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 struct static_key {
  86         atomic_t enabled;
  87 #ifdef CONFIG_JUMP_LABEL
  88 /*
  89  * Note:
  90  *   To make anonymous unions work with old compilers, the static
  91  *   initialization of them requires brackets. This creates a dependency
  92  *   on the order of the struct with the initializers. If any fields
  93  *   are added, STATIC_KEY_INIT_TRUE and STATIC_KEY_INIT_FALSE may need
  94  *   to be modified.
  95  *
  96  * bit 0 => 1 if key is initially true
  97  *          0 if initially false
  98  * bit 1 => 1 if points to struct static_key_mod
  99  *          0 if points to struct jump_entry
 100  */
 101         union {
 102                 unsigned long type;
 103                 struct jump_entry *entries;
 104                 struct static_key_mod *next;
 105         };
 106 #endif  /* CONFIG_JUMP_LABEL */
 107 };
 108
 109 #endif /* __ASSEMBLY__ */
 110
 111 #ifdef CONFIG_JUMP_LABEL
 112 #include <asm/jump_label.h>
 113
 114 #ifndef __ASSEMBLY__
 115 #ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE
 116
 117 struct jump_entry {
 118         s32 code;
 119         s32 target;
 120         long key;       // key may be far away from the core kernel under KASLR
 121 };
 122
 123 static inline unsigned long jump_entry_code(const struct jump_entry *entry)
 124 {
 125         return (unsigned long)&entry->code + entry->code;
 126 }
 127
 128 static inline unsigned long jump_entry_target(const struct jump_entry *entry)
 129 {
 130         return (unsigned long)&entry->target + entry->target;
 131 }
 132
 133 static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
 134 {
 135         long offset = entry->key & ~3L;
 136
 137         return (struct static_key *)((unsigned long)&entry->key + offset);
 138 }
 139
 140 #else
 141
 142 static inline unsigned long jump_entry_code(const struct jump_entry *entry)
 143 {
 144         return entry->code;
 145 }
 146
 147 static inline unsigned long jump_entry_target(const struct jump_entry *entry)
 148 {
 149         return entry->target;
 150 }
 151
 152 static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
 153 {
 154         return (struct static_key *)((unsigned long)entry->key & ~3UL);
 155 }
 156
 157 #endif
 158
 159 static inline bool jump_entry_is_branch(const struct jump_entry *entry)
 160 {
 161         return (unsigned long)entry->key & 1UL;
 162 }
 163
 164 static inline bool jump_entry_is_init(const struct jump_entry *entry)
 165 {
 166         return (unsigned long)entry->key & 2UL;
 167 }
 168
 169 static inline void jump_entry_set_init(struct jump_entry *entry, bool set)
 170 {
 171         if (set)
 172                 entry->key |= 2;
 173         else
 174                 entry->key &= ~2;
 175 }
 176
 177 static inline int jump_entry_size(struct jump_entry *entry)
 178 {
 179 #ifdef JUMP_LABEL_NOP_SIZE
 180         return JUMP_LABEL_NOP_SIZE;
 181 #else
 182         return arch_jump_entry_size(entry);
 183 #endif
 184 }
 185
 186 #endif
 187 #endif
 188
 189 #ifndef __ASSEMBLY__
 190
 191 enum jump_label_type {
 192         JUMP_LABEL_NOP = 0,
 193         JUMP_LABEL_JMP,
 194 };
 195
 196 struct module;
 197
 198 #ifdef CONFIG_JUMP_LABEL
 199
 200 #define JUMP_TYPE_FALSE         0UL
 201 #define JUMP_TYPE_TRUE          1UL
 202 #define JUMP_TYPE_LINKED        2UL
 203 #define JUMP_TYPE_MASK          3UL
 204
 205 static __always_inline bool static_key_false(struct static_key *key)
 206 {
 207         return arch_static_branch(key, false);
 208 }
 209
 210 static __always_inline bool static_key_true(struct static_key *key)
 211 {
 212         return !arch_static_branch(key, true);
 213 }
 214
 215 extern struct jump_entry __start___jump_table[];
 216 extern struct jump_entry __stop___jump_table[];
 217
 218 extern void jump_label_init(void);
 219 extern void jump_label_lock(void);
 220 extern void jump_label_unlock(void);
 221 extern void arch_jump_label_transform(struct jump_entry *entry,
 222                                       enum jump_label_type type);
 223 extern bool arch_jump_label_transform_queue(struct jump_entry *entry,
 224                                             enum jump_label_type type);
 225 extern void arch_jump_label_transform_apply(void);
 226 extern int jump_label_text_reserved(void *start, void *end);
 227 extern bool static_key_slow_inc(struct static_key *key);
 228 extern bool static_key_fast_inc_not_disabled(struct static_key *key);
 229 extern void static_key_slow_dec(struct static_key *key);
 230 extern bool static_key_slow_inc_cpuslocked(struct static_key *key);
