include/linux/jump_label.h

   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 #ifdef CONFIG_JUMP_LABEL
  86
  87 struct static_key {
  88         atomic_t enabled;
  89 /*
  90  * Note:
  91  *   To make anonymous unions work with old compilers, the static
  92  *   initialization of them requires brackets. This creates a dependency
  93  *   on the order of the struct with the initializers. If any fields
  94  *   are added, STATIC_KEY_INIT_TRUE and STATIC_KEY_INIT_FALSE may need
  95  *   to be modified.
  96  *
  97  * bit 0 => 1 if key is initially true
  98  *          0 if initially false
  99  * bit 1 => 1 if points to struct static_key_mod
 100  *          0 if points to struct jump_entry
 101  */
 102         union {
 103                 unsigned long type;
 104                 struct jump_entry *entries;
 105                 struct static_key_mod *next;
 106         };
 107 };
 108
 109 #else
 110 struct static_key {
 111         atomic_t enabled;
 112 };
 113 #endif  /* CONFIG_JUMP_LABEL */
 114 #endif /* __ASSEMBLY__ */
 115
 116 #ifdef CONFIG_JUMP_LABEL
 117 #include <asm/jump_label.h>
 118
 119 #ifndef __ASSEMBLY__
 120 #ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE
 121
 122 struct jump_entry {
 123         s32 code;
 124         s32 target;
 125         long key;       // key may be far away from the core kernel under KASLR
 126 };
 127
 128 static inline unsigned long jump_entry_code(const struct jump_entry *entry)
 129 {
 130         return (unsigned long)&entry->code + entry->code;
 131 }
 132
 133 static inline unsigned long jump_entry_target(const struct jump_entry *entry)
 134 {
 135         return (unsigned long)&entry->target + entry->target;
 136 }
 137
 138 static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
 139 {
 140         long offset = entry->key & ~3L;
 141
 142         return (struct static_key *)((unsigned long)&entry->key + offset);
 143 }
 144
 145 #else
 146
 147 static inline unsigned long jump_entry_code(const struct jump_entry *entry)
 148 {
 149         return entry->code;
 150 }
 151
 152 static inline unsigned long jump_entry_target(const struct jump_entry *entry)
 153 {
 154         return entry->target;
 155 }
 156
 157 static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
 158 {
 159         return (struct static_key *)((unsigned long)entry->key & ~3UL);
 160 }
 161
 162 #endif
 163
 164 static inline bool jump_entry_is_branch(const struct jump_entry *entry)
 165 {
 166         return (unsigned long)entry->key & 1UL;
 167 }
 168
 169 static inline bool jump_entry_is_init(const struct jump_entry *entry)
 170 {
 171         return (unsigned long)entry->key & 2UL;
 172 }
 173
 174 static inline void jump_entry_set_init(struct jump_entry *entry)
 175 {
 176         entry->key |= 2;
 177 }
 178
 179 #endif
 180 #endif
 181
 182 #ifndef __ASSEMBLY__
 183
 184 enum jump_label_type {
 185         JUMP_LABEL_NOP = 0,
 186         JUMP_LABEL_JMP,
 187 };
 188
 189 struct module;
 190
 191 #ifdef CONFIG_JUMP_LABEL
 192
 193 #define JUMP_TYPE_FALSE         0UL
 194 #define JUMP_TYPE_TRUE          1UL
 195 #define JUMP_TYPE_LINKED        2UL
 196 #define JUMP_TYPE_MASK          3UL
 197
 198 static __always_inline bool static_key_false(struct static_key *key)
 199 {
 200         return arch_static_branch(key, false);
 201 }
 202
 203 static __always_inline bool static_key_true(struct static_key *key)
 204 {
 205         return !arch_static_branch(key, true);
 206 }
 207
 208 extern struct jump_entry __start___jump_table[];
 209 extern struct jump_entry __stop___jump_table[];
 210
 211 extern void jump_label_init(void);
 212 extern void jump_label_lock(void);
 213 extern void jump_label_unlock(void);
 214 extern void arch_jump_label_transform(struct jump_entry *entry,
 215                                       enum jump_label_type type);
 216 extern void arch_jump_label_transform_static(struct jump_entry *entry,
 217                                              enum jump_label_type type);
 218 extern bool arch_jump_label_transform_queue(struct jump_entry *entry,
 219                                             enum jump_label_type type);
 220 extern void arch_jump_label_transform_apply(void);
 221 extern int jump_label_text_reserved(void *start, void *end);
 222 extern void static_key_slow_inc(struct static_key *key);
 223 extern void static_key_slow_dec(struct static_key *key);
 224 extern void static_key_slow_inc_cpuslocked(struct static_key *key);
 225 extern void static_key_slow_dec_cpuslocked(struct static_key *key);
 226 extern void jump_label_apply_nops(struct module *mod);
 227 extern int static_key_count(struct static_key *key);
 228 extern void static_key_enable(struct static_key *key);
 229 extern void static_key_disable(struct static_key *key);
 230 extern void static_key_enable_cpuslocked(struct static_key *key);
 231 extern void static_key_disable_cpuslocked(struct static_key *key);
 232
 233 /*
 234  * We should be using ATOMIC_INIT() for initializing .enabled, but
 235  * the inclusion of atomic.h is problematic for inclusion of jump_label.h
 236  * in 'low-level' headers. Thus, we are initializing .enabled with a
 237  * raw value, but have added a BUILD_BUG_ON() to catch any issues in
 238  * jump_label_init() see: kernel/jump_label.c.
