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/static-keys.txt 72 */ 73 74 #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL) 75 # define HAVE_JUMP_LABEL 76 #endif 77 78 #ifndef __ASSEMBLY__ 79 80 #include <linux/types.h> 81 #include <linux/compiler.h> 82 83 extern bool static_key_initialized; 84 85 #define STATIC_KEY_CHECK_USE(key) WARN(!static_key_initialized, \ 86 "%s(): static key '%pS' used before call to jump_label_init()", \ 87 __func__, (key)) 88 89 #ifdef HAVE_JUMP_LABEL 90 91 struct static_key { 92 atomic_t enabled; 93 /* 94 * Note: 95 * To make anonymous unions work with old compilers, the static 96 * initialization of them requires brackets. This creates a dependency 97 * on the order of the struct with the initializers. If any fields 98 * are added, STATIC_KEY_INIT_TRUE and STATIC_KEY_INIT_FALSE may need 99 * to be modified. 100 * 101 * bit 0 => 1 if key is initially true 102 * 0 if initially false 103 * bit 1 => 1 if points to struct static_key_mod 104 * 0 if points to struct jump_entry 105 */ 106 union { 107 unsigned long type; 108 struct jump_entry *entries; 109 struct static_key_mod *next; 110 }; 111 }; 112 113 #else 114 struct static_key { 115 atomic_t enabled; 116 }; 117 #endif /* HAVE_JUMP_LABEL */ 118 #endif /* __ASSEMBLY__ */ 119 120 #ifdef HAVE_JUMP_LABEL 121 #include <asm/jump_label.h> 122 #endif 123 124 #ifndef __ASSEMBLY__ 125 126 enum jump_label_type { 127 JUMP_LABEL_NOP = 0, 128 JUMP_LABEL_JMP, 129 }; 130 131 struct module; 132 133 #ifdef HAVE_JUMP_LABEL 134 135 #define JUMP_TYPE_FALSE 0UL 136 #define JUMP_TYPE_TRUE 1UL 137 #define JUMP_TYPE_LINKED 2UL 138 #define JUMP_TYPE_MASK 3UL 139 140 static __always_inline bool static_key_false(struct static_key *key) 141 { 142 return arch_static_branch(key, false); 143 } 144 145 static __always_inline bool static_key_true(struct static_key *key) 146 { 147 return !arch_static_branch(key, true); 148 } 149 150 extern struct jump_entry __start___jump_table[]; 151 extern struct jump_entry __stop___jump_table[]; 152 153 extern void jump_label_init(void); 154 extern void jump_label_lock(void); 155 extern void jump_label_unlock(void); 156 extern void arch_jump_label_transform(struct jump_entry *entry, 157 enum jump_label_type type); 158 extern void arch_jump_label_transform_static(struct jump_entry *entry, 159 enum jump_label_type type); 160 extern int jump_label_text_reserved(void *start, void *end); 161 extern void static_key_slow_inc(struct static_key *key); 162 extern void static_key_slow_dec(struct static_key *key); 163 extern void static_key_slow_inc_cpuslocked(struct static_key *key); 164 extern void static_key_slow_dec_cpuslocked(struct static_key *key); 165 extern void jump_label_apply_nops(struct module *mod); 166 extern int static_key_count(struct static_key *key); 167 extern void static_key_enable(struct static_key *key); 168 extern void static_key_disable(struct static_key *key); 169 extern void static_key_enable_cpuslocked(struct static_key *key); 170 extern void static_key_disable_cpuslocked(struct static_key *key); 171 172 /* 173 * We should be using ATOMIC_INIT() for initializing .enabled, but 174 * the inclusion of atomic.h is problematic for inclusion of jump_label.h 175 * in 'low-level' headers. Thus, we are initializing .enabled with a 176 * raw value, but have added a BUILD_BUG_ON() to catch any issues in 177 * jump_label_init() see: kernel/jump_label.c. 178 */ 179 #define STATIC_KEY_INIT_TRUE \ 180 { .enabled = { 1 }, \ 181 { .entries = (void *)JUMP_TYPE_TRUE } } 182 #define STATIC_KEY_INIT_FALSE \ 183 { .enabled = { 0 }, \ 184 { .entries = (void *)JUMP_TYPE_FALSE } } 185 186 #else /* !HAVE_JUMP_LABEL */ 187 188 #include <linux/atomic.h> 189 #include <linux/bug.h> 190 191 static inline int static_key_count(struct static_key *key) 192 { 193 return atomic_read(&key->enabled); 194 } 195 196 static __always_inline void jump_label_init(void) 197 { 198 static_key_initialized = true; 199 } 200 201 static __always_inline bool static_key_false(struct static_key *key) 202 { 203 if (unlikely(static_key_count(key) > 0)) 204 return true; 205 return false; 206 } 207 208 static __always_inline bool static_key_true(struct static_key *key) 209 { 210 if (likely(static_key_count(key) > 0)) 211 return true; 212 return false; 213 } 214 215 static inline void static_key_slow_inc(struct static_key *key) 216 { 217 STATIC_KEY_CHECK_USE(key); 218 atomic_inc(&key->enabled); 219 } 220 221 static inline void static_key_slow_dec(struct static_key *key) 222 { 223 STATIC_KEY_CHECK_USE(key); 224 atomic_dec(&key->enabled); 225 } 226 227 #define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key) 228 #define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key) 229 230 static inline int jump_label_text_reserved(void *start, void *end) 231 { 232 return 0; 233 } 234 235 static inline void jump_label_lock(void) {} 236 static inline void jump_label_unlock(void) {} 237 238 static inline int jump_label_apply_nops(struct module *mod) 239 { 240 return 0; 241 } 242 243 static inline void static_key_enable(struct static_key *key) 244 { 245 STATIC_KEY_CHECK_USE(key); 246 247 if (atomic_read(&key->enabled) != 0) { 248 WARN_ON_ONCE(atomic_read(&key->enabled) != 1); 249 return; 250 } 251 atomic_set(&key->enabled, 1); 252 } 253 254 static inline void static_key_disable(struct static_key *key) 255 { 256 STATIC_KEY_CHECK_USE(key); 257 258 if (atomic_read(&key->enabled) != 1) { 259 WARN_ON_ONCE(atomic_read(&key->enabled) != 0); 260 return; 261 } 262 atomic_set(&key->enabled, 0); 263 } 264 265 #define static_key_enable_cpuslocked(k) static_key_enable((k)) 266 #define static_key_disable_cpuslocked(k) static_key_disable((k)) 267 268 #define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) } 269 #define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) } 270 271 #endif /* HAVE_JUMP_LABEL */ 272 273 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE 274 #define jump_label_enabled static_key_enabled 275 276 /* -------------------------------------------------------------------------- */ 277 278 /* 279 * Two type wrappers around static_key, such that we can use compile time 280 * type differentiation to emit the right code. 281 * 282 * All the below code is macros in order to play type games. 283 */ 284 285 struct static_key_true { 286 struct static_key key; 287 }; 288 289 struct static_key_false { 290 struct static_key key; 291 }; 292 293 #define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, } 294 #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, } 295 296 #define DEFINE_STATIC_KEY_TRUE(name) \ 297 struct static_key_true name = STATIC_KEY_TRUE_INIT 298 299 #define DECLARE_STATIC_KEY_TRUE(name) \ 300 extern struct static_key_true name 301 302 #define DEFINE_STATIC_KEY_FALSE(name) \ 303 struct static_key_false name = STATIC_KEY_FALSE_INIT 304 305 #define DECLARE_STATIC_KEY_FALSE(name) \ 306 extern struct static_key_false name 307 308 #define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count) \ 309 struct static_key_true name[count] = { \ 310 [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT, \ 311 } 312 313 #define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count) \ 314 struct static_key_false name[count] = { \ 315 [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT, \ 316 } 317 318 extern bool ____wrong_branch_error(void); 319 320 #define static_key_enabled(x) \ 321 ({ \ 322 if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \ 323 !