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

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Message-ID: <4BC52505.6000502@cn.fujitsu.com>
Date:	Wed, 14 Apr 2010 10:14:29 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Marcelo Tosatti <mtosatti@...hat.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



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()?

Thanks,
Xiao
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