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

[Tony Krowiak]

On 6/16/20 11:45 AM, Christian Borntraeger wrote:
> 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@xxxxxxxxxxxxx>
> > ---
> >   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?

You are correct, we don't need it here; but, we will need it
in a subsequent patch where we introduce linking the
q to the matrix mdev to which it is assigned. Perhaps
the locking should be introduced in that patch.

>