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

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Message-ID: <20170818123649.GB20100@flask>
Date:   Fri, 18 Aug 2017 14:36:50 +0200
From:   Radim Krčmář <rkrcmar@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, wanpeng.li@...mail.com,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH 2/3] KVM: x86: Avoid guest page table walk when
 gpa_available is set

2017-08-18 09:57+0200, David Hildenbrand:
> 
> > +++ 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)

It does, I took the liberty to change that.

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

Thanks.