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 79extern 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 85struct 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 117struct jump_entry { 118 s32 code; 119 s32 target; 120 long key; // key may be far away from the core kernel under KASLR 121}; 122 123static inline unsigned long jump_entry_code(const struct jump_entry *entry) 124{ 125 return (unsigned long)&entry->code + entry->code; 126} 127 128static inline unsigned long jump_entry_target(const struct jump_entry *entry) 129{ 130 return (unsigned long)&entry->target + entry->target; 131} 132 133static 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 142static inline unsigned long jump_entry_code(const struct jump_entry *entry) 143{ 144 return entry->code; 145} 146 147static inline unsigned long jump_entry_target(const struct jump_entry *entry) 148{ 149 return entry->target; 150} 151 152static 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 159static inline bool jump_entry_is_branch(const struct jump_entry *entry) 160{ 161 return (unsigned long)entry->key & 1UL; 162} 163 164static inline bool jump_entry_is_init(const struct jump_entry *entry) 165{ 166 return (unsigned long)entry->key & 2UL; 167} 168 169static 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 177static 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 191enum jump_label_type { 192 JUMP_LABEL_NOP = 0, 193 JUMP_LABEL_JMP, 194}; 195 196struct 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 205static __always_inline bool static_key_false(struct static_key *key) 206{ 207 return arch_static_branch(key, false); 208} 209 210static __always_inline bool static_key_true(struct static_key *key) 211{ 212 return !arch_static_branch(key, true); 213} 214 215extern struct jump_entry __start___jump_table[]; 216extern struct jump_entry __stop___jump_table[]; 217 218extern void jump_label_init(void); 219extern void jump_label_lock(void); 220extern void jump_label_unlock(void); 221extern void arch_jump_label_transform(struct jump_entry *entry, 222 enum jump_label_type type); 223extern bool arch_jump_label_transform_queue(struct jump_entry *entry, 224 enum jump_label_type type); 225extern void arch_jump_label_transform_apply(void); 226extern int jump_label_text_reserved(void *start, void *end); 227extern bool static_key_slow_inc(struct static_key *key); 228extern bool static_key_fast_inc_not_disabled(struct static_key *key); 229extern void static_key_slow_dec(struct static_key *key); 230extern bool static_key_slow_inc_cpuslocked(struct static_key *key); 231extern void static_key_slow_dec_cpuslocked(struct static_key *key); 232extern int static_key_count(struct static_key *key); 233extern void static_key_enable(struct static_key *key); 234extern void static_key_disable(struct static_key *key); 235extern void static_key_enable_cpuslocked(struct static_key *key); 236extern void static_key_disable_cpuslocked(struct static_key *key); 237extern enum jump_label_type jump_label_init_type(struct jump_entry *entry); 238 239/* 240 * We should be using ATOMIC_INIT() for initializing .enabled, but 241 * the inclusion of atomic.h is problematic for inclusion of jump_label.h 242 * in 'low-level' headers. Thus, we are initializing .enabled with a 243 * raw value, but have added a BUILD_BUG_ON() to catch any issues in 244 * jump_label_init() see: kernel/jump_label.c. 245 */ 246#define STATIC_KEY_INIT_TRUE \ 247 { .enabled = { 1 }, \ 248 { .type = JUMP_TYPE_TRUE } } 249#define STATIC_KEY_INIT_FALSE \ 250 { .enabled = { 0 }, \ 251 { .type = JUMP_TYPE_FALSE } } 252 253#else /* !CONFIG_JUMP_LABEL */ 254 255#include <linux/atomic.h> 256#include <linux/bug.h> 257 258static __always_inline int static_key_count(struct static_key *key) 259{ 260 return raw_atomic_read(&key->enabled); 261} 262 263static __always_inline void jump_label_init(void) 264{ 265 static_key_initialized = true; 266} 267 268static __always_inline bool static_key_false(struct static_key *key) 269{ 270 if (unlikely_notrace(static_key_count(key) > 0)) 271 return true; 272 return false; 273} 274 275static __always_inline bool static_key_true(struct static_key *key) 276{ 277 if (likely_notrace(static_key_count(key) > 0)) 278 return true; 279 return false; 280} 281 282static inline bool static_key_fast_inc_not_disabled(struct static_key *key) 283{ 284 int v; 285 286 STATIC_KEY_CHECK_USE(key); 287 /* 288 * Prevent key->enabled getting negative to follow the same semantics 289 * as for CONFIG_JUMP_LABEL=y, see kernel/jump_label.c comment. 