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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 bool arch_jump_label_transform_queue(struct jump_entry *entry, | |
219 | enum jump_label_type type); | |
220 | extern void arch_jump_label_transform_apply(void); | |
221 | extern int jump_label_text_reserved(void *start, void *end); | |
222 | extern void static_key_slow_inc(struct static_key *key); | |
223 | extern void static_key_slow_dec(struct static_key *key); | |
224 | extern void static_key_slow_inc_cpuslocked(struct static_key *key); | |
225 | extern void static_key_slow_dec_cpuslocked(struct static_key *key); | |
226 | extern void jump_label_apply_nops(struct module *mod); | |
227 | extern int static_key_count(struct static_key *key); | |
228 | extern void static_key_enable(struct static_key *key); | |
229 | extern void static_key_disable(struct static_key *key); | |
230 | extern void static_key_enable_cpuslocked(struct static_key *key); | |
231 | extern void static_key_disable_cpuslocked(struct static_key *key); | |
232 | ||
233 | /* | |
234 | * We should be using ATOMIC_INIT() for initializing .enabled, but | |
235 | * the inclusion of atomic.h is problematic for inclusion of jump_label.h | |
236 | * in 'low-level' headers. Thus, we are initializing .enabled with a | |
237 | * raw value, but have added a BUILD_BUG_ON() to catch any issues in | |
238 | * jump_label_init() see: kernel/jump_label.c. | |
239 | */ | |
240 | #define STATIC_KEY_INIT_TRUE \ | |
241 | { .enabled = { 1 }, \ | |
242 | { .entries = (void *)JUMP_TYPE_TRUE } } | |
243 | #define STATIC_KEY_INIT_FALSE \ | |
244 | { .enabled = { 0 }, \ | |
245 | { .entries = (void *)JUMP_TYPE_FALSE } } | |
246 | ||
247 | #else /* !CONFIG_JUMP_LABEL */ | |
248 | ||
249 | #include <linux/atomic.h> | |
250 | #include <linux/bug.h> | |
251 | ||
252 | static inline int static_key_count(struct static_key *key) | |
253 | { | |
254 | return atomic_read(&key->enabled); | |
255 | } | |
256 | ||
257 | static __always_inline void jump_label_init(void) | |
258 | { | |
259 | static_key_initialized = true; | |
260 | } | |
261 | ||
262 | static __always_inline bool static_key_false(struct static_key *key) | |
263 | { | |
264 | if (unlikely(static_key_count(key) > 0)) | |
265 | return true; | |
266 | return false; | |
267 | } | |
268 | ||
269 | static __always_inline bool static_key_true(struct static_key *key) | |
270 | { | |
271 | if (likely(static_key_count(key) > 0)) | |
272 | return true; | |
273 | return false; | |
274 | } | |
275 | ||
276 | static inline void static_key_slow_inc(struct static_key *key) | |
277 | { | |
278 | STATIC_KEY_CHECK_USE(key); | |
279 | atomic_inc(&key->enabled); | |
280 | } | |
281 | ||
282 | static inline void static_key_slow_dec(struct static_key *key) | |
283 | { | |
284 | STATIC_KEY_CHECK_USE(key); | |
285 | atomic_dec(&key->enabled); | |
286 | } | |
287 | ||
288 | #define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key) | |
289 | #define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key) | |
290 | ||
291 | static inline int jump_label_text_reserved(void *start, void *end) | |
292 | { | |
293 | return 0; | |
294 | } | |
295 | ||
296 | static inline void jump_label_lock(void) {} | |
297 | static inline void jump_label_unlock(void) {} | |
298 | ||
299 | static inline int jump_label_apply_nops(struct module *mod) | |
300 | { | |
301 | return 0; | |
302 | } | |
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 | extern bool ____wrong_branch_error(void); | |
386 | ||
387 | #define static_key_enabled(x) \ | |
388 | ({ \ | |
389 | if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \ | |
390 | !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\ | |
391 | !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ | |
392 | ____wrong_branch_error(); \ | |
393 | static_key_count((struct static_key *)x) > 0; \ | |
