Re: [PATCH] KVM: x86/mmu: Do not create SPTEs for GFNs that exceed host.MAXPHYADDR

Sean Christopherson
2022-04-29T14:42:32Z

On Fri, Apr 29, 2022, Paolo Bonzini wrote:
> On 4/29/22 16:24, Sean Christopherson wrote:
> > I don't love the divergent memslot behavior, but it's technically correct, so I
> > can't really argue. Do we want to "officially" document the memslot behavior?
> >
>
> I don't know what you mean by officially document,

Something in kvm/api.rst under KVM_SET_USER_MEMORY_REGION.

> but at least I have relied on it to test KVM's MAXPHYADDR=52 cases before
> such hardware existed. :)

Ah, that's a very good reason to support this for shadow paging. Maybe throw
something about testing in the changelog? Without considering the testing angle,
it looks like KVM supports max=52 for !TDP just because it can, because practically
speaking there's unlikely to be a use case for exposing that much memory to a
guest when using shadow paging.