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

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Date:	Mon, 12 Apr 2010 15:49:21 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
CC:	Marcelo Tosatti <mtosatti@...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 04/12/2010 03:22 PM, Xiao Guangrong wrote:
>
>> But kvm_mmu_zap_page() will only destroy sp == tpos == pos; n points at
>> pos->next already, so it's safe.
>>
>>      
> kvm_mmu_zap_page(sp) not only zaps sp but also zaps all sp's unsync children
> pages, if n is just sp's unsyc child, just at the same hlist and just behind sp,
> it will crash. :-)
>    

Ouch.  I see now, thanks for explaining.

One way to fix it is to make kvm_mmu_zap_page() only zap the page it is 
given, and use sp->role.invalid on its children.  But it's better to fix 
it now quickly and do the more involved fixes later.

Just change the assignment to a 'goto restart;' please, I don't like 
playing with list_for_each internals.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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