use early console provided by serial driver available 1289 on Samsung SoCs, requires selecting proper type and 1290 a correct base address of the selected UART port. The 1291 serial port must already be setup and configured. 1292 Options are not yet supported. 1293 1294 lantiq,<addr> 1295 Start an early, polled-mode console on a lantiq serial 1296 (lqasc) port at the specified address. The serial port 1297 must already be setup and configured. Options are not 1298 yet supported. 1299 1300 lpuart,<addr> 1301 lpuart32,<addr> 1302 Use early console provided by Freescale LP UART driver 1303 found on Freescale Vybrid and QorIQ LS1021A processors. 1304 A valid base address must be provided, and the serial 1305 port must already be setup and configured. 1306 1307 ec_imx21,<addr> 1308 ec_imx6q,<addr> 1309 Start an early, polled-mode, output-only console on the 1310 Freescale i.MX UART at the specified address. The UART 1311 must already be setup and configured. 1312 1313 ar3700_uart,<addr> 1314 Start an early, polled-mode console on the 1315 Armada 3700 serial port at the specified 1316 address. The serial port must already be setup 1317 and configured. Options are not yet supported. 1318 1319 qcom_geni,<addr> 1320 Start an early, polled-mode console on a Qualcomm 1321 Generic Interface (GENI) based serial port at the 1322 specified address. The serial port must already be 1323 setup and configured. Options are not yet supported. 1324 1325 efifb,[options] 1326 Start an early, unaccelerated console on the EFI 1327 memory mapped framebuffer (if available). On cache 1328 coherent non-x86 systems that use system memory for 1329 the framebuffer, pass the 'ram' option so that it is 1330 mapped with the correct attributes. 1331 1332 linflex,<addr> 1333 Use early console provided by Freescale LINFlexD UART 1334 serial driver for NXP S32V234 SoCs. A valid base 1335 address must be provided, and the serial port must 1336 already be setup and configured. 1337 1338 earlyprintk= [X86,SH,ARM,M68k,S390] 1339 earlyprintk=vga 1340 earlyprintk=sclp 1341 earlyprintk=xen 1342 earlyprintk=serial[,ttySn[,baudrate]] 1343 earlyprintk=serial[,0x...[,baudrate]] 1344 earlyprintk=ttySn[,baudrate] 1345 earlyprintk=dbgp[debugController#] 1346 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1347 earlyprintk=xdbc[xhciController#] 1348 1349 earlyprintk is useful when the kernel crashes before 1350 the normal console is initialized. It is not enabled by 1351 default because it has some cosmetic problems. 1352 1353 Append ",keep" to not disable it when the real console 1354 takes over. 1355 1356 Only one of vga, serial, or usb debug port can 1357 be used at a time. 1358 1359 Currently only ttyS0 and ttyS1 may be specified by 1360 name. Other I/O ports may be explicitly specified 1361 on some architectures (x86 and arm at least) by 1362 replacing ttySn with an I/O port address, like this: 1363 earlyprintk=serial,0x1008,115200 1364 You can find the port for a given device in 1365 /proc/tty/driver/serial: 1366 2: uart:ST16650V2 port:00001008 irq:18 ... 1367 1368 Interaction with the standard serial driver is not 1369 very good. 1370 1371 The VGA output is eventually overwritten by 1372 the real console. 1373 1374 The xen option can only be used in Xen domains. 1375 1376 The sclp output can only be used on s390. 1377 1378 The optional "force" to "pciserial" enables use of a 1379 PCI device even when its classcode is not of the 1380 UART class. 1381 1382 edac_report= [HW,EDAC] Control how to report EDAC event 1383 Format: {"on" | "off" | "force"} 1384 on: enable EDAC to report H/W event. May be overridden 1385 by other higher priority error reporting module. 1386 off: disable H/W event reporting through EDAC. 1387 force: enforce the use of EDAC to report H/W event. 1388 default: on. 1389 1390 edd= [EDD] 1391 Format: {"off" | "on" | "skip[mbr]"} 1392 1393 efi= [EFI] 1394 Format: { "debug", "disable_early_pci_dma", 1395 "nochunk", "noruntime", "nosoftreserve", 1396 "novamap", "no_disable_early_pci_dma" } 1397 debug: enable misc debug output. 1398 disable_early_pci_dma: disable the busmaster bit on all 1399 PCI bridges while in the EFI boot stub. 1400 nochunk: disable reading files in "chunks" in the EFI 1401 boot stub, as chunking can cause problems with some 1402 firmware implementations. 1403 noruntime : disable EFI runtime services support 1404 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1405 attribute may cause the kernel to reserve the 1406 memory range for a memory mapping driver to 1407 claim. Specify efi=nosoftreserve to disable this 1408 reservation and treat the memory by its base type 1409 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1410 novamap: do not call SetVirtualAddressMap(). 1411 no_disable_early_pci_dma: Leave the busmaster bit set 1412 on all PCI bridges while in the EFI boot stub 1413 1414 efi_no_storage_paranoia [EFI; X86] 1415 Using this parameter you can use more than 50% of 1416 your efi variable storage. Use this parameter only if 1417 you are really sure that your UEFI does sane gc and 1418 fulfills the spec otherwise your board may brick. 1419 1420 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1421 Add arbitrary attribute to specific memory range by 1422 updating original EFI memory map. 1423 Region of memory which aa attribute is added to is 1424 from ss to ss+nn. 1425 1426 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1427 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1428 attribute is added to range 0x100000000-0x180000000 and 1429 0x10a0000000-0x1120000000. 1430 1431 If efi_fake_mem=8G@9G:0x40000 is specified, the 1432 EFI_MEMORY_SP(0x40000) attribute is added to 1433 range 0x240000000-0x43fffffff. 1434 1435 Using this parameter you can do debugging of EFI memmap 1436 related features. For example, you can do debugging of 1437 Address Range Mirroring feature even if your box 1438 doesn't support it, or mark specific memory as 1439 "soft reserved". 1440 1441 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1442 that is to be dynamically loaded by Linux. If there are 1443 multiple variables with the same name but with different 1444 vendor GUIDs, all of them will be loaded. See 1445 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1446 1447 1448 eisa_irq_edge= [PARISC,HW] 1449 See header of drivers/parisc/eisa.c. 1450 1451 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1452 Format: ekgdboc=kbd 1453 1454 This is designed to be used in conjunction with 1455 the boot argument: earlyprintk=vga 1456 1457 This parameter works in place of the kgdboc parameter 1458 but can only be used if the backing tty is available 1459 very early in the boot process. For early debugging 1460 via a serial port see kgdboc_earlycon instead. 1461 1462 elanfreq= [X86-32] 1463 See comment before function elanfreq_setup() in 1464 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1465 1466 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1467 Specifies physical address of start of kernel core 1468 image elf header and optionally the size. Generally 1469 kexec loader will pass this option to capture kernel. 1470 See Documentation/admin-guide/kdump/kdump.rst for details. 1471 1472 enable_mtrr_cleanup [X86] 1473 The kernel tries to adjust MTRR layout from continuous 1474 to discrete, to make X server driver able to add WB 1475 entry later. This parameter enables that. 1476 1477 enable_timer_pin_1 [X86] 1478 Enable PIN 1 of APIC timer 1479 Can be useful to work around chipset bugs 1480 (in particular on some ATI chipsets). 1481 The kernel tries to set a reasonable default. 1482 1483 enforcing= [SELINUX] Set initial enforcing status. 1484 Format: {"0" | "1"} 1485 See security/selinux/Kconfig help text. 1486 0 -- permissive (log only, no denials). 1487 1 -- enforcing (deny and log). 1488 Default value is 0. 1489 Value can be changed at runtime via 1490 /sys/fs/selinux/enforce. 1491 1492 erst_disable [ACPI] 1493 Disable Error Record Serialization Table (ERST) 1494 support. 1495 1496 ether= [HW,NET] Ethernet cards parameters 1497 This option is obsoleted by the "netdev=" option, which 1498 has equivalent usage. See its documentation for details. 1499 1500 evm= [EVM] 1501 Format: { "fix" } 1502 Permit 'security.evm' to be updated regardless of 1503 current integrity status. 1504 1505 early_page_ext [KNL] Enforces page_ext initialization to earlier 1506 stages so cover more early boot allocations. 1507 Please note that as side effect some optimizations 1508 might be disabled to achieve that (e.g. parallelized 1509 memory initialization is disabled) so the boot process 1510 might take longer, especially on systems with a lot of 1511 memory. Available with CONFIG_PAGE_EXTENSION=y. 1512 1513 failslab= 1514 fail_usercopy= 1515 fail_page_alloc= 1516 fail_make_request=[KNL] 1517 General fault injection mechanism. 1518 Format: <interval>,<probability>,<space>,<times> 1519 See also Documentation/fault-injection/. 1520 1521 fb_tunnels= [NET] 1522 Format: { initns | none } 1523 See Documentation/admin-guide/sysctl/net.rst for 1524 fb_tunnels_only_for_init_ns 1525 1526 floppy= [HW] 1527 See Documentation/admin-guide/blockdev/floppy.rst. 1528 1529 force_pal_cache_flush 1530 [IA-64] Avoid check_sal_cache_flush which may hang on 1531 buggy SAL_CACHE_FLUSH implementations. Using this 1532 parameter will force ia64_sal_cache_flush to call 1533 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1534 1535 forcepae [X86-32] 1536 Forcefully enable Physical Address Extension (PAE). 1537 Many Pentium M systems disable PAE but may have a 1538 functionally usable PAE implementation. 1539 Warning: use of this parameter will taint the kernel 1540 and may cause unknown problems. 1541 1542 ftrace=[tracer] 1543 [FTRACE] will set and start the specified tracer 1544 as early as possible in order to facilitate early 1545 boot debugging. 1546 1547 ftrace_boot_snapshot 1548 [FTRACE] On boot up, a snapshot will be taken of the 1549 ftrace ring buffer that can be read at: 1550 /sys/kernel/tracing/snapshot. 1551 This is useful if you need tracing information from kernel 1552 boot up that is likely to be overridden by user space 1553 start up functionality. 1554 1555 Optionally, the snapshot can also be defined for a tracing 1556 instance that was created by the trace_instance= command 1557 line parameter. 1558 1559 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo 1560 1561 The above will cause the "foo" tracing instance to trigger 1562 a snapshot at the end of boot up. 1563 1564 ftrace_dump_on_oops[=orig_cpu] 1565 [FTRACE] will dump the trace buffers on oops. 1566 If no parameter is passed, ftrace will dump 1567 buffers of all CPUs, but if you pass orig_cpu, it will 1568 dump only the buffer of the CPU that triggered the 1569 oops. 1570 1571 ftrace_filter=[function-list] 1572 [FTRACE] Limit the functions traced by the function 1573 tracer at boot up. function-list is a comma-separated 1574 list of functions. This list can be changed at run 1575 time by the set_ftrace_filter file in the debugfs 1576 tracing directory. 1577 1578 ftrace_notrace=[function-list] 1579 [FTRACE] Do not trace the functions specified in 1580 function-list. This list can be changed at run time 1581 by the set_ftrace_notrace file in the debugfs 1582 tracing directory. 1583 1584 ftrace_graph_filter=[function-list] 1585 [FTRACE] Limit the top level callers functions traced 1586 by the function graph tracer at boot up. 1587 function-list is a comma-separated list of functions 1588 that can be changed at run time by the 1589 set_graph_function file in the debugfs tracing directory. 1590 1591 ftrace_graph_notrace=[function-list] 1592 [FTRACE] Do not trace from the functions specified in 1593 function-list. This list is a comma-separated list of 1594 functions that can be changed at run time by the 1595 set_graph_notrace file in the debugfs tracing directory. 1596 1597 ftrace_graph_max_depth=<uint> 1598 [FTRACE] Used with the function graph tracer. This is 1599 the max depth it will trace into a function. This value 1600 can be changed at run time by the max_graph_depth file 1601 in the tracefs tracing directory. default: 0 (no limit) 1602 1603 fw_devlink= [KNL] Create device links between consumer and supplier 1604 devices by scanning the firmware to infer the 1605 consumer/supplier relationships. This feature is 1606 especially useful when drivers are loaded as modules as 1607 it ensures proper ordering of tasks like device probing 1608 (suppliers first, then consumers), supplier boot state 1609 clean up (only after all consumers have probed), 1610 suspend/resume & runtime PM (consumers first, then 1611 suppliers). 1612 Format: { off | permissive | on | rpm } 1613 off -- Don't create device links from firmware info. 1614 permissive -- Create device links from firmware info 1615 but use it only for ordering boot state clean 1616 up (sync_state() calls). 1617 on -- Create device links from firmware info and use it 1618 to enforce probe and suspend/resume ordering. 1619 rpm -- Like "on", but also use to order runtime PM. 1620 1621 fw_devlink.strict=<bool> 1622 [KNL] Treat all inferred dependencies as mandatory 1623 dependencies. This only applies for fw_devlink=on|rpm. 1624 Format: <bool> 1625 1626 fw_devlink.sync_state = 1627 [KNL] When all devices that could probe have finished 1628 probing, this parameter controls what to do with 1629 devices that haven't yet received their sync_state() 1630 calls. 1631 Format: { strict | timeout } 1632 strict -- Default. Continue waiting on consumers to 1633 probe successfully. 1634 timeout -- Give up waiting on consumers and call 1635 sync_state() on any devices that haven't yet 1636 received their sync_state() calls after 1637 deferred_probe_timeout has expired or by 1638 late_initcall() if !CONFIG_MODULES. 1639 1640 gamecon.map[2|3]= 1641 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1642 support via parallel port (up to 5 devices per port) 1643 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1644 See also Documentation/input/devices/joystick-parport.rst 1645 1646 gamma= [HW,DRM] 1647 1648 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART 1649 Format: off | on 1650 default: on 1651 1652 gather_data_sampling= 1653 [X86,INTEL] Control the Gather Data Sampling (GDS) 1654 mitigation. 1655 1656 Gather Data Sampling is a hardware vulnerability which 1657 allows unprivileged speculative access to data which was 1658 previously stored in vector registers. 1659 1660 This issue is mitigated by default in updated microcode. 1661 The mitigation may have a performance impact but can be 1662 disabled. On systems without the microcode mitigation 1663 disabling AVX serves as a mitigation. 1664 1665 force: Disable AVX to mitigate systems without 1666 microcode mitigation. No effect if the microcode 1667 mitigation is present. Known to cause crashes in 1668 userspace with buggy AVX enumeration. 1669 1670 off: Disable GDS mitigation. 1671 1672 gcov_persist= [GCOV] When non-zero (default), profiling data for 1673 kernel modules is saved and remains accessible via 1674 debugfs, even when the module is unloaded/reloaded. 1675 When zero, profiling data is discarded and associated 1676 debugfs files are removed at module unload time. 1677 1678 goldfish [X86] Enable the goldfish android emulator platform. 1679 Don't use this when you are not running on the 1680 android emulator 1681 1682 gpio-mockup.gpio_mockup_ranges 1683 [HW] Sets the ranges of gpiochip of for this device. 1684 Format: <start1>,<end1>,<start2>,<end2>... 1685 gpio-mockup.gpio_mockup_named_lines 1686 [HW] Let the driver know GPIO lines should be named. 1687 1688 gpt [EFI] Forces disk with valid GPT signature but 1689 invalid Protective MBR to be treated as GPT. If the 1690 primary GPT is corrupted, it enables the backup/alternate 1691 GPT to be used instead. 1692 1693 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1694 the "Enable 0" bit of the configuration register. 1695 Format: 0 | 1 1696 Default: 0 1697 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1698 the "Enable 0" bit of the configuration register. 1699 Format: 0 | 1 1700 Default: 0 1701 grcan.select= [HW] Select which physical interface to use. 1702 Format: 0 | 1 1703 Default: 0 1704 grcan.txsize= [HW] Sets the size of the tx buffer. 1705 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1706 Default: 1024 1707 grcan.rxsize= [HW] Sets the size of the rx buffer. 1708 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1709 Default: 1024 1710 1711 hardened_usercopy= 1712 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 1713 hardening is enabled for this boot. Hardened 1714 usercopy checking is used to protect the kernel 1715 from reading or writing beyond known memory 1716 allocation boundaries as a proactive defense 1717 against bounds-checking flaws in the kernel's 1718 copy_to_user()/copy_from_user() interface. 1719 on Perform hardened usercopy checks (default). 1720 off Disable hardened usercopy checks. 1721 1722 hardlockup_all_cpu_backtrace= 1723 [KNL] Should the hard-lockup detector generate 1724 backtraces on all cpus. 1725 Format: 0 | 1 1726 1727 hashdist= [KNL,NUMA] Large hashes allocated during boot 1728 are distributed across NUMA nodes. Defaults on 1729 for 64-bit NUMA, off otherwise. 1730 Format: 0 | 1 (for off | on) 1731 1732 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1733 1734 hd= [EIDE] (E)IDE hard drive subsystem geometry 1735 Format: <cyl>,<head>,<sect> 1736 1737 hest_disable [ACPI] 1738 Disable Hardware Error Source Table (HEST) support; 1739 corresponding firmware-first mode error processing 1740 logic will be disabled. 1741 1742 hibernate= [HIBERNATION] 1743 noresume Don't check if there's a hibernation image 1744 present during boot. 1745 nocompress Don't compress/decompress hibernation images. 1746 no Disable hibernation and resume. 1747 protect_image Turn on image protection during restoration 1748 (that will set all pages holding image data 1749 during restoration read-only). 1750 1751 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1752 size of <nn>. This works even on boxes that have no 1753 highmem otherwise. This also works to reduce highmem 1754 size on bigger boxes. 1755 1756 highres= [KNL] Enable/disable high resolution timer mode. 1757 Valid parameters: "on", "off" 1758 Default: "on" 1759 1760 hlt [BUGS=ARM,SH] 1761 1762 hostname= [KNL] Set the hostname (aka UTS nodename). 1763 Format: <string> 1764 This allows setting the system's hostname during early 1765 startup. This sets the name returned by gethostname. 1766 Using this parameter to set the hostname makes it 1767 possible to ensure the hostname is correctly set before 1768 any userspace processes run, avoiding the possibility 1769 that a process may call gethostname before the hostname 1770 has been explicitly set, resulting in the calling 1771 process getting an incorrect result. The string must 1772 not exceed the maximum allowed hostname length (usually 1773 64 characters) and will be truncated otherwise. 1774 1775 hpet= [X86-32,HPET] option to control HPET usage 1776 Format: { enable (default) | disable | force | 1777 verbose } 1778 disable: disable HPET and use PIT instead 1779 force: allow force enabled of undocumented chips (ICH4, 1780 VIA, nVidia) 1781 verbose: show contents of HPET registers during setup 1782 1783 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1784 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1785 1786 hugepages= [HW] Number of HugeTLB pages to allocate at boot. 1787 If this follows hugepagesz (below), it specifies 1788 the number of pages of hugepagesz to be allocated. 1789 If this is the first HugeTLB parameter on the command 1790 line, it specifies the number of pages to allocate for 1791 the default huge page size. If using node format, the 1792 number of pages to allocate per-node can be specified. 1793 See also Documentation/admin-guide/mm/hugetlbpage.rst. 1794 Format: <integer> or (node format) 1795 <node>:<integer>[,<node>:<integer>] 1796 1797 hugepagesz= 1798 [HW] The size of the HugeTLB pages. This is used in 1799 conjunction with hugepages (above) to allocate huge 1800 pages of a specific size at boot. The pair 1801 hugepagesz=X hugepages=Y can be specified once for 1802 each supported huge page size. Huge page sizes are 1803 architecture dependent. See also 1804 Documentation/admin-guide/mm/hugetlbpage.rst. 1805 Format: size[KMG] 1806 1807 hugetlb_cma= [HW,CMA] The size of a CMA area used for allocation 1808 of gigantic hugepages. Or using node format, the size 1809 of a CMA area per node can be specified. 1810 Format: nn[KMGTPE] or (node format) 1811 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]] 1812 1813 Reserve a CMA area of given size and allocate gigantic 1814 hugepages using the CMA allocator. If enabled, the 1815 boot-time allocation of gigantic hugepages is skipped. 1816 1817 hugetlb_free_vmemmap= 1818 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP 1819 enabled. 1820 Control if HugeTLB Vmemmap Optimization (HVO) is enabled. 1821 Allows heavy hugetlb users to free up some more 1822 memory (7 * PAGE_SIZE for each 2MB hugetlb page). 1823 Format: { on | off (default) } 1824 1825 on: enable HVO 1826 off: disable HVO 1827 1828 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y, 1829 the default is on. 1830 1831 Note that the vmemmap pages may be allocated from the added 1832 memory block itself when memory_hotplug.memmap_on_memory is 1833 enabled, those vmemmap pages cannot be optimized even if this 1834 feature is enabled. Other vmemmap pages not allocated from 1835 the added memory block itself do not be affected. 1836 1837 hung_task_panic= 1838 [KNL] Should the hung task detector generate panics. 1839 Format: 0 | 1 1840 1841 A value of 1 instructs the kernel to panic when a 1842 hung task is detected. The default value is controlled 1843 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1844 option. The value selected by this boot parameter can 1845 be changed later by the kernel.hung_task_panic sysctl. 1846 1847 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1848 terminal devices. Valid values: 0..8 1849 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1850 If specified, z/VM IUCV HVC accepts connections 1851 from listed z/VM user IDs only. 1852 1853 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1854 which allow the hypervisor to 'idle' the 1855 guest on lock contention. 1856 1857 i2c_bus= [HW] Override the default board specific I2C bus speed 1858 or register an additional I2C bus that is not 1859 registered from board initialization code. 1860 Format: 1861 <bus_id>,<clkrate> 1862 1863 i8042.debug [HW] Toggle i8042 debug mode 1864 i8042.unmask_kbd_data 1865 [HW] Enable printing of interrupt data from the KBD port 1866 (disabled by default, and as a pre-condition 1867 requires that i8042.debug=1 be enabled) 1868 i8042.direct [HW] Put keyboard port into non-translated mode 1869 i8042.dumbkbd [HW] Pretend that controller can only read data from 1870 keyboard and cannot control its state 1871 (Don't attempt to blink the leds) 1872 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1873 i8042.nokbd [HW] Don't check/create keyboard port 1874 i8042.noloop [HW] Disable the AUX Loopback command while probing 1875 for the AUX port 1876 i8042.nomux [HW] Don't check presence of an active multiplexing 1877 controller 1878 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1879 controllers 1880 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1881 i8042.reset [HW] Reset the controller during init, cleanup and 1882 suspend-to-ram transitions, only during s2r 1883 transitions, or never reset 1884 Format: { 1 | Y | y | 0 | N | n } 1885 1, Y, y: always reset controller 1886 0, N, n: don't ever reset controller 1887 Default: only on s2r transitions on x86; most other 1888 architectures force reset to be always executed 1889 i8042.unlock [HW] Unlock (ignore) the keylock 1890 i8042.kbdreset [HW] Reset device connected to KBD port 1891 i8042.probe_defer 1892 [HW] Allow deferred probing upon i8042 probe errors 1893 1894 i810= [HW,DRM] 1895 1896 i915.invert_brightness= 1897 [DRM] Invert the sense of the variable that is used to 1898 set the brightness of the panel backlight. Normally a 1899 brightness value of 0 indicates backlight switched off, 1900 and the maximum of the brightness value sets the backlight 1901 to maximum brightness. If this parameter is set to 0 1902 (default) and the machine requires it, or this parameter 1903 is set to 1, a brightness value of 0 sets the backlight 1904 to maximum brightness, and the maximum of the brightness 1905 value switches the backlight off. 1906 -1 -- never invert brightness 1907 0 -- machine default 1908 1 -- force brightness inversion 1909 1910 icn= [HW,ISDN] 1911 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1912 1913 1914 idle= [X86] 1915 Format: idle=poll, idle=halt, idle=nomwait 1916 Poll forces a polling idle loop that can slightly 1917 improve the performance of waking up a idle CPU, but 1918 will use a lot of power and make the system run hot. 1919 Not recommended. 1920 idle=halt: Halt is forced to be used for CPU idle. 1921 In such case C2/C3 won't be used again. 1922 idle=nomwait: Disable mwait for CPU C-states 1923 1924 idxd.sva= [HW] 1925 Format: <bool> 1926 Allow force disabling of Shared Virtual Memory (SVA) 1927 support for the idxd driver. By default it is set to 1928 true (1). 1929 1930 idxd.tc_override= [HW] 1931 Format: <bool> 1932 Allow override of default traffic class configuration 1933 for the device. By default it is set to false (0). 1934 1935 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1936 Format: { strict | legacy | 2008 | relaxed } 1937 Default: strict 1938 1939 Choose which programs will be accepted for execution 1940 based on the IEEE 754 NaN encoding(s) supported by 1941 the FPU and the NaN encoding requested with the value 1942 of an ELF file header flag individually set by each 1943 binary. Hardware implementations are permitted to 1944 support either or both of the legacy and the 2008 NaN 1945 encoding mode. 1946 1947 Available settings are as follows: 1948 strict accept binaries that request a NaN encoding 1949 supported by the FPU 1950 legacy only accept legacy-NaN binaries, if supported 1951 by the FPU 1952 2008 only accept 2008-NaN binaries, if supported 1953 by the FPU 1954 relaxed accept any binaries regardless of whether 1955 supported by the FPU 1956 1957 The FPU emulator is always able to support both NaN 1958 encodings, so if no FPU hardware is present or it has 1959 been disabled with 'nofpu', then the settings of 1960 'legacy' and '2008' strap the emulator accordingly, 1961 'relaxed' straps the emulator for both legacy-NaN and 1962 2008-NaN, whereas 'strict' enables legacy-NaN only on 1963 legacy processors and both NaN encodings on MIPS32 or 1964 MIPS64 CPUs. 1965 1966 The setting for ABS.fmt/NEG.fmt instruction execution 1967 mode generally follows that for the NaN encoding, 1968 except where unsupported by hardware. 1969 1970 ignore_loglevel [KNL] 1971 Ignore loglevel setting - this will print /all/ 1972 kernel messages to the console. Useful for debugging. 1973 We also add it as printk module parameter, so users 1974 could change it dynamically, usually by 1975 /sys/module/printk/parameters/ignore_loglevel. 1976 1977 ignore_rlimit_data 1978 Ignore RLIMIT_DATA setting for data mappings, 1979 print warning at first misuse. Can be changed via 1980 /sys/module/kernel/parameters/ignore_rlimit_data. 1981 1982 ihash_entries= [KNL] 1983 Set number of hash buckets for inode cache. 1984 1985 ima_appraise= [IMA] appraise integrity measurements 1986 Format: { "off" | "enforce" | "fix" | "log" } 1987 default: "enforce" 1988 1989 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1990 The builtin appraise policy appraises all files 1991 owned by uid=0. 1992 1993 ima_canonical_fmt [IMA] 1994 Use the canonical format for the binary runtime 1995 measurements, instead of host native format. 1996 1997 ima_hash= [IMA] 1998 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1999 | sha512 | ... } 2000 default: "sha1" 2001 2002 The list of supported hash algorithms is defined 2003 in crypto/hash_info.h. 2004 2005 ima_policy= [IMA] 2006 The builtin policies to load during IMA setup. 2007 Format: "tcb | appraise_tcb | secure_boot | 2008 fail_securely | critical_data" 2009 2010 The "tcb" policy measures all programs exec'd, files 2011 mmap'd for exec, and all files opened with the read 2012 mode bit set by either the effective uid (euid=0) or 2013 uid=0. 2014 2015 The "appraise_tcb" policy appraises the integrity of 2016 all files owned by root. 2017 2018 The "secure_boot" policy appraises the integrity 2019 of files (eg. kexec kernel image, kernel modules, 2020 firmware, policy, etc) based on file signatures. 