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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> | |
c4b2c0c5 HFS |
51 | #include <linux/bug.h> |
52 | ||
53 | extern bool static_key_initialized; | |
54 | ||
55 | #define STATIC_KEY_CHECK_USE() WARN(!static_key_initialized, \ | |
56 | "%s used before call to jump_label_init", \ | |
57 | __func__) | |
d430d3d7 | 58 | |
45f81b1c | 59 | #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL) |
d430d3d7 | 60 | |
c5905afb | 61 | struct static_key { |
d430d3d7 | 62 | atomic_t enabled; |
c5905afb | 63 | /* Set lsb bit to 1 if branch is default true, 0 ot */ |
d430d3d7 JB |
64 | struct jump_entry *entries; |
65 | #ifdef CONFIG_MODULES | |
c5905afb | 66 | struct static_key_mod *next; |
d430d3d7 JB |
67 | #endif |
68 | }; | |
69 | ||
bf5438fc JB |
70 | # include <asm/jump_label.h> |
71 | # define HAVE_JUMP_LABEL | |
ea5e9539 MG |
72 | #else |
73 | struct static_key { | |
74 | atomic_t enabled; | |
75 | }; | |
97ce2c88 | 76 | #endif /* CC_HAVE_ASM_GOTO && CONFIG_JUMP_LABEL */ |
bf5438fc JB |
77 | |
78 | enum jump_label_type { | |
d430d3d7 | 79 | JUMP_LABEL_DISABLE = 0, |
bf5438fc | 80 | JUMP_LABEL_ENABLE, |
bf5438fc JB |
81 | }; |
82 | ||
83 | struct module; | |
84 | ||
851cf6e7 | 85 | #include <linux/atomic.h> |
ea5e9539 MG |
86 | |
87 | static inline int static_key_count(struct static_key *key) | |
88 | { | |
89 | return atomic_read(&key->enabled); | |
90 | } | |
91 | ||
bf5438fc JB |
92 | #ifdef HAVE_JUMP_LABEL |
93 | ||
f4be8433 JL |
94 | #define JUMP_LABEL_TYPE_FALSE_BRANCH 0UL |
95 | #define JUMP_LABEL_TYPE_TRUE_BRANCH 1UL | |
96 | #define JUMP_LABEL_TYPE_MASK 1UL | |
c5905afb IM |
97 | |
98 | static | |
99 | inline struct jump_entry *jump_label_get_entries(struct static_key *key) | |
100 | { | |
101 | return (struct jump_entry *)((unsigned long)key->entries | |
f4be8433 | 102 | & ~JUMP_LABEL_TYPE_MASK); |
c5905afb IM |
103 | } |
104 | ||
105 | static inline bool jump_label_get_branch_default(struct static_key *key) | |
106 | { | |
f4be8433 JL |
107 | if (((unsigned long)key->entries & JUMP_LABEL_TYPE_MASK) == |
108 | JUMP_LABEL_TYPE_TRUE_BRANCH) | |
c5905afb IM |
109 | return true; |
110 | return false; | |
111 | } | |
112 | ||
113 | static __always_inline bool static_key_false(struct static_key *key) | |
114 | { | |
115 | return arch_static_branch(key); | |
116 | } | |
d430d3d7 | 117 | |
c5905afb IM |
118 | static __always_inline bool static_key_true(struct static_key *key) |
119 | { | |
120 | return !static_key_false(key); | |
121 | } | |
122 | ||
bf5438fc JB |
123 | extern struct jump_entry __start___jump_table[]; |
124 | extern struct jump_entry __stop___jump_table[]; | |
125 | ||
97ce2c88 | 126 | extern void jump_label_init(void); |
91bad2f8 JB |
127 | extern void jump_label_lock(void); |
128 | extern void jump_label_unlock(void); | |
bf5438fc | 129 | extern void arch_jump_label_transform(struct jump_entry *entry, |
37348804 | 130 | enum jump_label_type type); |
20284aa7 JF |
