1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _LINUX_JUMP_LABEL_H
3 #define _LINUX_JUMP_LABEL_H
8 * Copyright (C) 2009-2012 Jason Baron <jbaron@redhat.com>
9 * Copyright (C) 2011-2012 Red Hat, Inc., Peter Zijlstra
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:
16 * struct static_key false = STATIC_KEY_INIT_FALSE;
17 * struct static_key true = STATIC_KEY_INIT_TRUE;
21 * The updated API replacements are:
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()
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.
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.
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'.
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.
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.
68 * Lacking toolchain and or architecture support, static keys fall back to a
69 * simple conditional branch.
71 * Additional babbling in: Documentation/static-keys.txt
76 #include <linux/types.h>
77 #include <linux/compiler.h>
79 extern bool static_key_initialized;
81 #define STATIC_KEY_CHECK_USE(key) WARN(!static_key_initialized, \
82 "%s(): static key '%pS' used before call to jump_label_init()", \
85 #ifdef CONFIG_JUMP_LABEL
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
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
104 struct jump_entry *entries;
105 struct static_key_mod *next;
113 #endif /* CONFIG_JUMP_LABEL */
114 #endif /* __ASSEMBLY__ */
116 #ifdef CONFIG_JUMP_LABEL
117 #include <asm/jump_label.h>
122 enum jump_label_type {
129 #ifdef CONFIG_JUMP_LABEL
131 #define JUMP_TYPE_FALSE 0UL
132 #define JUMP_TYPE_TRUE 1UL
133 #define JUMP_TYPE_LINKED 2UL
134 #define JUMP_TYPE_MASK 3UL
136 static __always_inline bool static_key_false(struct static_key *key)
138 return arch_static_branch(key, false);
141 static __always_inline bool static_key_true(struct static_key *key)
143 return !arch_static_branch(key, true);
146 extern struct jump_entry __start___jump_table[];
147 extern struct jump_entry __stop___jump_table[];
149 extern void jump_label_init(void);
150 extern void jump_label_invalidate_initmem(void);
151 extern void jump_label_lock(void);
152 extern void jump_label_unlock(void);
153 extern void arch_jump_label_transform(struct jump_entry *entry,
154 enum jump_label_type type);
155 extern void arch_jump_label_transform_static(struct jump_entry *entry,
156 enum jump_label_type type);
157 extern int jump_label_text_reserved(void *start, void *end);
158 extern void static_key_slow_inc(struct static_key *key);
159 extern void static_key_slow_dec(struct static_key *key);
160 extern void static_key_slow_inc_cpuslocked(struct static_key *key);
161 extern void static_key_slow_dec_cpuslocked(struct static_key *key);
162 extern void jump_label_apply_nops(struct module *mod);
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);
166 extern void static_key_enable_cpuslocked(struct static_key *key);
167 extern void static_key_disable_cpuslocked(struct static_key *key);
170 * We should be using ATOMIC_INIT() for initializing .enabled, but
171 * the inclusion of atomic.h is problematic for inclusion of jump_label.h
172 * in 'low-level' headers. Thus, we are initializing .enabled with a
173 * raw value, but have added a BUILD_BUG_ON() to catch any issues in
174 * jump_label_init() see: kernel/jump_label.c.
176 #define STATIC_KEY_INIT_TRUE \
177 { .enabled = { 1 }, \
178 { .entries = (void *)JUMP_TYPE_TRUE } }
179 #define STATIC_KEY_INIT_FALSE \
180 { .enabled = { 0 }, \
181 { .entries = (void *)JUMP_TYPE_FALSE } }
183 #else /* !CONFIG_JUMP_LABEL */
185 #include <linux/atomic.h>
186 #include <linux/bug.h>
188 static inline int static_key_count(struct static_key *key)
190 return atomic_read(&key->enabled);
193 static __always_inline void jump_label_init(void)
195 static_key_initialized = true;
198 static inline void jump_label_invalidate_initmem(void) {}
200 static __always_inline bool static_key_false(struct static_key *key)
202 if (unlikely(static_key_count(key) > 0))
207 static __always_inline bool static_key_true(struct static_key *key)
209 if (likely(static_key_count(key) > 0))
214 static inline void static_key_slow_inc(struct static_key *key)
216 STATIC_KEY_CHECK_USE(key);
217 atomic_inc(&key->enabled);
220 static inline void static_key_slow_dec(struct static_key *key)
222 STATIC_KEY_CHECK_USE(key);
223 atomic_dec(&key->enabled);
226 #define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key)
227 #define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key)
229 static inline int jump_label_text_reserved(void *start, void *end)
234 static inline void jump_label_lock(void) {}
235 static inline void jump_label_unlock(void) {}
237 static inline int jump_label_apply_nops(struct module *mod)
242 static inline void static_key_enable(struct static_key *key)
244 STATIC_KEY_CHECK_USE(key);
246 if (atomic_read(&key->enabled) != 0) {
247 WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
250 atomic_set(&key->enabled, 1);
253 static inline void static_key_disable(struct static_key *key)
255 STATIC_KEY_CHECK_USE(key);
257 if (atomic_read(&key->enabled) != 1) {
258 WARN_ON_ONCE(atomic_read(&key->enabled) != 0);
261 atomic_set(&key->enabled, 0);
264 #define static_key_enable_cpuslocked(k) static_key_enable((k))
265 #define static_key_disable_cpuslocked(k) static_key_disable((k))
267 #define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) }
268 #define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) }
270 #endif /* CONFIG_JUMP_LABEL */
272 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
273 #define jump_label_enabled static_key_enabled
275 /* -------------------------------------------------------------------------- */
278 * Two type wrappers around static_key, such that we can use compile time
279 * type differentiation to emit the right code.
