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 11:10:15 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Avi Kivity <avi@...hat.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



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)?

As my origin thinking, for level = 2, one gfn has 4 shadow pages, so
every shadow page occupies PAGE_SIZE / 4, and sizeof(pt_element_t) is 4
in 32-bit guest, so the offset is:
q * (PAGE_SIZE/4/4) = q << (PAGE_SHIFT - 2 -2)
Obviously, my code is really ugly than your :-)

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