131 | extern void arch_jump_label_transform_static(struct jump_entry *entry, |
132 | enum jump_label_type type); | |
4c3ef6d7 | 133 | extern int jump_label_text_reserved(void *start, void *end); |
c5905afb IM |
134 | extern void static_key_slow_inc(struct static_key *key); |
135 | extern void static_key_slow_dec(struct static_key *key); | |
d430d3d7 | 136 | extern void jump_label_apply_nops(struct module *mod); |
c5905afb | 137 | |
f4be8433 JL |
138 | #define STATIC_KEY_INIT_TRUE ((struct static_key) \ |
139 | { .enabled = ATOMIC_INIT(1), \ | |
140 | .entries = (void *)JUMP_LABEL_TYPE_TRUE_BRANCH }) | |
141 | #define STATIC_KEY_INIT_FALSE ((struct static_key) \ | |
142 | { .enabled = ATOMIC_INIT(0), \ | |
143 | .entries = (void *)JUMP_LABEL_TYPE_FALSE_BRANCH }) | |
bf5438fc | 144 | |
97ce2c88 | 145 | #else /* !HAVE_JUMP_LABEL */ |
bf5438fc | 146 | |
97ce2c88 JF |
147 | static __always_inline void jump_label_init(void) |
148 | { | |
c4b2c0c5 | 149 | static_key_initialized = true; |
97ce2c88 JF |
150 | } |
151 | ||
c5905afb IM |
152 | static __always_inline bool static_key_false(struct static_key *key) |
153 | { | |
ea5e9539 | 154 | if (unlikely(static_key_count(key) > 0)) |
c5905afb IM |
155 | return true; |
156 | return false; | |
157 | } | |
158 | ||
159 | static __always_inline bool static_key_true(struct static_key *key) | |
d430d3d7 | 160 | { |
ea5e9539 | 161 | if (likely(static_key_count(key) > 0)) |
d430d3d7 JB |
162 | return true; |
163 | return false; | |
164 | } | |
bf5438fc | 165 | |
c5905afb | 166 | static inline void static_key_slow_inc(struct static_key *key) |
d430d3d7 | 167 | { |
c4b2c0c5 | 168 | STATIC_KEY_CHECK_USE(); |
d430d3d7 JB |
169 | atomic_inc(&key->enabled); |
170 | } | |
bf5438fc | 171 | |
c5905afb | 172 | static inline void static_key_slow_dec(struct static_key *key) |
bf5438fc | 173 | { |
c4b2c0c5 | 174 | STATIC_KEY_CHECK_USE(); |
d430d3d7 | 175 | atomic_dec(&key->enabled); |
bf5438fc JB |
176 | } |
177 | ||
4c3ef6d7 JB |
178 | static inline int jump_label_text_reserved(void *start, void *end) |
179 | { | |
180 | return 0; | |
181 | } | |
182 | ||
91bad2f8 JB |
183 | static inline void jump_label_lock(void) {} |
184 | static inline void jump_label_unlock(void) {} | |
185 | ||
d430d3d7 JB |
186 | static inline int jump_label_apply_nops(struct module *mod) |
187 | { | |
188 | return 0; | |
189 | } | |
b2029520 | 190 | |
c5905afb IM |
191 | #define STATIC_KEY_INIT_TRUE ((struct static_key) \ |
192 | { .enabled = ATOMIC_INIT(1) }) | |
193 | #define STATIC_KEY_INIT_FALSE ((struct static_key) \ | |
194 | { .enabled = ATOMIC_INIT(0) }) | |
195 | ||
97ce2c88 | 196 | #endif /* HAVE_JUMP_LABEL */ |
d430d3d7 | 197 | |
c5905afb IM |
198 | #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE |
199 | #define jump_label_enabled static_key_enabled | |
ac99b862 | 200 | |
8eedce99 JB |
201 | static inline bool static_key_enabled(struct static_key *key) |
202 | { | |
ea5e9539 | 203 | return static_key_count(key) > 0; |
8eedce99 JB |
204 | } |
205 | ||
97ce2c88 | 206 | #endif /* _LINUX_JUMP_LABEL_H */ |