1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _LINUX_JUMP_LABEL_H
3#define _LINUX_JUMP_LABEL_H
4
5/*
6 * Jump label support
7 *
8 * Copyright (C) 2009-2012 Jason Baron <jbaron@redhat.com>
9 * Copyright (C) 2011-2012 Red Hat, Inc., Peter Zijlstra
10 *
11 * DEPRECATED API:
12 *
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:
15 *
16 * struct static_key false = STATIC_KEY_INIT_FALSE;
17 * struct static_key true = STATIC_KEY_INIT_TRUE;
18 * static_key_true()
19 * static_key_false()
20 *
21 * The updated API replacements are:
22 *
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()
29 *
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.
41 *
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.
50 *
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'.
55 *
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.
62 *
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.
67 *
68 * Lacking toolchain and or architecture support, static keys fall back to a
69 * simple conditional branch.
70 *
71 * Additional babbling in: Documentation/static-keys.txt
72 */
73
74#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
75# define HAVE_JUMP_LABEL
76#endif
77
78#ifndef __ASSEMBLY__
79
80#include <linux/types.h>
81#include <linux/compiler.h>
82
83extern bool static_key_initialized;
84
85#define STATIC_KEY_CHECK_USE(key) WARN(!static_key_initialized, \
86 "%s(): static key '%pS' used before call to jump_label_init()", \
87 __func__, (key))
88
89#ifdef HAVE_JUMP_LABEL
90
91struct static_key {
92 atomic_t enabled;
93/*
94 * Note:
95 * To make anonymous unions work with old compilers, the static
96 * initialization of them requires brackets. This creates a dependency
97 * on the order of the struct with the initializers. If any fields
98 * are added, STATIC_KEY_INIT_TRUE and STATIC_KEY_INIT_FALSE may need
99 * to be modified.
100 *
101 * bit 0 => 1 if key is initially true
102 * 0 if initially false
103 * bit 1 => 1 if points to struct static_key_mod
104 * 0 if points to struct jump_entry
105 */
106 union {
107 unsigned long type;
108 struct jump_entry *entries;
109 struct static_key_mod *next;
110 };
111};
112
113#else
114struct static_key {
115 atomic_t enabled;
116};
117#endif /* HAVE_JUMP_LABEL */
118#endif /* __ASSEMBLY__ */
119
120#ifdef HAVE_JUMP_LABEL
121#include <asm/jump_label.h>
122#endif
123
124#ifndef __ASSEMBLY__
125
126enum jump_label_type {
127 JUMP_LABEL_NOP = 0,
128 JUMP_LABEL_JMP,
129};
130
131struct module;
132
133#ifdef HAVE_JUMP_LABEL
134
135#define JUMP_TYPE_FALSE 0UL
136#define JUMP_TYPE_TRUE 1UL
137#define JUMP_TYPE_LINKED 2UL
138#define JUMP_TYPE_MASK 3UL
139
140static __always_inline bool static_key_false(struct static_key *key)
141{
142 return arch_static_branch(key, false);
143}
144
145static __always_inline bool static_key_true(struct static_key *key)
146{
147 return !arch_static_branch(key, true);
148}
149
150extern struct jump_entry __start___jump_table[];
151extern struct jump_entry __stop___jump_table[];
152
153extern void jump_label_init(void);
154extern void jump_label_invalidate_initmem(void);
155extern void jump_label_lock(void);
156extern void jump_label_unlock(void);
157extern void arch_jump_label_transform(struct jump_entry *entry,
158 enum jump_label_type type);
159extern void arch_jump_label_transform_static(struct jump_entry *entry,
160 enum jump_label_type type);
161extern int jump_label_text_reserved(void *start, void *end);
162extern void static_key_slow_inc(struct static_key *key);
163extern void static_key_slow_dec(struct static_key *key);
164extern void static_key_slow_inc_cpuslocked(struct static_key *key);
165extern void static_key_slow_dec_cpuslocked(struct static_key *key);
166extern void jump_label_apply_nops(struct module *mod);
167extern int static_key_count(struct static_key *key);
168extern void static_key_enable(struct static_key *key);
169extern void static_key_disable(struct static_key *key);
170extern void static_key_enable_cpuslocked(struct static_key *key);
171extern void static_key_disable_cpuslocked(struct static_key *key);
172
173/*
174 * We should be using ATOMIC_INIT() for initializing .enabled, but
175 * the inclusion of atomic.h is problematic for inclusion of jump_label.h
176 * in 'low-level' headers. Thus, we are initializing .enabled with a
177 * raw value, but have added a BUILD_BUG_ON() to catch any issues in
178 * jump_label_init() see: kernel/jump_label.c.
