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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); | |
1975dbc2 JC |
24 | * static_branch_likely() |
25 | * static_branch_unlikely() | |
412758cb | 26 | * |
efb3040d | 27 | * Jump labels provide an interface to generate dynamic branches using |
412758cb JB |
28 | * self-modifying code. Assuming toolchain and architecture support, if we |
29 | * define a "key" that is initially false via "DEFINE_STATIC_KEY_FALSE(key)", | |
30 | * an "if (static_branch_unlikely(&key))" statement is an unconditional branch | |
31 | * (which defaults to false - and the true block is placed out of line). | |
32 | * Similarly, we can define an initially true key via | |
33 | * "DEFINE_STATIC_KEY_TRUE(key)", and use it in the same | |
34 | * "if (static_branch_unlikely(&key))", in which case we will generate an | |
35 | * unconditional branch to the out-of-line true branch. Keys that are | |
36 | * initially true or false can be using in both static_branch_unlikely() | |
37 | * and static_branch_likely() statements. | |
efb3040d | 38 | * |
412758cb JB |
39 | * At runtime we can change the branch target by setting the key |
40 | * to true via a call to static_branch_enable(), or false using | |
41 | * static_branch_disable(). If the direction of the branch is switched by | |
42 | * these calls then we run-time modify the branch target via a | |
43 | * no-op -> jump or jump -> no-op conversion. For example, for an | |
44 | * initially false key that is used in an "if (static_branch_unlikely(&key))" | |
45 | * statement, setting the key to true requires us to patch in a jump | |
46 | * to the out-of-line of true branch. | |
efb3040d | 47 | * |
1975dbc2 | 48 | * In addition to static_branch_{enable,disable}, we can also reference count |
412758cb JB |
49 | * the key or branch direction via static_branch_{inc,dec}. Thus, |
50 | * static_branch_inc() can be thought of as a 'make more true' and | |
1975dbc2 | 51 | * static_branch_dec() as a 'make more false'. |
412758cb JB |
52 | * |
53 | * Since this relies on modifying code, the branch modifying functions | |
efb3040d | 54 | * must be considered absolute slow paths (machine wide synchronization etc.). |
fd3cbdc0 | 55 | * OTOH, since the affected branches are unconditional, their runtime overhead |
efb3040d PZ |
56 | * will be absolutely minimal, esp. in the default (off) case where the total |
57 | * effect is a single NOP of appropriate size. The on case will patch in a jump | |
58 | * to the out-of-line block. | |
59 | * | |
fd3cbdc0 | 60 | * When the control is directly exposed to userspace, it is prudent to delay the |
efb3040d | 61 | * decrement to avoid high frequency code modifications which can (and do) |
c5905afb IM |
62 | * cause significant performance degradation. Struct static_key_deferred and |
63 | * static_key_slow_dec_deferred() provide for this. | |
efb3040d | 64 | * |
412758cb JB |
65 | * Lacking toolchain and or architecture support, static keys fall back to a |
66 | * simple conditional branch. | |
c5905afb | 67 | * |
412758cb | 68 | * Additional babbling in: Documentation/static-keys.txt |
fd3cbdc0 | 69 | */ |
efb3040d | 70 | |
c0ccf6f9 AB |
71 | #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL) |
72 | # define HAVE_JUMP_LABEL | |
73 | #endif | |
74 | ||
75 | #ifndef __ASSEMBLY__ | |
76 | ||
d430d3d7 JB |
77 | #include <linux/types.h> |
78 | #include <linux/compiler.h> | |
c4b2c0c5 HFS |
79 | |
80 | extern bool static_key_initialized; | |
81 | ||
82 | #define STATIC_KEY_CHECK_USE() WARN(!static_key_initialized, \ | |
83 | "%s used before call to jump_label_init", \ | |
84 | __func__) | |
