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SubjectRe: [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@cn.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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