Commit aad9729e authored by Dmitry Osipenko's avatar Dmitry Osipenko
Browse files

drm/virtio: Fix handling CONFIG_DRM_VIRTIO_GPU_KMS option 



VirtIO-GPU got a new config option for disabling KMS. There were two
problems left unnoticed during review when the new option was added:

1. The IS_ENABLED(CONFIG_DRM_VIRTIO_GPU_KMS) check in the code was
inverted, hence KMS was disabled when it should be enabled and vice versa.

2. The disabled KMS crashed kernel with a NULL dereference in
drm_kms_helper_hotplug_event(), which shall not be invoked with a
disabled KMS.

Fix the inverted config option check in the code and skip handling the
VIRTIO_GPU_EVENT_DISPLAY sent by host when KMS is disabled in guest to fix
the crash.

Acked-by: default avatarGerd Hoffmann <kraxel@redhat.com>
Reviewed-by: default avatarEmil Velikov <emil.velikov@collabora.com>
Fixes: 72122c69 ("drm/virtio: Add option to disable KMS support")
Signed-off-by: default avatarDmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230306163916.1595961-1-dmitry.osipenko@collabora.com
parent bf458e5b

drivers/gpu/drm/virtio/virtgpu_kms.c

+10 −8
Original line number Diff line number Diff line
@@ -43,11 +43,13 @@ static void virtio_gpu_config_changed_work_func(struct work_struct *work) 
	virtio_cread_le(vgdev->vdev, struct virtio_gpu_config,

			events_read, &events_read);

	if (events_read & VIRTIO_GPU_EVENT_DISPLAY) {

		if (vgdev->num_scanouts) {

			if (vgdev->has_edid)

				virtio_gpu_cmd_get_edids(vgdev);

			virtio_gpu_cmd_get_display_info(vgdev);

			virtio_gpu_notify(vgdev);

			drm_helper_hpd_irq_event(vgdev->ddev);

		}

		events_clear |= VIRTIO_GPU_EVENT_DISPLAY;

	}

	virtio_cwrite_le(vgdev->vdev, struct virtio_gpu_config,
@@ -224,7 +226,7 @@ int virtio_gpu_init(struct virtio_device *vdev, struct drm_device *dev) 
	vgdev->num_scanouts = min_t(uint32_t, num_scanouts,

				    VIRTIO_GPU_MAX_SCANOUTS);



	if (IS_ENABLED(CONFIG_DRM_VIRTIO_GPU_KMS) || !vgdev->num_scanouts) {

	if (!IS_ENABLED(CONFIG_DRM_VIRTIO_GPU_KMS) || !vgdev->num_scanouts) {

		DRM_INFO("KMS disabled\n");

		vgdev->num_scanouts = 0;

		vgdev->has_edid = false;
@@ -247,9 +249,9 @@ int virtio_gpu_init(struct virtio_device *vdev, struct drm_device *dev) 


	if (num_capsets)

		virtio_gpu_get_capsets(vgdev, num_capsets);

	if (vgdev->num_scanouts) {

		if (vgdev->has_edid)

			virtio_gpu_cmd_get_edids(vgdev);

	if (vgdev->num_scanouts) {

		virtio_gpu_cmd_get_display_info(vgdev);

		virtio_gpu_notify(vgdev);

		wait_event_timeout(vgdev->resp_wq, !vgdev->display_info_pending,