d430d3d7 | 85 | |
c0ccf6f9 | 86 | #ifdef HAVE_JUMP_LABEL |
d430d3d7 | 87 | |
c5905afb | 88 | struct static_key { |
d430d3d7 | 89 | atomic_t enabled; |
c5905afb | 90 | /* Set lsb bit to 1 if branch is default true, 0 ot */ |
d430d3d7 JB |
91 | struct jump_entry *entries; |
92 | #ifdef CONFIG_MODULES | |
c5905afb | 93 | struct static_key_mod *next; |
d430d3d7 JB |
94 | #endif |
95 | }; | |
96 | ||
ea5e9539 MG |
97 | #else |
98 | struct static_key { | |
99 | atomic_t enabled; | |
100 | }; | |
c0ccf6f9 AB |
101 | #endif /* HAVE_JUMP_LABEL */ |
102 | #endif /* __ASSEMBLY__ */ | |
103 | ||
104 | #ifdef HAVE_JUMP_LABEL | |
105 | #include <asm/jump_label.h> | |
106 | #endif | |
107 | ||
108 | #ifndef __ASSEMBLY__ | |
bf5438fc JB |
109 | |
110 | enum jump_label_type { | |
76b235c6 PZ |
111 | JUMP_LABEL_NOP = 0, |
112 | JUMP_LABEL_JMP, | |
bf5438fc JB |
113 | }; |
114 | ||
115 | struct module; | |
116 | ||
4c5ea0a9 PB |
117 | #ifdef HAVE_JUMP_LABEL |
118 | ||
a1efb01f PZ |
119 | #define JUMP_TYPE_FALSE 0UL |
120 | #define JUMP_TYPE_TRUE 1UL | |
121 | #define JUMP_TYPE_MASK 1UL | |
c5905afb IM |
122 | |
123 | static __always_inline bool static_key_false(struct static_key *key) | |
124 | { | |
11276d53 | 125 | return arch_static_branch(key, false); |
c5905afb | 126 | } |
d430d3d7 | 127 | |
c5905afb IM |
128 | static __always_inline bool static_key_true(struct static_key *key) |
129 | { | |
11276d53 | 130 | return !arch_static_branch(key, true); |
c5905afb IM |
131 | } |
132 | ||
bf5438fc JB |
133 | extern struct jump_entry __start___jump_table[]; |
134 | extern struct jump_entry __stop___jump_table[]; | |
135 | ||
97ce2c88 | 136 | extern void jump_label_init(void); |
91bad2f8 JB |
137 | extern void jump_label_lock(void); |
138 | extern void jump_label_unlock(void); | |
bf5438fc | 139 | extern void arch_jump_label_transform(struct jump_entry *entry, |
37348804 | 140 | enum jump_label_type type); |
20284aa7 JF |
141 | extern void arch_jump_label_transform_static(struct jump_entry *entry, |
142 | enum jump_label_type type); | |
4c3ef6d7 | 143 | extern int jump_label_text_reserved(void *start, void *end); |
c5905afb IM |
144 | extern void static_key_slow_inc(struct static_key *key); |
145 | extern void static_key_slow_dec(struct static_key *key); | |
d430d3d7 | 146 | extern void jump_label_apply_nops(struct module *mod); |
1f69bf9c JB |
147 | extern int static_key_count(struct static_key *key); |
148 | extern void static_key_enable(struct static_key *key); | |
149 | extern void static_key_disable(struct static_key *key); | |
c5905afb | 150 | |
1f69bf9c JB |
151 | /* |
152 | * We should be using ATOMIC_INIT() for initializing .enabled, but | |
153 | * the inclusion of atomic.h is problematic for inclusion of jump_label.h | |
154 | * in 'low-level' headers. Thus, we are initializing .enabled with a | |
155 | * raw value, but have added a BUILD_BUG_ON() to catch any issues in | |
156 | * jump_label_init() see: kernel/jump_label.c. | |
157 | */ | |
11276d53 | 158 | #define STATIC_KEY_INIT_TRUE \ |
1f69bf9c | 159 | { .enabled = { 1 }, \ |
11276d53 PZ |
160 | .entries = (void *)JUMP_TYPE_TRUE } |
161 | #define STATIC_KEY_INIT_FALSE \ | |
1f69bf9c | 162 | { .enabled = { 0 }, \ |
11276d53 | 163 | .entries = (void *)JUMP_TYPE_FALSE } |
bf5438fc | 164 | |
97ce2c88 | 165 | #else /* !HAVE_JUMP_LABEL */ |
bf5438fc | 166 | |
1f69bf9c JB |
167 | #include <linux/atomic.h> |
168 | #include <linux/bug.h> | |
169 | ||
4c5ea0a9 PB |
170 | static inline int static_key_count(struct static_key *key) |
171 | { | |
172 | return atomic_read(&key->enabled); | |
173 | } | |
174 | ||
97ce2c88 JF |
175 | static __always_inline void jump_label_init(void) |
