spapr: PEF: prevent migration

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>
Reviewed-by: Greg Kurz <groug@kaod.org>

hw/ppc/pef.c

@@ -44,6 +44,8 @@ struct PefGuest {
 static int kvmppc_svm_init(Error **errp)
 {
 #ifdef CONFIG_KVM
+    static Error *pef_mig_blocker;
+
     if (!kvm_check_extension(kvm_state, KVM_CAP_PPC_SECURE_GUEST)) {
         error_setg(errp,
                    "KVM implementation does not support Secure VMs (is an ultravisor running?)");
@@ -58,6 +60,11 @@ 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);
+
     return 0;
 #else
     g_assert_not_reached();