1 #ifndef _LINUX_JUMP_LABEL_H 2 #define _LINUX_JUMP_LABEL_H 3 4 /* 5 * Jump label support 6 * 7 * Copyright (C) 2009-2012 Jason Baron <[email protected]> 8 * Copyright (C) 2011-2012 Red Hat, Inc., Peter Zijlstra 9 * 10 * DEPRECATED API: 11 * 12 * The use of 'struct static_key' directly, is now DEPRECATED. In addition 13 * static_key_{true,false}() is also DEPRECATED. IE DO NOT use the following: 14 * 15 * struct static_key false = STATIC_KEY_INIT_FALSE; 16 * struct static_key true = STATIC_KEY_INIT_TRUE; 17 * static_key_true() 18 * static_key_false() 19 * 20 * The updated API replacements are: 21 * 22 * DEFINE_STATIC_KEY_TRUE(key); 23 * DEFINE_STATIC_KEY_FALSE(key); 24 * DEFINE_STATIC_KEY_ARRAY_TRUE(keys, count); 25 * DEFINE_STATIC_KEY_ARRAY_FALSE(keys, count); 26 * static_branch_likely() 27 * static_branch_unlikely() 28 * 29 * Jump labels provide an interface to generate dynamic branches using 30 * self-modifying code. Assuming toolchain and architecture support, if we 31 * define a "key" that is initially false via "DEFINE_STATIC_KEY_FALSE(key)", 32 * an "if (static_branch_unlikely(&key))" statement is an unconditional branch 33 * (which defaults to false - and the true block is placed out of line). 34 * Similarly, we can define an initially true key via 35 * "DEFINE_STATIC_KEY_TRUE(key)", and use it in the same 36 * "if (static_branch_unlikely(&key))", in which case we will generate an 37 * unconditional branch to the out-of-line true branch. Keys that are 38 * initially true or false can be using in both static_branch_unlikely() 39 * and static_branch_likely() statements. 40 * 41 * At runtime we can change the branch target by setting the key 42 * to true via a call to static_branch_enable(), or false using 43 * static_branch_disable(). If the direction of the branch is switched by 44 * these calls then we run-time modify the branch target via a 45 * no-op -> jump or jump -> no-op conversion. For example, for an 46 * initially false key that is used in an "if (static_branch_unlikely(&key))" 47 * statement, setting the key to true requires us to patch in a jump 48 * to the out-of-line of true branch. 49 * 50 * In addition to static_branch_{enable,disable}, we can also reference count 51 * the key or branch direction via static_branch_{inc,dec}. Thus, 52 * static_branch_inc() can be thought of as a 'make more true' and 53 * static_branch_dec() as a 'make more false'. 54 * 55 * Since this relies on modifying code, the branch modifying functions 56 * must be considered absolute slow paths (machine wide synchronization etc.). 57 * OTOH, since the affected branches are unconditional, their runtime overhead 58 * will be absolutely minimal, esp. in the default (off) case where the total 59 * effect is a single NOP of appropriate size. The on case will patch in a jump 60 * to the out-of-line block. 61 * 62 * When the control is directly exposed to userspace, it is prudent to delay the 63 * decrement to avoid high frequency code modifications which can (and do) 64 * cause significant performance degradation. Struct static_key_deferred and 65 * static_key_slow_dec_deferred() provide for this. 66 * 67 * Lacking toolchain and or architecture support, static keys fall back to a 68 * simple conditional branch. 69 * 70 * Additional babbling in: Documentation/static-keys.txt 71 */ 72 73 #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL) 74 # define HAVE_JUMP_LABEL 75 #endif 76 77 #ifndef __ASSEMBLY__ 78 79 #include <linux/types.h> 80 #include <linux/compiler.h> 81 82 extern bool static_key_initialized; 83 84 #define STATIC_KEY_CHECK_USE() WARN(!static_key_initialized, \ 85 "%s used before call to jump_label_init", \ 86 __func__) 87 88 #ifdef HAVE_JUMP_LABEL 89 90 struct static_key { 91 atomic_t enabled; 92 /* 93 * Note: 94 * To make anonymous unions work with old compilers, the static 95 * initialization of them requires brackets. This creates a dependency 96 * on the order of the struct with the initializers. If any fields 97 * are added, STATIC_KEY_INIT_TRUE and STATIC_KEY_INIT_FALSE may need 98 * to be modified. 