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    SubjectRe: [PATCH v5 1/9] KVM: MMU: fix forgot reserved bits check in speculative path
    On 07/12/2010 05:37 AM, Xiao Guangrong wrote:
    >
    >>> + if (is_rsvd_bits_set(vcpu, gentry, PT_PAGE_TABLE_LEVEL))
    >>> + gentry = 0;
    >>> +
    >>>
    >>>
    >> That only works if the gpte is for the same mode as the current vcpu mmu
    >> mode. In some cases it is too strict (vcpu in pae mode writing a 32-bit
    >> gpte), which is not too bad, in some cases it is too permissive (vcpu in
    >> nonpae mode writing a pae gpte).
    >>
    >>
    > Avi, thanks for your review.
    >
    > Do you mean that the VM has many different mode vcpu? For example, both
    > nonpae vcpu and pae vcpu are running in one VM? I forgot to consider this
    > case.
    >

    Yes. This happens while the guest brings up other vcpus, and when using
    nested virtualization.

    >> (once upon a time mixed modes were rare, only on OS setup, but with
    >> nested virt they happen all the time).
    >>
    > I'm afraid it's still has problem, it will cause access corruption:
    > 1: if nonpae vcpu write pae gpte, it will miss NX bit
    > 2: if pae vcpu write nonpae gpte, it will add NX bit that over gpte's width
    >
    > How about only update the shadow page which has the same pae set with the written
    > vcpu? Just like this:
    >
    > @@ -3000,6 +3000,10 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
    > while (npte--) {
    > entry = *spte;
    > mmu_pte_write_zap_pte(vcpu, sp, spte);
    > +
    > + if (!!is_pae(vcpu) != sp->role.cr4_pae)
    > + continue;
    > +
    >

    Not enough, one vcpu can have nx set while the other has it reset, etc.

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



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