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

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Date:	Wed, 07 Jul 2010 09:23:15 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Marcelo Tosatti <mtosatti@...hat.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



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. :-)
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