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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 | * | |
10 | * Jump labels provide an interface to generate dynamic branches using | |
fd3cbdc0 IM |
11 | * self-modifying code. Assuming toolchain and architecture support, the result |
12 | * of a "if (static_key_false(&key))" statement is an unconditional branch (which | |
efb3040d PZ |
13 | * defaults to false - and the true block is placed out of line). |
14 | * | |
c5905afb IM |
15 | * However at runtime we can change the branch target using |
16 | * static_key_slow_{inc,dec}(). These function as a 'reference' count on the key | |
fd3cbdc0 | 17 | * object, and for as long as there are references all branches referring to |
efb3040d PZ |
18 | * that particular key will point to the (out of line) true block. |
19 | * | |
fd3cbdc0 | 20 | * Since this relies on modifying code, the static_key_slow_{inc,dec}() functions |
efb3040d | 21 | * must be considered absolute slow paths (machine wide synchronization etc.). |
fd3cbdc0 | 22 | * OTOH, since the affected branches are unconditional, their runtime overhead |
efb3040d PZ |
23 | * will be absolutely minimal, esp. in the default (off) case where the total |
24 | * effect is a single NOP of appropriate size. The on case will patch in a jump | |
25 | * to the out-of-line block. | |
26 | * | |
fd3cbdc0 | 27 | * When the control is directly exposed to userspace, it is prudent to delay the |
efb3040d | 28 | * decrement to avoid high frequency code modifications which can (and do) |
c5905afb IM |
29 | * cause significant performance degradation. Struct static_key_deferred and |
30 | * static_key_slow_dec_deferred() provide for this. | |
efb3040d | 31 | * |
fd3cbdc0 | 32 | * Lacking toolchain and or architecture support, jump labels fall back to a simple |
efb3040d | 33 | * conditional branch. |
c5905afb IM |
34 | * |
35 | * struct static_key my_key = STATIC_KEY_INIT_TRUE; | |
36 | * | |
37 | * if (static_key_true(&my_key)) { | |
38 | * } | |
39 | * | |
40 | * will result in the true case being in-line and starts the key with a single | |
41 | * reference. Mixing static_key_true() and static_key_false() on the same key is not | |
42 | * allowed. | |
43 | * | |
44 | * Not initializing the key (static data is initialized to 0s anyway) is the | |
47fbc518 | 45 | * same as using STATIC_KEY_INIT_FALSE. |
fd3cbdc0 | 46 | */ |
efb3040d | 47 | |
c0ccf6f9 AB |
48 | #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL) |
49 | # define HAVE_JUMP_LABEL | |
50 | #endif | |
51 | ||
52 | #ifndef __ASSEMBLY__ | |
53 | ||
d430d3d7 JB |
54 | #include <linux/types.h> |
55 | #include <linux/compiler.h> | |
c4b2c0c5 HFS |
56 | #include <linux/bug.h> |
57 | ||
58 | extern bool static_key_initialized; | |
59 | ||
60 | #define STATIC_KEY_CHECK_USE() WARN(!static_key_initialized, \ | |
61 | "%s used before call to jump_label_init", \ | |
62 | __func__) | |
d430d3d7 | 63 | |
c0ccf6f9 | 64 | #ifdef HAVE_JUMP_LABEL |
d430d3d7 | 65 | |
c5905afb | 66 | struct static_key { |
d430d3d7 | 67 | atomic_t enabled; |
c5905afb | 68 | /* Set lsb bit to 1 if branch is default true, 0 ot */ |
d430d3d7 JB |
69 | struct jump_entry *entries; |
70 | #ifdef CONFIG_MODULES | |
c5905afb | 71 | struct static_key_mod *next; |
