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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/staging/static-keys.rst
72  */
73 
74 #ifndef __ASSEMBLY__
75 
76 #include <linux/types.h>
77 #include <linux/compiler.h>
78 
79 extern bool static_key_initialized;
80 
81 #define STATIC_KEY_CHECK_USE(key) WARN(!static_key_initialized,		      \
82 				    "%s(): static key '%pS' used before call to jump_label_init()", \
83 				    __func__, (key))
84 
85 #ifdef CONFIG_JUMP_LABEL
86 
87 struct static_key {
88 	atomic_t enabled;
89 /*
90  * Note:
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
95  *   to be modified.
96  *
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
101  */
102 	union {
103 		unsigned long type;
104 		struct jump_entry *entries;
105 		struct static_key_mod *next;
106 	};
107 };
108 
109 #else
110 struct static_key {
111 	atomic_t enabled;
112 };
113 #endif	/* CONFIG_JUMP_LABEL */
114 #endif /* __ASSEMBLY__ */
115 
116 #ifdef CONFIG_JUMP_LABEL
117 #include <asm/jump_label.h>
118 
119 #ifndef __ASSEMBLY__
120 #ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE
121 
122 struct jump_entry {
123 	s32 code;
124 	s32 target;
125 	long key;	// key may be far away from the core kernel under KASLR
126 };
127 
jump_entry_code(const struct jump_entry * entry)128 static inline unsigned long jump_entry_code(const struct jump_entry *entry)
129 {
130 	return (unsigned long)&entry->code + entry->code;
131 }
132 
jump_entry_target(const struct jump_entry * entry)133 static inline unsigned long jump_entry_target(const struct jump_entry *entry)
134 {
135 	return (unsigned long)&entry->target + entry->target;
136 }
137 
jump_entry_key(const struct jump_entry * entry)138 static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
139 {
140 	long offset = entry->key & ~3L;
141 
142 	return (struct static_key *)((unsigned long)&entry->key + offset);
143 }
144 
145 #else
146 
jump_entry_code(const struct jump_entry * entry)147 static inline unsigned long jump_entry_code(const struct jump_entry *entry)
148 {
149 	return entry->code;
150 }
151 
jump_entry_target(const struct jump_entry * entry)152 static inline unsigned long jump_entry_target(const struct jump_entry *entry)
153 {
154 	return entry->target;
155 }
156 
jump_entry_key(const struct jump_entry * entry)157 static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
158 {
159 	return (struct static_key *)((unsigned long)entry->key & ~3UL);
160 }
161 
162 #endif
163 
jump_entry_is_branch(const struct jump_entry * entry)164 static inline bool jump_entry_is_branch(const struct jump_entry *entry)
165 {
166 	return (unsigned long)entry->key & 1UL;
167 }
168 
jump_entry_is_init(const struct jump_entry * entry)169 static inline bool jump_entry_is_init(const struct jump_entry *entry)
170 {
171 	return (unsigned long)entry->key & 2UL;
172 }
173 
jump_entry_set_init(struct jump_entry * entry)174 static inline void jump_entry_set_init(struct jump_entry *entry)
175 {
176 	entry->key |= 2;
177 }
178 
179 #endif
180 #endif
181 
182 #ifndef __ASSEMBLY__
183 
184 enum jump_label_type {
185 	JUMP_LABEL_NOP = 0,
186 	JUMP_LABEL_JMP,
187 };
188 
189 struct module;
190 
191 #ifdef CONFIG_JUMP_LABEL
192 
193 #define JUMP_TYPE_FALSE		0UL
194 #define JUMP_TYPE_TRUE		1UL
195 #define JUMP_TYPE_LINKED	2UL
196 #define JUMP_TYPE_MASK		3UL
197 
static_key_false(struct static_key * key)198 static __always_inline bool static_key_false(struct static_key *key)
199 {
200 	return arch_static_branch(key, false);
201 }
202 
static_key_true(struct static_key * key)203 static __always_inline bool static_key_true(struct static_key *key)
