Re: [PATCH v2 0/6] KVM: x86: Apply NX mitigation more precisely

[Sean Christopherson]

On Fri, Jul 29, 2022, Paolo Bonzini wrote:
> On 7/28/22 23:20, Sean Christopherson wrote:
> > 
> > Anyways, the bug we really care about is that by not precisely checking if a
> > huge page is disallowed, KVM would refuse to create huge page after disabling
> > dirty logging, which is a very noticeable performance issue for large VMs if
> > a migration is canceled.  That particular bug has since been unintentionally
> > fixed in the TDP MMU by zapping the non-leaf SPTE, but there are other paths
> > that could similarly be affected, e.g. I believe zapping leaf SPTEs in response
> > to a host page migration (mmu_notifier invalidation) to create a huge page would
> > yield a similar result; KVM would see the shadow-present non-leaf SPTE and assume
> > a huge page is disallowed.
> 
> Ok, thanks.  So this will be 5.21 material even during the -rc phase

Yes, this definitely needs more time in the queue before being sent to Linus.