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 */
541
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