 231 extern void static_key_slow_dec_cpuslocked(struct static_key *key);
 232 extern int static_key_count(struct static_key *key);
 233 extern void static_key_enable(struct static_key *key);
 234 extern void static_key_disable(struct static_key *key);
 235 extern void static_key_enable_cpuslocked(struct static_key *key);
 236 extern void static_key_disable_cpuslocked(struct static_key *key);
 237 extern enum jump_label_type jump_label_init_type(struct jump_entry *entry);
 238
 239 /*
 240  * We should be using ATOMIC_INIT() for initializing .enabled, but
 241  * the inclusion of atomic.h is problematic for inclusion of jump_label.h
 242  * in 'low-level' headers. Thus, we are initializing .enabled with a
 243  * raw value, but have added a BUILD_BUG_ON() to catch any issues in
 244  * jump_label_init() see: kernel/jump_label.c.
 245  */
 246 #define STATIC_KEY_INIT_TRUE                                    \
 247         { .enabled = { 1 },                                     \
 248           { .type = JUMP_TYPE_TRUE } }
 249 #define STATIC_KEY_INIT_FALSE                                   \
 250         { .enabled = { 0 },                                     \
 251           { .type = JUMP_TYPE_FALSE } }
 252
 253 #else  /* !CONFIG_JUMP_LABEL */
 254
 255 #include <linux/atomic.h>
 256 #include <linux/bug.h>
 257
 258 static __always_inline int static_key_count(struct static_key *key)
 259 {
 260         return arch_atomic_read(&key->enabled);
 261 }
 262
 263 static __always_inline void jump_label_init(void)
 264 {
 265         static_key_initialized = true;
 266 }
 267
 268 static __always_inline bool static_key_false(struct static_key *key)
 269 {
 270         if (unlikely_notrace(static_key_count(key) > 0))
 271                 return true;
 272         return false;
 273 }
 274
 275 static __always_inline bool static_key_true(struct static_key *key)
 276 {
 277         if (likely_notrace(static_key_count(key) > 0))
 278                 return true;
 279         return false;
 280 }
 281
 282 static inline bool static_key_fast_inc_not_disabled(struct static_key *key)
 283 {
 284         int v;
 285
 286         STATIC_KEY_CHECK_USE(key);
 287         /*
 288          * Prevent key->enabled getting negative to follow the same semantics
 289          * as for CONFIG_JUMP_LABEL=y, see kernel/jump_label.c comment.
 290          */
 291         v = atomic_read(&key->enabled);
 292         do {
 293                 if (v < 0 || (v + 1) < 0)
 294                         return false;
 295         } while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1)));
 296         return true;
 297 }
 298 #define static_key_slow_inc(key)        static_key_fast_inc_not_disabled(key)
 299
 300 static inline void static_key_slow_dec(struct static_key *key)
 301 {
 302         STATIC_KEY_CHECK_USE(key);
 303         atomic_dec(&key->enabled);
 304 }
 305
 306 #define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key)
 307 #define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key)
 308
 309 static inline int jump_label_text_reserved(void *start, void *end)
 310 {
 311         return 0;
 312 }
 313
 314 static inline void jump_label_lock(void) {}
 315 static inline void jump_label_unlock(void) {}
 316
 317 static inline void static_key_enable(struct static_key *key)
 318 {
 319         STATIC_KEY_CHECK_USE(key);
 320
 321         if (atomic_read(&key->enabled) != 0) {
 322                 WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
 323                 return;
 324         }
 325         atomic_set(&key->enabled, 1);
 326 }
 327
 328 static inline void static_key_disable(struct static_key *key)
 329 {
 330         STATIC_KEY_CHECK_USE(key);
 331
 332         if (atomic_read(&key->enabled) != 1) {
 333                 WARN_ON_ONCE(atomic_read(&key->enabled) != 0);
 334                 return;
 335         }
 336         atomic_set(&key->enabled, 0);
 337 }
 338
 339 #define static_key_enable_cpuslocked(k)         static_key_enable((k))
 340 #define static_key_disable_cpuslocked(k)        static_key_disable((k))
 341
 342 #define STATIC_KEY_INIT_TRUE    { .enabled = ATOMIC_INIT(1) }
 343 #define STATIC_KEY_INIT_FALSE   { .enabled = ATOMIC_INIT(0) }
 344
 345 #endif  /* CONFIG_JUMP_LABEL */
 346
 347 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
 348 #define jump_label_enabled static_key_enabled
 349
 350 /* -------------------------------------------------------------------------- */
 351
 352 /*
 353  * Two type wrappers around static_key, such that we can use compile time
 354  * type differentiation to emit the right code.
