jump_label.h

  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#include <linux/cleanup.h>
 79
 80extern bool static_key_initialized;
 81
 82#define STATIC_KEY_CHECK_USE(key) WARN(!static_key_initialized,		      \
 83				    "%s(): static key '%pS' used before call to jump_label_init()", \
 84				    __func__, (key))
 85
 86struct static_key {
 87	atomic_t enabled;
 88#ifdef CONFIG_JUMP_LABEL
 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#endif	/* CONFIG_JUMP_LABEL */
108};
109
110#endif /* __ASSEMBLY__ */
111
112#ifdef CONFIG_JUMP_LABEL
113#include <asm/jump_label.h>
114
115#ifndef __ASSEMBLY__
116#ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE
117
118struct jump_entry {
119	s32 code;
120	s32 target;
121	long key;	// key may be far away from the core kernel under KASLR
122};
123
124static inline unsigned long jump_entry_code(const struct jump_entry *entry)
125{
126	return (unsigned long)&entry->code + entry->code;
127}
128
129static inline unsigned long jump_entry_target(const struct jump_entry *entry)
130{
131	return (unsigned long)&entry->target + entry->target;
132}
133
134static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
135{
136	long offset = entry->key & ~3L;
137
138	return (struct static_key *)((unsigned long)&entry->key + offset);
139}
140
141#else
142
143static inline unsigned long jump_entry_code(const struct jump_entry *entry)
144{
145	return entry->code;
146}
147
148static inline unsigned long jump_entry_target(const struct jump_entry *entry)
149{
150	return entry->target;
151}
152
153static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
154{
155	return (struct static_key *)((unsigned long)entry->key & ~3UL);
156}
157
158#endif
159
160static inline bool jump_entry_is_branch(const struct jump_entry *entry)
161{
162	return (unsigned long)entry->key & 1UL;
163}
164
165static inline bool jump_entry_is_init(const struct jump_entry *entry)
166{
167	return (unsigned long)entry->key & 2UL;
168}
169
170static inline void jump_entry_set_init(struct jump_entry *entry, bool set)
171{
172	if (set)
173		entry->key |= 2;
174	else
175		entry->key &= ~2;
176}
177
178static inline int jump_entry_size(struct jump_entry *entry)
179{
180#ifdef JUMP_LABEL_NOP_SIZE
181	return JUMP_LABEL_NOP_SIZE;
182#else
183	return arch_jump_entry_size(entry);
184#endif
185}
186
187#endif
188#endif
189
190#ifndef __ASSEMBLY__
191
192enum jump_label_type {
193	JUMP_LABEL_NOP = 0,
194	JUMP_LABEL_JMP,
195};
196
197struct module;
198
199#ifdef CONFIG_JUMP_LABEL
200
201#define JUMP_TYPE_FALSE		0UL
202#define JUMP_TYPE_TRUE		1UL
203#define JUMP_TYPE_LINKED	2UL
204#define JUMP_TYPE_MASK		3UL
205
206static __always_inline bool static_key_false(struct static_key *key)
207{
208	return arch_static_branch(key, false);
209}
210
211static __always_inline bool static_key_true(struct static_key *key)
212{
213	return !arch_static_branch(key, true);
214}
215
216extern struct jump_entry __start___jump_table[];
217extern struct jump_entry __stop___jump_table[];
218
219extern void jump_label_init(void);
220extern void jump_label_init_ro(void);
221extern void jump_label_lock(void);
222extern void jump_label_unlock(void);
223extern void arch_jump_label_transform(struct jump_entry *entry,
224				      enum jump_label_type type);
225extern bool arch_jump_label_transform_queue(struct jump_entry *entry,
226					    enum jump_label_type type);
227extern void arch_jump_label_transform_apply(void);
228extern int jump_label_text_reserved(void *start, void *end);
229extern bool static_key_slow_inc(struct static_key *key);
230extern bool static_key_fast_inc_not_disabled(struct static_key *key);
231extern void static_key_slow_dec(struct static_key *key);
232extern bool static_key_slow_inc_cpuslocked(struct static_key *key);
233extern void static_key_slow_dec_cpuslocked(struct static_key *key);
234extern int static_key_count(struct static_key *key);
235extern void static_key_enable(struct static_key *key);
236extern void static_key_disable(struct static_key *key);
237extern void static_key_enable_cpuslocked(struct static_key *key);
238extern void static_key_disable_cpuslocked(struct static_key *key);
239extern enum jump_label_type jump_label_init_type(struct jump_entry *entry);
240
241/*
242 * We should be using ATOMIC_INIT() for initializing .enabled, but
243 * the inclusion of atomic.h is problematic for inclusion of jump_label.h
244 * in 'low-level' headers. Thus, we are initializing .enabled with a
245 * raw value, but have added a BUILD_BUG_ON() to catch any issues in
246 * jump_label_init() see: kernel/jump_label.c.
