Commit 72122c69 authored by Rob Clark's avatar Rob Clark Committed by Dmitry Osipenko
Browse files

drm/virtio: Add option to disable KMS support 



Add a build option to disable modesetting support.  This is useful in
cases where the guest only needs to use the GPU in a headless mode, or
(such as in the CrOS usage) window surfaces are proxied to a host
compositor.

As the modesetting ioctls are a big surface area for potential security
bugs to be found (it's happened in the past, we should assume it will
again in the future), it makes sense to have a build option to disable
those ioctls in cases where they serve no legitimate purpose.

v2: Use more if (IS_ENABLED(...))
v3: Also permit the host to advertise no scanouts
v4: Spiff out commit msg
v5: Make num_scanouts==0 and DRM_VIRTIO_GPU_KMS=n behave the same
v6: Drop conditionally building virtgpu_display.c and early-out of
    it's init/fini fxns instead

Signed-off-by: default avatarRob Clark <robdclark@chromium.org>
Reviewed-by: default avatarDmitry Osipenko <dmitry.osipenko@collabora.com>
Reviewed-by: default avatarJavier Martinez Canillas <javierm@redhat.com>
Reviewed-by: default avatarGerd Hoffmann <kraxel@redhat.com>
Signed-off-by: default avatarDmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230302233506.3146290-1-robdclark@gmail.com
parent e3ecbd21

drivers/gpu/drm/virtio/Kconfig

+11 −0
Original line number Diff line number Diff line
@@ -11,3 +11,14 @@ config DRM_VIRTIO_GPU 
	   QEMU based VMMs (like KVM or Xen).



	   If unsure say M.



config DRM_VIRTIO_GPU_KMS

	bool "Virtio GPU driver modesetting support"

	depends on DRM_VIRTIO_GPU

	default y

	help

	   Enable modesetting support for virtio GPU driver.  This can be

	   disabled in cases where only "headless" usage of the GPU is

	   required.



	   If unsure, say Y.

drivers/gpu/drm/virtio/virtgpu_display.c

+6 −0
Original line number Diff line number Diff line
@@ -336,6 +336,9 @@ int virtio_gpu_modeset_init(struct virtio_gpu_device *vgdev) 
{

	int i, ret;



	if (!vgdev->num_scanouts)

		return 0;



	ret = drmm_mode_config_init(vgdev->ddev);

	if (ret)

		return ret;
@@ -362,6 +365,9 @@ void virtio_gpu_modeset_fini(struct virtio_gpu_device *vgdev) 
{

	int i;



	if (!vgdev->num_scanouts)

		return;



	for (i = 0 ; i < vgdev->num_scanouts; ++i)

		kfree(vgdev->outputs[i].edid);

}

drivers/gpu/drm/virtio/virtgpu_drv.c

+4 −0
Original line number Diff line number Diff line
@@ -172,6 +172,10 @@ MODULE_AUTHOR("Alon Levy"); 
DEFINE_DRM_GEM_FOPS(virtio_gpu_driver_fops);



static const struct drm_driver driver = {

	/*

	 * If KMS is disabled DRIVER_MODESET and DRIVER_ATOMIC are masked

	 * out via drm_device::driver_features:

	 */

	.driver_features = DRIVER_MODESET | DRIVER_GEM | DRIVER_RENDER | DRIVER_ATOMIC,

	.open = virtio_gpu_driver_open,

	.postclose = virtio_gpu_driver_postclose,

drivers/gpu/drm/virtio/virtgpu_kms.c

+14 −9
Original line number Diff line number Diff line
@@ -223,12 +223,15 @@ int virtio_gpu_init(struct virtio_device *vdev, struct drm_device *dev) 
			num_scanouts, &num_scanouts);

	vgdev->num_scanouts = min_t(uint32_t, num_scanouts,

				    VIRTIO_GPU_MAX_SCANOUTS);

	if (!vgdev->num_scanouts) {

		DRM_ERROR("num_scanouts is zero\n");

		ret = -EINVAL;

		goto err_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;

		dev->driver_features &= ~(DRIVER_MODESET | DRIVER_ATOMIC);

	} else {

		DRM_INFO("number of scanouts: %d\n", num_scanouts);

	}



	virtio_cread_le(vgdev->vdev, struct virtio_gpu_config,

			num_capsets, &num_capsets);
@@ -246,10 +249,12 @@ int virtio_gpu_init(struct virtio_device *vdev, struct drm_device *dev) 
		virtio_gpu_get_capsets(vgdev, num_capsets);

	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,

				   5 * HZ);

	}

	return 0;



err_scanouts: