Re: [PATCH 0/7] KVM: x86: guest MAXPHYADDR and C-bit fixes

[Sean Christopherson]

On Thu, Jun 24, 2021, Tom Lendacky wrote:
> > 
> > Here's an explanation of the physical address reduction for bare-metal and
> > guest.
> > 
> > With MSR 0xC001_0010[SMEE] = 0:
> >   No reduction in host or guest max physical address.
> > 
> > With MSR 0xC001_0010[SMEE] = 1:
> > - Reduction in the host is enumerated by CPUID 0x8000_001F_EBX[11:6],
> >   regardless of whether SME is enabled in the host or not. So, for example
> >   on EPYC generation 2 (Rome) you would see a reduction from 48 to 43.
> > - There is no reduction in physical address in a legacy guest (non-SEV
> >   guest), so the guest can use a 48-bit physical address

So the behavior I'm seeing is either a CPU bug or user error.  Can you verify
the unexpected #PF behavior to make sure I'm not doing something stupid?

Thanks!

> > - There is a reduction of only the encryption bit in an SEV guest, so
> >   the guest can use up to a 47-bit physical address. This is why the
> >   Qemu command line sev-guest option uses a value of 1 for the
> >   "reduced-phys-bits" parameter.
> > 
> 
> The guest statements all assume that NPT is enabled.
> 
> Thanks,
> Tom