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

Halil Pasic
2020-09-29T13:38:43Z

On Tue, 29 Sep 2020 09:07:40 -0400
Tony Krowiak <akrowiak@linux.ibm.com> wrote:

>
>
> On 9/24/20 10:27 PM, Halil Pasic wrote:
> > On Fri, 21 Aug 2020 15:56:02 -0400
> > Tony Krowiak <akrowiak@linux.ibm.com> wrote:
> >
> >> --- 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))
> >> + 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);
> > Is this cast here safe? (I don't think it is.)
>
> In the probe, we execute:
> dev_set_drvdata(&queue->ap_dev.device, q);
>
> I don't get any compile nor execution errors. Why wouldn't it be safe?
>

Because the queue may or may not be bound to the vfio_ap driver. AFAICT
this function can be called with an arbitrary APQN.

If it is bound to another driver then drvdata is not likely to hold a
struct vfio_ap_queue.

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