99 * 100 * bit 0 => 1 if key is initially true 101 * 0 if initially false 102 * bit 1 => 1 if points to struct static_key_mod 103 * 0 if points to struct jump_entry 104 */ 105 union { 106 unsigned long type; 107 struct jump_entry *entries; 108 struct static_key_mod *next; 109 }; 110 }; 111 112 #else 113 struct static_key { 114 atomic_t enabled; 115 }; 116 #endif /* HAVE_JUMP_LABEL */ 117 #endif /* __ASSEMBLY__ */ 118 119 #ifdef HAVE_JUMP_LABEL 120 #include <asm/jump_label.h> 121 #endif 122 123 #ifndef __ASSEMBLY__ 124 125 enum jump_label_type { 126 JUMP_LABEL_NOP = 0, 127 JUMP_LABEL_JMP, 128 }; 129 130 struct module; 131 132 #ifdef HAVE_JUMP_LABEL 133 134 #define JUMP_TYPE_FALSE 0UL 135 #define JUMP_TYPE_TRUE 1UL 136 #define JUMP_TYPE_LINKED 2UL 137 #define JUMP_TYPE_MASK 3UL 138 139 static __always_inline bool static_key_false(struct static_key *key) 140 { 141 return arch_static_branch(key, false); 142 } 143 144 static __always_inline bool static_key_true(struct static_key *key) 145 { 146 return !arch_static_branch(key, true); 147 } 148 149 extern struct jump_entry __start___jump_table[]; 150 extern struct jump_entry __stop___jump_table[]; 151 152 extern void jump_label_init(void); 153 extern void jump_label_lock(void); 154 extern void jump_label_unlock(void); 155 extern void arch_jump_label_transform(struct jump_entry *entry, 156 enum jump_label_type type); 157 extern void arch_jump_label_transform_static(struct jump_entry *entry, 158 enum jump_label_type type); 159 extern int jump_label_text_reserved(void *start, void *end); 160 extern void static_key_slow_inc(struct static_key *key); 161 extern void static_key_slow_dec(struct static_key *key); 162 extern void jump_label_apply_nops(struct module *mod); 163 extern int static_key_count(struct static_key *key); 164 extern void static_key_enable(struct static_key *key); 165 extern void static_key_disable(struct static_key *key); 166 extern void static_key_enable_cpuslocked(struct static_key *key); 167 extern void static_key_disable_cpuslocked(struct static_key *key); 168 169 /* 170 * We should be using ATOMIC_INIT() for initializing .enabled, but 171 * the inclusion of atomic.h is problematic for inclusion of jump_label.h 172 * in 'low-level' headers. Thus, we are initializing .enabled with a 173 * raw value, but have added a BUILD_BUG_ON() to catch any issues in 174 * jump_label_init() see: kernel/jump_label.c. 175 */ 176 #define STATIC_KEY_INIT_TRUE \ 177 { .enabled = { 1 }, \ 178 { .entries = (void *)JUMP_TYPE_TRUE } } 179 #define STATIC_KEY_INIT_FALSE \ 180 { .enabled = { 0 }, \ 181 { .entries = (void *)JUMP_TYPE_FALSE } } 182 183 #else /* !HAVE_JUMP_LABEL */ 184 185 #include <linux/atomic.h> 186 #include <linux/bug.h> 187 188 static inline int static_key_count(struct static_key *key) 189 { 190 return atomic_read(&key->enabled); 191 } 192 193 static __always_inline void jump_label_init(void) 194 { 195 static_key_initialized = true; 196 } 197 198 static __always_inline bool static_key_false(struct static_key *key) 199 { 200 if (unlikely(static_key_count(key) > 0)) 201 return true; 202 return false; 203 } 204 205 static __always_inline bool static_key_true(struct static_key *key) 206 { 207 if (likely(static_key_count(key) > 0)) 208 return true; 209 return false; 210 } 211 212 static inline void static_key_slow_inc(struct static_key *key) 213 { 214 STATIC_KEY_CHECK_USE(); 215 atomic_inc(&key->enabled); 216 } 217 218 static inline void static_key_slow_dec(struct static_key *key) 219 { 220 STATIC_KEY_CHECK_USE(); 221 atomic_dec(&key->enabled); 222 } 223 224 static inline int jump_label_text_reserved(void *start, void *end) 225 { 226 return 0; 227 } 228 229 static inline void jump_label_lock(void) {} 230 static inline void jump_label_unlock(void) {} 231 232 static inline int jump_label_apply_nops(struct module *mod) 233 { 234 return 0; 235 } 236 237 static inline void static_key_enable(struct static_key *key) 238 { 239 STATIC_KEY_CHECK_USE(); 240 241 if (atomic_read(&key->enabled) != 0) { 242 WARN_ON_ONCE(atomic_read(&key->enabled) != 1); 243 return; 244 } 245 atomic_set(&key->enabled, 1); 246 } 247 248 static inline void static_key_disable(struct static_key *key) 249 { 250 STATIC_KEY_CHECK_USE(); 251 252 if (atomic_read(&key->enabled) != 1) { 253 WARN_ON_ONCE(atomic_read(&key->enabled) != 0); 254 return; 255 } 256 atomic_set(&key->enabled, 0); 257 } 258 259 #define static_key_enable_cpuslocked(k) static_key_enable((k)) 260 #define static_key_disable_cpuslocked(k) static_key_disable((k)) 261 262 #define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) } 263 #define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) } 264 265 #endif /* HAVE_JUMP_LABEL */ 266 267 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE 268 #define jump_label_enabled static_key_enabled 269 270 /* -------------------------------------------------------------------------- */ 271 272 /* 273 * Two type wrappers around static_key, such that we can use compile time 274 * type differentiation to emit the right code. 275 * 276 * All the below code is macros in order to play type games. 