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 #include <linux/cleanup.h> 79 80 extern bool static_key_initialized; 81 82 #define STATIC_KEY_CHECK_USE(key) WARN(!static_key_initialized, \ 83 "%s(): static key '%pS' used before call to jump_label_init()", \ 84 __func__, (key)) 85 86 struct static_key { 87 atomic_t enabled; 88 #ifdef CONFIG_JUMP_LABEL 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 #endif /* CONFIG_JUMP_LABEL */ 108 }; 109 110 #endif /* __ASSEMBLY__ */ 111 112 #ifdef CONFIG_JUMP_LABEL 113 #include <asm/jump_label.h> 114 115 #ifndef __ASSEMBLY__ 116 #ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE 117 118 struct jump_entry { 119 s32 code; 120 s32 target; 121 long key; // key may be far away from the core kernel under KASLR 122 }; 123 124 static inline unsigned long jump_entry_code(const struct jump_entry *entry) 125 { 126 return (unsigned long)&entry->code + entry->code; 127 } 128 129 static inline unsigned long jump_entry_target(const struct jump_entry *entry) 130 { 131 return (unsigned long)&entry->target + entry->target; 132 } 133 134 static inline struct static_key *jump_entry_key(const struct jump_entry *entry) 135 { 136 long offset = entry->key & ~3L; 137 138 return (struct static_key *)((unsigned long)&entry->key + offset); 139 } 140 141 #else 142 143 static inline unsigned long jump_entry_code(const struct jump_entry *entry) 144 { 145 return entry->code; 146 } 147 148 static inline unsigned long jump_entry_target(const struct jump_entry *entry) 149 { 150 return entry->target; 151 } 152 153 static inline struct static_key *jump_entry_key(const struct jump_entry *entry) 154 { 155 return (struct static_key *)((unsigned long)entry->key & ~3UL); 156 } 157 158 #endif 159 160 static inline bool jump_entry_is_branch(const struct jump_entry *entry) 161 { 162 return (unsigned long)entry->key & 1UL; 163 } 164 165 static inline bool jump_entry_is_init(const struct jump_entry *entry) 166 { 167 return (unsigned long)entry->key & 2UL; 168 } 169 170 static inline void jump_entry_set_init(struct jump_entry *entry, bool set) 171 { 172 if (set) 173 entry->key |= 2; 174 else 175 entry->key &= ~2; 176 } 177 178 static inline int jump_entry_size(struct jump_entry *entry) 179 { 180 #ifdef JUMP_LABEL_NOP_SIZE 181 return JUMP_LABEL_NOP_SIZE; 182 #else 183 return arch_jump_entry_size(entry); 184 #endif 185 } 186 187 #endif 188 #endif 189 190 #ifndef __ASSEMBLY__ 191 192 enum jump_label_type { 193 JUMP_LABEL_NOP = 0, 194 JUMP_LABEL_JMP, 195 }; 196 197 struct module; 198 199 #ifdef CONFIG_JUMP_LABEL 200 201 #define JUMP_TYPE_FALSE 0UL 202 #define JUMP_TYPE_TRUE 1UL 203 #define JUMP_TYPE_LINKED 2UL 204 #define JUMP_TYPE_MASK 3UL 205 206 static __always_inline bool static_key_false(struct static_key *key) 207 { 208 return arch_static_branch(key, false); 209 } 210 211 static __always_inline bool static_key_true(struct static_key *key) 212 { 213 return !arch_static_branch(key, true); 214 } 215 216 extern struct jump_entry __start___jump_table[]; 217 extern struct jump_entry __stop___jump_table[]; 218 219 extern void jump_label_init(void); 220 extern void jump_label_init_ro(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 bool arch_jump_label_transform_queue(struct jump_entry *entry, 226 enum jump_label_type type); 227 extern void arch_jump_label_transform_apply(void); 228 extern int jump_label_text_reserved(void *start, void *end); 229 extern bool static_key_slow_inc(struct static_key *key); 230 extern bool static_key_fast_inc_not_disabled(struct static_key *key); 231 extern void static_key_slow_dec(struct static_key *key); 232 extern bool static_key_slow_inc_cpuslocked(struct static_key *key); 233 extern void static_key_slow_dec_cpuslocked(struct static_key *key); 234 extern int static_key_count(struct static_key *key); 235 extern void static_key_enable(struct static_key *key); 236 extern void static_key_disable(struct static_key *key); 237 extern void static_key_enable_cpuslocked(struct static_key *key); 238 extern void static_key_disable_cpuslocked(struct static_key *key); 239 extern enum jump_label_type jump_label_init_type(struct jump_entry *entry); 240 241 /* 242 * We should be using ATOMIC_INIT() for initializing .enabled, but 243 * the inclusion of atomic.h is problematic for inclusion of jump_label.h 244 * in 'low-level' headers. Thus, we are initializing .enabled with a 245 * raw value, but have added a BUILD_BUG_ON() to catch any issues in 246 * jump_label_init() see: kernel/jump_label.c. 247 */ 248 #define STATIC_KEY_INIT_TRUE \ 249 { .enabled = { 1 }, \ 250 { .type = JUMP_TYPE_TRUE } } 251 #define STATIC_KEY_INIT_FALSE \ 252 { .enabled = { 0 }, \ 253 { .type = JUMP_TYPE_FALSE } } 254 255 #else /* !CONFIG_JUMP_LABEL */ 256 257 #include <linux/atomic.h> 258 #include <linux/bug.h> 259 260 static __always_inline int static_key_count(struct static_key *key) 261 { 262 return raw_atomic_read(&key->enabled); 263 } 264 265 static __always_inline void jump_label_init(void) 266 { 267 static_key_initialized = true; 268 } 269 270 static __always_inline void jump_label_init_ro(void) { } 271 272 static __always_inline bool static_key_false(struct static_key *key) 273 { 274 if (unlikely_notrace(static_key_count(key) > 0)) 275 return true; 276 return false; 277 } 278 279 static __always_inline bool static_key_true(struct static_key *key) 280 { 281 if (likely_notrace(static_key_count(key) > 0)) 282 return true; 283 return false; 284 } 285 286 static inline bool static_key_fast_inc_not_disabled(struct static_key *key) 287 { 288 int v; 289 290 STATIC_KEY_CHECK_USE(key); 291 /* 292 * Prevent key->enabled getting negative to follow the same semantics 293 * as for CONFIG_JUMP_LABEL=y, see kernel/jump_label.c comment. 294 */ 295 v = atomic_read(&key->enabled); 296 do { 297 if (v < 0 || (v + 1) < 0) 298 return false; 299 } while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1))); 300 return true; 301 } 302 #define static_key_slow_inc(key) static_key_fast_inc_not_disabled(key) 303 304 static inline void static_key_slow_dec(struct static_key *key) 305 { 306 STATIC_KEY_CHECK_USE(key); 307 atomic_dec(&key->enabled); 308 } 309 310 #define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key) 311 #define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key) 312 313 static inline int jump_label_text_reserved(void *start, void *end) 314 { 315 return 0; 316 } 317 318 static inline void jump_label_lock(void) {} 319 static inline void jump_label_unlock(void) {} 320 321 static inline void static_key_enable(struct static_key *key) 322 { 323 STATIC_KEY_CHECK_USE(key); 324 325 if (atomic_read(&key->enabled) != 0) { 326 WARN_ON_ONCE(atomic_read(&key->enabled) != 1); 327 return; 328 } 329 atomic_set(&key->enabled, 1); 330 } 331 332 static inline void static_key_disable(struct static_key *key) 333 { 334 STATIC_KEY_CHECK_USE(key); 335 336 if (atomic_read(&key->enabled) != 1) { 337 WARN_ON_ONCE(atomic_read(&key->enabled) != 0); 338 return; 339 } 340 atomic_set(&key->enabled, 0); 341 } 342 343 #define static_key_enable_cpuslocked(k) static_key_enable((k)) 344 #define static_key_disable_cpuslocked(k) static_key_disable((k)) 345 346 #define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) } 347 #define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) } 348 349 #endif /* CONFIG_JUMP_LABEL */ 350 351 DEFINE_LOCK_GUARD_0(jump_label_lock, jump_label_lock(), jump_label_unlock()) 352 353 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE 354 #define jump_label_enabled static_key_enabled 355 356 /* -------------------------------------------------------------------------- */ 357 358 /* 359 * Two type wrappers around static_key, such that we can use compile time 360 * type differentiation to emit the right code. 361 * 362 * All the below code is macros in order to play type games. 363 */ 364 365 struct static_key_true { 366 struct static_key key; 367 }; 368 369 struct static_key_false { 370 struct static_key key; 371 }; 372 373 #define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, } 374 #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, } 375 376 #define DEFINE_STATIC_KEY_TRUE(name) \ 377 struct static_key_true name = STATIC_KEY_TRUE_INIT 378 379 #define DEFINE_STATIC_KEY_TRUE_RO(name) \ 380 struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT 381 382 #define DECLARE_STATIC_KEY_TRUE(name) \ 383 extern struct static_key_true name 384 385 #define DEFINE_STATIC_KEY_FALSE(name) \ 386 struct static_key_false name = STATIC_KEY_FALSE_INIT 387 388 #define DEFINE_STATIC_KEY_FALSE_RO(name) \ 389 struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT 390 391 #define DECLARE_STATIC_KEY_FALSE(name) \ 392 extern struct static_key_false name 393 394 #define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count) \ 395 struct static_key_true name[count] = { \ 396 [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT, \ 397 } 398 399 #define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count) \ 400 struct static_key_false name[count] = { \ 401 [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT, \ 