KVM: s390: add debug statement for diag 318 CPNC data

The diag 318 data contains values that denote information regarding the
guest's environment. Currently, it is unecessarily difficult to observe
this value (either manually-inserted debug statements, gdb stepping, mem
dumping etc). It's useful to observe this information to obtain an
at-a-glance view of the guest's environment, so lets add a simple VCPU
event that prints the CPNC to the s390dbf logs.

Signed-off-by: Collin Walling <walling@linux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Link: https://lore.kernel.org/r/20211027025451.290124-1-walling@linux.ibm.com
[borntraeger@de.ibm.com]: change debug level to 3
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

Author: collinwalling

arch/s390/kvm/kvm-s390.c

@@ -4255,6 +4255,7 @@ static void sync_regs_fmt2(struct kvm_vcpu *vcpu)
 	if (kvm_run->kvm_dirty_regs & KVM_SYNC_DIAG318) {
 		vcpu->arch.diag318_info.val = kvm_run->s.regs.diag318;
 		vcpu->arch.sie_block->cpnc = vcpu->arch.diag318_info.cpnc;
+		VCPU_EVENT(vcpu, 3, "setting cpnc to %d", vcpu->arch.diag318_info.cpnc);
 	}
 	/*
 	 * If userspace sets the riccb (e.g. after migration) to a valid state,