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bf5438fc JB |
1 | #ifndef _LINUX_JUMP_LABEL_H |
2 | #define _LINUX_JUMP_LABEL_H | |
3 | ||
efb3040d PZ |
4 | /* |
5 | * Jump label support | |
6 | * | |
7 | * Copyright (C) 2009-2012 Jason Baron <jbaron@redhat.com> | |
90eec103 | 8 | * Copyright (C) 2011-2012 Red Hat, Inc., Peter Zijlstra |
efb3040d | 9 | * |
412758cb JB |
10 | * DEPRECATED API: |
11 | * | |
12 | * The use of 'struct static_key' directly, is now DEPRECATED. In addition | |
13 | * static_key_{true,false}() is also DEPRECATED. IE DO NOT use the following: | |
14 | * | |
15 | * struct static_key false = STATIC_KEY_INIT_FALSE; | |
16 | * struct static_key true = STATIC_KEY_INIT_TRUE; | |
17 | * static_key_true() | |
18 | * static_key_false() | |
19 | * | |
20 | * The updated API replacements are: | |
21 | * | |
22 | * DEFINE_STATIC_KEY_TRUE(key); | |
23 | * DEFINE_STATIC_KEY_FALSE(key); | |
ef0da55a CM |
24 | * DEFINE_STATIC_KEY_ARRAY_TRUE(keys, count); |
25 | * DEFINE_STATIC_KEY_ARRAY_FALSE(keys, count); | |
1975dbc2 JC |
26 | * static_branch_likely() |
27 | * static_branch_unlikely() | |
412758cb | 28 | * |
efb3040d | 29 | * Jump labels provide an interface to generate dynamic branches using |
412758cb JB |
30 | * self-modifying code. Assuming toolchain and architecture support, if we |
31 | * define a "key" that is initially false via "DEFINE_STATIC_KEY_FALSE(key)", | |
32 | * an "if (static_branch_unlikely(&key))" statement is an unconditional branch | |
33 | * (which defaults to false - and the true block is placed out of line). | |
34 | * Similarly, we can define an initially true key via | |
35 | * "DEFINE_STATIC_KEY_TRUE(key)", and use it in the same | |
36 | * "if (static_branch_unlikely(&key))", in which case we will generate an | |
37 | * unconditional branch to the out-of-line true branch. Keys that are | |
38 | * initially true or false can be using in both static_branch_unlikely() | |
39 | * and static_branch_likely() statements. | |
efb3040d | 40 | * |
412758cb JB |
41 | * At runtime we can change the branch target by setting the key |
42 | * to true via a call to static_branch_enable(), or false using | |
43 | * static_branch_disable(). If the direction of the branch is switched by | |
44 | * these calls then we run-time modify the branch target via a | |
45 | * no-op -> jump or jump -> no-op conversion. For example, for an | |
46 | * initially false key that is used in an "if (static_branch_unlikely(&key))" | |
47 | * statement, setting the key to true requires us to patch in a jump | |
48 | * to the out-of-line of true branch. | |
efb3040d | 49 | * |
1975dbc2 | 50 | * In addition to static_branch_{enable,disable}, we can also reference count |
412758cb JB |
51 | * the key or branch direction via static_branch_{inc,dec}. Thus, |
52 | * static_branch_inc() can be thought of as a 'make more true' and | |
1975dbc2 | 53 | * static_branch_dec() as a 'make more false'. |
412758cb JB |
54 | * |
55 | * Since this relies on modifying code, the branch modifying functions | |
efb3040d | 56 | * must be considered absolute slow paths (machine wide synchronization etc.). |
fd3cbdc0 | 57 | * OTOH, since the affected branches are unconditional, their runtime overhead |
efb3040d PZ |
58 | * will be absolutely minimal, esp. in the default (off) case where the total |
