1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #ifndef _LINUX_JUMP_LABEL_H 3 #define _LINUX_JUMP_LABEL_H 4 5 /* 6 * Jump label support 7 * 8 * Copyright (C) 2009-2012 Jason Baron <jbaron@redhat.com> 9 * Copyright (C) 2011-2012 Red Hat, Inc., Peter Zijlstra 10 * 11 * DEPRECATED API: 12 * 13 * The use of 'struct static_key' directly, is now DEPRECATED. In addition 14 * static_key_{true,false}() is also DEPRECATED. IE DO NOT use the following: 15 * 16 * struct static_key false = STATIC_KEY_INIT_FALSE; 17 * struct static_key true = STATIC_KEY_INIT_TRUE; 18 * static_key_true() 19 * static_key_false() 20 * 21 * The updated API replacements are: 22 * 23 * DEFINE_STATIC_KEY_TRUE(key); 24 * DEFINE_STATIC_KEY_FALSE(key); 25 * DEFINE_STATIC_KEY_ARRAY_TRUE(keys, count); 26 * DEFINE_STATIC_KEY_ARRAY_FALSE(keys, count); 27 * static_branch_likely() 28 * static_branch_unlikely() 29 * 30 * Jump labels provide an interface to generate dynamic branches using 31 * self-modifying code. Assuming toolchain and architecture support, if we 32 * define a "key" that is initially false via "DEFINE_STATIC_KEY_FALSE(key)", 33 * an "if (static_branch_unlikely(&key))" statement is an unconditional branch 34 * (which defaults to false - and the true block is placed out of line). 35 * Similarly, we can define an initially true key via 36 * "DEFINE_STATIC_KEY_TRUE(key)", and use it in the same 37 * "if (static_branch_unlikely(&key))", in which case we will generate an 38 * unconditional branch to the out-of-line true branch. Keys that are 39 * initially true or false can be using in both static_branch_unlikely() 40 * and static_branch_likely() statements. 41 * 42 * At runtime we can change the branch target by setting the key 43 * to true via a call to static_branch_enable(), or false using 44 * static_branch_disable(). If the direction of the branch is switched by 45 * these calls then we run-time modify the branch target via a 46 * no-op -> jump or jump -> no-op conversion. For example, for an 47 * initially false key that is used in an "if (static_branch_unlikely(&key))" 48 * statement, setting the key to true requires us to patch in a jump 49 * to the out-of-line of true branch. 50 * 51 * In addition to static_branch_{enable,disable}, we can also reference count 52 * the key or branch direction via static_branch_{inc,dec}. Thus, 53 * static_branch_inc() can be thought of as a 'make more true' and 54 * static_branch_dec() as a 'make more false'. 55 * 56 * Since this relies on modifying code, the branch modifying functions 57 * must be considered absolute slow paths (machine wide synchronization etc.). 58 * OTOH, since the affected branches are unconditional, their runtime overhead 59 * will be absolutely minimal, esp. in the default (off) case where the total 60 * effect is a single NOP of appropriate size. The on case will patch in a jump 61 * to the out-of-line block. 62 * 63 * When the control is directly exposed to userspace, it is prudent to delay the 64 * decrement to avoid high frequency code modifications which can (and do) 65 * cause significant performance degradation. Struct static_key_deferred and 66 * static_key_slow_dec_deferred() provide for this. 67 * 68 * Lacking toolchain and or architecture support, static keys fall back to a 69 * simple conditional branch. 70 * 71 * Additional babbling in: Documentation/staging/static-keys.rst 72 */ 73 74 #ifndef __ASSEMBLY__ 75 76 #include <linux/types.h> 77 #include <linux/compiler.h> 78 79 extern bool static_key_initialized; 80 81 #define STATIC_KEY_CHECK_USE(key) WARN(!static_key_initialized, \ 82 "%s(): static key '%pS' used before call to jump_label_init()", \ 83 __func__, (key)) 84 85 #ifdef CONFIG_JUMP_LABEL 86 87 struct static_key { 88 atomic_t enabled; 89 /* 90 * Note: 91 * To make anonymous unions work with old compilers, the static 92 * initialization of them requires brackets. This creates a dependency 93 * on the order of the struct with the initializers. If any fields 94 * are added, STATIC_KEY_INIT_TRUE and STATIC_KEY_INIT_FALSE may need 95 * to be modified. 