Re: [PATCH 08/12] KVM: MMU: do not consult levels when freeing roots

Sean Christopherson
2022-02-11T01:44:14Z

On Fri, Feb 11, 2022, Sean Christopherson wrote:
> On Fri, Feb 11, 2022, Paolo Bonzini wrote:
> > On 2/11/22 01:54, Sean Christopherson wrote:
> > > > > @@ -3242,8 +3245,7 @@ void kvm_mmu_free_roots(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
> > > > > &invalid_list);
> > > > > if (free_active_root) {
> > > > > - if (mmu->shadow_root_level >= PT64_ROOT_4LEVEL &&
> > > > > - (mmu->root_level >= PT64_ROOT_4LEVEL || mmu->direct_map)) {
> > > > > + if (to_shadow_page(mmu->root.hpa)) {
> > > > > mmu_free_root_page(kvm, &mmu->root.hpa, &invalid_list);
> > > > > } else if (mmu->pae_root) {
> > >
> > > Gah, this is technically wrong. It shouldn't truly matter, but it's wrong. root.hpa
> > > will not be backed by shadow page if the root is pml4_root or pml5_root, in which
> > > case freeing the PAE root is wrong. They should obviously be invalid already, but
> > > it's a little confusing because KVM wanders down a path that may not be relevant
> > > to the current mode.
> >
> > pml4_root and pml5_root are dummy, and the first "real" level of page tables
> > is stored in pae_root for that case too, so I think that should DTRT.
>
> Ugh, completely forgot that detail. You're correct. Probably worth a comment?

Actually, can't this be

if (to_shadow_page(mmu->root.hpa)) {
...
else if (!WARN_ON(!mmu->pae_root)) {
...
}

now that it's wrapped with VALID_PAGE(root.hpa)?