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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 | |
11 | * self-modifying code. Assuming toolchain and architecture support the result | |
12 | * of a "if (static_branch(&key))" statement is a unconditional branch (which | |
13 | * defaults to false - and the true block is placed out of line). | |
14 | * | |
15 | * However at runtime we can change the 'static' branch target using | |
16 | * jump_label_{inc,dec}(). These function as a 'reference' count on the key | |
17 | * object and for as long as there are references all branches referring to | |
18 | * that particular key will point to the (out of line) true block. | |
19 | * | |
20 | * Since this relies on modifying code the jump_label_{inc,dec}() functions | |
21 | * must be considered absolute slow paths (machine wide synchronization etc.). | |
22 | * OTOH, since the affected branches are unconditional their runtime overhead | |
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 | * | |
27 | * When the control is directly exposed to userspace it is prudent to delay the | |
28 | * decrement to avoid high frequency code modifications which can (and do) | |
29 | * cause significant performance degradation. Struct jump_label_key_deferred and | |
30 | * jump_label_dec_deferred() provide for this. | |
31 | * | |
32 | * Lacking toolchain and or architecture support, it falls back to a simple | |
33 | * conditional branch. | |
34 | */ | |
35 | ||
d430d3d7 JB |
36 | #include <linux/types.h> |
37 | #include <linux/compiler.h> | |
b2029520 | 38 | #include <linux/workqueue.h> |
d430d3d7 | 39 | |
45f81b1c | 40 | #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL) |
d430d3d7 JB |
41 | |
42 | struct jump_label_key { | |
43 | atomic_t enabled; | |
44 | struct jump_entry *entries; | |
45 | #ifdef CONFIG_MODULES | |
46 | struct jump_label_mod *next; | |
47 | #endif | |
48 | }; | |
49 | ||
b2029520 GN |
50 | struct jump_label_key_deferred { |
51 | struct jump_label_key key; | |
52 | unsigned long timeout; | |
53 | struct delayed_work work; | |
54 | }; | |
55 | ||
bf5438fc JB |
56 | # include <asm/jump_label.h> |
57 | # define HAVE_JUMP_LABEL | |
97ce2c88 | 58 | #endif /* CC_HAVE_ASM_GOTO && CONFIG_JUMP_LABEL */ |
bf5438fc JB |
59 | |
60 | enum jump_label_type { | |
d430d3d7 | 61 | JUMP_LABEL_DISABLE = 0, |
bf5438fc | 62 | JUMP_LABEL_ENABLE, |
bf5438fc JB |
63 | }; |
64 | ||
65 | struct module; | |
66 | ||
67 | #ifdef HAVE_JUMP_LABEL | |
68 | ||
d430d3d7 | 69 | #ifdef CONFIG_MODULES |
d5d9a3b1 | 70 | #define JUMP_LABEL_INIT {ATOMIC_INIT(0), NULL, NULL} |
d430d3d7 | 71 | #else |
d5d9a3b1 | 72 | #define JUMP_LABEL_INIT {ATOMIC_INIT(0), NULL} |
d430d3d7 JB |
73 | #endif |
74 | ||
75 | static __always_inline bool static_branch(struct jump_label_key *key) | |
76 | { | |
77 | return arch_static_branch(key); | |
78 | } | |
79 | ||
bf5438fc JB |
80 | extern struct jump_entry __start___jump_table[]; |
81 | extern struct jump_entry __stop___jump_table[]; | |
82 | ||
97ce2c88 | 83 | extern void jump_label_init(void); |
91bad2f8 JB |
84 | extern void jump_label_lock(void); |
85 | extern void jump_label_unlock(void); | |
