linux-kernel - Re: [PATCH 2/3] KVM: x86: Avoid guest page table walk when gpa

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Date:   Fri, 18 Aug 2017 09:57:38 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     wanpeng.li@...mail.com, rkrcmar@...hat.com,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH 2/3] KVM: x86: Avoid guest page table walk when
 gpa_available is set


> +++ b/arch/x86/kvm/x86.c
> @@ -4657,25 +4657,18 @@ static int emulator_read_write_onepage(unsigned long addr, void *val,
>  	 */
>  	if (vcpu->arch.gpa_available &&
>  	    emulator_can_use_gpa(ctxt) &&
> -	    vcpu_is_mmio_gpa(vcpu, addr, exception->address, write) &&
> -	    (addr & ~PAGE_MASK) == (exception->address & ~PAGE_MASK)) {
> -		gpa = exception->address;
> -		goto mmio;
> +	    (addr & ~PAGE_MASK) == (vcpu->arch.gpa_val & ~PAGE_MASK)) {
> +		gpa = vcpu->arch.gpa_val;
> +		ret = vcpu_is_mmio_gpa(vcpu, addr, gpa, write);
> +	} else {
> +		ret = vcpu_mmio_gva_to_gpa(vcpu, addr, &gpa, exception, write);
>  	}
>  
> -	ret = vcpu_mmio_gva_to_gpa(vcpu, addr, &gpa, exception, write);
> -
>  	if (ret < 0)
>  		return X86EMUL_PROPAGATE_FAULT;

just wondering if it makes sense to move this into the else branch (as
it logically only belongs to vcpu_mmio_gva_to_gpa)

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 

Thanks,

David