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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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