290 */ 291 v = atomic_read(&key->enabled); 292 do { 293 if (v < 0 || (v + 1) < 0) 294 return false; 295 } while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1))); 296 return true; 297} 298#define static_key_slow_inc(key) static_key_fast_inc_not_disabled(key) 299 300static inline void static_key_slow_dec(struct static_key *key) 301{ 302 STATIC_KEY_CHECK_USE(key); 303 atomic_dec(&key->enabled); 304} 305 306#define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key) 307#define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key) 308 309static inline int jump_label_text_reserved(void *start, void *end) 310{ 311 return 0; 312} 313 314static inline void jump_label_lock(void) {} 315static inline void jump_label_unlock(void) {} 316 317static inline void static_key_enable(struct static_key *key) 318{ 319 STATIC_KEY_CHECK_USE(key); 320 321 if (atomic_read(&key->enabled) != 0) { 322 WARN_ON_ONCE(atomic_read(&key->enabled) != 1); 323 return; 324 } 325 atomic_set(&key->enabled, 1); 326} 327 328static inline void static_key_disable(struct static_key *key) 329{ 330 STATIC_KEY_CHECK_USE(key); 331 332 if (atomic_read(&key->enabled) != 1) { 333 WARN_ON_ONCE(atomic_read(&key->enabled) != 0); 334 return; 335 } 336 atomic_set(&key->enabled, 0); 337} 338 339#define static_key_enable_cpuslocked(k) static_key_enable((k)) 340#define static_key_disable_cpuslocked(k) static_key_disable((k)) 341 342#define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) } 343#define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) } 344 345#endif /* CONFIG_JUMP_LABEL */ 346 347#define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE 348#define jump_label_enabled static_key_enabled 349 350/* -------------------------------------------------------------------------- */ 351 352/* 353 * Two type wrappers around static_key, such that we can use compile time 354 * type differentiation to emit the right code. 355 * 356 * All the below code is macros in order to play type games. 357 */ 358 359struct static_key_true { 360 struct static_key key; 361}; 362 363struct static_key_false { 364 struct static_key key; 365}; 366 367#define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, } 368#define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, } 369 370#define DEFINE_STATIC_KEY_TRUE(name) \ 371 struct static_key_true name = STATIC_KEY_TRUE_INIT 372 373#define DEFINE_STATIC_KEY_TRUE_RO(name) \ 374 struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT 375 376#define DECLARE_STATIC_KEY_TRUE(name) \ 377 extern struct static_key_true name 378 379#define DEFINE_STATIC_KEY_FALSE(name) \ 380 struct static_key_false name = STATIC_KEY_FALSE_INIT 381 382#define DEFINE_STATIC_KEY_FALSE_RO(name) \ 383 struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT 384 385#define DECLARE_STATIC_KEY_FALSE(name) \ 386 extern struct static_key_false name 387 388#define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count) \ 389 struct static_key_true name[count] = { \ 390 [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT, \ 391 } 392 393#define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count) \ 394 struct static_key_false name[count] = { \ 395 [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT, \ 396 } 397 398#define _DEFINE_STATIC_KEY_1(name) DEFINE_STATIC_KEY_TRUE(name) 399#define _DEFINE_STATIC_KEY_0(name) DEFINE_STATIC_KEY_FALSE(name) 400#define DEFINE_STATIC_KEY_MAYBE(cfg, name) \ 401 __PASTE(_DEFINE_STATIC_KEY_, IS_ENABLED(cfg))(name) 402 403#define _DEFINE_STATIC_KEY_RO_1(name) DEFINE_STATIC_KEY_TRUE_RO(name) 404#define _DEFINE_STATIC_KEY_RO_0(name) DEFINE_STATIC_KEY_FALSE_RO(name) 405#define DEFINE_STATIC_KEY_MAYBE_RO(cfg, name) \ 406 __PASTE(_DEFINE_STATIC_KEY_RO_, IS_ENABLED(cfg))(name) 407 408#define _DECLARE_STATIC_KEY_1(name) DECLARE_STATIC_KEY_TRUE(name) 409#define _DECLARE_STATIC_KEY_0(name) DECLARE_STATIC_KEY_FALSE(name) 410#define DECLARE_STATIC_KEY_MAYBE(cfg, name) \ 411 __PASTE(_DECLARE_STATIC_KEY_, IS_ENABLED(cfg))(name) 412 413extern bool ____wrong_branch_error(void); 414 415#define static_key_enabled(x) \ 416({ \ 417 if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \ 418 !