Re: [PATCH v5 03/15] KVM: SVM: Disable SEV/SEV-ES if NPT is disabled

Sean Christopherson
2021-04-22T18:11:59Z

On Thu, Apr 22, 2021, Paolo Bonzini wrote:
> On 22/04/21 18:15, Sean Christopherson wrote:
> > > Support for 5-level page tables on NPT is not hard to fix and could be
> > > tested by patching QEMU. However, the !NPT case would also have to be fixed
> > > by extending the PDP and PML4 stacking trick to a PML5.
> > Isn't that backwards? It's the nested NPT case that requires the stacking trick.
> > When !NPT is disabled in L0 KVM, 32-bit guests are run with PAE paging. Maybe
> > I'm misunderstanding what you're suggesting.
>
> Yes, you're right. NPT is easy but we would have to guess what the spec
> would say about MAXPHYADDR, while nNPT would require the stacking of a PML5.
> Either way, blocking KVM is the easiest thing todo.

How about I fold that into the s/lm_root/pml4_root rename[*]? I.e. make the
blocking of PML5 a functional change, and the rename an opportunistic change?

[*] https://lkml.kernel.org/r/20210318201131.3242619-1-seanjc@google.com