/* SPDX-License-Identifier: GPL-2.0-only */
#include <linux/linkage.h>
#include <asm/percpu.h>
#include <asm/processor-flags.h>

.text

/*
 * Emulate 'cmpxchg16b %gs:(%rsi)'
 *
 * Inputs:
 * %rsi : memory location to compare
 * %rax : low 64 bits of old value
 * %rdx : high 64 bits of old value
 * %rbx : low 64 bits of new value
 * %rcx : high 64 bits of new value
 *
 * Notably this is not LOCK prefixed and is not safe against NMIs
 */
SYM_FUNC_START(this_cpu_cmpxchg16b_emu)

        pushfq
        cli

        /* if (*ptr == old) */
        cmpq    __percpu (%rsi), %rax
        jne     .Lnot_same
        cmpq    __percpu 8(%rsi), %rdx
        jne     .Lnot_same

        /* *ptr = new */
        movq    %rbx, __percpu (%rsi)
        movq    %rcx, __percpu 8(%rsi)

        /* set ZF in EFLAGS to indicate success */
        orl     $X86_EFLAGS_ZF, (%rsp)

        popfq
        RET

.Lnot_same:
        /* *ptr != old */

        /* old = *ptr */
        movq    __percpu (%rsi), %rax
        movq    __percpu 8(%rsi), %rdx

        /* clear ZF in EFLAGS to indicate failure */
        andl    $(~X86_EFLAGS_ZF), (%rsp)

        popfq
        RET

SYM_FUNC_END(this_cpu_cmpxchg16b_emu)