drm/virtio: Factor out common dmabuf unmapping code

Move out dmabuf detachment and unmapping into separate function. This
removes duplicated code and there is no need to check the GEM's kref now,
since both bo->attached and bo->sgt are unset under held reservation lock.

Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Acked-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241202053955.2451321-1-dmitry.osipenko@collabora.com

drivers/gpu/drm/virtio/virtgpu_prime.c

@@ -184,6 +184,23 @@ int virtgpu_dma_buf_import_sgt(struct virtio_gpu_mem_entry **ents,
 	return 0;
 }
 
+static void virtgpu_dma_buf_unmap(struct virtio_gpu_object *bo)
+{
+	struct dma_buf_attachment *attach = bo->base.base.import_attach;
+
+	dma_resv_assert_held(attach->dmabuf->resv);
+
+	if (bo->created) {
+		virtio_gpu_detach_object_fenced(bo);
+
+		if (bo->sgt)
+			dma_buf_unmap_attachment(attach, bo->sgt,
+						 DMA_BIDIRECTIONAL);
+
+		bo->sgt = NULL;
+	}
+}
+
 static void virtgpu_dma_buf_free_obj(struct drm_gem_object *obj)
 {
 	struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(obj);
@@ -194,13 +211,7 @@ static void virtgpu_dma_buf_free_obj(struct drm_gem_object *obj)
 		struct dma_buf *dmabuf = attach->dmabuf;
 
 		dma_resv_lock(dmabuf->resv, NULL);
-
-		virtio_gpu_detach_object_fenced(bo);
-
-		if (bo->sgt)
-			dma_buf_unmap_attachment(attach, bo->sgt,
-						 DMA_BIDIRECTIONAL);
-
+		virtgpu_dma_buf_unmap(bo);
 		dma_resv_unlock(dmabuf->resv);
 
 		dma_buf_detach(dmabuf, attach);
@@ -273,15 +284,7 @@ static void virtgpu_dma_buf_move_notify(struct dma_buf_attachment *attach)
 	struct drm_gem_object *obj = attach->importer_priv;
 	struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(obj);
 
-	if (bo->created && kref_read(&obj->refcount)) {
-		virtio_gpu_detach_object_fenced(bo);
-
-		if (bo->sgt)
-			dma_buf_unmap_attachment(attach, bo->sgt,
-						 DMA_BIDIRECTIONAL);
-
-		bo->sgt = NULL;
-	}
+	virtgpu_dma_buf_unmap(bo);
 }
 
 static const struct dma_buf_attach_ops virtgpu_dma_buf_attach_ops = {