Re: [PATCH] vmx: use mov instead of lea in __vmx_vcpu_run()

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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@xxxxxxxxx>
> ---
> 
>  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



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