On Wed, Mar 08, 2023, Paolo Bonzini wrote: > On Tue, Mar 7, 2023 at 6:36 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote: > > Thinking about this more, I would rather revert commit 1e0c7d40758b ("KVM: SVM: > > hyper-v: Remote TLB flush for SVM") or fix the thing properly straitaway. KVM > > doesn't magically handle the flushes correctly for the shadow/legacy MMU, KVM just > > happens to get lucky and not run afoul of the underlying bugs. > > I don't think it's about luck---the legacy MMU's zapping/invalidation > seems to invoke the flush hypercall correctly: ...for the paths that Jeremi has exercised, and for which a stale TLB entry is fatal to L2. E.g. kvm_unmap_gfn_range() does not have a range-based TLB flush in its path and fully relies on the buggy kvm_flush_remote_tlbs(). In other words, KVM is getting lucky :-) > Jeremi, did you ever track the call stack where > hyperv_nested_flush_guest_mapping is triggered? I don't think it matters. As above, it only takes one path where KVM is fully relying on kvm_flush_remote_tlbs() for the whole thing to fall apart.