247 */
248#define STATIC_KEY_INIT_TRUE					\
249	{ .enabled = { 1 },					\
250	  { .type = JUMP_TYPE_TRUE } }
251#define STATIC_KEY_INIT_FALSE					\
252	{ .enabled = { 0 },					\
253	  { .type = JUMP_TYPE_FALSE } }
254
255#else  /* !CONFIG_JUMP_LABEL */
256
257#include <linux/atomic.h>
258#include <linux/bug.h>
259
260static __always_inline int static_key_count(struct static_key *key)
261{
262	return raw_atomic_read(&key->enabled);
263}
264
265static __always_inline void jump_label_init(void)
266{
267	static_key_initialized = true;
268}
269
270static __always_inline void jump_label_init_ro(void) { }
271
272static __always_inline bool static_key_false(struct static_key *key)
273{
274	if (unlikely_notrace(static_key_count(key) > 0))
275		return true;
276	return false;
277}
278
279static __always_inline bool static_key_true(struct static_key *key)
280{
281	if (likely_notrace(static_key_count(key) > 0))
282		return true;
283	return false;
284}
285
286static inline bool static_key_fast_inc_not_disabled(struct static_key *key)
287{
288	int v;
289
290	STATIC_KEY_CHECK_USE(key);
291	/*
292	 * Prevent key->enabled getting negative to follow the same semantics
293	 * as for CONFIG_JUMP_LABEL=y, see kernel/jump_label.c comment.
294	 */
295	v = atomic_read(&key->enabled);
296	do {
297		if (v < 0 || (v + 1) < 0)
298			return false;
299	} while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1)));
300	return true;
301}
302#define static_key_slow_inc(key)	static_key_fast_inc_not_disabled(key)
303
304static inline void static_key_slow_dec(struct static_key *key)
305{
306	STATIC_KEY_CHECK_USE(key);
307	atomic_dec(&key->enabled);
308}
309
310#define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key)
311#define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key)
312
313static inline int jump_label_text_reserved(void *start, void *end)
314{
315	return 0;
316}
317
318static inline void jump_label_lock(void) {}
319static inline void jump_label_unlock(void) {}
320
321static inline void static_key_enable(struct static_key *key)
322{
323	STATIC_KEY_CHECK_USE(key);
324
325	if (atomic_read(&key->enabled) != 0) {
326		WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
327		return;
328	}
329	atomic_set(&key->enabled, 1);
330}
331
332static inline void static_key_disable(struct static_key *key)
333{
334	STATIC_KEY_CHECK_USE(key);
335
336	if (atomic_read(&key->enabled) != 1) {
337		WARN_ON_ONCE(atomic_read(&key->enabled) != 0);
338		return;
339	}
340	atomic_set(&key->enabled, 0);
341}
342
343#define static_key_enable_cpuslocked(k)		static_key_enable((k))
344#define static_key_disable_cpuslocked(k)	static_key_disable((k))
345
346#define STATIC_KEY_INIT_TRUE	{ .enabled = ATOMIC_INIT(1) }
347#define STATIC_KEY_INIT_FALSE	{ .enabled = ATOMIC_INIT(0) }
348
349#endif	/* CONFIG_JUMP_LABEL */
350
351DEFINE_LOCK_GUARD_0(jump_label_lock, jump_label_lock(), jump_label_unlock())
352
353#define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
354#define jump_label_enabled static_key_enabled
355
356/* -------------------------------------------------------------------------- */
357
358/*
359 * Two type wrappers around static_key, such that we can use compile time
360 * type differentiation to emit the right code.
