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

[Avi Kivity]

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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