Re: [PATCH V2 3/4] KVM: VMX: Don't consult original exit qualification for nested EPT violation injection

[Yosry Ahmed]

> > @@ -496,7 +510,7 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
> >        * [2:0] - Derive from the access bits. The exit_qualification might be
> >        *         out of date if it is serving an EPT misconfiguration.
> >        * [5:3] - Calculated by the page walk of the guest EPT page tables
> > -      * [7:8] - Derived from [7:8] of real exit_qualification
> > +      * [7:8] - Set at the kvm_translate_gpa() call sites above
> >        *
> >        * The other bits are set to 0.
> >        */
> > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> > index 248635da67661..6a167b1d51595 100644
> > --- a/arch/x86/kvm/vmx/nested.c
> > +++ b/arch/x86/kvm/vmx/nested.c
> > @@ -444,9 +444,6 @@ static void nested_ept_inject_page_fault(struct kvm_vcpu *vcpu,
> >                       exit_qualification = 0;
> >               } else {
> >                       exit_qualification = fault->exit_qualification;
> > -                     exit_qualification |= vmx_get_exit_qual(vcpu) &
> > -                                           (EPT_VIOLATION_GVA_IS_VALID |
> > -                                            EPT_VIOLATION_GVA_TRANSLATED);
>
> Hmm, this isn't quite correct.  If KVM injects an EPT Violation (or a #NPF) when
> handling an EPT Violation (or #NPF) from L2, then KVM _should_ follow hardware.
>
> Aha!  I think the easiest way to deal with that is to flag nested page faults
> that were the result of walking L1's TDP when handling an L2 TDP page fault, and
> then let vendor code extract the fault information out of hardaware.

Is it not possible that KVM gets an EPT Violation (or a #NPF) on an L2
memory access while the CPU is walking L2's page tables, then KVM
walks L1's TDP and finds mappings for the L2 page tables but not the
final translation? Or will KVM always just fixup the immediate EPT
Violation (or #NPF) by inserting a shadow mapping of L2's page tables
and retry the instruction immediately?