KVM: s390: vsie: correctly set and handle guest TOD

Guest 2 sets up the epoch of guest 3 from his point of view. Therefore,
we have to add the guest 2 epoch to the guest 3 epoch. We also have to take
care of guest 2 epoch changes on STP syncs. This will work just fine by
also updating the guest 3 epoch when a vsie_block has been set for a VCPU.

Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 8ba7a98..6fdf1f7 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -176,6 +176,8 @@
 			vcpu->arch.sie_block->epoch -= *delta;
 			if (vcpu->arch.cputm_enabled)
 				vcpu->arch.cputm_start += *delta;
+			if (vcpu->arch.vsie_block)
+				vcpu->arch.vsie_block->epoch -= *delta;
 		}
 	}
 	return NOTIFY_OK;