Re: [PATCH v4 5/6] KVM: MMU: combine guest pte read between walk and pte prefetch

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On 07/05/2010 12:09 PM, Xiao Guangrong wrote:

Avi Kivity wrote:

I'm not convinced we can bypass the checks.  Consider:


VCPU0                 VCPU1

#PF
walk_addr
->  gpml4e0,gpdpe0,gpde0,gpte0

                       replace gpdpe0 with gpdpe1
                       #PF
                       walk_addr
->  gpml4e0,gpdpe1,gpde1,gpte1
                       fetch
                       ->  establish hpml4e0,hpdpte1,hpde0,hpte1
fetch
read hpdpe1
if (present(hpdpe1))
     continue;
...
write hpte0 using shadow hieratchy for hpte1

Ah, i missed this case, thanks for you point it out, i'll fix it in
the next version.

Note: I think we have to check _after_ kvm_mmu_get_page(), otherwise we might be checking a page that is not write-protected and can change again.

So the logic needs to be something like

for_each_shadow_entry:
    if (!last_level && !present(*spte))
        kvm_mmu_get_page
    verify gpte
    if (last_level)
        mmu_set_spte()

--
error compiling committee.c: too many arguments to function

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