2026-01-21 18:59:54 +08:00
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/* SPDX-License-Identifier: GPL-2.0-only */
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#include <linux/linkage.h>
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#include <asm/percpu.h>
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2026-01-29 22:25:33 +08:00
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#include <asm/processor-flags.h>
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2026-01-21 18:59:54 +08:00
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.text
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/*
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2026-01-29 22:25:33 +08:00
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* Emulate 'cmpxchg16b %gs:(%rsi)'
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*
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2026-01-21 18:59:54 +08:00
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* Inputs:
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* %rsi : memory location to compare
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* %rax : low 64 bits of old value
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* %rdx : high 64 bits of old value
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* %rbx : low 64 bits of new value
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* %rcx : high 64 bits of new value
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2026-01-29 22:25:33 +08:00
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*
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* Notably this is not LOCK prefixed and is not safe against NMIs
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2026-01-21 18:59:54 +08:00
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*/
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SYM_FUNC_START(this_cpu_cmpxchg16b_emu)
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pushfq
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cli
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2026-01-29 22:25:33 +08:00
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/* if (*ptr == old) */
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cmpq PER_CPU_VAR(0(%rsi)), %rax
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jne .Lnot_same
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cmpq PER_CPU_VAR(8(%rsi)), %rdx
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jne .Lnot_same
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2026-01-21 18:59:54 +08:00
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2026-01-29 22:25:33 +08:00
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/* *ptr = new */
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movq %rbx, PER_CPU_VAR(0(%rsi))
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movq %rcx, PER_CPU_VAR(8(%rsi))
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/* set ZF in EFLAGS to indicate success */
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orl $X86_EFLAGS_ZF, (%rsp)
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2026-01-21 18:59:54 +08:00
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popfq
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RET
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.Lnot_same:
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2026-01-29 22:25:33 +08:00
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/* *ptr != old */
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/* old = *ptr */
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movq PER_CPU_VAR(0(%rsi)), %rax
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movq PER_CPU_VAR(8(%rsi)), %rdx
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/* clear ZF in EFLAGS to indicate failure */
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andl $(~X86_EFLAGS_ZF), (%rsp)
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2026-01-21 18:59:54 +08:00
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popfq
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RET
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SYM_FUNC_END(this_cpu_cmpxchg16b_emu)
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