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/static-keys.txt
  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 #endif
 119
 120 #ifndef __ASSEMBLY__
 121
 122 enum jump_label_type {
 123         JUMP_LABEL_NOP = 0,
 124         JUMP_LABEL_JMP,
 125 };
 126
 127 struct module;
 128
 129 #ifdef CONFIG_JUMP_LABEL
 130
 131 #define JUMP_TYPE_FALSE         0UL
 132 #define JUMP_TYPE_TRUE          1UL
 133 #define JUMP_TYPE_LINKED        2UL
 134 #define JUMP_TYPE_MASK          3UL
 135
 136 static __always_inline bool static_key_false(struct static_key *key)
 137 {
 138         return arch_static_branch(key, false);
 139 }
 140
 141 static __always_inline bool static_key_true(struct static_key *key)
 142 {
 143         return !arch_static_branch(key, true);
 144 }
 145
 146 extern struct jump_entry __start___jump_table[];
 147 extern struct jump_entry __stop___jump_table[];
 148
 149 extern void jump_label_init(void);
 150 extern void jump_label_invalidate_initmem(void);
 151 extern void jump_label_lock(void);
 152 extern void jump_label_unlock(void);
 153 extern void arch_jump_label_transform(struct jump_entry *entry,
 154                                       enum jump_label_type type);
 155 extern void arch_jump_label_transform_static(struct jump_entry *entry,
 156                                              enum jump_label_type type);
 157 extern int jump_label_text_reserved(void *start, void *end);
 158 extern void static_key_slow_inc(struct static_key *key);
 159 extern void static_key_slow_dec(struct static_key *key);
 160 extern void static_key_slow_inc_cpuslocked(struct static_key *key);
 161 extern void static_key_slow_dec_cpuslocked(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  /* !CONFIG_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 inline void jump_label_invalidate_initmem(void) {}
 199
 200 static __always_inline bool static_key_false(struct static_key *key)
 201 {
 202         if (unlikely(static_key_count(key) > 0))
 203                 return true;
 204         return false;
 205 }
 206
 207 static __always_inline bool static_key_true(struct static_key *key)
 208 {
 209         if (likely(static_key_count(key) > 0))
 210                 return true;
 211         return false;
 212 }
 213
 214 static inline void static_key_slow_inc(struct static_key *key)
 215 {
 216         STATIC_KEY_CHECK_USE(key);
 217         atomic_inc(&key->enabled);
 218 }
 219
 220 static inline void static_key_slow_dec(struct static_key *key)
 221 {
 222         STATIC_KEY_CHECK_USE(key);
 223         atomic_dec(&key->enabled);
 224 }
 225
 226 #define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key)
 227 #define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key)
 228
 229 static inline int jump_label_text_reserved(void *start, void *end)
 230 {
 231         return 0;
 232 }
 233
 234 static inline void jump_label_lock(void) {}
 235 static inline void jump_label_unlock(void) {}
 236
 237 static inline int jump_label_apply_nops(struct module *mod)
 238 {
 239         return 0;
 240 }
 241
 242 static inline void static_key_enable(struct static_key *key)
 243 {
 244         STATIC_KEY_CHECK_USE(key);
 245
 246         if (atomic_read(&key->enabled) != 0) {
 247                 WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
 248                 return;
 249         }
 250         atomic_set(&key->enabled, 1);
 251 }
 252
 253 static inline void static_key_disable(struct static_key *key)
 254 {
 255         STATIC_KEY_CHECK_USE(key);
 256
 257         if (atomic_read(&key->enabled) != 1) {
 258                 WARN_ON_ONCE(atomic_read(&key->enabled) != 0);
 259                 return;
 260         }
 261         atomic_set(&key->enabled, 0);
 262 }
 263
 264 #define static_key_enable_cpuslocked(k)         static_key_enable((k))
 265 #define static_key_disable_cpuslocked(k)        static_key_disable((k))
 266
 267 #define STATIC_KEY_INIT_TRUE    { .enabled = ATOMIC_INIT(1) }
 268 #define STATIC_KEY_INIT_FALSE   { .enabled = ATOMIC_INIT(0) }
 269
 270 #endif  /* CONFIG_JUMP_LABEL */
 271
 272 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
 273 #define jump_label_enabled static_key_enabled
 274
 275 /* -------------------------------------------------------------------------- */
 276
 277 /*
 278  * Two type wrappers around static_key, such that we can use compile time
 279  * type differentiation to emit the right code.
 280  *
 281  * All the below code is macros in order to play type games.