 239  */
 240 #define STATIC_KEY_INIT_TRUE                                    \
 241         { .enabled = { 1 },                                     \
 242           { .entries = (void *)JUMP_TYPE_TRUE } }
 243 #define STATIC_KEY_INIT_FALSE                                   \
 244         { .enabled = { 0 },                                     \
 245           { .entries = (void *)JUMP_TYPE_FALSE } }
 246
 247 #else  /* !CONFIG_JUMP_LABEL */
 248
 249 #include <linux/atomic.h>
 250 #include <linux/bug.h>
 251
 252 static inline int static_key_count(struct static_key *key)
 253 {
 254         return atomic_read(&key->enabled);
 255 }
 256
 257 static __always_inline void jump_label_init(void)
 258 {
 259         static_key_initialized = true;
 260 }
 261
 262 static __always_inline bool static_key_false(struct static_key *key)
 263 {
 264         if (unlikely_notrace(static_key_count(key) > 0))
 265                 return true;
 266         return false;
 267 }
 268
 269 static __always_inline bool static_key_true(struct static_key *key)
 270 {
 271         if (likely_notrace(static_key_count(key) > 0))
 272                 return true;
 273         return false;
 274 }
 275
 276 static inline void static_key_slow_inc(struct static_key *key)
 277 {
 278         STATIC_KEY_CHECK_USE(key);
 279         atomic_inc(&key->enabled);
 280 }
 281
 282 static inline void static_key_slow_dec(struct static_key *key)
 283 {
 284         STATIC_KEY_CHECK_USE(key);
 285         atomic_dec(&key->enabled);
 286 }
 287
 288 #define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key)
 289 #define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key)
 290
 291 static inline int jump_label_text_reserved(void *start, void *end)
 292 {
 293         return 0;
 294 }
 295
 296 static inline void jump_label_lock(void) {}
 297 static inline void jump_label_unlock(void) {}
 298
 299 static inline int jump_label_apply_nops(struct module *mod)
 300 {
 301         return 0;
 302 }
 303
 304 static inline void static_key_enable(struct static_key *key)
 305 {
 306         STATIC_KEY_CHECK_USE(key);
 307
 308         if (atomic_read(&key->enabled) != 0) {
 309                 WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
 310                 return;
 311         }
 312         atomic_set(&key->enabled, 1);
 313 }
 314
 315 static inline void static_key_disable(struct static_key *key)
 316 {
 317         STATIC_KEY_CHECK_USE(key);
 318
 319         if (atomic_read(&key->enabled) != 1) {
 320                 WARN_ON_ONCE(atomic_read(&key->enabled) != 0);
 321                 return;
 322         }
 323         atomic_set(&key->enabled, 0);
 324 }
 325
 326 #define static_key_enable_cpuslocked(k)         static_key_enable((k))
 327 #define static_key_disable_cpuslocked(k)        static_key_disable((k))
 328
 329 #define STATIC_KEY_INIT_TRUE    { .enabled = ATOMIC_INIT(1) }
 330 #define STATIC_KEY_INIT_FALSE   { .enabled = ATOMIC_INIT(0) }
 331
 332 #endif  /* CONFIG_JUMP_LABEL */
 333
 334 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
 335 #define jump_label_enabled static_key_enabled
 336
 337 /* -------------------------------------------------------------------------- */
 338
 339 /*
 340  * Two type wrappers around static_key, such that we can use compile time
 341  * type differentiation to emit the right code.
 342  *
 343  * All the below code is macros in order to play type games.
 344  */
 345
 346 struct static_key_true {
 347         struct static_key key;
 348 };
 349
 350 struct static_key_false {
 351         struct static_key key;
 352 };
 353
 354 #define STATIC_KEY_TRUE_INIT  (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE,  }
 355 #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, }
 356
 357 #define DEFINE_STATIC_KEY_TRUE(name)    \
 358         struct static_key_true name = STATIC_KEY_TRUE_INIT
 359
 360 #define DEFINE_STATIC_KEY_TRUE_RO(name) \
 361         struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT
 362
 363 #define DECLARE_STATIC_KEY_TRUE(name)   \
 364         extern struct static_key_true name
 365
 366 #define DEFINE_STATIC_KEY_FALSE(name)   \
 367         struct static_key_false name = STATIC_KEY_FALSE_INIT
 368
 369 #define DEFINE_STATIC_KEY_FALSE_RO(name)        \
 370         struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT
 371
 372 #define DECLARE_STATIC_KEY_FALSE(name)  \
 373         extern struct static_key_false name
 374
 375 #define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count)               \
 376         struct static_key_true name[count] = {                  \
 377                 [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT,     \
 378         }
 379
 380 #define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count)              \
 381         struct static_key_false name[count] = {                 \
 382                 [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT,    \
 383         }
 384
 385 extern bool ____wrong_branch_error(void);
 386
 387 #define static_key_enabled(x)                                                   \
 388 ({                                                                              \
 389         if (!__builtin_types_compatible_p(typeof(*x), struct static_key) &&     \
 390             !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\
 391             !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
 392                 ____wrong_branch_error();                                       \
 393         static_key_count((struct static_key *)x) > 0;                           \
 394 })
 395
 396 #ifdef CONFIG_JUMP_LABEL
 397
 398 /*
 399  * Combine the right initial value (type) with the right branch order
 400  * to generate the desired result.