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\ 419 !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 420 ____wrong_branch_error(); \ 421 static_key_count((struct static_key *)x) > 0; \ 422}) 423 424#ifdef CONFIG_JUMP_LABEL 425 426/* 427 * Combine the right initial value (type) with the right branch order 428 * to generate the desired result. 429 * 430 * 431 * type\branch| likely (1) | unlikely (0) 432 * -----------+-----------------------+------------------ 433 * | | 434 * true (1) | ... | ... 435 * | NOP | JMP L 436 * | <br-stmts> | 1: ... 437 * | L: ... | 438 * | | 439 * | | L: <br-stmts> 440 * | | jmp 1b 441 * | | 442 * -----------+-----------------------+------------------ 443 * | | 444 * false (0) | ... | ... 445 * | JMP L | NOP 446 * | <br-stmts> | 1: ... 447 * | L: ... | 448 * | | 449 * | | L: <br-stmts> 450 * | | jmp 1b 451 * | | 452 * -----------+-----------------------+------------------ 453 * 454 * The initial value is encoded in the LSB of static_key::entries, 455 * type: 0 = false, 1 = true. 456 * 457 * The branch type is encoded in the LSB of jump_entry::key, 458 * branch: 0 = unlikely, 1 = likely. 459 * 460 * This gives the following logic table: 461 * 462 * enabled type branch instuction 463 * -----------------------------+----------- 464 * 0 0 0 | NOP 465 * 0 0 1 | JMP 466 * 0 1 0 | NOP 467 * 0 1 1 | JMP 468 * 469 * 1 0 0 | JMP 470 * 1 0 1 | NOP 471 * 1 1 0 | JMP 472 * 1 1 1 | NOP 473 * 474 * Which gives the following functions: 475 * 476 * dynamic: instruction = enabled ^ branch 477 * static: instruction = type ^ branch 478 * 479 * See jump_label_type() / jump_label_init_type(). 480 */ 481 482#define static_branch_likely(x) \ 483({ \ 484 bool branch; \ 485 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ 486 branch = !arch_static_branch(&(x)->key, true); \ 487 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 488 branch = !arch_static_branch_jump(&(x)->key, true); \ 489 else \ 490 branch = ____wrong_branch_error(); \ 491 likely_notrace(branch); \ 492}) 493 494#define static_branch_unlikely(x) \ 495({ \ 496 bool branch; \ 497 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ 498 branch = arch_static_branch_jump(&(x)->key, false); \ 499 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 500 branch = arch_static_branch(&(x)->key, false); \ 501 else \ 502 branch = ____wrong_branch_error(); \ 503 unlikely_notrace(branch); \ 504}) 505 506#else /* !CONFIG_JUMP_LABEL */ 507 508#define static_branch_likely(x) likely_notrace(static_key_enabled(&(x)->key)) 509#define static_branch_unlikely(x) unlikely_notrace(static_key_enabled(&(x)->key)) 510 511#endif /* CONFIG_JUMP_LABEL */ 512 513#define static_branch_maybe(config, x) \ 514 (IS_ENABLED(config) ? static_branch_likely(x) \ 515 : static_branch_unlikely(x)) 516 517/* 518 * Advanced usage; refcount, branch is enabled when: count != 0 519 */ 520 521#define static_branch_inc(x) static_key_slow_inc(&(x)->key) 522#define static_branch_dec(x) static_key_slow_dec(&(x)->key) 523#define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key) 524#define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(x)->key) 525 526/* 527 * Normal usage; boolean enable/disable. 528 */ 529 530#define static_branch_enable(x) static_key_enable(&(x)->key) 531#define static_branch_disable(x) static_key_disable(&(x)->key) 532#define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key) 533#define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key) 534 535#endif /* __ASSEMBLY__ */ 536 537#endif /* _LINUX_JUMP_LABEL_H */ 538