59 | * effect is a single NOP of appropriate size. The on case will patch in a jump | |
60 | * to the out-of-line block. | |
61 | * | |
fd3cbdc0 | 62 | * When the control is directly exposed to userspace, it is prudent to delay the |
efb3040d | 63 | * decrement to avoid high frequency code modifications which can (and do) |
c5905afb IM |
64 | * cause significant performance degradation. Struct static_key_deferred and |
65 | * static_key_slow_dec_deferred() provide for this. | |
efb3040d | 66 | * |
412758cb JB |
67 | * Lacking toolchain and or architecture support, static keys fall back to a |
68 | * simple conditional branch. | |
c5905afb | 69 | * |
412758cb | 70 | * Additional babbling in: Documentation/static-keys.txt |
fd3cbdc0 | 71 | */ |
efb3040d | 72 | |
c0ccf6f9 AB |
73 | #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL) |
74 | # define HAVE_JUMP_LABEL | |
75 | #endif | |
76 | ||
77 | #ifndef __ASSEMBLY__ | |
78 | ||
d430d3d7 JB |
79 | #include <linux/types.h> |
80 | #include <linux/compiler.h> | |
c4b2c0c5 HFS |
81 | |
82 | extern bool static_key_initialized; | |
83 | ||
84 | #define STATIC_KEY_CHECK_USE() WARN(!static_key_initialized, \ | |
85 | "%s used before call to jump_label_init", \ | |
86 | __func__) | |
d430d3d7 | 87 | |
c0ccf6f9 | 88 | #ifdef HAVE_JUMP_LABEL |
d430d3d7 | 89 | |
c5905afb | 90 | struct static_key { |
d430d3d7 | 91 | atomic_t enabled; |
3821fd35 | 92 | /* |
b17ef2ed SRV |
93 | * Note: |
94 | * To make anonymous unions work with old compilers, the static | |
95 | * initialization of them requires brackets. This creates a dependency | |
96 | * on the order of the struct with the initializers. If any fields | |
97 | * are added, STATIC_KEY_INIT_TRUE and STATIC_KEY_INIT_FALSE may need | |
98 | * to be modified. | |
99 | * | |
3821fd35 JB |
100 | * bit 0 => 1 if key is initially true |
101 | * 0 if initially false | |
102 | * bit 1 => 1 if points to struct static_key_mod | |
103 | * 0 if points to struct jump_entry | |
104 | */ | |
105 | union { | |
106 | unsigned long type; | |
107 | struct jump_entry *entries; | |
108 | struct static_key_mod *next; | |
109 | }; | |
d430d3d7 JB |
110 | }; |
111 | ||
ea5e9539 MG |
112 | #else |
113 | struct static_key { | |
114 | atomic_t enabled; | |
115 | }; | |
c0ccf6f9 AB |
116 | #endif /* HAVE_JUMP_LABEL */ |
117 | #endif /* __ASSEMBLY__ */ | |
118 | ||
119 | #ifdef HAVE_JUMP_LABEL | |
120 | #include <asm/jump_label.h> | |
121 | #endif | |
122 | ||
123 | #ifndef __ASSEMBLY__ | |
bf5438fc JB |
124 | |
125 | enum jump_label_type { | |
76b235c6 PZ |
126 | JUMP_LABEL_NOP = 0, |
127 | JUMP_LABEL_JMP, | |
bf5438fc JB |
128 | }; |
129 | ||
130 | struct module; | |
131 | ||
4c5ea0a9 PB |
132 | #ifdef HAVE_JUMP_LABEL |
133 | ||
3821fd35 JB |
134 | #define JUMP_TYPE_FALSE 0UL |
135 | #define JUMP_TYPE_TRUE 1UL | |
136 | #define JUMP_TYPE_LINKED 2UL | |
137 | #define JUMP_TYPE_MASK 3UL | |
c5905afb IM |
138 | |
139 | static __always_inline bool static_key_false(struct static_key *key) | |
140 | { | |
11276d53 | 141 | return arch_static_branch(key, false); |
c5905afb | 142 | } |
d430d3d7 | 143 | |
c5905afb IM |
144 | static __always_inline bool static_key_true(struct static_key *key) |
145 | { | |
11276d53 | 146 | return !arch_static_branch(key, true); |
c5905afb IM |
147 | } |
148 | ||
bf5438fc JB |
149 | extern struct jump_entry __start___jump_table[]; |
150 | extern struct jump_entry __stop___jump_table[]; | |
