s390x: Disable storage key migration on old machine type

This code disables storage key migration when an older machine type is
specified.
Reviewed-by: NDavid Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: NJason J. Herne <jjherne@linux.vnet.ibm.com>
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>

hw/s390x/s390-skeys.c

@@ -353,12 +353,39 @@ static int s390_storage_keys_load(QEMUFile *f, void *opaque, int version_id)
     return ret;
 }
 
-static void s390_skeys_instance_init(Object *obj)
+static inline bool s390_skeys_get_migration_enabled(Object *obj, Error **errp)
+{
+    S390SKeysState *ss = S390_SKEYS(obj);
+
+    return ss->migration_enabled;
+}
+
+static inline void s390_skeys_set_migration_enabled(Object *obj, bool value,
+                                            Error **errp)
 {
     S390SKeysState *ss = S390_SKEYS(obj);
 
-    register_savevm(NULL, TYPE_S390_SKEYS, 0, 1, s390_storage_keys_save,
-                    s390_storage_keys_load, ss);
+    /* Prevent double registration of savevm handler */
+    if (ss->migration_enabled == value) {
+        return;
+    }
+
+    ss->migration_enabled = value;
+
+    if (ss->migration_enabled) {
+        register_savevm(NULL, TYPE_S390_SKEYS, 0, 1, s390_storage_keys_save,
+                        s390_storage_keys_load, ss);
+    } else {
+        unregister_savevm(DEVICE(ss), TYPE_S390_SKEYS, ss);
+    }
+}
+
+static void s390_skeys_instance_init(Object *obj)
+{
+    object_property_add_bool(obj, "migration-enabled",
+                             s390_skeys_get_migration_enabled,
+                             s390_skeys_set_migration_enabled, NULL);
+    object_property_set_bool(obj, true, "migration-enabled", NULL);
 }
 
 static void s390_skeys_class_init(ObjectClass *oc, void *data)

hw/s390x/s390-virtio-ccw.c

@@ -282,12 +282,24 @@ static const TypeInfo ccw_machine_info = {
     },
 };
 
+#define CCW_COMPAT_2_4 \
+        {\
+            .driver   = TYPE_S390_SKEYS,\
+            .property = "migration-enabled",\
+            .value    = "off",\
+        },
+
 static void ccw_machine_2_4_class_init(ObjectClass *oc, void *data)
 {
     MachineClass *mc = MACHINE_CLASS(oc);
+    static GlobalProperty compat_props[] = {
+        CCW_COMPAT_2_4
+        { /* end of list */ }
+    };
 
     mc->name = "s390-ccw-virtio-2.4";
     mc->desc = "VirtIO-ccw based S390 machine v2.4";
+    mc->compat_props = compat_props;
 }
 
 static const TypeInfo ccw_machine_2_4_info = {

include/hw/s390x/storage-keys.h

@@ -21,6 +21,7 @@
 
 typedef struct S390SKeysState {
     DeviceState parent_obj;
+    bool migration_enabled;
 
 } S390SKeysState;