394 | }) | |
395 | ||
396 | #ifdef CONFIG_JUMP_LABEL | |
397 | ||
398 | /* | |
399 | * Combine the right initial value (type) with the right branch order | |
400 | * to generate the desired result. | |
401 | * | |
402 | * | |
403 | * type\branch| likely (1) | unlikely (0) | |
404 | * -----------+-----------------------+------------------ | |
405 | * | | | |
406 | * true (1) | ... | ... | |
407 | * | NOP | JMP L | |
408 | * | <br-stmts> | 1: ... | |
409 | * | L: ... | | |
410 | * | | | |
411 | * | | L: <br-stmts> | |
412 | * | | jmp 1b | |
413 | * | | | |
414 | * -----------+-----------------------+------------------ | |
415 | * | | | |
416 | * false (0) | ... | ... | |
417 | * | JMP L | NOP | |
418 | * | <br-stmts> | 1: ... | |
419 | * | L: ... | | |
420 | * | | | |
421 | * | | L: <br-stmts> | |
422 | * | | jmp 1b | |
423 | * | | | |
424 | * -----------+-----------------------+------------------ | |
425 | * | |
426 | * The initial value is encoded in the LSB of static_key::entries, | |
427 | * type: 0 = false, 1 = true. | |
428 | * | |
429 | * The branch type is encoded in the LSB of jump_entry::key, | |
430 | * branch: 0 = unlikely, 1 = likely. | |
431 | * | |
432 | * This gives the following logic table: | |
433 | * | |
434 | * enabled type branch instuction | |
435 | * -----------------------------+----------- | |
436 | * 0 0 0 | NOP | |
437 | * 0 0 1 | JMP | |
438 | * 0 1 0 | NOP | |
439 | * 0 1 1 | JMP | |
440 | * | |
441 | * 1 0 0 | JMP | |
442 | * 1 0 1 | NOP | |
443 | * 1 1 0 | JMP | |
444 | * 1 1 1 | NOP | |
445 | * | |
446 | * Which gives the following functions: | |
447 | * | |
448 | * dynamic: instruction = enabled ^ branch | |
449 | * static: instruction = type ^ branch | |
450 | * | |
451 | * See jump_label_type() / jump_label_init_type(). | |
452 | */ | |
453 | ||
454 | #define static_branch_likely(x) \ | |
455 | ({ \ | |
456 | bool branch; \ | |
457 | if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ | |
458 | branch = !arch_static_branch(&(x)->key, true); \ | |
459 | else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ | |
460 | branch = !arch_static_branch_jump(&(x)->key, true); \ | |
461 | else \ | |
462 | branch = ____wrong_branch_error(); \ | |
463 | likely(branch); \ | |
464 | }) | |
465 | ||
466 | #define static_branch_unlikely(x) \ | |
467 | ({ \ | |
468 | bool branch; \ | |
469 | if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ | |
470 | branch = arch_static_branch_jump(&(x)->key, false); \ | |
471 | else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ | |
472 | branch = arch_static_branch(&(x)->key, false); \ | |
473 | else \ | |
474 | branch = ____wrong_branch_error(); \ | |
475 | unlikely(branch); \ | |
476 | }) | |
477 | ||
478 | #else /* !CONFIG_JUMP_LABEL */ | |
479 | ||
480 | #define static_branch_likely(x) likely(static_key_enabled(&(x)->key)) | |
481 | #define static_branch_unlikely(x) unlikely(static_key_enabled(&(x)->key)) | |
482 | ||
483 | #endif /* CONFIG_JUMP_LABEL */ | |
484 | ||
485 | /* | |
486 | * Advanced usage; refcount, branch is enabled when: count != 0 | |
487 | */ | |
488 | ||
489 | #define static_branch_inc(x) static_key_slow_inc(&(x)->key) | |
490 | #define static_branch_dec(x) static_key_slow_dec(&(x)->key) | |
491 | #define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key) | |
492 | #define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(x)->key) | |
493 | ||
494 | /* | |
495 | * Normal usage; boolean enable/disable. | |
496 | */ | |
497 | ||
498 | #define static_branch_enable(x) static_key_enable(&(x)->key) | |
499 | #define static_branch_disable(x) static_key_disable(&(x)->key) | |
500 | #define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key) | |
501 | #define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key) | |
502 | ||
503 | #endif /* __ASSEMBLY__ */ | |
504 | ||
505 | #endif /* _LINUX_JUMP_LABEL_H */ |