151 | ||
97ce2c88 | 152 | extern void jump_label_init(void); |
91bad2f8 JB |
153 | extern void jump_label_lock(void); |
154 | extern void jump_label_unlock(void); | |
bf5438fc | 155 | extern void arch_jump_label_transform(struct jump_entry *entry, |
37348804 | 156 | enum jump_label_type type); |
20284aa7 JF |
157 | extern void arch_jump_label_transform_static(struct jump_entry *entry, |
158 | enum jump_label_type type); | |
4c3ef6d7 | 159 | extern int jump_label_text_reserved(void *start, void *end); |
c5905afb IM |
160 | extern void static_key_slow_inc(struct static_key *key); |
161 | extern void static_key_slow_dec(struct static_key *key); | |
d430d3d7 | 162 | extern void jump_label_apply_nops(struct module *mod); |
1f69bf9c JB |
163 | extern int static_key_count(struct static_key *key); |
164 | extern void static_key_enable(struct static_key *key); | |
165 | extern void static_key_disable(struct static_key *key); | |
c5905afb | 166 | |
1f69bf9c JB |
167 | /* |
168 | * We should be using ATOMIC_INIT() for initializing .enabled, but | |
169 | * the inclusion of atomic.h is problematic for inclusion of jump_label.h | |
170 | * in 'low-level' headers. Thus, we are initializing .enabled with a | |
171 | * raw value, but have added a BUILD_BUG_ON() to catch any issues in | |
172 | * jump_label_init() see: kernel/jump_label.c. | |
173 | */ | |
11276d53 | 174 | #define STATIC_KEY_INIT_TRUE \ |
1f69bf9c | 175 | { .enabled = { 1 }, \ |
cd8d860d | 176 | { .entries = (void *)JUMP_TYPE_TRUE } } |
11276d53 | 177 | #define STATIC_KEY_INIT_FALSE \ |
1f69bf9c | 178 | { .enabled = { 0 }, \ |
cd8d860d | 179 | { .entries = (void *)JUMP_TYPE_FALSE } } |
bf5438fc | 180 | |
97ce2c88 | 181 | #else /* !HAVE_JUMP_LABEL */ |
bf5438fc | 182 | |
1f69bf9c JB |
183 | #include <linux/atomic.h> |
184 | #include <linux/bug.h> | |
185 | ||
4c5ea0a9 PB |
186 | static inline int static_key_count(struct static_key *key) |
187 | { | |
188 | return atomic_read(&key->enabled); | |
189 | } | |
190 | ||
97ce2c88 JF |
191 | static __always_inline void jump_label_init(void) |
192 | { | |
c4b2c0c5 | 193 | static_key_initialized = true; |
97ce2c88 JF |
194 | } |
195 | ||
c5905afb IM |
196 | static __always_inline bool static_key_false(struct static_key *key) |
197 | { | |
ea5e9539 | 198 | if (unlikely(static_key_count(key) > 0)) |
c5905afb IM |
199 | return true; |
200 | return false; | |
201 | } | |
202 | ||
203 | static __always_inline bool static_key_true(struct static_key *key) | |
d430d3d7 | 204 | { |
ea5e9539 | 205 | if (likely(static_key_count(key) > 0)) |
d430d3d7 JB |
206 | return true; |
207 | return false; | |
208 | } | |
bf5438fc | 209 | |
c5905afb | 210 | static inline void static_key_slow_inc(struct static_key *key) |
d430d3d7 | 211 | { |
c4b2c0c5 | 212 | STATIC_KEY_CHECK_USE(); |
d430d3d7 JB |
213 | atomic_inc(&key->enabled); |
214 | } | |
bf5438fc | 215 | |
c5905afb | 216 | static inline void static_key_slow_dec(struct static_key *key) |
bf5438fc | 217 | { |
c4b2c0c5 | 218 | STATIC_KEY_CHECK_USE(); |
d430d3d7 | 219 | atomic_dec(&key->enabled); |
bf5438fc JB |
220 | } |
221 | ||
4c3ef6d7 JB |
222 | static inline int jump_label_text_reserved(void *start, void *end) |
223 | { | |
224 | return 0; | |
225 | } | |
226 | ||
91bad2f8 JB |
227 | static inline void jump_label_lock(void) {} |
228 | static inline void jump_label_unlock(void) {} | |