d430d3d7 JB |
72 | #endif |
73 | }; | |
74 | ||
ea5e9539 MG |
75 | #else |
76 | struct static_key { | |
77 | atomic_t enabled; | |
78 | }; | |
c0ccf6f9 AB |
79 | #endif /* HAVE_JUMP_LABEL */ |
80 | #endif /* __ASSEMBLY__ */ | |
81 | ||
82 | #ifdef HAVE_JUMP_LABEL | |
83 | #include <asm/jump_label.h> | |
84 | #endif | |
85 | ||
86 | #ifndef __ASSEMBLY__ | |
bf5438fc JB |
87 | |
88 | enum jump_label_type { | |
76b235c6 PZ |
89 | JUMP_LABEL_NOP = 0, |
90 | JUMP_LABEL_JMP, | |
bf5438fc JB |
91 | }; |
92 | ||
93 | struct module; | |
94 | ||
851cf6e7 | 95 | #include <linux/atomic.h> |
ea5e9539 MG |
96 | |
97 | static inline int static_key_count(struct static_key *key) | |
98 | { | |
99 | return atomic_read(&key->enabled); | |
100 | } | |
101 | ||
bf5438fc JB |
102 | #ifdef HAVE_JUMP_LABEL |
103 | ||
a1efb01f PZ |
104 | #define JUMP_TYPE_FALSE 0UL |
105 | #define JUMP_TYPE_TRUE 1UL | |
106 | #define JUMP_TYPE_MASK 1UL | |
c5905afb IM |
107 | |
108 | static __always_inline bool static_key_false(struct static_key *key) | |
109 | { | |
11276d53 | 110 | return arch_static_branch(key, false); |
c5905afb | 111 | } |
d430d3d7 | 112 | |
c5905afb IM |
113 | static __always_inline bool static_key_true(struct static_key *key) |
114 | { | |
11276d53 | 115 | return !arch_static_branch(key, true); |
c5905afb IM |
116 | } |
117 | ||
bf5438fc JB |
118 | extern struct jump_entry __start___jump_table[]; |
119 | extern struct jump_entry __stop___jump_table[]; | |
120 | ||
97ce2c88 | 121 | extern void jump_label_init(void); |
91bad2f8 JB |
122 | extern void jump_label_lock(void); |
123 | extern void jump_label_unlock(void); | |
bf5438fc | 124 | extern void arch_jump_label_transform(struct jump_entry *entry, |
37348804 | 125 | enum jump_label_type type); |
20284aa7 JF |
126 | extern void arch_jump_label_transform_static(struct jump_entry *entry, |
127 | enum jump_label_type type); | |
4c3ef6d7 | 128 | extern int jump_label_text_reserved(void *start, void *end); |
c5905afb IM |
129 | extern void static_key_slow_inc(struct static_key *key); |
130 | extern void static_key_slow_dec(struct static_key *key); | |
d430d3d7 | 131 | extern void jump_label_apply_nops(struct module *mod); |
c5905afb | 132 | |
11276d53 | 133 | #define STATIC_KEY_INIT_TRUE \ |
f4be8433 | 134 | { .enabled = ATOMIC_INIT(1), \ |
11276d53 PZ |
135 | .entries = (void *)JUMP_TYPE_TRUE } |
136 | #define STATIC_KEY_INIT_FALSE \ | |
f4be8433 | 137 | { .enabled = ATOMIC_INIT(0), \ |
11276d53 | 138 | .entries = (void *)JUMP_TYPE_FALSE } |
bf5438fc | 139 | |
97ce2c88 | 140 | #else /* !HAVE_JUMP_LABEL */ |
bf5438fc | 141 | |
97ce2c88 JF |
142 | static __always_inline void jump_label_init(void) |
143 | { | |
c4b2c0c5 | 144 | static_key_initialized = true; |
97ce2c88 JF |
145 | } |
146 | ||
c5905afb IM |
147 | static __always_inline bool static_key_false(struct static_key *key) |
148 | { | |
ea5e9539 | 149 | if (unlikely(static_key_count(key) > 0)) |
c5905afb IM |
150 | return true; |
151 | return false; | |
152 | } | |
153 | ||
154 | static __always_inline bool static_key_true(struct static_key *key) | |
d430d3d7 | 155 | { |
ea5e9539 | 156 | if (likely(static_key_count(key) > 0)) |
d430d3d7 JB |
157 | return true; |
158 | return false; | |
159 | } | |
bf5438fc | 160 | |
