linux-kernel - Re: [PATCH 2/6] KVM MMU: fix kvm_mmu_zap

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Message-ID: <20100414163120.GA5489@amt.cnet>
Date:	Wed, 14 Apr 2010 13:31:20 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc:	Avi Kivity <avi@...hat.com>, KVM list <kvm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/6] KVM MMU: fix kvm_mmu_zap_page() and its calling path

On Wed, Apr 14, 2010 at 10:14:29AM +0800, Xiao Guangrong wrote:
> 
> 
> Marcelo Tosatti wrote:
> > On Tue, Apr 13, 2010 at 09:34:14AM +0800, Xiao Guangrong wrote:
> >>
> >> Marcelo Tosatti wrote:
> >>
> >>>> @@ -1483,8 +1483,8 @@ static int mmu_zap_unsync_children(struct kvm *kvm,
> >>>>  		for_each_sp(pages, sp, parents, i) {
> >>>>  			kvm_mmu_zap_page(kvm, sp);
> >>>>  			mmu_pages_clear_parents(&parents);
> >>>> +			zapped++;
> >>>>  		}
> >>>> -		zapped += pages.nr;
> >>>>  		kvm_mmu_pages_init(parent, &parents, &pages);
> >>>>  	}
> >>> Don't see why this is needed? The for_each_sp loop uses pvec.nr.
> >> I think mmu_zap_unsync_children() should return the number of zapped pages then we
> >> can adjust the number of free pages in kvm_mmu_change_mmu_pages(), but pages.nr no
> >> only includes the unsync/zapped pages but also includes their parents.
> > 
> > Oh i see. I think its safer to check for list_empty then to rely on
> > proper accounting there, like __kvm_mmu_free_some_pages does.
> 
> Do you mean that we'd better add WARN_ON(list_empty()) code in kvm_mmu_zap_page()?

Just break out of the loop if
list_empty(&vcpu->kvm->arch.active_mmu_pages).

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