229 | ||
d430d3d7 JB |
230 | static inline int jump_label_apply_nops(struct module *mod) |
231 | { | |
232 | return 0; | |
233 | } | |
b2029520 | 234 | |
e33886b3 PZ |
235 | static inline void static_key_enable(struct static_key *key) |
236 | { | |
237 | int count = static_key_count(key); | |
238 | ||
239 | WARN_ON_ONCE(count < 0 || count > 1); | |
240 | ||
241 | if (!count) | |
242 | static_key_slow_inc(key); | |
243 | } | |
244 | ||
245 | static inline void static_key_disable(struct static_key *key) | |
246 | { | |
247 | int count = static_key_count(key); | |
248 | ||
249 | WARN_ON_ONCE(count < 0 || count > 1); | |
250 | ||
251 | if (count) | |
252 | static_key_slow_dec(key); | |
253 | } | |
254 | ||
1f69bf9c JB |
255 | #define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) } |
256 | #define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) } | |
257 | ||
258 | #endif /* HAVE_JUMP_LABEL */ | |
259 | ||
260 | #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE | |
261 | #define jump_label_enabled static_key_enabled | |
262 | ||
11276d53 PZ |
263 | /* -------------------------------------------------------------------------- */ |
264 | ||
265 | /* | |
266 | * Two type wrappers around static_key, such that we can use compile time | |
267 | * type differentiation to emit the right code. | |
268 | * | |
269 | * All the below code is macros in order to play type games. | |
270 | */ | |
271 | ||
272 | struct static_key_true { | |
273 | struct static_key key; | |
274 | }; | |
275 | ||
276 | struct static_key_false { | |
277 | struct static_key key; | |
278 | }; | |
279 | ||
280 | #define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, } | |
281 | #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, } | |
282 | ||
283 | #define DEFINE_STATIC_KEY_TRUE(name) \ | |
284 | struct static_key_true name = STATIC_KEY_TRUE_INIT | |
285 | ||
b8fb0378 TL |
286 | #define DECLARE_STATIC_KEY_TRUE(name) \ |
287 | extern struct static_key_true name | |
288 | ||
11276d53 PZ |
289 | #define DEFINE_STATIC_KEY_FALSE(name) \ |
290 | struct static_key_false name = STATIC_KEY_FALSE_INIT | |
291 | ||
b8fb0378 TL |
292 | #define DECLARE_STATIC_KEY_FALSE(name) \ |
293 | extern struct static_key_false name | |
294 | ||
ef0da55a CM |
295 | #define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count) \ |
296 | struct static_key_true name[count] = { \ | |
297 | [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT, \ | |
298 | } | |
299 | ||
300 | #define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count) \ | |
301 | struct static_key_false name[count] = { \ | |
302 | [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT, \ | |
303 | } | |
304 | ||
fa128fd7 TH |
305 | extern bool ____wrong_branch_error(void); |
306 | ||
307 | #define static_key_enabled(x) \ | |
308 | ({ \ | |
309 | if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \ | |
310 | !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\ | |
311 | !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ | |
312 | ____wrong_branch_error(); \ | |
313 | static_key_count((struct static_key *)x) > 0; \ | |
314 | }) | |
315 | ||
11276d53 PZ |
316 | #ifdef HAVE_JUMP_LABEL |
317 | ||
318 | /* | |
319 | * Combine the right initial value (type) with the right branch order | |
320 | * to generate the desired result. | |
321 | * | |