176 | { | |
c4b2c0c5 | 177 | static_key_initialized = true; |
97ce2c88 JF |
178 | } |
179 | ||
c5905afb IM |
180 | static __always_inline bool static_key_false(struct static_key *key) |
181 | { | |
ea5e9539 | 182 | if (unlikely(static_key_count(key) > 0)) |
c5905afb IM |
183 | return true; |
184 | return false; | |
185 | } | |
186 | ||
187 | static __always_inline bool static_key_true(struct static_key *key) | |
d430d3d7 | 188 | { |
ea5e9539 | 189 | if (likely(static_key_count(key) > 0)) |
d430d3d7 JB |
190 | return true; |
191 | return false; | |
192 | } | |
bf5438fc | 193 | |
c5905afb | 194 | static inline void static_key_slow_inc(struct static_key *key) |
d430d3d7 | 195 | { |
c4b2c0c5 | 196 | STATIC_KEY_CHECK_USE(); |
d430d3d7 JB |
197 | atomic_inc(&key->enabled); |
198 | } | |
bf5438fc | 199 | |
c5905afb | 200 | static inline void static_key_slow_dec(struct static_key *key) |
bf5438fc | 201 | { |
c4b2c0c5 | 202 | STATIC_KEY_CHECK_USE(); |
d430d3d7 | 203 | atomic_dec(&key->enabled); |
bf5438fc JB |
204 | } |
205 | ||
4c3ef6d7 JB |
206 | static inline int jump_label_text_reserved(void *start, void *end) |
207 | { | |
208 | return 0; | |
209 | } | |
210 | ||
91bad2f8 JB |
211 | static inline void jump_label_lock(void) {} |
212 | static inline void jump_label_unlock(void) {} | |
213 | ||
d430d3d7 JB |
214 | static inline int jump_label_apply_nops(struct module *mod) |
215 | { | |
216 | return 0; | |
217 | } | |
b2029520 | 218 | |
e33886b3 PZ |
219 | static inline void static_key_enable(struct static_key *key) |
220 | { | |
221 | int count = static_key_count(key); | |
222 | ||
223 | WARN_ON_ONCE(count < 0 || count > 1); | |
224 | ||
225 | if (!count) | |
226 | static_key_slow_inc(key); | |
227 | } | |
228 | ||
229 | static inline void static_key_disable(struct static_key *key) | |
230 | { | |
231 | int count = static_key_count(key); | |
232 | ||
233 | WARN_ON_ONCE(count < 0 || count > 1); | |
234 | ||
235 | if (count) | |
236 | static_key_slow_dec(key); | |
237 | } | |
238 | ||
1f69bf9c JB |
239 | #define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) } |
240 | #define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) } | |
241 | ||
242 | #endif /* HAVE_JUMP_LABEL */ | |
243 | ||
244 | #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE | |
245 | #define jump_label_enabled static_key_enabled | |
246 | ||
11276d53 PZ |
247 | /* -------------------------------------------------------------------------- */ |
248 | ||
249 | /* | |
250 | * Two type wrappers around static_key, such that we can use compile time | |
251 | * type differentiation to emit the right code. | |
252 | * | |
253 | * All the below code is macros in order to play type games. | |
254 | */ | |
255 | ||
256 | struct static_key_true { | |
257 | struct static_key key; | |
258 | }; | |
259 | ||
260 | struct static_key_false { | |
261 | struct static_key key; | |
262 | }; | |
263 | ||
264 | #define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, } | |
265 | #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, } | |
266 | ||
267 | #define DEFINE_STATIC_KEY_TRUE(name) \ | |
268 | struct static_key_true name = STATIC_KEY_TRUE_INIT | |
269 | ||
270 | #define DEFINE_STATIC_KEY_FALSE(name) \ | |
271 | struct static_key_false name = STATIC_KEY_FALSE_INIT | |
272 | ||
fa128fd7 TH |
273 | extern bool ____wrong_branch_error(void); |
274 | ||
275 | #define static_key_enabled(x) \ | |
276 | ({ \ | |
277 | if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \ | |
278 | !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\ | |
279 | !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ | |
280 | ____wrong_branch_error(); \ | |
