1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
|
#ifndef _LINUX_JUMP_LABEL_H
#define _LINUX_JUMP_LABEL_H
/*
* Jump label support
*
* Copyright (C) 2009-2012 Jason Baron <jbaron@redhat.com>
* Copyright (C) 2011-2012 Peter Zijlstra <pzijlstr@redhat.com>
*
* Jump labels provide an interface to generate dynamic branches using
* self-modifying code. Assuming toolchain and architecture support the result
* of a "if (static_key_false(&key))" statement is a unconditional branch (which
* defaults to false - and the true block is placed out of line).
*
* However at runtime we can change the branch target using
* static_key_slow_{inc,dec}(). These function as a 'reference' count on the key
* object and for as long as there are references all branches referring to
* that particular key will point to the (out of line) true block.
*
* Since this relies on modifying code the static_key_slow_{inc,dec}() functions
* must be considered absolute slow paths (machine wide synchronization etc.).
* OTOH, since the affected branches are unconditional their runtime overhead
* will be absolutely minimal, esp. in the default (off) case where the total
* effect is a single NOP of appropriate size. The on case will patch in a jump
* to the out-of-line block.
*
* When the control is directly exposed to userspace it is prudent to delay the
* decrement to avoid high frequency code modifications which can (and do)
* cause significant performance degradation. Struct static_key_deferred and
* static_key_slow_dec_deferred() provide for this.
*
* Lacking toolchain and or architecture support, it falls back to a simple
* conditional branch.
*
* struct static_key my_key = STATIC_KEY_INIT_TRUE;
*
* if (static_key_true(&my_key)) {
* }
*
* will result in the true case being in-line and starts the key with a single
* reference. Mixing static_key_true() and static_key_false() on the same key is not
* allowed.
*
* Not initializing the key (static data is initialized to 0s anyway) is the
* same as using STATIC_KEY_INIT_FALSE.
*
*/
#include <linux/types.h>
#include <linux/compiler.h>
#include <linux/workqueue.h>
#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
struct static_key {
atomic_t enabled;
/* Set lsb bit to 1 if branch is default true, 0 ot */
struct jump_entry *entries;
#ifdef CONFIG_MODULES
struct static_key_mod *next;
#endif
};
struct static_key_deferred {
struct static_key key;
unsigned long timeout;
struct delayed_work work;
};
# include <asm/jump_label.h>
# define HAVE_JUMP_LABEL
#endif /* CC_HAVE_ASM_GOTO && CONFIG_JUMP_LABEL */
enum jump_label_type {
JUMP_LABEL_DISABLE = 0,
JUMP_LABEL_ENABLE,
};
struct module;
#ifdef HAVE_JUMP_LABEL
#define JUMP_LABEL_TRUE_BRANCH 1UL
static
inline struct jump_entry *jump_label_get_entries(struct static_key *key)
{
return (struct jump_entry *)((unsigned long)key->entries
& ~JUMP_LABEL_TRUE_BRANCH);
}
static inline bool jump_label_get_branch_default(struct static_key *key)
{
if ((unsigned long)key->entries & JUMP_LABEL_TRUE_BRANCH)
return true;
return false;
}
static __always_inline bool static_key_false(struct static_key *key)
{
return arch_static_branch(key);
}
static __always_inline bool static_key_true(struct static_key *key)
{
return !static_key_false(key);
}
extern struct jump_entry __start___jump_table[];
extern struct jump_entry __stop___jump_table[];
extern void jump_label_init(void);
extern void jump_label_lock(void);
extern void jump_label_unlock(void);
extern void arch_jump_label_transform(struct jump_entry *entry,
enum jump_label_type type);
extern void arch_jump_label_transform_static(struct jump_entry *entry,
enum jump_label_type type);
extern int jump_label_text_reserved(void *start, void *end);
extern void static_key_slow_inc(struct static_key *key);
extern void static_key_slow_dec(struct static_key *key);
extern void static_key_slow_dec_deferred(struct static_key_deferred *key);
extern void jump_label_apply_nops(struct module *mod);
extern void
jump_label_rate_limit(struct static_key_deferred *key, unsigned long rl);
#define STATIC_KEY_INIT_TRUE ((struct static_key) \
{ .enabled = ATOMIC_INIT(1), .entries = (void *)1 })
#define STATIC_KEY_INIT_FALSE ((struct static_key) \
{ .enabled = ATOMIC_INIT(0), .entries = (void *)0 })
#else /* !HAVE_JUMP_LABEL */
#include <linux/atomic.h>
struct static_key {
atomic_t enabled;
};
static __always_inline void jump_label_init(void)
{
}
struct static_key_deferred {
struct static_key key;
};
static __always_inline bool static_key_false(struct static_key *key)
{
if (unlikely(atomic_read(&key->enabled)) > 0)
return true;
return false;
}
static __always_inline bool static_key_true(struct static_key *key)
{
if (likely(atomic_read(&key->enabled)) > 0)
return true;
return false;
}
static inline void static_key_slow_inc(struct static_key *key)
{
atomic_inc(&key->enabled);
}
static inline void static_key_slow_dec(struct static_key *key)
{
atomic_dec(&key->enabled);
}
static inline void static_key_slow_dec_deferred(struct static_key_deferred *key)
{
static_key_slow_dec(&key->key);
}
static inline int jump_label_text_reserved(void *start, void *end)
{
return 0;
}
static inline void jump_label_lock(void) {}
static inline void jump_label_unlock(void) {}
static inline int jump_label_apply_nops(struct module *mod)
{
return 0;
}
static inline void
jump_label_rate_limit(struct static_key_deferred *key,
unsigned long rl)
{
}
#define STATIC_KEY_INIT_TRUE ((struct static_key) \
{ .enabled = ATOMIC_INIT(1) })
#define STATIC_KEY_INIT_FALSE ((struct static_key) \
{ .enabled = ATOMIC_INIT(0) })
#endif /* HAVE_JUMP_LABEL */
#define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
#define jump_label_enabled static_key_enabled
static inline bool static_key_enabled(struct static_key *key)
{
return (atomic_read(&key->enabled) > 0);
}
#endif /* _LINUX_JUMP_LABEL_H */
|
