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
79extern 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
85struct 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
117struct jump_entry {
118 s32 code;
119 s32 target;
120 long key; // key may be far away from the core kernel under KASLR
121};
122
123static inline unsigned long jump_entry_code(const struct jump_entry *entry)
124{
125 return (unsigned long)&entry->code + entry->code;
126}
127
128static inline unsigned long jump_entry_target(const struct jump_entry *entry)
129{
130 return (unsigned long)&entry->target + entry->target;
131}
132
133static 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
142static inline unsigned long jump_entry_code(const struct jump_entry *entry)
143{
144 return entry->code;
145}
146
147static inline unsigned long jump_entry_target(const struct jump_entry *entry)
148{
149 return entry->target;
150}
151
152static 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
159static inline bool jump_entry_is_branch(const struct jump_entry *entry)
160{
161 return (unsigned long)entry->key & 1UL;
162}
163
164static inline bool jump_entry_is_init(const struct jump_entry *entry)
165{
166 return (unsigned long)entry->key & 2UL;
167}
168
169static 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
177static 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
191enum jump_label_type {
192 JUMP_LABEL_NOP = 0,
193 JUMP_LABEL_JMP,
194};
195
196struct 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
205static __always_inline bool static_key_false(struct static_key *key)
206{
207 return arch_static_branch(key, branch: false);
208}
209
210static __always_inline bool static_key_true(struct static_key *key)
211{
212 return !arch_static_branch(key, branch: true);
213}
214
215extern struct jump_entry __start___jump_table[];
216extern struct jump_entry __stop___jump_table[];
217
218extern void jump_label_init(void);
219extern void jump_label_lock(void);
220extern void jump_label_unlock(void);
221extern void arch_jump_label_transform(struct jump_entry *entry,
222 enum jump_label_type type);
223extern bool arch_jump_label_transform_queue(struct jump_entry *entry,
224 enum jump_label_type type);
225extern void arch_jump_label_transform_apply(void);
226extern int jump_label_text_reserved(void *start, void *end);
227extern bool static_key_slow_inc(struct static_key *key);
228extern bool static_key_fast_inc_not_disabled(struct static_key *key);
229extern void static_key_slow_dec(struct static_key *key);
230extern bool static_key_slow_inc_cpuslocked(struct static_key *key);
231extern void static_key_slow_dec_cpuslocked(struct static_key *key);
232extern int static_key_count(struct static_key *key);
233extern void static_key_enable(struct static_key *key);
234extern void static_key_disable(struct static_key *key);
235extern void static_key_enable_cpuslocked(struct static_key *key);
236extern void static_key_disable_cpuslocked(struct static_key *key);
237extern 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
258static __always_inline int static_key_count(struct static_key *key)
259{
260 return raw_atomic_read(&key->enabled);
261}
262
263static __always_inline void jump_label_init(void)
264{
265 static_key_initialized = true;
266}
267
268static __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
275static __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
282static 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
300static 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
309static inline int jump_label_text_reserved(void *start, void *end)
310{
311 return 0;
312}
313
314static inline void jump_label_lock(void) {}
315static inline void jump_label_unlock(void) {}
316
317static 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
328static 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
359struct static_key_true {
360 struct static_key key;
361};
362
363struct 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
413extern 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 */
538

source code of linux/include/linux/jump_label.h