Subject: Re: [PATCH v3] virtio: rtc: tear down old virtqueues before restore

From: "Michael S. Tsirkin" <[email-masked]>
Date: Sat, 25 Apr 2026 11:10:43 -0400

On Sat, Apr 25, 2026 at 03:08:40PM +0800, physicalmtea wrote:
> From: JiaJia <[email-masked]>
> 
> virtio_device_restore() resets the device and restores the negotiated
> features before calling ->restore(). viortc_freeze() intentionally
> leaves the existing virtqueues in place so the alarm queue can still
> wake the system, but viortc_restore() immediately calls
> viortc_init_vqs() without first deleting those old queues.
> 
> If virtqueue reinitialization fails on virtio-pci, the transport error
> path can run vp_del_vqs() against a newly allocated vp_dev->vqs array
> while vdev->vqs still contains the old virtqueues. vp_del_vqs() then
> looks up queue state through the new array and can dereference a NULL
> info pointer in vp_del_vq(), crashing the guest kernel during restore.
> 
> This can also happen during a non-faulty reinitialization, when one of
> the vp_find_vqs_msix() attempts is unsuccessful before a later attempt
> would succeed.
> 
> Delete the stale virtqueues before rebuilding them. If restore fails
> before virtio_device_ready(), reuse the remove path to stop the device.
> Once the device is ready, return errors directly instead of deleting the
> virtqueues again.
> 
> Fixes: 0623c7592768 ("virtio_rtc: Add module and driver core")
> Signed-off-by: JiaJia <[email-masked]>

Sorry is this just the 1st name or the 1st and the last name?
I think it's preferred to have the full name here.

> Reviewed-by: Peter Hilber <[email-masked]>
> ---
> v3:
>   - Add Fixes tag.
>   - Add Peter's Reviewed-by tag.
>   - Clarify commit message regarding reinitialization scenarios.
> 
> Apologies for missing the Fixes tag, and thanks for catching that! 
> I've also updated the commit message to include the scenario you 
> mentioned.
> 
>  drivers/virtio/virtio_rtc_driver.c | 28 ++++++++++++++++++++--------
>  1 file changed, 20 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_rtc_driver.c b/drivers/virtio/virtio_rtc_driver.c
> index a57d5e06e..4419735b0 100644
> --- a/drivers/virtio/virtio_rtc_driver.c
> +++ b/drivers/virtio/virtio_rtc_driver.c
> @@ -1257,6 +1257,15 @@ static int viortc_init_vqs(struct viortc_dev *viortc)
>  	return 0;
>  }
>  
> +static void __viortc_remove(struct viortc_dev *viortc)
> +{
> +	struct virtio_device *vdev = viortc->vdev;
> +
> +	viortc_clocks_deinit(viortc);
> +	virtio_reset_device(vdev);
> +	vdev->config->del_vqs(vdev);
> +}
> +
>  /**
>   * viortc_probe() - probe a virtio_rtc virtio device
>   * @vdev: virtio device
> @@ -1282,7 +1291,7 @@ static int viortc_probe(struct virtio_device *vdev)
>  
>  	ret = viortc_init_vqs(viortc);
>  	if (ret)
> -		return ret;
> +		goto err_reset_vdev;
>  
>  	virtio_device_ready(vdev);
>  
> @@ -1329,10 +1338,7 @@ static void viortc_remove(struct virtio_device *vdev)
>  {
>  	struct viortc_dev *viortc = vdev->priv;
>  
> -	viortc_clocks_deinit(viortc);
> -
> -	virtio_reset_device(vdev);
> -	vdev->config->del_vqs(vdev);
> +	__viortc_remove(viortc);
>  }
>  
>  static int viortc_freeze(struct virtio_device *dev)
> @@ -1353,9 +1359,11 @@ static int viortc_restore(struct virtio_device *dev)
>  	bool notify = false;
>  	int ret;
>  
> +	dev->config->del_vqs(dev);
> +
>  	ret = viortc_init_vqs(viortc);
>  	if (ret)
> -		return ret;
> +		goto err_remove;
>  
>  	alarm_viortc_vq = &viortc->vqs[VIORTC_ALARMQ];
>  	alarm_vq = alarm_viortc_vq->vq;
> @@ -1364,7 +1372,7 @@ static int viortc_restore(struct virtio_device *dev)
>  		ret = viortc_populate_vq(viortc, alarm_viortc_vq,
>  					 VIORTC_ALARMQ_BUF_CAP, false);
>  		if (ret)
> -			return ret;
> +			goto err_remove;
>  
>  		notify = virtqueue_kick_prepare(alarm_vq);
>  	}
> @@ -1372,8 +1380,12 @@ static int viortc_restore(struct virtio_device *dev)
>  	virtio_device_ready(dev);
>  
>  	if (notify && !virtqueue_notify(alarm_vq))
> -		ret = -EIO;
> +		return -EIO;
> +
> +	return 0;
>  
> +err_remove:
> +	__viortc_remove(viortc);
>  	return ret;
>  }
>  
> -- 
> 2.34.1