2021 2022 The "fail_securely" policy forces file signature 2023 verification failure also on privileged mounted 2024 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 2025 flag. 2026 2027 The "critical_data" policy measures kernel integrity 2028 critical data. 2029 2030 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 2031 Load a policy which meets the needs of the Trusted 2032 Computing Base. This means IMA will measure all 2033 programs exec'd, files mmap'd for exec, and all files 2034 opened for read by uid=0. 2035 2036 ima_template= [IMA] 2037 Select one of defined IMA measurements template formats. 2038 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" | 2039 "ima-sigv2" } 2040 Default: "ima-ng" 2041 2042 ima_template_fmt= 2043 [IMA] Define a custom template format. 2044 Format: { "field1|...|fieldN" } 2045 2046 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 2047 Format: <min_file_size> 2048 Set the minimal file size for using asynchronous hash. 2049 If left unspecified, ahash usage is disabled. 2050 2051 ahash performance varies for different data sizes on 2052 different crypto accelerators. This option can be used 2053 to achieve the best performance for a particular HW. 2054 2055 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 2056 Format: <bufsize> 2057 Set hashing buffer size. Default: 4k. 2058 2059 ahash performance varies for different chunk sizes on 2060 different crypto accelerators. This option can be used 2061 to achieve best performance for particular HW. 2062 2063 init= [KNL] 2064 Format: <full_path> 2065 Run specified binary instead of /sbin/init as init 2066 process. 2067 2068 initcall_debug [KNL] Trace initcalls as they are executed. Useful 2069 for working out where the kernel is dying during 2070 startup. 2071 2072 initcall_blacklist= [KNL] Do not execute a comma-separated list of 2073 initcall functions. Useful for debugging built-in 2074 modules and initcalls. 2075 2076 initramfs_async= [KNL] 2077 Format: <bool> 2078 Default: 1 2079 This parameter controls whether the initramfs 2080 image is unpacked asynchronously, concurrently 2081 with devices being probed and 2082 initialized. This should normally just work, 2083 but as a debugging aid, one can get the 2084 historical behaviour of the initramfs 2085 unpacking being completed before device_ and 2086 late_ initcalls. 2087 2088 initrd= [BOOT] Specify the location of the initial ramdisk 2089 2090 initrdmem= [KNL] Specify a physical address and size from which to 2091 load the initrd. If an initrd is compiled in or 2092 specified in the bootparams, it takes priority over this 2093 setting. 2094 Format: ss[KMG],nn[KMG] 2095 Default is 0, 0 2096 2097 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 2098 zeroes. 2099 Format: 0 | 1 2100 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 2101 2102 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 2103 Format: 0 | 1 2104 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 2105 2106 init_pkru= [X86] Specify the default memory protection keys rights 2107 register contents for all processes. 0x55555554 by 2108 default (disallow access to all but pkey 0). Can 2109 override in debugfs after boot. 2110 2111 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 2112 Format: <irq> 2113 2114 int_pln_enable [X86] Enable power limit notification interrupt 2115 2116 integrity_audit=[IMA] 2117 Format: { "0" | "1" } 2118 0 -- basic integrity auditing messages. (Default) 2119 1 -- additional integrity auditing messages. 2120 2121 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 2122 on 2123 Enable intel iommu driver. 2124 off 2125 Disable intel iommu driver. 2126 igfx_off [Default Off] 2127 By default, gfx is mapped as normal device. If a gfx 2128 device has a dedicated DMAR unit, the DMAR unit is 2129 bypassed by not enabling DMAR with this option. In 2130 this case, gfx device will use physical address for 2131 DMA. 2132 strict [Default Off] 2133 Deprecated, equivalent to iommu.strict=1. 2134 sp_off [Default Off] 2135 By default, super page will be supported if Intel IOMMU 2136 has the capability. With this option, super page will 2137 not be supported. 2138 sm_on 2139 Enable the Intel IOMMU scalable mode if the hardware 2140 advertises that it has support for the scalable mode 2141 translation. 2142 sm_off 2143 Disallow use of the Intel IOMMU scalable mode. 2144 tboot_noforce [Default Off] 2145 Do not force the Intel IOMMU enabled under tboot. 2146 By default, tboot will force Intel IOMMU on, which 2147 could harm performance of some high-throughput 2148 devices like 40GBit network cards, even if identity 2149 mapping is enabled. 2150 Note that using this option lowers the security 2151 provided by tboot because it makes the system 2152 vulnerable to DMA attacks. 2153 2154 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 2155 0 disables intel_idle and fall back on acpi_idle. 2156 1 to 9 specify maximum depth of C-state. 2157 2158 intel_pstate= [X86] 2159 disable 2160 Do not enable intel_pstate as the default 2161 scaling driver for the supported processors 2162 active 2163 Use intel_pstate driver to bypass the scaling 2164 governors layer of cpufreq and provides it own 2165 algorithms for p-state selection. There are two 2166 P-state selection algorithms provided by 2167 intel_pstate in the active mode: powersave and 2168 performance. The way they both operate depends 2169 on whether or not the hardware managed P-states 2170 (HWP) feature has been enabled in the processor 2171 and possibly on the processor model. 2172 passive 2173 Use intel_pstate as a scaling driver, but configure it 2174 to work with generic cpufreq governors (instead of 2175 enabling its internal governor). This mode cannot be 2176 used along with the hardware-managed P-states (HWP) 2177 feature. 2178 force 2179 Enable intel_pstate on systems that prohibit it by default 2180 in favor of acpi-cpufreq. Forcing the intel_pstate driver 2181 instead of acpi-cpufreq may disable platform features, such 2182 as thermal controls and power capping, that rely on ACPI 2183 P-States information being indicated to OSPM and therefore 2184 should be used with caution. This option does not work with 2185 processors that aren't supported by the intel_pstate driver 2186 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 2187 no_hwp 2188 Do not enable hardware P state control (HWP) 2189 if available. 2190 hwp_only 2191 Only load intel_pstate on systems which support 2192 hardware P state control (HWP) if available. 2193 support_acpi_ppc 2194 Enforce ACPI _PPC performance limits. If the Fixed ACPI 2195 Description Table, specifies preferred power management 2196 profile as "Enterprise Server" or "Performance Server", 2197 then this feature is turned on by default. 2198 per_cpu_perf_limits 2199 Allow per-logical-CPU P-State performance control limits using 2200 cpufreq sysfs interface 2201 2202 intremap= [X86-64, Intel-IOMMU] 2203 on enable Interrupt Remapping (default) 2204 off disable Interrupt Remapping 2205 nosid disable Source ID checking 2206 no_x2apic_optout 2207 BIOS x2APIC opt-out request will be ignored 2208 nopost disable Interrupt Posting 2209 2210 iomem= Disable strict checking of access to MMIO memory 2211 strict regions from userspace. 2212 relaxed 2213 2214 iommu= [X86] 2215 off 2216 force 2217 noforce 2218 biomerge 2219 panic 2220 nopanic 2221 merge 2222 nomerge 2223 soft 2224 pt [X86] 2225 nopt [X86] 2226 nobypass [PPC/POWERNV] 2227 Disable IOMMU bypass, using IOMMU for PCI devices. 2228 2229 iommu.forcedac= [ARM64, X86] Control IOVA allocation for PCI devices. 2230 Format: { "0" | "1" } 2231 0 - Try to allocate a 32-bit DMA address first, before 2232 falling back to the full range if needed. 2233 1 - Allocate directly from the full usable range, 2234 forcing Dual Address Cycle for PCI cards supporting 2235 greater than 32-bit addressing. 2236 2237 iommu.strict= [ARM64, X86] Configure TLB invalidation behaviour 2238 Format: { "0" | "1" } 2239 0 - Lazy mode. 2240 Request that DMA unmap operations use deferred 2241 invalidation of hardware TLBs, for increased 2242 throughput at the cost of reduced device isolation. 2243 Will fall back to strict mode if not supported by 2244 the relevant IOMMU driver. 2245 1 - Strict mode. 2246 DMA unmap operations invalidate IOMMU hardware TLBs 2247 synchronously. 2248 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}. 2249 Note: on x86, strict mode specified via one of the 2250 legacy driver-specific options takes precedence. 2251 2252 iommu.passthrough= 2253 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 2254 Format: { "0" | "1" } 2255 0 - Use IOMMU translation for DMA. 2256 1 - Bypass the IOMMU for DMA. 2257 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 2258 2259 io7= [HW] IO7 for Marvel-based Alpha systems 2260 See comment before marvel_specify_io7 in 2261 arch/alpha/kernel/core_marvel.c. 2262 2263 io_delay= [X86] I/O delay method 2264 0x80 2265 Standard port 0x80 based delay 2266 0xed 2267 Alternate port 0xed based delay (needed on some systems) 2268 udelay 2269 Simple two microseconds delay 2270 none 2271 No delay 2272 2273 ip= [IP_PNP] 2274 See Documentation/admin-guide/nfs/nfsroot.rst. 2275 2276 ipcmni_extend [KNL] Extend the maximum number of unique System V 2277 IPC identifiers from 32,768 to 16,777,216. 2278 2279 irqaffinity= [SMP] Set the default irq affinity mask 2280 The argument is a cpu list, as described above. 2281 2282 irqchip.gicv2_force_probe= 2283 [ARM, ARM64] 2284 Format: <bool> 2285 Force the kernel to look for the second 4kB page 2286 of a GICv2 controller even if the memory range 2287 exposed by the device tree is too small. 2288 2289 irqchip.gicv3_nolpi= 2290 [ARM, ARM64] 2291 Force the kernel to ignore the availability of 2292 LPIs (and by consequence ITSs). Intended for system 2293 that use the kernel as a bootloader, and thus want 2294 to let secondary kernels in charge of setting up 2295 LPIs. 2296 2297 irqchip.gicv3_pseudo_nmi= [ARM64] 2298 Enables support for pseudo-NMIs in the kernel. This 2299 requires the kernel to be built with 2300 CONFIG_ARM64_PSEUDO_NMI. 2301 2302 irqfixup [HW] 2303 When an interrupt is not handled search all handlers 2304 for it. Intended to get systems with badly broken 2305 firmware running. 2306 2307 irqpoll [HW] 2308 When an interrupt is not handled search all handlers 2309 for it. Also check all handlers each timer 2310 interrupt. Intended to get systems with badly broken 2311 firmware running. 2312 2313 isapnp= [ISAPNP] 2314 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2315 2316 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2317 [Deprecated - use cpusets instead] 2318 Format: [flag-list,]<cpu-list> 2319 2320 Specify one or more CPUs to isolate from disturbances 2321 specified in the flag list (default: domain): 2322 2323 nohz 2324 Disable the tick when a single task runs. 2325 2326 A residual 1Hz tick is offloaded to workqueues, which you 2327 need to affine to housekeeping through the global 2328 workqueue's affinity configured via the 2329 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2330 by using the 'domain' flag described below. 2331 2332 NOTE: by default the global workqueue runs on all CPUs, 2333 so to protect individual CPUs the 'cpumask' file has to 2334 be configured manually after bootup. 2335 2336 domain 2337 Isolate from the general SMP balancing and scheduling 2338 algorithms. Note that performing domain isolation this way 2339 is irreversible: it's not possible to bring back a CPU to 2340 the domains once isolated through isolcpus. It's strongly 2341 advised to use cpusets instead to disable scheduler load 2342 balancing through the "cpuset.sched_load_balance" file. 2343 It offers a much more flexible interface where CPUs can 2344 move in and out of an isolated set anytime. 2345 2346 You can move a process onto or off an "isolated" CPU via 2347 the CPU affinity syscalls or cpuset. 2348 <cpu number> begins at 0 and the maximum value is 2349 "number of CPUs in system - 1". 2350 2351 managed_irq 2352 2353 Isolate from being targeted by managed interrupts 2354 which have an interrupt mask containing isolated 2355 CPUs. The affinity of managed interrupts is 2356 handled by the kernel and cannot be changed via 2357 the /proc/irq/* interfaces. 2358 2359 This isolation is best effort and only effective 2360 if the automatically assigned interrupt mask of a 2361 device queue contains isolated and housekeeping 2362 CPUs. If housekeeping CPUs are online then such 2363 interrupts are directed to the housekeeping CPU 2364 so that IO submitted on the housekeeping CPU 2365 cannot disturb the isolated CPU. 2366 2367 If a queue's affinity mask contains only isolated 2368 CPUs then this parameter has no effect on the 2369 interrupt routing decision, though interrupts are 2370 only delivered when tasks running on those 2371 isolated CPUs submit IO. IO submitted on 2372 housekeeping CPUs has no influence on those 2373 queues. 2374 2375 The format of <cpu-list> is described above. 2376 2377 iucv= [HW,NET] 2378 2379 ivrs_ioapic [HW,X86-64] 2380 Provide an override to the IOAPIC-ID<->DEVICE-ID 2381 mapping provided in the IVRS ACPI table. 2382 By default, PCI segment is 0, and can be omitted. 2383 2384 For example, to map IOAPIC-ID decimal 10 to 2385 PCI segment 0x1 and PCI device 00:14.0, 2386 write the parameter as: 2387 ivrs_ioapic=10@0001:00:14.0 2388 2389 Deprecated formats: 2390 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0 2391 write the parameter as: 2392 ivrs_ioapic[10]=00:14.0 2393 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and 2394 PCI device 00:14.0 write the parameter as: 2395 ivrs_ioapic[10]=0001:00:14.0 2396 2397 ivrs_hpet [HW,X86-64] 2398 Provide an override to the HPET-ID<->DEVICE-ID 2399 mapping provided in the IVRS ACPI table. 2400 By default, PCI segment is 0, and can be omitted. 2401 2402 For example, to map HPET-ID decimal 10 to 2403 PCI segment 0x1 and PCI device 00:14.0, 2404 write the parameter as: 2405 ivrs_hpet=10@0001:00:14.0 2406 2407 Deprecated formats: 2408 * To map HPET-ID decimal 0 to PCI device 00:14.0 2409 write the parameter as: 2410 ivrs_hpet[0]=00:14.0 2411 * To map HPET-ID decimal 10 to PCI segment 0x1 and 2412 PCI device 00:14.0 write the parameter as: 2413 ivrs_ioapic[10]=0001:00:14.0 2414 2415 ivrs_acpihid [HW,X86-64] 2416 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2417 mapping provided in the IVRS ACPI table. 2418 By default, PCI segment is 0, and can be omitted. 2419 2420 For example, to map UART-HID:UID AMD0020:0 to 2421 PCI segment 0x1 and PCI device ID 00:14.5, 2422 write the parameter as: 2423 ivrs_acpihid=AMD0020:0@0001:00:14.5 2424 2425 Deprecated formats: 2426 * To map UART-HID:UID AMD0020:0 to PCI segment is 0, 2427 PCI device ID 00:14.5, write the parameter as: 2428 ivrs_acpihid[00:14.5]=AMD0020:0 2429 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and 2430 PCI device ID 00:14.5, write the parameter as: 2431 ivrs_acpihid[0001:00:14.5]=AMD0020:0 2432 2433 js= [HW,JOY] Analog joystick 2434 See Documentation/input/joydev/joystick.rst. 2435 2436 kasan_multi_shot 2437 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2438 report on every invalid memory access. Without this 2439 parameter KASAN will print report only for the first 2440 invalid access. 2441 2442 keep_bootcon [KNL] 2443 Do not unregister boot console at start. This is only 2444 useful for debugging when something happens in the window 2445 between unregistering the boot console and initializing 2446 the real console. 2447 2448 keepinitrd [HW,ARM] 2449 2450 kernelcore= [KNL,X86,IA-64,PPC] 2451 Format: nn[KMGTPE] | nn% | "mirror" 2452 This parameter specifies the amount of memory usable by 2453 the kernel for non-movable allocations. The requested 2454 amount is spread evenly throughout all nodes in the 2455 system as ZONE_NORMAL. The remaining memory is used for 2456 movable memory in its own zone, ZONE_MOVABLE. In the 2457 event, a node is too small to have both ZONE_NORMAL and 2458 ZONE_MOVABLE, kernelcore memory will take priority and 2459 other nodes will have a larger ZONE_MOVABLE. 2460 2461 ZONE_MOVABLE is used for the allocation of pages that 2462 may be reclaimed or moved by the page migration 2463 subsystem. Note that allocations like PTEs-from-HighMem 2464 still use the HighMem zone if it exists, and the Normal 2465 zone if it does not. 2466 2467 It is possible to specify the exact amount of memory in 2468 the form of "nn[KMGTPE]", a percentage of total system 2469 memory in the form of "nn%", or "mirror". If "mirror" 2470 option is specified, mirrored (reliable) memory is used 2471 for non-movable allocations and remaining memory is used 2472 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2473 are exclusive, so you cannot specify multiple forms. 2474 2475 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2476 Format: <Controller#>[,poll interval] 2477 The controller # is the number of the ehci usb debug 2478 port as it is probed via PCI. The poll interval is 2479 optional and is the number seconds in between 2480 each poll cycle to the debug port in case you need 2481 the functionality for interrupting the kernel with 2482 gdb or control-c on the dbgp connection. When 2483 not using this parameter you use sysrq-g to break into 2484 the kernel debugger. 2485 2486 kgdboc= [KGDB,HW] kgdb over consoles. 2487 Requires a tty driver that supports console polling, 2488 or a supported polling keyboard driver (non-usb). 2489 Serial only format: <serial_device>[,baud] 2490 keyboard only format: kbd 2491 keyboard and serial format: kbd,<serial_device>[,baud] 2492 Optional Kernel mode setting: 2493 kms, kbd format: kms,kbd 2494 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2495 2496 kgdboc_earlycon= [KGDB,HW] 2497 If the boot console provides the ability to read 2498 characters and can work in polling mode, you can use 2499 this parameter to tell kgdb to use it as a backend 2500 until the normal console is registered. Intended to 2501 be used together with the kgdboc parameter which 2502 specifies the normal console to transition to. 2503 2504 The name of the early console should be specified 2505 as the value of this parameter. Note that the name of 2506 the early console might be different than the tty 2507 name passed to kgdboc. It's OK to leave the value 2508 blank and the first boot console that implements 2509 read() will be picked. 2510 2511 kgdbwait [KGDB] Stop kernel execution and enter the 2512 kernel debugger at the earliest opportunity. 2513 2514 kmac= [MIPS] Korina ethernet MAC address. 2515 Configure the RouterBoard 532 series on-chip 2516 Ethernet adapter MAC address. 2517 2518 kmemleak= [KNL] Boot-time kmemleak enable/disable 2519 Valid arguments: on, off 2520 Default: on 2521 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2522 the default is off. 2523 2524 kprobe_event=[probe-list] 2525 [FTRACE] Add kprobe events and enable at boot time. 2526 The probe-list is a semicolon delimited list of probe 2527 definitions. Each definition is same as kprobe_events 2528 interface, but the parameters are comma delimited. 2529 For example, to add a kprobe event on vfs_read with 2530 arg1 and arg2, add to the command line; 2531 2532 kprobe_event=p,vfs_read,$arg1,$arg2 2533 2534 See also Documentation/trace/kprobetrace.rst "Kernel 2535 Boot Parameter" section. 2536 2537 kpti= [ARM64] Control page table isolation of user 2538 and kernel address spaces. 2539 Default: enabled on cores which need mitigation. 2540 0: force disabled 2541 1: force enabled 2542 2543 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires 2544 CONFIG_KUNIT to be set to be fully enabled. The 2545 default value can be overridden via 2546 KUNIT_DEFAULT_ENABLED. 2547 Default is 1 (enabled) 2548 2549 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2550 Default is 0 (don't ignore, but inject #GP) 2551 2552 kvm.eager_page_split= 2553 [KVM,X86] Controls whether or not KVM will try to 2554 proactively split all huge pages during dirty logging. 2555 Eager page splitting reduces interruptions to vCPU 2556 execution by eliminating the write-protection faults 2557 and MMU lock contention that would otherwise be 2558 required to split huge pages lazily. 2559 2560 VM workloads that rarely perform writes or that write 2561 only to a small region of VM memory may benefit from 2562 disabling eager page splitting to allow huge pages to 2563 still be used for reads. 2564 2565 The behavior of eager page splitting depends on whether 2566 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If 2567 disabled, all huge pages in a memslot will be eagerly 2568 split when dirty logging is enabled on that memslot. If 2569 enabled, eager page splitting will be performed during 2570 the KVM_CLEAR_DIRTY ioctl, and only for the pages being 2571 cleared. 2572 2573 Eager page splitting is only supported when kvm.tdp_mmu=Y. 2574 2575 Default is Y (on). 2576 2577 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2578 Default is false (don't support). 2579 2580 kvm.nx_huge_pages= 2581 [KVM] Controls the software workaround for the 2582 X86_BUG_ITLB_MULTIHIT bug. 2583 force : Always deploy workaround. 2584 off : Never deploy workaround. 2585 auto : Deploy workaround based on the presence of 2586 X86_BUG_ITLB_MULTIHIT. 2587 2588 Default is 'auto'. 2589 2590 If the software workaround is enabled for the host, 2591 guests do need not to enable it for nested guests. 2592 2593 kvm.nx_huge_pages_recovery_ratio= 2594 [KVM] Controls how many 4KiB pages are periodically zapped 2595 back to huge pages. 0 disables the recovery, otherwise if 2596 the value is N KVM will zap 1/Nth of the 4KiB pages every 2597 period (see below). The default is 60. 2598 2599 kvm.nx_huge_pages_recovery_period_ms= 2600 [KVM] Controls the time period at which KVM zaps 4KiB pages 2601 back to huge pages. If the value is a non-zero N, KVM will 2602 zap a portion (see ratio above) of the pages every N msecs. 2603 If the value is 0 (the default), KVM will pick a period based 2604 on the ratio, such that a page is zapped after 1 hour on average. 2605 2606 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in 2607 KVM/SVM. Default is 1 (enabled). 2608 2609 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables, 2610 a.k.a. Two-Dimensional Page Tables. Default is 1 2611 (enabled). Disable by KVM if hardware lacks support 2612 for NPT. 2613 2614 kvm-arm.mode= 2615 [KVM,ARM] Select one of KVM/arm64's modes of operation. 2616 2617 none: Forcefully disable KVM. 2618 2619 nvhe: Standard nVHE-based mode, without support for 2620 protected guests. 2621 2622 protected: nVHE-based mode with support for guests whose 2623 state is kept private from the host. 2624 2625 nested: VHE-based mode with support for nested 2626 virtualization. Requires at least ARMv8.3 2627 hardware. 2628 2629 Defaults to VHE/nVHE based on hardware support. Setting 2630 mode to "protected" will disable kexec and hibernation 2631 for the host. "nested" is experimental and should be 2632 used with extreme caution. 2633 2634 kvm-arm.vgic_v3_group0_trap= 2635 [KVM,ARM] Trap guest accesses to GICv3 group-0 2636 system registers 2637 2638 kvm-arm.vgic_v3_group1_trap= 2639 [KVM,ARM] Trap guest accesses to GICv3 group-1 2640 system registers 2641 2642 kvm-arm.vgic_v3_common_trap= 2643 [KVM,ARM] Trap guest accesses to GICv3 common 2644 system registers 2645 2646 kvm-arm.vgic_v4_enable= 2647 [KVM,ARM] Allow use of GICv4 for direct injection of 2648 LPIs. 2649 2650 kvm_cma_resv_ratio=n [PPC] 2651 Reserves given percentage from system memory area for 2652 contiguous memory allocation for KVM hash pagetable 2653 allocation. 2654 By default it reserves 5% of total system memory. 2655 Format: <integer> 2656 Default: 5 2657 2658 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables, 2659 a.k.a. Two-Dimensional Page Tables. Default is 1 2660 (enabled). Disable by KVM if hardware lacks support 2661 for EPT. 2662 2663 kvm-intel.emulate_invalid_guest_state= 2664 [KVM,Intel] Control whether to emulate invalid guest 2665 state. Ignored if kvm-intel.enable_unrestricted_guest=1, 2666 as guest state is never invalid for unrestricted 2667 guests. This param doesn't apply to nested guests (L2), 2668 as KVM never emulates invalid L2 guest state. 2669 Default is 1 (enabled). 2670 2671 kvm-intel.flexpriority= 2672 [KVM,Intel] Control KVM's use of FlexPriority feature 2673 (TPR shadow). Default is 1 (enabled). Disable by KVM if 2674 hardware lacks support for it. 2675 2676 kvm-intel.nested= 2677 [KVM,Intel] Control nested virtualization feature in 2678 KVM/VMX. Default is 1 (enabled). 2679 2680 kvm-intel.unrestricted_guest= 2681 [KVM,Intel] Control KVM's use of unrestricted guest 2682 feature (virtualized real and unpaged mode). Default 2683 is 1 (enabled). Disable by KVM if EPT is disabled or 2684 hardware lacks support for it. 2685 2686 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2687 CVE-2018-3620. 2688 2689 Valid arguments: never, cond, always 2690 2691 always: L1D cache flush on every VMENTER. 2692 cond: Flush L1D on VMENTER only when the code between 2693 VMEXIT and VMENTER can leak host memory. 2694 never: Disables the mitigation 2695 2696 Default is cond (do L1 cache flush in specific instances) 2697 2698 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor 2699 Identification feature (tagged TLBs). Default is 1 2700 (enabled). Disable by KVM if hardware lacks support 2701 for it. 2702 2703 l1d_flush= [X86,INTEL] 2704 Control mitigation for L1D based snooping vulnerability. 2705 2706 Certain CPUs are vulnerable to an exploit against CPU 2707 internal buffers which can forward information to a 2708 disclosure gadget under certain conditions. 2709 2710 In vulnerable processors, the speculatively 2711 forwarded data can be used in a cache side channel 2712 attack, to access data to which the attacker does 2713 not have direct access. 2714 2715 This parameter controls the mitigation. The 2716 options are: 2717 2718 on - enable the interface for the mitigation 2719 2720 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2721 affected CPUs 2722 2723 The kernel PTE inversion protection is unconditionally 2724 enabled and cannot be disabled. 2725 2726 full 2727 Provides all available mitigations for the 2728 L1TF vulnerability. Disables SMT and 2729 enables all mitigations in the 2730 hypervisors, i.e. unconditional L1D flush. 2731 2732 SMT control and L1D flush control via the 2733 sysfs interface is still possible after 2734 boot. Hypervisors will issue a warning 2735 when the first VM is started in a 2736 potentially insecure configuration, 2737 i.e. SMT enabled or L1D flush disabled. 2738 2739 full,force 2740 Same as 'full', but disables SMT and L1D 2741 flush runtime control. Implies the 2742 'nosmt=force' command line option. 2743 (i.e. sysfs control of SMT is disabled.) 2744 2745 flush 2746 Leaves SMT enabled and enables the default 2747 hypervisor mitigation, i.e. conditional 2748 L1D flush. 2749 2750 SMT control and L1D flush control via the 2751 sysfs interface is still possible after 2752 boot. Hypervisors will issue a warning 2753 when the first VM is started in a 2754 potentially insecure configuration, 2755 i.e. SMT enabled or L1D flush disabled. 2756 2757 flush,nosmt 2758 2759 Disables SMT and enables the default 2760 hypervisor mitigation. 2761 2762 SMT control and L1D flush control via the 2763 sysfs interface is still possible after 2764 boot. Hypervisors will issue a warning 2765 when the first VM is started in a 2766 potentially insecure configuration, 2767 i.e. SMT enabled or L1D flush disabled. 2768 2769 flush,nowarn 2770 Same as 'flush', but hypervisors will not 2771 warn when a VM is started in a potentially 2772 insecure configuration. 2773 2774 off 2775 Disables hypervisor mitigations and doesn't 2776 emit any warnings. 2777 It also drops the swap size and available 2778 RAM limit restriction on both hypervisor and 2779 bare metal. 2780 2781 Default is 'flush'. 2782 2783 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2784 2785 l2cr= [PPC] 2786 2787 l3cr= [PPC] 2788 2789 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2790 disabled it. 2791 2792 lapic= [X86,APIC] Do not use TSC deadline 2793 value for LAPIC timer one-shot implementation. Default 2794 back to the programmable timer unit in the LAPIC. 2795 Format: notscdeadline 2796 2797 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2798 in C2 power state. 