Re: [PATCH 1/2] KVM: x86: Add emulation support for #GP triggered by VM instructions

Andy Lutomirski
2021-01-12T18:59:41Z

On Tue, Jan 12, 2021 at 9:59 AM Sean Christopherson <seanjc@google.com> wrote:
>
> On Tue, Jan 12, 2021, Sean Christopherson wrote:
> > On Tue, Jan 12, 2021, Wei Huang wrote:
> > > From: Bandan Das <bsd@redhat.com>
> > >
> > > While running VM related instructions (VMRUN/VMSAVE/VMLOAD), some AMD
> > > CPUs check EAX against reserved memory regions (e.g. SMM memory on host)
> > > before checking VMCB's instruction intercept.
> >
> > It would be very helpful to list exactly which CPUs are/aren't affected, even if
> > that just means stating something like "all CPUs before XYZ". Given patch 2/2,
> > I assume it's all CPUs without the new CPUID flag?
>
> Ah, despite calling this an 'errata', the bad behavior is explicitly documented
> in the APM, i.e. it's an architecture bug, not a silicon bug.
>
> Can you reword the changelog to make it clear that the premature #GP is the
> correct architectural behavior for CPUs without the new CPUID flag?

Andrew Cooper points out that there may be a nicer workaround. Make
sure that the SMRAM and HT region (FFFD00000000 - FFFFFFFFFFFF) are
marked as reserved in the guest, too.

--Andy