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\ 324 !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 325 ____wrong_branch_error(); \ 326 static_key_count((struct static_key *)x) > 0; \ 327 }) 328 329 #ifdef HAVE_JUMP_LABEL 330 331 /* 332 * Combine the right initial value (type) with the right branch order 333 * to generate the desired result. 334 * 335 * 336 * type\branch| likely (1) | unlikely (0) 337 * -----------+-----------------------+------------------ 338 * | | 339 * true (1) | ... | ... 340 * | NOP | JMP L 341 * | <br-stmts> | 1: ... 342 * | L: ... | 343 * | | 344 * | | L: <br-stmts> 345 * | | jmp 1b 346 * | | 347 * -----------+-----------------------+------------------ 348 * | | 349 * false (0) | ... | ... 350 * | JMP L | NOP 351 * | <br-stmts> | 1: ... 352 * | L: ... | 353 * | | 354 * | | L: <br-stmts> 355 * | | jmp 1b 356 * | | 357 * -----------+-----------------------+------------------ 358 * 359 * The initial value is encoded in the LSB of static_key::entries, 360 * type: 0 = false, 1 = true. 361 * 362 * The branch type is encoded in the LSB of jump_entry::key, 363 * branch: 0 = unlikely, 1 = likely. 364 * 365 * This gives the following logic table: 366 * 367 * enabled type branch instuction 368 * -----------------------------+----------- 369 * 0 0 0 | NOP 370 * 0 0 1 | JMP 371 * 0 1 0 | NOP 372 * 0 1 1 | JMP 373 * 374 * 1 0 0 | JMP 375 * 1 0 1 | NOP 376 * 1 1 0 | JMP 377 * 1 1 1 | NOP 378 * 379 * Which gives the following functions: 380 * 381 * dynamic: instruction = enabled ^ branch 382 * static: instruction = type ^ branch 383 * 384 * See jump_label_type() / jump_label_init_type(). 385 */ 386 387 #define static_branch_likely(x) \ 388 ({ \ 389 bool branch; \ 390 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ 391 branch = !arch_static_branch(&(x)->key, true); \ 392 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 393 branch = !arch_static_branch_jump(&(x)->key, true); \ 394 else \ 395 branch = ____wrong_branch_error(); \ 396 likely(branch); \ 397 }) 398 399 #define static_branch_unlikely(x) \ 400 ({ \ 401 bool branch; \ 402 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ 403 branch = arch_static_branch_jump(&(x)->key, false); \ 404 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 405 branch = arch_static_branch(&(x)->key, false); \ 406 else \ 407 branch = ____wrong_branch_error(); \ 408 unlikely(branch); \ 409 }) 410 411 #else /* !HAVE_JUMP_LABEL */ 412 413 #define static_branch_likely(x) likely(static_key_enabled(&(x)->key)) 414 #define static_branch_unlikely(x) unlikely(static_key_enabled(&(x)->key)) 415 416 #endif /* HAVE_JUMP_LABEL */ 417 418 /* 419 * Advanced usage; refcount, branch is enabled when: count != 0 420 */ 421 422 #define static_branch_inc(x) static_key_slow_inc(&(x)->key) 423 #define static_branch_dec(x) static_key_slow_dec(&(x)->key) 424 #define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key) 425 #define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(x)->key) 426 427 /* 428 * Normal usage; boolean enable/disable. 429 */ 430 431 #define static_branch_enable(x) static_key_enable(&(x)->key) 432 #define static_branch_disable(x) static_key_disable(&(x)->key) 433 #define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key) 434 #define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key) 435 436 #endif /* __ASSEMBLY__ */ 437 438 #endif /* _LINUX_JUMP_LABEL_H */ 439