2799 2800 libata.dma= [LIBATA] DMA control 2801 libata.dma=0 Disable all PATA and SATA DMA 2802 libata.dma=1 PATA and SATA Disk DMA only 2803 libata.dma=2 ATAPI (CDROM) DMA only 2804 libata.dma=4 Compact Flash DMA only 2805 Combinations also work, so libata.dma=3 enables DMA 2806 for disks and CDROMs, but not CFs. 2807 2808 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2809 libata.ignore_hpa=0 keep BIOS limits (default) 2810 libata.ignore_hpa=1 ignore limits, using full disk 2811 2812 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2813 when set. 2814 Format: <int> 2815 2816 libata.force= [LIBATA] Force configurations. The format is a comma- 2817 separated list of "[ID:]VAL" where ID is PORT[.DEVICE]. 2818 PORT and DEVICE are decimal numbers matching port, link 2819 or device. Basically, it matches the ATA ID string 2820 printed on console by libata. If the whole ID part is 2821 omitted, the last PORT and DEVICE values are used. If 2822 ID hasn't been specified yet, the configuration applies 2823 to all ports, links and devices. 2824 2825 If only DEVICE is omitted, the parameter applies to 2826 the port and all links and devices behind it. DEVICE 2827 number of 0 either selects the first device or the 2828 first fan-out link behind PMP device. It does not 2829 select the host link. DEVICE number of 15 selects the 2830 host link and device attached to it. 2831 2832 The VAL specifies the configuration to force. As long 2833 as there is no ambiguity, shortcut notation is allowed. 2834 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2835 The following configurations can be forced. 2836 2837 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2838 Any ID with matching PORT is used. 2839 2840 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2841 2842 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2843 udma[/][16,25,33,44,66,100,133] notation is also 2844 allowed. 2845 2846 * nohrst, nosrst, norst: suppress hard, soft and both 2847 resets. 2848 2849 * rstonce: only attempt one reset during hot-unplug 2850 link recovery. 2851 2852 * [no]dbdelay: Enable or disable the extra 200ms delay 2853 before debouncing a link PHY and device presence 2854 detection. 2855 2856 * [no]ncq: Turn on or off NCQ. 2857 2858 * [no]ncqtrim: Enable or disable queued DSM TRIM. 2859 2860 * [no]ncqati: Enable or disable NCQ trim on ATI chipset. 2861 2862 * [no]trim: Enable or disable (unqueued) TRIM. 2863 2864 * trim_zero: Indicate that TRIM command zeroes data. 2865 2866 * max_trim_128m: Set 128M maximum trim size limit. 2867 2868 * [no]dma: Turn on or off DMA transfers. 2869 2870 * atapi_dmadir: Enable ATAPI DMADIR bridge support. 2871 2872 * atapi_mod16_dma: Enable the use of ATAPI DMA for 2873 commands that are not a multiple of 16 bytes. 2874 2875 * [no]dmalog: Enable or disable the use of the 2876 READ LOG DMA EXT command to access logs. 2877 2878 * [no]iddevlog: Enable or disable access to the 2879 identify device data log. 2880 2881 * [no]logdir: Enable or disable access to the general 2882 purpose log directory. 2883 2884 * max_sec_128: Set transfer size limit to 128 sectors. 2885 2886 * max_sec_1024: Set or clear transfer size limit to 2887 1024 sectors. 2888 2889 * max_sec_lba48: Set or clear transfer size limit to 2890 65535 sectors. 2891 2892 * [no]lpm: Enable or disable link power management. 2893 2894 * [no]setxfer: Indicate if transfer speed mode setting 2895 should be skipped. 2896 2897 * [no]fua: Disable or enable FUA (Force Unit Access) 2898 support for devices supporting this feature. 2899 2900 * dump_id: Dump IDENTIFY data. 2901 2902 * disable: Disable this device. 2903 2904 If there are multiple matching configurations changing 2905 the same attribute, the last one is used. 2906 2907 load_ramdisk= [RAM] [Deprecated] 2908 2909 lockd.nlm_grace_period=P [NFS] Assign grace period. 2910 Format: <integer> 2911 2912 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2913 Format: <integer> 2914 2915 lockd.nlm_timeout=T [NFS] Assign timeout value. 2916 Format: <integer> 2917 2918 lockd.nlm_udpport=M [NFS] Assign UDP port. 2919 Format: <integer> 2920 2921 lockdown= [SECURITY] 2922 { integrity | confidentiality } 2923 Enable the kernel lockdown feature. If set to 2924 integrity, kernel features that allow userland to 2925 modify the running kernel are disabled. If set to 2926 confidentiality, kernel features that allow userland 2927 to extract confidential information from the kernel 2928 are also disabled. 2929 2930 locktorture.nreaders_stress= [KNL] 2931 Set the number of locking read-acquisition kthreads. 2932 Defaults to being automatically set based on the 2933 number of online CPUs. 2934 2935 locktorture.nwriters_stress= [KNL] 2936 Set the number of locking write-acquisition kthreads. 2937 2938 locktorture.onoff_holdoff= [KNL] 2939 Set time (s) after boot for CPU-hotplug testing. 2940 2941 locktorture.onoff_interval= [KNL] 2942 Set time (s) between CPU-hotplug operations, or 2943 zero to disable CPU-hotplug testing. 2944 2945 locktorture.shuffle_interval= [KNL] 2946 Set task-shuffle interval (jiffies). Shuffling 2947 tasks allows some CPUs to go into dyntick-idle 2948 mode during the locktorture test. 2949 2950 locktorture.shutdown_secs= [KNL] 2951 Set time (s) after boot system shutdown. This 2952 is useful for hands-off automated testing. 2953 2954 locktorture.stat_interval= [KNL] 2955 Time (s) between statistics printk()s. 2956 2957 locktorture.stutter= [KNL] 2958 Time (s) to stutter testing, for example, 2959 specifying five seconds causes the test to run for 2960 five seconds, wait for five seconds, and so on. 2961 This tests the locking primitive's ability to 2962 transition abruptly to and from idle. 2963 2964 locktorture.torture_type= [KNL] 2965 Specify the locking implementation to test. 2966 2967 locktorture.writer_fifo= [KNL] 2968 Run the write-side locktorture kthreads at 2969 sched_set_fifo() real-time priority. 2970 2971 locktorture.verbose= [KNL] 2972 Enable additional printk() statements. 2973 2974 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2975 Format: <irq> 2976 2977 loglevel= All Kernel Messages with a loglevel smaller than the 2978 console loglevel will be printed to the console. It can 2979 also be changed with klogd or other programs. The 2980 loglevels are defined as follows: 2981 2982 0 (KERN_EMERG) system is unusable 2983 1 (KERN_ALERT) action must be taken immediately 2984 2 (KERN_CRIT) critical conditions 2985 3 (KERN_ERR) error conditions 2986 4 (KERN_WARNING) warning conditions 2987 5 (KERN_NOTICE) normal but significant condition 2988 6 (KERN_INFO) informational 2989 7 (KERN_DEBUG) debug-level messages 2990 2991 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2992 in bytes. n must be a power of two and greater 2993 than the minimal size. The minimal size is defined 2994 by LOG_BUF_SHIFT kernel config parameter. There is 2995 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2996 that allows to increase the default size depending on 2997 the number of CPUs. See init/Kconfig for more details. 2998 2999 logo.nologo [FB] Disables display of the built-in Linux logo. 3000 This may be used to provide more screen space for 3001 kernel log messages and is useful when debugging 3002 kernel boot problems. 3003 3004 lp=0 [LP] Specify parallel ports to use, e.g, 3005 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 3006 lp=reset first parallel port). 'lp=0' disables the 3007 lp=auto printer driver. 'lp=reset' (which can be 3008 specified in addition to the ports) causes 3009 attached printers to be reset. Using 3010 lp=port1,port2,... specifies the parallel ports 3011 to associate lp devices with, starting with 3012 lp0. A port specification may be 'none' to skip 3013 that lp device, or a parport name such as 3014 'parport0'. Specifying 'lp=auto' instead of a 3015 port specification list means that device IDs 3016 from each port should be examined, to see if 3017 an IEEE 1284-compliant printer is attached; if 3018 so, the driver will manage that printer. 3019 See also header of drivers/char/lp.c. 3020 3021 lpj=n [KNL] 3022 Sets loops_per_jiffy to given constant, thus avoiding 3023 time-consuming boot-time autodetection (up to 250 ms per 3024 CPU). 0 enables autodetection (default). To determine 3025 the correct value for your kernel, boot with normal 3026 autodetection and see what value is printed. Note that 3027 on SMP systems the preset will be applied to all CPUs, 3028 which is likely to cause problems if your CPUs need 3029 significantly divergent settings. An incorrect value 3030 will cause delays in the kernel to be wrong, leading to 3031 unpredictable I/O errors and other breakage. Although 3032 unlikely, in the extreme case this might damage your 3033 hardware. 3034 3035 ltpc= [NET] 3036 Format: <io>,<irq>,<dma> 3037 3038 lsm.debug [SECURITY] Enable LSM initialization debugging output. 3039 3040 lsm=lsm1,...,lsmN 3041 [SECURITY] Choose order of LSM initialization. This 3042 overrides CONFIG_LSM, and the "security=" parameter. 3043 3044 machvec= [IA-64] Force the use of a particular machine-vector 3045 (machvec) in a generic kernel. 3046 Example: machvec=hpzx1 3047 3048 machtype= [Loongson] Share the same kernel image file between 3049 different yeeloong laptops. 3050 Example: machtype=lemote-yeeloong-2f-7inch 3051 3052 max_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory greater 3053 than or equal to this physical address is ignored. 3054 3055 maxcpus= [SMP] Maximum number of processors that an SMP kernel 3056 will bring up during bootup. maxcpus=n : n >= 0 limits 3057 the kernel to bring up 'n' processors. Surely after 3058 bootup you can bring up the other plugged cpu by executing 3059 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 3060 only takes effect during system bootup. 3061 While n=0 is a special case, it is equivalent to "nosmp", 3062 which also disables the IO APIC. 3063 3064 max_loop= [LOOP] The number of loop block devices that get 3065 (loop.max_loop) unconditionally pre-created at init time. The default 3066 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 3067 of statically allocating a predefined number, loop 3068 devices can be requested on-demand with the 3069 /dev/loop-control interface. 3070 3071 mce [X86-32] Machine Check Exception 3072 3073 mce=option [X86-64] See Documentation/arch/x86/x86_64/boot-options.rst 3074 3075 md= [HW] RAID subsystems devices and level 3076 See Documentation/admin-guide/md.rst. 3077 3078 mdacon= [MDA] 3079 Format: <first>,<last> 3080 Specifies range of consoles to be captured by the MDA. 3081 3082 mds= [X86,INTEL] 3083 Control mitigation for the Micro-architectural Data 3084 Sampling (MDS) vulnerability. 3085 3086 Certain CPUs are vulnerable to an exploit against CPU 3087 internal buffers which can forward information to a 3088 disclosure gadget under certain conditions. 3089 3090 In vulnerable processors, the speculatively 3091 forwarded data can be used in a cache side channel 3092 attack, to access data to which the attacker does 3093 not have direct access. 3094 3095 This parameter controls the MDS mitigation. The 3096 options are: 3097 3098 full - Enable MDS mitigation on vulnerable CPUs 3099 full,nosmt - Enable MDS mitigation and disable 3100 SMT on vulnerable CPUs 3101 off - Unconditionally disable MDS mitigation 3102 3103 On TAA-affected machines, mds=off can be prevented by 3104 an active TAA mitigation as both vulnerabilities are 3105 mitigated with the same mechanism so in order to disable 3106 this mitigation, you need to specify tsx_async_abort=off 3107 too. 3108 3109 Not specifying this option is equivalent to 3110 mds=full. 3111 3112 For details see: Documentation/admin-guide/hw-vuln/mds.rst 3113 3114 mem=nn[KMG] [HEXAGON] Set the memory size. 3115 Must be specified, otherwise memory size will be 0. 3116 3117 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 3118 Amount of memory to be used in cases as follows: 3119 3120 1 for test; 3121 2 when the kernel is not able to see the whole system memory; 3122 3 memory that lies after 'mem=' boundary is excluded from 3123 the hypervisor, then assigned to KVM guests. 3124 4 to limit the memory available for kdump kernel. 3125 3126 [ARC,MICROBLAZE] - the limit applies only to low memory, 3127 high memory is not affected. 3128 3129 [ARM64] - only limits memory covered by the linear 3130 mapping. The NOMAP regions are not affected. 3131 3132 [X86] Work as limiting max address. Use together 3133 with memmap= to avoid physical address space collisions. 3134 Without memmap= PCI devices could be placed at addresses 3135 belonging to unused RAM. 3136 3137 Note that this only takes effects during boot time since 3138 in above case 3, memory may need be hot added after boot 3139 if system memory of hypervisor is not sufficient. 3140 3141 mem=nn[KMG]@ss[KMG] 3142 [ARM,MIPS] - override the memory layout reported by 3143 firmware. 3144 Define a memory region of size nn[KMG] starting at 3145 ss[KMG]. 3146 Multiple different regions can be specified with 3147 multiple mem= parameters on the command line. 3148 3149 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 3150 memory. 3151 3152 memblock=debug [KNL] Enable memblock debug messages. 3153 3154 memchunk=nn[KMG] 3155 [KNL,SH] Allow user to override the default size for 3156 per-device physically contiguous DMA buffers. 3157 3158 memhp_default_state=online/offline/online_kernel/online_movable 3159 [KNL] Set the initial state for the memory hotplug 3160 onlining policy. If not specified, the default value is 3161 set according to the 3162 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 3163 option. 3164 See Documentation/admin-guide/mm/memory-hotplug.rst. 3165 3166 memmap=exactmap [KNL,X86] Enable setting of an exact 3167 E820 memory map, as specified by the user. 3168 Such memmap=exactmap lines can be constructed based on 3169 BIOS output or other requirements. See the memmap=nn@ss 3170 option description. 3171 3172 memmap=nn[KMG]@ss[KMG] 3173 [KNL, X86, MIPS, XTENSA] Force usage of a specific region of memory. 3174 Region of memory to be used is from ss to ss+nn. 3175 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 3176 which limits max address to nn[KMG]. 3177 Multiple different regions can be specified, 3178 comma delimited. 3179 Example: 3180 memmap=100M@2G,100M#3G,1G!1024G 3181 3182 memmap=nn[KMG]#ss[KMG] 3183 [KNL,ACPI] Mark specific memory as ACPI data. 3184 Region of memory to be marked is from ss to ss+nn. 3185 3186 memmap=nn[KMG]$ss[KMG] 3187 [KNL,ACPI] Mark specific memory as reserved. 3188 Region of memory to be reserved is from ss to ss+nn. 3189 Example: Exclude memory from 0x18690000-0x1869ffff 3190 memmap=64K$0x18690000 3191 or 3192 memmap=0x10000$0x18690000 3193 Some bootloaders may need an escape character before '$', 3194 like Grub2, otherwise '$' and the following number 3195 will be eaten. 3196 3197 memmap=nn[KMG]!ss[KMG] 3198 [KNL,X86] Mark specific memory as protected. 3199 Region of memory to be used, from ss to ss+nn. 3200 The memory region may be marked as e820 type 12 (0xc) 3201 and is NVDIMM or ADR memory. 3202 3203 memmap=<size>%<offset>-<oldtype>+<newtype> 3204 [KNL,ACPI] Convert memory within the specified region 3205 from <oldtype> to <newtype>. If "-<oldtype>" is left 3206 out, the whole region will be marked as <newtype>, 3207 even if previously unavailable. If "+<newtype>" is left 3208 out, matching memory will be removed. Types are 3209 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 3210 3 = ACPI, 12 = PRAM. 3211 3212 memory_corruption_check=0/1 [X86] 3213 Some BIOSes seem to corrupt the first 64k of 3214 memory when doing things like suspend/resume. 3215 Setting this option will scan the memory 3216 looking for corruption. Enabling this will 3217 both detect corruption and prevent the kernel 3218 from using the memory being corrupted. 3219 However, its intended as a diagnostic tool; if 3220 repeatable BIOS-originated corruption always 3221 affects the same memory, you can use memmap= 3222 to prevent the kernel from using that memory. 3223 3224 memory_corruption_check_size=size [X86] 3225 By default it checks for corruption in the low 3226 64k, making this memory unavailable for normal 3227 use. Use this parameter to scan for 3228 corruption in more or less memory. 3229 3230 memory_corruption_check_period=seconds [X86] 3231 By default it checks for corruption every 60 3232 seconds. Use this parameter to check at some 3233 other rate. 0 disables periodic checking. 3234 3235 memory_hotplug.memmap_on_memory 3236 [KNL,X86,ARM] Boolean flag to enable this feature. 3237 Format: {on | off (default)} 3238 When enabled, runtime hotplugged memory will 3239 allocate its internal metadata (struct pages, 3240 those vmemmap pages cannot be optimized even 3241 if hugetlb_free_vmemmap is enabled) from the 3242 hotadded memory which will allow to hotadd a 3243 lot of memory without requiring additional 3244 memory to do so. 3245 This feature is disabled by default because it 3246 has some implication on large (e.g. GB) 3247 allocations in some configurations (e.g. small 3248 memory blocks). 3249 The state of the flag can be read in 3250 /sys/module/memory_hotplug/parameters/memmap_on_memory. 3251 Note that even when enabled, there are a few cases where 3252 the feature is not effective. 3253 3254 memtest= [KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest 3255 Format: <integer> 3256 default : 0 <disable> 3257 Specifies the number of memtest passes to be 3258 performed. Each pass selects another test 3259 pattern from a given set of patterns. Memtest 3260 fills the memory with this pattern, validates 3261 memory contents and reserves bad memory 3262 regions that are detected. 3263 3264 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 3265 Valid arguments: on, off 3266 Default: off 3267 mem_encrypt=on: Activate SME 3268 mem_encrypt=off: Do not activate SME 3269 3270 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst 3271 for details on when memory encryption can be activated. 3272 3273 mem_sleep_default= [SUSPEND] Default system suspend mode: 3274 s2idle - Suspend-To-Idle 3275 shallow - Power-On Suspend or equivalent (if supported) 3276 deep - Suspend-To-RAM or equivalent (if supported) 3277 See Documentation/admin-guide/pm/sleep-states.rst. 3278 3279 mem.devmem= Activate the /dev/mem device 3280 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3281 3282 mfgpt_irq= [IA-32] Specify the IRQ to use for the 3283 Multi-Function General Purpose Timers on AMD Geode 3284 platforms. 3285 3286 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 3287 the BIOS has incorrectly applied a workaround. TinyBIOS 3288 version 0.98 is known to be affected, 0.99 fixes the 3289 problem by letting the user disable the workaround. 3290 3291 mga= [HW,DRM] 3292 3293 min_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory below this 3294 physical address is ignored. 3295 3296 mini2440= [ARM,HW,KNL] 3297 Format:[0..2][b][c][t] 3298 Default: "0tb" 3299 MINI2440 configuration specification: 3300 0 - The attached screen is the 3.5" TFT 3301 1 - The attached screen is the 7" TFT 3302 2 - The VGA Shield is attached (1024x768) 3303 Leaving out the screen size parameter will not load 3304 the TFT driver, and the framebuffer will be left 3305 unconfigured. 3306 b - Enable backlight. The TFT backlight pin will be 3307 linked to the kernel VESA blanking code and a GPIO 3308 LED. This parameter is not necessary when using the 3309 VGA shield. 3310 c - Enable the s3c camera interface. 3311 t - Reserved for enabling touchscreen support. The 3312 touchscreen support is not enabled in the mainstream 3313 kernel as of 2.6.30, a preliminary port can be found 3314 in the "bleeding edge" mini2440 support kernel at 3315 https://repo.or.cz/w/linux-2.6/mini2440.git 3316 3317 mitigations= 3318 [X86,PPC,S390,ARM64] Control optional mitigations for 3319 CPU vulnerabilities. This is a set of curated, 3320 arch-independent options, each of which is an 3321 aggregation of existing arch-specific options. 3322 3323 Note, "mitigations" is supported if and only if the 3324 kernel was built with CPU_MITIGATIONS=y. 3325 3326 off 3327 Disable all optional CPU mitigations. This 3328 improves system performance, but it may also 3329 expose users to several CPU vulnerabilities. 3330 Equivalent to: if nokaslr then kpti=0 [ARM64] 3331 gather_data_sampling=off [X86] 3332 kvm.nx_huge_pages=off [X86] 3333 l1tf=off [X86] 3334 mds=off [X86] 3335 mmio_stale_data=off [X86] 3336 no_entry_flush [PPC] 3337 no_uaccess_flush [PPC] 3338 nobp=0 [S390] 3339 nopti [X86,PPC] 3340 nospectre_bhb [ARM64] 3341 nospectre_v1 [X86,PPC] 3342 nospectre_v2 [X86,PPC,S390,ARM64] 3343 reg_file_data_sampling=off [X86] 3344 retbleed=off [X86] 3345 spec_store_bypass_disable=off [X86,PPC] 3346 spectre_bhi=off [X86] 3347 spectre_v2_user=off [X86] 3348 srbds=off [X86,INTEL] 3349 ssbd=force-off [ARM64] 3350 tsx_async_abort=off [X86] 3351 3352 Exceptions: 3353 This does not have any effect on 3354 kvm.nx_huge_pages when 3355 kvm.nx_huge_pages=force. 3356 3357 auto (default) 3358 Mitigate all CPU vulnerabilities, but leave SMT 3359 enabled, even if it's vulnerable. This is for 3360 users who don't want to be surprised by SMT 3361 getting disabled across kernel upgrades, or who 3362 have other ways of avoiding SMT-based attacks. 3363 Equivalent to: (default behavior) 3364 3365 auto,nosmt 3366 Mitigate all CPU vulnerabilities, disabling SMT 3367 if needed. This is for users who always want to 3368 be fully mitigated, even if it means losing SMT. 3369 Equivalent to: l1tf=flush,nosmt [X86] 3370 mds=full,nosmt [X86] 3371 tsx_async_abort=full,nosmt [X86] 3372 mmio_stale_data=full,nosmt [X86] 3373 retbleed=auto,nosmt [X86] 3374 3375 mminit_loglevel= 3376 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 3377 parameter allows control of the logging verbosity for 3378 the additional memory initialisation checks. A value 3379 of 0 disables mminit logging and a level of 4 will 3380 log everything. Information is printed at KERN_DEBUG 3381 so loglevel=8 may also need to be specified. 3382 3383 mmio_stale_data= 3384 [X86,INTEL] Control mitigation for the Processor 3385 MMIO Stale Data vulnerabilities. 3386 3387 Processor MMIO Stale Data is a class of 3388 vulnerabilities that may expose data after an MMIO 3389 operation. Exposed data could originate or end in 3390 the same CPU buffers as affected by MDS and TAA. 3391 Therefore, similar to MDS and TAA, the mitigation 3392 is to clear the affected CPU buffers. 3393 3394 This parameter controls the mitigation. The 3395 options are: 3396 3397 full - Enable mitigation on vulnerable CPUs 3398 3399 full,nosmt - Enable mitigation and disable SMT on 3400 vulnerable CPUs. 3401 3402 off - Unconditionally disable mitigation 3403 3404 On MDS or TAA affected machines, 3405 mmio_stale_data=off can be prevented by an active 3406 MDS or TAA mitigation as these vulnerabilities are 3407 mitigated with the same mechanism so in order to 3408 disable this mitigation, you need to specify 3409 mds=off and tsx_async_abort=off too. 3410 3411 Not specifying this option is equivalent to 3412 mmio_stale_data=full. 3413 3414 For details see: 3415 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst 3416 3417 <module>.async_probe[=<bool>] [KNL] 3418 If no <bool> value is specified or if the value 3419 specified is not a valid <bool>, enable asynchronous 3420 probe on this module. Otherwise, enable/disable 3421 asynchronous probe on this module as indicated by the 3422 <bool> value. See also: module.async_probe 3423 3424 module.async_probe=<bool> 3425 [KNL] When set to true, modules will use async probing 3426 by default. To enable/disable async probing for a 3427 specific module, use the module specific control that 3428 is documented under <module>.async_probe. When both 3429 module.async_probe and <module>.async_probe are 3430 specified, <module>.async_probe takes precedence for 3431 the specific module. 3432 3433 module.enable_dups_trace 3434 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set, 3435 this means that duplicate request_module() calls will 3436 trigger a WARN_ON() instead of a pr_warn(). Note that 3437 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s 3438 will always be issued and this option does nothing. 3439 module.sig_enforce 3440 [KNL] When CONFIG_MODULE_SIG is set, this means that 3441 modules without (valid) signatures will fail to load. 3442 Note that if CONFIG_MODULE_SIG_FORCE is set, that 3443 is always true, so this option does nothing. 3444 3445 module_blacklist= [KNL] Do not load a comma-separated list of 3446 modules. Useful for debugging problem modules. 3447 3448 mousedev.tap_time= 3449 [MOUSE] Maximum time between finger touching and 3450 leaving touchpad surface for touch to be considered 3451 a tap and be reported as a left button click (for 3452 touchpads working in absolute mode only). 3453 Format: <msecs> 3454 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 3455 reporting absolute coordinates, such as tablets 3456 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 3457 reporting absolute coordinates, such as tablets 3458 3459 movablecore= [KNL,X86,IA-64,PPC] 3460 Format: nn[KMGTPE] | nn% 3461 This parameter is the complement to kernelcore=, it 3462 specifies the amount of memory used for migratable 3463 allocations. If both kernelcore and movablecore is 3464 specified, then kernelcore will be at *least* the 3465 specified value but may be more. If movablecore on its 3466 own is specified, the administrator must be careful 3467 that the amount of memory usable for all allocations 3468 is not too small. 3469 3470 movable_node [KNL] Boot-time switch to make hotplugable memory 3471 NUMA nodes to be movable. This means that the memory 3472 of such nodes will be usable only for movable 3473 allocations which rules out almost all kernel 3474 allocations. Use with caution! 3475 3476 MTD_Partition= [MTD] 3477 Format: <name>,<region-number>,<size>,<offset> 3478 3479 MTD_Region= [MTD] Format: 3480 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 3481 3482 mtdparts= [MTD] 3483 See drivers/mtd/parsers/cmdlinepart.c 3484 3485 mtdset= [ARM] 3486 ARM/S3C2412 JIVE boot control 3487 3488 See arch/arm/mach-s3c/mach-jive.c 3489 3490 mtouchusb.raw_coordinates= 3491 [HW] Make the MicroTouch USB driver use raw coordinates 3492 ('y', default) or cooked coordinates ('n') 3493 3494 mtrr=debug [X86] 3495 Enable printing debug information related to MTRR 3496 registers at boot time. 3497 3498 mtrr_chunk_size=nn[KMG] [X86] 3499 used for mtrr cleanup. It is largest continuous chunk 3500 that could hold holes aka. UC entries. 3501 3502 mtrr_gran_size=nn[KMG] [X86] 3503 Used for mtrr cleanup. It is granularity of mtrr block. 3504 Default is 1. 3505 Large value could prevent small alignment from 3506 using up MTRRs. 3507 3508 mtrr_spare_reg_nr=n [X86] 3509 Format: <integer> 3510 Range: 0,7 : spare reg number 3511 Default : 1 3512 Used for mtrr cleanup. It is spare mtrr entries number. 3513 Set to 2 or more if your graphical card needs more. 3514 3515 multitce=off [PPC] This parameter disables the use of the pSeries 3516 firmware feature for updating multiple TCE entries 3517 at a time. 3518 3519 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 3520 3521 netdev= [NET] Network devices parameters 3522 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 3523 Note that mem_start is often overloaded to mean 3524 something different and driver-specific. 3525 This usage is only documented in each driver source 3526 file if at all. 3527 3528 netpoll.carrier_timeout= 3529 [NET] Specifies amount of time (in seconds) that 3530 netpoll should wait for a carrier. By default netpoll 3531 waits 4 seconds. 3532 3533 nf_conntrack.acct= 3534 [NETFILTER] Enable connection tracking flow accounting 3535 0 to disable accounting 3536 1 to enable accounting 3537 Default value is 0. 3538 3539 nfs.cache_getent= 3540 [NFS] sets the pathname to the program which is used 3541 to update the NFS client cache entries. 3542 3543 nfs.cache_getent_timeout= 3544 [NFS] sets the timeout after which an attempt to 3545 update a cache entry is deemed to have failed. 3546 3547 nfs.callback_nr_threads= 3548 [NFSv4] set the total number of threads that the 3549 NFS client will assign to service NFSv4 callback 3550 requests. 3551 3552 nfs.callback_tcpport= 3553 [NFS] set the TCP port on which the NFSv4 callback 3554 channel should listen. 3555 3556 nfs.enable_ino64= 3557 [NFS] enable 64-bit inode numbers. 3558 If zero, the NFS client will fake up a 32-bit inode 3559 number for the readdir() and stat() syscalls instead 3560 of returning the full 64-bit number. 3561 The default is to return 64-bit inode numbers. 3562 3563 nfs.idmap_cache_timeout= 3564 [NFS] set the maximum lifetime for idmapper cache 3565 entries. 