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 struct static_key { 86 atomic_t enabled; 87 #ifdef CONFIG_JUMP_LABEL 88 /* 89 * Note: 90 * To make anonymous unions work with old compilers, the static 91 * initialization of them requires brackets. This creates a dependency 92 * on the order of the struct with the initializers. If any fields 93 * are added, STATIC_KEY_INIT_TRUE and STATIC_KEY_INIT_FALSE may need 94 * to be modified. 95 * 96 * bit 0 => 1 if key is initially true 97 * 0 if initially false 98 * bit 1 => 1 if points to struct static_key_mod 99 * 0 if points to struct jump_entry 100 */ 101 union { 102 unsigned long type; 103 struct jump_entry *entries; 104 struct static_key_mod *next; 105 }; 106 #endif /* CONFIG_JUMP_LABEL */ 107 }; 108 109 #endif /* __ASSEMBLY__ */ 110 111 #ifdef CONFIG_JUMP_LABEL 112 #include <asm/jump_label.h> 113 114 #ifndef __ASSEMBLY__ 115 #ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE 116 117 struct jump_entry { 118 s32 code; 119 s32 target; 120 long key; // key may be far away from the core kernel under KASLR 121 }; 122 jump_entry_code(const struct jump_entry * entry)123 static inline unsigned long jump_entry_code(const struct jump_entry *entry) 124 { 125 return (unsigned long)&entry->code + entry->code; 126 } 127 jump_entry_target(const struct jump_entry * entry)128 static inline unsigned long jump_entry_target(const struct jump_entry *entry) 129 { 130 return (unsigned long)&entry->target + entry->target; 131 } 132 jump_entry_key(const struct jump_entry * entry)133 static inline struct static_key *jump_entry_key(const struct jump_entry *entry) 134 { 135 long offset = entry->key & ~3L; 136 137 return (struct static_key *)((unsigned long)&entry->key + offset); 138 } 139 140 #else 141 jump_entry_code(const struct jump_entry * entry)142 static inline unsigned long jump_entry_code(const struct jump_entry *entry) 143 { 144 return entry->code; 145 } 146 jump_entry_target(const struct jump_entry * entry)147 static inline unsigned long jump_entry_target(const struct jump_entry *entry) 148 { 149 return entry->target; 150 } 151 jump_entry_key(const struct jump_entry * entry)152 static inline struct static_key *jump_entry_key(const struct jump_entry *entry) 153 { 154 return (struct static_key *)((unsigned long)entry->key & ~3UL); 155 } 156 157 #endif 158 jump_entry_is_branch(const struct jump_entry * entry)159 static inline bool jump_entry_is_branch(const struct jump_entry *entry) 160 { 161 return (unsigned long)entry->key & 1UL; 162 } 163 jump_entry_is_init(const struct jump_entry * entry)164 static inline bool jump_entry_is_init(const struct jump_entry *entry) 165 { 166 return (unsigned long)entry->key & 2UL; 167 } 168 jump_entry_set_init(struct jump_entry * entry,bool set)169 static inline void jump_entry_set_init(struct jump_entry *entry, bool set) 170 { 171 if (set) 172 entry->key |= 2; 173 else 174 entry->key &= ~2; 175 } 176 jump_entry_size(struct jump_entry * entry)177 static inline int jump_entry_size(struct jump_entry *entry) 178 { 179 #ifdef JUMP_LABEL_NOP_SIZE 180 return JUMP_LABEL_NOP_SIZE; 181 #else 182 return arch_jump_entry_size(entry); 183 #endif 184 } 185 186 #endif 187 #endif 188 189 #ifndef __ASSEMBLY__ 190 191 enum jump_label_type { 192 JUMP_LABEL_NOP = 0, 193 JUMP_LABEL_JMP, 194 }; 195 196 struct module; 197 198 #ifdef CONFIG_JUMP_LABEL 199 200 #define JUMP_TYPE_FALSE 0UL 201 #define JUMP_TYPE_TRUE 1UL 202 #define JUMP_TYPE_LINKED 2UL 203 #define JUMP_TYPE_MASK 3UL 204 static_key_false(struct static_key * key)205 static __always_inline bool static_key_false(struct static_key *key) 206 { 207 return arch_static_branch(key, false); 208 } 209 static_key_true(struct