Linux Virtualization - Mar 2023 - [PATCH v2] drm/virtio: Fix handling CONFIG_DRM_VIRTIO_GPU_KMS option

On Mon, Mar 06, 2023 at 05:32:34PM +0300, Dmitry Osipenko
wrote:
> 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.
> 
> Fixes: 72122c69d717 ("drm/virtio: Add option to disable KMS
support")
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko at collabora.com>
> ---
> 
> Changelog:
> 
> v2: - Moved the "has_edid" under the "num_scanouts"
condition, like was
>       suggested by Gerd Hoffmann.
Acked-by: Gerd Hoffmann <kraxel at redhat.com>