361 *
362 * All the below code is macros in order to play type games.
363 */
364
365struct static_key_true {
366	struct static_key key;
367};
368
369struct static_key_false {
370	struct static_key key;
371};
372
373#define STATIC_KEY_TRUE_INIT  (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE,  }
374#define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, }
375
376#define DEFINE_STATIC_KEY_TRUE(name)	\
377	struct static_key_true name = STATIC_KEY_TRUE_INIT
378
379#define DEFINE_STATIC_KEY_TRUE_RO(name)	\
380	struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT
381
382#define DECLARE_STATIC_KEY_TRUE(name)	\
383	extern struct static_key_true name
384
385#define DEFINE_STATIC_KEY_FALSE(name)	\
386	struct static_key_false name = STATIC_KEY_FALSE_INIT
387
388#define DEFINE_STATIC_KEY_FALSE_RO(name)	\
389	struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT
390
391#define DECLARE_STATIC_KEY_FALSE(name)	\
392	extern struct static_key_false name
393
394#define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count)		\
395	struct static_key_true name[count] = {			\
396		[0 ... (count) - 1] = STATIC_KEY_TRUE_INIT,	\
397	}
398
399#define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count)		\
400	struct static_key_false name[count] = {			\
401		[0 ... (count) - 1] = STATIC_KEY_FALSE_INIT,	\
402	}
403
404#define _DEFINE_STATIC_KEY_1(name)	DEFINE_STATIC_KEY_TRUE(name)
405#define _DEFINE_STATIC_KEY_0(name)	DEFINE_STATIC_KEY_FALSE(name)
406#define DEFINE_STATIC_KEY_MAYBE(cfg, name)			\
407	__PASTE(_DEFINE_STATIC_KEY_, IS_ENABLED(cfg))(name)
408
409#define _DEFINE_STATIC_KEY_RO_1(name)	DEFINE_STATIC_KEY_TRUE_RO(name)
410#define _DEFINE_STATIC_KEY_RO_0(name)	DEFINE_STATIC_KEY_FALSE_RO(name)
411#define DEFINE_STATIC_KEY_MAYBE_RO(cfg, name)			\
412	__PASTE(_DEFINE_STATIC_KEY_RO_, IS_ENABLED(cfg))(name)
413
414#define _DECLARE_STATIC_KEY_1(name)	DECLARE_STATIC_KEY_TRUE(name)
415#define _DECLARE_STATIC_KEY_0(name)	DECLARE_STATIC_KEY_FALSE(name)
416#define DECLARE_STATIC_KEY_MAYBE(cfg, name)			\
417	__PASTE(_DECLARE_STATIC_KEY_, IS_ENABLED(cfg))(name)
418
419extern bool ____wrong_branch_error(void);
420
421#define static_key_enabled(x)							\
422({										\
423	if (!__builtin_types_compatible_p(typeof(*x), struct static_key) &&	\
424	    !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\
425	    !__builtin_types_compatible_p(typeof(*x), struct static_key_false))	\
426		____wrong_branch_error();					\
427	static_key_count((struct static_key *)x) > 0;				\
428})
429
430#ifdef CONFIG_JUMP_LABEL
431
432/*
433 * Combine the right initial value (type) with the right branch order
434 * to generate the desired result.
435 *
436 *
437 * type\branch|	likely (1)	      |	unlikely (0)
438 * -----------+-----------------------+------------------
439 *            |                       |
440 *  true (1)  |	   ...		      |	   ...
441 *            |    NOP		      |	   JMP L
442 *            |    <br-stmts>	      |	1: ...
