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 <[email protected]> 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 static inline int jump_entry_size(struct jump_entry *entry) 180 { 181 #ifdef JUMP_LABEL_NOP_SIZE 182 return JUMP_LABEL_NOP_SIZE; 183 #else 184 return arch_jump_entry_size(entry); 185 #endif 186 } 187 188 #endif 189 #endif 190 191 #ifndef __ASSEMBLY__ 192 193 enum jump_label_type { 194 JUMP_LABEL_NOP = 0, 195 JUMP_LABEL_JMP, 196 }; 197 198 struct module; 199 200 #ifdef CONFIG_JUMP_LABEL 201 202 #define JUMP_TYPE_FALSE 0UL 203 #define JUMP_TYPE_TRUE 1UL 204 #define JUMP_TYPE_LINKED 2UL 205 #define JUMP_TYPE_MASK 3UL 206 207 static __always_inline bool static_key_false(struct static_key *key) 208 { 209 return arch_static_branch(key, false); 210 } 211 212 static __always_inline bool static_key_true(struct static_key *key) 213 { 214 return !arch_static_branch(key, true); 215 } 216 217 extern struct jump_entry __start___jump_table[]; 218 extern struct jump_entry __stop___jump_table[]; 219 220 extern void jump_label_init(void); 221 extern void jump_label_lock(void); 222 extern void jump_label_unlock(void); 223 extern void arch_jump_label_transform(struct jump_entry *entry, 224 enum jump_label_type type); 225 extern void arch_jump_label_transform_static(struct jump_entry *entry, 226 enum jump_label_type type); 227 extern bool arch_jump_label_transform_queue(struct jump_entry *entry, 228 enum jump_label_type type); 229 extern void arch_jump_label_transform_apply(void); 230 extern int jump_label_text_reserved(void *start, void *end); 231 extern void static_key_slow_inc(struct static_key *key); 232 extern void static_key_slow_dec(struct static_key *key); 233 extern void static_key_slow_inc_cpuslocked(struct static_key *key); 234 extern void static_key_slow_dec_cpuslocked(struct static_key *key); 235 extern void jump_label_apply_nops(struct module *mod); 236 extern int static_key_count(struct static_key *key); 237 extern void static_key_enable(struct static_key *key); 238 extern void static_key_disable(struct static_key *key); 239 extern void static_key_enable_cpuslocked(struct static_key *key); 240 extern void static_key_disable_cpuslocked(struct static_key *key); 241 242 /* 243 * We should be using ATOMIC_INIT() for initializing .enabled, but 244 * the inclusion of atomic.h is problematic for inclusion of jump_label.h 245 * in 'low-level' headers. Thus, we are initializing .enabled with a 246 * raw value, but have added a BUILD_BUG_ON() to catch any issues in 247 * jump_label_init() see: kernel/jump_label.c. 248 */ 249 #define STATIC_KEY_INIT_TRUE \ 250 { .enabled = { 1 }, \ 251 { .entries = (void *)JUMP_TYPE_TRUE } } 252 #define STATIC_KEY_INIT_FALSE \ 253 { .enabled = { 0 }, \ 254 { .entries = (void *)JUMP_TYPE_FALSE } } 255 256 #else /* !CONFIG_JUMP_LABEL */ 257 258 #include <linux/atomic.h> 259 #include <linux/bug.h> 260 261 static inline int static_key_count(struct static_key *key) 262 { 263 return atomic_read(&key->enabled); 264 } 265 266 static __always_inline void jump_label_init(void) 267 { 268 static_key_initialized = true; 269 } 270 271 static __always_inline bool static_key_false(struct static_key *key) 272 { 273 if (unlikely_notrace(static_key_count(key) > 0)) 274 return true; 275 return false; 276 } 277 278 static __always_inline bool static_key_true(struct static_key *key) 279 { 280 if (likely_notrace(static_key_count(key) > 0)) 281 return true; 282 return false; 283 } 284 285 static inline void static_key_slow_inc(struct static_key *key) 286 { 287 STATIC_KEY_CHECK_USE(key); 288 atomic_inc(&key->enabled); 289 } 290 291 static inline void static_key_slow_dec(struct static_key *key) 292 { 293 STATIC_KEY_CHECK_USE(key); 294 atomic_dec(&key->enabled); 