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

[Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>]

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, :-)