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

Cornelia Huck
2020-08-28T08:14:14Z

On Thu, 27 Aug 2020 10:24:07 -0400
Tony Krowiak <akrowiak@linux.ibm.com> wrote:

> On 8/25/20 6:13 AM, Cornelia Huck wrote:
> > On Fri, 21 Aug 2020 15:56:02 -0400
> > Tony Krowiak<akrowiak@linux.ibm.com> wrote:

> >> /**
> >> - * 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.

Should you add a comment that vfio_ap_get_queue() assumes that the
caller makes sure that this is only called for APQNs that are assigned
to a matrix?

>
>
> > + 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;
> > }
> > (...)
> >
>