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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 | |
c5905afb | 12 | * of a "if (static_key_false(&key))" statement is a unconditional branch (which |
efb3040d PZ |
13 | * defaults to false - and the true block is placed out of line). |
14 | * | |
c5905afb IM |
15 | * However at runtime we can change the branch target using |
16 | * static_key_slow_{inc,dec}(). These function as a 'reference' count on the key | |
efb3040d PZ |
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 | * | |
c5905afb | 20 | * Since this relies on modifying code the static_key_slow_{inc,dec}() functions |
efb3040d PZ |
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) | |
c5905afb IM |
29 | * cause significant performance degradation. Struct static_key_deferred and |
30 | * static_key_slow_dec_deferred() provide for this. | |
efb3040d PZ |
31 | * |
32 | * Lacking toolchain and or architecture support, it falls back to a simple | |
33 | * conditional branch. | |
c5905afb IM |
34 | * |
35 | * struct static_key my_key = STATIC_KEY_INIT_TRUE; | |
36 | * | |
37 | * if (static_key_true(&my_key)) { | |
38 | * } | |
39 | * | |
40 | * will result in the true case being in-line and starts the key with a single | |
41 | * reference. Mixing static_key_true() and static_key_false() on the same key is not | |
42 | * allowed. | |
43 | * | |
44 | * Not initializing the key (static data is initialized to 0s anyway) is the | |
47fbc518 | 45 | * same as using STATIC_KEY_INIT_FALSE. |
c5905afb IM |
46 | * |
47 | */ | |
efb3040d | 48 | |
d430d3d7 JB |
49 | #include <linux/types.h> |
50 | #include <linux/compiler.h> | |
51 | ||
45f81b1c | 52 | #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL) |
d430d3d7 | 53 | |
c5905afb | 54 | struct static_key { |
d430d3d7 | 55 | atomic_t enabled; |
c5905afb | 56 | /* Set lsb bit to 1 if branch is default true, 0 ot */ |
d430d3d7 JB |
57 | struct jump_entry *entries; |
58 | #ifdef CONFIG_MODULES | |
c5905afb | 59 | struct static_key_mod *next; |
d430d3d7 JB |
60 | #endif |
61 | }; | |
62 | ||
bf5438fc JB |
63 | # include <asm/jump_label.h> |
64 | # define HAVE_JUMP_LABEL | |
97ce2c88 | 65 | #endif /* CC_HAVE_ASM_GOTO && CONFIG_JUMP_LABEL */ |
bf5438fc JB |
66 | |
67 | enum jump_label_type { | |
d430d3d7 | 68 | JUMP_LABEL_DISABLE = 0, |
bf5438fc | 69 | JUMP_LABEL_ENABLE, |
bf5438fc JB |
70 | }; |
71 | ||
72 | struct module; | |
73 | ||
851cf6e7 | 74 | #include <linux/atomic.h> |
bf5438fc JB |
75 | #ifdef HAVE_JUMP_LABEL |
76 | ||
c5905afb IM |
77 | #define JUMP_LABEL_TRUE_BRANCH 1UL |
78 | ||
79 | static | |
80 | inline struct jump_entry *jump_label_get_entries(struct static_key *key) | |
81 | { | |
82 | return (struct jump_entry *)((unsigned long)key->entries | |
83 | & ~JUMP_LABEL_TRUE_BRANCH); | |
84 | } | |
85 | ||
86 | static inline bool jump_label_get_branch_default(struct static_key *key) | |
87 | { | |
88 | if ((unsigned long)key->entries & JUMP_LABEL_TRUE_BRANCH) | |
89 | return true; | |
90 | return false; | |
91 | } | |
92 | ||
93 | static __always_inline bool static_key_false(struct static_key *key) | |
94 | { | |
95 | return arch_static_branch(key); | |
96 | } | |
d430d3d7 | 97 | |
c5905afb IM |
98 | static __always_inline bool static_key_true(struct static_key *key) |
99 | { | |
100 | return !static_key_false(key); | |
101 | } | |