3566 3567 nfs.max_session_cb_slots= 3568 [NFSv4.1] Sets the maximum number of session 3569 slots the client will assign to the callback 3570 channel. This determines the maximum number of 3571 callbacks the client will process in parallel for 3572 a particular server. 3573 3574 nfs.max_session_slots= 3575 [NFSv4.1] Sets the maximum number of session slots 3576 the client will attempt to negotiate with the server. 3577 This limits the number of simultaneous RPC requests 3578 that the client can send to the NFSv4.1 server. 3579 Note that there is little point in setting this 3580 value higher than the max_tcp_slot_table_limit. 3581 3582 nfs.nfs4_disable_idmapping= 3583 [NFSv4] When set to the default of '1', this option 3584 ensures that both the RPC level authentication 3585 scheme and the NFS level operations agree to use 3586 numeric uids/gids if the mount is using the 3587 'sec=sys' security flavour. In effect it is 3588 disabling idmapping, which can make migration from 3589 legacy NFSv2/v3 systems to NFSv4 easier. 3590 Servers that do not support this mode of operation 3591 will be autodetected by the client, and it will fall 3592 back to using the idmapper. 3593 To turn off this behaviour, set the value to '0'. 3594 3595 nfs.nfs4_unique_id= 3596 [NFS4] Specify an additional fixed unique ident- 3597 ification string that NFSv4 clients can insert into 3598 their nfs_client_id4 string. This is typically a 3599 UUID that is generated at system install time. 3600 3601 nfs.recover_lost_locks= 3602 [NFSv4] Attempt to recover locks that were lost due 3603 to a lease timeout on the server. Please note that 3604 doing this risks data corruption, since there are 3605 no guarantees that the file will remain unchanged 3606 after the locks are lost. 3607 If you want to enable the kernel legacy behaviour of 3608 attempting to recover these locks, then set this 3609 parameter to '1'. 3610 The default parameter value of '0' causes the kernel 3611 not to attempt recovery of lost locks. 3612 3613 nfs.send_implementation_id= 3614 [NFSv4.1] Send client implementation identification 3615 information in exchange_id requests. 3616 If zero, no implementation identification information 3617 will be sent. 3618 The default is to send the implementation identification 3619 information. 3620 3621 nfs4.layoutstats_timer= 3622 [NFSv4.2] Change the rate at which the kernel sends 3623 layoutstats to the pNFS metadata server. 3624 3625 Setting this to value to 0 causes the kernel to use 3626 whatever value is the default set by the layout 3627 driver. A non-zero value sets the minimum interval 3628 in seconds between layoutstats transmissions. 3629 3630 nfsd.inter_copy_offload_enable= 3631 [NFSv4.2] When set to 1, the server will support 3632 server-to-server copies for which this server is 3633 the destination of the copy. 3634 3635 nfsd.nfs4_disable_idmapping= 3636 [NFSv4] When set to the default of '1', the NFSv4 3637 server will return only numeric uids and gids to 3638 clients using auth_sys, and will accept numeric uids 3639 and gids from such clients. This is intended to ease 3640 migration from NFSv2/v3. 3641 3642 nfsd.nfsd4_ssc_umount_timeout= 3643 [NFSv4.2] When used as the destination of a 3644 server-to-server copy, knfsd temporarily mounts 3645 the source server. It caches the mount in case 3646 it will be needed again, and discards it if not 3647 used for the number of milliseconds specified by 3648 this parameter. 3649 3650 nfsaddrs= [NFS] Deprecated. Use ip= instead. 3651 See Documentation/admin-guide/nfs/nfsroot.rst. 3652 3653 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 3654 See Documentation/admin-guide/nfs/nfsroot.rst. 3655 3656 nfsrootdebug [NFS] enable nfsroot debugging messages. 3657 See Documentation/admin-guide/nfs/nfsroot.rst. 3658 3659 nmi_backtrace.backtrace_idle [KNL] 3660 Dump stacks even of idle CPUs in response to an 3661 NMI stack-backtrace request. 3662 3663 nmi_debug= [KNL,SH] Specify one or more actions to take 3664 when a NMI is triggered. 3665 Format: [state][,regs][,debounce][,die] 3666 3667 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3668 Format: [panic,][nopanic,][num] 3669 Valid num: 0 or 1 3670 0 - turn hardlockup detector in nmi_watchdog off 3671 1 - turn hardlockup detector in nmi_watchdog on 3672 When panic is specified, panic when an NMI watchdog 3673 timeout occurs (or 'nopanic' to not panic on an NMI 3674 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3675 To disable both hard and soft lockup detectors, 3676 please see 'nowatchdog'. 3677 This is useful when you use a panic=... timeout and 3678 need the box quickly up again. 3679 3680 These settings can be accessed at runtime via 3681 the nmi_watchdog and hardlockup_panic sysctls. 3682 3683 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3684 emulation library even if a 387 maths coprocessor 3685 is present. 3686 3687 no4lvl [RISCV] Disable 4-level and 5-level paging modes. Forces 3688 kernel to use 3-level paging instead. 3689 3690 no5lvl [X86-64,RISCV] Disable 5-level paging mode. Forces 3691 kernel to use 4-level paging instead. 3692 3693 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3694 caches in the slab allocator. Saves per-node memory, 3695 but will impact performance. 3696 3697 noalign [KNL,ARM] 3698 3699 noaltinstr [S390] Disables alternative instructions patching 3700 (CPU alternatives feature). 3701 3702 noapic [SMP,APIC] Tells the kernel to not make use of any 3703 IOAPICs that may be present in the system. 3704 3705 noautogroup Disable scheduler automatic task group creation. 3706 3707 nocache [ARM] 3708 3709 no_console_suspend 3710 [HW] Never suspend the console 3711 Disable suspending of consoles during suspend and 3712 hibernate operations. Once disabled, debugging 3713 messages can reach various consoles while the rest 3714 of the system is being put to sleep (ie, while 3715 debugging driver suspend/resume hooks). This may 3716 not work reliably with all consoles, but is known 3717 to work with serial and VGA consoles. 3718 To facilitate more flexible debugging, we also add 3719 console_suspend, a printk module parameter to control 3720 it. Users could use console_suspend (usually 3721 /sys/module/printk/parameters/console_suspend) to 3722 turn on/off it dynamically. 3723 3724 no_debug_objects 3725 [KNL] Disable object debugging 3726 3727 nodsp [SH] Disable hardware DSP at boot time. 3728 3729 noefi Disable EFI runtime services support. 3730 3731 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel. 3732 3733 noexec [IA-64] 3734 3735 noexec32 [X86-64] 3736 This affects only 32-bit executables. 3737 noexec32=on: enable non-executable mappings (default) 3738 read doesn't imply executable mappings 3739 noexec32=off: disable non-executable mappings 3740 read implies executable mappings 3741 3742 no_file_caps Tells the kernel not to honor file capabilities. The 3743 only way then for a file to be executed with privilege 3744 is to be setuid root or executed by root. 3745 3746 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3747 3748 nofsgsbase [X86] Disables FSGSBASE instructions. 3749 3750 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3751 register save and restore. The kernel will only save 3752 legacy floating-point registers on task switch. 3753 3754 nohalt [IA-64] Tells the kernel not to use the power saving 3755 function PAL_HALT_LIGHT when idle. This increases 3756 power-consumption. On the positive side, it reduces 3757 interrupt wake-up latency, which may improve performance 3758 in certain environments such as networked servers or 3759 real-time systems. 3760 3761 no_hash_pointers 3762 Force pointers printed to the console or buffers to be 3763 unhashed. By default, when a pointer is printed via %p 3764 format string, that pointer is "hashed", i.e. obscured 3765 by hashing the pointer value. This is a security feature 3766 that hides actual kernel addresses from unprivileged 3767 users, but it also makes debugging the kernel more 3768 difficult since unequal pointers can no longer be 3769 compared. However, if this command-line option is 3770 specified, then all normal pointers will have their true 3771 value printed. This option should only be specified when 3772 debugging the kernel. Please do not use on production 3773 kernels. 3774 3775 nohibernate [HIBERNATION] Disable hibernation and resume. 3776 3777 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,SH] Forces the kernel to 3778 busy wait in do_idle() and not use the arch_cpu_idle() 3779 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 3780 to be effective. This is useful on platforms where the 3781 sleep(SH) or wfi(ARM,ARM64) instructions do not work 3782 correctly or when doing power measurements to evaluate 3783 the impact of the sleep instructions. This is also 3784 useful when using JTAG debugger. 3785 3786 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings. 3787 3788 nohugevmalloc [KNL,X86,PPC,ARM64] Disable kernel huge vmalloc mappings. 3789 3790 nohz= [KNL] Boottime enable/disable dynamic ticks 3791 Valid arguments: on, off 3792 Default: on 3793 3794 nohz_full= [KNL,BOOT,SMP,ISOL] 3795 The argument is a cpu list, as described above. 3796 In kernels built with CONFIG_NO_HZ_FULL=y, set 3797 the specified list of CPUs whose tick will be stopped 3798 whenever possible. The boot CPU will be forced outside 3799 the range to maintain the timekeeping. Any CPUs 3800 in this list will have their RCU callbacks offloaded, 3801 just as if they had also been called out in the 3802 rcu_nocbs= boot parameter. 3803 3804 Note that this argument takes precedence over 3805 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 3806 3807 noinitrd [RAM] Tells the kernel not to load any configured 3808 initial RAM disk. 3809 3810 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3811 remapping. 3812 [Deprecated - use intremap=off] 3813 3814 nointroute [IA-64] 3815 3816 noinvpcid [X86] Disable the INVPCID cpu feature. 3817 3818 noiotrap [SH] Disables trapped I/O port accesses. 3819 3820 noirqdebug [X86-32] Disables the code which attempts to detect and 3821 disable unhandled interrupt sources. 3822 3823 noisapnp [ISAPNP] Disables ISA PnP code. 3824 3825 nojitter [IA-64] Disables jitter checking for ITC timers. 3826 3827 nokaslr [KNL] 3828 When CONFIG_RANDOMIZE_BASE is set, this disables 3829 kernel and module base offset ASLR (Address Space 3830 Layout Randomization). 3831 3832 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3833 fault handling. 3834 3835 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3836 3837 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3838 3839 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3840 3841 nomca [IA-64] Disable machine check abort handling 3842 3843 nomce [X86-32] Disable Machine Check Exception 3844 3845 nomfgpt [X86-32] Disable Multi-Function General Purpose 3846 Timer usage (for AMD Geode machines). 3847 3848 nomodeset Disable kernel modesetting. Most systems' firmware 3849 sets up a display mode and provides framebuffer memory 3850 for output. With nomodeset, DRM and fbdev drivers will 3851 not load if they could possibly displace the pre- 3852 initialized output. Only the system framebuffer will 3853 be available for use. The respective drivers will not 3854 perform display-mode changes or accelerated rendering. 3855 3856 Useful as error fallback, or for testing and debugging. 3857 3858 nomodule Disable module load 3859 3860 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3861 shutdown the other cpus. Instead use the REBOOT_VECTOR 3862 irq. 3863 3864 nopat [X86] Disable PAT (page attribute table extension of 3865 pagetables) support. 3866 3867 nopcid [X86-64] Disable the PCID cpu feature. 3868 3869 nopku [X86] Disable Memory Protection Keys CPU feature found 3870 in some Intel CPUs. 3871 3872 nopti [X86-64] 3873 Equivalent to pti=off 3874 3875 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 3876 Disables the PV optimizations forcing the guest to run 3877 as generic guest with no PV drivers. Currently support 3878 XEN HVM, KVM, HYPER_V and VMWARE guest. 3879 3880 nopvspin [X86,XEN,KVM] 3881 Disables the qspinlock slow path using PV optimizations 3882 which allow the hypervisor to 'idle' the guest on lock 3883 contention. 3884 3885 norandmaps Don't use address space randomization. Equivalent to 3886 echo 0 > /proc/sys/kernel/randomize_va_space 3887 3888 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3889 with UP alternatives 3890 3891 noresume [SWSUSP] Disables resume and restores original swap 3892 space. 3893 3894 nosbagart [IA-64] 3895 3896 no-scroll [VGA] Disables scrollback. 3897 This is required for the Braillex ib80-piezo Braille 3898 reader made by F.H. Papenmeier (Germany). 3899 3900 nosgx [X86-64,SGX] Disables Intel SGX kernel support. 3901 3902 nosmap [PPC] 3903 Disable SMAP (Supervisor Mode Access Prevention) 3904 even if it is supported by processor. 3905 3906 nosmep [PPC64s] 3907 Disable SMEP (Supervisor Mode Execution Prevention) 3908 even if it is supported by processor. 3909 3910 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3911 and disable the IO APIC. legacy for "maxcpus=0". 3912 3913 nosmt [KNL,MIPS,PPC,S390] Disable symmetric multithreading (SMT). 3914 Equivalent to smt=1. 3915 3916 [KNL,X86,PPC] Disable symmetric multithreading (SMT). 3917 nosmt=force: Force disable SMT, cannot be undone 3918 via the sysfs control file. 3919 3920 nosoftlockup [KNL] Disable the soft-lockup detector. 3921 3922 nospec_store_bypass_disable 3923 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3924 3925 nospectre_bhb [ARM64] Disable all mitigations for Spectre-BHB (branch 3926 history injection) vulnerability. System may allow data leaks 3927 with this option. 3928 3929 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3930 (bounds check bypass). With this option data leaks are 3931 possible in the system. 3932 3933 nospectre_v2 [X86,PPC_E500,ARM64] Disable all mitigations for 3934 the Spectre variant 2 (indirect branch prediction) 3935 vulnerability. System may allow data leaks with this 3936 option. 3937 3938 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES] Disable paravirtualized 3939 steal time accounting. steal time is computed, but 3940 won't influence scheduler behaviour 3941 3942 nosync [HW,M68K] Disables sync negotiation for all devices. 3943 3944 no_timer_check [X86,APIC] Disables the code which tests for 3945 broken timer IRQ sources. 3946 3947 no_uaccess_flush 3948 [PPC] Don't flush the L1-D cache after accessing user data. 3949 3950 novmcoredd [KNL,KDUMP] 3951 Disable device dump. Device dump allows drivers to 3952 append dump data to vmcore so you can collect driver 3953 specified debug info. Drivers can append the data 3954 without any limit and this data is stored in memory, 3955 so this may cause significant memory stress. Disabling 3956 device dump can help save memory but the driver debug 3957 data will be no longer available. This parameter 3958 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3959 is set. 3960 3961 no-vmw-sched-clock 3962 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3963 clock and use the default one. 3964 3965 nowatchdog [KNL] Disable both lockup detectors, i.e. 3966 soft-lockup and NMI watchdog (hard-lockup). 3967 3968 nowb [ARM] 3969 3970 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3971 3972 NOTE: this parameter will be ignored on systems with the 3973 LEGACY_XAPIC_DISABLED bit set in the 3974 IA32_XAPIC_DISABLE_STATUS MSR. 3975 3976 noxsave [BUGS=X86] Disables x86 extended register state save 3977 and restore using xsave. The kernel will fallback to 3978 enabling legacy floating-point and sse state. 3979 3980 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3981 register states. The kernel will fall back to use 3982 xsave to save the states. By using this parameter, 3983 performance of saving the states is degraded because 3984 xsave doesn't support modified optimization while 3985 xsaveopt supports it on xsaveopt enabled systems. 3986 3987 noxsaves [X86] Disables xsaves and xrstors used in saving and 3988 restoring x86 extended register state in compacted 3989 form of xsave area. The kernel will fall back to use 3990 xsaveopt and xrstor to save and restore the states 3991 in standard form of xsave area. By using this 3992 parameter, xsave area per process might occupy more 3993 memory on xsaves enabled systems. 3994 3995 nps_mtm_hs_ctr= [KNL,ARC] 3996 This parameter sets the maximum duration, in 3997 cycles, each HW thread of the CTOP can run 3998 without interruptions, before HW switches it. 3999 The actual maximum duration is 16 times this 4000 parameter's value. 4001 Format: integer between 1 and 255 4002 Default: 255 4003 4004 nptcg= [IA-64] Override max number of concurrent global TLB 4005 purges which is reported from either PAL_VM_SUMMARY or 4006 SAL PALO. 4007 4008 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 4009 could support. nr_cpus=n : n >= 1 limits the kernel to 4010 support 'n' processors. It could be larger than the 4011 number of already plugged CPU during bootup, later in 4012 runtime you can physically add extra cpu until it reaches 4013 n. So during boot up some boot time memory for per-cpu 4014 variables need be pre-allocated for later physical cpu 4015 hot plugging. 4016 4017 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 4018 4019 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86] Disable NUMA, Only 4020 set up a single NUMA node spanning all memory. 4021 4022 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 4023 NUMA balancing. 4024 Allowed values are enable and disable 4025 4026 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 4027 'node', 'default' can be specified 4028 This can be set from sysctl after boot. 4029 See Documentation/admin-guide/sysctl/vm.rst for details. 4030 4031 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 4032 See Documentation/core-api/debugging-via-ohci1394.rst for more 4033 info. 4034 4035 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 4036 Rather than timing out after 20 ms if an EC 4037 command is not properly ACKed, override the length 4038 of the timeout. We have interrupts disabled while 4039 waiting for the ACK, so if this is set too high 4040 interrupts *may* be lost! 4041 4042 omap_mux= [OMAP] Override bootloader pin multiplexing. 4043 Format: <mux_mode0.mode_name=value>... 4044 For example, to override I2C bus2: 4045 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 4046 4047 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 4048 4049 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 4050 4051 boundary - index of last SLC block on Flex-OneNAND. 4052 The remaining blocks are configured as MLC blocks. 4053 lock - Configure if Flex-OneNAND boundary should be locked. 4054 Once locked, the boundary cannot be changed. 4055 1 indicates lock status, 0 indicates unlock status. 4056 4057 oops=panic Always panic on oopses. Default is to just kill the 4058 process, but there is a small probability of 4059 deadlocking the machine. 4060 This will also cause panics on machine check exceptions. 4061 Useful together with panic=30 to trigger a reboot. 4062 4063 page_alloc.shuffle= 4064 [KNL] Boolean flag to control whether the page allocator 4065 should randomize its free lists. The randomization may 4066 be automatically enabled if the kernel detects it is 4067 running on a platform with a direct-mapped memory-side 4068 cache, and this parameter can be used to 4069 override/disable that behavior. The state of the flag 4070 can be read from sysfs at: 4071 /sys/module/page_alloc/parameters/shuffle. 4072 4073 page_owner= [KNL] Boot-time page_owner enabling option. 4074 Storage of the information about who allocated 4075 each page is disabled in default. With this switch, 4076 we can turn it on. 4077 on: enable the feature 4078 4079 page_poison= [KNL] Boot-time parameter changing the state of 4080 poisoning on the buddy allocator, available with 4081 CONFIG_PAGE_POISONING=y. 4082 off: turn off poisoning (default) 4083 on: turn on poisoning 4084 4085 page_reporting.page_reporting_order= 4086 [KNL] Minimal page reporting order 4087 Format: <integer> 4088 Adjust the minimal page reporting order. The page 4089 reporting is disabled when it exceeds MAX_ORDER. 4090 4091 panic= [KNL] Kernel behaviour on panic: delay <timeout> 4092 timeout > 0: seconds before rebooting 4093 timeout = 0: wait forever 4094 timeout < 0: reboot immediately 4095 Format: <timeout> 4096 4097 panic_on_taint= Bitmask for conditionally calling panic() in add_taint() 4098 Format: <hex>[,nousertaint] 4099 Hexadecimal bitmask representing the set of TAINT flags 4100 that will cause the kernel to panic when add_taint() is 4101 called with any of the flags in this set. 4102 The optional switch "nousertaint" can be utilized to 4103 prevent userspace forced crashes by writing to sysctl 4104 /proc/sys/kernel/tainted any flagset matching with the 4105 bitmask set on panic_on_taint. 4106 See Documentation/admin-guide/tainted-kernels.rst for 4107 extra details on the taint flags that users can pick 4108 to compose the bitmask to assign to panic_on_taint. 4109 4110 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump 4111 on a WARN(). 4112 4113 panic_print= Bitmask for printing system info when panic happens. 4114 User can chose combination of the following bits: 4115 bit 0: print all tasks info 4116 bit 1: print system memory info 4117 bit 2: print timer info 4118 bit 3: print locks info if CONFIG_LOCKDEP is on 4119 bit 4: print ftrace buffer 4120 bit 5: print all printk messages in buffer 4121 bit 6: print all CPUs backtrace (if available in the arch) 4122 *Be aware* that this option may print a _lot_ of lines, 4123 so there are risks of losing older messages in the log. 4124 Use this option carefully, maybe worth to setup a 4125 bigger log buffer with "log_buf_len" along with this. 4126 4127 parkbd.port= [HW] Parallel port number the keyboard adapter is 4128 connected to, default is 0. 4129 Format: <parport#> 4130 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 4131 0 for XT, 1 for AT (default is AT). 4132 Format: <mode> 4133 4134 parport= [HW,PPT] Specify parallel ports. 0 disables. 4135 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 4136 Use 'auto' to force the driver to use any 4137 IRQ/DMA settings detected (the default is to 4138 ignore detected IRQ/DMA settings because of 4139 possible conflicts). You can specify the base 4140 address, IRQ, and DMA settings; IRQ and DMA 4141 should be numbers, or 'auto' (for using detected 4142 settings on that particular port), or 'nofifo' 4143 (to avoid using a FIFO even if it is detected). 4144 Parallel ports are assigned in the order they 4145 are specified on the command line, starting 4146 with parport0. 4147 4148 parport_init_mode= [HW,PPT] 4149 Configure VIA parallel port to operate in 4150 a specific mode. This is necessary on Pegasos 4151 computer where firmware has no options for setting 4152 up parallel port mode and sets it to spp. 4153 Currently this function knows 686a and 8231 chips. 4154 Format: [spp|ps2|epp|ecp|ecpepp] 4155 4156 pata_legacy.all= [HW,LIBATA] 4157 Format: <int> 4158 Set to non-zero to probe primary and secondary ISA 4159 port ranges on PCI systems where no PCI PATA device 4160 has been found at either range. Disabled by default. 4161 4162 pata_legacy.autospeed= [HW,LIBATA] 4163 Format: <int> 4164 Set to non-zero if a chip is present that snoops speed 4165 changes. Disabled by default. 4166 4167 pata_legacy.ht6560a= [HW,LIBATA] 4168 Format: <int> 4169 Set to 1, 2, or 3 for HT 6560A on the primary channel, 4170 the secondary channel, or both channels respectively. 4171 Disabled by default. 4172 4173 pata_legacy.ht6560b= [HW,LIBATA] 4174 Format: <int> 4175 Set to 1, 2, or 3 for HT 6560B on the primary channel, 4176 the secondary channel, or both channels respectively. 4177 Disabled by default. 4178 4179 pata_legacy.iordy_mask= [HW,LIBATA] 4180 Format: <int> 4181 IORDY enable mask. Set individual bits to allow IORDY 4182 for the respective channel. Bit 0 is for the first 4183 legacy channel handled by this driver, bit 1 is for 4184 the second channel, and so on. The sequence will often 4185 correspond to the primary legacy channel, the secondary 4186 legacy channel, and so on, but the handling of a PCI 4187 bus and the use of other driver options may interfere 4188 with the sequence. By default IORDY is allowed across 4189 all channels. 4190 4191 pata_legacy.opti82c46x= [HW,LIBATA] 4192 Format: <int> 4193 Set to 1, 2, or 3 for Opti 82c611A on the primary 4194 channel, the secondary channel, or both channels 4195 respectively. Disabled by default. 4196 4197 pata_legacy.opti82c611a= [HW,LIBATA] 4198 Format: <int> 4199 Set to 1, 2, or 3 for Opti 82c465MV on the primary 4200 channel, the secondary channel, or both channels 4201 respectively. Disabled by default. 4202 4203 pata_legacy.pio_mask= [HW,LIBATA] 4204 Format: <int> 4205 PIO mode mask for autospeed devices. Set individual 4206 bits to allow the use of the respective PIO modes. 4207 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 4208 All modes allowed by default. 4209 4210 pata_legacy.probe_all= [HW,LIBATA] 4211 Format: <int> 4212 Set to non-zero to probe tertiary and further ISA 4213 port ranges on PCI systems. Disabled by default. 4214 4215 pata_legacy.probe_mask= [HW,LIBATA] 4216 Format: <int> 4217 Probe mask for legacy ISA PATA ports. Depending on 4218 platform configuration and the use of other driver 4219 options up to 6 legacy ports are supported: 0x1f0, 4220 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 4221 of individual ports can be disabled by setting the 4222 corresponding bits in the mask to 1. Bit 0 is for 4223 the first port in the list above (0x1f0), and so on. 4224 By default all supported ports are probed. 4225 4226 pata_legacy.qdi= [HW,LIBATA] 4227 Format: <int> 4228 Set to non-zero to probe QDI controllers. By default 4229 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. 4230 4231 pata_legacy.winbond= [HW,LIBATA] 4232 Format: <int> 4233 Set to non-zero to probe Winbond controllers. Use 4234 the standard I/O port (0x130) if 1, otherwise the 4235 value given is the I/O port to use (typically 0x1b0). 4236 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 4237 0 otherwise. 4238 4239 pata_platform.pio_mask= [HW,LIBATA] 4240 Format: <int> 4241 Supported PIO mode mask. Set individual bits to allow 4242 the use of the respective PIO modes. Bit 0 is for 4243 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 4244 allowed by default. 4245 4246 pause_on_oops=<int> 4247 Halt all CPUs after the first oops has been printed for 4248 the specified number of seconds. This is to be used if 4249 your oopses keep scrolling off the screen. 4250 4251 pcbit= [HW,ISDN] 4252 4253 pci=option[,option...] [PCI] various PCI subsystem options. 4254 4255 Some options herein operate on a specific device 4256 or a set of devices (<pci_dev>). These are 4257 specified in one of the following formats: 4258 4259 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 4260 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 4261 4262 Note: the first format specifies a PCI 4263 bus/device/function address which may change 4264 if new hardware is inserted, if motherboard 4265 firmware changes, or due to changes caused 4266 by other kernel parameters. If the 4267 domain is left unspecified, it is 4268 taken to be zero. Optionally, a path 4269 to a device through multiple device/function 4270 addresses can be specified after the base 4271 address (this is more robust against 4272 renumbering issues). The second format 4273 selects devices using IDs from the 4274 configuration space which may match multiple 4275 devices in the system. 4276 4277 earlydump dump PCI config space before the kernel 4278 changes anything 4279 off [X86] don't probe for the PCI bus 4280 bios [X86-32] force use of PCI BIOS, don't access 4281 the hardware directly. Use this if your machine 4282 has a non-standard PCI host bridge. 4283 nobios [X86-32] disallow use of PCI BIOS, only direct 4284 hardware access methods are allowed. Use this 4285 if you experience crashes upon bootup and you 4286 suspect they are caused by the BIOS. 4287 conf1 [X86] Force use of PCI Configuration Access 4288 Mechanism 1 (config address in IO port 0xCF8, 4289 data in IO port 0xCFC, both 32-bit). 4290 conf2 [X86] Force use of PCI Configuration Access 4291 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 4292 the function, IO port 0xCFA, also 8-bit, sets 4293 bus number. The config space is then accessed 4294 through ports 0xC000-0xCFFF). 4295 See http://wiki.osdev.org/PCI for more info 4296 on the configuration access mechanisms. 