vm: controller: implement detach of vm-object whose attachment was deferred

vm/vm-controller.c

@@ -216,6 +216,15 @@ kern_status_t vm_controller_detach_object(
 		return KERN_INVALID_ARGUMENT;
 	}
 
+	if (vmo->vo_key == 0) {
+		/* this vmo isn't actually attached to this controller yet.
+		 * this can happen if a controller-attached vmo was duplicated
+		 * via copy-on-write, and the duplicate vmo has not yet been
+		 * accessed. */
+		vmo->vo_ctrl = NULL;
+		return KERN_OK;
+	}
+
 	struct page_request *req
 		= vm_cache_alloc(&page_request_cache, VM_NORMAL);
 	req->req_type = PAGE_REQUEST_DETACH;