179 */
180#define STATIC_KEY_INIT_TRUE \
181 { .enabled = { 1 }, \
182 { .entries = (void *)JUMP_TYPE_TRUE } }
183#define STATIC_KEY_INIT_FALSE \
184 { .enabled = { 0 }, \
185 { .entries = (void *)JUMP_TYPE_FALSE } }
186
187#else /* !HAVE_JUMP_LABEL */
188
189#include <linux/atomic.h>
190#include <linux/bug.h>
191
192static inline int static_key_count(struct static_key *key)
193{
194 return atomic_read(&key->enabled);
195}
196
197static __always_inline void jump_label_init(void)
198{
199 static_key_initialized = true;
200}
201
202static inline void jump_label_invalidate_initmem(void) {}
203
204static __always_inline bool static_key_false(struct static_key *key)
205{
206 if (unlikely(static_key_count(key) > 0))
207 return true;
208 return false;
209}
210
211static __always_inline bool static_key_true(struct static_key *key)
212{
213 if (likely(static_key_count(key) > 0))
214 return true;
215 return false;
216}
217
218static inline void static_key_slow_inc(struct static_key *key)
219{
220 STATIC_KEY_CHECK_USE(key);
221 atomic_inc(&key->enabled);
222}
223
224static inline void static_key_slow_dec(struct static_key *key)
225{
226 STATIC_KEY_CHECK_USE(key);
227 atomic_dec(&key->enabled);
228}
229
230#define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key)
231#define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key)
232
233static inline int jump_label_text_reserved(void *start, void *end)
234{
235 return 0;
236}
237
238static inline void jump_label_lock(void) {}
239static inline void jump_label_unlock(void) {}
240
241static inline int jump_label_apply_nops(struct module *mod)
242{
243 return 0;
244}
245
246static inline void static_key_enable(struct static_key *key)
247{
248 STATIC_KEY_CHECK_USE(key);
249
250 if (atomic_read(&key->enabled) != 0) {
251 WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
252 return;
253 }
254 atomic_set(&key->enabled, 1);
255}
256
257static inline void static_key_disable(struct static_key *key)
258{
259 STATIC_KEY_CHECK_USE(key);
260
261 if (atomic_read(&key->enabled) != 1) {
262 WARN_ON_ONCE(atomic_read(&key->enabled) != 0);
263 return;
264 }
265 atomic_set(&key->enabled, 0);
266}
267
268#define static_key_enable_cpuslocked(k) static_key_enable((k))
269#define static_key_disable_cpuslocked(k) static_key_disable((k))
270
271#define STATIC_KEY_INIT_TRUE { .enabled = ATOMIC_INIT(1) }
272#define STATIC_KEY_INIT_FALSE { .enabled = ATOMIC_INIT(0) }
273
274#endif /* HAVE_JUMP_LABEL */
275
276#define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
277#define jump_label_enabled static_key_enabled
278
279/* -------------------------------------------------------------------------- */
280
281/*
282 * Two type wrappers around static_key, such that we can use compile time
283 * type differentiation to emit the right code.
284 *
285 * All the below code is macros in order to play type games.
