linux-kernel - Re: [PATCH v2 01/15] virtio_pci: fix virtio spec compliance on restore

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Date:	Tue, 7 Oct 2014 15:53:55 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	kvm@...r.kernel.org, Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org, stable@...r.kernel.org,
	Amit Shah <amit.shah@...hat.com>
Subject: Re: [PATCH v2 01/15] virtio_pci: fix virtio spec compliance on
 restore

On Mon, Oct 06, 2014 at 06:10:40PM +0300, Michael S. Tsirkin wrote:
> On restore, virtio pci does the following:
> + set features
> + init vqs etc - device can be used at this point!
> + set ACKNOWLEDGE,DRIVER and DRIVER_OK status bits
> 
> This is in violation of the virtio spec, which
> requires the following order:
> - ACKNOWLEDGE
> - DRIVER
> - init vqs
> - DRIVER_OK
> 
> This behaviour will break with hypervisors that assume spec compliant
> behaviour.  It seems like a good idea to have this patch applied to
> stable branches to reduce the support butden for the hypervisors.

Tested suspend to ram with virtio net and blk.

> 
> Cc: stable@...r.kernel.org
> Cc: Amit Shah <amit.shah@...hat.com>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>  drivers/virtio/virtio_pci.c | 36 ++++++++++++++++++++++++++++++++----
>  1 file changed, 32 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
> index 3d1463c..0f2db51 100644
> --- a/drivers/virtio/virtio_pci.c
> +++ b/drivers/virtio/virtio_pci.c
> @@ -789,6 +789,7 @@ static int virtio_pci_restore(struct device *dev)
>  	struct pci_dev *pci_dev = to_pci_dev(dev);
>  	struct virtio_pci_device *vp_dev = pci_get_drvdata(pci_dev);
>  	struct virtio_driver *drv;
> +	unsigned status = 0;
>  	int ret;
>  
>  	drv = container_of(vp_dev->vdev.dev.driver,
> @@ -799,14 +800,41 @@ static int virtio_pci_restore(struct device *dev)
>  		return ret;
>  
>  	pci_set_master(pci_dev);
> +	/* We always start by resetting the device, in case a previous
> +	 * driver messed it up. */
> +	vp_reset(&vp_dev->vdev);
> +
> +	/* Acknowledge that we've seen the device. */
> +	status |= VIRTIO_CONFIG_S_ACKNOWLEDGE;
> +	vp_set_status(&vp_dev->vdev, status);
> +
> +	/* Maybe driver failed before freeze.
> +	 * Restore the failed status, for debugging. */
> +	status |= vp_dev->saved_status & VIRTIO_CONFIG_S_FAILED;
> +	vp_set_status(&vp_dev->vdev, status);
> +
> +	if (!drv)
> +		return 0;
> +
> +	/* We have a driver! */
> +	status |= VIRTIO_CONFIG_S_DRIVER;
> +	vp_set_status(&vp_dev->vdev, status);
> +
>  	vp_finalize_features(&vp_dev->vdev);
>  
> -	if (drv && drv->restore)
> -		ret = drv->restore(&vp_dev->vdev);
> +	if (!drv->restore)
> +		return 0;

As Amit points out, this is a bug: for a driver without restore
callback we should still set DRIVER_OK.
Will post v3.

> +
> +	ret = drv->restore(&vp_dev->vdev);
> +	if (ret) {
> +		status |= VIRTIO_CONFIG_S_FAILED;
> +		vp_set_status(&vp_dev->vdev, status);
> +		return ret;
> +	}
>  
>  	/* Finally, tell the device we're all set */
> -	if (!ret)
> -		vp_set_status(&vp_dev->vdev, vp_dev->saved_status);
> +	status |= VIRTIO_CONFIG_S_DRIVER_OK;
> +	vp_set_status(&vp_dev->vdev, status);
>  
>  	return ret;
>  }
> -- 
> MST
> 
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