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SubjectRe: [PATCH 1/3] KVM: MMU: Fix 32 bit legacy paging with NPT
On Thu, Sep 02, 2010 at 11:56:10AM -0400, Avi Kivity wrote:
> On 09/02/2010 06:29 PM, Joerg Roedel wrote:
> > This patch fixes 32 bit legacy paging with NPT enabled. The
> > mmu_check_root call on the top-level of the loop causes
> > root_gfn to take values (in the tdp_enabled path) which are
> > outside of guest memory. So the mmu_check_root call fails at
> > some point in the loop interation causing the guest to
> > tiple-fault.
> > This patch changes the mmu_check_root calls to the places
> > where they are really necessary. As a side-effect it
> > introduces a check for the root of a pae page table too.
> >
> >
> > @@ -2387,6 +2387,10 @@ static int mmu_alloc_roots(struct kvm_vcpu *vcpu)
> > return 0;
> > }
> > direct = !is_paging(vcpu);
> > +
> > + if (mmu_check_root(vcpu, root_gfn))
> > + return 1;
> > +
> > for (i = 0; i< 4; ++i) {
> > hpa_t root = vcpu->arch.mmu.pae_root[i];
> >
> > @@ -2398,10 +2402,10 @@ static int mmu_alloc_roots(struct kvm_vcpu *vcpu)
> > continue;
> > }
> > root_gfn = pdptr>> PAGE_SHIFT;
> > + if (mmu_check_root(vcpu, root_gfn))
> > + return 1;
> > } else if (vcpu->arch.mmu.root_level == 0)
> > root_gfn = 0;
> > - if (mmu_check_root(vcpu, root_gfn))
> > - return 1;
> > if (tdp_enabled) {
> > direct = 1;
> > root_gfn = i<< 30;
>
> The overloading of root_gfn is pretty bad. Also, we don't really need
> to check root_gfn for the direct case (the guest can easily switch cr3
> later to one that would fail the check).
>
> However, I'll apply the patch since it fixes the direct problem. More
> involved fixes can come later (esp. after the nnpt patches land).

Ok, great. I will rebase my nnpt patches on-top of this and do some more
final testing before I post them.

Thanks,

Joerg

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