286 */
287
288struct static_key_true {
289 struct static_key key;
290};
291
292struct static_key_false {
293 struct static_key key;
294};
295
296#define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE, }
297#define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, }
298
299#define DEFINE_STATIC_KEY_TRUE(name) \
300 struct static_key_true name = STATIC_KEY_TRUE_INIT
301
302#define DEFINE_STATIC_KEY_TRUE_RO(name) \
303 struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT
304
305#define DECLARE_STATIC_KEY_TRUE(name) \
306 extern struct static_key_true name
307
308#define DEFINE_STATIC_KEY_FALSE(name) \
309 struct static_key_false name = STATIC_KEY_FALSE_INIT
310
311#define DEFINE_STATIC_KEY_FALSE_RO(name) \
312 struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT
313
314#define DECLARE_STATIC_KEY_FALSE(name) \
315 extern struct static_key_false name
316
317#define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count) \
318 struct static_key_true name[count] = { \
319 [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT, \
320 }
321
322#define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count) \
323 struct static_key_false name[count] = { \
324 [0 ... (count) - 1] = STATIC_KEY_FALSE_INIT, \
325 }
326
327extern bool ____wrong_branch_error(void);
328
329#define static_key_enabled(x) \
330({ \
331 if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \
332 !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\
333 !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
334 ____wrong_branch_error(); \
335 static_key_count((struct static_key *)x) > 0; \
336})
337
338#ifdef HAVE_JUMP_LABEL
339
340/*
341 * Combine the right initial value (type) with the right branch order
342 * to generate the desired result.
343 *
344 *
345 * type\branch| likely (1) | unlikely (0)
346 * -----------+-----------------------+------------------
347 * | |
348 * true (1) | ... | ...
349 * | NOP | JMP L
350 * | <br-stmts> | 1: ...
351 * | L: ... |
352 * | |
353 * | | L: <br-stmts>
354 * | | jmp 1b
355 * | |
356 * -----------+-----------------------+------------------
357 * | |
358 * false (0) | ... | ...
359 * | JMP L | NOP
360 * | <br-stmts> | 1: ...
361 * | L: ... |
362 * | |
363 * | | L: <br-stmts>
364 * | | jmp 1b
365 * | |
366 * -----------+-----------------------+------------------
367 *
368 * The initial value is encoded in the LSB of static_key::entries,
369 * type: 0 = false, 1 = true.
370 *
371 * The branch type is encoded in the LSB of jump_entry::key,
372 * branch: 0 = unlikely, 1 = likely.
373 *
374 * This gives the following logic table:
375 *
376 * enabled type branch instuction
377 * -----------------------------+-----------
378 * 0 0 0 | NOP
379 * 0 0 1 | JMP
380 * 0 1 0 | NOP
381 * 0 1 1 | JMP
382 *
383 * 1 0 0 | JMP
384 * 1 0 1 | NOP
385 * 1 1 0 | JMP
386 * 1 1 1 | NOP
387 *
388 * Which gives the following functions:
389 *
390 * dynamic: instruction = enabled ^ branch
391 * static: instruction = type ^ branch
392 *
393 * See jump_label_type() / jump_label_init_type().
394 */
395
396#define static_branch_likely(x) \
397({ \
398 bool branch; \
399 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \
400 branch = !arch_static_branch(&(x)->key, true); \
401 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
402 branch = !arch_static_branch_jump(&(x)->key, true); \
403 else \
404 branch = ____wrong_branch_error(); \
405 likely(branch); \
406})
407
408#define static_branch_unlikely(x) \
409({ \
410 bool branch; \
411 if (__builtin_types_compatible_p(typeof(*x), struct static_key_true)) \
412 branch = arch_static_branch_jump(&(x)->key, false); \
413 else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
414 branch = arch_static_branch(&(x)->key, false); \
415 else \
416 branch = ____wrong_branch_error(); \
417 unlikely(branch); \
418})
419
420#else /* !HAVE_JUMP_LABEL */
421
422#define static_branch_likely(x) likely(static_key_enabled(&(x)->key))
423#define static_branch_unlikely(x) unlikely(static_key_enabled(&(x)->key))
424
425#endif /* HAVE_JUMP_LABEL */
426
427/*
428 * Advanced usage; refcount, branch is enabled when: count != 0
429 */
430
431#define static_branch_inc(x) static_key_slow_inc(&(x)->key)
432#define static_branch_dec(x) static_key_slow_dec(&(x)->key)
433#define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key)
434#define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(x)->key)
435
436/*
437 * Normal usage; boolean enable/disable.
438 */
439
440#define static_branch_enable(x) static_key_enable(&(x)->key)
441#define static_branch_disable(x) static_key_disable(&(x)->key)
442#define static_branch_enable_cpuslocked(x) static_key_enable_cpuslocked(&(x)->key)
443#define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key)
444
445#endif /* __ASSEMBLY__ */
446
447#endif /* _LINUX_JUMP_LABEL_H */
448