1 /*
2 * Copyright (C) 2018, Emilio G. Cota <cota@braap.org>
3 *
4 * License: GNU GPL, version 2 or later.
5 * See the COPYING file in the top-level directory.
6 */
7 #include "qemu/osdep.h"
8 #include "qemu/atomic.h"
9 #include "qemu/thread.h"
10 #include "qemu/cacheinfo.h"
11 #include "qemu/memalign.h"
12
13 #ifdef CONFIG_ATOMIC64
14 #error This file must only be compiled if !CONFIG_ATOMIC64
15 #endif
16
17 /*
18 * When !CONFIG_ATOMIC64, we serialize both reads and writes with spinlocks.
19 * We use an array of spinlocks, with padding computed at run-time based on
20 * the host's dcache line size.
21 * We point to the array with a void * to simplify the padding's computation.
22 * Each spinlock is located every lock_size bytes.
23 */
24 static void *lock_array;
25 static size_t lock_size;
26
27 /*
28 * Systems without CONFIG_ATOMIC64 are unlikely to have many cores, so we use a
29 * small array of locks.
30 */
31 #define NR_LOCKS 16
32
addr_to_lock(const void * addr)33 static QemuSpin *addr_to_lock(const void *addr)
34 {
35 uintptr_t a = (uintptr_t)addr;
36 uintptr_t idx;
37
38 idx = a >> qemu_dcache_linesize_log;
39 idx ^= (idx >> 8) ^ (idx >> 16);
40 idx &= NR_LOCKS - 1;
41 return lock_array + idx * lock_size;
42 }
43
44 #define GEN_READ(name, type) \
45 type name(const type *ptr) \
46 { \
47 QemuSpin *lock = addr_to_lock(ptr); \
48 type ret; \
49 \
50 qemu_spin_lock(lock); \
51 ret = *ptr; \
52 qemu_spin_unlock(lock); \
53 return ret; \
54 }
55
GEN_READ(qatomic_read_i64,int64_t)56 GEN_READ(qatomic_read_i64, int64_t)
57 GEN_READ(qatomic_read_u64, uint64_t)
58 #undef GEN_READ
59
60 #define GEN_SET(name, type) \
61 void name(type *ptr, type val) \
62 { \
63 QemuSpin *lock = addr_to_lock(ptr); \
64 \
65 qemu_spin_lock(lock); \
66 *ptr = val; \
67 qemu_spin_unlock(lock); \
68 }
69
70 GEN_SET(qatomic_set_i64, int64_t)
71 GEN_SET(qatomic_set_u64, uint64_t)
72 #undef GEN_SET
73
74 void qatomic64_init(void)
75 {
76 int i;
77
78 lock_size = ROUND_UP(sizeof(QemuSpin), qemu_dcache_linesize);
79 lock_array = qemu_memalign(qemu_dcache_linesize, lock_size * NR_LOCKS);
80 for (i = 0; i < NR_LOCKS; i++) {
81 QemuSpin *lock = lock_array + i * lock_size;
82
83 qemu_spin_init(lock);
84 }
85 }
86