KVM: PPC: BOOK3S: PR: Emulate virtual timebase register

virtual time base register is a per VM, per cpu register that needs
to be saved and restored on vm exit and entry. Writing to VTB is not
allowed in the privileged mode.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
[agraf: fix compile error]
Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
index c254c27..ddce1ea 100644
--- a/arch/powerpc/kvm/book3s.c
+++ b/arch/powerpc/kvm/book3s.c
@@ -646,6 +646,9 @@
 		case KVM_REG_PPC_BESCR:
 			val = get_reg_val(reg->id, vcpu->arch.bescr);
 			break;
+		case KVM_REG_PPC_VTB:
+			val = get_reg_val(reg->id, vcpu->arch.vtb);
+			break;
 		default:
 			r = -EINVAL;
 			break;
@@ -750,6 +753,9 @@
 		case KVM_REG_PPC_BESCR:
 			vcpu->arch.bescr = set_reg_val(reg->id, val);
 			break;
+		case KVM_REG_PPC_VTB:
+			vcpu->arch.vtb = set_reg_val(reg->id, val);
+			break;
 		default:
 			r = -EINVAL;
 			break;