1/* SPDX-License-Identifier: GPL-2.0-only */
2#include <linux/linkage.h>
3#include <asm/percpu.h>
4#include <asm/processor-flags.h>
5
6.text
7
8/*
9 * Emulate 'cmpxchg16b %gs:(%rsi)'
10 *
11 * Inputs:
12 * %rsi : memory location to compare
13 * %rax : low 64 bits of old value
14 * %rdx : high 64 bits of old value
15 * %rbx : low 64 bits of new value
16 * %rcx : high 64 bits of new value
17 *
18 * Notably this is not LOCK prefixed and is not safe against NMIs
19 */
20SYM_FUNC_START(this_cpu_cmpxchg16b_emu)
21
22 pushfq
23 cli
24
25 /* if (*ptr == old) */
26 cmpq __percpu (%rsi), %rax
27 jne .Lnot_same
28 cmpq __percpu 8(%rsi), %rdx
29 jne .Lnot_same
30
31 /* *ptr = new */
32 movq %rbx, __percpu (%rsi)
33 movq %rcx, __percpu 8(%rsi)
34
35 /* set ZF in EFLAGS to indicate success */
36 orl $X86_EFLAGS_ZF, (%rsp)
37
38 popfq
39 RET
40
41.Lnot_same:
42 /* *ptr != old */
43
44 /* old = *ptr */
45 movq __percpu (%rsi), %rax
46 movq __percpu 8(%rsi), %rdx
47
48 /* clear ZF in EFLAGS to indicate failure */
49 andl $(~X86_EFLAGS_ZF), (%rsp)
50
51 popfq
52 RET
53
54SYM_FUNC_END(this_cpu_cmpxchg16b_emu)
55