4297 noaer [PCIE] If the PCIEAER kernel config parameter is 4298 enabled, this kernel boot option can be used to 4299 disable the use of PCIE advanced error reporting. 4300 nodomains [PCI] Disable support for multiple PCI 4301 root domains (aka PCI segments, in ACPI-speak). 4302 nommconf [X86] Disable use of MMCONFIG for PCI 4303 Configuration 4304 check_enable_amd_mmconf [X86] check for and enable 4305 properly configured MMIO access to PCI 4306 config space on AMD family 10h CPU 4307 nomsi [MSI] If the PCI_MSI kernel config parameter is 4308 enabled, this kernel boot option can be used to 4309 disable the use of MSI interrupts system-wide. 4310 noioapicquirk [APIC] Disable all boot interrupt quirks. 4311 Safety option to keep boot IRQs enabled. This 4312 should never be necessary. 4313 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 4314 primary IO-APIC for bridges that cannot disable 4315 boot IRQs. This fixes a source of spurious IRQs 4316 when the system masks IRQs. 4317 noioapicreroute [APIC] Disable workaround that uses the 4318 boot IRQ equivalent of an IRQ that connects to 4319 a chipset where boot IRQs cannot be disabled. 4320 The opposite of ioapicreroute. 4321 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 4322 routing table. These calls are known to be buggy 4323 on several machines and they hang the machine 4324 when used, but on other computers it's the only 4325 way to get the interrupt routing table. Try 4326 this option if the kernel is unable to allocate 4327 IRQs or discover secondary PCI buses on your 4328 motherboard. 4329 rom [X86] Assign address space to expansion ROMs. 4330 Use with caution as certain devices share 4331 address decoders between ROMs and other 4332 resources. 4333 norom [X86] Do not assign address space to 4334 expansion ROMs that do not already have 4335 BIOS assigned address ranges. 4336 nobar [X86] Do not assign address space to the 4337 BARs that weren't assigned by the BIOS. 4338 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 4339 assigned automatically to PCI devices. You can 4340 make the kernel exclude IRQs of your ISA cards 4341 this way. 4342 pirqaddr=0xAAAAA [X86] Specify the physical address 4343 of the PIRQ table (normally generated 4344 by the BIOS) if it is outside the 4345 F0000h-100000h range. 4346 lastbus=N [X86] Scan all buses thru bus #N. Can be 4347 useful if the kernel is unable to find your 4348 secondary buses and you want to tell it 4349 explicitly which ones they are. 4350 assign-busses [X86] Always assign all PCI bus 4351 numbers ourselves, overriding 4352 whatever the firmware may have done. 4353 usepirqmask [X86] Honor the possible IRQ mask stored 4354 in the BIOS $PIR table. This is needed on 4355 some systems with broken BIOSes, notably 4356 some HP Pavilion N5400 and Omnibook XE3 4357 notebooks. This will have no effect if ACPI 4358 IRQ routing is enabled. 4359 noacpi [X86] Do not use ACPI for IRQ routing 4360 or for PCI scanning. 4361 use_crs [X86] Use PCI host bridge window information 4362 from ACPI. On BIOSes from 2008 or later, this 4363 is enabled by default. If you need to use this, 4364 please report a bug. 4365 nocrs [X86] Ignore PCI host bridge windows from ACPI. 4366 If you need to use this, please report a bug. 4367 use_e820 [X86] Use E820 reservations to exclude parts of 4368 PCI host bridge windows. This is a workaround 4369 for BIOS defects in host bridge _CRS methods. 4370 If you need to use this, please report a bug to 4371 <linux-pci@vger.kernel.org>. 4372 no_e820 [X86] Ignore E820 reservations for PCI host 4373 bridge windows. This is the default on modern 4374 hardware. If you need to use this, please report 4375 a bug to <linux-pci@vger.kernel.org>. 4376 routeirq Do IRQ routing for all PCI devices. 4377 This is normally done in pci_enable_device(), 4378 so this option is a temporary workaround 4379 for broken drivers that don't call it. 4380 skip_isa_align [X86] do not align io start addr, so can 4381 handle more pci cards 4382 noearly [X86] Don't do any early type 1 scanning. 4383 This might help on some broken boards which 4384 machine check when some devices' config space 4385 is read. But various workarounds are disabled 4386 and some IOMMU drivers will not work. 4387 bfsort Sort PCI devices into breadth-first order. 4388 This sorting is done to get a device 4389 order compatible with older (<= 2.4) kernels. 4390 nobfsort Don't sort PCI devices into breadth-first order. 4391 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 4392 tuning and use the BIOS-configured MPS defaults. 4393 pcie_bus_safe Set every device's MPS to the largest value 4394 supported by all devices below the root complex. 4395 pcie_bus_perf Set device MPS to the largest allowable MPS 4396 based on its parent bus. Also set MRRS (Max 4397 Read Request Size) to the largest supported 4398 value (no larger than the MPS that the device 4399 or bus can support) for best performance. 4400 pcie_bus_peer2peer Set every device's MPS to 128B, which 4401 every device is guaranteed to support. This 4402 configuration allows peer-to-peer DMA between 4403 any pair of devices, possibly at the cost of 4404 reduced performance. This also guarantees 4405 that hot-added devices will work. 4406 cbiosize=nn[KMG] The fixed amount of bus space which is 4407 reserved for the CardBus bridge's IO window. 4408 The default value is 256 bytes. 4409 cbmemsize=nn[KMG] The fixed amount of bus space which is 4410 reserved for the CardBus bridge's memory 4411 window. The default value is 64 megabytes. 4412 resource_alignment= 4413 Format: 4414 [<order of align>@]<pci_dev>[; ...] 4415 Specifies alignment and device to reassign 4416 aligned memory resources. How to 4417 specify the device is described above. 4418 If <order of align> is not specified, 4419 PAGE_SIZE is used as alignment. 4420 A PCI-PCI bridge can be specified if resource 4421 windows need to be expanded. 4422 To specify the alignment for several 4423 instances of a device, the PCI vendor, 4424 device, subvendor, and subdevice may be 4425 specified, e.g., 12@pci:8086:9c22:103c:198f 4426 for 4096-byte alignment. 4427 ecrc= Enable/disable PCIe ECRC (transaction layer 4428 end-to-end CRC checking). Only effective if 4429 OS has native AER control (either granted by 4430 ACPI _OSC or forced via "pcie_ports=native") 4431 bios: Use BIOS/firmware settings. This is the 4432 the default. 4433 off: Turn ECRC off 4434 on: Turn ECRC on. 4435 hpiosize=nn[KMG] The fixed amount of bus space which is 4436 reserved for hotplug bridge's IO window. 4437 Default size is 256 bytes. 4438 hpmmiosize=nn[KMG] The fixed amount of bus space which is 4439 reserved for hotplug bridge's MMIO window. 4440 Default size is 2 megabytes. 4441 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 4442 reserved for hotplug bridge's MMIO_PREF window. 4443 Default size is 2 megabytes. 4444 hpmemsize=nn[KMG] The fixed amount of bus space which is 4445 reserved for hotplug bridge's MMIO and 4446 MMIO_PREF window. 4447 Default size is 2 megabytes. 4448 hpbussize=nn The minimum amount of additional bus numbers 4449 reserved for buses below a hotplug bridge. 4450 Default is 1. 4451 realloc= Enable/disable reallocating PCI bridge resources 4452 if allocations done by BIOS are too small to 4453 accommodate resources required by all child 4454 devices. 4455 off: Turn realloc off 4456 on: Turn realloc on 4457 realloc same as realloc=on 4458 noari do not use PCIe ARI. 4459 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 4460 do not use PCIe ATS (and IOMMU device IOTLB). 4461 pcie_scan_all Scan all possible PCIe devices. Otherwise we 4462 only look for one device below a PCIe downstream 4463 port. 4464 big_root_window Try to add a big 64bit memory window to the PCIe 4465 root complex on AMD CPUs. Some GFX hardware 4466 can resize a BAR to allow access to all VRAM. 4467 Adding the window is slightly risky (it may 4468 conflict with unreported devices), so this 4469 taints the kernel. 4470 disable_acs_redir=<pci_dev>[; ...] 4471 Specify one or more PCI devices (in the format 4472 specified above) separated by semicolons. 4473 Each device specified will have the PCI ACS 4474 redirect capabilities forced off which will 4475 allow P2P traffic between devices through 4476 bridges without forcing it upstream. Note: 4477 this removes isolation between devices and 4478 may put more devices in an IOMMU group. 4479 force_floating [S390] Force usage of floating interrupts. 4480 nomio [S390] Do not use MIO instructions. 4481 norid [S390] ignore the RID field and force use of 4482 one PCI domain per PCI function 4483 4484 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 4485 Management. 4486 off Disable ASPM. 4487 force Enable ASPM even on devices that claim not to support it. 4488 WARNING: Forcing ASPM on may cause system lockups. 4489 4490 pcie_ports= [PCIE] PCIe port services handling: 4491 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 4492 even if the platform doesn't give the OS permission to 4493 use them. This may cause conflicts if the platform 4494 also tries to use these services. 4495 dpc-native Use native PCIe service for DPC only. May 4496 cause conflicts if firmware uses AER or DPC. 4497 compat Disable native PCIe services (PME, AER, DPC, PCIe 4498 hotplug). 4499 4500 pcie_port_pm= [PCIE] PCIe port power management handling: 4501 off Disable power management of all PCIe ports 4502 force Forcibly enable power management of all PCIe ports 4503 4504 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 4505 nomsi Do not use MSI for native PCIe PME signaling (this makes 4506 all PCIe root ports use INTx for all services). 4507 4508 pcmv= [HW,PCMCIA] BadgePAD 4 4509 4510 pd_ignore_unused 4511 [PM] 4512 Keep all power-domains already enabled by bootloader on, 4513 even if no driver has claimed them. This is useful 4514 for debug and development, but should not be 4515 needed on a platform with proper driver support. 4516 4517 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 4518 boot time. 4519 Format: { 0 | 1 } 4520 See arch/parisc/kernel/pdc_chassis.c 4521 4522 percpu_alloc= Select which percpu first chunk allocator to use. 4523 Currently supported values are "embed" and "page". 4524 Archs may support subset or none of the selections. 4525 See comments in mm/percpu.c for details on each 4526 allocator. This parameter is primarily for debugging 4527 and performance comparison. 4528 4529 pirq= [SMP,APIC] Manual mp-table setup 4530 See Documentation/arch/x86/i386/IO-APIC.rst. 4531 4532 plip= [PPT,NET] Parallel port network link 4533 Format: { parport<nr> | timid | 0 } 4534 See also Documentation/admin-guide/parport.rst. 4535 4536 pmtmr= [X86] Manual setup of pmtmr I/O Port. 4537 Override pmtimer IOPort with a hex value. 4538 e.g. pmtmr=0x508 4539 4540 pmu_override= [PPC] Override the PMU. 4541 This option takes over the PMU facility, so it is no 4542 longer usable by perf. Setting this option starts the 4543 PMU counters by setting MMCR0 to 0 (the FC bit is 4544 cleared). If a number is given, then MMCR1 is set to 4545 that number, otherwise (e.g., 'pmu_override=on'), MMCR1 4546 remains 0. 4547 4548 pm_debug_messages [SUSPEND,KNL] 4549 Enable suspend/resume debug messages during boot up. 4550 4551 pnp.debug=1 [PNP] 4552 Enable PNP debug messages (depends on the 4553 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 4554 via /sys/module/pnp/parameters/debug. We always show 4555 current resource usage; turning this on also shows 4556 possible settings and some assignment information. 4557 4558 pnpacpi= [ACPI] 4559 { off } 4560 4561 pnpbios= [ISAPNP] 4562 { on | off | curr | res | no-curr | no-res } 4563 4564 pnp_reserve_irq= 4565 [ISAPNP] Exclude IRQs for the autoconfiguration 4566 4567 pnp_reserve_dma= 4568 [ISAPNP] Exclude DMAs for the autoconfiguration 4569 4570 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 4571 Ranges are in pairs (I/O port base and size). 4572 4573 pnp_reserve_mem= 4574 [ISAPNP] Exclude memory regions for the 4575 autoconfiguration. 4576 Ranges are in pairs (memory base and size). 4577 4578 ports= [IP_VS_FTP] IPVS ftp helper module 4579 Default is 21. 4580 Up to 8 (IP_VS_APP_MAX_PORTS) ports 4581 may be specified. 4582 Format: <port>,<port>.... 4583 4584 powersave=off [PPC] This option disables power saving features. 4585 It specifically disables cpuidle and sets the 4586 platform machine description specific power_save 4587 function to NULL. On Idle the CPU just reduces 4588 execution priority. 4589 4590 ppc_strict_facility_enable 4591 [PPC] This option catches any kernel floating point, 4592 Altivec, VSX and SPE outside of regions specifically 4593 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 4594 There is some performance impact when enabling this. 4595 4596 ppc_tm= [PPC] 4597 Format: {"off"} 4598 Disable Hardware Transactional Memory 4599 4600 preempt= [KNL] 4601 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 4602 none - Limited to cond_resched() calls 4603 voluntary - Limited to cond_resched() and might_sleep() calls 4604 full - Any section that isn't explicitly preempt disabled 4605 can be preempted anytime. 4606 4607 print-fatal-signals= 4608 [KNL] debug: print fatal signals 4609 4610 If enabled, warn about various signal handling 4611 related application anomalies: too many signals, 4612 too many POSIX.1 timers, fatal signals causing a 4613 coredump - etc. 4614 4615 If you hit the warning due to signal overflow, 4616 you might want to try "ulimit -i unlimited". 4617 4618 default: off. 4619 4620 printk.always_kmsg_dump= 4621 Trigger kmsg_dump for cases other than kernel oops or 4622 panics 4623 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4624 default: disabled 4625 4626 printk.console_no_auto_verbose= 4627 Disable console loglevel raise on oops, panic 4628 or lockdep-detected issues (only if lock debug is on). 4629 With an exception to setups with low baudrate on 4630 serial console, keeping this 0 is a good choice 4631 in order to provide more debug information. 4632 Format: <bool> 4633 default: 0 (auto_verbose is enabled) 4634 4635 printk.devkmsg={on,off,ratelimit} 4636 Control writing to /dev/kmsg. 4637 on - unlimited logging to /dev/kmsg from userspace 4638 off - logging to /dev/kmsg disabled 4639 ratelimit - ratelimit the logging 4640 Default: ratelimit 4641 4642 printk.time= Show timing data prefixed to each printk message line 4643 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4644 4645 proc_mem.force_override= [KNL] 4646 Format: {always | ptrace | never} 4647 Traditionally /proc/pid/mem allows memory permissions to be 4648 overridden without restrictions. This option may be set to 4649 restrict that. Can be one of: 4650 - 'always': traditional behavior always allows mem overrides. 4651 - 'ptrace': only allow mem overrides for active ptracers. 4652 - 'never': never allow mem overrides. 4653 If not specified, default is the CONFIG_PROC_MEM_* choice. 4654 4655 processor.max_cstate= [HW,ACPI] 4656 Limit processor to maximum C-state 4657 max_cstate=9 overrides any DMI blacklist limit. 4658 4659 processor.nocst [HW,ACPI] 4660 Ignore the _CST method to determine C-states, 4661 instead using the legacy FADT method 4662 4663 profile= [KNL] Enable kernel profiling via /proc/profile 4664 Format: [<profiletype>,]<number> 4665 Param: <profiletype>: "schedule" or "kvm" 4666 [defaults to kernel profiling] 4667 Param: "schedule" - profile schedule points. 4668 Param: "kvm" - profile VM exits. 4669 Param: <number> - step/bucket size as a power of 2 for 4670 statistical time based profiling. 4671 4672 prompt_ramdisk= [RAM] [Deprecated] 4673 4674 prot_virt= [S390] enable hosting protected virtual machines 4675 isolated from the hypervisor (if hardware supports 4676 that). 4677 Format: <bool> 4678 4679 psi= [KNL] Enable or disable pressure stall information 4680 tracking. 4681 Format: <bool> 4682 4683 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 4684 probe for; one of (bare|imps|exps|lifebook|any). 4685 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 4686 per second. 4687 psmouse.resetafter= [HW,MOUSE] 4688 Try to reset the device after so many bad packets 4689 (0 = never). 4690 psmouse.resolution= 4691 [HW,MOUSE] Set desired mouse resolution, in dpi. 4692 psmouse.smartscroll= 4693 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 4694 0 = disabled, 1 = enabled (default). 4695 4696 pstore.backend= Specify the name of the pstore backend to use 4697 4698 pti= [X86-64] Control Page Table Isolation of user and 4699 kernel address spaces. Disabling this feature 4700 removes hardening, but improves performance of 4701 system calls and interrupts. 4702 4703 on - unconditionally enable 4704 off - unconditionally disable 4705 auto - kernel detects whether your CPU model is 4706 vulnerable to issues that PTI mitigates 4707 4708 Not specifying this option is equivalent to pti=auto. 4709 4710 pty.legacy_count= 4711 [KNL] Number of legacy pty's. Overwrites compiled-in 4712 default number. 4713 4714 quiet [KNL] Disable most log messages 4715 4716 r128= [HW,DRM] 4717 4718 radix_hcall_invalidate=on [PPC/PSERIES] 4719 Disable RADIX GTSE feature and use hcall for TLB 4720 invalidate. 4721 4722 raid= [HW,RAID] 4723 See Documentation/admin-guide/md.rst. 4724 4725 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 4726 See Documentation/admin-guide/blockdev/ramdisk.rst. 4727 4728 ramdisk_start= [RAM] RAM disk image start address 4729 4730 random.trust_cpu=off 4731 [KNL] Disable trusting the use of the CPU's 4732 random number generator (if available) to 4733 initialize the kernel's RNG. 4734 4735 random.trust_bootloader=off 4736 [KNL] Disable trusting the use of the a seed 4737 passed by the bootloader (if available) to 4738 initialize the kernel's RNG. 4739 4740 randomize_kstack_offset= 4741 [KNL] Enable or disable kernel stack offset 4742 randomization, which provides roughly 5 bits of 4743 entropy, frustrating memory corruption attacks 4744 that depend on stack address determinism or 4745 cross-syscall address exposures. This is only 4746 available on architectures that have defined 4747 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 4748 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4749 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 4750 4751 ras=option[,option,...] [KNL] RAS-specific options 4752 4753 cec_disable [X86] 4754 Disable the Correctable Errors Collector, 4755 see CONFIG_RAS_CEC help text. 4756 4757 rcu_nocbs[=cpu-list] 4758 [KNL] The optional argument is a cpu list, 4759 as described above. 4760 4761 In kernels built with CONFIG_RCU_NOCB_CPU=y, 4762 enable the no-callback CPU mode, which prevents 4763 such CPUs' callbacks from being invoked in 4764 softirq context. Invocation of such CPUs' RCU 4765 callbacks will instead be offloaded to "rcuox/N" 4766 kthreads created for that purpose, where "x" is 4767 "p" for RCU-preempt, "s" for RCU-sched, and "g" 4768 for the kthreads that mediate grace periods; and 4769 "N" is the CPU number. This reduces OS jitter on 4770 the offloaded CPUs, which can be useful for HPC 4771 and real-time workloads. It can also improve 4772 energy efficiency for asymmetric multiprocessors. 4773 4774 If a cpulist is passed as an argument, the specified 4775 list of CPUs is set to no-callback mode from boot. 4776 4777 Otherwise, if the '=' sign and the cpulist 4778 arguments are omitted, no CPU will be set to 4779 no-callback mode from boot but the mode may be 4780 toggled at runtime via cpusets. 4781 4782 Note that this argument takes precedence over 4783 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 4784 4785 rcu_nocb_poll [KNL] 4786 Rather than requiring that offloaded CPUs 4787 (specified by rcu_nocbs= above) explicitly 4788 awaken the corresponding "rcuoN" kthreads, 4789 make these kthreads poll for callbacks. 4790 This improves the real-time response for the 4791 offloaded CPUs by relieving them of the need to 4792 wake up the corresponding kthread, but degrades 4793 energy efficiency by requiring that the kthreads 4794 periodically wake up to do the polling. 4795 4796 rcutree.blimit= [KNL] 4797 Set maximum number of finished RCU callbacks to 4798 process in one batch. 4799 4800 rcutree.dump_tree= [KNL] 4801 Dump the structure of the rcu_node combining tree 4802 out at early boot. This is used for diagnostic 4803 purposes, to verify correct tree setup. 4804 4805 rcutree.gp_cleanup_delay= [KNL] 4806 Set the number of jiffies to delay each step of 4807 RCU grace-period cleanup. 4808 4809 rcutree.gp_init_delay= [KNL] 4810 Set the number of jiffies to delay each step of 4811 RCU grace-period initialization. 4812 4813 rcutree.gp_preinit_delay= [KNL] 4814 Set the number of jiffies to delay each step of 4815 RCU grace-period pre-initialization, that is, 4816 the propagation of recent CPU-hotplug changes up 4817 the rcu_node combining tree. 4818 4819 rcutree.jiffies_till_first_fqs= [KNL] 4820 Set delay from grace-period initialization to 4821 first attempt to force quiescent states. 4822 Units are jiffies, minimum value is zero, 4823 and maximum value is HZ. 4824 4825 rcutree.jiffies_till_next_fqs= [KNL] 4826 Set delay between subsequent attempts to force 4827 quiescent states. Units are jiffies, minimum 4828 value is one, and maximum value is HZ. 4829 4830 rcutree.jiffies_till_sched_qs= [KNL] 4831 Set required age in jiffies for a 4832 given grace period before RCU starts 4833 soliciting quiescent-state help from 4834 rcu_note_context_switch() and cond_resched(). 4835 If not specified, the kernel will calculate 4836 a value based on the most recent settings 4837 of rcutree.jiffies_till_first_fqs 4838 and rcutree.jiffies_till_next_fqs. 4839 This calculated value may be viewed in 4840 rcutree.jiffies_to_sched_qs. Any attempt to set 4841 rcutree.jiffies_to_sched_qs will be cheerfully 4842 overwritten. 4843 4844 rcutree.kthread_prio= [KNL,BOOT] 4845 Set the SCHED_FIFO priority of the RCU per-CPU 4846 kthreads (rcuc/N). This value is also used for 4847 the priority of the RCU boost threads (rcub/N) 4848 and for the RCU grace-period kthreads (rcu_bh, 4849 rcu_preempt, and rcu_sched). If RCU_BOOST is 4850 set, valid values are 1-99 and the default is 1 4851 (the least-favored priority). Otherwise, when 4852 RCU_BOOST is not set, valid values are 0-99 and 4853 the default is zero (non-realtime operation). 4854 When RCU_NOCB_CPU is set, also adjust the 4855 priority of NOCB callback kthreads. 4856 4857 rcutree.nocb_nobypass_lim_per_jiffy= [KNL] 4858 On callback-offloaded (rcu_nocbs) CPUs, 4859 RCU reduces the lock contention that would 4860 otherwise be caused by callback floods through 4861 use of the ->nocb_bypass list. However, in the 4862 common non-flooded case, RCU queues directly to 4863 the main ->cblist in order to avoid the extra 4864 overhead of the ->nocb_bypass list and its lock. 4865 But if there are too many callbacks queued during 4866 a single jiffy, RCU pre-queues the callbacks into 4867 the ->nocb_bypass queue. The definition of "too 4868 many" is supplied by this kernel boot parameter. 4869 4870 rcutree.qhimark= [KNL] 4871 Set threshold of queued RCU callbacks beyond which 4872 batch limiting is disabled. 4873 4874 rcutree.qlowmark= [KNL] 4875 Set threshold of queued RCU callbacks below which 4876 batch limiting is re-enabled. 4877 4878 rcutree.qovld= [KNL] 4879 Set threshold of queued RCU callbacks beyond which 4880 RCU's force-quiescent-state scan will aggressively 4881 enlist help from cond_resched() and sched IPIs to 4882 help CPUs more quickly reach quiescent states. 4883 Set to less than zero to make this be set based 4884 on rcutree.qhimark at boot time and to zero to 4885 disable more aggressive help enlistment. 4886 4887 rcutree.rcu_delay_page_cache_fill_msec= [KNL] 4888 Set the page-cache refill delay (in milliseconds) 4889 in response to low-memory conditions. The range 4890 of permitted values is in the range 0:100000. 4891 4892 rcutree.rcu_divisor= [KNL] 4893 Set the shift-right count to use to compute 4894 the callback-invocation batch limit bl from 4895 the number of callbacks queued on this CPU. 4896 The result will be bounded below by the value of 4897 the rcutree.blimit kernel parameter. Every bl 4898 callbacks, the softirq handler will exit in 4899 order to allow the CPU to do other work. 4900 4901 Please note that this callback-invocation batch 4902 limit applies only to non-offloaded callback 4903 invocation. Offloaded callbacks are instead 4904 invoked in the context of an rcuoc kthread, which 4905 scheduler will preempt as it does any other task. 4906 4907 rcutree.rcu_fanout_exact= [KNL] 4908 Disable autobalancing of the rcu_node combining 4909 tree. This is used by rcutorture, and might 4910 possibly be useful for architectures having high 4911 cache-to-cache transfer latencies. 4912 4913 rcutree.rcu_fanout_leaf= [KNL] 4914 Change the number of CPUs assigned to each 4915 leaf rcu_node structure. Useful for very 4916 large systems, which will choose the value 64, 4917 and for NUMA systems with large remote-access 4918 latencies, which will choose a value aligned 4919 with the appropriate hardware boundaries. 4920 4921 rcutree.rcu_min_cached_objs= [KNL] 4922 Minimum number of objects which are cached and 4923 maintained per one CPU. Object size is equal 4924 to PAGE_SIZE. The cache allows to reduce the 4925 pressure to page allocator, also it makes the 4926 whole algorithm to behave better in low memory 4927 condition. 4928 4929 rcutree.rcu_nocb_gp_stride= [KNL] 4930 Set the number of NOCB callback kthreads in 4931 each group, which defaults to the square root 4932 of the number of CPUs. Larger numbers reduce 4933 the wakeup overhead on the global grace-period 4934 kthread, but increases that same overhead on 4935 each group's NOCB grace-period kthread. 4936 4937 rcutree.rcu_kick_kthreads= [KNL] 4938 Cause the grace-period kthread to get an extra 4939 wake_up() if it sleeps three times longer than 4940 it should at force-quiescent-state time. 4941 This wake_up() will be accompanied by a 4942 WARN_ONCE() splat and an ftrace_dump(). 4943 4944 rcutree.rcu_resched_ns= [KNL] 4945 Limit the time spend invoking a batch of RCU 4946 callbacks to the specified number of nanoseconds. 4947 By default, this limit is checked only once 4948 every 32 callbacks in order to limit the pain 4949 inflicted by local_clock() overhead. 4950 4951 rcutree.rcu_unlock_delay= [KNL] 4952 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 4953 this specifies an rcu_read_unlock()-time delay 4954 in microseconds. This defaults to zero. 4955 Larger delays increase the probability of 4956 catching RCU pointer leaks, that is, buggy use 4957 of RCU-protected pointers after the relevant 4958 rcu_read_unlock() has completed. 4959 4960 rcutree.sysrq_rcu= [KNL] 4961 Commandeer a sysrq key to dump out Tree RCU's 4962 rcu_node tree with an eye towards determining 4963 why a new grace period has not yet started. 4964 4965 rcutree.use_softirq= [KNL] 4966 If set to zero, move all RCU_SOFTIRQ processing to 4967 per-CPU rcuc kthreads. Defaults to a non-zero 4968 value, meaning that RCU_SOFTIRQ is used by default. 4969 Specify rcutree.use_softirq=0 to use rcuc kthreads. 4970 4971 But note that CONFIG_PREEMPT_RT=y kernels disable 4972 this kernel boot parameter, forcibly setting it 4973 to zero. 4974 4975 rcuscale.gp_async= [KNL] 4976 Measure performance of asynchronous 4977 grace-period primitives such as call_rcu(). 4978 4979 rcuscale.gp_async_max= [KNL] 4980 Specify the maximum number of outstanding 4981 callbacks per writer thread. When a writer 4982 thread exceeds this limit, it invokes the 4983 corresponding flavor of rcu_barrier() to allow 4984 previously posted callbacks to drain. 4985 4986 rcuscale.gp_exp= [KNL] 4987 Measure performance of expedited synchronous 4988 grace-period primitives. 4989 4990 rcuscale.holdoff= [KNL] 4991 Set test-start holdoff period. The purpose of 4992 this parameter is to delay the start of the 4993 test until boot completes in order to avoid 4994 interference. 4995 4996 rcuscale.kfree_by_call_rcu= [KNL] 4997 In kernels built with CONFIG_RCU_LAZY=y, test 4998 call_rcu() instead of kfree_rcu(). 4999 5000 rcuscale.kfree_mult= [KNL] 5001 Instead of allocating an object of size kfree_obj, 5002 allocate one of kfree_mult * sizeof(kfree_obj). 5003 Defaults to 1. 5004 5005 rcuscale.kfree_rcu_test= [KNL] 5006 Set to measure performance of kfree_rcu() flooding. 5007 5008 rcuscale.kfree_rcu_test_double= [KNL] 5009 Test the double-argument variant of kfree_rcu(). 5010 If this parameter has the same value as 5011 rcuscale.kfree_rcu_test_single, both the single- 5012 and double-argument variants are tested. 5013 5014 rcuscale.kfree_rcu_test_single= [KNL] 5015 Test the single-argument variant of kfree_rcu(). 