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

[Tony Krowiak]

On 9/29/20 9:37 AM, Halil Pasic wrote:
> On Tue, 29 Sep 2020 09:07:40 -0400
> Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
>
> > On 9/24/20 10:27 PM, Halil Pasic wrote:
> > > On Fri, 21 Aug 2020 15:56:02 -0400
> > > Tony Krowiak <akrowiak@xxxxxxxxxxxxx> 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.

Then the function will return NULL. All callers must check for
NULL before using it which is the case in all places where this
function is called.

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