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_init_ro(void);
 220 extern void jump_label_lock(void);
 221 extern void jump_label_unlock(void);
 222 extern void arch_jump_label_transform(struct jump_entry *entry,
 223                                       enum jump_label_type type);
 224 extern bool arch_jump_label_transform_queue(struct jump_entry *entry,
 225                                             enum jump_label_type type);
 226 extern void arch_jump_label_transform_apply(void);
 227 extern int jump_label_text_reserved(void *start, void *end);
 228 extern bool static_key_slow_inc(struct static_key *key);
 229 extern bool static_key_fast_inc_not_disabled(struct static_key *key);
 230 extern void static_key_slow_dec(struct static_key *key);
 231 extern bool static_key_slow_inc_cpuslocked(struct static_key *key);
 232 extern void static_key_slow_dec_cpuslocked(struct static_key *key);
 233 extern int static_key_count(struct static_key *key);
 234 extern void static_key_enable(struct static_key *key);
 235 extern void static_key_disable(struct static_key *key);
 236 extern void static_key_enable_cpuslocked(struct static_key *key);
 237 extern void static_key_disable_cpuslocked(struct static_key *key);
 238 extern enum jump_label_type jump_label_init_type(struct jump_entry *entry);
 239
 240 /*
 241  * We should be using ATOMIC_INIT() for initializing .enabled, but
 242  * the inclusion of atomic.h is problematic for inclusion of jump_label.h
 243  * in 'low-level' headers. Thus, we are initializing .enabled with a
 244  * raw value, but have added a BUILD_BUG_ON() to catch any issues in
 245  * jump_label_init() see: kernel/jump_label.c.
 246  */
 247 #define STATIC_KEY_INIT_TRUE                                    \
 248         { .enabled = { 1 },                                     \
 249           { .type = JUMP_TYPE_TRUE } }
 250 #define STATIC_KEY_INIT_FALSE                                   \
 251         { .enabled = { 0 },                                     \
 252           { .type = JUMP_TYPE_FALSE } }
 253
 254 #else  /* !CONFIG_JUMP_LABEL */
 255
 256 #include <linux/atomic.h>
 257 #include <linux/bug.h>
 258
 259 static __always_inline int static_key_count(struct static_key *key)
 260 {
 261         return raw_atomic_read(&key->enabled);
 262 }
 263
 264 static __always_inline void jump_label_init(void)
 265 {
 266         static_key_initialized = true;
 267 }
 268
 269 static __always_inline void jump_label_init_ro(void) { }
 270
 271 static __always_inline bool static_key_false(struct static_key *key)
 272 {
 273         if (unlikely_notrace(static_key_count(key) > 0))
 274                 return true;
 275         return false;
 276 }
 277
 278 static __always_inline bool static_key_true(struct static_key *key)
 279 {
 280         if (likely_notrace(static_key_count(key) > 0))
 281                 return true;
 282         return false;
 283 }
 284
 285 static inline bool static_key_fast_inc_not_disabled(struct static_key *key)
 286 {
 287         int v;
 288
 289         STATIC_KEY_CHECK_USE(key);
 290         /*
 291          * Prevent key->enabled getting negative to follow the same semantics
 292          * as for CONFIG_JUMP_LABEL=y, see kernel/jump_label.c comment.
 293          */
 294         v = atomic_read(&key->enabled);
 295         do {
 296                 if (v < 0 || (v + 1) < 0)
 297                         return false;
 298         } while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1)));
 299         return true;
 300 }
 301 #define static_key_slow_inc(key)        static_key_fast_inc_not_disabled(key)
 302
 303 static inline void static_key_slow_dec(struct static_key *key)
 304 {
 305         STATIC_KEY_CHECK_USE(key);
 306         atomic_dec(&key->enabled);
 307 }
 308
 309 #define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key)
 310 #define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key)
 311
 312 static inline int jump_label_text_reserved(void *start, void *end)
 313 {
 314         return 0;
 315 }
 316
 317 static inline void jump_label_lock(void) {}
 318 static inline void jump_label_unlock(void) {}
 319
 320 static inline void static_key_enable(struct static_key *key)
 321 {
 322         STATIC_KEY_CHECK_USE(key);
 323
 324         if (atomic_read(&key->enabled) != 0) {
 325                 WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
 326                 return;
 327         }
 328         atomic_set(&key->enabled, 1);
 329 }
 330
 331 static inline void static_key_disable(struct static_key *key)
 332 {
 333         STATIC_KEY_CHECK_USE(key);
 334
 335         if (atomic_read(&key->enabled) != 1) {
 336                 WARN_ON_ONCE(atomic_read(&key->enabled) != 0);
 337                 return;
 338         }
 339         atomic_set(&key->enabled, 0);
 340 }
 341
 342 #define static_key_enable_cpuslocked(k)         static_key_enable((k))
 343 #define static_key_disable_cpuslocked(k)        static_key_disable((k))
 344
 345 #define STATIC_KEY_INIT_TRUE    { .enabled = ATOMIC_INIT(1) }
 346 #define STATIC_KEY_INIT_FALSE   { .enabled = ATOMIC_INIT(0) }
 347
 348 #endif  /* CONFIG_JUMP_LABEL */
 349
 350 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
 351 #define jump_label_enabled static_key_enabled
 352
 353 /* -------------------------------------------------------------------------- */
 354
 355 /*
 356  * Two type wrappers around static_key, such that we can use compile time
 357  * type differentiation to emit the right code.
