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
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
85#ifdef CONFIG_JUMP_LABEL
86
87struct 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
110struct 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
122struct jump_entry {
123 s32 code;
124 s32 target;
125 long key; // key may be far away from the core kernel under KASLR
126};
127
128static inline unsigned long jump_entry_code(const struct jump_entry *entry)
129{
130 return (unsigned long)&entry->code + entry->code;
131}
132
133static inline unsigned long jump_entry_target(const struct jump_entry *entry)
134{
135 return (unsigned long)&entry->target + entry->target;
136}
137
138static 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
147static inline unsigned long jump_entry_code(const struct jump_entry *entry)
148{
149 return entry->code;
150}
151
152static inline unsigned long jump_entry_target(const struct jump_entry *entry)
153{
154 return entry->target;
155}
156
157static 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
164static inline bool jump_entry_is_branch(const struct jump_entry *entry)
165{
166 return (unsigned long)entry->key & 1UL;
167}
168
169static inline bool jump_entry_is_init(const struct jump_entry *entry)
170{
171 return (unsigned long)entry->key & 2UL;
172}
173
174static 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
184enum jump_label_type {
185 JUMP_LABEL_NOP = 0,
186 JUMP_LABEL_JMP,
187};
188
189struct 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
198static __always_inline bool static_key_false(struct static_key *key)
199{
200 return arch_static_branch(key, false);
201}
202
203static __always_inline bool static_key_true(struct static_key *key)
204{
205 return !arch_static_branch(key, true);
206}
207
208extern struct jump_entry __start___jump_table[];
209extern struct jump_entry __stop___jump_table[];
210
211extern void jump_label_init(void);
212extern void jump_label_lock(void);
213extern void jump_label_unlock(void);
214extern void arch_jump_label_transform(struct jump_entry *entry,
215 enum jump_label_type type);
216extern void arch_jump_label_transform_static(struct jump_entry *entry,
217 enum jump_label_type type);
218extern int jump_label_text_reserved(void *start, void *end);
219extern void static_key_slow_inc(struct static_key *key);
220extern void static_key_slow_dec(struct static_key *key);
221extern void static_key_slow_inc_cpuslocked(struct static_key *key);
222extern void static_key_slow_dec_cpuslocked(struct static_key *key);
223extern void jump_label_apply_nops(struct module *mod);
224extern int static_key_count(struct static_key *key);
225extern void static_key_enable(struct static_key *key);
226extern void static_key_disable(struct static_key *key);
227extern void static_key_enable_cpuslocked(struct static_key *key);
228extern 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
249static inline int static_key_count(struct static_key *key)
250{
251 return atomic_read(&key->enabled);
252}
253
254static __always_inline void jump_label_init(void)
255{
256 static_key_initialized = true;
257}
258
259static __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
266static __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
273static inline void static_key_slow_inc(struct static_key *key)
274{
275 STATIC_KEY_CHECK_USE(key);
276 atomic_inc(&key->enabled);
277}
278
279static 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
288static inline int jump_label_text_reserved(void *start, void *end)
289{
290 return 0;
291}
292
293static inline void jump_label_lock(void) {}
294static inline void jump_label_unlock(void) {}
295
296static inline int jump_label_apply_nops(struct module *mod)
297{
298 return 0;
299}
300
301static 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
312static 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
343struct static_key_true {
344 struct static_key key;
345};
346
347struct 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
382extern 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 */
503