On Mon, Sep 04, 2023, Kai Huang wrote: > On Fri, 2023-09-01 at 09:48 -0700, Sean Christopherson wrote: > > @@ -3447,6 +3447,14 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault) > > else > > sptep = fast_pf_get_last_sptep(vcpu, fault->addr, &spte); > > > > + /* > > + * It's entirely possible for the mapping to have been zapped > > + * by a different task, but the root page is should always be > > + * available as the vCPU holds a reference to its root(s). > > + */ > > + if (WARN_ON_ONCE(!sptep)) > > + spte = REMOVED_SPTE; > > If I recall correctly, REMOVED_SPTE is only used by TDP MMU code. Should we use > 0 (or initial SPTE value for case like TDX) instead of REMOVED_SPTE? I deliberately suggested REMOVED_SPTE in part because of TDX introducing "initial SPTE"; finding/remembering '0' initialization of SPTEs is hard. Though FWIW, '0' would be totally fine for TDX because the value is never exposed to hardware. I think it's totally fine to use REMOVED_SPTE like this in common code, I would be quite surprised if it causes confusion. Even though REMOVED_SPTE was introduced by the TDP MMU, its value/semantics are generic.
