linux-kernel - Re: [PATCH v2 3/10] KVM: MMU: fix direct sp's access corruptted

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Message-ID: <4C29B81C.3040605@cn.fujitsu.com>
Date:	Tue, 29 Jun 2010 17:08:44 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 3/10] KVM: MMU: fix direct sp's access corruptted



Avi Kivity wrote:
> On 06/29/2010 10:45 AM, Xiao Guangrong wrote:
>>
>>> - there was once talk that instead of folding pt_access and pte_access
>>> together into the leaf sp->role.access, each sp level would have its own
>>> access permissions.  In this case we don't even have to get a new direct
>>> sp, only change the PT_DIRECTORY_LEVEL spte to add write permissions
>>> (all direct sp's would be writeable and permissions would be controlled
>>> at their parent_pte level).  Of course that's a much bigger change than
>>> this bug fix.
>>>
>>>      
>> Yeah, i have considered this way, but it will change the shadow page's
>> mapping
>> way: it control the access at the upper level, but in the current
>> code, we allow
>> the upper level have the ALL_ACCESS and control the access right at
>> the last level.
>> It will break many things, such as write-protected...
>>    
> 
> spte's access bits have dual purpose, both to map guest protection and
> for host protection (like for shadowed pages, or ksm pages).  So the
> last level sptes still need to consider host write protection.
> 

Yeah, i see your mean, thanks, :-)
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