281 * All the below code is macros in order to play type games.
284 struct static_key_true {
285 struct static_key key;
288 struct static_key_false {
289 struct static_key key;
292 #define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, }
293 #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, }
295 #define DEFINE_STATIC_KEY_TRUE(name) \
296 struct static_key_true name = STATIC_KEY_TRUE_INIT
298 #define DEFINE_STATIC_KEY_TRUE_RO(name) \
299 struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT
301 #define DECLARE_STATIC_KEY_TRUE(name) \
302 extern struct static_key_true name
304 #define DEFINE_STATIC_KEY_FALSE(name) \
305 struct static_key_false name = STATIC_KEY_FALSE_INIT
307 #define DEFINE_STATIC_KEY_FALSE_RO(name) \
308 struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT
310 #define DECLARE_STATIC_KEY_FALSE(name) \
311 extern struct static_key_false name
313 #define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count) \
314 struct static_key_true name[count] = { \
315 [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT, \
318 #define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count) \
319 struct static_key_false name[count] = { \
320 [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT, \
323 extern bool ____wrong_branch_error(void);
325 #define static_key_enabled(x) \
327 if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \
328 !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\
329 !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
330 ____wrong_branch_error(); \
331 static_key_count((struct static_key *)x) > 0; \
334 #ifdef CONFIG_JUMP_LABEL
337 * Combine the right initial value (type) with the right branch order
338 * to generate the desired result.
341 * type\branch| likely (1) | unlikely (0)
342 * -----------+-----------------------+------------------
344 * true (1) | ... | ...
346 * | <br-stmts> | 1: ...
352 * -----------+-----------------------+------------------
354 * false (0) | ... | ...
356 * | <br-stmts> | 1: ...
362 * -----------+-----------------------+------------------
364 * The initial value is encoded in the LSB of static_key::entries,
365 * type: 0 = false, 1 = true.
367 * The branch type is encoded in the LSB of jump_entry::key,
368 * branch: 0 = unlikely, 1 = likely.
370 * This gives the following logic table:
372 * enabled type branch instuction
373 * -----------------------------+-----------
384 * Which gives the following functions:
386 * dynamic: instruction = enabled ^ branch
387 * static: instruction = type ^ branch
389 * See jump_label_type() / jump_label_init_type().
392 #define static_branch_likely(x) \
395 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \
396 branch = !arch_static_branch(&(x)->key, true); \
397 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
398 branch = !arch_static_branch_jump(&(x)->key, true); \
400 branch = ____wrong_branch_error(); \
404 #define static_branch_unlikely(x) \
407 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \
408 branch = arch_static_branch_jump(&(x)->key, false); \
409 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
410 branch = arch_static_branch(&(x)->key, false); \
412 branch = ____wrong_branch_error(); \
416 #else /* !CONFIG_JUMP_LABEL */
418 #define static_branch_likely(x) likely(static_key_enabled(&(x)->key))
419 #define static_branch_unlikely(x) unlikely(static_key_enabled(&(x)->key))
421 #endif /* CONFIG_JUMP_LABEL */
424 * Advanced usage; refcount, branch is enabled when: count != 0
427 #define static_branch_inc(x) static_key_slow_inc(&(x)->key)
428 #define static_branch_dec(x) static_key_slow_dec(&(x)->key)
429 #define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key)
430 #define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(x)->key)
433 * Normal usage; boolean enable/disable.
436 #define static_branch_enable(x) static_key_enable(&(x)->key)
437 #define static_branch_disable(x) static_key_disable(&(x)->key)
438 #define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key)
439 #define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key)
441 #endif /* __ASSEMBLY__ */
443 #endif /* _LINUX_JUMP_LABEL_H */