Re: [PATCH v10 02/16] s390/vfio-ap: use new AP bus interface to search for queue devices

[Tony Krowiak]

On 8/25/20 6:13 AM, Cornelia Huck wrote:
> On Fri, 21 Aug 2020 15:56:02 -0400
> Tony Krowiak<akrowiak@xxxxxxxxxxxxx>  wrote:
>
> > This patch refactor's the vfio_ap device driver to use the AP bus's
> s/refactor's/refactors/

Of course, what was I thinking?:)

> > 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>
> > Reported-by: kernel test robot<lkp@xxxxxxxxx>
> > ---
> >   drivers/s390/crypto/vfio_ap_drv.c     | 27 ++-------
> >   drivers/s390/crypto/vfio_ap_ops.c     | 86 +++++++++++++++------------
> >   drivers/s390/crypto/vfio_ap_private.h |  8 ++-
> >   3 files changed, 59 insertions(+), 62 deletions(-)
> (...)
>
> > diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> > index e0bde8518745..ad3925f04f61 100644
> > --- a/drivers/s390/crypto/vfio_ap_ops.c
> > +++ b/drivers/s390/crypto/vfio_ap_ops.c
> > @@ -26,43 +26,26 @@
> >   
> >   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
> > - * @matrix_mdev: the associated mediated matrix
> > + * vfio_ap_get_queue: Retrieve a queue with a specific APQN.
> >    * @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)
> > +static struct vfio_ap_queue *vfio_ap_get_queue(unsigned long apqn)
> >   {
> > +	struct ap_queue *queue;
> >   	struct vfio_ap_queue *q;
> > -	struct device *dev;
> >   
> > -	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))
> I think you should add some explanation to the patch description why
> testing the matrix bitmasks is not needed anymore.

As a result of this comment, I took a closer look at the code to
determine the reason for eliminating the matrix_mdev
parameter. The reason is because the code below (i.e., find the device
and get the driver data) was also repeated in the vfio_ap_irq_disable_apqn()
function, so I replaced it with a call to the function above; however, the
vfio_ap_irq_disable_apqn() function  does not have a reference to the
matrix_mdev, so I eliminated the matrix_mdev parameter. Note that the
vfio_ap_irq_disable_apqn() is called for each APQN assigned to a matrix
mdev, so there is no need to test the bitmasks there.

The other place from which the function above is called is
the handle_pqap() function which does have a reference to the
matrix_mdev. In order to ensure the integrity of the instruction
being intercepted - i.e., PQAP(AQIC) enable/disable IRQ for aN
AP queue - the testing of the matrix bitmasks probably ought to
be performed, so it will be done there instead of in the
vfio_ap_get_queue() function above.


> +	queue = ap_get_qdev(apqn);
> +	if (!queue)
>   		return NULL;
>   
> -	dev = driver_find_device(&matrix_dev->vfio_ap_drv->driver, NULL,
> -				 &apqn, match_apqn);
> -	if (!dev)
> -		return NULL;
> -	q = dev_get_drvdata(dev);
> -	q->matrix_mdev = matrix_mdev;
> -	put_device(dev);
> +	q = dev_get_drvdata(&queue->ap_dev.device);
> +	put_device(&queue->ap_dev.device);
>   
>   	return q;
>   }
> (...)