96 * 97 * bit 0 => 1 if key is initially true 98 * 0 if initially false 99 * bit 1 => 1 if points to struct static_key_mod 100 * 0 if points to struct jump_entry 101 */ 102 union { 103 unsigned long type; 104 struct jump_entry *entries; 105 struct static_key_mod *next; 106 }; 107 }; 108 109 #else 110 struct static_key { 111 atomic_t enabled; 112 }; 113 #endif /* CONFIG_JUMP_LABEL */ 114 #endif /* __ASSEMBLY__ */ 115 116 #ifdef CONFIG_JUMP_LABEL 117 #include <asm/jump_label.h> 118 119 #ifndef __ASSEMBLY__ 120 #ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE 121 122 struct jump_entry { 123 s32 code; 124 s32 target; 125 long key; // key may be far away from the core kernel under KASLR 126 }; 127 128 static inline unsigned long jump_entry_code(const struct jump_entry *entry) 129 { 130 return (unsigned long)&entry->code + entry->code; 131 } 132 133 static inline unsigned long jump_entry_target(const struct jump_entry *entry) 134 { 135 return (unsigned long)&entry->target + entry->target; 136 } 137 138 static inline struct static_key *jump_entry_key(const struct jump_entry *entry) 139 { 140 long offset = entry->key & ~3L; 141 142 return (struct static_key *)((unsigned long)&entry->key + offset); 143 } 144 145 #else 146 147 static inline unsigned long jump_entry_code(const struct jump_entry *entry) 148 { 149 return entry->code; 150 } 151 152 static inline unsigned long jump_entry_target(const struct jump_entry *entry) 153 { 154 return entry->target; 155 } 156 157 static inline struct static_key *jump_entry_key(const struct jump_entry *entry) 158 { 159 return (struct static_key *)((unsigned long)entry->key & ~3UL); 160 } 161 162 #endif 163 164 static inline bool jump_entry_is_branch(const struct jump_entry *entry) 165 { 166 return (unsigned long)entry->key & 1UL; 167 } 168 169 static inline bool jump_entry_is_init(const struct jump_entry *entry) 170 { 171 return (unsigned long)entry->key & 2UL; 172 } 173 174 static inline void jump_entry_set_init(struct jump_entry *entry) 175 { 176 entry->key |= 2; 177 } 178 179 #endif 180 #endif 181 182 #ifndef __ASSEMBLY__ 183 184 enum jump_label_type { 185 JUMP_LABEL_NOP = 0, 186 JUMP_LABEL_JMP, 187 }; 188 189 struct module; 190 191 #ifdef CONFIG_JUMP_LABEL 192 193 #define JUMP_TYPE_FALSE 0UL 194 #define JUMP_TYPE_TRUE 1UL 195 #define JUMP_TYPE_LINKED 2UL 196 #define JUMP_TYPE_MASK 3UL 197 198 static __always_inline bool static_key_false(struct static_key *key) 199 { 200 return arch_static_branch(key, false); 201 } 202 203 static __always_inline bool static_key_true(struct static_key *key) 204 { 205 return !arch_static_branch(key, true); 206 } 207 208 extern struct jump_entry __start___jump_table[]; 209 extern struct jump_entry __stop___jump_table[]; 210 211 extern void jump_label_init(void); 212 extern void jump_label_lock(void); 213 extern void jump_label_unlock(void); 214 extern void arch_jump_label_transform(struct jump_entry *entry, 215 enum jump_label_type type); 216 extern void arch_jump_label_transform_static(struct jump_entry *entry, 217 enum jump_label_type type); 218 extern bool arch_jump_label_transform_queue(struct jump_entry *entry, 219 enum jump_label_type type); 220 extern void arch_jump_label_transform_apply(void); 221 extern int jump_label_text_reserved(void *start, void *end); 222 extern void static_key_slow_inc(struct static_key *key); 223 extern void static_key_slow_dec(struct static_key *key); 224 extern void static_key_slow_inc_cpuslocked(struct static_key *key); 225 extern void static_key_slow_dec_cpuslocked(struct static_key *key); 226 extern void jump_label_apply_nops(struct module *mod); 227 extern int static_key_count(struct static_key *key); 228 extern void static_key_enable(struct static_key *key); 229 extern void static_key_disable(struct static_key *key); 230 extern void static_key_enable_cpuslocked(struct static_key *key); 231 extern void static_key_disable_cpuslocked(struct static_key *key); 232 233 /* 234 * We should be using ATOMIC_INIT() for