5016 If this parameter has the same value as 5017 rcuscale.kfree_rcu_test_double, both the single- 5018 and double-argument variants are tested. 5019 5020 rcuscale.kfree_nthreads= [KNL] 5021 The number of threads running loops of kfree_rcu(). 5022 5023 rcuscale.kfree_alloc_num= [KNL] 5024 Number of allocations and frees done in an iteration. 5025 5026 rcuscale.kfree_loops= [KNL] 5027 Number of loops doing rcuscale.kfree_alloc_num number 5028 of allocations and frees. 5029 5030 rcuscale.minruntime= [KNL] 5031 Set the minimum test run time in seconds. This 5032 does not affect the data-collection interval, 5033 but instead allows better measurement of things 5034 like CPU consumption. 5035 5036 rcuscale.nreaders= [KNL] 5037 Set number of RCU readers. The value -1 selects 5038 N, where N is the number of CPUs. A value 5039 "n" less than -1 selects N-n+1, where N is again 5040 the number of CPUs. For example, -2 selects N 5041 (the number of CPUs), -3 selects N+1, and so on. 5042 A value of "n" less than or equal to -N selects 5043 a single reader. 5044 5045 rcuscale.nwriters= [KNL] 5046 Set number of RCU writers. The values operate 5047 the same as for rcuscale.nreaders. 5048 N, where N is the number of CPUs 5049 5050 rcuscale.scale_type= [KNL] 5051 Specify the RCU implementation to test. 5052 5053 rcuscale.shutdown= [KNL] 5054 Shut the system down after performance tests 5055 complete. This is useful for hands-off automated 5056 testing. 5057 5058 rcuscale.verbose= [KNL] 5059 Enable additional printk() statements. 5060 5061 rcuscale.writer_holdoff= [KNL] 5062 Write-side holdoff between grace periods, 5063 in microseconds. The default of zero says 5064 no holdoff. 5065 5066 rcuscale.writer_holdoff_jiffies= [KNL] 5067 Additional write-side holdoff between grace 5068 periods, but in jiffies. The default of zero 5069 says no holdoff. 5070 5071 rcutorture.fqs_duration= [KNL] 5072 Set duration of force_quiescent_state bursts 5073 in microseconds. 5074 5075 rcutorture.fqs_holdoff= [KNL] 5076 Set holdoff time within force_quiescent_state bursts 5077 in microseconds. 5078 5079 rcutorture.fqs_stutter= [KNL] 5080 Set wait time between force_quiescent_state bursts 5081 in seconds. 5082 5083 rcutorture.fwd_progress= [KNL] 5084 Specifies the number of kthreads to be used 5085 for RCU grace-period forward-progress testing 5086 for the types of RCU supporting this notion. 5087 Defaults to 1 kthread, values less than zero or 5088 greater than the number of CPUs cause the number 5089 of CPUs to be used. 5090 5091 rcutorture.fwd_progress_div= [KNL] 5092 Specify the fraction of a CPU-stall-warning 5093 period to do tight-loop forward-progress testing. 5094 5095 rcutorture.fwd_progress_holdoff= [KNL] 5096 Number of seconds to wait between successive 5097 forward-progress tests. 5098 5099 rcutorture.fwd_progress_need_resched= [KNL] 5100 Enclose cond_resched() calls within checks for 5101 need_resched() during tight-loop forward-progress 5102 testing. 5103 5104 rcutorture.gp_cond= [KNL] 5105 Use conditional/asynchronous update-side 5106 primitives, if available. 5107 5108 rcutorture.gp_exp= [KNL] 5109 Use expedited update-side primitives, if available. 5110 5111 rcutorture.gp_normal= [KNL] 5112 Use normal (non-expedited) asynchronous 5113 update-side primitives, if available. 5114 5115 rcutorture.gp_sync= [KNL] 5116 Use normal (non-expedited) synchronous 5117 update-side primitives, if available. If all 5118 of rcutorture.gp_cond=, rcutorture.gp_exp=, 5119 rcutorture.gp_normal=, and rcutorture.gp_sync= 5120 are zero, rcutorture acts as if is interpreted 5121 they are all non-zero. 5122 5123 rcutorture.irqreader= [KNL] 5124 Run RCU readers from irq handlers, or, more 5125 accurately, from a timer handler. Not all RCU 5126 flavors take kindly to this sort of thing. 5127 5128 rcutorture.leakpointer= [KNL] 5129 Leak an RCU-protected pointer out of the reader. 5130 This can of course result in splats, and is 5131 intended to test the ability of things like 5132 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 5133 such leaks. 5134 5135 rcutorture.n_barrier_cbs= [KNL] 5136 Set callbacks/threads for rcu_barrier() testing. 5137 5138 rcutorture.nfakewriters= [KNL] 5139 Set number of concurrent RCU writers. These just 5140 stress RCU, they don't participate in the actual 5141 test, hence the "fake". 5142 5143 rcutorture.nocbs_nthreads= [KNL] 5144 Set number of RCU callback-offload togglers. 5145 Zero (the default) disables toggling. 5146 5147 rcutorture.nocbs_toggle= [KNL] 5148 Set the delay in milliseconds between successive 5149 callback-offload toggling attempts. 5150 5151 rcutorture.nreaders= [KNL] 5152 Set number of RCU readers. The value -1 selects 5153 N-1, where N is the number of CPUs. A value 5154 "n" less than -1 selects N-n-2, where N is again 5155 the number of CPUs. For example, -2 selects N 5156 (the number of CPUs), -3 selects N+1, and so on. 5157 5158 rcutorture.object_debug= [KNL] 5159 Enable debug-object double-call_rcu() testing. 5160 5161 rcutorture.onoff_holdoff= [KNL] 5162 Set time (s) after boot for CPU-hotplug testing. 5163 5164 rcutorture.onoff_interval= [KNL] 5165 Set time (jiffies) between CPU-hotplug operations, 5166 or zero to disable CPU-hotplug testing. 5167 5168 rcutorture.read_exit= [KNL] 5169 Set the number of read-then-exit kthreads used 5170 to test the interaction of RCU updaters and 5171 task-exit processing. 5172 5173 rcutorture.read_exit_burst= [KNL] 5174 The number of times in a given read-then-exit 5175 episode that a set of read-then-exit kthreads 5176 is spawned. 5177 5178 rcutorture.read_exit_delay= [KNL] 5179 The delay, in seconds, between successive 5180 read-then-exit testing episodes. 5181 5182 rcutorture.shuffle_interval= [KNL] 5183 Set task-shuffle interval (s). Shuffling tasks 5184 allows some CPUs to go into dyntick-idle mode 5185 during the rcutorture test. 5186 5187 rcutorture.shutdown_secs= [KNL] 5188 Set time (s) after boot system shutdown. This 5189 is useful for hands-off automated testing. 5190 5191 rcutorture.stall_cpu= [KNL] 5192 Duration of CPU stall (s) to test RCU CPU stall 5193 warnings, zero to disable. 5194 5195 rcutorture.stall_cpu_block= [KNL] 5196 Sleep while stalling if set. This will result 5197 in warnings from preemptible RCU in addition to 5198 any other stall-related activity. Note that 5199 in kernels built with CONFIG_PREEMPTION=n and 5200 CONFIG_PREEMPT_COUNT=y, this parameter will 5201 cause the CPU to pass through a quiescent state. 5202 Given CONFIG_PREEMPTION=n, this will suppress 5203 RCU CPU stall warnings, but will instead result 5204 in scheduling-while-atomic splats. 5205 5206 Use of this module parameter results in splats. 5207 5208 5209 rcutorture.stall_cpu_holdoff= [KNL] 5210 Time to wait (s) after boot before inducing stall. 5211 5212 rcutorture.stall_cpu_irqsoff= [KNL] 5213 Disable interrupts while stalling if set. 5214 5215 rcutorture.stall_gp_kthread= [KNL] 5216 Duration (s) of forced sleep within RCU 5217 grace-period kthread to test RCU CPU stall 5218 warnings, zero to disable. If both stall_cpu 5219 and stall_gp_kthread are specified, the 5220 kthread is starved first, then the CPU. 5221 5222 rcutorture.stat_interval= [KNL] 5223 Time (s) between statistics printk()s. 5224 5225 rcutorture.stutter= [KNL] 5226 Time (s) to stutter testing, for example, specifying 5227 five seconds causes the test to run for five seconds, 5228 wait for five seconds, and so on. This tests RCU's 5229 ability to transition abruptly to and from idle. 5230 5231 rcutorture.test_boost= [KNL] 5232 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 5233 "Maybe" means test if the RCU implementation 5234 under test support RCU priority boosting. 5235 5236 rcutorture.test_boost_duration= [KNL] 5237 Duration (s) of each individual boost test. 5238 5239 rcutorture.test_boost_interval= [KNL] 5240 Interval (s) between each boost test. 5241 5242 rcutorture.test_no_idle_hz= [KNL] 5243 Test RCU's dyntick-idle handling. See also the 5244 rcutorture.shuffle_interval parameter. 5245 5246 rcutorture.torture_type= [KNL] 5247 Specify the RCU implementation to test. 5248 5249 rcutorture.verbose= [KNL] 5250 Enable additional printk() statements. 5251 5252 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 5253 Dump ftrace buffer after reporting RCU CPU 5254 stall warning. 5255 5256 rcupdate.rcu_cpu_stall_suppress= [KNL] 5257 Suppress RCU CPU stall warning messages. 5258 5259 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 5260 Suppress RCU CPU stall warning messages and 5261 rcutorture writer stall warnings that occur 5262 during early boot, that is, during the time 5263 before the init task is spawned. 5264 5265 rcupdate.rcu_cpu_stall_timeout= [KNL] 5266 Set timeout for RCU CPU stall warning messages. 5267 The value is in seconds and the maximum allowed 5268 value is 300 seconds. 5269 5270 rcupdate.rcu_exp_cpu_stall_timeout= [KNL] 5271 Set timeout for expedited RCU CPU stall warning 5272 messages. The value is in milliseconds 5273 and the maximum allowed value is 21000 5274 milliseconds. Please note that this value is 5275 adjusted to an arch timer tick resolution. 5276 Setting this to zero causes the value from 5277 rcupdate.rcu_cpu_stall_timeout to be used (after 5278 conversion from seconds to milliseconds). 5279 5280 rcupdate.rcu_cpu_stall_cputime= [KNL] 5281 Provide statistics on the cputime and count of 5282 interrupts and tasks during the sampling period. For 5283 multiple continuous RCU stalls, all sampling periods 5284 begin at half of the first RCU stall timeout. 5285 5286 rcupdate.rcu_exp_stall_task_details= [KNL] 5287 Print stack dumps of any tasks blocking the 5288 current expedited RCU grace period during an 5289 expedited RCU CPU stall warning. 5290 5291 rcupdate.rcu_expedited= [KNL] 5292 Use expedited grace-period primitives, for 5293 example, synchronize_rcu_expedited() instead 5294 of synchronize_rcu(). This reduces latency, 5295 but can increase CPU utilization, degrade 5296 real-time latency, and degrade energy efficiency. 5297 No effect on CONFIG_TINY_RCU kernels. 5298 5299 rcupdate.rcu_normal= [KNL] 5300 Use only normal grace-period primitives, 5301 for example, synchronize_rcu() instead of 5302 synchronize_rcu_expedited(). This improves 5303 real-time latency, CPU utilization, and 5304 energy efficiency, but can expose users to 5305 increased grace-period latency. This parameter 5306 overrides rcupdate.rcu_expedited. No effect on 5307 CONFIG_TINY_RCU kernels. 5308 5309 rcupdate.rcu_normal_after_boot= [KNL] 5310 Once boot has completed (that is, after 5311 rcu_end_inkernel_boot() has been invoked), use 5312 only normal grace-period primitives. No effect 5313 on CONFIG_TINY_RCU kernels. 5314 5315 But note that CONFIG_PREEMPT_RT=y kernels enables 5316 this kernel boot parameter, forcibly setting 5317 it to the value one, that is, converting any 5318 post-boot attempt at an expedited RCU grace 5319 period to instead use normal non-expedited 5320 grace-period processing. 5321 5322 rcupdate.rcu_task_collapse_lim= [KNL] 5323 Set the maximum number of callbacks present 5324 at the beginning of a grace period that allows 5325 the RCU Tasks flavors to collapse back to using 5326 a single callback queue. This switching only 5327 occurs when rcupdate.rcu_task_enqueue_lim is 5328 set to the default value of -1. 5329 5330 rcupdate.rcu_task_contend_lim= [KNL] 5331 Set the minimum number of callback-queuing-time 5332 lock-contention events per jiffy required to 5333 cause the RCU Tasks flavors to switch to per-CPU 5334 callback queuing. This switching only occurs 5335 when rcupdate.rcu_task_enqueue_lim is set to 5336 the default value of -1. 5337 5338 rcupdate.rcu_task_enqueue_lim= [KNL] 5339 Set the number of callback queues to use for the 5340 RCU Tasks family of RCU flavors. The default 5341 of -1 allows this to be automatically (and 5342 dynamically) adjusted. This parameter is intended 5343 for use in testing. 5344 5345 rcupdate.rcu_task_ipi_delay= [KNL] 5346 Set time in jiffies during which RCU tasks will 5347 avoid sending IPIs, starting with the beginning 5348 of a given grace period. Setting a large 5349 number avoids disturbing real-time workloads, 5350 but lengthens grace periods. 5351 5352 rcupdate.rcu_task_lazy_lim= [KNL] 5353 Number of callbacks on a given CPU that will 5354 cancel laziness on that CPU. Use -1 to disable 5355 cancellation of laziness, but be advised that 5356 doing so increases the danger of OOM due to 5357 callback flooding. 5358 5359 rcupdate.rcu_task_stall_info= [KNL] 5360 Set initial timeout in jiffies for RCU task stall 5361 informational messages, which give some indication 5362 of the problem for those not patient enough to 5363 wait for ten minutes. Informational messages are 5364 only printed prior to the stall-warning message 5365 for a given grace period. Disable with a value 5366 less than or equal to zero. Defaults to ten 5367 seconds. A change in value does not take effect 5368 until the beginning of the next grace period. 5369 5370 rcupdate.rcu_task_stall_info_mult= [KNL] 5371 Multiplier for time interval between successive 5372 RCU task stall informational messages for a given 5373 RCU tasks grace period. This value is clamped 5374 to one through ten, inclusive. It defaults to 5375 the value three, so that the first informational 5376 message is printed 10 seconds into the grace 5377 period, the second at 40 seconds, the third at 5378 160 seconds, and then the stall warning at 600 5379 seconds would prevent a fourth at 640 seconds. 5380 5381 rcupdate.rcu_task_stall_timeout= [KNL] 5382 Set timeout in jiffies for RCU task stall 5383 warning messages. Disable with a value less 5384 than or equal to zero. Defaults to ten minutes. 5385 A change in value does not take effect until 5386 the beginning of the next grace period. 5387 5388 rcupdate.rcu_tasks_lazy_ms= [KNL] 5389 Set timeout in milliseconds RCU Tasks asynchronous 5390 callback batching for call_rcu_tasks(). 5391 A negative value will take the default. A value 5392 of zero will disable batching. Batching is 5393 always disabled for synchronize_rcu_tasks(). 5394 5395 rcupdate.rcu_tasks_rude_lazy_ms= [KNL] 5396 Set timeout in milliseconds RCU Tasks 5397 Rude asynchronous callback batching for 5398 call_rcu_tasks_rude(). A negative value 5399 will take the default. A value of zero will 5400 disable batching. Batching is always disabled 5401 for synchronize_rcu_tasks_rude(). 5402 5403 rcupdate.rcu_tasks_trace_lazy_ms= [KNL] 5404 Set timeout in milliseconds RCU Tasks 5405 Trace asynchronous callback batching for 5406 call_rcu_tasks_trace(). A negative value 5407 will take the default. A value of zero will 5408 disable batching. Batching is always disabled 5409 for synchronize_rcu_tasks_trace(). 5410 5411 rcupdate.rcu_self_test= [KNL] 5412 Run the RCU early boot self tests 5413 5414 rdinit= [KNL] 5415 Format: <full_path> 5416 Run specified binary instead of /init from the ramdisk, 5417 used for early userspace startup. See initrd. 5418 5419 rdrand= [X86] 5420 force - Override the decision by the kernel to hide the 5421 advertisement of RDRAND support (this affects 5422 certain AMD processors because of buggy BIOS 5423 support, specifically around the suspend/resume 5424 path). 5425 5426 rdt= [HW,X86,RDT] 5427 Turn on/off individual RDT features. List is: 5428 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 5429 mba, smba, bmec. 5430 E.g. to turn on cmt and turn off mba use: 5431 rdt=cmt,!mba 5432 5433 reboot= [KNL] 5434 Format (x86 or x86_64): 5435 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ 5436 [[,]s[mp]#### \ 5437 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 5438 [[,]f[orce] 5439 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 5440 (prefix with 'panic_' to set mode for panic 5441 reboot only), 5442 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 5443 reboot_force is either force or not specified, 5444 reboot_cpu is s[mp]#### with #### being the processor 5445 to be used for rebooting. 5446 5447 refscale.holdoff= [KNL] 5448 Set test-start holdoff period. The purpose of 5449 this parameter is to delay the start of the 5450 test until boot completes in order to avoid 5451 interference. 5452 5453 refscale.loops= [KNL] 5454 Set the number of loops over the synchronization 5455 primitive under test. Increasing this number 5456 reduces noise due to loop start/end overhead, 5457 but the default has already reduced the per-pass 5458 noise to a handful of picoseconds on ca. 2020 5459 x86 laptops. 5460 5461 refscale.nreaders= [KNL] 5462 Set number of readers. The default value of -1 5463 selects N, where N is roughly 75% of the number 5464 of CPUs. A value of zero is an interesting choice. 5465 5466 refscale.nruns= [KNL] 5467 Set number of runs, each of which is dumped onto 5468 the console log. 5469 5470 refscale.readdelay= [KNL] 5471 Set the read-side critical-section duration, 5472 measured in microseconds. 5473 5474 refscale.scale_type= [KNL] 5475 Specify the read-protection implementation to test. 5476 5477 refscale.shutdown= [KNL] 5478 Shut down the system at the end of the performance 5479 test. This defaults to 1 (shut it down) when 5480 refscale is built into the kernel and to 0 (leave 5481 it running) when refscale is built as a module. 5482 5483 refscale.verbose= [KNL] 5484 Enable additional printk() statements. 5485 5486 refscale.verbose_batched= [KNL] 5487 Batch the additional printk() statements. If zero 5488 (the default) or negative, print everything. Otherwise, 5489 print every Nth verbose statement, where N is the value 5490 specified. 5491 5492 relax_domain_level= 5493 [KNL, SMP] Set scheduler's default relax_domain_level. 5494 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 5495 5496 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 5497 Format: <base1>,<size1>[,<base2>,<size2>,...] 5498 Reserve I/O ports or memory so the kernel won't use 5499 them. If <base> is less than 0x10000, the region 5500 is assumed to be I/O ports; otherwise it is memory. 5501 5502 reservetop= [X86-32] 5503 Format: nn[KMG] 5504 Reserves a hole at the top of the kernel virtual 5505 address space. 5506 5507 reset_devices [KNL] Force drivers to reset the underlying device 5508 during initialization. 5509 5510 resume= [SWSUSP] 5511 Specify the partition device for software suspend 5512 Format: 5513 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 5514 5515 resume_offset= [SWSUSP] 5516 Specify the offset from the beginning of the partition 5517 given by "resume=" at which the swap header is located, 5518 in <PAGE_SIZE> units (needed only for swap files). 5519 See Documentation/power/swsusp-and-swap-files.rst 5520 5521 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 5522 read the resume files 5523 5524 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 5525 Useful for devices that are detected asynchronously 5526 (e.g. USB and MMC devices). 5527 5528 retain_initrd [RAM] Keep initrd memory after extraction 5529 5530 retbleed= [X86] Control mitigation of RETBleed (Arbitrary 5531 Speculative Code Execution with Return Instructions) 5532 vulnerability. 5533 5534 AMD-based UNRET and IBPB mitigations alone do not stop 5535 sibling threads from influencing the predictions of other 5536 sibling threads. For that reason, STIBP is used on pro- 5537 cessors that support it, and mitigate SMT on processors 5538 that don't. 5539 5540 off - no mitigation 5541 auto - automatically select a migitation 5542 auto,nosmt - automatically select a mitigation, 5543 disabling SMT if necessary for 5544 the full mitigation (only on Zen1 5545 and older without STIBP). 5546 ibpb - On AMD, mitigate short speculation 5547 windows on basic block boundaries too. 5548 Safe, highest perf impact. It also 5549 enables STIBP if present. Not suitable 5550 on Intel. 5551 ibpb,nosmt - Like "ibpb" above but will disable SMT 5552 when STIBP is not available. This is 5553 the alternative for systems which do not 5554 have STIBP. 5555 unret - Force enable untrained return thunks, 5556 only effective on AMD f15h-f17h based 5557 systems. 5558 unret,nosmt - Like unret, but will disable SMT when STIBP 5559 is not available. This is the alternative for 5560 systems which do not have STIBP. 5561 5562 Selecting 'auto' will choose a mitigation method at run 5563 time according to the CPU. 5564 5565 Not specifying this option is equivalent to retbleed=auto. 5566 5567 rfkill.default_state= 5568 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 5569 etc. communication is blocked by default. 5570 1 Unblocked. 5571 5572 rfkill.master_switch_mode= 5573 0 The "airplane mode" button does nothing. 5574 1 The "airplane mode" button toggles between everything 5575 blocked and the previous configuration. 5576 2 The "airplane mode" button toggles between everything 5577 blocked and everything unblocked. 5578 5579 rhash_entries= [KNL,NET] 5580 Set number of hash buckets for route cache 5581 5582 ring3mwait=disable 5583 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 5584 CPUs. 5585 5586 riscv_isa_fallback [RISCV] 5587 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit 5588 falling back to detecting extension support by parsing 5589 "riscv,isa" property on devicetree systems when the 5590 replacement properties are not found. See the Kconfig 5591 entry for RISCV_ISA_FALLBACK. 5592 5593 ro [KNL] Mount root device read-only on boot 5594 5595 rodata= [KNL] 5596 on Mark read-only kernel memory as read-only (default). 5597 off Leave read-only kernel memory writable for debugging. 5598 full Mark read-only kernel memory and aliases as read-only 5599 [arm64] 5600 5601 rockchip.usb_uart 5602 Enable the uart passthrough on the designated usb port 5603 on Rockchip SoCs. When active, the signals of the 5604 debug-uart get routed to the D+ and D- pins of the usb 5605 port and the regular usb controller gets disabled. 5606 5607 root= [KNL] Root filesystem 5608 Usually this a a block device specifier of some kind, 5609 see the early_lookup_bdev comment in 5610 block/early-lookup.c for details. 5611 Alternatively this can be "ram" for the legacy initial 5612 ramdisk, "nfs" and "cifs" for root on a network file 5613 system, or "mtd" and "ubi" for mounting from raw flash. 5614 5615 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 5616 mount the root filesystem 5617 5618 rootflags= [KNL] Set root filesystem mount option string 5619 5620 rootfstype= [KNL] Set root filesystem type 5621 5622 rootwait [KNL] Wait (indefinitely) for root device to show up. 5623 Useful for devices that are detected asynchronously 5624 (e.g. USB and MMC devices). 5625 5626 rootwait= [KNL] Maximum time (in seconds) to wait for root device 5627 to show up before attempting to mount the root 5628 filesystem. 5629 5630 rproc_mem=nn[KMG][@address] 5631 [KNL,ARM,CMA] Remoteproc physical memory block. 5632 Memory area to be used by remote processor image, 5633 managed by CMA. 5634 5635 rw [KNL] Mount root device read-write on boot 5636 5637 S [KNL] Run init in single mode 5638 5639 s390_iommu= [HW,S390] 5640 Set s390 IOTLB flushing mode 5641 strict 5642 With strict flushing every unmap operation will result in 5643 an IOTLB flush. Default is lazy flushing before reuse, 5644 which is faster. 5645 5646 s390_iommu_aperture= [KNL,S390] 5647 Specifies the size of the per device DMA address space 5648 accessible through the DMA and IOMMU APIs as a decimal 5649 factor of the size of main memory. 5650 The default is 1 meaning that one can concurrently use 5651 as many DMA addresses as physical memory is installed, 5652 if supported by hardware, and thus map all of memory 5653 once. With a value of 2 one can map all of memory twice 5654 and so on. As a special case a factor of 0 imposes no 5655 restrictions other than those given by hardware at the 5656 cost of significant additional memory use for tables. 5657 5658 sa1100ir [NET] 5659 See drivers/net/irda/sa1100_ir.c. 5660 5661 sched_verbose [KNL] Enables verbose scheduler debug messages. 5662 5663 schedstats= [KNL,X86] Enable or disable scheduled statistics. 5664 Allowed values are enable and disable. This feature 5665 incurs a small amount of overhead in the scheduler 5666 but is useful for debugging and performance tuning. 5667 5668 sched_thermal_decay_shift= 5669 [KNL, SMP] Set a decay shift for scheduler thermal 5670 pressure signal. Thermal pressure signal follows the 5671 default decay period of other scheduler pelt 5672 signals(usually 32 ms but configurable). Setting 5673 sched_thermal_decay_shift will left shift the decay 5674 period for the thermal pressure signal by the shift 5675 value. 5676 i.e. with the default pelt decay period of 32 ms 5677 sched_thermal_decay_shift thermal pressure decay pr 5678 1 64 ms 5679 2 128 ms 5680 and so on. 5681 Format: integer between 0 and 10 5682 Default is 0. 5683 5684 scftorture.holdoff= [KNL] 5685 Number of seconds to hold off before starting 5686 test. Defaults to zero for module insertion and 5687 to 10 seconds for built-in smp_call_function() 5688 tests. 5689 5690 scftorture.longwait= [KNL] 5691 Request ridiculously long waits randomly selected 5692 up to the chosen limit in seconds. Zero (the 5693 default) disables this feature. Please note 5694 that requesting even small non-zero numbers of 5695 seconds can result in RCU CPU stall warnings, 5696 softlockup complaints, and so on. 5697 5698 scftorture.nthreads= [KNL] 5699 Number of kthreads to spawn to invoke the 5700 smp_call_function() family of functions. 5701 The default of -1 specifies a number of kthreads 5702 equal to the number of CPUs. 5703 5704 scftorture.onoff_holdoff= [KNL] 5705 Number seconds to wait after the start of the 5706 test before initiating CPU-hotplug operations. 5707 5708 scftorture.onoff_interval= [KNL] 5709 Number seconds to wait between successive 5710 CPU-hotplug operations. Specifying zero (which 5711 is the default) disables CPU-hotplug operations. 5712 5713 scftorture.shutdown_secs= [KNL] 5714 The number of seconds following the start of the 5715 test after which to shut down the system. The 5716 default of zero avoids shutting down the system. 5717 Non-zero values are useful for automated tests. 5718 5719 scftorture.stat_interval= [KNL] 5720 The number of seconds between outputting the 5721 current test statistics to the console. A value 5722 of zero disables statistics output. 5723 5724 scftorture.stutter_cpus= [KNL] 5725 The number of jiffies to wait between each change 5726 to the set of CPUs under test. 5727 5728 scftorture.use_cpus_read_lock= [KNL] 5729 Use use_cpus_read_lock() instead of the default 5730 preempt_disable() to disable CPU hotplug 5731 while invoking one of the smp_call_function*() 5732 functions. 5733 5734 scftorture.verbose= [KNL] 5735 Enable additional printk() statements. 5736 5737 scftorture.weight_single= [KNL] 5738 The probability weighting to use for the 5739 smp_call_function_single() function with a zero 5740 "wait" parameter. A value of -1 selects the 5741 default if all other weights are -1. However, 5742 if at least one weight has some other value, a 5743 value of -1 will instead select a weight of zero. 5744 5745 scftorture.weight_single_wait= [KNL] 5746 The probability weighting to use for the 5747 smp_call_function_single() function with a 5748 non-zero "wait" parameter. See weight_single. 5749 5750 scftorture.weight_many= [KNL] 5751 The probability weighting to use for the 5752 smp_call_function_many() function with a zero 5753 "wait" parameter. See weight_single. 5754 Note well that setting a high probability for 5755 this weighting can place serious IPI load 5756 on the system. 5757 5758 scftorture.weight_many_wait= [KNL] 5759 The probability weighting to use for the 5760 smp_call_function_many() function with a 5761 non-zero "wait" parameter. See weight_single 5762 and weight_many. 5763 5764 scftorture.weight_all= [KNL] 5765 The probability weighting to use for the 5766 smp_call_function_all() function with a zero 5767 "wait" parameter. See weight_single and 5768 weight_many. 5769 5770 scftorture.weight_all_wait= [KNL] 5771 The probability weighting to use for the 5772 smp_call_function_all() function with a 5773 non-zero "wait" parameter. See weight_single 5774 and weight_many. 5775 5776 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 5777 xtime_lock contention on larger systems, and/or RCU lock 5778 contention on all systems with CONFIG_MAXSMP set. 5779 Format: { "0" | "1" } 5780 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 5781 1 -- enable. 5782 Note: increases power consumption, thus should only be 5783 enabled if running jitter sensitive (HPC/RT) workloads. 5784 5785 security= [SECURITY] Choose a legacy "major" security module to 5786 enable at boot. This has been deprecated by the 5787 "lsm=" parameter. 