204 {
205 	return !arch_static_branch(key, true);
206 }
207 
208 extern struct jump_entry __start___jump_table[];
209 extern struct jump_entry __stop___jump_table[];
210 
211 extern void jump_label_init(void);
212 extern void jump_label_lock(void);
213 extern void jump_label_unlock(void);
214 extern void arch_jump_label_transform(struct jump_entry *entry,
215 				      enum jump_label_type type);
216 extern void arch_jump_label_transform_static(struct jump_entry *entry,
217 					     enum jump_label_type type);
218 extern bool arch_jump_label_transform_queue(struct jump_entry *entry,
219 					    enum jump_label_type type);
220 extern void arch_jump_label_transform_apply(void);
221 extern int jump_label_text_reserved(void *start, void *end);
222 extern void static_key_slow_inc(struct static_key *key);
223 extern void static_key_slow_dec(struct static_key *key);
224 extern void static_key_slow_inc_cpuslocked(struct static_key *key);
225 extern void static_key_slow_dec_cpuslocked(struct static_key *key);
226 extern void jump_label_apply_nops(struct module *mod);
227 extern int static_key_count(struct static_key *key);
228 extern void static_key_enable(struct static_key *key);
229 extern void static_key_disable(struct static_key *key);
230 extern void static_key_enable_cpuslocked(struct static_key *key);
231 extern void static_key_disable_cpuslocked(struct static_key *key);
232 
233 /*
234  * We should be using ATOMIC_INIT() for initializing .enabled, but
235  * the inclusion of atomic.h is problematic for inclusion of jump_label.h
236  * in 'low-level' headers. Thus, we are initializing .enabled with a
237  * raw value, but have added a BUILD_BUG_ON() to catch any issues in
238  * jump_label_init() see: kernel/jump_label.c.
239  */
240 #define STATIC_KEY_INIT_TRUE					\
241 	{ .enabled = { 1 },					\
242 	  { .entries = (void *)JUMP_TYPE_TRUE } }
243 #define STATIC_KEY_INIT_FALSE					\
244 	{ .enabled = { 0 },					\
245 	  { .entries = (void *)JUMP_TYPE_FALSE } }
246 
247 #else  /* !CONFIG_JUMP_LABEL */
248 
249 #include <linux/atomic.h>
250 #include <linux/bug.h>
251 
static_key_count(struct static_key * key)252 static __always_inline int static_key_count(struct static_key *key)
253 {
254 	return arch_atomic_read(&key->enabled);
255 }
256 
jump_label_init(void)257 static __always_inline void jump_label_init(void)
258 {
259 	static_key_initialized = true;
260 }
261 
static_key_false(struct static_key * key)262 static __always_inline bool static_key_false(struct static_key *key)
263 {
264 	if (unlikely(static_key_count(key) > 0))
265 		return true;
266 	return false;
267 }
268 
static_key_true(struct static_key * key)269 static __always_inline bool static_key_true(struct static_key *key)
270 {
271 	if (likely(static_key_count(key) > 0))
272 		return true;
273 	return false;
274 }
275 
static_key_slow_inc(struct static_key * key)276 static inline void static_key_slow_inc(struct static_key *key)
277 {
278 	STATIC_KEY_CHECK_USE(key);
279 	atomic_inc(&key->enabled);
280 }
281 
static_key_slow_dec(struct static_key * key)282 static inline void static_key_slow_dec(struct static_key *key)
283 {
284 	STATIC_KEY_CHECK_USE(key);
285 	atomic_dec(&key->enabled);
286 }
287 
288 #define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key)
289 #define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key)
290 
jump_label_text_reserved(void * start,void * end)291 static inline int jump_label_text_reserved(void *start, void *end)
292 {
293 	return 0;
294 }
295 
jump_label_lock(void)296 static inline void jump_label_lock(void) {}
jump_label_unlock(void)297 static inline void jump_label_unlock(void) {}