initializing .enabled, but 235 * the inclusion of atomic.h is problematic for inclusion of jump_label.h 236 * in 'low-level' headers. Thus, we are initializing .enabled with a 237 * raw value, but have added a BUILD_BUG_ON() to catch any issues in 238 * jump_label_init() see: kernel/jump_label.c. 239 */ 240 #define STATIC_KEY_INIT_TRUE \ 241 { .enabled = { 1 }, \ 242 { .entries = (void *)JUMP_TYPE_TRUE } } 243 #define STATIC_KEY_INIT_FALSE \ 244 { .enabled = { 0 }, \ 245 { .entries = (void *)JUMP_TYPE_FALSE } } 246 247 #else /* !CONFIG_JUMP_LABEL */ 248 249 #include <linux/atomic.h> 250 #include <linux/bug.h> 251 252 static inline int static_key_count(struct static_key *key) 253 { 254 return atomic_read(&key->enabled); 255 } 256 257 static __always_inline void jump_label_init(void) 258 { 259 static_key_initialized = true; 260 } 261 262 static __always_inline bool static_key_false(struct static_key *key) 263 { 264 if (unlikely_notrace(static_key_count(key) > 0)) 265 return true; 266 return false; 267 } 268 269 static __always_inline bool static_key_true(struct static_key *key) 270 { 271 if (likely_notrace(static_key_count(key) > 0)) 272 return true; 273 return false; 274 } 275 276 static inline void static_key_slow_inc(struct static_key *key) 277 { 278 STATIC_KEY_CHECK_USE(key); 279 atomic_inc(&key->enabled); 280 } 281 282 static inline void static_key_slow_dec(struct static_key *key) 283 { 284 STATIC_KEY_CHECK_USE(key); 285 atomic_dec(&key->enabled); 286 } 287 288 #define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key) 289 #define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key) 290 291 static inline int jump_label_text_reserved(void *start, void *end) 292 { 293 return 0; 294 } 295 296 static inline void jump_label_lock(void) {} 297 static inline void jump_label_unlock(void) {} 298 299 static inline int jump_label_apply_nops(struct module *mod) 300 { 301 return 0; 302 } 303 304 static inline void static_key_enable(struct static_key *key) 305 { 306 STATIC_KEY_CHECK_USE(key); 307 308 if (atomic_read(&key->enabled) != 0) { 309 WARN_ON_ONCE(atomic_read(&key->enabled) != 1); 310 return; 311 } 312 atomic_set(&key->enabled, 1); 313 } 314 315 static inline void static_key_disable(struct static_key *key) 316 { 317 STATIC_KEY_CHECK_USE(key); 318 319 if (atomic_read(&key->enabled) != 1) { 320 WARN_ON_ONCE(atomic_read(&key->enabled) != 0); 321 return; 322 } 323 atomic_set(&key->enabled, 0); 324 } 325 326 #define static_key_enable_cpuslocked(k) static_key_enable((k)) 327 #define static_key_disable_cpuslocked(k) static_key_disable((k)) 328 329 #define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) } 330 #define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) } 331 332 #endif /* CONFIG_JUMP_LABEL */ 333 334 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE 335 #define jump_label_enabled static_key_enabled 336 337 /* -------------------------------------------------------------------------- */ 338 339 /* 340 * Two type wrappers around static_key, such that we can use compile time 341 * type differentiation to emit the right code. 342 * 343 * All the below code is macros in order to play type games. 344 */ 345 346 struct static_key_true { 347 struct static_key key; 348 }; 349 350 struct static_key_false { 351 struct static_key key; 352 }; 353 354 #define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, } 355 #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, } 356 357 #define DEFINE_STATIC_KEY_TRUE(name) \ 358 struct static_key_true name = STATIC_KEY_TRUE_INIT 359 360 #define DEFINE_STATIC_KEY_TRUE_RO(name) \ 361 struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT 362 363 #define DECLARE_STATIC_KEY_TRUE(name) \ 364 extern struct static_key_true name 365 366 #define DEFINE_STATIC_KEY_FALSE(name) \ 367 struct static_key_false name = STATIC_KEY_FALSE_INIT 368 369 #define DEFINE_STATIC_KEY_FALSE_RO(name) \ 370 struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT 371 372 #define DECLARE_STATIC_KEY_FALSE(name) \ 373 extern struct static_key_false name 374 375 #define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count) \ 376 struct static_key_true name[count] = { \ 377 [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT, \ 378 } 379 380 #define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count) \ 381 struct static_key_false name[count] = { \ 382 [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT, \ 383 } 384 385 extern bool ____wrong_branch_error(void); 386 387 #define static_key_enabled(x) \ 388 ({ \ 389 if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \ 390 !