 358  *
 359  * All the below code is macros in order to play type games.
 360  */
 361
 362 struct static_key_true {
 363         struct static_key key;
 364 };
 365
 366 struct static_key_false {
 367         struct static_key key;
 368 };
 369
 370 #define STATIC_KEY_TRUE_INIT  (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE,  }
 371 #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, }
 372
 373 #define DEFINE_STATIC_KEY_TRUE(name)    \
 374         struct static_key_true name = STATIC_KEY_TRUE_INIT
 375
 376 #define DEFINE_STATIC_KEY_TRUE_RO(name) \
 377         struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT
 378
 379 #define DECLARE_STATIC_KEY_TRUE(name)   \
 380         extern struct static_key_true name
 381
 382 #define DEFINE_STATIC_KEY_FALSE(name)   \
 383         struct static_key_false name = STATIC_KEY_FALSE_INIT
 384
 385 #define DEFINE_STATIC_KEY_FALSE_RO(name)        \
 386         struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT
 387
 388 #define DECLARE_STATIC_KEY_FALSE(name)  \
 389         extern struct static_key_false name
 390
 391 #define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count)               \
 392         struct static_key_true name[count] = {                  \
 393                 [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT,     \
 394         }
 395
 396 #define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count)              \
 397         struct static_key_false name[count] = {                 \
 398                 [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT,    \
 399         }
 400
 401 #define _DEFINE_STATIC_KEY_1(name)      DEFINE_STATIC_KEY_TRUE(name)
 402 #define _DEFINE_STATIC_KEY_0(name)      DEFINE_STATIC_KEY_FALSE(name)
 403 #define DEFINE_STATIC_KEY_MAYBE(cfg, name)                      \
 404         __PASTE(_DEFINE_STATIC_KEY_, IS_ENABLED(cfg))(name)
 405
 406 #define _DEFINE_STATIC_KEY_RO_1(name)   DEFINE_STATIC_KEY_TRUE_RO(name)
 407 #define _DEFINE_STATIC_KEY_RO_0(name)   DEFINE_STATIC_KEY_FALSE_RO(name)
 408 #define DEFINE_STATIC_KEY_MAYBE_RO(cfg, name)                   \
 409         __PASTE(_DEFINE_STATIC_KEY_RO_, IS_ENABLED(cfg))(name)
 410
 411 #define _DECLARE_STATIC_KEY_1(name)     DECLARE_STATIC_KEY_TRUE(name)
 412 #define _DECLARE_STATIC_KEY_0(name)     DECLARE_STATIC_KEY_FALSE(name)
 413 #define DECLARE_STATIC_KEY_MAYBE(cfg, name)                     \
 414         __PASTE(_DECLARE_STATIC_KEY_, IS_ENABLED(cfg))(name)
 415
 416 extern bool ____wrong_branch_error(void);
 417
 418 #define static_key_enabled(x)                                                   \
 419 ({                                                                              \
 420         if (!__builtin_types_compatible_p(typeof(*x), struct static_key) &&     \
 421             !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\
 422             !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
 423                 ____wrong_branch_error();                                       \
 424         static_key_count((struct static_key *)x) > 0;                           \
 425 })
 426
 427 #ifdef CONFIG_JUMP_LABEL
 428
 429 /*
 430  * Combine the right initial value (type) with the right branch order
 431  * to generate the desired result.
 432  *
 433  *
 434  * type\branch| likely (1)            | unlikely (0)
 435  * -----------+-----------------------+------------------
 436  *            |                       |
 437  *  true (1)  |    ...                |    ...
 438  *            |    NOP                |    JMP L
 439  *            |    <br-stmts>         | 1: ...
 440  *            | L: ...                |
 441  *            |                       |
 442  *            |                       | L: <br-stmts>
 443  *            |                       |    jmp 1b
 444  *            |                       |
 445  * -----------+-----------------------+------------------
 446  *            |                       |
 447  *  false (0) |    ...                |    ...
 448  *            |    JMP L              |    NOP
 449  *            |    <br-stmts>         | 1: ...
 450  *            | L: ...                |
 451  *            |                       |
 452  *            |                       | L: <br-stmts>
 453  *            |                       |    jmp 1b
 454  *            |                       |
 455  * -----------+-----------------------+------------------
 456  *
 457  * The initial value is encoded in the LSB of static_key::entries,
 458  * type: 0 = false, 1 = true.
 459  *
 460  * The branch type is encoded in the LSB of jump_entry::key,
 461  * branch: 0 = unlikely, 1 = likely.
 462  *
 463  * This gives the following logic table:
 464  *
 465  *      enabled type    branch    instuction
 466  * -----------------------------+-----------
 467  *      0       0       0       | NOP
 468  *      0       0       1       | JMP
 469  *      0       1       0       | NOP
 470  *      0       1       1       | JMP
 471  *
 472  *      1       0       0       | JMP
 473  *      1       0       1       | NOP
 474  *      1       1       0       | JMP
 475  *      1       1       1       | NOP
 476  *
 477  * Which gives the following functions:
 478  *
 479  *   dynamic: instruction = enabled ^ branch
 480  *   static:  instruction = type ^ branch
 481  *
 482  * See jump_label_type() / jump_label_init_type().
 483  */
 484
 485 #define static_branch_likely(x)                                                 \
 486 ({                                                                              \
 487         bool branch;                                                            \
 488         if (__builtin_types_compatible_p(typeof(*x), struct static_key_true))   \
 489                 branch = !arch_static_branch(&(x)->key, true);                  \
 490         else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
 491                 branch = !arch_static_branch_jump(&(x)->key, true);             \
 492         else                                                                    \
 493                 branch = ____wrong_branch_error();                              \
 494         likely_notrace(branch);                                                         \
 495 })
 496
 497 #define static_branch_unlikely(x)                                               \
 498 ({                                                                              \
 499         bool branch;                                                            \
 500         if (__builtin_types_compatible_p(typeof(*x), struct static_key_true))   \
 501                 branch = arch_static_branch_jump(&(x)->key, false);             \
 502         else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
 503                 branch = arch_static_branch(&(x)->key, false);                  \
 504         else                                                                    \
 505                 branch = ____wrong_branch_error();                              \
 506         unlikely_notrace(branch);                                                       \
 507 })
 508
 509 #else /* !CONFIG_JUMP_LABEL */
 510
 511 #define static_branch_likely(x)         likely_notrace(static_key_enabled(&(x)->key))
 512 #define static_branch_unlikely(x)       unlikely_notrace(static_key_enabled(&(x)->key))
 513
 514 #endif /* CONFIG_JUMP_LABEL */
 515
 516 #define static_branch_maybe(config, x)                                  \
 517         (IS_ENABLED(config) ? static_branch_likely(x)                   \
 518                             : static_branch_unlikely(x))
 519
 520 /*
 521  * Advanced usage; refcount, branch is enabled when: count != 0
 522  */
 523
 524 #define static_branch_inc(x)            static_key_slow_inc(&(x)->key)
 525 #define static_branch_dec(x)            static_key_slow_dec(&(x)->key)
 526 #define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key)
 527 #define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(x)->key)
 528
 529 /*
 530  * Normal usage; boolean enable/disable.
 531  */
 532
 533 #define static_branch_enable(x)                 static_key_enable(&(x)->key)
 534 #define static_branch_disable(x)                static_key_disable(&(x)->key)
 535 #define static_branch_enable_cpuslocked(x)      static_key_enable_cpuslocked(&(x)->key)
 536 #define static_branch_disable_cpuslocked(x)     static_key_disable_cpuslocked(&(x)->key)
 537
 538 #endif /* __ASSEMBLY__ */
 539
 540 #endif  /* _LINUX_JUMP_LABEL_H */