5788 5789 selinux= [SELINUX] Disable or enable SELinux at boot time. 5790 Format: { "0" | "1" } 5791 See security/selinux/Kconfig help text. 5792 0 -- disable. 5793 1 -- enable. 5794 Default value is 1. 5795 5796 serialnumber [BUGS=X86-32] 5797 5798 sev=option[,option...] [X86-64] See Documentation/arch/x86/x86_64/boot-options.rst 5799 5800 shapers= [NET] 5801 Maximal number of shapers. 5802 5803 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 5804 Limit apic dumping. The parameter defines the maximal 5805 number of local apics being dumped. Also it is possible 5806 to set it to "all" by meaning -- no limit here. 5807 Format: { 1 (default) | 2 | ... | all }. 5808 The parameter valid if only apic=debug or 5809 apic=verbose is specified. 5810 Example: apic=debug show_lapic=all 5811 5812 simeth= [IA-64] 5813 simscsi= 5814 5815 slram= [HW,MTD] 5816 5817 slab_merge [MM] 5818 Enable merging of slabs with similar size when the 5819 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 5820 5821 slab_nomerge [MM] 5822 Disable merging of slabs with similar size. May be 5823 necessary if there is some reason to distinguish 5824 allocs to different slabs, especially in hardened 5825 environments where the risk of heap overflows and 5826 layout control by attackers can usually be 5827 frustrated by disabling merging. This will reduce 5828 most of the exposure of a heap attack to a single 5829 cache (risks via metadata attacks are mostly 5830 unchanged). Debug options disable merging on their 5831 own. 5832 For more information see Documentation/mm/slub.rst. 5833 5834 slab_max_order= [MM, SLAB] 5835 Determines the maximum allowed order for slabs. 5836 A high setting may cause OOMs due to memory 5837 fragmentation. Defaults to 1 for systems with 5838 more than 32MB of RAM, 0 otherwise. 5839 5840 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB] 5841 Enabling slub_debug allows one to determine the 5842 culprit if slab objects become corrupted. Enabling 5843 slub_debug can create guard zones around objects and 5844 may poison objects when not in use. Also tracks the 5845 last alloc / free. For more information see 5846 Documentation/mm/slub.rst. 5847 5848 slub_max_order= [MM, SLUB] 5849 Determines the maximum allowed order for slabs. 5850 A high setting may cause OOMs due to memory 5851 fragmentation. For more information see 5852 Documentation/mm/slub.rst. 5853 5854 slub_min_objects= [MM, SLUB] 5855 The minimum number of objects per slab. SLUB will 5856 increase the slab order up to slub_max_order to 5857 generate a sufficiently large slab able to contain 5858 the number of objects indicated. The higher the number 5859 of objects the smaller the overhead of tracking slabs 5860 and the less frequently locks need to be acquired. 5861 For more information see Documentation/mm/slub.rst. 5862 5863 slub_min_order= [MM, SLUB] 5864 Determines the minimum page order for slabs. Must be 5865 lower than slub_max_order. 5866 For more information see Documentation/mm/slub.rst. 5867 5868 slub_merge [MM, SLUB] 5869 Same with slab_merge. 5870 5871 slub_nomerge [MM, SLUB] 5872 Same with slab_nomerge. This is supported for legacy. 5873 See slab_nomerge for more information. 5874 5875 smart2= [HW] 5876 Format: <io1>[,<io2>[,...,<io8>]] 5877 5878 smp.csd_lock_timeout= [KNL] 5879 Specify the period of time in milliseconds 5880 that smp_call_function() and friends will wait 5881 for a CPU to release the CSD lock. This is 5882 useful when diagnosing bugs involving CPUs 5883 disabling interrupts for extended periods 5884 of time. Defaults to 5,000 milliseconds, and 5885 setting a value of zero disables this feature. 5886 This feature may be more efficiently disabled 5887 using the csdlock_debug- kernel parameter. 5888 5889 smp.panic_on_ipistall= [KNL] 5890 If a csd_lock_timeout extends for more than 5891 the specified number of milliseconds, panic the 5892 system. By default, let CSD-lock acquisition 5893 take as long as they take. Specifying 300,000 5894 for this value provides a 5-minute timeout. 5895 5896 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 5897 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 5898 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 5899 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 5900 smsc-ircc2.ircc_irq= [HW] IRQ line 5901 smsc-ircc2.ircc_dma= [HW] DMA channel 5902 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 5903 0: Toshiba Satellite 1800 (GP data pin select) 5904 1: Fast pin select (default) 5905 2: ATC IRMode 5906 5907 smt= [KNL,MIPS,S390] Set the maximum number of threads (logical 5908 CPUs) to use per physical CPU on systems capable of 5909 symmetric multithreading (SMT). Will be capped to the 5910 actual hardware limit. 5911 Format: <integer> 5912 Default: -1 (no limit) 5913 5914 softlockup_panic= 5915 [KNL] Should the soft-lockup detector generate panics. 5916 Format: 0 | 1 5917 5918 A value of 1 instructs the soft-lockup detector 5919 to panic the machine when a soft-lockup occurs. It is 5920 also controlled by the kernel.softlockup_panic sysctl 5921 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 5922 respective build-time switch to that functionality. 5923 5924 softlockup_all_cpu_backtrace= 5925 [KNL] Should the soft-lockup detector generate 5926 backtraces on all cpus. 5927 Format: 0 | 1 5928 5929 sonypi.*= [HW] Sony Programmable I/O Control Device driver 5930 See Documentation/admin-guide/laptops/sonypi.rst 5931 5932 spectre_bhi= [X86] Control mitigation of Branch History Injection 5933 (BHI) vulnerability. This setting affects the 5934 deployment of the HW BHI control and the SW BHB 5935 clearing sequence. 5936 5937 on - (default) Enable the HW or SW mitigation 5938 as needed. 5939 off - Disable the mitigation. 5940 5941 spectre_v2= [X86] Control mitigation of Spectre variant 2 5942 (indirect branch speculation) vulnerability. 5943 The default operation protects the kernel from 5944 user space attacks. 5945 5946 on - unconditionally enable, implies 5947 spectre_v2_user=on 5948 off - unconditionally disable, implies 5949 spectre_v2_user=off 5950 auto - kernel detects whether your CPU model is 5951 vulnerable 5952 5953 Selecting 'on' will, and 'auto' may, choose a 5954 mitigation method at run time according to the 5955 CPU, the available microcode, the setting of the 5956 CONFIG_RETPOLINE configuration option, and the 5957 compiler with which the kernel was built. 5958 5959 Selecting 'on' will also enable the mitigation 5960 against user space to user space task attacks. 5961 5962 Selecting 'off' will disable both the kernel and 5963 the user space protections. 5964 5965 Specific mitigations can also be selected manually: 5966 5967 retpoline - replace indirect branches 5968 retpoline,generic - Retpolines 5969 retpoline,lfence - LFENCE; indirect branch 5970 retpoline,amd - alias for retpoline,lfence 5971 eibrs - Enhanced/Auto IBRS 5972 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines 5973 eibrs,lfence - Enhanced/Auto IBRS + LFENCE 5974 ibrs - use IBRS to protect kernel 5975 5976 Not specifying this option is equivalent to 5977 spectre_v2=auto. 5978 5979 spectre_v2_user= 5980 [X86] Control mitigation of Spectre variant 2 5981 (indirect branch speculation) vulnerability between 5982 user space tasks 5983 5984 on - Unconditionally enable mitigations. Is 5985 enforced by spectre_v2=on 5986 5987 off - Unconditionally disable mitigations. Is 5988 enforced by spectre_v2=off 5989 5990 prctl - Indirect branch speculation is enabled, 5991 but mitigation can be enabled via prctl 5992 per thread. The mitigation control state 5993 is inherited on fork. 5994 5995 prctl,ibpb 5996 - Like "prctl" above, but only STIBP is 5997 controlled per thread. IBPB is issued 5998 always when switching between different user 5999 space processes. 6000 6001 seccomp 6002 - Same as "prctl" above, but all seccomp 6003 threads will enable the mitigation unless 6004 they explicitly opt out. 6005 6006 seccomp,ibpb 6007 - Like "seccomp" above, but only STIBP is 6008 controlled per thread. IBPB is issued 6009 always when switching between different 6010 user space processes. 6011 6012 auto - Kernel selects the mitigation depending on 6013 the available CPU features and vulnerability. 6014 6015 Default mitigation: "prctl" 6016 6017 Not specifying this option is equivalent to 6018 spectre_v2_user=auto. 6019 6020 spec_rstack_overflow= 6021 [X86] Control RAS overflow mitigation on AMD Zen CPUs 6022 6023 off - Disable mitigation 6024 microcode - Enable microcode mitigation only 6025 safe-ret - Enable sw-only safe RET mitigation (default) 6026 ibpb - Enable mitigation by issuing IBPB on 6027 kernel entry 6028 ibpb-vmexit - Issue IBPB only on VMEXIT 6029 (cloud-specific mitigation) 6030 6031 spec_store_bypass_disable= 6032 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 6033 (Speculative Store Bypass vulnerability) 6034 6035 Certain CPUs are vulnerable to an exploit against a 6036 a common industry wide performance optimization known 6037 as "Speculative Store Bypass" in which recent stores 6038 to the same memory location may not be observed by 6039 later loads during speculative execution. The idea 6040 is that such stores are unlikely and that they can 6041 be detected prior to instruction retirement at the 6042 end of a particular speculation execution window. 6043 6044 In vulnerable processors, the speculatively forwarded 6045 store can be used in a cache side channel attack, for 6046 example to read memory to which the attacker does not 6047 directly have access (e.g. inside sandboxed code). 6048 6049 This parameter controls whether the Speculative Store 6050 Bypass optimization is used. 6051 6052 On x86 the options are: 6053 6054 on - Unconditionally disable Speculative Store Bypass 6055 off - Unconditionally enable Speculative Store Bypass 6056 auto - Kernel detects whether the CPU model contains an 6057 implementation of Speculative Store Bypass and 6058 picks the most appropriate mitigation. If the 6059 CPU is not vulnerable, "off" is selected. If the 6060 CPU is vulnerable the default mitigation is 6061 architecture and Kconfig dependent. See below. 6062 prctl - Control Speculative Store Bypass per thread 6063 via prctl. Speculative Store Bypass is enabled 6064 for a process by default. The state of the control 6065 is inherited on fork. 6066 seccomp - Same as "prctl" above, but all seccomp threads 6067 will disable SSB unless they explicitly opt out. 6068 6069 Default mitigations: 6070 X86: "prctl" 6071 6072 On powerpc the options are: 6073 6074 on,auto - On Power8 and Power9 insert a store-forwarding 6075 barrier on kernel entry and exit. On Power7 6076 perform a software flush on kernel entry and 6077 exit. 6078 off - No action. 6079 6080 Not specifying this option is equivalent to 6081 spec_store_bypass_disable=auto. 6082 6083 spia_io_base= [HW,MTD] 6084 spia_fio_base= 6085 spia_pedr= 6086 spia_peddr= 6087 6088 split_lock_detect= 6089 [X86] Enable split lock detection or bus lock detection 6090 6091 When enabled (and if hardware support is present), atomic 6092 instructions that access data across cache line 6093 boundaries will result in an alignment check exception 6094 for split lock detection or a debug exception for 6095 bus lock detection. 6096 6097 off - not enabled 6098 6099 warn - the kernel will emit rate-limited warnings 6100 about applications triggering the #AC 6101 exception or the #DB exception. This mode is 6102 the default on CPUs that support split lock 6103 detection or bus lock detection. Default 6104 behavior is by #AC if both features are 6105 enabled in hardware. 6106 6107 fatal - the kernel will send SIGBUS to applications 6108 that trigger the #AC exception or the #DB 6109 exception. Default behavior is by #AC if 6110 both features are enabled in hardware. 6111 6112 ratelimit:N - 6113 Set system wide rate limit to N bus locks 6114 per second for bus lock detection. 6115 0 < N <= 1000. 6116 6117 N/A for split lock detection. 6118 6119 6120 If an #AC exception is hit in the kernel or in 6121 firmware (i.e. not while executing in user mode) 6122 the kernel will oops in either "warn" or "fatal" 6123 mode. 6124 6125 #DB exception for bus lock is triggered only when 6126 CPL > 0. 6127 6128 srbds= [X86,INTEL] 6129 Control the Special Register Buffer Data Sampling 6130 (SRBDS) mitigation. 6131 6132 Certain CPUs are vulnerable to an MDS-like 6133 exploit which can leak bits from the random 6134 number generator. 6135 6136 By default, this issue is mitigated by 6137 microcode. However, the microcode fix can cause 6138 the RDRAND and RDSEED instructions to become 6139 much slower. Among other effects, this will 6140 result in reduced throughput from /dev/urandom. 6141 6142 The microcode mitigation can be disabled with 6143 the following option: 6144 6145 off: Disable mitigation and remove 6146 performance impact to RDRAND and RDSEED 6147 6148 srcutree.big_cpu_lim [KNL] 6149 Specifies the number of CPUs constituting a 6150 large system, such that srcu_struct structures 6151 should immediately allocate an srcu_node array. 6152 This kernel-boot parameter defaults to 128, 6153 but takes effect only when the low-order four 6154 bits of srcutree.convert_to_big is equal to 3 6155 (decide at boot). 6156 6157 srcutree.convert_to_big [KNL] 6158 Specifies under what conditions an SRCU tree 6159 srcu_struct structure will be converted to big 6160 form, that is, with an rcu_node tree: 6161 6162 0: Never. 6163 1: At init_srcu_struct() time. 6164 2: When rcutorture decides to. 6165 3: Decide at boot time (default). 6166 0x1X: Above plus if high contention. 6167 6168 Either way, the srcu_node tree will be sized based 6169 on the actual runtime number of CPUs (nr_cpu_ids) 6170 instead of the compile-time CONFIG_NR_CPUS. 6171 6172 srcutree.counter_wrap_check [KNL] 6173 Specifies how frequently to check for 6174 grace-period sequence counter wrap for the 6175 srcu_data structure's ->srcu_gp_seq_needed field. 6176 The greater the number of bits set in this kernel 6177 parameter, the less frequently counter wrap will 6178 be checked for. Note that the bottom two bits 6179 are ignored. 6180 6181 srcutree.exp_holdoff [KNL] 6182 Specifies how many nanoseconds must elapse 6183 since the end of the last SRCU grace period for 6184 a given srcu_struct until the next normal SRCU 6185 grace period will be considered for automatic 6186 expediting. Set to zero to disable automatic 6187 expediting. 6188 6189 srcutree.srcu_max_nodelay [KNL] 6190 Specifies the number of no-delay instances 6191 per jiffy for which the SRCU grace period 6192 worker thread will be rescheduled with zero 6193 delay. Beyond this limit, worker thread will 6194 be rescheduled with a sleep delay of one jiffy. 6195 6196 srcutree.srcu_max_nodelay_phase [KNL] 6197 Specifies the per-grace-period phase, number of 6198 non-sleeping polls of readers. Beyond this limit, 6199 grace period worker thread will be rescheduled 6200 with a sleep delay of one jiffy, between each 6201 rescan of the readers, for a grace period phase. 6202 6203 srcutree.srcu_retry_check_delay [KNL] 6204 Specifies number of microseconds of non-sleeping 6205 delay between each non-sleeping poll of readers. 6206 6207 srcutree.small_contention_lim [KNL] 6208 Specifies the number of update-side contention 6209 events per jiffy will be tolerated before 6210 initiating a conversion of an srcu_struct 6211 structure to big form. Note that the value of 6212 srcutree.convert_to_big must have the 0x10 bit 6213 set for contention-based conversions to occur. 6214 6215 ssbd= [ARM64,HW] 6216 Speculative Store Bypass Disable control 6217 6218 On CPUs that are vulnerable to the Speculative 6219 Store Bypass vulnerability and offer a 6220 firmware based mitigation, this parameter 6221 indicates how the mitigation should be used: 6222 6223 force-on: Unconditionally enable mitigation for 6224 for both kernel and userspace 6225 force-off: Unconditionally disable mitigation for 6226 for both kernel and userspace 6227 kernel: Always enable mitigation in the 6228 kernel, and offer a prctl interface 6229 to allow userspace to register its 6230 interest in being mitigated too. 6231 6232 stack_guard_gap= [MM] 6233 override the default stack gap protection. The value 6234 is in page units and it defines how many pages prior 6235 to (for stacks growing down) resp. after (for stacks 6236 growing up) the main stack are reserved for no other 6237 mapping. Default value is 256 pages. 6238 6239 stack_depot_disable= [KNL] 6240 Setting this to true through kernel command line will 6241 disable the stack depot thereby saving the static memory 6242 consumed by the stack hash table. By default this is set 6243 to false. 6244 6245 stacktrace [FTRACE] 6246 Enabled the stack tracer on boot up. 6247 6248 stacktrace_filter=[function-list] 6249 [FTRACE] Limit the functions that the stack tracer 6250 will trace at boot up. function-list is a comma-separated 6251 list of functions. This list can be changed at run 6252 time by the stack_trace_filter file in the debugfs 6253 tracing directory. Note, this enables stack tracing 6254 and the stacktrace above is not needed. 6255 6256 sti= [PARISC,HW] 6257 Format: <num> 6258 Set the STI (builtin display/keyboard on the HP-PARISC 6259 machines) console (graphic card) which should be used 6260 as the initial boot-console. 6261 See also comment in drivers/video/console/sticore.c. 6262 6263 sti_font= [HW] 6264 See comment in drivers/video/console/sticore.c. 6265 6266 stifb= [HW] 6267 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 6268 6269 strict_sas_size= 6270 [X86] 6271 Format: <bool> 6272 Enable or disable strict sigaltstack size checks 6273 against the required signal frame size which 6274 depends on the supported FPU features. This can 6275 be used to filter out binaries which have 6276 not yet been made aware of AT_MINSIGSTKSZ. 6277 6278 stress_hpt [PPC] 6279 Limits the number of kernel HPT entries in the hash 6280 page table to increase the rate of hash page table 6281 faults on kernel addresses. 6282 6283 stress_slb [PPC] 6284 Limits the number of kernel SLB entries, and flushes 6285 them frequently to increase the rate of SLB faults 6286 on kernel addresses. 6287 6288 sunrpc.min_resvport= 6289 sunrpc.max_resvport= 6290 [NFS,SUNRPC] 6291 SunRPC servers often require that client requests 6292 originate from a privileged port (i.e. a port in the 6293 range 0 < portnr < 1024). 6294 An administrator who wishes to reserve some of these 6295 ports for other uses may adjust the range that the 6296 kernel's sunrpc client considers to be privileged 6297 using these two parameters to set the minimum and 6298 maximum port values. 6299 6300 sunrpc.svc_rpc_per_connection_limit= 6301 [NFS,SUNRPC] 6302 Limit the number of requests that the server will 6303 process in parallel from a single connection. 6304 The default value is 0 (no limit). 6305 6306 sunrpc.pool_mode= 6307 [NFS] 6308 Control how the NFS server code allocates CPUs to 6309 service thread pools. Depending on how many NICs 6310 you have and where their interrupts are bound, this 6311 option will affect which CPUs will do NFS serving. 6312 Note: this parameter cannot be changed while the 6313 NFS server is running. 6314 6315 auto the server chooses an appropriate mode 6316 automatically using heuristics 6317 global a single global pool contains all CPUs 6318 percpu one pool for each CPU 6319 pernode one pool for each NUMA node (equivalent 6320 to global on non-NUMA machines) 6321 6322 sunrpc.tcp_slot_table_entries= 6323 sunrpc.udp_slot_table_entries= 6324 [NFS,SUNRPC] 6325 Sets the upper limit on the number of simultaneous 6326 RPC calls that can be sent from the client to a 6327 server. Increasing these values may allow you to 6328 improve throughput, but will also increase the 6329 amount of memory reserved for use by the client. 6330 6331 suspend.pm_test_delay= 6332 [SUSPEND] 6333 Sets the number of seconds to remain in a suspend test 6334 mode before resuming the system (see 6335 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 6336 is set. Default value is 5. 6337 6338 svm= [PPC] 6339 Format: { on | off | y | n | 1 | 0 } 6340 This parameter controls use of the Protected 6341 Execution Facility on pSeries. 6342 6343 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 6344 Format: { <int> [,<int>] | force | noforce } 6345 <int> -- Number of I/O TLB slabs 6346 <int> -- Second integer after comma. Number of swiotlb 6347 areas with their own lock. Will be rounded up 6348 to a power of 2. 6349 force -- force using of bounce buffers even if they 6350 wouldn't be automatically used by the kernel 6351 noforce -- Never use bounce buffers (for debugging) 6352 6353 switches= [HW,M68k] 6354 6355 sysctl.*= [KNL] 6356 Set a sysctl parameter, right before loading the init 6357 process, as if the value was written to the respective 6358 /proc/sys/... file. Both '.' and '/' are recognized as 6359 separators. Unrecognized parameters and invalid values 6360 are reported in the kernel log. Sysctls registered 6361 later by a loaded module cannot be set this way. 6362 Example: sysctl.vm.swappiness=40 6363 6364 sysrq_always_enabled 6365 [KNL] 6366 Ignore sysrq setting - this boot parameter will 6367 neutralize any effect of /proc/sys/kernel/sysrq. 6368 Useful for debugging. 6369 6370 tcpmhash_entries= [KNL,NET] 6371 Set the number of tcp_metrics_hash slots. 6372 Default value is 8192 or 16384 depending on total 6373 ram pages. This is used to specify the TCP metrics 6374 cache size. See Documentation/networking/ip-sysctl.rst 6375 "tcp_no_metrics_save" section for more details. 6376 6377 tdfx= [HW,DRM] 6378 6379 test_suspend= [SUSPEND] 6380 Format: { "mem" | "standby" | "freeze" }[,N] 6381 Specify "mem" (for Suspend-to-RAM) or "standby" (for 6382 standby suspend) or "freeze" (for suspend type freeze) 6383 as the system sleep state during system startup with 6384 the optional capability to repeat N number of times. 6385 The system is woken from this state using a 6386 wakeup-capable RTC alarm. 6387 6388 thash_entries= [KNL,NET] 6389 Set number of hash buckets for TCP connection 6390 6391 thermal.act= [HW,ACPI] 6392 -1: disable all active trip points in all thermal zones 6393 <degrees C>: override all lowest active trip points 6394 6395 thermal.crt= [HW,ACPI] 6396 -1: disable all critical trip points in all thermal zones 6397 <degrees C>: override all critical trip points 6398 6399 thermal.off= [HW,ACPI] 6400 1: disable ACPI thermal control 6401 6402 thermal.psv= [HW,ACPI] 6403 -1: disable all passive trip points 6404 <degrees C>: override all passive trip points to this 6405 value 6406 6407 thermal.tzp= [HW,ACPI] 6408 Specify global default ACPI thermal zone polling rate 6409 <deci-seconds>: poll all this frequency 6410 0: no polling (default) 6411 6412 threadirqs [KNL] 6413 Force threading of all interrupt handlers except those 6414 marked explicitly IRQF_NO_THREAD. 6415 6416 topology= [S390] 6417 Format: {off | on} 6418 Specify if the kernel should make use of the cpu 6419 topology information if the hardware supports this. 6420 The scheduler will make use of this information and 6421 e.g. base its process migration decisions on it. 6422 Default is on. 6423 6424 topology_updates= [KNL, PPC, NUMA] 6425 Format: {off} 6426 Specify if the kernel should ignore (off) 6427 topology updates sent by the hypervisor to this 6428 LPAR. 6429 6430 torture.disable_onoff_at_boot= [KNL] 6431 Prevent the CPU-hotplug component of torturing 6432 until after init has spawned. 6433 6434 torture.ftrace_dump_at_shutdown= [KNL] 6435 Dump the ftrace buffer at torture-test shutdown, 6436 even if there were no errors. This can be a 6437 very costly operation when many torture tests 6438 are running concurrently, especially on systems 6439 with rotating-rust storage. 6440 6441 torture.verbose_sleep_frequency= [KNL] 6442 Specifies how many verbose printk()s should be 6443 emitted between each sleep. The default of zero 6444 disables verbose-printk() sleeping. 6445 6446 torture.verbose_sleep_duration= [KNL] 6447 Duration of each verbose-printk() sleep in jiffies. 6448 6449 tp720= [HW,PS2] 6450 6451 tpm_suspend_pcr=[HW,TPM] 6452 Format: integer pcr id 6453 Specify that at suspend time, the tpm driver 6454 should extend the specified pcr with zeros, 6455 as a workaround for some chips which fail to 6456 flush the last written pcr on TPM_SaveState. 6457 This will guarantee that all the other pcrs 6458 are saved. 6459 6460 tpm_tis.interrupts= [HW,TPM] 6461 Enable interrupts for the MMIO based physical layer 6462 for the FIFO interface. By default it is set to false 6463 (0). For more information about TPM hardware interfaces 6464 defined by Trusted Computing Group (TCG) see 6465 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/ 6466 6467 tp_printk [FTRACE] 6468 Have the tracepoints sent to printk as well as the 6469 tracing ring buffer. This is useful for early boot up 6470 where the system hangs or reboots and does not give the 6471 option for reading the tracing buffer or performing a 6472 ftrace_dump_on_oops. 6473 6474 To turn off having tracepoints sent to printk, 6475 echo 0 > /proc/sys/kernel/tracepoint_printk 6476 Note, echoing 1 into this file without the 6477 tracepoint_printk kernel cmdline option has no effect. 6478 6479 The tp_printk_stop_on_boot (see below) can also be used 6480 to stop the printing of events to console at 6481 late_initcall_sync. 6482 6483 ** CAUTION ** 6484 6485 Having tracepoints sent to printk() and activating high 6486 frequency tracepoints such as irq or sched, can cause 6487 the system to live lock. 6488 6489 tp_printk_stop_on_boot [FTRACE] 6490 When tp_printk (above) is set, it can cause a lot of noise 6491 on the console. It may be useful to only include the 6492 printing of events during boot up, as user space may 6493 make the system inoperable. 6494 6495 This command line option will stop the printing of events 6496 to console at the late_initcall_sync() time frame. 6497 6498 trace_buf_size=nn[KMG] 6499 [FTRACE] will set tracing buffer size on each cpu. 6500 6501 trace_clock= [FTRACE] Set the clock used for tracing events 6502 at boot up. 6503 local - Use the per CPU time stamp counter 6504 (converted into nanoseconds). Fast, but 6505 depending on the architecture, may not be 6506 in sync between CPUs. 6507 global - Event time stamps are synchronize across 6508 CPUs. May be slower than the local clock, 6509 but better for some race conditions. 6510 counter - Simple counting of events (1, 2, ..) 6511 note, some counts may be skipped due to the 6512 infrastructure grabbing the clock more than 6513 once per event. 6514 uptime - Use jiffies as the time stamp. 6515 perf - Use the same clock that perf uses. 6516 mono - Use ktime_get_mono_fast_ns() for time stamps. 6517 mono_raw - Use ktime_get_raw_fast_ns() for time 6518 stamps. 6519 boot - Use ktime_get_boot_fast_ns() for time stamps. 6520 Architectures may add more clocks. See 6521 Documentation/trace/ftrace.rst for more details. 6522 6523 trace_event=[event-list] 6524 [FTRACE] Set and start specified trace events in order 6525 to facilitate early boot debugging. The event-list is a 6526 comma-separated list of trace events to enable. See 6527 also Documentation/trace/events.rst 6528 6529 trace_instance=[instance-info] 6530 [FTRACE] Create a ring buffer instance early in boot up. 6531 This will be listed in: 6532 6533 /sys/kernel/tracing/instances 6534 6535 Events can be enabled at the time the instance is created 6536 via: 6537 6538 trace_instance=<name>,<system1>:<event1>,<system2>:<event2> 6539 6540 Note, the "<system*>:" portion is optional if the event is 6541 unique. 6542 6543 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall 6544 6545 will enable the "sched_switch" event (note, the "sched:" is optional, and 6546 the same thing would happen if it was left off). The irq_handler_entry 6547 event, and all events under the "initcall" system. 6548 6549 trace_options=[option-list] 6550 [FTRACE] Enable or disable tracer options at boot. 6551 The option-list is a comma delimited list of options 6552 that can be enabled or disabled just as if you were 6553 to echo the option name into 6554 6555 /sys/kernel/tracing/trace_options 6556 6557 For example, to enable stacktrace option (to dump the 6558 stack trace of each event), add to the command line: 6559 6560 trace_options=stacktrace 6561 6562 See also Documentation/trace/ftrace.rst "trace options" 6563 section. 6564 6565 trace_trigger=[trigger-list] 6566 [FTRACE] Add a event trigger on specific events. 6567 Set a trigger on top of a specific event, with an optional 6568 filter. 6569 6570 The format is is "trace_trigger=<event>.