Re: [PATCH RESEND 2/2] x86/paravirt: Use XOR r32,r32 to clear register in pv_vcpu_is_preempted()

[Alexey Makhalov]

On 1/5/26 1:39 AM, Uros Bizjak wrote:
> x86_64 zero extends 32bit operations, so for 64bit operands,
> XOR r32,r32 is functionally equal to XOR r64,r64, but avoids
> a REX prefix byte when legacy registers are used.
>
> Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
> Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
> Cc: Ajay Kaher <ajay.kaher@xxxxxxxxxxxx>
> Cc: Alexey Makhalov <alexey.makhalov@xxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> ---
>   arch/x86/include/asm/paravirt.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
> index 4f6ec60b4cb3..59aec695ae5f 100644
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -577,7 +577,7 @@ static __always_inline void pv_kick(int cpu)
>   static __always_inline bool pv_vcpu_is_preempted(long cpu)
>   {
>   	return PVOP_ALT_CALLEE1(bool, lock.vcpu_is_preempted, cpu,
> -				"xor %%" _ASM_AX ", %%" _ASM_AX,
> +				"xor %%eax, %%eax",
>   				ALT_NOT(X86_FEATURE_VCPUPREEMPT));
>   }
>   

Acked-by: Alexey Makhalov <alexey.makhalov@xxxxxxxxxxxx>