443 *            |	L: ...		      |
444 *            |			      |
445 *            |			      |	L: <br-stmts>
446 *            |			      |	   jmp 1b
447 *            |                       |
448 * -----------+-----------------------+------------------
449 *            |                       |
450 *  false (0) |	   ...		      |	   ...
451 *            |    JMP L	      |	   NOP
452 *            |    <br-stmts>	      |	1: ...
453 *            |	L: ...		      |
454 *            |			      |
455 *            |			      |	L: <br-stmts>
456 *            |			      |	   jmp 1b
457 *            |                       |
458 * -----------+-----------------------+------------------
459 *
460 * The initial value is encoded in the LSB of static_key::entries,
461 * type: 0 = false, 1 = true.
462 *
463 * The branch type is encoded in the LSB of jump_entry::key,
464 * branch: 0 = unlikely, 1 = likely.
465 *
466 * This gives the following logic table:
467 *
468 *	enabled	type	branch	  instuction
469 * -----------------------------+-----------
470 *	0	0	0	| NOP
471 *	0	0	1	| JMP
472 *	0	1	0	| NOP
473 *	0	1	1	| JMP
474 *
475 *	1	0	0	| JMP
476 *	1	0	1	| NOP
477 *	1	1	0	| JMP
478 *	1	1	1	| NOP
479 *
480 * Which gives the following functions:
481 *
482 *   dynamic: instruction = enabled ^ branch
483 *   static:  instruction = type ^ branch
484 *
485 * See jump_label_type() / jump_label_init_type().
486 */
487
488#define static_branch_likely(x)							\
489({										\
490	bool branch;								\
491	if (__builtin_types_compatible_p(typeof(*x), struct static_key_true))	\
492		branch = !arch_static_branch(&(x)->key, true);			\
493	else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
494		branch = !arch_static_branch_jump(&(x)->key, true);		\
495	else									\
496		branch = ____wrong_branch_error();				\
497	likely_notrace(branch);								\
498})
499
500#define static_branch_unlikely(x)						\
501({										\
502	bool branch;								\
503	if (__builtin_types_compatible_p(typeof(*x), struct static_key_true))	\
504		branch = arch_static_branch_jump(&(x)->key, false);		\
505	else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
506		branch = arch_static_branch(&(x)->key, false);			\
507	else									\
508		branch = ____wrong_branch_error();				\
509	unlikely_notrace(branch);							\
510})
511
512#else /* !CONFIG_JUMP_LABEL */
513
514#define static_branch_likely(x)		likely_notrace(static_key_enabled(&(x)->key))
515#define static_branch_unlikely(x)	unlikely_notrace(static_key_enabled(&(x)->key))
516
517#endif /* CONFIG_JUMP_LABEL */
518
519#define static_branch_maybe(config, x)					\
520	(IS_ENABLED(config) ? static_branch_likely(x)			\
521			    : static_branch_unlikely(x))
522
523/*
524 * Advanced usage; refcount, branch is enabled when: count != 0
525 */
526
527#define static_branch_inc(x)		static_key_slow_inc(&(x)->key)
528#define static_branch_dec(x)		static_key_slow_dec(&(x)->key)
529#define static_branch_inc_cpuslocked(x)	static_key_slow_inc_cpuslocked(&(x)->key)
530#define static_branch_dec_cpuslocked(x)	static_key_slow_dec_cpuslocked(&(x)->key)
531
532/*
533 * Normal usage; boolean enable/disable.
534 */
535
536#define static_branch_enable(x)			static_key_enable(&(x)->key)
537#define static_branch_disable(x)		static_key_disable(&(x)->key)
538#define static_branch_enable_cpuslocked(x)	static_key_enable_cpuslocked(&(x)->key)
539#define static_branch_disable_cpuslocked(x)	static_key_disable_cpuslocked(&(x)->key)
540
541#endif /* __ASSEMBLY__ */
542
543#endif	/* _LINUX_JUMP_LABEL_H */