linux-kernel - Re: [PATCH 1/4] KVM: MMU: fix forgot reserved bits check in speculative path

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Date:	Wed, 14 Jul 2010 21:24:39 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Avi Kivity <avi@...hat.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>,
	Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH 1/4] KVM: MMU: fix forgot reserved bits check in speculative
 path



Avi Kivity wrote:

>> +
>> +            if (!!is_pae(vcpu) != sp->role.cr4_pae ||
>> +                  is_nx(vcpu) != sp->role.nxe)
>> +                continue;
>> +
>>    
> 
> Do we also need to check cr0.wp?  I think so.

I think it's not too bad since we just decrease the access right, for example,
we mark the mapping readonly for cr0.wp=0's page, the later write-access will
cause #PF, and the read-access is OK.

> 
>>               if (gentry)
>>                   mmu_pte_write_new_pte(vcpu, sp, spte,&gentry);
>>    
> 
> Please move the checks to mmu_pte_write_new_pte(), it's a more logical
> place.
> 
> It means the reserved bits check happens multiple times, but that's ok.
> 

OK

> Also, you can use arch.mmu.base_role to compare:
> 
>     static const kvm_mmu_page_role mask = { .level = -1U, .cr4_pae = 1,
> ... };
> 
>     if ((sp->role.word ^ base_role.word) & mask.word)
>          return;

OK, will update it :-)
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