linux-kernel - Re: [PATCH v5 8/9] KVM: MMU: combine guest pte read between fetch and pte prefetch

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Date:	Wed, 7 Jul 2010 10:07:05 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>
Subject: Re: [PATCH v5 8/9] KVM: MMU: combine guest pte read between fetch
 and pte prefetch

On Wed, Jul 07, 2010 at 09:23:15AM +0800, Xiao Guangrong wrote:
> 
> 
> Marcelo Tosatti wrote:
> 
> >> -
> >> -	first_pte_gpa = gfn_to_gpa(sp->gfn) +
> >> -				(offset + i) * sizeof(pt_element_t);
> >> -
> >> -	if (kvm_read_guest_atomic(vcpu->kvm, first_pte_gpa, gptep,
> >> -					sizeof(gptep)) < 0)
> >> -		return;
> >> +	gptep = gw->prefetch_ptes;
> > 
> > Where do you reread the gpte in the prefetch path?
> > 
> 
> Marcelo,
> 
> Thanks for your review.
> 
> Below codes read gptes in the prefetch path:
> 
> 	index = sptep - sp->spt;
> 	i = index & ~(PTE_PREFETCH_NUM - 1);
> 	max = index | (PTE_PREFETCH_NUM - 1);
> 
> 	if (PTTYPE == 32)
> 		offset = sp->role.quadrant << PT64_LEVEL_BITS;
> 
> 	first_pte_gpa = gfn_to_gpa(sp->gfn) +
> 				(offset + i) * sizeof(pt_element_t);
> 
> 	if (kvm_read_guest_atomic(vcpu->kvm, first_pte_gpa, gptep,
> 					sizeof(gptep)) < 0)
> 		return;
> 
> It reads the 16 aligned items around sptep's corresponding gpte and this gpte
> is also in this area. :-)

But you removed that in patch 8?
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