linux-kernel - Re: [PATCH v2 1/6] KVM: MMU: fix forgot flush vcpu tlbs

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Message-ID: <4CE4024B.4090600@redhat.com>
Date:	Wed, 17 Nov 2010 18:26:51 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 1/6] KVM: MMU: fix forgot flush vcpu tlbs

On 11/17/2010 05:29 PM, Marcelo Tosatti wrote:
> >  diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
> >  index ba00eef..58b4d9a 100644
> >  --- a/arch/x86/kvm/paging_tmpl.h
> >  +++ b/arch/x86/kvm/paging_tmpl.h
> >  @@ -781,6 +781,7 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
> >   			else
> >   				nonpresent = shadow_notrap_nonpresent_pte;
> >   			drop_spte(vcpu->kvm,&sp->spt[i], nonpresent);
> >  +			kvm_flush_remote_tlbs(vcpu->kvm);
> >   			continue;
> >   		}
>
> This is not needed. Guest is responsible for flushing on
> present->nonpresent change.

sync_page
drop_spte
kvm_mmu_notifier_invalidate_page
kvm_unmap_rmapp
spte doesn't exist -> no flush
page is freed
guest can write into freed page?

I don't think we need to flush immediately; set a "tlb dirty" bit 
somewhere that is cleareded when we flush the tlb.  
kvm_mmu_notifier_invalidate_page() can consult the bit and force a flush 
if set.

-- 
error compiling committee.c: too many arguments to function

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