c5905afb | 161 | static inline void static_key_slow_inc(struct static_key *key) |
d430d3d7 | 162 | { |
c4b2c0c5 | 163 | STATIC_KEY_CHECK_USE(); |
d430d3d7 JB |
164 | atomic_inc(&key->enabled); |
165 | } | |
bf5438fc | 166 | |
c5905afb | 167 | static inline void static_key_slow_dec(struct static_key *key) |
bf5438fc | 168 | { |
c4b2c0c5 | 169 | STATIC_KEY_CHECK_USE(); |
d430d3d7 | 170 | atomic_dec(&key->enabled); |
bf5438fc JB |
171 | } |
172 | ||
4c3ef6d7 JB |
173 | static inline int jump_label_text_reserved(void *start, void *end) |
174 | { | |
175 | return 0; | |
176 | } | |
177 | ||
91bad2f8 JB |
178 | static inline void jump_label_lock(void) {} |
179 | static inline void jump_label_unlock(void) {} | |
180 | ||
d430d3d7 JB |
181 | static inline int jump_label_apply_nops(struct module *mod) |
182 | { | |
183 | return 0; | |
184 | } | |
b2029520 | 185 | |
11276d53 PZ |
186 | #define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) } |
187 | #define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) } | |
c5905afb | 188 | |
97ce2c88 | 189 | #endif /* HAVE_JUMP_LABEL */ |
d430d3d7 | 190 | |
c5905afb IM |
191 | #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE |
192 | #define jump_label_enabled static_key_enabled | |
ac99b862 | 193 | |
8eedce99 JB |
194 | static inline bool static_key_enabled(struct static_key *key) |
195 | { | |
ea5e9539 | 196 | return static_key_count(key) > 0; |
8eedce99 JB |
197 | } |
198 | ||
e33886b3 PZ |
199 | static inline void static_key_enable(struct static_key *key) |
200 | { | |
201 | int count = static_key_count(key); | |
202 | ||
203 | WARN_ON_ONCE(count < 0 || count > 1); | |
204 | ||
205 | if (!count) | |
206 | static_key_slow_inc(key); | |
207 | } | |
208 | ||
209 | static inline void static_key_disable(struct static_key *key) | |
210 | { | |
211 | int count = static_key_count(key); | |
212 | ||
213 | WARN_ON_ONCE(count < 0 || count > 1); | |
214 | ||
215 | if (count) | |
216 | static_key_slow_dec(key); | |
217 | } | |
218 | ||
11276d53 PZ |
219 | /* -------------------------------------------------------------------------- */ |
220 | ||
221 | /* | |
222 | * Two type wrappers around static_key, such that we can use compile time | |
223 | * type differentiation to emit the right code. | |
224 | * | |
225 | * All the below code is macros in order to play type games. | |
226 | */ | |
227 | ||
228 | struct static_key_true { | |
229 | struct static_key key; | |
230 | }; | |
231 | ||
232 | struct static_key_false { | |
233 | struct static_key key; | |
234 | }; | |
235 | ||
236 | #define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, } | |
237 | #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, } | |
238 | ||
239 | #define DEFINE_STATIC_KEY_TRUE(name) \ | |
240 | struct static_key_true name = STATIC_KEY_TRUE_INIT | |
241 | ||
242 | #define DEFINE_STATIC_KEY_FALSE(name) \ | |
243 | struct static_key_false name = STATIC_KEY_FALSE_INIT | |
244 | ||
245 | #ifdef HAVE_JUMP_LABEL | |
246 | ||
247 | /* | |
248 | * Combine the right initial value (type) with the right branch order | |
249 | * to generate the desired result. | |
250 | * | |
251 | * | |
252 | * type\branch| likely (1) | unlikely (0) | |
253 | * -----------+-----------------------+------------------ | |
254 | * | | | |