static_key * key)210 static __always_inline bool static_key_true(struct static_key *key) 211 { 212 return !arch_static_branch(key, true); 213 } 214 215 extern struct jump_entry __start___jump_table[]; 216 extern struct jump_entry __stop___jump_table[]; 217 218 extern void jump_label_init(void); 219 extern void jump_label_init_ro(void); 220 extern void jump_label_lock(void); 221 extern void jump_label_unlock(void); 222 extern void arch_jump_label_transform(struct jump_entry *entry, 223 enum jump_label_type type); 224 extern bool arch_jump_label_transform_queue(struct jump_entry *entry, 225 enum jump_label_type type); 226 extern void arch_jump_label_transform_apply(void); 227 extern int jump_label_text_reserved(void *start, void *end); 228 extern bool static_key_slow_inc(struct static_key *key); 229 extern bool static_key_fast_inc_not_disabled(struct static_key *key); 230 extern void static_key_slow_dec(struct static_key *key); 231 extern bool static_key_slow_inc_cpuslocked(struct static_key *key); 232 extern void static_key_slow_dec_cpuslocked(struct static_key *key); 233 extern int static_key_count(struct static_key *key); 234 extern void static_key_enable(struct static_key *key); 235 extern void static_key_disable(struct static_key *key); 236 extern void static_key_enable_cpuslocked(struct static_key *key); 237 extern void static_key_disable_cpuslocked(struct static_key *key); 238 extern enum jump_label_type jump_label_init_type(struct jump_entry *entry); 239 240 /* 241 * We should be using ATOMIC_INIT() for initializing .enabled, but 242 * the inclusion of atomic.h is problematic for inclusion of jump_label.h 243 * in 'low-level' headers. Thus, we are initializing .enabled with a 244 * raw value, but have added a BUILD_BUG_ON() to catch any issues in 245 * jump_label_init() see: kernel/jump_label.c. 246 */ 247 #define STATIC_KEY_INIT_TRUE \ 248 { .enabled = { 1 }, \ 249 { .type = JUMP_TYPE_TRUE } } 250 #define STATIC_KEY_INIT_FALSE \ 251 { .enabled = { 0 }, \ 252 { .type = JUMP_TYPE_FALSE } } 253 254 #else /* !CONFIG_JUMP_LABEL */ 255 256 #include <linux/atomic.h> 257 #include <linux/bug.h> 258 static_key_count(struct static_key * key)259 static __always_inline int static_key_count(struct static_key *key) 260 { 261 return raw_atomic_read(&key->enabled); 262 } 263 jump_label_init(void)264 static __always_inline void jump_label_init(void) 265 { 266 static_key_initialized = true; 267 } 268 jump_label_init_ro(void)269 static __always_inline void jump_label_init_ro(void) { } 270 static_key_false(struct static_key * key)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 static_key_true(struct static_key * key)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 static_key_fast_inc_not_disabled(struct static_key * key)285 static inline bool static_key_fast_inc_not_disabled(struct static_key *key) 286 { 287 int v; 288 289 STATIC_KEY_CHECK_USE(key); 290 /* 291 * Prevent key->enabled getting negative to follow the same semantics 292 * as for CONFIG_JUMP_LABEL=y, see kernel/jump_label.c comment. 293 */ 294 v = atomic_read(&key->enabled); 295 do { 296 if (v < 0 || (v + 1) < 0) 297 return false; 298 } while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1))); 299 return true; 300 } 301 #define static_key_slow_inc(key) static_key_fast_inc_not_disabled(key) 302 static_key_slow_dec(struct static_key * key)303 static inline void static_key_slow_dec(struct static_key *key) 304 { 305 STATIC_KEY_CHECK_USE(key); 306 atomic_dec(&key->enabled); 307 } 308 309 #define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key) 310 #define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key) 311 jump_label_text_reserved(void * start,void * end)312 static inline int jump_label_text_reserved(void *start, void *end) 313 { 314 return 0; 315 } 316 jump_label_lock(void)317 static inline void jump_label_lock(void) {} jump_label_unlock(void)318 static inline void jump_label_unlock(void) {} 319 static_key_enable(struct static_key * key)320 static inline void static_key_enable(struct static_key *key) 321 { 322 STATIC_KEY_CHECK_USE(key); 323 324 if (atomic_read(&key->enabled) != 0) { 325 WARN_ON_ONCE(atomic_read(&key->enabled) != 1); 326 return; 327 } 328 atomic_set(&key->enabled, 1); 329 } 330 static_key_disable(struct static_key * key)331 static inline void static_key_disable(struct static_key *key) 332 { 333 STATIC_KEY_CHECK_USE(key); 334 335 if (atomic_read(&key->enabled) != 1) { 336 WARN_ON_ONCE(atomic_read(&key->enabled) != 0); 337 return; 338 } 339 atomic_set(&key->enabled, 0); 340 } 341 342 #define static_key_enable_cpuslocked(k) static_key_enable((k)) 343 #define static_key_disable_cpuslocked(k) static_key_disable((k)) 344 345 #define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) } 346 #define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) } 347 348 #endif /* CONFIG_JUMP_LABEL */ 349 350 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE 351 #define jump_label_enabled static_key_enabled 352 353 /* -------------------------------------------------------------------------- */ 354 355 /* 356 * Two type wrappers around static_key, such that we can use compile time 357 * type differentiation to emit the right code. 358 * 359 * All the below code is macros in order to play type games. 360 */ 361 362 struct static_key_true { 363 struct static_key key; 364 }; 365 366 struct static_key_false { 367 struct static_key key; 368 }; 369 370 #define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, } 371 #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, } 372 373 #define DEFINE_STATIC_KEY_TRUE(name) \ 374 struct static_key_true name = STATIC_KEY_TRUE_INIT 375 376 #define DEFINE_STATIC_KEY_TRUE_RO(name) \ 377 struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT 378 379 #define DECLARE_STATIC_KEY_TRUE(name) \ 380 extern struct static_key_true name 381 382 #define DEFINE_STATIC_KEY_FALSE(name) \ 383 struct static_key_false name = STATIC_KEY_FALSE_INIT 384 385 #define DEFINE_STATIC_KEY_FALSE_RO(name) \ 386 struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT 387 388 #define DECLARE_STATIC_KEY_FALSE(name) \ 389 extern struct static_key_false name 390 391 #define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count) \ 392 struct static_key_true name[count] = { \ 393 [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT, \ 394 } 395 396 #define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count) \ 397 struct static_key_false name[count] = { \ 398 [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT, \ 399 } 400 401 #define _DEFINE_STATIC_KEY_1(name) DEFINE_STATIC_KEY_TRUE(name) 402 #define _DEFINE_STATIC_KEY_0(name) DEFINE_STATIC_KEY_FALSE(name) 403 #define DEFINE_STATIC_KEY_MAYBE(cfg, name) \ 404 __PASTE(_DEFINE_STATIC_KEY_, IS_ENABLED(cfg))(name) 405 406 #define _DEFINE_STATIC_KEY_RO_1(name) DEFINE_STATIC_KEY_TRUE_RO(name) 407 #define _DEFINE_STATIC_KEY_RO_0(name) DEFINE_STATIC_KEY_FALSE_RO(name) 408 #define DEFINE_STATIC_KEY_MAYBE_RO(cfg, name) \ 409 __PASTE(_DEFINE_STATIC_KEY_RO_, IS_ENABLED(cfg))(name) 410 411 #define _DECLARE_STATIC_KEY_1(name) DECLARE_STATIC_KEY_TRUE(name) 412 #define _DECLARE_STATIC_KEY_0(name) DECLARE_STATIC_KEY_FALSE(name) 413 #define DECLARE_STATIC_KEY_MAYBE(cfg, name) \ 414 __PASTE(_DECLARE_STATIC_KEY_, IS_ENABLED(cfg))(name) 415 416 extern bool ____wrong_branch_error(void); 417 418 #define static_key_enabled(x) \ 419 ({ \ 420 if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \ 421 !