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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 | |
97ce2c88 | 72 | #endif /* CC_HAVE_ASM_GOTO && CONFIG_JUMP_LABEL */ |
bf5438fc JB |
73 | |
74 | enum jump_label_type { | |
d430d3d7 | 75 | JUMP_LABEL_DISABLE = 0, |
bf5438fc | 76 | JUMP_LABEL_ENABLE, |
bf5438fc JB |
77 | }; |
78 | ||
79 | struct module; | |
80 | ||
851cf6e7 | 81 | #include <linux/atomic.h> |
bf5438fc JB |
82 | #ifdef HAVE_JUMP_LABEL |
83 | ||
f4be8433 JL |
84 | #define JUMP_LABEL_TYPE_FALSE_BRANCH 0UL |
85 | #define JUMP_LABEL_TYPE_TRUE_BRANCH 1UL | |
86 | #define JUMP_LABEL_TYPE_MASK 1UL | |
c5905afb IM |
87 | |
88 | static | |
89 | inline struct jump_entry *jump_label_get_entries(struct static_key *key) | |
90 | { | |
91 | return (struct jump_entry *)((unsigned long)key->entries | |
f4be8433 | 92 | & ~JUMP_LABEL_TYPE_MASK); |
c5905afb IM |
93 | } |
94 | ||
95 | static inline bool jump_label_get_branch_default(struct static_key *key) | |
96 | { | |
f4be8433 JL |
97 | if (((unsigned long)key->entries & JUMP_LABEL_TYPE_MASK) == |
98 | JUMP_LABEL_TYPE_TRUE_BRANCH) | |
c5905afb IM |
99 | return true; |
100 | return false; | |
101 | } | |
102 | ||
103 | static __always_inline bool static_key_false(struct static_key *key) | |
104 | { | |
105 | return arch_static_branch(key); | |
106 | } | |
d430d3d7 | 107 | |
c5905afb IM |
108 | static __always_inline bool static_key_true(struct static_key *key) |
109 | { | |
110 | return !static_key_false(key); | |
111 | } | |
112 | ||
bf5438fc JB |
113 | extern struct jump_entry __start___jump_table[]; |
114 | extern struct jump_entry __stop___jump_table[]; | |
115 | ||
97ce2c88 | 116 | extern void jump_label_init(void); |
91bad2f8 JB |
117 | extern void jump_label_lock(void); |
118 | extern void jump_label_unlock(void); | |
bf5438fc | 119 | extern void arch_jump_label_transform(struct jump_entry *entry, |
37348804 | 120 | enum jump_label_type type); |
20284aa7 JF |
121 | extern void arch_jump_label_transform_static(struct jump_entry *entry, |
122 | enum jump_label_type type); | |
4c3ef6d7 | 123 | extern int jump_label_text_reserved(void *start, void *end); |
c5905afb IM |
124 | extern void static_key_slow_inc(struct static_key *key); |
125 | extern void static_key_slow_dec(struct static_key *key); | |
d430d3d7 | 126 | extern void jump_label_apply_nops(struct module *mod); |
c5905afb | 127 | |
f4be8433 JL |
128 | #define STATIC_KEY_INIT_TRUE ((struct static_key) \ |
129 | { .enabled = ATOMIC_INIT(1), \ | |
130 | .entries = (void *)JUMP_LABEL_TYPE_TRUE_BRANCH }) | |
131 | #define STATIC_KEY_INIT_FALSE ((struct static_key) \ | |
132 | { .enabled = ATOMIC_INIT(0), \ | |
133 | .entries = (void *)JUMP_LABEL_TYPE_FALSE_BRANCH }) | |
bf5438fc | 134 | |
97ce2c88 | 135 | #else /* !HAVE_JUMP_LABEL */ |
bf5438fc | 136 | |
c5905afb | 137 | struct static_key { |
d430d3d7 JB |
138 | atomic_t enabled; |
139 | }; | |
bf5438fc | 140 | |
97ce2c88 JF |
141 | static __always_inline void jump_label_init(void) |
142 | { | |
c4b2c0c5 | 143 | static_key_initialized = true; |
97ce2c88 JF |
144 | } |
145 | ||
c5905afb IM |
146 | static __always_inline bool static_key_false(struct static_key *key) |
147 | { | |
261adc9a | 148 | if (unlikely(atomic_read(&key->enabled) > 0)) |
c5905afb IM |
149 | return true; |
150 | return false; | |
151 | } | |
152 | ||
153 | static __always_inline bool static_key_true(struct static_key *key) | |
d430d3d7 | 154 | { |
261adc9a | 155 | if (likely(atomic_read(&key->enabled) > 0)) |
d430d3d7 JB |
156 | return true; |
157 | return false; | |
158 | } | |
bf5438fc | 159 | |
c5905afb | 160 | static inline void static_key_slow_inc(struct static_key *key) |
d430d3d7 | 161 | { |
c4b2c0c5 | 162 | STATIC_KEY_CHECK_USE(); |
d430d3d7 JB |
163 | atomic_inc(&key->enabled); |
164 | } | |
bf5438fc | 165 | |
c5905afb | 166 | static inline void static_key_slow_dec(struct static_key *key) |
bf5438fc | 167 | { |
c4b2c0c5 | 168 | STATIC_KEY_CHECK_USE(); |
d430d3d7 | 169 | atomic_dec(&key->enabled); |
bf5438fc JB |
170 | } |
171 | ||
4c3ef6d7 JB |
172 | static inline int jump_label_text_reserved(void *start, void *end) |
173 | { | |
174 | return 0; | |
175 | } | |
176 | ||
91bad2f8 JB |
177 | static inline void jump_label_lock(void) {} |
178 | static inline void jump_label_unlock(void) {} | |
179 | ||
d430d3d7 JB |
180 | static inline int jump_label_apply_nops(struct module *mod) |
181 | { | |
182 | return 0; | |
183 | } | |
b2029520 | 184 | |
c5905afb IM |
185 | #define STATIC_KEY_INIT_TRUE ((struct static_key) \ |
186 | { .enabled = ATOMIC_INIT(1) }) | |
187 | #define STATIC_KEY_INIT_FALSE ((struct static_key) \ | |
188 | { .enabled = ATOMIC_INIT(0) }) | |
189 | ||
97ce2c88 | 190 | #endif /* HAVE_JUMP_LABEL */ |
d430d3d7 | 191 | |
c5905afb IM |
192 | #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE |
193 | #define jump_label_enabled static_key_enabled | |
ac99b862 | 194 | |
8eedce99 JB |
195 | static inline bool static_key_enabled(struct static_key *key) |
196 | { | |
197 | return (atomic_read(&key->enabled) > 0); | |
198 | } | |
199 | ||
97ce2c88 | 200 | #endif /* _LINUX_JUMP_LABEL_H */ |