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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> | |
8 | * Copyright (C) 2011-2012 Peter Zijlstra <pzijlstr@redhat.com> | |
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 | #include <linux/bug.h> |
80 | ||
81 | extern bool static_key_initialized; | |
82 | ||
83 | #define STATIC_KEY_CHECK_USE() WARN(!static_key_initialized, \ | |
84 | "%s used before call to jump_label_init", \ | |
85 | __func__) | |
d430d3d7 | 86 | |
c0ccf6f9 | 87 | #ifdef HAVE_JUMP_LABEL |
d430d3d7 | 88 | |
c5905afb | 89 | struct static_key { |
d430d3d7 | 90 | atomic_t enabled; |
c5905afb | 91 | /* Set lsb bit to 1 if branch is default true, 0 ot */ |
d430d3d7 JB |
92 | struct jump_entry *entries; |
93 | #ifdef CONFIG_MODULES | |
c5905afb | 94 | struct static_key_mod *next; |
d430d3d7 JB |
95 | #endif |
96 | }; | |
97 | ||
ea5e9539 MG |
98 | #else |
99 | struct static_key { | |
100 | atomic_t enabled; | |
101 | }; | |
c0ccf6f9 AB |
102 | #endif /* HAVE_JUMP_LABEL */ |
103 | #endif /* __ASSEMBLY__ */ | |
104 | ||
105 | #ifdef HAVE_JUMP_LABEL | |
106 | #include <asm/jump_label.h> | |
107 | #endif | |
108 | ||
109 | #ifndef __ASSEMBLY__ | |
bf5438fc JB |
110 | |
111 | enum jump_label_type { | |
76b235c6 PZ |
112 | JUMP_LABEL_NOP = 0, |
113 | JUMP_LABEL_JMP, | |
bf5438fc JB |
114 | }; |
115 | ||
116 | struct module; | |
117 | ||
851cf6e7 | 118 | #include <linux/atomic.h> |
ea5e9539 MG |
119 | |
120 | static inline int static_key_count(struct static_key *key) | |
121 | { | |
122 | return atomic_read(&key->enabled); | |
123 | } | |
124 | ||
bf5438fc JB |
125 | #ifdef HAVE_JUMP_LABEL |
126 | ||
a1efb01f PZ |
127 | #define JUMP_TYPE_FALSE 0UL |
128 | #define JUMP_TYPE_TRUE 1UL | |
129 | #define JUMP_TYPE_MASK 1UL | |
c5905afb IM |
130 | |
131 | static __always_inline bool static_key_false(struct static_key *key) | |
132 | { | |
11276d53 | 133 | return arch_static_branch(key, false); |
c5905afb | 134 | } |
d430d3d7 | 135 | |
c5905afb IM |
136 | static __always_inline bool static_key_true(struct static_key *key) |
137 | { | |
11276d53 | 138 | return !arch_static_branch(key, true); |
c5905afb IM |
139 | } |
140 | ||
bf5438fc JB |
141 | extern struct jump_entry __start___jump_table[]; |
142 | extern struct jump_entry __stop___jump_table[]; | |
143 | ||
97ce2c88 | 144 | extern void jump_label_init(void); |
91bad2f8 JB |
145 | extern void jump_label_lock(void); |
146 | extern void jump_label_unlock(void); | |
bf5438fc | 147 | extern void arch_jump_label_transform(struct jump_entry *entry, |
37348804 | 148 | enum jump_label_type type); |
20284aa7 JF |
149 | extern void arch_jump_label_transform_static(struct jump_entry *entry, |
150 | enum jump_label_type type); | |
4c3ef6d7 | 151 | extern int jump_label_text_reserved(void *start, void *end); |
c5905afb IM |
152 | extern void static_key_slow_inc(struct static_key *key); |
153 | extern void static_key_slow_dec(struct static_key *key); | |
d430d3d7 | 154 | extern void jump_label_apply_nops(struct module *mod); |
c5905afb | 155 | |
11276d53 | 156 | #define STATIC_KEY_INIT_TRUE \ |
f4be8433 | 157 | { .enabled = ATOMIC_INIT(1), \ |
11276d53 PZ |
158 | .entries = (void *)JUMP_TYPE_TRUE } |
159 | #define STATIC_KEY_INIT_FALSE \ | |
f4be8433 | 160 | { .enabled = ATOMIC_INIT(0), \ |
11276d53 | 161 | .entries = (void *)JUMP_TYPE_FALSE } |
bf5438fc | 162 | |
97ce2c88 | 163 | #else /* !HAVE_JUMP_LABEL */ |
bf5438fc | 164 | |
97ce2c88 JF |
165 | static __always_inline void jump_label_init(void) |
166 | { | |
c4b2c0c5 | 167 | static_key_initialized = true; |
