KVM: s390: track synchronous pfault events in kvm_stat

Right now we do count pfault (pseudo page faults aka async page faults
start and completion events). What we do not count is, if an async page
fault would have been possible by the host, but it was disabled by the
guest (e.g. interrupts off, pfault disabled, secure execution....).  Let
us count those as well in the pfault_sync counter.
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Link: https://lore.kernel.org/r/20201125090658.38463-1-borntraeger@de.ibm.com

arch/s390/include/asm/kvm_host.h

@@ -459,6 +459,7 @@ struct kvm_vcpu_stat {
 	u64 diagnose_308;
 	u64 diagnose_500;
 	u64 diagnose_other;
+	u64 pfault_sync;
 };
 
 #define PGM_OPERATION			0x01

arch/s390/kvm/kvm-s390.c

@@ -60,6 +60,7 @@
 struct kvm_stats_debugfs_item debugfs_entries[] = {
 	VCPU_STAT("userspace_handled", exit_userspace),
 	VCPU_STAT("exit_null", exit_null),
+	VCPU_STAT("pfault_sync", pfault_sync),
 	VCPU_STAT("exit_validity", exit_validity),
 	VCPU_STAT("exit_stop_request", exit_stop_request),
 	VCPU_STAT("exit_external_request", exit_external_request),
@@ -4111,6 +4112,7 @@ static int vcpu_post_run(struct kvm_vcpu *vcpu, int exit_reason)
 		current->thread.gmap_pfault = 0;
 		if (kvm_arch_setup_async_pf(vcpu))
 			return 0;
+		vcpu->stat.pfault_sync++;
 		return kvm_arch_fault_in_page(vcpu, current->thread.gmap_addr, 1);
 	}
 	return vcpu_post_run_fault_in_sie(vcpu);