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 <[email protected]>
Fixes: 72122c69d717 ("drm/virtio: Add option to disable KMS support")
Signed-off-by: Dmitry Osipenko <[email protected]>
---
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(-)
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,
--
2.39.2
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 <[email protected]>
> Fixes: 72122c69d717 ("drm/virtio: Add option to disable KMS support")
> Signed-off-by: Dmitry Osipenko <[email protected]>
> ---
Added r-b from Emil and applied to misc-next
--
Best regards,
Dmitry
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 <[email protected]>
> > Fixes: 72122c69d717 ("drm/virtio: Add option to disable KMS support")
> > Signed-off-by: Dmitry Osipenko <[email protected]>
> > ---
>
> 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 <[email protected]>
-Emil