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 jump_label_apply_nops(struct module *mod); 164 extern int static_key_count(struct static_key *key); 165 extern void static_key_enable(struct static_key *key); 166 extern void static_key_disable(struct static_key *key); 167 extern void static_key_enable_cpuslocked(struct static_key *key); 168 extern void static_key_disable_cpuslocked(struct static_key *key); 169 170 /* 171 * We should be using ATOMIC_INIT() for initializing .enabled, but 172 * the inclusion of atomic.h is problematic for inclusion of jump_label.h 173 * in 'low-level' headers. Thus, we are initializing .enabled with a 174 * raw value, but have added a BUILD_BUG_ON() to catch any issues in 175 * jump_label_init() see: kernel/jump_label.c. 176 */ 177 #define STATIC_KEY_INIT_TRUE \ 178 { .enabled = { 1 }, \ 179 { .entries = (void *)JUMP_TYPE_TRUE } } 180 #define STATIC_KEY_INIT_FALSE \ 181 { .enabled = { 0 }, \ 182 { .entries = (void *)JUMP_TYPE_FALSE } } 183 184 #else /* !HAVE_JUMP_LABEL */ 185 186 #include <linux/atomic.h> 187 #include <linux/bug.h> 188 189 static inline int static_key_count(struct static_key *key) 190 { 191 return atomic_read(&key->enabled); 192 } 193 194 static __always_inline void jump_label_init(void) 195 { 196 static_key_initialized = true; 197 } 198 199 static __always_inline bool static_key_false(struct static_key *key) 200 { 201 if (unlikely(static_key_count(key) > 0)) 202 return true; 203 return false; 204 } 205 206 static __always_inline bool static_key_true(struct static_key *key) 207 { 208 if (likely(static_key_count(key) > 0)) 209 return true; 210 return false; 211 } 212 213 static inline void static_key_slow_inc(struct static_key *key) 214 { 215 STATIC_KEY_CHECK_USE(key); 216 atomic_inc(&key->enabled); 217 } 218 219 static inline void static_key_slow_dec(struct static_key *key) 220 { 221 STATIC_KEY_CHECK_USE(key); 222 atomic_dec(&key->enabled); 223 } 224 225 static inline int jump_label_text_reserved(void *start, void *end) 226 { 227 return 0; 228 } 229 230 static inline void jump_label_lock(void) {} 231 static inline void jump_label_unlock(void) {} 232 233 static inline int jump_label_apply_nops(struct module *mod) 234 { 235 return 0; 236 } 237 238 static inline void static_key_enable(struct static_key *key) 239 { 240 STATIC_KEY_CHECK_USE(key); 241 242 if (atomic_read(&key->enabled) != 0) { 243 WARN_ON_ONCE(atomic_read(&key->enabled) != 1); 244 return; 245 } 246 atomic_set(&key->enabled, 1); 247 } 248 249 static inline void static_key_disable(struct static_key *key) 250 { 251 STATIC_KEY_CHECK_USE(key); 252 253 if (atomic_read(&key->enabled) != 1) { 254 WARN_ON_ONCE(atomic_read(&key->enabled) != 0); 255 return; 256 } 257 atomic_set(&key->enabled, 0); 258 } 259 260 #define static_key_enable_cpuslocked(k) static_key_enable((k)) 261 #define static_key_disable_cpuslocked(k) static_key_disable((k)) 262 263 #define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) } 264 #define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) } 265 266 #endif /* HAVE_JUMP_LABEL */ 267 268 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE 269 #define jump_label_enabled static_key_enabled 270 271 /* -------------------------------------------------------------------------- */ 272 273 /* 274 * Two type wrappers around static_key, such that we can use compile time 275 * type differentiation to emit the right code. 276 * 277 * All the below code is macros in order to play type games. 