KVM: PPC: Ignore PIR writes

While technically it's legal to write to PIR and have the identifier changed,
we don't implement logic to do so because we simply expose vcpu_id to the guest.

So instead, let's ignore writes to PIR. This ensures that we don't inject faults
into the guest for something the guest is allowed to do. While at it, we cross
our fingers hoping that it also doesn't mind that we broke its PIR read values.
Signed-off-by: NAlexander Graf <agraf@suse.de>

arch/powerpc/kvm/emulate.c

@@ -169,6 +169,9 @@ static int kvmppc_emulate_mtspr(struct kvm_vcpu *vcpu, int sprn, int rs)
 		vcpu->arch.shared->sprg3 = spr_val;
 		break;
 
+	/* PIR can legally be written, but we ignore it */
+	case SPRN_PIR: break;
+
 	default:
 		emulated = kvmppc_core_emulate_mtspr(vcpu, sprn,
 						     spr_val);