298 
jump_label_apply_nops(struct module * mod)299 static inline int jump_label_apply_nops(struct module *mod)
300 {
301 	return 0;
302 }
303 
static_key_enable(struct static_key * key)304 static inline void static_key_enable(struct static_key *key)
305 {
306 	STATIC_KEY_CHECK_USE(key);
307 
308 	if (atomic_read(&key->enabled) != 0) {
309 		WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
310 		return;
311 	}
312 	atomic_set(&key->enabled, 1);
313 }
314 
static_key_disable(struct static_key * key)315 static inline void static_key_disable(struct static_key *key)
316 {
317 	STATIC_KEY_CHECK_USE(key);
318 
319 	if (atomic_read(&key->enabled) != 1) {
320 		WARN_ON_ONCE(atomic_read(&key->enabled) != 0);
321 		return;
322 	}
323 	atomic_set(&key->enabled, 0);
324 }
325 
326 #define static_key_enable_cpuslocked(k)		static_key_enable((k))
327 #define static_key_disable_cpuslocked(k)	static_key_disable((k))
328 
329 #define STATIC_KEY_INIT_TRUE	{ .enabled = ATOMIC_INIT(1) }
330 #define STATIC_KEY_INIT_FALSE	{ .enabled = ATOMIC_INIT(0) }
331 
332 #endif	/* CONFIG_JUMP_LABEL */
333 
334 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
335 #define jump_label_enabled static_key_enabled
336 
337 /* -------------------------------------------------------------------------- */
338 
339 /*
340  * Two type wrappers around static_key, such that we can use compile time
341  * type differentiation to emit the right code.
342  *
343  * All the below code is macros in order to play type games.
344  */
345 
346 struct static_key_true {
347 	struct static_key key;
348 };
349 
350 struct static_key_false {
351 	struct static_key key;
352 };
353 
354 #define STATIC_KEY_TRUE_INIT  (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE,  }
355 #define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, }
356 
357 #define DEFINE_STATIC_KEY_TRUE(name)	\
358 	struct static_key_true name = STATIC_KEY_TRUE_INIT
359 
360 #define DEFINE_STATIC_KEY_TRUE_RO(name)	\
361 	struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT
362 
363 #define DECLARE_STATIC_KEY_TRUE(name)	\
364 	extern struct static_key_true name
365 
366 #define DEFINE_STATIC_KEY_FALSE(name)	\
367 	struct static_key_false name = STATIC_KEY_FALSE_INIT
368 
369 #define DEFINE_STATIC_KEY_FALSE_RO(name)	\
370 	struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT
371 
372 #define DECLARE_STATIC_KEY_FALSE(name)	\
373 	extern struct static_key_false name
374 
375 #define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count)		\
376 	struct static_key_true name[count] = {			\
377 		[0 ... (count) - 1] = STATIC_KEY_TRUE_INIT,	\
378 	}
379 
380 #define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count)		\
381 	struct static_key_false name[count] = {			\
382 		[0 ... (count) - 1] = STATIC_KEY_FALSE_INIT,	\
383 	}
384 
385 extern bool ____wrong_branch_error(void);
386 
387 #define static_key_enabled(x)							\
388 ({										\
389 	if (!__builtin_types_compatible_p(typeof(*x), struct static_key) &&	\
390 	    !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\
391 	    !__builtin_types_compatible_p(typeof(*x), struct static_key_false))	\
392 		____wrong_branch_error();					\
393 	static_key_count((struct static_key *)x) > 0;				\
394 })
395 
396 #ifdef CONFIG_JUMP_LABEL
397 
398 /*
399  * Combine the right initial value (type) with the right branch order
400  * to generate the desired result.
401  *
402  *
403  * type\branch|	likely (1)	      |	unlikely (0)
404  * -----------+-----------------------+------------------
405  *            |                       |
406  *  true (1)  |	   ...		      |	   ...
