cmpxchg16b_emu.S

 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)