s390x/kvm: Fixed bad SIGP SET-ARCHITECTURE handler

The SET-ARCHITECTURE handler in QEMU caused a program interruption.
This is wrong according to the "Principles of Operations" specification
(since SIGP should never cause a program interrupt) and was likely only
introduced for debugging purposes. Since we handle SET-ARCHITECTURE in
the kernel already and only dropped to user space in case of bad mode
parameters, we should just report INVALID PARAMETER in QEMU instead.
Signed-off-by: NThomas Huth <thuth@linux.vnet.ibm.com>
Reviewed-by: NCornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: NChristian Borntraeger <borntraeger@de.ibm.com>

target-s390x/kvm.c

@@ -676,8 +676,10 @@ static int handle_sigp(S390CPU *cpu, struct kvm_run *run, uint8_t ipa1)
         cc = kvm_s390_cpu_restart(target_cpu);
         break;
     case SIGP_SET_ARCH:
-        /* make the caller panic */
-        return -1;
+        *statusreg &= 0xffffffff00000000UL;
+        *statusreg |= SIGP_STAT_INVALID_PARAMETER;
+        cc = 1;   /* status stored */
+        break;
     case SIGP_INITIAL_CPU_RESET:
         cc = s390_cpu_initial_reset(target_cpu);
         break;