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

[Halil Pasic <pasic@linux.ibm.com>]

On Thu, 22 Oct 2020 13:11:57 -0400
Tony Krowiak <akrowiak@linux.ibm.com> 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@linux.ibm.com>

Reviewed-by: Halil Pasic <pasic@linux.ibm.com>

> ---
>  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.

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