 355  *
 356  * All the below code is macros in order to play type games.
 357  */
 358
 359 struct static_key_true {
 360         struct static_key key;
 361 };
 362
 363 struct static_key_false {
 364         struct static_key key;
 365 };
 366
 367 #define STATIC_KEY_TRUE_INIT  (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE,  }
 368 #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, }
 369
 370 #define DEFINE_STATIC_KEY_TRUE(name)    \
 371         struct static_key_true name = STATIC_KEY_TRUE_INIT
 372
 373 #define DEFINE_STATIC_KEY_TRUE_RO(name) \
 374         struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT
 375
 376 #define DECLARE_STATIC_KEY_TRUE(name)   \
 377         extern struct static_key_true name
 378
 379 #define DEFINE_STATIC_KEY_FALSE(name)   \
 380         struct static_key_false name = STATIC_KEY_FALSE_INIT
 381
 382 #define DEFINE_STATIC_KEY_FALSE_RO(name)        \
 383         struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT
 384
 385 #define DECLARE_STATIC_KEY_FALSE(name)  \
 386         extern struct static_key_false name
 387
 388 #define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count)               \
 389         struct static_key_true name[count] = {                  \
 390                 [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT,     \
 391         }
 392
 393 #define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count)              \
 394         struct static_key_false name[count] = {                 \
 395                 [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT,    \
 396         }
 397
 398 #define _DEFINE_STATIC_KEY_1(name)      DEFINE_STATIC_KEY_TRUE(name)
 399 #define _DEFINE_STATIC_KEY_0(name)      DEFINE_STATIC_KEY_FALSE(name)
 400 #define DEFINE_STATIC_KEY_MAYBE(cfg, name)                      \
 401         __PASTE(_DEFINE_STATIC_KEY_, IS_ENABLED(cfg))(name)
 402
 403 #define _DEFINE_STATIC_KEY_RO_1(name)   DEFINE_STATIC_KEY_TRUE_RO(name)
 404 #define _DEFINE_STATIC_KEY_RO_0(name)   DEFINE_STATIC_KEY_FALSE_RO(name)
 405 #define DEFINE_STATIC_KEY_MAYBE_RO(cfg, name)                   \
 406         __PASTE(_DEFINE_STATIC_KEY_RO_, IS_ENABLED(cfg))(name)
 407
 408 #define _DECLARE_STATIC_KEY_1(name)     DECLARE_STATIC_KEY_TRUE(name)
 409 #define _DECLARE_STATIC_KEY_0(name)     DECLARE_STATIC_KEY_FALSE(name)
 410 #define DECLARE_STATIC_KEY_MAYBE(cfg, name)                     \
 411         __PASTE(_DECLARE_STATIC_KEY_, IS_ENABLED(cfg))(name)
 412
 413 extern bool ____wrong_branch_error(void);
 414
 415 #define static_key_enabled(x)                                                   \
 416 ({                                                                              \
 417         if (!__builtin_types_compatible_p(typeof(*x), struct static_key) &&     \
 418             !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\
 419             !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
 420                 ____wrong_branch_error();                                       \
 421         static_key_count((struct static_key *)x) > 0;                           \
 422 })
 423
 424 #ifdef CONFIG_JUMP_LABEL
 425
 426 /*
 427  * Combine the right initial value (type) with the right branch order
 428  * to generate the desired result.
 429  *
 430  *
 431  * type\branch| likely (1)            | unlikely (0)
 432  * -----------+-----------------------+------------------
 433  *            |                       |
 434  *  true (1)  |    ...                |    ...
