diff options
Diffstat (limited to 'arch/x86/lib/cmpxchg16b_emu.S')
| -rw-r--r-- | arch/x86/lib/cmpxchg16b_emu.S | 61 |
1 files changed, 31 insertions, 30 deletions
diff --git a/arch/x86/lib/cmpxchg16b_emu.S b/arch/x86/lib/cmpxchg16b_emu.S index 9b330242e740..4fb44894ad87 100644 --- a/arch/x86/lib/cmpxchg16b_emu.S +++ b/arch/x86/lib/cmpxchg16b_emu.S @@ -1,53 +1,54 @@ -/* - * This program is free software; you can redistribute it and/or - * modify it under the terms of the GNU General Public License - * as published by the Free Software Foundation; version 2 - * of the License. - * - */ +/* 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 - * %al : Operation successful + * + * Notably this is not LOCK prefixed and is not safe against NMIs */ -ENTRY(this_cpu_cmpxchg16b_emu) - -# -# Emulate 'cmpxchg16b %gs:(%rsi)' except we return the result in %al not -# via the ZF. Caller will access %al to get result. -# -# Note that this is only useful for a cpuops operation. Meaning that we -# do *not* have a fully atomic operation but just an operation that is -# *atomic* on a single cpu (as provided by the this_cpu_xx class of -# macros). -# +SYM_FUNC_START(this_cpu_cmpxchg16b_emu) + pushfq cli - cmpq PER_CPU_VAR((%rsi)), %rax - jne .Lnot_same - cmpq PER_CPU_VAR(8(%rsi)), %rdx - jne .Lnot_same + /* 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) - movq %rbx, PER_CPU_VAR((%rsi)) - movq %rcx, PER_CPU_VAR(8(%rsi)) + /* set ZF in EFLAGS to indicate success */ + orl $X86_EFLAGS_ZF, (%rsp) popfq - mov $1, %al - ret + 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 - xor %al,%al - ret + RET -ENDPROC(this_cpu_cmpxchg16b_emu) +SYM_FUNC_END(this_cpu_cmpxchg16b_emu) |