 282  */
 283
 284 struct static_key_true {
 285         struct static_key key;
 286 };
 287
 288 struct static_key_false {
 289         struct static_key key;
 290 };
 291
 292 #define STATIC_KEY_TRUE_INIT  (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE,  }
 293 #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, }
 294
 295 #define DEFINE_STATIC_KEY_TRUE(name)    \
 296         struct static_key_true name = STATIC_KEY_TRUE_INIT
 297
 298 #define DEFINE_STATIC_KEY_TRUE_RO(name) \
 299         struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT
 300
 301 #define DECLARE_STATIC_KEY_TRUE(name)   \
 302         extern struct static_key_true name
 303
 304 #define DEFINE_STATIC_KEY_FALSE(name)   \
 305         struct static_key_false name = STATIC_KEY_FALSE_INIT
 306
 307 #define DEFINE_STATIC_KEY_FALSE_RO(name)        \
 308         struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT
 309
 310 #define DECLARE_STATIC_KEY_FALSE(name)  \
 311         extern struct static_key_false name
 312
 313 #define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count)               \
 314         struct static_key_true name[count] = {                  \
 315                 [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT,     \
 316         }
 317
 318 #define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count)              \
 319         struct static_key_false name[count] = {                 \
 320                 [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT,    \
 321         }
 322
 323 extern bool ____wrong_branch_error(void);
 324
 325 #define static_key_enabled(x)                                                   \
 326 ({                                                                              \
 327         if (!__builtin_types_compatible_p(typeof(*x), struct static_key) &&     \
 328             !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\
 329             !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
 330                 ____wrong_branch_error();                                       \
 331         static_key_count((struct static_key *)x) > 0;                           \
 332 })
 333
 334 #ifdef CONFIG_JUMP_LABEL
 335
 336 /*
 337  * Combine the right initial value (type) with the right branch order
 338  * to generate the desired result.
 339  *
 340  *
 341  * type\branch| likely (1)            | unlikely (0)
 342  * -----------+-----------------------+------------------
 343  *            |                       |
 344  *  true (1)  |    ...                |    ...
 345  *            |    NOP                |    JMP L
 346  *            |    <br-stmts>         | 1: ...
 347  *            | L: ...                |
 348  *            |                       |
 349  *            |                       | L: <br-stmts>
 350  *            |                       |    jmp 1b
 351  *            |                       |
 352  * -----------+-----------------------+------------------
 353  *            |                       |
 354  *  false (0) |    ...                |    ...
 355  *            |    JMP L              |    NOP
 356  *            |    <br-stmts>         | 1: ...
 357  *            | L: ...                |
 358  *            |                       |
 359  *            |                       | L: <br-stmts>
 360  *            |                       |    jmp 1b
 361  *            |                       |
 362  * -----------+-----------------------+------------------
 363  *
 364  * The initial value is encoded in the LSB of static_key::entries,
 365  * type: 0 = false, 1 = true.
 366  *
 367  * The branch type is encoded in the LSB of jump_entry::key,
 368  * branch: 0 = unlikely, 1 = likely.
 369  *
 370  * This gives the following logic table:
 371  *
 372  *      enabled type    branch    instuction
 373  * -----------------------------+-----------
 374  *      0       0       0       | NOP
 375  *      0       0       1       | JMP
 376  *      0       1       0       | NOP
 377  *      0       1       1       | JMP
 378  *
 379  *      1       0       0       | JMP
 380  *      1       0       1       | NOP
 381  *      1       1       0       | JMP
 382  *      1       1       1       | NOP
 383  *
 384  * Which gives the following functions:
 385  *
 386  *   dynamic: instruction = enabled ^ branch
 387  *   static:  instruction = type ^ branch
 388  *
 389  * See jump_label_type() / jump_label_init_type().
 390  */
 391
 392 #define static_branch_likely(x)                                                 \
 393 ({                                                                              \
 394         bool branch;                                                            \
 395         if (__builtin_types_compatible_p(typeof(*x), struct static_key_true))   \
 396                 branch = !arch_static_branch(&(x)->key, true);                  \
 397         else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
 398                 branch = !arch_static_branch_jump(&(x)->key, true);             \
 399         else                                                                    \
 400                 branch = ____wrong_branch_error();                              \
 401         likely(branch);                                                         \
 402 })
 403
 404 #define static_branch_unlikely(x)                                               \
 405 ({                                                                              \
 406         bool branch;                                                            \
 407         if (__builtin_types_compatible_p(typeof(*x), struct static_key_true))   \
 408                 branch = arch_static_branch_jump(&(x)->key, false);             \
 409         else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
 410                 branch = arch_static_branch(&(x)->key, false);                  \
 411         else                                                                    \
 412                 branch = ____wrong_branch_error();                              \
 413         unlikely(branch);                                                       \
 414 })
 415
 416 #else /* !CONFIG_JUMP_LABEL */
 417
 418 #define static_branch_likely(x)         likely(static_key_enabled(&(x)->key))
 419 #define static_branch_unlikely(x)       unlikely(static_key_enabled(&(x)->key))
 420
 421 #endif /* CONFIG_JUMP_LABEL */
 422
 423 /*
 424  * Advanced usage; refcount, branch is enabled when: count != 0
 425  */
 426
 427 #define static_branch_inc(x)            static_key_slow_inc(&(x)->key)
 428 #define static_branch_dec(x)            static_key_slow_dec(&(x)->key)
 429 #define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key)
 430 #define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(x)->key)
 431
 432 /*
 433  * Normal usage; boolean enable/disable.
 434  */
 435
 436 #define static_branch_enable(x)                 static_key_enable(&(x)->key)
 437 #define static_branch_disable(x)                static_key_disable(&(x)->key)
 438 #define static_branch_enable_cpuslocked(x)      static_key_enable_cpuslocked(&(x)->key)
 439 #define static_branch_disable_cpuslocked(x)     static_key_disable_cpuslocked(&(x)->key)
 440
 441 #endif /* __ASSEMBLY__ */
 442
 443 #endif  /* _LINUX_JUMP_LABEL_H */