pc-dimm: do not allow setting an in-use memdev

using the same memdev backend more than once will cause
assertion at MemoryRegion mapping time because it's already
mapped. Prevent it by checking that the associated MemoryRegion
is not mapped.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Acked-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

MST: tweak commit log

hw/mem/pc-dimm.c

@@ -43,6 +43,21 @@ static void pc_dimm_get_size(Object *obj, Visitor *v, void *opaque,
     visit_type_int(v, &value, name, errp);
 }
 
+static void pc_dimm_check_memdev_is_busy(Object *obj, const char *name,
+                                      Object *val, Error **errp)
+{
+    MemoryRegion *mr;
+
+    mr = host_memory_backend_get_memory(MEMORY_BACKEND(val), errp);
+    if (memory_region_is_mapped(mr)) {
+        char *path = object_get_canonical_path_component(val);
+        error_setg(errp, "can't use already busy memdev: %s", path);
+        g_free(path);
+    } else {
+        qdev_prop_allow_set_link_before_realize(obj, name, val, errp);
+    }
+}
+
 static void pc_dimm_init(Object *obj)
 {
     PCDIMMDevice *dimm = PC_DIMM(obj);
@@ -51,7 +66,7 @@ static void pc_dimm_init(Object *obj)
                         NULL, NULL, NULL, &error_abort);
     object_property_add_link(obj, PC_DIMM_MEMDEV_PROP, TYPE_MEMORY_BACKEND,
                              (Object **)&dimm->hostmem,
-                             qdev_prop_allow_set_link_before_realize,
+                             pc_dimm_check_memdev_is_busy,
                              OBJ_PROP_LINK_UNREF_ON_RELEASE,
                              &error_abort);
 }