407  *            |    NOP		      |	   JMP L
408  *            |    <br-stmts>	      |	1: ...
409  *            |	L: ...		      |
410  *            |			      |
411  *            |			      |	L: <br-stmts>
412  *            |			      |	   jmp 1b
413  *            |                       |
414  * -----------+-----------------------+------------------
415  *            |                       |
416  *  false (0) |	   ...		      |	   ...
417  *            |    JMP L	      |	   NOP
418  *            |    <br-stmts>	      |	1: ...
419  *            |	L: ...		      |
420  *            |			      |
421  *            |			      |	L: <br-stmts>
422  *            |			      |	   jmp 1b
423  *            |                       |
424  * -----------+-----------------------+------------------
425  *
426  * The initial value is encoded in the LSB of static_key::entries,
427  * type: 0 = false, 1 = true.
428  *
429  * The branch type is encoded in the LSB of jump_entry::key,
430  * branch: 0 = unlikely, 1 = likely.
431  *
432  * This gives the following logic table:
433  *
434  *	enabled	type	branch	  instuction
435  * -----------------------------+-----------
436  *	0	0	0	| NOP
437  *	0	0	1	| JMP
438  *	0	1	0	| NOP
439  *	0	1	1	| JMP
440  *
441  *	1	0	0	| JMP
442  *	1	0	1	| NOP
443  *	1	1	0	| JMP
444  *	1	1	1	| NOP
445  *
446  * Which gives the following functions:
447  *
448  *   dynamic: instruction = enabled ^ branch
449  *   static:  instruction = type ^ branch
450  *
451  * See jump_label_type() / jump_label_init_type().
452  */
453 
454 #define static_branch_likely(x)							\
455 ({										\
456 	bool branch;								\
457 	if (__builtin_types_compatible_p(typeof(*x), struct static_key_true))	\
458 		branch = !arch_static_branch(&(x)->key, true);			\
459 	else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
460 		branch = !arch_static_branch_jump(&(x)->key, true);		\
461 	else									\
462 		branch = ____wrong_branch_error();				\
463 	likely(branch);								\
464 })
465 
466 #define static_branch_unlikely(x)						\
467 ({										\
468 	bool branch;								\
469 	if (__builtin_types_compatible_p(typeof(*x), struct static_key_true))	\
470 		branch = arch_static_branch_jump(&(x)->key, false);		\
471 	else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
472 		branch = arch_static_branch(&(x)->key, false);			\
473 	else									\
474 		branch = ____wrong_branch_error();				\
475 	unlikely(branch);							\
476 })
477 
478 #else /* !CONFIG_JUMP_LABEL */
479 
480 #define static_branch_likely(x)		likely(static_key_enabled(&(x)->key))
481 #define static_branch_unlikely(x)	unlikely(static_key_enabled(&(x)->key))
482 
483 #endif /* CONFIG_JUMP_LABEL */
484 
485 /*
486  * Advanced usage; refcount, branch is enabled when: count != 0
487  */
488 
489 #define static_branch_inc(x)		static_key_slow_inc(&(x)->key)
490 #define static_branch_dec(x)		static_key_slow_dec(&(x)->key)
491 #define static_branch_inc_cpuslocked(x)	static_key_slow_inc_cpuslocked(&(x)->key)
492 #define static_branch_dec_cpuslocked(x)	static_key_slow_dec_cpuslocked(&(x)->key)
493 
494 /*
495  * Normal usage; boolean enable/disable.
496  */
497 
498 #define static_branch_enable(x)			static_key_enable(&(x)->key)
499 #define static_branch_disable(x)		static_key_disable(&(x)->key)
500 #define static_branch_enable_cpuslocked(x)	static_key_enable_cpuslocked(&(x)->key)
501 #define static_branch_disable_cpuslocked(x)	static_key_disable_cpuslocked(&(x)->key)
502 
503 #endif /* __ASSEMBLY__ */
504 
505 #endif	/* _LINUX_JUMP_LABEL_H */
506