Re: [PATCH v8 02/16] s390/vfio-ap: use new AP bus interface to search for queue devices

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 05.06.20 23:39, Tony Krowiak wrote:
> This patch refactor's the vfio_ap device driver to use the AP bus's
> ap_get_qdev() function to retrieve the vfio_ap_queue struct containing
> information about a queue that is bound to the vfio_ap device driver.
> The bus's ap_get_qdev() function retrieves the queue device from a
> hashtable keyed by APQN. This is much more efficient than looping over
> the list of devices attached to the AP bus by several orders of
> magnitude.
> 
> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> ---
>  drivers/s390/crypto/vfio_ap_drv.c     | 27 ++-------
>  drivers/s390/crypto/vfio_ap_ops.c     | 82 +++++++++++++++------------
>  drivers/s390/crypto/vfio_ap_private.h |  8 ++-
>  3 files changed, 58 insertions(+), 59 deletions(-)
> 
> diff --git a/drivers/s390/crypto/vfio_ap_drv.c b/drivers/s390/crypto/vfio_ap_drv.c
> index be2520cc010b..59233cf7419d 100644
> --- a/drivers/s390/crypto/vfio_ap_drv.c
> +++ b/drivers/s390/crypto/vfio_ap_drv.c
> @@ -51,15 +51,9 @@ MODULE_DEVICE_TABLE(vfio_ap, ap_queue_ids);
>   */
>  static int vfio_ap_queue_dev_probe(struct ap_device *apdev)
>  {
> -	struct vfio_ap_queue *q;
> -
> -	q = kzalloc(sizeof(*q), GFP_KERNEL);
> -	if (!q)
> -		return -ENOMEM;
> -	dev_set_drvdata(&apdev->device, q);
> -	q->apqn = to_ap_queue(&apdev->device)->qid;
> -	q->saved_isc = VFIO_AP_ISC_INVALID;
> -	return 0;
> +	struct ap_queue *queue = to_ap_queue(&apdev->device);
> +
> +	return vfio_ap_mdev_probe_queue(queue);
>  }

Here we did not hold a mutex in the old code 
[...]

> +int vfio_ap_mdev_probe_queue(struct ap_queue *queue)
> +{
> +	struct vfio_ap_queue *q;
> +
> +	q = kzalloc(sizeof(*q), GFP_KERNEL);
> +	if (!q)
> +		return -ENOMEM;
> +
> +	mutex_lock(&matrix_dev->lock);
> +	dev_set_drvdata(&queue->ap_dev.device, q);
> +	q->apqn = queue->qid;
> +	q->saved_isc = VFIO_AP_ISC_INVALID;
> +	mutex_unlock(&matrix_dev->lock);
> +

here we do. Why do we need the matrix_dev->lock here?