278 */ 279 280 struct static_key_true { 281 struct static_key key; 282 }; 283 284 struct static_key_false { 285 struct static_key key; 286 }; 287 288 #define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, } 289 #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, } 290 291 #define DEFINE_STATIC_KEY_TRUE(name) \ 292 struct static_key_true name = STATIC_KEY_TRUE_INIT 293 294 #define DECLARE_STATIC_KEY_TRUE(name) \ 295 extern struct static_key_true name 296 297 #define DEFINE_STATIC_KEY_FALSE(name) \ 298 struct static_key_false name = STATIC_KEY_FALSE_INIT 299 300 #define DECLARE_STATIC_KEY_FALSE(name) \ 301 extern struct static_key_false name 302 303 #define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count) \ 304 struct static_key_true name[count] = { \ 305 [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT, \ 306 } 307 308 #define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count) \ 309 struct static_key_false name[count] = { \ 310 [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT, \ 311 } 312 313 extern bool ____wrong_branch_error(void); 314 315 #define static_key_enabled(x) \ 316 ({ \ 317 if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \ 318 !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\ 319 !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 320 ____wrong_branch_error(); \ 321 static_key_count((struct static_key *)x) > 0; \ 322 }) 323 324 #ifdef HAVE_JUMP_LABEL 325 326 /* 327 * Combine the right initial value (type) with the right branch order 328 * to generate the desired result. 329 * 330 * 331 * type\branch| likely (1) | unlikely (0) 332 * -----------+-----------------------+------------------ 333 * | | 334 * true (1) | ... | ... 335 * | NOP | JMP L 336 * | <br-stmts> | 1: ... 337 * | L: ... | 338 * | | 339 * | | L: <br-stmts> 340 * | | jmp 1b 341 * | | 342 * -----------+-----------------------+------------------ 343 * | | 344 * false (0) | ... | ... 345 * | JMP L | NOP 346 * | <br-stmts> | 1: ... 347 * | L: ... | 348 * | | 349 * | | L: <br-stmts> 350 * | | jmp 1b 351 * | | 352 * -----------+-----------------------+------------------ 353 * 354 * The initial value is encoded in the LSB of static_key::entries, 355 * type: 0 = false, 1 = true. 356 * 357 * The branch type is encoded in the LSB of jump_entry::key, 358 * branch: 0 = unlikely, 1 = likely. 359 * 360 * This gives the following logic table: 361 * 362 * enabled type branch instuction 363 * -----------------------------+----------- 364 * 0 0 0 | NOP 365 * 0 0 1 | JMP 366 * 0 1 0 | NOP 367 * 0 1 1 | JMP 368 * 369 * 1 0 0 | JMP 370 * 1 0 1 | NOP 371 * 1 1 0 | JMP 372 * 1 1 1 | NOP 373 * 374 * Which gives the following functions: 375 * 376 * dynamic: instruction = enabled ^ branch 377 * static: instruction = type ^ branch 378 * 379 * See jump_label_type() / jump_label_init_type(). 380 */ 381 382 #define static_branch_likely(x) \ 383 ({ \ 384 bool branch; \ 385 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ 386 branch = !arch_static_branch(&(x)->key, true); \ 387 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 388 branch = !arch_static_branch_jump(&(x)->key, true); \ 389 else \ 390 branch = ____wrong_branch_error(); \ 391 branch; \ 392 }) 393 394 #define static_branch_unlikely(x) \ 395 ({ \ 396 bool branch; \ 397 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ 398 branch = arch_static_branch_jump(&(x)->key, false); \ 399 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 400 branch = arch_static_branch(&(x)->key, false); \ 401 else \ 402 branch = ____wrong_branch_error(); \ 403 branch; \ 404 }) 405 406 #else /* !HAVE_JUMP_LABEL */ 407 408 #define static_branch_likely(x) likely(static_key_enabled(&(x)->key)) 409 #define static_branch_unlikely(x) unlikely(static_key_enabled(&(x)->key)) 410 411 #endif /* HAVE_JUMP_LABEL */ 412 413 /* 414 * Advanced usage; refcount, branch is enabled when: count != 0 415 */ 416 417 #define static_branch_inc(x) static_key_slow_inc(&(x)->key) 418 #define static_branch_dec(x) static_key_slow_dec(&(x)->key) 419 420 /* 421 * Normal usage; boolean enable/disable. 422 */ 423 424 #define static_branch_enable(x) static_key_enable(&(x)->key) 425 #define static_branch_disable(x) static_key_disable(&(x)->key) 426 #define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key) 427 #define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key) 428 429 #endif /* __ASSEMBLY__ */ 430 431 #endif /* _LINUX_JUMP_LABEL_H */ 432