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