322 | * | |
323 | * type\branch| likely (1) | unlikely (0) | |
324 | * -----------+-----------------------+------------------ | |
325 | * | | | |
326 | * true (1) | ... | ... | |
327 | * | NOP | JMP L | |
328 | * | <br-stmts> | 1: ... | |
329 | * | L: ... | | |
330 | * | | | |
331 | * | | L: <br-stmts> | |
332 | * | | jmp 1b | |
333 | * | | | |
334 | * -----------+-----------------------+------------------ | |
335 | * | | | |
336 | * false (0) | ... | ... | |
337 | * | JMP L | NOP | |
338 | * | <br-stmts> | 1: ... | |
339 | * | L: ... | | |
340 | * | | | |
341 | * | | L: <br-stmts> | |
342 | * | | jmp 1b | |
343 | * | | | |
344 | * -----------+-----------------------+------------------ | |
345 | * | |
346 | * The initial value is encoded in the LSB of static_key::entries, | |
347 | * type: 0 = false, 1 = true. | |
348 | * | |
349 | * The branch type is encoded in the LSB of jump_entry::key, | |
350 | * branch: 0 = unlikely, 1 = likely. | |
351 | * | |
352 | * This gives the following logic table: | |
353 | * | |
354 | * enabled type branch instuction | |
355 | * -----------------------------+----------- | |
356 | * 0 0 0 | NOP | |
357 | * 0 0 1 | JMP | |
358 | * 0 1 0 | NOP | |
359 | * 0 1 1 | JMP | |
360 | * | |
361 | * 1 0 0 | JMP | |
362 | * 1 0 1 | NOP | |
363 | * 1 1 0 | JMP | |
364 | * 1 1 1 | NOP | |
365 | * | |
366 | * Which gives the following functions: | |
367 | * | |
368 | * dynamic: instruction = enabled ^ branch | |
369 | * static: instruction = type ^ branch | |
370 | * | |
371 | * See jump_label_type() / jump_label_init_type(). | |
372 | */ | |
373 | ||
11276d53 PZ |
374 | #define static_branch_likely(x) \ |
375 | ({ \ | |
376 | bool branch; \ | |
377 | if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ | |
378 | branch = !arch_static_branch(&(x)->key, true); \ | |
379 | else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ | |
380 | branch = !arch_static_branch_jump(&(x)->key, true); \ | |
381 | else \ | |
382 | branch = ____wrong_branch_error(); \ | |
383 | branch; \ | |
384 | }) | |
385 | ||
386 | #define static_branch_unlikely(x) \ | |
387 | ({ \ | |
388 | bool branch; \ | |
389 | if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ | |
390 | branch = arch_static_branch_jump(&(x)->key, false); \ | |
391 | else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ | |
392 | branch = arch_static_branch(&(x)->key, false); \ | |
393 | else \ | |
394 | branch = ____wrong_branch_error(); \ | |
395 | branch; \ | |
396 | }) | |
397 | ||
398 | #else /* !HAVE_JUMP_LABEL */ | |
399 | ||
400 | #define static_branch_likely(x) likely(static_key_enabled(&(x)->key)) | |
401 | #define static_branch_unlikely(x) unlikely(static_key_enabled(&(x)->key)) | |
402 | ||
403 | #endif /* HAVE_JUMP_LABEL */ | |
404 | ||
405 | /* | |
406 | * Advanced usage; refcount, branch is enabled when: count != 0 | |
407 | */ | |
408 | ||
409 | #define static_branch_inc(x) static_key_slow_inc(&(x)->key) | |
410 | #define static_branch_dec(x) static_key_slow_dec(&(x)->key) | |
411 | ||
412 | /* | |
413 | * Normal usage; boolean enable/disable. | |
414 | */ | |
415 | ||
416 | #define static_branch_enable(x) static_key_enable(&(x)->key) | |
417 | #define static_branch_disable(x) static_key_disable(&(x)->key) | |
418 | ||
c0ccf6f9 | 419 | #endif /* __ASSEMBLY__ */ |
85b36c93 LR |
420 | |
421 | #endif /* _LINUX_JUMP_LABEL_H */ |