linux-kernel - Re: [PATCH v2] drm/virtio: Fix handling CONFIG_DRM_VIRTIO_GPU

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Message-ID: <20230306144640.ta7jca5iabg66uoy@sirius.home.kraxel.org>
Date:   Mon, 6 Mar 2023 15:46:40 +0100
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>
Cc:     Rob Clark <robdclark@...il.com>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Chia-I Wu <olvaffe@...il.com>,
        Ryan Neph <ryanneph@...omium.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Javier Martinez Canillas <javierm@...hat.com>,
        David Airlie <airlied@...hat.com>, kernel@...labora.com,
        virtualization@...ts.linux-foundation.org
Subject: Re: [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@...labora.com>
> ---
> 
> Changelog:
> 
> v2: - Moved the "has_edid" under the "num_scanouts" condition, like was
>       suggested by Gerd Hoffmann.

Acked-by: Gerd Hoffmann <kraxel@...hat.com>