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\ 422 !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 423 ____wrong_branch_error(); \ 424 static_key_count((struct static_key *)x) > 0; \ 425 }) 426 427 #ifdef CONFIG_JUMP_LABEL 428 429 /* 430 * Combine the right initial value (type) with the right branch order 431 * to generate the desired result. 432 * 433 * 434 * type\branch| likely (1) | unlikely (0) 435 * -----------+-----------------------+------------------ 436 * | | 437 * true (1) | ... | ... 438 * | NOP | JMP L 439 * | <br-stmts> | 1: ... 440 * | L: ... | 441 * | | 442 * | | L: <br-stmts> 443 * | | jmp 1b 444 * | | 445 * -----------+-----------------------+------------------ 446 * | | 447 * false (0) | ... | ... 448 * | JMP L | NOP 449 * | <br-stmts> | 1: ... 450 * | L: ... | 451 * | | 452 * | | L: <br-stmts> 453 * | | jmp 1b 454 * | | 455 * -----------+-----------------------+------------------ 456 * 457 * The initial value is encoded in the LSB of static_key::entries, 458 * type: 0 = false, 1 = true. 459 * 460 * The branch type is encoded in the LSB of jump_entry::key, 461 * branch: 0 = unlikely, 1 = likely. 462 * 463 * This gives the following logic table: 464 * 465 * enabled type branch instuction 466 * -----------------------------+----------- 467 * 0 0 0 | NOP 468 * 0 0 1 | JMP 469 * 0 1 0 | NOP 470 * 0 1 1 | JMP 471 * 472 * 1 0 0 | JMP 473 * 1 0 1 | NOP 474 * 1 1 0 | JMP 475 * 1 1 1 | NOP 476 * 477 * Which gives the following functions: 478 * 479 * dynamic: instruction = enabled ^ branch 480 * static: instruction = type ^ branch 481 * 482 * See jump_label_type() / jump_label_init_type(). 483 */ 484 485 #define static_branch_likely(x) \ 486 ({ \ 487 bool branch; \ 488 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ 489 branch = !arch_static_branch(&(x)->key, true); \ 490 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 491 branch = !arch_static_branch_jump(&(x)->key, true); \ 492 else \ 493 branch = ____wrong_branch_error(); \ 494 likely_notrace(branch); \ 495 }) 496 497 #define static_branch_unlikely(x) \ 498 ({ \ 499 bool branch; \ 500 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ 501 branch = arch_static_branch_jump(&(x)->key, false); \ 502 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 503 branch = arch_static_branch(&(x)->key, false); \ 504 else \ 505 branch = ____wrong_branch_error(); \ 506 unlikely_notrace(branch); \ 507 }) 508 509 #else /* !CONFIG_JUMP_LABEL */ 510 511 #define static_branch_likely(x) likely_notrace(static_key_enabled(&(x)->key)) 512 #define static_branch_unlikely(x) unlikely_notrace(static_key_enabled(&(x)->key)) 513 514 #endif /* CONFIG_JUMP_LABEL */ 515 516 #define static_branch_maybe(config, x) \ 517 (IS_ENABLED(config) ? static_branch_likely(x) \ 518 : static_branch_unlikely(x)) 519 520 /* 521 * Advanced usage; refcount, branch is enabled when: count != 0 522 */ 523 524 #define static_branch_inc(x) static_key_slow_inc(&(x)->key) 525 #define static_branch_dec(x) static_key_slow_dec(&(x)->key) 526 #define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key) 527 #define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(x)->key) 528 529 /* 530 * Normal usage; boolean enable/disable. 531 */ 532 533 #define static_branch_enable(x) static_key_enable(&(x)->key) 534 #define static_branch_disable(x) static_key_disable(&(x)->key) 535 #define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key) 536 #define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key) 537 538 #endif /* __ASSEMBLY__ */ 539 540 #endif /* _LINUX_JUMP_LABEL_H */ 541