295 } 296 297 #define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key) 298 #define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key) 299 300 static inline int jump_label_text_reserved(void *start, void *end) 301 { 302 return 0; 303 } 304 305 static inline void jump_label_lock(void) {} 306 static inline void jump_label_unlock(void) {} 307 308 static inline int jump_label_apply_nops(struct module *mod) 309 { 310 return 0; 311 } 312 313 static inline void static_key_enable(struct static_key *key) 314 { 315 STATIC_KEY_CHECK_USE(key); 316 317 if (atomic_read(&key->enabled) != 0) { 318 WARN_ON_ONCE(atomic_read(&key->enabled) != 1); 319 return; 320 } 321 atomic_set(&key->enabled, 1); 322 } 323 324 static inline void static_key_disable(struct static_key *key) 325 { 326 STATIC_KEY_CHECK_USE(key); 327 328 if (atomic_read(&key->enabled) != 1) { 329 WARN_ON_ONCE(atomic_read(&key->enabled) != 0); 330 return; 331 } 332 atomic_set(&key->enabled, 0); 333 } 334 335 #define static_key_enable_cpuslocked(k) static_key_enable((k)) 336 #define static_key_disable_cpuslocked(k) static_key_disable((k)) 337 338 #define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) } 339 #define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) } 340 341 #endif /* CONFIG_JUMP_LABEL */ 342 343 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE 344 #define jump_label_enabled static_key_enabled 345 346 /* -------------------------------------------------------------------------- */ 347 348 /* 349 * Two type wrappers around static_key, such that we can use compile time 350 * type differentiation to emit the right code. 351 * 352 * All the below code is macros in order to play type games. 353 */ 354 355 struct static_key_true { 356 struct static_key key; 357 }; 358 359 struct static_key_false { 360 struct static_key key; 361 }; 362 363 #define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, } 364 #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, } 365 366 #define DEFINE_STATIC_KEY_TRUE(name) \ 367 struct static_key_true name = STATIC_KEY_TRUE_INIT 368 369 #define DEFINE_STATIC_KEY_TRUE_RO(name) \ 370 struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT 371 372 #define DECLARE_STATIC_KEY_TRUE(name) \ 373 extern struct static_key_true name 374 375 #define DEFINE_STATIC_KEY_FALSE(name) \ 376 struct static_key_false name = STATIC_KEY_FALSE_INIT 377 378 #define DEFINE_STATIC_KEY_FALSE_RO(name) \ 379 struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT 380 381 #define DECLARE_STATIC_KEY_FALSE(name) \ 382 extern struct static_key_false name 383 384 #define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count) \ 385 struct static_key_true name[count] = { \ 386 [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT, \ 387 } 388 389 #define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count) \ 390 struct static_key_false name[count] = { \ 391 [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT, \ 392 } 393 394 #define _DEFINE_STATIC_KEY_1(name) DEFINE_STATIC_KEY_TRUE(name) 395 #define _DEFINE_STATIC_KEY_0(name) DEFINE_STATIC_KEY_FALSE(name) 396 #define DEFINE_STATIC_KEY_MAYBE(cfg, name) \ 397 __PASTE(_DEFINE_STATIC_KEY_, IS_ENABLED(cfg))(name) 398 399 #define _DEFINE_STATIC_KEY_RO_1(name) DEFINE_STATIC_KEY_TRUE_RO(name) 400 #define _DEFINE_STATIC_KEY_RO_0(name) DEFINE_STATIC_KEY_FALSE_RO(name) 401 #define DEFINE_STATIC_KEY_MAYBE_RO(cfg, name) \ 402 __PASTE(_DEFINE_STATIC_KEY_RO_, IS_ENABLED(cfg))(name) 403 404 #define _DECLARE_STATIC_KEY_1(name) DECLARE_STATIC_KEY_TRUE(name) 405 #define _DECLARE_STATIC_KEY_0(name) DECLARE_STATIC_KEY_FALSE(name) 406 #define DECLARE_STATIC_KEY_MAYBE(cfg, name) \ 407 __PASTE(_DECLARE_STATIC_KEY_, IS_ENABLED(cfg))(name) 408 409 extern bool ____wrong_branch_error(void); 410 411 #define static_key_enabled(x) \ 412 ({ \ 413 if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \ 414 !