 401  *
 402  *
 403  * type\branch| likely (1)            | unlikely (0)
 404  * -----------+-----------------------+------------------
 405  *            |                       |
 406  *  true (1)  |    ...                |    ...
 407  *            |    NOP                |    JMP L
 408  *            |    <br-stmts>         | 1: ...
 409  *            | L: ...                |
 410  *            |                       |
 411  *            |                       | L: <br-stmts>
 412  *            |                       |    jmp 1b
 413  *            |                       |
 414  * -----------+-----------------------+------------------
 415  *            |                       |
 416  *  false (0) |    ...                |    ...
 417  *            |    JMP L              |    NOP
 418  *            |    <br-stmts>         | 1: ...
 419  *            | L: ...                |
 420  *            |                       |
 421  *            |                       | L: <br-stmts>
 422  *            |                       |    jmp 1b
 423  *            |                       |
 424  * -----------+-----------------------+------------------
 425  *
 426  * The initial value is encoded in the LSB of static_key::entries,
 427  * type: 0 = false, 1 = true.
 428  *
 429  * The branch type is encoded in the LSB of jump_entry::key,
 430  * branch: 0 = unlikely, 1 = likely.
 431  *
 432  * This gives the following logic table:
 433  *
 434  *      enabled type    branch    instuction
 435  * -----------------------------+-----------
 436  *      0       0       0       | NOP
 437  *      0       0       1       | JMP
 438  *      0       1       0       | NOP
 439  *      0       1       1       | JMP
 440  *
 441  *      1       0       0       | JMP
 442  *      1       0       1       | NOP
 443  *      1       1       0       | JMP
 444  *      1       1       1       | NOP
 445  *
 446  * Which gives the following functions:
 447  *
 448  *   dynamic: instruction = enabled ^ branch
 449  *   static:  instruction = type ^ branch
 450  *
 451  * See jump_label_type() / jump_label_init_type().
 452  */
 453
 454 #define static_branch_likely(x)                                                 \
 455 ({                                                                              \
 456         bool branch;                                                            \
 457         if (__builtin_types_compatible_p(typeof(*x), struct static_key_true))   \
 458                 branch = !arch_static_branch(&(x)->key, true);                  \
 459         else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
 460                 branch = !arch_static_branch_jump(&(x)->key, true);             \
 461         else                                                                    \
 462                 branch = ____wrong_branch_error();                              \
 463         likely_notrace(branch);                                                         \
 464 })
 465
 466 #define static_branch_unlikely(x)                                               \
 467 ({                                                                              \
 468         bool branch;                                                            \
 469         if (__builtin_types_compatible_p(typeof(*x), struct static_key_true))   \
 470                 branch = arch_static_branch_jump(&(x)->key, false);             \
 471         else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
 472                 branch = arch_static_branch(&(x)->key, false);                  \
 473         else                                                                    \
 474                 branch = ____wrong_branch_error();                              \
 475         unlikely_notrace(branch);                                                       \
 476 })
 477
 478 #else /* !CONFIG_JUMP_LABEL */
 479
 480 #define static_branch_likely(x)         likely_notrace(static_key_enabled(&(x)->key))
 481 #define static_branch_unlikely(x)       unlikely_notrace(static_key_enabled(&(x)->key))
 482
 483 #endif /* CONFIG_JUMP_LABEL */
 484
 485 /*
 486  * Advanced usage; refcount, branch is enabled when: count != 0
 487  */
 488
 489 #define static_branch_inc(x)            static_key_slow_inc(&(x)->key)
 490 #define static_branch_dec(x)            static_key_slow_dec(&(x)->key)
 491 #define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key)
 492 #define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(x)->key)
 493
 494 /*
 495  * Normal usage; boolean enable/disable.
 496  */
 497
 498 #define static_branch_enable(x)                 static_key_enable(&(x)->key)
 499 #define static_branch_disable(x)                static_key_disable(&(x)->key)
 500 #define static_branch_enable_cpuslocked(x)      static_key_enable_cpuslocked(&(x)->key)
 501 #define static_branch_disable_cpuslocked(x)     static_key_disable_cpuslocked(&(x)->key)
 502
 503 #endif /* __ASSEMBLY__ */
 504
 505 #endif  /* _LINUX_JUMP_LABEL_H */