linux-kernel - Re: [PATCH] kvm:vmx:code changes in handle

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Date:   Sat, 12 Dec 2020 01:34:47 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Stephen Zhang <starzhangzsd@...il.com>, seanjc@...gle.com,
        vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com,
        joro@...tes.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kvm:vmx:code changes in handle_io() to save some CPU
 cycles.

On 10/12/20 09:15, Stephen Zhang wrote:
> code changes in handle_io() to save some CPU cycles.
> 
> Signed-off-by: Stephen Zhang <starzhangzsd@...il.com>
> ---
>   arch/x86/kvm/vmx/vmx.c | 5 ++---
>   1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 47b8357..109bcf64 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -4899,15 +4899,14 @@ static int handle_triple_fault(struct kvm_vcpu *vcpu)
>   static int handle_io(struct kvm_vcpu *vcpu)
>   {
>   	unsigned long exit_qualification;
> -	int size, in, string;
> +	int size, in;
>   	unsigned port;
>   
>   	exit_qualification = vmx_get_exit_qual(vcpu);
> -	string = (exit_qualification & 16) != 0;
>   
>   	++vcpu->stat.io_exits;
>   
> -	if (string)
> +	if (exit_qualification & 16)
>   		return kvm_emulate_instruction(vcpu, 0);
>   
>   	port = exit_qualification >> 16;
> 

I would be very surprised if there's any change in the assembly code 
after this patch.

Paolo