KVM: s390: interrupt: Fix single-stepping keyless mode exits

kvm_s390_skey_check_enable() does not emulate any instructions, rather,
it clears CPUSTAT_KSS and arranges the instruction that caused the exit
(e.g., ISKE, SSKE, RRBE or LPSWE with a keyed PSW) to run again.

Therefore, skip the PER check and let the instruction execution happen.
Otherwise, a debugger will see two single-step events on the same
instruction.

Reviewed-by: Christian Borntraeger <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Signed-off-by: Ilya Leoshkevich <[email protected]>
Message-ID: <[email protected]>
Signed-off-by: Claudio Imbrenda <[email protected]>
Signed-off-by: Janosch Frank <[email protected]>

arch/s390/kvm/intercept.c

@@ -630,8 +630,8 @@ int kvm_handle_sie_intercept(struct kvm_vcpu *vcpu)
 		rc = handle_partial_execution(vcpu);
 		break;
 	case ICPT_KSS:
-		rc = kvm_s390_skey_check_enable(vcpu);
-		break;
+		/* Instruction will be redriven, skip the PER check. */
+		return kvm_s390_skey_check_enable(vcpu);
 	case ICPT_MCHKREQ:
 	case ICPT_INT_ENABLE:
 		/*