Merge tag 'imx-fixes-5.15-4' of git://git.kernel.org/pub/scm/linux/kernel/git/shawngu...
[platform/kernel/linux-starfive.git] / include / asm-generic / rwonce.h
1 /* SPDX-License-Identifier: GPL-2.0 */
2 /*
3  * Prevent the compiler from merging or refetching reads or writes. The
4  * compiler is also forbidden from reordering successive instances of
5  * READ_ONCE and WRITE_ONCE, but only when the compiler is aware of some
6  * particular ordering. One way to make the compiler aware of ordering is to
7  * put the two invocations of READ_ONCE or WRITE_ONCE in different C
8  * statements.
9  *
10  * These two macros will also work on aggregate data types like structs or
11  * unions.
12  *
13  * Their two major use cases are: (1) Mediating communication between
14  * process-level code and irq/NMI handlers, all running on the same CPU,
15  * and (2) Ensuring that the compiler does not fold, spindle, or otherwise
16  * mutilate accesses that either do not require ordering or that interact
17  * with an explicit memory barrier or atomic instruction that provides the
18  * required ordering.
19  */
20 #ifndef __ASM_GENERIC_RWONCE_H
21 #define __ASM_GENERIC_RWONCE_H
22
23 #ifndef __ASSEMBLY__
24
25 #include <linux/compiler_types.h>
26 #include <linux/kasan-checks.h>
27 #include <linux/kcsan-checks.h>
28
29 /*
30  * Yes, this permits 64-bit accesses on 32-bit architectures. These will
31  * actually be atomic in some cases (namely Armv7 + LPAE), but for others we
32  * rely on the access being split into 2x32-bit accesses for a 32-bit quantity
33  * (e.g. a virtual address) and a strong prevailing wind.
34  */
35 #define compiletime_assert_rwonce_type(t)                                       \
36         compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long),  \
37                 "Unsupported access size for {READ,WRITE}_ONCE().")
38
39 /*
40  * Use __READ_ONCE() instead of READ_ONCE() if you do not require any
41  * atomicity. Note that this may result in tears!
42  */
43 #ifndef __READ_ONCE
44 #define __READ_ONCE(x)  (*(const volatile __unqual_scalar_typeof(x) *)&(x))
45 #endif
46
47 #define READ_ONCE(x)                                                    \
48 ({                                                                      \
49         compiletime_assert_rwonce_type(x);                              \
50         __READ_ONCE(x);                                                 \
51 })
52
53 #define __WRITE_ONCE(x, val)                                            \
54 do {                                                                    \
55         *(volatile typeof(x) *)&(x) = (val);                            \
56 } while (0)
57
58 #define WRITE_ONCE(x, val)                                              \
59 do {                                                                    \
60         compiletime_assert_rwonce_type(x);                              \
61         __WRITE_ONCE(x, val);                                           \
62 } while (0)
63
64 static __no_sanitize_or_inline
65 unsigned long __read_once_word_nocheck(const void *addr)
66 {
67         return __READ_ONCE(*(unsigned long *)addr);
68 }
69
70 /*
71  * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need to load a
72  * word from memory atomically but without telling KASAN/KCSAN. This is
73  * usually used by unwinding code when walking the stack of a running process.
74  */
75 #define READ_ONCE_NOCHECK(x)                                            \
76 ({                                                                      \
77         compiletime_assert(sizeof(x) == sizeof(unsigned long),          \
78                 "Unsupported access size for READ_ONCE_NOCHECK().");    \
79         (typeof(x))__read_once_word_nocheck(&(x));                      \
80 })
81
82 static __no_kasan_or_inline
83 unsigned long read_word_at_a_time(const void *addr)
84 {
85         kasan_check_read(addr, 1);
86         return *(unsigned long *)addr;
87 }
88
89 #endif /* __ASSEMBLY__ */
90 #endif  /* __ASM_GENERIC_RWONCE_H */