102 | ||
bf5438fc JB |
103 | extern struct jump_entry __start___jump_table[]; |
104 | extern struct jump_entry __stop___jump_table[]; | |
105 | ||
97ce2c88 | 106 | extern void jump_label_init(void); |
91bad2f8 JB |
107 | extern void jump_label_lock(void); |
108 | extern void jump_label_unlock(void); | |
bf5438fc | 109 | extern void arch_jump_label_transform(struct jump_entry *entry, |
37348804 | 110 | enum jump_label_type type); |
20284aa7 JF |
111 | extern void arch_jump_label_transform_static(struct jump_entry *entry, |
112 | enum jump_label_type type); | |
4c3ef6d7 | 113 | extern int jump_label_text_reserved(void *start, void *end); |
c5905afb IM |
114 | extern void static_key_slow_inc(struct static_key *key); |
115 | extern void static_key_slow_dec(struct static_key *key); | |
d430d3d7 | 116 | extern void jump_label_apply_nops(struct module *mod); |
c5905afb IM |
117 | |
118 | #define STATIC_KEY_INIT_TRUE ((struct static_key) \ | |
119 | { .enabled = ATOMIC_INIT(1), .entries = (void *)1 }) | |
120 | #define STATIC_KEY_INIT_FALSE ((struct static_key) \ | |
121 | { .enabled = ATOMIC_INIT(0), .entries = (void *)0 }) | |
bf5438fc | 122 | |
97ce2c88 | 123 | #else /* !HAVE_JUMP_LABEL */ |
bf5438fc | 124 | |
c5905afb | 125 | struct static_key { |
d430d3d7 JB |
126 | atomic_t enabled; |
127 | }; | |
bf5438fc | 128 | |
97ce2c88 JF |
129 | static __always_inline void jump_label_init(void) |
130 | { | |
131 | } | |
132 | ||
c5905afb IM |
133 | static __always_inline bool static_key_false(struct static_key *key) |
134 | { | |
135 | if (unlikely(atomic_read(&key->enabled)) > 0) | |
136 | return true; | |
137 | return false; | |
138 | } | |
139 | ||
140 | static __always_inline bool static_key_true(struct static_key *key) | |
d430d3d7 | 141 | { |
c5905afb | 142 | if (likely(atomic_read(&key->enabled)) > 0) |
d430d3d7 JB |
143 | return true; |
144 | return false; | |
145 | } | |
bf5438fc | 146 | |
c5905afb | 147 | static inline void static_key_slow_inc(struct static_key *key) |
d430d3d7 JB |
148 | { |
149 | atomic_inc(&key->enabled); | |
150 | } | |
bf5438fc | 151 | |
c5905afb | 152 | static inline void static_key_slow_dec(struct static_key *key) |
bf5438fc | 153 | { |
d430d3d7 | 154 | atomic_dec(&key->enabled); |
bf5438fc JB |
155 | } |
156 | ||
4c3ef6d7 JB |
157 | static inline int jump_label_text_reserved(void *start, void *end) |
158 | { | |
159 | return 0; | |
160 | } | |
161 | ||
91bad2f8 JB |
162 | static inline void jump_label_lock(void) {} |
163 | static inline void jump_label_unlock(void) {} | |
164 | ||
d430d3d7 JB |
165 | static inline int jump_label_apply_nops(struct module *mod) |
166 | { | |
167 | return 0; | |
168 | } | |
b2029520 | 169 | |
c5905afb IM |
170 | #define STATIC_KEY_INIT_TRUE ((struct static_key) \ |
171 | { .enabled = ATOMIC_INIT(1) }) | |
172 | #define STATIC_KEY_INIT_FALSE ((struct static_key) \ | |
173 | { .enabled = ATOMIC_INIT(0) }) | |
174 | ||
97ce2c88 | 175 | #endif /* HAVE_JUMP_LABEL */ |
d430d3d7 | 176 | |
c5905afb IM |
177 | #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE |
178 | #define jump_label_enabled static_key_enabled | |
ac99b862 | 179 | |
8eedce99 JB |
180 | static inline bool static_key_enabled(struct static_key *key) |
181 | { | |
182 | return (atomic_read(&key->enabled) > 0); | |
183 | } | |
184 | ||
97ce2c88 | 185 | #endif /* _LINUX_JUMP_LABEL_H */ |