s390x/kvm: Set default cpu model for all machine classes

We have to set the default model of all machine classes, not just for
the active one. Otherwise, "query-machines" will indicate the wrong
CPU model ("qemu-s390x-cpu" instead of "host-s390x-cpu") as
"default-cpu-type".

Doing a
    {"execute":"query-machines"}
under KVM now results in
    {"return": [
        {
            "hotpluggable-cpus": true,
            "name": "s390-ccw-virtio-4.0",
            "numa-mem-supported": false,
            "default-cpu-type": "host-s390x-cpu",
            "cpu-max": 248,
            "deprecated": false},
        {
            "hotpluggable-cpus": true,
            "name": "s390-ccw-virtio-2.7",
            "numa-mem-supported": false,
            "default-cpu-type": "host-s390x-cpu",
            "cpu-max": 248,
            "deprecated": false
        } ...

Libvirt probes all machines via "-machine none,accel=kvm:tcg" and will
currently see the wrong CPU model under KVM.

Reported-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Fixes: b6805e1 ("s390x: use generic cpu_model parsing")
Cc: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20191021100515.6978-1-david@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

target/s390x/kvm.c

@@ -320,11 +320,17 @@ void kvm_s390_set_max_pagesize(uint64_t pagesize, Error **errp)
     cap_hpage_1m = 1;
 }
 
-int kvm_arch_init(MachineState *ms, KVMState *s)
+static void ccw_machine_class_foreach(ObjectClass *oc, void *opaque)
 {
-    MachineClass *mc = MACHINE_GET_CLASS(ms);
+    MachineClass *mc = MACHINE_CLASS(oc);
 
     mc->default_cpu_type = S390_CPU_TYPE_NAME("host");
+}
+
+int kvm_arch_init(MachineState *ms, KVMState *s)
+{
+    object_class_foreach(ccw_machine_class_foreach, TYPE_S390_CCW_MACHINE,
+                         false, NULL);
 
     if (!kvm_check_extension(kvm_state, KVM_CAP_DEVICE_CTRL)) {
         error_report("KVM is missing capability KVM_CAP_DEVICE_CTRL - "