* [PATCH] vmx: use mov instead of lea in __vmx_vcpu_run()
@ 2022-11-17 20:36 Alexey Dobriyan
2022-11-18 0:20 ` Sean Christopherson
0 siblings, 1 reply; 2+ messages in thread
From: Alexey Dobriyan @ 2022-11-17 20:36 UTC (permalink / raw)
To: pbonzini; +Cc: kvm, adobriyan
"mov rsi, rsp" is equivalent to "lea rsi, [rsp]" but 1 byte shorter.
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---
arch/x86/kvm/vmx/vmenter.S | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/x86/kvm/vmx/vmenter.S
+++ b/arch/x86/kvm/vmx/vmenter.S
@@ -72,7 +72,7 @@ SYM_FUNC_START(__vmx_vcpu_run)
/* Copy @flags to BL, _ASM_ARG3 is volatile. */
mov %_ASM_ARG3B, %bl
- lea (%_ASM_SP), %_ASM_ARG2
+ mov %_ASM_SP, %_ASM_ARG2
call vmx_update_host_rsp
ALTERNATIVE "jmp .Lspec_ctrl_done", "", X86_FEATURE_MSR_SPEC_CTRL
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] vmx: use mov instead of lea in __vmx_vcpu_run()
2022-11-17 20:36 [PATCH] vmx: use mov instead of lea in __vmx_vcpu_run() Alexey Dobriyan
@ 2022-11-18 0:20 ` Sean Christopherson
0 siblings, 0 replies; 2+ messages in thread
From: Sean Christopherson @ 2022-11-18 0:20 UTC (permalink / raw)
To: Alexey Dobriyan; +Cc: pbonzini, kvm
KVM: VMX: for the shortlog please.
On Thu, Nov 17, 2022, Alexey Dobriyan wrote:
> "mov rsi, rsp" is equivalent to "lea rsi, [rsp]" but 1 byte shorter.
Eww, Intel syntax ;-)
> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
> ---
>
> arch/x86/kvm/vmx/vmenter.S | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- a/arch/x86/kvm/vmx/vmenter.S
> +++ b/arch/x86/kvm/vmx/vmenter.S
> @@ -72,7 +72,7 @@ SYM_FUNC_START(__vmx_vcpu_run)
> /* Copy @flags to BL, _ASM_ARG3 is volatile. */
> mov %_ASM_ARG3B, %bl
>
> - lea (%_ASM_SP), %_ASM_ARG2
> + mov %_ASM_SP, %_ASM_ARG2
I don't have a strong preference. It's probably worth converting, e.g. move
elimination on modern CPUs might shave a whole uop.
I'm pretty sure LEA is a holdover from when this code pre-calculated RSP before
a series of pushes.
> call vmx_update_host_rsp
>
> ALTERNATIVE "jmp .Lspec_ctrl_done", "", X86_FEATURE_MSR_SPEC_CTRL
^ permalink raw reply [flat|nested] 2+ messages in thread
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2022-11-17 20:36 [PATCH] vmx: use mov instead of lea in __vmx_vcpu_run() Alexey Dobriyan
2022-11-18 0:20 ` Sean Christopherson
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