97ce2c88 JF |
168 | } |
169 | ||
c5905afb IM |
170 | static __always_inline bool static_key_false(struct static_key *key) |
171 | { | |
ea5e9539 | 172 | if (unlikely(static_key_count(key) > 0)) |
c5905afb IM |
173 | return true; |
174 | return false; | |
175 | } | |
176 | ||
177 | static __always_inline bool static_key_true(struct static_key *key) | |
d430d3d7 | 178 | { |
ea5e9539 | 179 | if (likely(static_key_count(key) > 0)) |
d430d3d7 JB |
180 | return true; |
181 | return false; | |
182 | } | |
bf5438fc | 183 | |
c5905afb | 184 | static inline void static_key_slow_inc(struct static_key *key) |
d430d3d7 | 185 | { |
c4b2c0c5 | 186 | STATIC_KEY_CHECK_USE(); |
d430d3d7 JB |
187 | atomic_inc(&key->enabled); |
188 | } | |
bf5438fc | 189 | |
c5905afb | 190 | static inline void static_key_slow_dec(struct static_key *key) |
bf5438fc | 191 | { |
c4b2c0c5 | 192 | STATIC_KEY_CHECK_USE(); |
d430d3d7 | 193 | atomic_dec(&key->enabled); |
bf5438fc JB |
194 | } |
195 | ||
4c3ef6d7 JB |
196 | static inline int jump_label_text_reserved(void *start, void *end) |
197 | { | |
198 | return 0; | |
199 | } | |
200 | ||
91bad2f8 JB |
201 | static inline void jump_label_lock(void) {} |
202 | static inline void jump_label_unlock(void) {} | |
203 | ||
d430d3d7 JB |
204 | static inline int jump_label_apply_nops(struct module *mod) |
205 | { | |
206 | return 0; | |
207 | } | |
b2029520 | 208 | |
11276d53 PZ |
209 | #define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) } |
210 | #define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) } | |
c5905afb | 211 | |
97ce2c88 | 212 | #endif /* HAVE_JUMP_LABEL */ |
d430d3d7 | 213 | |
c5905afb IM |
214 | #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE |
215 | #define jump_label_enabled static_key_enabled | |
ac99b862 | 216 | |
8eedce99 JB |
217 | static inline bool static_key_enabled(struct static_key *key) |
218 | { | |
ea5e9539 | 219 | return static_key_count(key) > 0; |
8eedce99 JB |
220 | } |
221 | ||
e33886b3 PZ |
222 | static inline void static_key_enable(struct static_key *key) |
223 | { | |
224 | int count = static_key_count(key); | |
225 | ||
226 | WARN_ON_ONCE(count < 0 || count > 1); | |
227 | ||
228 | if (!count) | |
229 | static_key_slow_inc(key); | |
230 | } | |
231 | ||
232 | static inline void static_key_disable(struct static_key *key) | |
233 | { | |
234 | int count = static_key_count(key); | |
235 | ||
236 | WARN_ON_ONCE(count < 0 || count > 1); | |
237 | ||
238 | if (count) | |
239 | static_key_slow_dec(key); | |
240 | } | |
241 | ||
11276d53 PZ |
242 | /* -------------------------------------------------------------------------- */ |
243 | ||
244 | /* | |
245 | * Two type wrappers around static_key, such that we can use compile time | |
246 | * type differentiation to emit the right code. | |
247 | * | |
248 | * All the below code is macros in order to play type games. | |
249 | */ | |
250 | ||
251 | struct static_key_true { | |
252 | struct static_key key; | |
253 | }; | |
254 | ||
255 | struct static_key_false { | |
256 | struct static_key key; | |
257 | }; | |
258 | ||
259 | #define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, } | |
260 | #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, } | |
261 | ||
262 | #define DEFINE_STATIC_KEY_TRUE(name) \ | |
263 | struct static_key_true name = STATIC_KEY_TRUE_INIT | |
264 | ||
265 | #define DEFINE_STATIC_KEY_FALSE(name) \ | |
266 | struct static_key_false name = STATIC_KEY_FALSE_INIT | |
267 | ||
268 | #ifdef HAVE_JUMP_LABEL | |
269 | ||
270 | /* | |