 435  *            |    NOP                |    JMP L
 436  *            |    <br-stmts>         | 1: ...
 437  *            | L: ...                |
 438  *            |                       |
 439  *            |                       | L: <br-stmts>
 440  *            |                       |    jmp 1b
 441  *            |                       |
 442  * -----------+-----------------------+------------------
 443  *            |                       |
 444  *  false (0) |    ...                |    ...
 445  *            |    JMP L              |    NOP
 446  *            |    <br-stmts>         | 1: ...
 447  *            | L: ...                |
 448  *            |                       |
 449  *            |                       | L: <br-stmts>
 450  *            |                       |    jmp 1b
 451  *            |                       |
 452  * -----------+-----------------------+------------------
 453  *
 454  * The initial value is encoded in the LSB of static_key::entries,
 455  * type: 0 = false, 1 = true.
 456  *
 457  * The branch type is encoded in the LSB of jump_entry::key,
 458  * branch: 0 = unlikely, 1 = likely.
 459  *
 460  * This gives the following logic table:
 461  *
 462  *      enabled type    branch    instuction
 463  * -----------------------------+-----------
 464  *      0       0       0       | NOP
 465  *      0       0       1       | JMP
 466  *      0       1       0       | NOP
 467  *      0       1       1       | JMP
 468  *
 469  *      1       0       0       | JMP
 470  *      1       0       1       | NOP
 471  *      1       1       0       | JMP
 472  *      1       1       1       | NOP
 473  *
 474  * Which gives the following functions:
 475  *
 476  *   dynamic: instruction = enabled ^ branch
 477  *   static:  instruction = type ^ branch
 478  *
 479  * See jump_label_type() / jump_label_init_type().
 480  */
 481
 482 #define static_branch_likely(x)                                                 \
 483 ({                                                                              \
 484         bool branch;                                                            \
 485         if (__builtin_types_compatible_p(typeof(*x), struct static_key_true))   \
 486                 branch = !arch_static_branch(&(x)->key, true);                  \
 487         else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
 488                 branch = !arch_static_branch_jump(&(x)->key, true);             \
 489         else                                                                    \
 490                 branch = ____wrong_branch_error();                              \
 491         likely_notrace(branch);                                                         \
 492 })
 493
 494 #define static_branch_unlikely(x)                                               \
 495 ({                                                                              \
 496         bool branch;                                                            \
 497         if (__builtin_types_compatible_p(typeof(*x), struct static_key_true))   \
 498                 branch = arch_static_branch_jump(&(x)->key, false);             \
 499         else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
 500                 branch = arch_static_branch(&(x)->key, false);                  \
 501         else                                                                    \
 502                 branch = ____wrong_branch_error();                              \
 503         unlikely_notrace(branch);                                                       \
 504 })
 505
 506 #else /* !CONFIG_JUMP_LABEL */
 507
 508 #define static_branch_likely(x)         likely_notrace(static_key_enabled(&(x)->key))
 509 #define static_branch_unlikely(x)       unlikely_notrace(static_key_enabled(&(x)->key))
 510
 511 #endif /* CONFIG_JUMP_LABEL */
 512
 513 #define static_branch_maybe(config, x)                                  \
 514         (IS_ENABLED(config) ? static_branch_likely(x)                   \
 515                             : static_branch_unlikely(x))
 516
 517 /*
 518  * Advanced usage; refcount, branch is enabled when: count != 0
 519  */
 520
 521 #define static_branch_inc(x)            static_key_slow_inc(&(x)->key)
 522 #define static_branch_dec(x)            static_key_slow_dec(&(x)->key)
 523 #define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key)
 524 #define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(x)->key)
 525
 526 /*
 527  * Normal usage; boolean enable/disable.
 528  */
 529
 530 #define static_branch_enable(x)                 static_key_enable(&(x)->key)
 531 #define static_branch_disable(x)                static_key_disable(&(x)->key)
 532 #define static_branch_enable_cpuslocked(x)      static_key_enable_cpuslocked(&(x)->key)
 533 #define static_branch_disable_cpuslocked(x)     static_key_disable_cpuslocked(&(x)->key)
 534
 535 #endif /* __ASSEMBLY__ */
 536
 537 #endif  /* _LINUX_JUMP_LABEL_H */