diff options
Diffstat (limited to 'arch/x86/lib/cmpxchg16b_emu.S')
| -rw-r--r-- | arch/x86/lib/cmpxchg16b_emu.S | 54 |
1 files changed, 54 insertions, 0 deletions
diff --git a/arch/x86/lib/cmpxchg16b_emu.S b/arch/x86/lib/cmpxchg16b_emu.S new file mode 100644 index 0000000000..6962df3157 --- /dev/null +++ b/arch/x86/lib/cmpxchg16b_emu.S @@ -0,0 +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 + * + * 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 PER_CPU_VAR(0(%rsi)), %rax + jne .Lnot_same + cmpq PER_CPU_VAR(8(%rsi)), %rdx + jne .Lnot_same + + /* *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 + 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 + RET + +SYM_FUNC_END(this_cpu_cmpxchg16b_emu) |