<trigger>[ if <filter>],..." 6571 Where more than one trigger may be specified that are comma deliminated. 6572 6573 For example: 6574 6575 trace_trigger="sched_switch.stacktrace if prev_state == 2" 6576 6577 The above will enable the "stacktrace" trigger on the "sched_switch" 6578 event but only trigger it if the "prev_state" of the "sched_switch" 6579 event is "2" (TASK_UNINTERUPTIBLE). 6580 6581 See also "Event triggers" in Documentation/trace/events.rst 6582 6583 6584 traceoff_on_warning 6585 [FTRACE] enable this option to disable tracing when a 6586 warning is hit. This turns off "tracing_on". Tracing can 6587 be enabled again by echoing '1' into the "tracing_on" 6588 file located in /sys/kernel/tracing/ 6589 6590 This option is useful, as it disables the trace before 6591 the WARNING dump is called, which prevents the trace to 6592 be filled with content caused by the warning output. 6593 6594 This option can also be set at run time via the sysctl 6595 option: kernel/traceoff_on_warning 6596 6597 transparent_hugepage= 6598 [KNL] 6599 Format: [always|madvise|never] 6600 Can be used to control the default behavior of the system 6601 with respect to transparent hugepages. 6602 See Documentation/admin-guide/mm/transhuge.rst 6603 for more details. 6604 6605 trusted.source= [KEYS] 6606 Format: <string> 6607 This parameter identifies the trust source as a backend 6608 for trusted keys implementation. Supported trust 6609 sources: 6610 - "tpm" 6611 - "tee" 6612 - "caam" 6613 If not specified then it defaults to iterating through 6614 the trust source list starting with TPM and assigns the 6615 first trust source as a backend which is initialized 6616 successfully during iteration. 6617 6618 trusted.rng= [KEYS] 6619 Format: <string> 6620 The RNG used to generate key material for trusted keys. 6621 Can be one of: 6622 - "kernel" 6623 - the same value as trusted.source: "tpm" or "tee" 6624 - "default" 6625 If not specified, "default" is used. In this case, 6626 the RNG's choice is left to each individual trust source. 6627 6628 tsc= Disable clocksource stability checks for TSC. 6629 Format: <string> 6630 [x86] reliable: mark tsc clocksource as reliable, this 6631 disables clocksource verification at runtime, as well 6632 as the stability checks done at bootup. Used to enable 6633 high-resolution timer mode on older hardware, and in 6634 virtualized environment. 6635 [x86] noirqtime: Do not use TSC to do irq accounting. 6636 Used to run time disable IRQ_TIME_ACCOUNTING on any 6637 platforms where RDTSC is slow and this accounting 6638 can add overhead. 6639 [x86] unstable: mark the TSC clocksource as unstable, this 6640 marks the TSC unconditionally unstable at bootup and 6641 avoids any further wobbles once the TSC watchdog notices. 6642 [x86] nowatchdog: disable clocksource watchdog. Used 6643 in situations with strict latency requirements (where 6644 interruptions from clocksource watchdog are not 6645 acceptable). 6646 [x86] recalibrate: force recalibration against a HW timer 6647 (HPET or PM timer) on systems whose TSC frequency was 6648 obtained from HW or FW using either an MSR or CPUID(0x15). 6649 Warn if the difference is more than 500 ppm. 6650 [x86] watchdog: Use TSC as the watchdog clocksource with 6651 which to check other HW timers (HPET or PM timer), but 6652 only on systems where TSC has been deemed trustworthy. 6653 This will be suppressed by an earlier tsc=nowatchdog and 6654 can be overridden by a later tsc=nowatchdog. A console 6655 message will flag any such suppression or overriding. 6656 6657 tsc_early_khz= [X86] Skip early TSC calibration and use the given 6658 value instead. Useful when the early TSC frequency discovery 6659 procedure is not reliable, such as on overclocked systems 6660 with CPUID.16h support and partial CPUID.15h support. 6661 Format: <unsigned int> 6662 6663 tsx= [X86] Control Transactional Synchronization 6664 Extensions (TSX) feature in Intel processors that 6665 support TSX control. 6666 6667 This parameter controls the TSX feature. The options are: 6668 6669 on - Enable TSX on the system. Although there are 6670 mitigations for all known security vulnerabilities, 6671 TSX has been known to be an accelerator for 6672 several previous speculation-related CVEs, and 6673 so there may be unknown security risks associated 6674 with leaving it enabled. 6675 6676 off - Disable TSX on the system. (Note that this 6677 option takes effect only on newer CPUs which are 6678 not vulnerable to MDS, i.e., have 6679 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 6680 the new IA32_TSX_CTRL MSR through a microcode 6681 update. This new MSR allows for the reliable 6682 deactivation of the TSX functionality.) 6683 6684 auto - Disable TSX if X86_BUG_TAA is present, 6685 otherwise enable TSX on the system. 6686 6687 Not specifying this option is equivalent to tsx=off. 6688 6689 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 6690 for more details. 6691 6692 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 6693 Abort (TAA) vulnerability. 6694 6695 Similar to Micro-architectural Data Sampling (MDS) 6696 certain CPUs that support Transactional 6697 Synchronization Extensions (TSX) are vulnerable to an 6698 exploit against CPU internal buffers which can forward 6699 information to a disclosure gadget under certain 6700 conditions. 6701 6702 In vulnerable processors, the speculatively forwarded 6703 data can be used in a cache side channel attack, to 6704 access data to which the attacker does not have direct 6705 access. 6706 6707 This parameter controls the TAA mitigation. The 6708 options are: 6709 6710 full - Enable TAA mitigation on vulnerable CPUs 6711 if TSX is enabled. 6712 6713 full,nosmt - Enable TAA mitigation and disable SMT on 6714 vulnerable CPUs. If TSX is disabled, SMT 6715 is not disabled because CPU is not 6716 vulnerable to cross-thread TAA attacks. 6717 off - Unconditionally disable TAA mitigation 6718 6719 On MDS-affected machines, tsx_async_abort=off can be 6720 prevented by an active MDS mitigation as both vulnerabilities 6721 are mitigated with the same mechanism so in order to disable 6722 this mitigation, you need to specify mds=off too. 6723 6724 Not specifying this option is equivalent to 6725 tsx_async_abort=full. On CPUs which are MDS affected 6726 and deploy MDS mitigation, TAA mitigation is not 6727 required and doesn't provide any additional 6728 mitigation. 6729 6730 For details see: 6731 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 6732 6733 turbografx.map[2|3]= [HW,JOY] 6734 TurboGraFX parallel port interface 6735 Format: 6736 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 6737 See also Documentation/input/devices/joystick-parport.rst 6738 6739 udbg-immortal [PPC] When debugging early kernel crashes that 6740 happen after console_init() and before a proper 6741 console driver takes over, this boot options might 6742 help "seeing" what's going on. 6743 6744 uhash_entries= [KNL,NET] 6745 Set number of hash buckets for UDP/UDP-Lite connections 6746 6747 uhci-hcd.ignore_oc= 6748 [USB] Ignore overcurrent events (default N). 6749 Some badly-designed motherboards generate lots of 6750 bogus events, for ports that aren't wired to 6751 anything. Set this parameter to avoid log spamming. 6752 Note that genuine overcurrent events won't be 6753 reported either. 6754 6755 unknown_nmi_panic 6756 [X86] Cause panic on unknown NMI. 6757 6758 unwind_debug [X86-64] 6759 Enable unwinder debug output. This can be 6760 useful for debugging certain unwinder error 6761 conditions, including corrupt stacks and 6762 bad/missing unwinder metadata. 6763 6764 usbcore.authorized_default= 6765 [USB] Default USB device authorization: 6766 (default -1 = authorized (same as 1), 6767 0 = not authorized, 1 = authorized, 2 = authorized 6768 if device connected to internal port) 6769 6770 usbcore.autosuspend= 6771 [USB] The autosuspend time delay (in seconds) used 6772 for newly-detected USB devices (default 2). This 6773 is the time required before an idle device will be 6774 autosuspended. Devices for which the delay is set 6775 to a negative value won't be autosuspended at all. 6776 6777 usbcore.usbfs_snoop= 6778 [USB] Set to log all usbfs traffic (default 0 = off). 6779 6780 usbcore.usbfs_snoop_max= 6781 [USB] Maximum number of bytes to snoop in each URB 6782 (default = 65536). 6783 6784 usbcore.blinkenlights= 6785 [USB] Set to cycle leds on hubs (default 0 = off). 6786 6787 usbcore.old_scheme_first= 6788 [USB] Start with the old device initialization 6789 scheme (default 0 = off). 6790 6791 usbcore.usbfs_memory_mb= 6792 [USB] Memory limit (in MB) for buffers allocated by 6793 usbfs (default = 16, 0 = max = 2047). 6794 6795 usbcore.use_both_schemes= 6796 [USB] Try the other device initialization scheme 6797 if the first one fails (default 1 = enabled). 6798 6799 usbcore.initial_descriptor_timeout= 6800 [USB] Specifies timeout for the initial 64-byte 6801 USB_REQ_GET_DESCRIPTOR request in milliseconds 6802 (default 5000 = 5.0 seconds). 6803 6804 usbcore.nousb [USB] Disable the USB subsystem 6805 6806 usbcore.quirks= 6807 [USB] A list of quirk entries to augment the built-in 6808 usb core quirk list. List entries are separated by 6809 commas. Each entry has the form 6810 VendorID:ProductID:Flags. The IDs are 4-digit hex 6811 numbers and Flags is a set of letters. Each letter 6812 will change the built-in quirk; setting it if it is 6813 clear and clearing it if it is set. The letters have 6814 the following meanings: 6815 a = USB_QUIRK_STRING_FETCH_255 (string 6816 descriptors must not be fetched using 6817 a 255-byte read); 6818 b = USB_QUIRK_RESET_RESUME (device can't resume 6819 correctly so reset it instead); 6820 c = USB_QUIRK_NO_SET_INTF (device can't handle 6821 Set-Interface requests); 6822 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 6823 handle its Configuration or Interface 6824 strings); 6825 e = USB_QUIRK_RESET (device can't be reset 6826 (e.g morph devices), don't use reset); 6827 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 6828 more interface descriptions than the 6829 bNumInterfaces count, and can't handle 6830 talking to these interfaces); 6831 g = USB_QUIRK_DELAY_INIT (device needs a pause 6832 during initialization, after we read 6833 the device descriptor); 6834 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 6835 high speed and super speed interrupt 6836 endpoints, the USB 2.0 and USB 3.0 spec 6837 require the interval in microframes (1 6838 microframe = 125 microseconds) to be 6839 calculated as interval = 2 ^ 6840 (bInterval-1). 6841 Devices with this quirk report their 6842 bInterval as the result of this 6843 calculation instead of the exponent 6844 variable used in the calculation); 6845 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 6846 handle device_qualifier descriptor 6847 requests); 6848 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 6849 generates spurious wakeup, ignore 6850 remote wakeup capability); 6851 k = USB_QUIRK_NO_LPM (device can't handle Link 6852 Power Management); 6853 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 6854 (Device reports its bInterval as linear 6855 frames instead of the USB 2.0 6856 calculation); 6857 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 6858 to be disconnected before suspend to 6859 prevent spurious wakeup); 6860 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 6861 pause after every control message); 6862 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 6863 delay after resetting its port); 6864 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT 6865 (Reduce timeout of the SET_ADDRESS 6866 request from 5000 ms to 500 ms); 6867 Example: quirks=0781:5580:bk,0a5c:5834:gij 6868 6869 usbhid.mousepoll= 6870 [USBHID] The interval which mice are to be polled at. 6871 6872 usbhid.jspoll= 6873 [USBHID] The interval which joysticks are to be polled at. 6874 6875 usbhid.kbpoll= 6876 [USBHID] The interval which keyboards are to be polled at. 6877 6878 usb-storage.delay_use= 6879 [UMS] The delay in seconds before a new device is 6880 scanned for Logical Units (default 1). 6881 6882 usb-storage.quirks= 6883 [UMS] A list of quirks entries to supplement or 6884 override the built-in unusual_devs list. List 6885 entries are separated by commas. Each entry has 6886 the form VID:PID:Flags where VID and PID are Vendor 6887 and Product ID values (4-digit hex numbers) and 6888 Flags is a set of characters, each corresponding 6889 to a common usb-storage quirk flag as follows: 6890 a = SANE_SENSE (collect more than 18 bytes 6891 of sense data, not on uas); 6892 b = BAD_SENSE (don't collect more than 18 6893 bytes of sense data, not on uas); 6894 c = FIX_CAPACITY (decrease the reported 6895 device capacity by one sector); 6896 d = NO_READ_DISC_INFO (don't use 6897 READ_DISC_INFO command, not on uas); 6898 e = NO_READ_CAPACITY_16 (don't use 6899 READ_CAPACITY_16 command); 6900 f = NO_REPORT_OPCODES (don't use report opcodes 6901 command, uas only); 6902 g = MAX_SECTORS_240 (don't transfer more than 6903 240 sectors at a time, uas only); 6904 h = CAPACITY_HEURISTICS (decrease the 6905 reported device capacity by one 6906 sector if the number is odd); 6907 i = IGNORE_DEVICE (don't bind to this 6908 device); 6909 j = NO_REPORT_LUNS (don't use report luns 6910 command, uas only); 6911 k = NO_SAME (do not use WRITE_SAME, uas only) 6912 l = NOT_LOCKABLE (don't try to lock and 6913 unlock ejectable media, not on uas); 6914 m = MAX_SECTORS_64 (don't transfer more 6915 than 64 sectors = 32 KB at a time, 6916 not on uas); 6917 n = INITIAL_READ10 (force a retry of the 6918 initial READ(10) command, not on uas); 6919 o = CAPACITY_OK (accept the capacity 6920 reported by the device, not on uas); 6921 p = WRITE_CACHE (the device cache is ON 6922 by default, not on uas); 6923 r = IGNORE_RESIDUE (the device reports 6924 bogus residue values, not on uas); 6925 s = SINGLE_LUN (the device has only one 6926 Logical Unit); 6927 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 6928 commands, uas only); 6929 u = IGNORE_UAS (don't bind to the uas driver); 6930 w = NO_WP_DETECT (don't test whether the 6931 medium is write-protected). 6932 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 6933 even if the device claims no cache, 6934 not on uas) 6935 Example: quirks=0419:aaf5:rl,0421:0433:rc 6936 6937 user_debug= [KNL,ARM] 6938 Format: <int> 6939 See arch/arm/Kconfig.debug help text. 6940 1 - undefined instruction events 6941 2 - system calls 6942 4 - invalid data aborts 6943 8 - SIGSEGV faults 6944 16 - SIGBUS faults 6945 Example: user_debug=31 6946 6947 userpte= 6948 [X86] Flags controlling user PTE allocations. 6949 6950 nohigh = do not allocate PTE pages in 6951 HIGHMEM regardless of setting 6952 of CONFIG_HIGHPTE. 6953 6954 vdso= [X86,SH,SPARC] 6955 On X86_32, this is an alias for vdso32=. Otherwise: 6956 6957 vdso=1: enable VDSO (the default) 6958 vdso=0: disable VDSO mapping 6959 6960 vdso32= [X86] Control the 32-bit vDSO 6961 vdso32=1: enable 32-bit VDSO 6962 vdso32=0 or vdso32=2: disable 32-bit VDSO 6963 6964 See the help text for CONFIG_COMPAT_VDSO for more 6965 details. If CONFIG_COMPAT_VDSO is set, the default is 6966 vdso32=0; otherwise, the default is vdso32=1. 6967 6968 For compatibility with older kernels, vdso32=2 is an 6969 alias for vdso32=0. 6970 6971 Try vdso32=0 if you encounter an error that says: 6972 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 6973 6974 vector= [IA-64,SMP] 6975 vector=percpu: enable percpu vector domain 6976 6977 video= [FB] Frame buffer configuration 6978 See Documentation/fb/modedb.rst. 6979 6980 video.brightness_switch_enabled= [ACPI] 6981 Format: [0|1] 6982 If set to 1, on receiving an ACPI notify event 6983 generated by hotkey, video driver will adjust brightness 6984 level and then send out the event to user space through 6985 the allocated input device. If set to 0, video driver 6986 will only send out the event without touching backlight 6987 brightness level. 6988 default: 1 6989 6990 virtio_mmio.device= 6991 [VMMIO] Memory mapped virtio (platform) device. 6992 6993 <size>@<baseaddr>:<irq>[:<id>] 6994 where: 6995 <size> := size (can use standard suffixes 6996 like K, M and G) 6997 <baseaddr> := physical base address 6998 <irq> := interrupt number (as passed to 6999 request_irq()) 7000 <id> := (optional) platform device id 7001 example: 7002 virtio_mmio.device=1K@0x100b0000:48:7 7003 7004 Can be used multiple times for multiple devices. 7005 7006 vga= [BOOT,X86-32] Select a particular video mode 7007 See Documentation/arch/x86/boot.rst and 7008 Documentation/admin-guide/svga.rst. 7009 Use vga=ask for menu. 7010 This is actually a boot loader parameter; the value is 7011 passed to the kernel using a special protocol. 7012 7013 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 7014 May slow down system boot speed, especially when 7015 enabled on systems with a large amount of memory. 7016 All options are enabled by default, and this 7017 interface is meant to allow for selectively 7018 enabling or disabling specific virtual memory 7019 debugging features. 7020 7021 Available options are: 7022 P Enable page structure init time poisoning 7023 - Disable all of the above options 7024 7025 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 7026 size of <nn>. This can be used to increase the 7027 minimum size (128MB on x86). It can also be used to 7028 decrease the size and leave more room for directly 7029 mapped kernel RAM. 7030 7031 vmcp_cma=nn[MG] [KNL,S390] 7032 Sets the memory size reserved for contiguous memory 7033 allocations for the vmcp device driver. 7034 7035 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 7036 Format: <command> 7037 7038 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 7039 Format: <command> 7040 7041 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 7042 Format: <command> 7043 7044 vsyscall= [X86-64] 7045 Controls the behavior of vsyscalls (i.e. calls to 7046 fixed addresses of 0xffffffffff600x00 from legacy 7047 code). Most statically-linked binaries and older 7048 versions of glibc use these calls. Because these 7049 functions are at fixed addresses, they make nice 7050 targets for exploits that can control RIP. 7051 7052 emulate Vsyscalls turn into traps and are emulated 7053 reasonably safely. The vsyscall page is 7054 readable. 7055 7056 xonly [default] Vsyscalls turn into traps and are 7057 emulated reasonably safely. The vsyscall 7058 page is not readable. 7059 7060 none Vsyscalls don't work at all. This makes 7061 them quite hard to use for exploits but 7062 might break your system. 7063 7064 vt.color= [VT] Default text color. 7065 Format: 0xYX, X = foreground, Y = background. 7066 Default: 0x07 = light gray on black. 7067 7068 vt.cur_default= [VT] Default cursor shape. 7069 Format: 0xCCBBAA, where AA, BB, and CC are the same as 7070 the parameters of the <Esc>[?A;B;Cc escape sequence; 7071 see VGA-softcursor.txt. Default: 2 = underline. 7072 7073 vt.default_blu= [VT] 7074 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 7075 Change the default blue palette of the console. 7076 This is a 16-member array composed of values 7077 ranging from 0-255. 7078 7079 vt.default_grn= [VT] 7080 Format: <green0>,<green1>,<green2>,...,<green15> 7081 Change the default green palette of the console. 7082 This is a 16-member array composed of values 7083 ranging from 0-255. 7084 7085 vt.default_red= [VT] 7086 Format: <red0>,<red1>,<red2>,...,<red15> 7087 Change the default red palette of the console. 7088 This is a 16-member array composed of values 7089 ranging from 0-255. 7090 7091 vt.default_utf8= 7092 [VT] 7093 Format=<0|1> 7094 Set system-wide default UTF-8 mode for all tty's. 7095 Default is 1, i.e. UTF-8 mode is enabled for all 7096 newly opened terminals. 7097 7098 vt.global_cursor_default= 7099 [VT] 7100 Format=<-1|0|1> 7101 Set system-wide default for whether a cursor 7102 is shown on new VTs. Default is -1, 7103 i.e. cursors will be created by default unless 7104 overridden by individual drivers. 0 will hide 7105 cursors, 1 will display them. 7106 7107 vt.italic= [VT] Default color for italic text; 0-15. 7108 Default: 2 = green. 7109 7110 vt.underline= [VT] Default color for underlined text; 0-15. 7111 Default: 3 = cyan. 7112 7113 watchdog timers [HW,WDT] For information on watchdog timers, 7114 see Documentation/watchdog/watchdog-parameters.rst 7115 or other driver-specific files in the 7116 Documentation/watchdog/ directory. 7117 7118 watchdog_thresh= 7119 [KNL] 7120 Set the hard lockup detector stall duration 7121 threshold in seconds. The soft lockup detector 7122 threshold is set to twice the value. A value of 0 7123 disables both lockup detectors. Default is 10 7124 seconds. 7125 7126 workqueue.unbound_cpus= 7127 [KNL,SMP] Specify to constrain one or some CPUs 7128 to use in unbound workqueues. 7129 Format: <cpu-list> 7130 By default, all online CPUs are available for 7131 unbound workqueues. 7132 7133 workqueue.watchdog_thresh= 7134 If CONFIG_WQ_WATCHDOG is configured, workqueue can 7135 warn stall conditions and dump internal state to 7136 help debugging. 0 disables workqueue stall 7137 detection; otherwise, it's the stall threshold 7138 duration in seconds. The default value is 30 and 7139 it can be updated at runtime by writing to the 7140 corresponding sysfs file. 7141 7142 workqueue.cpu_intensive_thresh_us= 7143 Per-cpu work items which run for longer than this 7144 threshold are automatically considered CPU intensive 7145 and excluded from concurrency management to prevent 7146 them from noticeably delaying other per-cpu work 7147 items. Default is 10000 (10ms). 7148 7149 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 7150 will report the work functions which violate this 7151 threshold repeatedly. They are likely good 7152 candidates for using WQ_UNBOUND workqueues instead. 7153 7154 workqueue.power_efficient 7155 Per-cpu workqueues are generally preferred because 7156 they show better performance thanks to cache 7157 locality; unfortunately, per-cpu workqueues tend to 7158 be more power hungry than unbound workqueues. 7159 7160 Enabling this makes the per-cpu workqueues which 7161 were observed to contribute significantly to power 7162 consumption unbound, leading to measurably lower 7163 power usage at the cost of small performance 7164 overhead. 7165 7166 The default value of this parameter is determined by 7167 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 7168 7169 workqueue.default_affinity_scope= 7170 Select the default affinity scope to use for unbound 7171 workqueues. Can be one of "cpu", "smt", "cache", 7172 "numa" and "system". Default is "cache". For more 7173 information, see the Affinity Scopes section in 7174 Documentation/core-api/workqueue.rst. 7175 7176 This can be changed after boot by writing to the 7177 matching /sys/module/workqueue/parameters file. All 7178 workqueues with the "default" affinity scope will be 7179 updated accordignly. 7180 7181 workqueue.debug_force_rr_cpu 7182 Workqueue used to implicitly guarantee that work 7183 items queued without explicit CPU specified are put 7184 on the local CPU. This guarantee is no longer true 7185 and while local CPU is still preferred work items 7186 may be put on foreign CPUs. This debug option 7187 forces round-robin CPU selection to flush out 7188 usages which depend on the now broken guarantee. 7189 When enabled, memory and cache locality will be 7190 impacted. 7191 7192 writecombine= [LOONGARCH] Control the MAT (Memory Access Type) of 7193 ioremap_wc(). 7194 7195 on - Enable writecombine, use WUC for ioremap_wc() 7196 off - Disable writecombine, use SUC for ioremap_wc() 7197 7198 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 7199 default x2apic cluster mode on platforms 7200 supporting x2apic. 7201 7202 xen_512gb_limit [KNL,X86-64,XEN] 7203 Restricts the kernel running paravirtualized under Xen 7204 to use only up to 512 GB of RAM. The reason to do so is 7205 crash analysis tools and Xen tools for doing domain 7206 save/restore/migration must be enabled to handle larger 7207 domains. 7208 7209 xen_emul_unplug= [HW,X86,XEN] 7210 Unplug Xen emulated devices 7211 Format: [unplug0,][unplug1] 7212 ide-disks -- unplug primary master IDE devices 7213 aux-ide-disks -- unplug non-primary-master IDE devices 7214 nics -- unplug network devices 7215 all -- unplug all emulated devices (NICs and IDE disks) 7216 unnecessary -- unplugging emulated devices is 7217 unnecessary even if the host did not respond to 7218 the unplug protocol 7219 never -- do not unplug even if version check succeeds 7220 7221 xen_legacy_crash [X86,XEN] 7222 Crash from Xen panic notifier, without executing late 7223 panic() code such as dumping handler. 7224 7225 xen_msr_safe= [X86,XEN] 7226 Format: <bool> 7227 Select whether to always use non-faulting (safe) MSR 7228 access functions when running as Xen PV guest. The 7229 default value is controlled by CONFIG_XEN_PV_MSR_SAFE. 7230 7231 xen_nopvspin [X86,XEN] 7232 Disables the qspinlock slowpath using Xen PV optimizations. 7233 This parameter is obsoleted by "nopvspin" parameter, which 7234 has equivalent effect for XEN platform. 7235 7236 xen_nopv [X86] 7237 Disables the PV optimizations forcing the HVM guest to 7238 run as generic HVM guest with no PV drivers. 7239 This option is obsoleted by the "nopv" option, which 7240 has equivalent effect for XEN platform. 7241 7242 xen_no_vector_callback 7243 [KNL,X86,XEN] Disable the vector callback for Xen 7244 event channel interrupts. 7245 7246 xen_scrub_pages= [XEN] 7247 Boolean option to control scrubbing pages before giving them back 7248 to Xen, for use by other domains. Can be also changed at runtime 7249 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 7250 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 7251 7252 xen_timer_slop= [X86-64,XEN] 7253 Set the timer slop (in nanoseconds) for the virtual Xen 7254 timers (default is 100000). This adjusts the minimum 7255 delta of virtualized Xen timers, where lower values 7256 improve timer resolution at the expense of processing 7257 more timer interrupts. 7258 7259 xen.balloon_boot_timeout= [XEN] 7260 The time (in seconds) to wait before giving up to boot 7261 in case initial ballooning fails to free enough memory. 7262 Applies only when running as HVM or PVH guest and 7263 started with less memory configured than allowed at 7264 max. Default is 180. 7265 7266 xen.event_eoi_delay= [XEN] 7267 How long to delay EOI handling in case of event 7268 storms (jiffies). Default is 10. 7269 7270 xen.event_loop_timeout= [XEN] 7271 After which time (jiffies) the event handling loop 7272 should start to delay EOI handling. Default is 2. 7273 7274 xen.fifo_events= [XEN] 7275 Boolean parameter to disable using fifo event handling 7276 even if available. Normally fifo event handling is 7277 preferred over the 2-level event handling, as it is 7278 fairer and the number of possible event channels is 7279 much higher. Default is on (use fifo events). 7280 7281 xirc2ps_cs= [NET,PCMCIA] 7282 Format: 7283 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 7284 7285 xive= [PPC] 7286 By default on POWER9 and above, the kernel will 7287 natively use the XIVE interrupt controller. This option 7288 allows the fallback firmware mode to be used: 7289 7290 off Fallback to firmware control of XIVE interrupt 7291 controller on both pseries and powernv 7292 platforms. Only useful on POWER9 and above. 7293 7294 xive.store-eoi=off [PPC] 7295 By default on POWER10 and above, the kernel will use 7296 stores for EOI handling when the XIVE interrupt mode 7297 is active. This option allows the XIVE driver to use 7298 loads instead, as on POWER9. 7299 7300 xhci-hcd.quirks [USB,KNL] 7301 A hex value specifying bitmask with supplemental xhci 7302 host controller quirks. Meaning of each bit can be 7303 consulted in header drivers/usb/host/xhci.h. 7304 7305 xmon [PPC] 7306 Format: { early | on | rw | ro | off } 7307 Controls if xmon debugger is enabled. Default is off. 7308 Passing only "xmon" is equivalent to "xmon=early". 7309 early Call xmon as early as possible on boot; xmon 7310 debugger is called from setup_arch(). 7311 on xmon debugger hooks will be installed so xmon 7312 is only called on a kernel crash. Default mode, 7313 i.e. either "ro" or "rw" mode, is controlled 7314 with CONFIG_XMON_DEFAULT_RO_MODE. 7315 rw xmon debugger hooks will be installed so xmon 7316 is called only on a kernel crash, mode is write, 7317 meaning SPR registers, memory and, other data 7318 can be written using xmon commands. 7319 ro same as "rw" option above but SPR registers, 7320 memory, and other data can't be written using 7321 xmon commands. 7322 off xmon is disabled. 7323 7324