Re: [RFC PATCH 20/32] KVM: PPC: Book3S HV: Nested guest entry via hypercall

[Paul Mackerras <paulus@ozlabs.org>]

On Thu, Sep 27, 2018 at 10:57:17AM +1000, David Gibson wrote:
> On Wed, Sep 26, 2018 at 08:59:22PM +1000, Paul Mackerras wrote:
> > On Wed, Sep 26, 2018 at 03:41:07PM +1000, David Gibson wrote:
> > > On Fri, Sep 21, 2018 at 08:01:51PM +1000, Paul Mackerras wrote:
> > > > +	if (!kvm_is_radix(vcpu->kvm))
> > > > +		return H_FUNCTION;
> > > 
> > > Would it be safer / cleaner to have this instead check that the L1 has
> > > completed an H_SET_PARTITION_TABLE?  Which wouldn't be allowed for an
> > > HPT guest.
> > 
> > There is no valid bit in the PTCR value, and the PTCR could have been
> > set via the one-reg interface without there having been a
> > H_SET_PARTITION_TABLE in the lifetime of this KVM instance (for
> > example when the L1 guest has been migrated in from another machine),
> > so I don't see a foolproof way to do what you suggest.
> 
> Ah, right.
> 
> Would checking if the vPTCR is != it's initial value (0?) do the job?
> (AFAICT PTCR=0 would be unusable, even if technically allowed).

If I did check PTCR, what error code would you suggest?  I'm sure
you'd tell me not to use H_FUNCTION. :)

Paul.