402 } 403 404 #define _DEFINE_STATIC_KEY_1(name) DEFINE_STATIC_KEY_TRUE(name) 405 #define _DEFINE_STATIC_KEY_0(name) DEFINE_STATIC_KEY_FALSE(name) 406 #define DEFINE_STATIC_KEY_MAYBE(cfg, name) \ 407 __PASTE(_DEFINE_STATIC_KEY_, IS_ENABLED(cfg))(name) 408 409 #define _DEFINE_STATIC_KEY_RO_1(name) DEFINE_STATIC_KEY_TRUE_RO(name) 410 #define _DEFINE_STATIC_KEY_RO_0(name) DEFINE_STATIC_KEY_FALSE_RO(name) 411 #define DEFINE_STATIC_KEY_MAYBE_RO(cfg, name) \ 412 __PASTE(_DEFINE_STATIC_KEY_RO_, IS_ENABLED(cfg))(name) 413 414 #define _DECLARE_STATIC_KEY_1(name) DECLARE_STATIC_KEY_TRUE(name) 415 #define _DECLARE_STATIC_KEY_0(name) DECLARE_STATIC_KEY_FALSE(name) 416 #define DECLARE_STATIC_KEY_MAYBE(cfg, name) \ 417 __PASTE(_DECLARE_STATIC_KEY_, IS_ENABLED(cfg))(name) 418 419 extern bool ____wrong_branch_error(void); 420 421 #define static_key_enabled(x) \ 422 ({ \ 423 if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \ 424 !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\ 425 !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 426 ____wrong_branch_error(); \ 427 static_key_count((struct static_key *)x) > 0; \ 428 }) 429 430 #ifdef CONFIG_JUMP_LABEL 431 432 /* 433 * Combine the right initial value (type) with the right branch order 434 * to generate the desired result. 435 * 436 * 437 * type\branch| likely (1) | unlikely (0) 438 * -----------+-----------------------+------------------ 439 * | | 440 * true (1) | ... | ... 441 * | NOP | JMP L 442 * | <br-stmts> | 1: ... 443 * | L: ... | 444 * | | 445 * | | L: <br-stmts> 446 * | | jmp 1b 447 * | | 448 * -----------+-----------------------+------------------ 449 * | | 450 * false (0) | ... | ... 451 * | JMP L | NOP 452 * | <br-stmts> | 1: ... 453 * | L: ... | 454 * | | 455 * | | L: <br-stmts> 456 * | | jmp 1b 457 * | | 458 * -----------+-----------------------+------------------ 459 * 460 * The initial value is encoded in the LSB of static_key::entries, 461 * type: 0 = false, 1 = true. 462 * 463 * The branch type is encoded in the LSB of jump_entry::key, 464 * branch: 0 = unlikely, 1 = likely. 465 * 466 * This gives the following logic table: 467 * 468 * enabled type branch instuction 469 * -----------------------------+----------- 470 * 0 0 0 | NOP 471 * 0 0 1 | JMP 472 * 0 1 0 | NOP 473 * 0 1 1 | JMP 474 * 475 * 1 0 0 | JMP 476 * 1 0 1 | NOP 477 * 1 1 0 | JMP 478 * 1 1 1 | NOP 479 * 480 * Which gives the following functions: 481 * 482 * dynamic: instruction = enabled ^ branch 483 * static: instruction = type ^ branch 484 * 485 * See jump_label_type() / jump_label_init_type(). 486 */ 487 488 #define static_branch_likely(x) \ 489 ({ \ 490 bool branch; \ 491 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ 492 branch = !arch_static_branch(&(x)->key, true); \ 493 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 494 branch = !arch_static_branch_jump(&(x)->key, true); \ 495 else \ 496 branch = ____wrong_branch_error(); \ 497 likely_notrace(branch); \ 498 }) 499 500 #define static_branch_unlikely(x) \ 501 ({ \ 502 bool branch; \ 503 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ 504 branch = arch_static_branch_jump(&(x)->key, false); \ 505 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 506 branch = arch_static_branch(&(x)->key, false); \ 507 else \ 508 branch = ____wrong_branch_error(); \ 509 unlikely_notrace(branch); \ 510 }) 511 512 #else /* !CONFIG_JUMP_LABEL */ 513 514 #define static_branch_likely(x) likely_notrace(static_key_enabled(&(x)->key)) 515 #define static_branch_unlikely(x) unlikely_notrace(static_key_enabled(&(x)->key)) 516 517 #endif /* CONFIG_JUMP_LABEL */ 518 519 #define static_branch_maybe(config, x) \ 520 (IS_ENABLED(config) ? static_branch_likely(x) \ 521 : static_branch_unlikely(x)) 522 523 /* 524 * Advanced usage; refcount, branch is enabled when: count != 0 525 */ 526 527 #define static_branch_inc(x) static_key_slow_inc(&(x)->key) 528 #define static_branch_dec(x) static_key_slow_dec(&(x)->key) 529 #define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key) 530 #define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(x)->key) 531 532 /* 533 * Normal usage; boolean enable/disable. 534 */ 535 536 #define static_branch_enable(x) static_key_enable(&(x)->key) 537 #define static_branch_disable(x) static_key_disable(&(x)->key) 538 #define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key) 539 #define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key) 540 541 #endif /* __ASSEMBLY__ */ 542 543 #endif /* _LINUX_JUMP_LABEL_H */ 544