xref: /openbmc/linux/arch/um/Kconfig (revision 63bcf87c) 
1# SPDX-License-Identifier: GPL-2.0
2
3menu "UML-specific options"
4
5config UML
6	bool
7	default y
8	select ARCH_HAS_KCOV
9	select ARCH_NO_PREEMPT
10	select HAVE_ARCH_AUDITSYSCALL
11	select HAVE_ARCH_SECCOMP_FILTER
12	select HAVE_ASM_MODVERSIONS
13	select HAVE_UID16
14	select HAVE_FUTEX_CMPXCHG if FUTEX
15	select HAVE_DEBUG_KMEMLEAK
16	select HAVE_DEBUG_BUGVERBOSE
17	select NO_DMA
18	select GENERIC_IRQ_SHOW
19	select GENERIC_CPU_DEVICES
20	select GENERIC_CLOCKEVENTS
21	select HAVE_GCC_PLUGINS
22	select TTY # Needed for line.c
23
24config MMU
25	bool
26	default y
27
28config NO_IOMEM
29	def_bool y
30
31config ISA
32	bool
33
34config SBUS
35	bool
36
37config TRACE_IRQFLAGS_SUPPORT
38	bool
39	default y
40
41config LOCKDEP_SUPPORT
42	bool
43	default y
44
45config STACKTRACE_SUPPORT
46	bool
47	default y
48	select STACKTRACE
49
50config GENERIC_CALIBRATE_DELAY
51	bool
52	default y
53
54config HZ
55	int
56	default 100
57
58config NR_CPUS
59	int
60	range 1 1
61	default 1
62
63source "arch/$(HEADER_ARCH)/um/Kconfig"
64
65config FORBID_STATIC_LINK
66	bool
67
68config STATIC_LINK
69	bool "Force a static link"
70	depends on !FORBID_STATIC_LINK
71	help
72	  This option gives you the ability to force a static link of UML.
73	  Normally, UML is linked as a shared binary.  This is inconvenient for
74	  use in a chroot jail.  So, if you intend to run UML inside a chroot,
75	  you probably want to say Y here.
76	  Additionally, this option enables using higher memory spaces (up to
77	  2.75G) for UML.
78
79	  NOTE: This option is incompatible with some networking features which
80	  depend on features that require being dynamically loaded (like NSS).
81
82config LD_SCRIPT_STATIC
83	bool
84	default y
85	depends on STATIC_LINK
86
87config LD_SCRIPT_DYN
88	bool
89	default y
90	depends on !LD_SCRIPT_STATIC
91	select MODULE_REL_CRCS if MODVERSIONS
92
93config HOSTFS
94	tristate "Host filesystem"
95	help
96	  While the User-Mode Linux port uses its own root file system for
97	  booting and normal file access, this module lets the UML user
98	  access files stored on the host.  It does not require any
99	  network connection between the Host and UML.  An example use of
100	  this might be:
101
102	  mount none /tmp/fromhost -t hostfs -o /tmp/umlshare
103
104	  where /tmp/fromhost is an empty directory inside UML and
105	  /tmp/umlshare is a directory on the host with files the UML user
106	  wishes to access.
107
108	  For more information, see
109	  <http://user-mode-linux.sourceforge.net/hostfs.html>.
110
111	  If you'd like to be able to work with files stored on the host,
112	  say Y or M here; otherwise say N.
113
114config MCONSOLE
115	bool "Management console"
116	depends on PROC_FS
117	default y
118	help
119	  The user mode linux management console is a low-level interface to
120	  the kernel, somewhat like the i386 SysRq interface.  Since there is
121	  a full-blown operating system running under every user mode linux
122	  instance, there is much greater flexibility possible than with the
123	  SysRq mechanism.
124
125	  If you answer 'Y' to this option, to use this feature, you need the
126	  mconsole client (called uml_mconsole) which is present in CVS in
127	  2.4.5-9um and later (path /tools/mconsole), and is also in the
128	  distribution RPM package in 2.4.6 and later.
129
130	  It is safe to say 'Y' here.
131
132config MAGIC_SYSRQ
133	bool "Magic SysRq key"
134	depends on MCONSOLE
135	help
136	  If you say Y here, you will have some control over the system even
137	  if the system crashes for example during kernel debugging (e.g., you
138	  will be able to flush the buffer cache to disk, reboot the system
139	  immediately or dump some status information). A key for each of the
140	  possible requests is provided.
141
142	  This is the feature normally accomplished by pressing a key
143	  while holding SysRq (Alt+PrintScreen).
144
145	  On UML, this is accomplished by sending a "sysrq" command with
146	  mconsole, followed by the letter for the requested command.
147
148	  The keys are documented in <file:Documentation/admin-guide/sysrq.rst>. Don't say Y
149	  unless you really know what this hack does.
150
151config KERNEL_STACK_ORDER
152	int "Kernel stack size order"
153	default 2 if 64BIT
154	range 2 10 if 64BIT
155	default 1 if !64BIT
156	help
157	  This option determines the size of UML kernel stacks.  They will
158	  be 1 << order pages.  The default is OK unless you're running Valgrind
159	  on UML, in which case, set this to 3.
160	  It is possible to reduce the stack to 1 for 64BIT and 0 for 32BIT on
161	  older (pre-2017) CPUs. It is not recommended on newer CPUs due to the
162	  increase in the size of the state which needs to be saved when handling
163	  signals.
164
165config MMAPPER
166	tristate "iomem emulation driver"
167	help
168	  This driver allows a host file to be used as emulated IO memory inside
169	  UML.
170
171config PGTABLE_LEVELS
172	int
173	default 3 if 3_LEVEL_PGTABLES
174	default 2
175
176config SECCOMP
177	def_bool y
178	prompt "Enable seccomp to safely compute untrusted bytecode"
179	help
180	  This kernel feature is useful for number crunching applications
181	  that may need to compute untrusted bytecode during their
182	  execution. By using pipes or other transports made available to
183	  the process as file descriptors supporting the read/write
184	  syscalls, it's possible to isolate those applications in
185	  their own address space using seccomp. Once seccomp is
186	  enabled via prctl(PR_SET_SECCOMP), it cannot be disabled
187	  and the task is only allowed to execute a few safe syscalls
188	  defined by each seccomp mode.
189
190	  If unsure, say Y.
191
192config UML_TIME_TRAVEL_SUPPORT
193	bool
194	prompt "Support time-travel mode (e.g. for test execution)"
195	# inf-cpu mode is incompatible with the benchmarking
196	depends on !RAID6_PQ_BENCHMARK
197	depends on !SMP
198	help
199	  Enable this option to support time travel inside the UML instance.
200
201	  After enabling this option, two modes are accessible at runtime
202	  (selected by the kernel command line), see the kernel's command-
203	  line help for more details.
204
205	  It is safe to say Y, but you probably don't need this.
206
207endmenu
208
209source "arch/um/drivers/Kconfig"
210