271 | * Combine the right initial value (type) with the right branch order | |
272 | * to generate the desired result. | |
273 | * | |
274 | * | |
275 | * type\branch| likely (1) | unlikely (0) | |
276 | * -----------+-----------------------+------------------ | |
277 | * | | | |
278 | * true (1) | ... | ... | |
279 | * | NOP | JMP L | |
280 | * | <br-stmts> | 1: ... | |
281 | * | L: ... | | |
282 | * | | | |
283 | * | | L: <br-stmts> | |
284 | * | | jmp 1b | |
285 | * | | | |
286 | * -----------+-----------------------+------------------ | |
287 | * | | | |
288 | * false (0) | ... | ... | |
289 | * | JMP L | NOP | |
290 | * | <br-stmts> | 1: ... | |
291 | * | L: ... | | |
292 | * | | | |
293 | * | | L: <br-stmts> | |
294 | * | | jmp 1b | |
295 | * | | | |
296 | * -----------+-----------------------+------------------ | |
297 | * | |
298 | * The initial value is encoded in the LSB of static_key::entries, | |
299 | * type: 0 = false, 1 = true. | |
300 | * | |
301 | * The branch type is encoded in the LSB of jump_entry::key, | |
302 | * branch: 0 = unlikely, 1 = likely. | |
303 | * | |
304 | * This gives the following logic table: | |
305 | * | |
306 | * enabled type branch instuction | |
307 | * -----------------------------+----------- | |
308 | * 0 0 0 | NOP | |
309 | * 0 0 1 | JMP | |
310 | * 0 1 0 | NOP | |
311 | * 0 1 1 | JMP | |
312 | * | |
313 | * 1 0 0 | JMP | |
314 | * 1 0 1 | NOP | |
315 | * 1 1 0 | JMP | |
316 | * 1 1 1 | NOP | |
317 | * | |
318 | * Which gives the following functions: | |
319 | * | |
320 | * dynamic: instruction = enabled ^ branch | |
321 | * static: instruction = type ^ branch | |
322 | * | |
323 | * See jump_label_type() / jump_label_init_type(). | |
324 | */ | |
325 | ||
326 | extern bool ____wrong_branch_error(void); | |
327 | ||
328 | #define static_branch_likely(x) \ | |
329 | ({ \ | |
330 | bool branch; \ | |
331 | if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ | |
332 | branch = !arch_static_branch(&(x)->key, true); \ | |
333 | else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ | |
334 | branch = !arch_static_branch_jump(&(x)->key, true); \ | |
335 | else \ | |
336 | branch = ____wrong_branch_error(); \ | |
337 | branch; \ | |
338 | }) | |
339 | ||
340 | #define static_branch_unlikely(x) \ | |
341 | ({ \ | |
342 | bool branch; \ | |
343 | if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ | |
344 | branch = arch_static_branch_jump(&(x)->key, false); \ | |
345 | else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ | |
346 | branch = arch_static_branch(&(x)->key, false); \ | |
347 | else \ | |
348 | branch = ____wrong_branch_error(); \ | |
349 | branch; \ | |
350 | }) | |
351 | ||
352 | #else /* !HAVE_JUMP_LABEL */ | |
353 | ||
354 | #define static_branch_likely(x) likely(static_key_enabled(&(x)->key)) | |
355 | #define static_branch_unlikely(x) unlikely(static_key_enabled(&(x)->key)) | |
356 | ||
357 | #endif /* HAVE_JUMP_LABEL */ | |
358 | ||
359 | /* | |
360 | * Advanced usage; refcount, branch is enabled when: count != 0 | |
361 | */ | |
362 | ||
363 | #define static_branch_inc(x) static_key_slow_inc(&(x)->key) | |
364 | #define static_branch_dec(x) static_key_slow_dec(&(x)->key) | |
365 | ||
366 | /* | |
367 | * Normal usage; boolean enable/disable. | |
368 | */ | |
369 | ||
370 | #define static_branch_enable(x) static_key_enable(&(x)->key) | |
371 | #define static_branch_disable(x) static_key_disable(&(x)->key) | |
372 | ||
97ce2c88 | 373 | #endif /* _LINUX_JUMP_LABEL_H */ |
c0ccf6f9 AB |
374 | |
375 | #endif /* __ASSEMBLY__ */ |