277 */ 278 279 struct static_key_true { 280 struct static_key key; 281 }; 282 283 struct static_key_false { 284 struct static_key key; 285 }; 286 287 #define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, } 288 #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, } 289 290 #define DEFINE_STATIC_KEY_TRUE(name) \ 291 struct static_key_true name = STATIC_KEY_TRUE_INIT 292 293 #define DECLARE_STATIC_KEY_TRUE(name) \ 294 extern struct static_key_true name 295 296 #define DEFINE_STATIC_KEY_FALSE(name) \ 297 struct static_key_false name = STATIC_KEY_FALSE_INIT 298 299 #define DECLARE_STATIC_KEY_FALSE(name) \ 300 extern struct static_key_false name 301 302 #define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count) \ 303 struct static_key_true name[count] = { \ 304 [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT, \ 305 } 306 307 #define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count) \ 308 struct static_key_false name[count] = { \ 309 [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT, \ 310 } 311 312 extern bool ____wrong_branch_error(void); 313 314 #define static_key_enabled(x) \ 315 ({ \ 316 if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \ 317 !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\ 318 !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 319 ____wrong_branch_error(); \ 320 static_key_count((struct static_key *)x) > 0; \ 321 }) 322 323 #ifdef HAVE_JUMP_LABEL 324 325 /* 326 * Combine the right initial value (type) with the right branch order 327 * to generate the desired result. 328 * 329 * 330 * type\branch| likely (1) | unlikely (0) 331 * -----------+-----------------------+------------------ 332 * | | 333 * true (1) | ... | ... 334 * | NOP | JMP L 335 * | <br-stmts> | 1: ... 336 * | L: ... | 337 * | | 338 * | | L: <br-stmts> 339 * | | jmp 1b 340 * | | 341 * -----------+-----------------------+------------------ 342 * | | 343 * false (0) | ... | ... 344 * | JMP L | NOP 345 * | <br-stmts> | 1: ... 346 * | L: ... | 347 * | | 348 * | | L: <br-stmts> 349 * | | jmp 1b 350 * | | 351 * -----------+-----------------------+------------------ 352 * 353 * The initial value is encoded in the LSB of static_key::entries, 354 * type: 0 = false, 1 = true. 355 * 356 * The branch type is encoded in the LSB of jump_entry::key, 357 * branch: 0 = unlikely, 1 = likely. 358 * 359 * This gives the following logic table: 360 * 361 * enabled type branch instuction 362 * -----------------------------+----------- 363 * 0 0 0 | NOP 364 * 0 0 1 | JMP 365 * 0 1 0 | NOP 366 * 0 1 1 | JMP 367 * 368 * 1 0 0 | JMP 369 * 1 0 1 | NOP 370 * 1 1 0 | JMP 371 * 1 1 1 | NOP 372 * 373 * Which gives the following functions: 374 * 375 * dynamic: instruction = enabled ^ branch 376 * static: instruction = type ^ branch 377 * 378 * See jump_label_type() / jump_label_init_type(). 379 */ 380 381 #define static_branch_likely(x) \ 382 ({ \ 383 bool branch; \ 384 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ 385 branch = !arch_static_branch(&(x)->key, true); \ 386 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 387 branch = !arch_static_branch_jump(&(x)->key, true); \ 388 else \ 389 branch = ____wrong_branch_error(); \ 390 branch; \ 391 }) 392 393 #define static_branch_unlikely(x) \ 394 ({ \ 395 bool branch; \ 396 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ 397 branch = arch_static_branch_jump(&(x)->key, false); \ 398 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ 399 branch = arch_static_branch(&(x)->key, false); \ 400 else \ 401 branch = ____wrong_branch_error(); \ 402 branch; \ 403 }) 404 405 #else /* !HAVE_JUMP_LABEL */ 406 407 #define static_branch_likely(x) likely(static_key_enabled(&(x)->key)) 408 #define static_branch_unlikely(x) unlikely(static_key_enabled(&(x)->key)) 409 410 #endif /* HAVE_JUMP_LABEL */ 411 412 /* 413 * Advanced usage; refcount, branch is enabled when: count != 0 414 */ 415 416 #define static_branch_inc(x) static_key_slow_inc(&(x)->key) 417 #define static_branch_dec(x) static_key_slow_dec(&(x)->key) 418 419 /* 420 * Normal usage; boolean enable/disable. 421 */ 422 423 #define static_branch_enable(x) static_key_enable(&(x)->key) 424 #define static_branch_disable(x) static_key_disable(&(x)->key) 425 #define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key) 426 #define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key) 427 428 #endif /* __ASSEMBLY__ */ 429 430 #endif /* _LINUX_JUMP_LABEL_H */ 431