linux-kernel - Re: [PATCH v3 3/11] KVM: MMU: fix direct sp's access corruptted

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Date:	Thu, 1 Jul 2010 09:03:15 -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 v3 3/11] KVM: MMU: fix direct sp's access corruptted

On Thu, Jul 01, 2010 at 08:50:58AM +0800, Xiao Guangrong wrote:
> 
> 
> Marcelo Tosatti wrote:
> 
> >> -		if (is_shadow_present_pte(*sptep) && !is_large_pte(*sptep))
> >> -			continue;
> >> +		if (is_shadow_present_pte(*sptep) && !is_large_pte(*sptep)) {
> >> +			struct kvm_mmu_page *child;
> >> +			unsigned direct_access;
> >> +
> >> +			if (level != gw->level)
> >> +				continue;
> > 
> > This will skip the check for the sp at level 1 when emulating 1GB pages
> > with 4k host pages (where there are direct sp's at level 2 and 1).
> > Should be > instead of !=.
> > 
> 
> Marcelo,
> 
> I think the patch is right.
> 
> Every level's direct sp has the same access in the mapping since while we setup the
> mapping we find the direct sp with the same access.
> (Note: we have encode the D bit to the sp->role.access)
> 
> Consider guest 1G writable clean pages and host 4K pages, the shadow pages mapping
> is like this:
> 
> indirect L4 --> indirect L3 --> direct ReadOnly L2 --> direct ReadOnly L1
> 
> When change guest pte to dirty, we update L3' spte and find the direct writable L2 sp,
> assume it's A, then we can sure that A's children sps should also writable, the final
> mapping is like this:
> 
> indirect L4 --> indirect L3 --> direct Writable L2 --> direct Writable L1.
> 
> So, i think we not broken anything in this patch :-)

You're right. Applied.
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