bf5438fc | 86 | extern void arch_jump_label_transform(struct jump_entry *entry, |
37348804 | 87 | enum jump_label_type type); |
20284aa7 JF |
88 | extern void arch_jump_label_transform_static(struct jump_entry *entry, |
89 | enum jump_label_type type); | |
4c3ef6d7 | 90 | extern int jump_label_text_reserved(void *start, void *end); |
d430d3d7 JB |
91 | extern void jump_label_inc(struct jump_label_key *key); |
92 | extern void jump_label_dec(struct jump_label_key *key); | |
b2029520 | 93 | extern void jump_label_dec_deferred(struct jump_label_key_deferred *key); |
d430d3d7 JB |
94 | extern bool jump_label_enabled(struct jump_label_key *key); |
95 | extern void jump_label_apply_nops(struct module *mod); | |
b2029520 GN |
96 | extern void jump_label_rate_limit(struct jump_label_key_deferred *key, |
97 | unsigned long rl); | |
bf5438fc | 98 | |
97ce2c88 | 99 | #else /* !HAVE_JUMP_LABEL */ |
bf5438fc | 100 | |
60063497 | 101 | #include <linux/atomic.h> |
bf5438fc | 102 | |
d430d3d7 | 103 | #define JUMP_LABEL_INIT {ATOMIC_INIT(0)} |
bf5438fc | 104 | |
d430d3d7 JB |
105 | struct jump_label_key { |
106 | atomic_t enabled; | |
107 | }; | |
bf5438fc | 108 | |
97ce2c88 JF |
109 | static __always_inline void jump_label_init(void) |
110 | { | |
111 | } | |
112 | ||
b2029520 GN |
113 | struct jump_label_key_deferred { |
114 | struct jump_label_key key; | |
115 | }; | |
116 | ||
d430d3d7 JB |
117 | static __always_inline bool static_branch(struct jump_label_key *key) |
118 | { | |
119 | if (unlikely(atomic_read(&key->enabled))) | |
120 | return true; | |
121 | return false; | |
122 | } | |
bf5438fc | 123 | |
d430d3d7 JB |
124 | static inline void jump_label_inc(struct jump_label_key *key) |
125 | { | |
126 | atomic_inc(&key->enabled); | |
127 | } | |
bf5438fc | 128 | |
d430d3d7 | 129 | static inline void jump_label_dec(struct jump_label_key *key) |
bf5438fc | 130 | { |
d430d3d7 | 131 | atomic_dec(&key->enabled); |
bf5438fc JB |
132 | } |
133 | ||
b2029520 GN |
134 | static inline void jump_label_dec_deferred(struct jump_label_key_deferred *key) |
135 | { | |
136 | jump_label_dec(&key->key); | |
137 | } | |
138 | ||
4c3ef6d7 JB |
139 | static inline int jump_label_text_reserved(void *start, void *end) |
140 | { | |
141 | return 0; | |
142 | } | |
143 | ||
91bad2f8 JB |
144 | static inline void jump_label_lock(void) {} |
145 | static inline void jump_label_unlock(void) {} | |
146 | ||
d430d3d7 JB |
147 | static inline bool jump_label_enabled(struct jump_label_key *key) |
148 | { | |
149 | return !!atomic_read(&key->enabled); | |
150 | } | |
bf5438fc | 151 | |
d430d3d7 JB |
152 | static inline int jump_label_apply_nops(struct module *mod) |
153 | { | |
154 | return 0; | |
155 | } | |
b2029520 GN |
156 | |
157 | static inline void jump_label_rate_limit(struct jump_label_key_deferred *key, | |
158 | unsigned long rl) | |
159 | { | |
160 | } | |
97ce2c88 | 161 | #endif /* HAVE_JUMP_LABEL */ |
d430d3d7 | 162 | |
ac99b862 PZ |
163 | #define jump_label_key_enabled ((struct jump_label_key){ .enabled = ATOMIC_INIT(1), }) |
164 | #define jump_label_key_disabled ((struct jump_label_key){ .enabled = ATOMIC_INIT(0), }) | |
165 | ||
97ce2c88 | 166 | #endif /* _LINUX_JUMP_LABEL_H */ |