diff mbox series

[v3] drm/virtio: Fix handling CONFIG_DRM_VIRTIO_GPU_KMS option

Message ID 20230306163916.1595961-1-dmitry.osipenko@collabora.com
State New
Headers
Series [v3] drm/virtio: Fix handling CONFIG_DRM_VIRTIO_GPU_KMS option |

Commit Message

Dmitry Osipenko March 6, 2023, 4:39 p.m. UTC 
  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: Gerd Hoffmann <kraxel@redhat.com>
Fixes: 72122c69d717 ("drm/virtio: Add option to disable KMS support")
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---

Changelog:

v3: - Moved another similar "has_edid" occurence under the "num_scanouts"
      condition in virtio_gpu_init(), like was suggested by Emil Velikov.

    - Added ack from Gerd Hoffmann.

v2: - Moved the "has_edid" under the "num_scanouts" condition, like was
      suggested by Gerd Hoffmann.

 drivers/gpu/drm/virtio/virtgpu_kms.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

Comments

Dmitry Osipenko March 6, 2023, 5:44 p.m. UTC | #1 
On 3/6/23 19:39, 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.
> 
> Acked-by: Gerd Hoffmann <kraxel@redhat.com>
> Fixes: 72122c69d717 ("drm/virtio: Add option to disable KMS support")
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> ---

Added r-b from Emil and applied to misc-next
Emil Velikov March 6, 2023, 9:31 p.m. UTC | #2 
On 2023/03/06, Dmitry Osipenko wrote:
> On 3/6/23 19:39, 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.
> > 
> > Acked-by: Gerd Hoffmann <kraxel@redhat.com>
> > Fixes: 72122c69d717 ("drm/virtio: Add option to disable KMS support")
> > Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> > ---
> 
> Added r-b from Emil and applied to misc-next
> 

For anyone wondering: I've sent that in private, adding here for posterity

Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

-Emil
diff mbox series

Patch

diff --git a/drivers/gpu/drm/virtio/virtgpu_kms.c b/drivers/gpu/drm/virtio/virtgpu_kms.c
index 874ad6c2621a..43e237082cec 100644
--- a/drivers/gpu/drm/virtio/virtgpu_kms.c
+++ b/drivers/gpu/drm/virtio/virtgpu_kms.c
@@ -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->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);
+		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;
@@ -253,9 +255,9 @@  int virtio_gpu_init(struct virtio_device *vdev, struct drm_device *dev)
 
 	if (num_capsets)
 		virtio_gpu_get_capsets(vgdev, num_capsets);
-	if (vgdev->has_edid)
-		virtio_gpu_cmd_get_edids(vgdev);
 	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);
 		wait_event_timeout(vgdev->resp_wq, !vgdev->display_info_pending,