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

[Avi Kivity]

On 07/03/2010 03:44 PM, Avi Kivity wrote:
> On 07/03/2010 03:31 PM, Xiao Guangrong wrote:
> > Avi Kivity wrote:
> >
> > > >
> > >          if (!direct) {
> > >              r = kvm_read_guest_atomic(vcpu->kvm,
> > >                            gw->pte_gpa[level - 2],
> > > &curr_pte, sizeof(curr_pte));
> > >              if (r || curr_pte != gw->ptes[level - 2]) {
> > >                  kvm_mmu_put_page(shadow_page, sptep);
> > >                  kvm_release_pfn_clean(pfn);
> > >                  sptep = NULL;
> > >                  break;
> > >              }
> > >          }
> > >
> > > the code you moved... under what scenario is it not sufficient?
> > I not move those code, just use common function instead, that it's
> > FNAME(check_level_mapping)(), there are do the same work.
> >
> > And this check is not sufficient, since it's only checked if the
> > mapping is zapped or not exist, for other words only when broken this
> > judgment:
> >     is_shadow_present_pte(*sptep)&&  !is_large_pte(*sptep)
> >
> > but if the middle level is present and it's not the large mapping,
> > this check is skipped.
>
>
> Well, in the description, it looked like everything was using small 
> pages (in kvm, level=1 means PTE level, we need to change this one 
> day).  Please describe again and say exactly when the guest or host 
> uses large pages.

Oh, I see what you mean.

Regarding the patch, is it possible just to move the check before, 
instead of adding the 'check' variable?

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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