diff options
Diffstat (limited to 'arch/x86/lib/cmpxchg16b_emu.S')
| -rw-r--r-- | arch/x86/lib/cmpxchg16b_emu.S | 43 |
1 files changed, 25 insertions, 18 deletions
diff --git a/arch/x86/lib/cmpxchg16b_emu.S b/arch/x86/lib/cmpxchg16b_emu.S index 33c70c0160ea..6962df315793 100644 --- a/arch/x86/lib/cmpxchg16b_emu.S +++ b/arch/x86/lib/cmpxchg16b_emu.S @@ -1,47 +1,54 @@ /* 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 */ SYM_FUNC_START(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). -# 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 PER_CPU_VAR(0(%rsi)), %rax + jne .Lnot_same + cmpq PER_CPU_VAR(8(%rsi)), %rdx + jne .Lnot_same - movq %rbx, PER_CPU_VAR((%rsi)) - movq %rcx, PER_CPU_VAR(8(%rsi)) + /* *ptr = new */ + movq %rbx, PER_CPU_VAR(0(%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 .Lnot_same: + /* *ptr != old */ + + /* old = *ptr */ + movq PER_CPU_VAR(0(%rsi)), %rax + movq PER_CPU_VAR(8(%rsi)), %rdx + + /* clear ZF in EFLAGS to indicate failure */ + andl $(~X86_EFLAGS_ZF), (%rsp) + popfq - xor %al,%al RET SYM_FUNC_END(this_cpu_cmpxchg16b_emu) |