Re: [PATCH v11 02/14] 390/vfio-ap: use new AP bus interface to search for queue devices

[Tony Krowiak]

On 10/27/20 3:01 AM, Halil Pasic wrote:
> On Thu, 22 Oct 2020 13:11:57 -0400
> Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
>
> > This patch refactors 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>
> Reviewed-by: Halil Pasic <pasic@xxxxxxxxxxxxx>

Thank you for your review.

> > ---
> >   drivers/s390/crypto/vfio_ap_ops.c | 35 +++++++++++++------------------
> >   1 file changed, 14 insertions(+), 21 deletions(-)
> >
> > diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> > index c471832f0a30..049b97d7444c 100644
> > --- a/drivers/s390/crypto/vfio_ap_ops.c
> > +++ b/drivers/s390/crypto/vfio_ap_ops.c
> > @@ -26,43 +26,36 @@
> >   
> >   static int vfio_ap_mdev_reset_queues(struct mdev_device *mdev);
> >   
> > -static int match_apqn(struct device *dev, const void *data)
> > -{
> > -	struct vfio_ap_queue *q = dev_get_drvdata(dev);
> > -
> > -	return (q->apqn == *(int *)(data)) ? 1 : 0;
> > -}
> > -
> >   /**
> > - * vfio_ap_get_queue: Retrieve a queue with a specific APQN from a list
> > + * vfio_ap_get_queue: Retrieve a queue with a specific APQN.
> >    * @matrix_mdev: the associated mediated matrix
> >    * @apqn: The queue APQN
> >    *
> > - * Retrieve a queue with a specific APQN from the list of the
> > - * devices of the vfio_ap_drv.
> > - * Verify that the APID and the APQI are set in the matrix.
> > + * Retrieve a queue with a specific APQN from the AP queue devices attached to
> > + * the AP bus.
> >    *
> > - * Returns the pointer to the associated vfio_ap_queue
> > + * Returns the pointer to the vfio_ap_queue with the specified APQN, or NULL.
> >    */
> >   static struct vfio_ap_queue *vfio_ap_get_queue(
> >   					struct ap_matrix_mdev *matrix_mdev,
> > -					int apqn)
> > +					unsigned long apqn)
> >   {
> > -	struct vfio_ap_queue *q;
> > -	struct device *dev;
> > +	struct ap_queue *queue;
> > +	struct vfio_ap_queue *q = NULL;
> >   
> >   	if (!test_bit_inv(AP_QID_CARD(apqn), matrix_mdev->matrix.apm))
> >   		return NULL;
> >   	if (!test_bit_inv(AP_QID_QUEUE(apqn), matrix_mdev->matrix.aqm))
> >   		return NULL;
> >   
> > -	dev = driver_find_device(&matrix_dev->vfio_ap_drv->driver, NULL,
> > -				 &apqn, match_apqn);
> > -	if (!dev)
> > +	queue = ap_get_qdev(apqn);
> > +	if (!queue)
> >   		return NULL;
> > -	q = dev_get_drvdata(dev);
> > -	q->matrix_mdev = matrix_mdev;
> > -	put_device(dev);
> > +
> > +	if (queue->ap_dev.device.driver == &matrix_dev->vfio_ap_drv->driver)
> > +		q = dev_get_drvdata(&queue->ap_dev.device);
> > +
> Needs to be called with the vfio_ap lock held, right? Otherwise the queue could
> get unbound while we are working with it as a vfio_ap_queue... Noting
> new, but might we worth documenting.

This is always called with the vfio_ap lock held.

> > +	put_device(&queue->ap_dev.device);
> >   
> >   	return q;
> >   }