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SubjectRe: [PATCH v3] drm/virtio: Add option to disable KMS support
From
Hi

Am 27.02.23 um 19:15 schrieb Rob Clark:
> On Mon, Feb 27, 2023 at 9:57 AM Dmitry Osipenko
> <dmitry.osipenko@collabora.com> wrote:
>>
>> On 2/27/23 20:38, Rob Clark wrote:
>> ...
>>> + if (IS_ENABLED(CONFIG_DRM_VIRTIO_GPU_KMS)) {
>>> + /* get display info */
>>> + virtio_cread_le(vgdev->vdev, struct virtio_gpu_config,
>>> + num_scanouts, &num_scanouts);
>>> + vgdev->num_scanouts = min_t(uint32_t, num_scanouts,
>>> + VIRTIO_GPU_MAX_SCANOUTS);
>>> + if (!vgdev->num_scanouts) {
>>> + /*
>>> + * Having an EDID but no scanouts is non-sensical,
>>> + * but it is permitted to have no scanouts and no
>>> + * EDID (in which case DRIVER_MODESET and
>>> + * DRIVER_ATOMIC are not advertised)
>>> + */
>>> + if (vgdev->has_edid) {
>>> + DRM_ERROR("num_scanouts is zero\n");
>>> + ret = -EINVAL;
>>> + goto err_scanouts;
>>> + }
>>> + dev->driver_features &= ~(DRIVER_MODESET | DRIVER_ATOMIC);
>>
>> If it's now configurable by host, why do we need the
>> CONFIG_DRM_VIRTIO_GPU_KMS?
>
> Because a kernel config option makes it more obvious that
> modeset/atomic ioctls are blocked. Which makes it more obvious about
> where any potential security issues apply and where fixes need to get
> backported to. The config option is the only thing _I_ want,
> everything else is just a bonus to help other people's use-cases.

I find this very vague. What's the security thread?

And if the config option is useful, shouldn't it be DRM-wide? The
modesetting ioctl calls are shared among all drivers.

Best regards
Thomas

>
> BR,
> -R

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev
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