281 | static_key_count((struct static_key *)x) > 0; \ | |
282 | }) | |
283 | ||
11276d53 PZ |
284 | #ifdef HAVE_JUMP_LABEL |
285 | ||
286 | /* | |
287 | * Combine the right initial value (type) with the right branch order | |
288 | * to generate the desired result. | |
289 | * | |
290 | * | |
291 | * type\branch| likely (1) | unlikely (0) | |
292 | * -----------+-----------------------+------------------ | |
293 | * | | | |
294 | * true (1) | ... | ... | |
295 | * | NOP | JMP L | |
296 | * | <br-stmts> | 1: ... | |
297 | * | L: ... | | |
298 | * | | | |
299 | * | | L: <br-stmts> | |
300 | * | | jmp 1b | |
301 | * | | | |
302 | * -----------+-----------------------+------------------ | |
303 | * | | | |
304 | * false (0) | ... | ... | |
305 | * | JMP L | NOP | |
306 | * | <br-stmts> | 1: ... | |
307 | * | L: ... | | |
308 | * | | | |
309 | * | | L: <br-stmts> | |
310 | * | | jmp 1b | |
311 | * | | | |
312 | * -----------+-----------------------+------------------ | |
313 | * | |
314 | * The initial value is encoded in the LSB of static_key::entries, | |
315 | * type: 0 = false, 1 = true. | |
316 | * | |
317 | * The branch type is encoded in the LSB of jump_entry::key, | |
318 | * branch: 0 = unlikely, 1 = likely. | |
319 | * | |
320 | * This gives the following logic table: | |
321 | * | |
322 | * enabled type branch instuction | |
323 | * -----------------------------+----------- | |
324 | * 0 0 0 | NOP | |
325 | * 0 0 1 | JMP | |
326 | * 0 1 0 | NOP | |
327 | * 0 1 1 | JMP | |
328 | * | |
329 | * 1 0 0 | JMP | |
330 | * 1 0 1 | NOP | |
331 | * 1 1 0 | JMP | |
332 | * 1 1 1 | NOP | |
333 | * | |
334 | * Which gives the following functions: | |
335 | * | |
336 | * dynamic: instruction = enabled ^ branch | |
337 | * static: instruction = type ^ branch | |
338 | * | |
339 | * See jump_label_type() / jump_label_init_type(). | |
340 | */ | |
341 | ||
11276d53 PZ |
342 | #define static_branch_likely(x) \ |
343 | ({ \ | |
344 | bool branch; \ | |
345 | if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ | |
346 | branch = !arch_static_branch(&(x)->key, true); \ | |
347 | else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ | |
348 | branch = !arch_static_branch_jump(&(x)->key, true); \ | |
349 | else \ | |
350 | branch = ____wrong_branch_error(); \ | |
351 | branch; \ | |
352 | }) | |
353 | ||
354 | #define static_branch_unlikely(x) \ | |
355 | ({ \ | |
356 | bool branch; \ | |
357 | if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ | |
358 | branch = arch_static_branch_jump(&(x)->key, false); \ | |
359 | else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ | |
360 | branch = arch_static_branch(&(x)->key, false); \ | |
361 | else \ | |
362 | branch = ____wrong_branch_error(); \ | |
363 | branch; \ | |
364 | }) | |
365 | ||
366 | #else /* !HAVE_JUMP_LABEL */ | |
367 | ||
368 | #define static_branch_likely(x) likely(static_key_enabled(&(x)->key)) | |
369 | #define static_branch_unlikely(x) unlikely(static_key_enabled(&(x)->key)) | |
370 | ||
371 | #endif /* HAVE_JUMP_LABEL */ | |
372 | ||
373 | /* | |
374 | * Advanced usage; refcount, branch is enabled when: count != 0 | |
375 | */ | |
376 | ||
377 | #define static_branch_inc(x) static_key_slow_inc(&(x)->key) | |
378 | #define static_branch_dec(x) static_key_slow_dec(&(x)->key) | |
379 | ||
380 | /* | |
381 | * Normal usage; boolean enable/disable. | |
382 | */ | |
383 | ||
384 | #define static_branch_enable(x) static_key_enable(&(x)->key) | |
385 | #define static_branch_disable(x) static_key_disable(&(x)->key) | |
386 | ||
97ce2c88 | 387 | #endif /* _LINUX_JUMP_LABEL_H */ |
c0ccf6f9 AB |
388 | |
389 | #endif /* __ASSEMBLY__ */ |