Re: [PATCH 1/4] KVM: X86: Fix tlb flush for tdp in kvm_invalidate_pcid()

[Paolo Bonzini]

On 21/10/21 16:52, Sean Christopherson wrote:
> > I think the EPT violation happens*after*  the cr3 write.  So the instruction to be
> > emulated is not "cr3 write".  The emulation will queue fault into guest though,
> > recursive EPT violation happens since the cr3 exceeds maxphyaddr limit.
> Doh, you're correct.  I think my mind wandered into thinking about what would
> happen with PDPTRs and forgot to get back to normal MOV CR3.
>
> So yeah, the only way to correctly handle this would be to intercept CR3 loads.
> I'm guessing that would have a noticeable impact on guest performance.

Ouch... yeah, allow_smaller_maxphyaddr already has bad performance, but 
intercepting CR3 loads would be another kind of slow.

Paolo

> Paolo, I'll leave this one for you to decide, we have pretty much written off
> allow_smaller_maxphyaddr:-)