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\ 391 !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 392 ____wrong_branch_error(); \ 393 static_key_count((struct static_key *)x) > 0; \ 394 }) 395 396 #ifdef CONFIG_JUMP_LABEL 397 398 /* 399 * Combine the right initial value (type) with the right branch order 400 * to generate the desired result. 401 * 402 * 403 * type\branch| likely (1) | unlikely (0) 404 * -----------+-----------------------+------------------ 405 * | | 406 * true (1) | ... | ... 407 * | NOP | JMP L 408 * | <br-stmts> | 1: ... 409 * | L: ... | 410 * | | 411 * | | L: <br-stmts> 412 * | | jmp 1b 413 * | | 414 * -----------+-----------------------+------------------ 415 * | | 416 * false (0) | ... | ... 417 * | JMP L | NOP 418 * | <br-stmts> | 1: ... 419 * | L: ... | 420 * | | 421 * | | L: <br-stmts> 422 * | | jmp 1b 423 * | | 424 * -----------+-----------------------+------------------ 425 * 426 * The initial value is encoded in the LSB of static_key::entries, 427 * type: 0 = false, 1 = true. 428 * 429 * The branch type is encoded in the LSB of jump_entry::key, 430 * branch: 0 = unlikely, 1 = likely. 431 * 432 * This gives the following logic table: 433 * 434 * enabled type branch instuction 435 * -----------------------------+----------- 436 * 0 0 0 | NOP 437 * 0 0 1 | JMP 438 * 0 1 0 | NOP 439 * 0 1 1 | JMP 440 * 441 * 1 0 0 | JMP 442 * 1 0 1 | NOP 443 * 1 1 0 | JMP 444 * 1 1 1 | NOP 445 * 446 * Which gives the following functions: 447 * 448 * dynamic: instruction = enabled ^ branch 449 * static: instruction = type ^ branch 450 * 451 * See jump_label_type() / jump_label_init_type(). 452 */ 453 454 #define static_branch_likely(x) \ 455 ({ \ 456 bool branch; \ 457 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ 458 branch = !arch_static_branch(&(x)->key, true); \ 459 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 460 branch = !arch_static_branch_jump(&(x)->key, true); \ 461 else \ 462 branch = ____wrong_branch_error(); \ 463 likely_notrace(branch); \ 464 }) 465 466 #define static_branch_unlikely(x) \ 467 ({ \ 468 bool branch; \ 469 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ 470 branch = arch_static_branch_jump(&(x)->key, false); \ 471 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 472 branch = arch_static_branch(&(x)->key, false); \ 473 else \ 474 branch = ____wrong_branch_error(); \ 475 unlikely_notrace(branch); \ 476 }) 477 478 #else /* !CONFIG_JUMP_LABEL */ 479 480 #define static_branch_likely(x) likely_notrace(static_key_enabled(&(x)->key)) 481 #define static_branch_unlikely(x) unlikely_notrace(static_key_enabled(&(x)->key)) 482 483 #endif /* CONFIG_JUMP_LABEL */ 484 485 /* 486 * Advanced usage; refcount, branch is enabled when: count != 0 487 */ 488 489 #define static_branch_inc(x) static_key_slow_inc(&(x)->key) 490 #define static_branch_dec(x) static_key_slow_dec(&(x)->key) 491 #define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key) 492 #define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(x)->key) 493 494 /* 495 * Normal usage; boolean enable/disable. 496 */ 497 498 #define static_branch_enable(x) static_key_enable(&(x)->key) 499 #define static_branch_disable(x) static_key_disable(&(x)->key) 500 #define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key) 501 #define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key) 502 503 #endif /* __ASSEMBLY__ */ 504 505 #endif /* _LINUX_JUMP_LABEL_H */ 506