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
|
/*
* Simple interface for 128-bit atomic operations.
*
* Copyright (C) 2018 Linaro, Ltd.
*
* This work is licensed under the terms of the GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*
* See docs/devel/atomics.txt for discussion about the guarantees each
* atomic primitive is meant to provide.
*/
#ifndef QEMU_ATOMIC128_H
#define QEMU_ATOMIC128_H
#include "qemu/int128.h"
/*
* GCC is a house divided about supporting large atomic operations.
*
* For hosts that only have large compare-and-swap, a legalistic reading
* of the C++ standard means that one cannot implement __atomic_read on
* read-only memory, and thus all atomic operations must synchronize
* through libatomic.
*
* See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80878
*
* This interpretation is not especially helpful for QEMU.
* For softmmu, all RAM is always read/write from the hypervisor.
* For user-only, if the guest doesn't implement such an __atomic_read
* then the host need not worry about it either.
*
* Moreover, using libatomic is not an option, because its interface is
* built for std::atomic<T>, and requires that *all* accesses to such an
* object go through the library. In our case we do not have an object
* in the C/C++ sense, but a view of memory as seen by the guest.
* The guest may issue a large atomic operation and then access those
* pieces using word-sized accesses. From the hypervisor, we have no
* way to connect those two actions.
*
* Therefore, special case each platform.
*/
#if defined(CONFIG_ATOMIC128)
static inline Int128 atomic16_cmpxchg(Int128 *ptr, Int128 cmp, Int128 new)
{
return qatomic_cmpxchg__nocheck(ptr, cmp, new);
}
# define HAVE_CMPXCHG128 1
#elif defined(CONFIG_CMPXCHG128)
static inline Int128 atomic16_cmpxchg(Int128 *ptr, Int128 cmp, Int128 new)
{
return __sync_val_compare_and_swap_16(ptr, cmp, new);
}
# define HAVE_CMPXCHG128 1
#elif defined(__aarch64__)
/* Through gcc 8, aarch64 has no support for 128-bit at all. */
static inline Int128 atomic16_cmpxchg(Int128 *ptr, Int128 cmp, Int128 new)
{
uint64_t cmpl = int128_getlo(cmp), cmph = int128_gethi(cmp);
uint64_t newl = int128_getlo(new), newh = int128_gethi(new);
uint64_t oldl, oldh;
uint32_t tmp;
asm("0: ldaxp %[oldl], %[oldh], %[mem]\n\t"
"cmp %[oldl], %[cmpl]\n\t"
"ccmp %[oldh], %[cmph], #0, eq\n\t"
"b.ne 1f\n\t"
"stlxp %w[tmp], %[newl], %[newh], %[mem]\n\t"
"cbnz %w[tmp], 0b\n"
"1:"
: [mem] "+m"(*ptr), [tmp] "=&r"(tmp),
[oldl] "=&r"(oldl), [oldh] "=&r"(oldh)
: [cmpl] "r"(cmpl), [cmph] "r"(cmph),
[newl] "r"(newl), [newh] "r"(newh)
: "memory", "cc");
return int128_make128(oldl, oldh);
}
# define HAVE_CMPXCHG128 1
#else
/* Fallback definition that must be optimized away, or error. */
Int128 QEMU_ERROR("unsupported atomic")
atomic16_cmpxchg(Int128 *ptr, Int128 cmp, Int128 new);
# define HAVE_CMPXCHG128 0
#endif /* Some definition for HAVE_CMPXCHG128 */
#if defined(CONFIG_ATOMIC128)
static inline Int128 atomic16_read(Int128 *ptr)
{
return qatomic_read__nocheck(ptr);
}
static inline void atomic16_set(Int128 *ptr, Int128 val)
{
qatomic_set__nocheck(ptr, val);
}
# define HAVE_ATOMIC128 1
#elif !defined(CONFIG_USER_ONLY) && defined(__aarch64__)
/* We can do better than cmpxchg for AArch64. */
static inline Int128 atomic16_read(Int128 *ptr)
{
uint64_t l, h;
uint32_t tmp;
/* The load must be paired with the store to guarantee not tearing. */
asm("0: ldxp %[l], %[h], %[mem]\n\t"
"stxp %w[tmp], %[l], %[h], %[mem]\n\t"
"cbnz %w[tmp], 0b"
: [mem] "+m"(*ptr), [tmp] "=r"(tmp), [l] "=r"(l), [h] "=r"(h));
return int128_make128(l, h);
}
static inline void atomic16_set(Int128 *ptr, Int128 val)
{
uint64_t l = int128_getlo(val), h = int128_gethi(val);
uint64_t t1, t2;
/* Load into temporaries to acquire the exclusive access lock. */
asm("0: ldxp %[t1], %[t2], %[mem]\n\t"
"stxp %w[t1], %[l], %[h], %[mem]\n\t"
"cbnz %w[t1], 0b"
: [mem] "+m"(*ptr), [t1] "=&r"(t1), [t2] "=&r"(t2)
: [l] "r"(l), [h] "r"(h));
}
# define HAVE_ATOMIC128 1
#elif !defined(CONFIG_USER_ONLY) && HAVE_CMPXCHG128
static inline Int128 atomic16_read(Int128 *ptr)
{
/* Maybe replace 0 with 0, returning the old value. */
return atomic16_cmpxchg(ptr, 0, 0);
}
static inline void atomic16_set(Int128 *ptr, Int128 val)
{
Int128 old = *ptr, cmp;
do {
cmp = old;
old = atomic16_cmpxchg(ptr, cmp, val);
} while (old != cmp);
}
# define HAVE_ATOMIC128 1
#else
/* Fallback definitions that must be optimized away, or error. */
Int128 QEMU_ERROR("unsupported atomic") atomic16_read(Int128 *ptr);
void QEMU_ERROR("unsupported atomic") atomic16_set(Int128 *ptr, Int128 val);
# define HAVE_ATOMIC128 0
#endif /* Some definition for HAVE_ATOMIC128 */
#endif /* QEMU_ATOMIC128_H */
|
