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 <[email protected]>
---
Changelog:
v2: - Moved the "has_edid" under the "num_scanouts" condition, like was
suggested by Gerd Hoffmann.
drivers/gpu/drm/virtio/virtgpu_kms.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)
diff --git a/drivers/gpu/drm/virtio/virtgpu_kms.c b/drivers/gpu/drm/virtio/virtgpu_kms.c
index 874ad6c2621a..15f2519988e7 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;
--
2.39.2
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 <[email protected]>
> ---
>
> Changelog:
>
> v2: - Moved the "has_edid" under the "num_scanouts" condition, like was
> suggested by Gerd Hoffmann.
Acked-by: Gerd Hoffmann <[email protected]>
On 2023/03/06, 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 <[email protected]>
> ---
>
> Changelog:
>
> v2: - Moved the "has_edid" under the "num_scanouts" condition, like was
> suggested by Gerd Hoffmann.
>
Hi Dmitry, I think there's more than one piece like that in the driver.
> drivers/gpu/drm/virtio/virtgpu_kms.c | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/virtio/virtgpu_kms.c b/drivers/gpu/drm/virtio/virtgpu_kms.c
> index 874ad6c2621a..15f2519988e7 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);
Worth doing the same thing in virtio_gpu_init()? Aka move the has_edid
&& get_edids within the num_scanouts if block.
HTH
Emil
On 3/6/23 18:02, Emil Velikov wrote:
> On 2023/03/06, 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 <[email protected]>
>> ---
>>
>> Changelog:
>>
>> v2: - Moved the "has_edid" under the "num_scanouts" condition, like was
>> suggested by Gerd Hoffmann.
>>
>
> Hi Dmitry, I think there's more than one piece like that in the driver.
>
>> drivers/gpu/drm/virtio/virtgpu_kms.c | 14 ++++++++------
>> 1 file changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/virtio/virtgpu_kms.c b/drivers/gpu/drm/virtio/virtgpu_kms.c
>> index 874ad6c2621a..15f2519988e7 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);
>
> Worth doing the same thing in virtio_gpu_init()? Aka move the has_edid
> && get_edids within the num_scanouts if block.
Good catch, that could be done for consistency.
--
Best regards,
Dmitry