linux-kernel - Re: [PATCH v2 1/10] KVM MMU: fix for calculating gpa in invlpg code

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Date:	Mon, 26 Apr 2010 10:39:24 +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 v2 1/10] KVM MMU: fix for calculating gpa in invlpg code

On 04/26/2010 06:10 AM, Xiao Guangrong wrote:
>
> Avi Kivity wrote:
>    
>> On 04/25/2010 10:00 AM, Xiao Guangrong wrote:
>>      
>>> If the guest is 32-bit, we should use 'quadrant' to adjust gpa
>>> offset
>>>
>>> Changlog v2:
>>> - when level is PT_DIRECTORY_LEVEL, the 'offset' should be
>>>     'role.quadrant<<   8', thanks Avi for point it out
>>>
>>> Signed-off-by: Xiao Guangrong<xiaoguangrong@...fujitsu.com>
>>> ---
>>>    arch/x86/kvm/paging_tmpl.h |   13 +++++++++++--
>>>    1 files changed, 11 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
>>> index d0cc07e..83cc72f 100644
>>> --- a/arch/x86/kvm/paging_tmpl.h
>>> +++ b/arch/x86/kvm/paging_tmpl.h
>>> @@ -478,9 +478,18 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu,
>>> gva_t gva)
>>>                ((level == PT_DIRECTORY_LEVEL&&   is_large_pte(*sptep))) ||
>>>                ((level == PT_PDPE_LEVEL&&   is_large_pte(*sptep)))) {
>>>                struct kvm_mmu_page *sp = page_header(__pa(sptep));
>>> -
>>> +            int offset = 0;
>>> +
>>> +            if (PTTYPE == 32) {
>>> +                if (level == PT_DIRECTORY_LEVEL)
>>> +                    offset = PAGE_SHIFT - 4;
>>> +                else
>>> +                    offset = PT64_LEVEL_BITS;
>>> +                offset = sp->role.quadrant<<   offset;
>>> +            }
>>>
>>>        
>> The calculation is really
>>
>>    shift = (PT32_LEVEL_BITS - PT64_LEVEL_BITS) * level;
>>
>>      
> So, the offset is q<<  (PAGE_SHIFT - (PT32_LEVEL_BITS - PT64_LEVEL_BITS) * level - 2)?
>    

Ugh, what I meant was

   shift = PAGE_SHIFT - (PT_LEVEL_BITS - PT64_LEVEL_BITS) * level;
   offset  = q << shift

so,

   pte_gpa = (sp->gfn << PAGE_SHIFT) + offset + (spte - sp->spt) * 
sizeof(pt_element_t)

No magic numbers please.  Note it could work without the 'if (PTTYPE == 
32)'.


-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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