255 | * true (1) | ... | ... | |
256 | * | NOP | JMP L | |
257 | * | <br-stmts> | 1: ... | |
258 | * | L: ... | | |
259 | * | | | |
260 | * | | L: <br-stmts> | |
261 | * | | jmp 1b | |
262 | * | | | |
263 | * -----------+-----------------------+------------------ | |
264 | * | | | |
265 | * false (0) | ... | ... | |
266 | * | JMP L | NOP | |
267 | * | <br-stmts> | 1: ... | |
268 | * | L: ... | | |
269 | * | | | |
270 | * | | L: <br-stmts> | |
271 | * | | jmp 1b | |
272 | * | | | |
273 | * -----------+-----------------------+------------------ | |
274 | * | |
275 | * The initial value is encoded in the LSB of static_key::entries, | |
276 | * type: 0 = false, 1 = true. | |
277 | * | |
278 | * The branch type is encoded in the LSB of jump_entry::key, | |
279 | * branch: 0 = unlikely, 1 = likely. | |
280 | * | |
281 | * This gives the following logic table: | |
282 | * | |
283 | * enabled type branch instuction | |
284 | * -----------------------------+----------- | |
285 | * 0 0 0 | NOP | |
286 | * 0 0 1 | JMP | |
287 | * 0 1 0 | NOP | |
288 | * 0 1 1 | JMP | |
289 | * | |
290 | * 1 0 0 | JMP | |
291 | * 1 0 1 | NOP | |
292 | * 1 1 0 | JMP | |
293 | * 1 1 1 | NOP | |
294 | * | |
295 | * Which gives the following functions: | |
296 | * | |
297 | * dynamic: instruction = enabled ^ branch | |
298 | * static: instruction = type ^ branch | |
299 | * | |
300 | * See jump_label_type() / jump_label_init_type(). | |
301 | */ | |
302 | ||
303 | extern bool ____wrong_branch_error(void); | |
304 | ||
305 | #define static_branch_likely(x) \ | |
306 | ({ \ | |
307 | bool branch; \ | |
308 | if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ | |
309 | branch = !arch_static_branch(&(x)->key, true); \ | |
310 | else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ | |
311 | branch = !arch_static_branch_jump(&(x)->key, true); \ | |
312 | else \ | |
313 | branch = ____wrong_branch_error(); \ | |
314 | branch; \ | |
315 | }) | |
316 | ||
317 | #define static_branch_unlikely(x) \ | |
318 | ({ \ | |
319 | bool branch; \ | |
320 | if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \ | |
321 | branch = arch_static_branch_jump(&(x)->key, false); \ | |
322 | else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \ | |
323 | branch = arch_static_branch(&(x)->key, false); \ | |
324 | else \ | |
325 | branch = ____wrong_branch_error(); \ | |
326 | branch; \ | |
327 | }) | |
328 | ||
329 | #else /* !HAVE_JUMP_LABEL */ | |
330 | ||
331 | #define static_branch_likely(x) likely(static_key_enabled(&(x)->key)) | |
332 | #define static_branch_unlikely(x) unlikely(static_key_enabled(&(x)->key)) | |
333 | ||
334 | #endif /* HAVE_JUMP_LABEL */ | |
335 | ||
336 | /* | |
337 | * Advanced usage; refcount, branch is enabled when: count != 0 | |
338 | */ | |
339 | ||
340 | #define static_branch_inc(x) static_key_slow_inc(&(x)->key) | |
341 | #define static_branch_dec(x) static_key_slow_dec(&(x)->key) | |
342 | ||
343 | /* | |
344 | * Normal usage; boolean enable/disable. | |
345 | */ | |
346 | ||
347 | #define static_branch_enable(x) static_key_enable(&(x)->key) | |
348 | #define static_branch_disable(x) static_key_disable(&(x)->key) | |
349 | ||
97ce2c88 | 350 | #endif /* _LINUX_JUMP_LABEL_H */ |
c0ccf6f9 AB |
351 | |
352 | #endif /* __ASSEMBLY__ */ |