Re: [for-6.0 v5 11/13] spapr: PEF: prevent migration

[David Gibson]

On Mon, Dec 14, 2020 at 06:22:40PM +0100, Cornelia Huck wrote:
> On Fri,  4 Dec 2020 16:44:13 +1100
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > We haven't yet implemented the fairly involved handshaking that will be
> > needed to migrate PEF protected guests.  For now, just use a migration
> > blocker so we get a meaningful error if someone attempts this (this is the
> > same approach used by AMD SEV).
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > ---
> >  hw/ppc/pef.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/hw/ppc/pef.c b/hw/ppc/pef.c
> > index 3ae3059cfe..edc3e744ba 100644
> > --- a/hw/ppc/pef.c
> > +++ b/hw/ppc/pef.c
> > @@ -38,7 +38,11 @@ struct PefGuestState {
> >  };
> >  
> >  #ifdef CONFIG_KVM
> > +static Error *pef_mig_blocker;
> > +
> >  static int kvmppc_svm_init(Error **errp)
> 
> This looks weird?

Oops.  Not sure how that made it past even my rudimentary compile
testing.

> > +
> > +int kvmppc_svm_init(SecurableGuestMemory *sgm, Error **errp)
> >  {
> >      if (!kvm_check_extension(kvm_state, KVM_CAP_PPC_SECURABLE_GUEST)) {
> >          error_setg(errp,
> > @@ -54,6 +58,11 @@ static int kvmppc_svm_init(Error **errp)
> >          }
> >      }
> >  
> > +    /* add migration blocker */
> > +    error_setg(&pef_mig_blocker, "PEF: Migration is not implemented");
> > +    /* NB: This can fail if --only-migratable is used */
> > +    migrate_add_blocker(pef_mig_blocker, &error_fatal);
> 
> Just so that I understand: is PEF something that is enabled by the host
> (and the guest is either secured or doesn't start), or is it using a
> model like s390x PV where the guest initiates the transition into
> secured mode?

Like s390x PV it's initiated by the guest.

> Asking because s390x adds the migration blocker only when the
> transition is actually happening (i.e. guests that do not transition
> into secure mode remain migratable.) This has the side effect that you
> might be able to start a machine with --only-migratable that
> transitions into a non-migratable machine via a guest action, if I'm
> not mistaken. Without the new object, I don't see a way to block with
> --only-migratable; with it, we should be able to do that. Not sure what
> the desirable behaviour is here.

Hm, I'm not sure what the best option is here either.

> 
> > +
> >      return 0;
> >  }
> >  
> 

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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