drm/virtio: Implement VIRTIO_GPU_CMD_RESOURCE_DETACH_BACKING cmd

This cmd is useful to let the VMM (i.e, Qemu) know that the backing
store associated with a resource is no longer valid, so that the VMM
can perform any cleanup or unmap operations.

The fence related changes and virtio_gpu_object_detach()/
virtio_gpu_detach_object_fenced() routines are extracted from a
patch by Dmitry Osipenko <dmitry.osipenko@collabora.com>.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Gurchetan Singh <gurchetansingh@chromium.org>
Cc: Chia-I Wu <olvaffe@gmail.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241126031643.3490496-2-vivek.kasireddy@intel.com

drivers/gpu/drm/virtio/virtgpu_drv.h

@@ -92,6 +92,7 @@ struct virtio_gpu_object {
 	uint32_t hw_res_handle;
 	bool dumb;
 	bool created;
+	bool attached;
 	bool host3d_blob, guest_blob;
 	uint32_t blob_mem, blob_flags;
 
@@ -353,6 +354,10 @@ void virtio_gpu_object_attach(struct virtio_gpu_device *vgdev,
 			      struct virtio_gpu_object *obj,
 			      struct virtio_gpu_mem_entry *ents,
 			      unsigned int nents);
+void virtio_gpu_object_detach(struct virtio_gpu_device *vgdev,
+			      struct virtio_gpu_object *obj,
+			      struct virtio_gpu_fence *fence);
+int virtio_gpu_detach_object_fenced(struct virtio_gpu_object *bo);
 void virtio_gpu_cursor_ping(struct virtio_gpu_device *vgdev,
 			    struct virtio_gpu_output *output);
 int virtio_gpu_cmd_get_display_info(struct virtio_gpu_device *vgdev);

drivers/gpu/drm/virtio/virtgpu_object.c

@@ -97,6 +97,27 @@ static void virtio_gpu_free_object(struct drm_gem_object *obj)
 	virtio_gpu_cleanup_object(bo);
 }
 
+int virtio_gpu_detach_object_fenced(struct virtio_gpu_object *bo)
+{
+	struct virtio_gpu_device *vgdev = bo->base.base.dev->dev_private;
+	struct virtio_gpu_fence *fence;
+
+	if (!bo->attached)
+		return 0;
+
+	fence = virtio_gpu_fence_alloc(vgdev, vgdev->fence_drv.context, 0);
+	if (!fence)
+		return -ENOMEM;
+
+	virtio_gpu_object_detach(vgdev, bo, fence);
+	virtio_gpu_notify(vgdev);
+
+	dma_fence_wait(&fence->f, false);
+	dma_fence_put(&fence->f);
+
+	return 0;
+}
+
 static const struct drm_gem_object_funcs virtio_gpu_shmem_funcs = {
 	.free = virtio_gpu_free_object,
 	.open = virtio_gpu_gem_object_open,

drivers/gpu/drm/virtio/virtgpu_vq.c

@@ -645,6 +645,23 @@ virtio_gpu_cmd_resource_attach_backing(struct virtio_gpu_device *vgdev,
 	virtio_gpu_queue_fenced_ctrl_buffer(vgdev, vbuf, fence);
 }
 
+static void
+virtio_gpu_cmd_resource_detach_backing(struct virtio_gpu_device *vgdev,
+				       uint32_t resource_id,
+				       struct virtio_gpu_fence *fence)
+{
+	struct virtio_gpu_resource_detach_backing *cmd_p;
+	struct virtio_gpu_vbuffer *vbuf;
+
+	cmd_p = virtio_gpu_alloc_cmd(vgdev, &vbuf, sizeof(*cmd_p));
+	memset(cmd_p, 0, sizeof(*cmd_p));
+
+	cmd_p->hdr.type = cpu_to_le32(VIRTIO_GPU_CMD_RESOURCE_DETACH_BACKING);
+	cmd_p->resource_id = cpu_to_le32(resource_id);
+
+	virtio_gpu_queue_fenced_ctrl_buffer(vgdev, vbuf, fence);
+}
+
 static void virtio_gpu_cmd_get_display_info_cb(struct virtio_gpu_device *vgdev,
 					       struct virtio_gpu_vbuffer *vbuf)
 {
@@ -1103,8 +1120,26 @@ void virtio_gpu_object_attach(struct virtio_gpu_device *vgdev,
 			      struct virtio_gpu_mem_entry *ents,
 			      unsigned int nents)
 {
+	if (obj->attached)
+		return;
+
 	virtio_gpu_cmd_resource_attach_backing(vgdev, obj->hw_res_handle,
 					       ents, nents, NULL);
+
+	obj->attached = true;
+}
+
+void virtio_gpu_object_detach(struct virtio_gpu_device *vgdev,
+			      struct virtio_gpu_object *obj,
+			      struct virtio_gpu_fence *fence)
+{
+	if (!obj->attached)
+		return;
+
+	virtio_gpu_cmd_resource_detach_backing(vgdev, obj->hw_res_handle,
+					       fence);
+
+	obj->attached = false;
 }
 
 void virtio_gpu_cursor_ping(struct virtio_gpu_device *vgdev,