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\ 415 !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 416 ____wrong_branch_error(); \ 417 static_key_count((struct static_key *)x) > 0; \ 418 }) 419 420 #ifdef CONFIG_JUMP_LABEL 421 422 /* 423 * Combine the right initial value (type) with the right branch order 424 * to generate the desired result. 425 * 426 * 427 * type\branch| likely (1) | unlikely (0) 428 * -----------+-----------------------+------------------ 429 * | | 430 * true (1) | ... | ... 431 * | NOP | JMP L 432 * | <br-stmts> | 1: ... 433 * | L: ... | 434 * | | 435 * | | L: <br-stmts> 436 * | | jmp 1b 437 * | | 438 * -----------+-----------------------+------------------ 439 * | | 440 * false (0) | ... | ... 441 * | JMP L | NOP 442 * | <br-stmts> | 1: ... 443 * | L: ... | 444 * | | 445 * | | L: <br-stmts> 446 * | | jmp 1b 447 * | | 448 * -----------+-----------------------+------------------ 449 * 450 * The initial value is encoded in the LSB of static_key::entries, 451 * type: 0 = false, 1 = true. 452 * 453 * The branch type is encoded in the LSB of jump_entry::key, 454 * branch: 0 = unlikely, 1 = likely. 455 * 456 * This gives the following logic table: 457 * 458 * enabled type branch instuction 459 * -----------------------------+----------- 460 * 0 0 0 | NOP 461 * 0 0 1 | JMP 462 * 0 1 0 | NOP 463 * 0 1 1 | JMP 464 * 465 * 1 0 0 | JMP 466 * 1 0 1 | NOP 467 * 1 1 0 | JMP 468 * 1 1 1 | NOP 469 * 470 * Which gives the following functions: 471 * 472 * dynamic: instruction = enabled ^ branch 473 * static: instruction = type ^ branch 474 * 475 * See jump_label_type() / jump_label_init_type(). 476 */ 477 478 #define static_branch_likely(x) \ 479 ({ \ 480 bool branch; \ 481 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ 482 branch = !arch_static_branch(&(x)->key, true); \ 483 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 484 branch = !arch_static_branch_jump(&(x)->key, true); \ 485 else \ 486 branch = ____wrong_branch_error(); \ 487 likely_notrace(branch); \ 488 }) 489 490 #define static_branch_unlikely(x) \ 491 ({ \ 492 bool branch; \ 493 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ 494 branch = arch_static_branch_jump(&(x)->key, false); \ 495 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 496 branch = arch_static_branch(&(x)->key, false); \ 497 else \ 498 branch = ____wrong_branch_error(); \ 499 unlikely_notrace(branch); \ 500 }) 501 502 #else /* !CONFIG_JUMP_LABEL */ 503 504 #define static_branch_likely(x) likely_notrace(static_key_enabled(&(x)->key)) 505 #define static_branch_unlikely(x) unlikely_notrace(static_key_enabled(&(x)->key)) 506 507 #endif /* CONFIG_JUMP_LABEL */ 508 509 #define static_branch_maybe(config, x) \ 510 (IS_ENABLED(config) ? static_branch_likely(x) \ 511 : static_branch_unlikely(x)) 512 513 /* 514 * Advanced usage; refcount, branch is enabled when: count != 0 515 */ 516 517 #define static_branch_inc(x) static_key_slow_inc(&(x)->key) 518 #define static_branch_dec(x) static_key_slow_dec(&(x)->key) 519 #define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key) 520 #define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(x)->key) 521 522 /* 523 * Normal usage; boolean enable/disable. 524 */ 525 526 #define static_branch_enable(x) static_key_enable(&(x)->key) 527 #define static_branch_disable(x) static_key_disable(&(x)->key) 528 #define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key) 529 #define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key) 530 531 #endif /* __ASSEMBLY__ */ 532 533 #endif /* _LINUX_JUMP_LABEL_H */ 534