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