Re: [PATCH v4 3/7] s390: ap: associate a ap_vfio_queue and a matrix mdev

[Tony Krowiak]

On 3/3/19 9:09 PM, Halil Pasic wrote:
> On Fri, 22 Feb 2019 16:29:56 +0100
> Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote:
>
> > We need to associate the ap_vfio_queue, which will hold the
> > per queue information for interrupt with a matrix mediated device
> > which hold the configuration and the way to the CRYCB.
> [..]
> > +static int vfio_ap_get_all_domains(struct ap_matrix_mdev *matrix_mdev, int apid)
> > +{
> > +	int apqi, apqn;
> > +	int ret = 0;
> > +	struct vfio_ap_queue *q;
> > +	struct list_head q_list;
> > +
> > +	INIT_LIST_HEAD(&q_list);
> > +
> > +	for_each_set_bit_inv(apqi, matrix_mdev->matrix.aqm, AP_DOMAINS) {
> > +		apqn = AP_MKQID(apid, apqi);
> > +		q = vfio_ap_get_queue(apqn, &matrix_dev->free_list);
> > +		if (!q) {
> > +			ret = -EADDRNOTAVAIL;
> > +			goto rewind;
> > +		}
> > +		if (q->matrix_mdev) {
> > +			ret = -EADDRINUSE;
>
> You tried to get the q from matrix_dev->free_list thus modulo races
> q->matrix_mdev should be 0. This change breaks the error codes in a
> sense that it becomes impossible to provoke EADDRINUSE (the proper
> error code for taken by another matrix_mdev).

I don't understand what you are saying here. AFIU, the idea here is to
pull the q from the free list. If there is no q for the apqn on the free
list, then that would indicate the queue has not been bound to a driver
in which case the appropriate rc is EADDRNOTAVAIL. If the queue has
been bound, then a check is done to see whether the queue has been
associated with an mdev device. If so, the rc is -EADDRINUSE, which is
also appropriate. What am I missing?

> > +			goto rewind;
> > +		}
> > +		list_move(&q->list, &q_list);
> > +	}
> > +	move_and_set(&q_list, &matrix_mdev->qlist, matrix_mdev);
> >   	return 0;
> > +rewind:
> > +	move_and_set(&q_list, &matrix_dev->free_list, NULL);
> > +	return ret;
> >   }
> > -
> >   /**
> > - * vfio_ap_mdev_verify_no_sharing
> > + * vfio_ap_get_all_cards:
> >    *
> > - * Verifies that the APQNs derived from the cross product of the AP adapter IDs
> > - * and AP queue indexes comprising the AP matrix are not configured for another
> > - * mediated device. AP queue sharing is not allowed.
> > + * @matrix_mdev: the matrix mediated device for which we want to associate
> > + *		 all available queues with a given apqi.
> > + * @apqi:	 The apqi which associated with all defined APID of the
> > + *		 mediated device will define a AP queue.
> >    *
> > - * @matrix_mdev: the mediated matrix device
> > + * We define a local list to put all queues we find on the matrix device
> > + * free list when associating the apqi with all already defined apid for
> > + * this matrix mediated device.
> >    *
> > - * Returns 0 if the APQNs are not shared, otherwise; returns -EADDRINUSE.
> > + * If we can get all the devices we roll them to the mediated device list
> > + * If we get errors we unroll them to the free list.
> >    */
> > -static int vfio_ap_mdev_verify_no_sharing(struct ap_matrix_mdev *matrix_mdev)
> > +static int vfio_ap_get_all_cards(struct ap_matrix_mdev *matrix_mdev, int apqi)
> >   {
> > -	struct ap_matrix_mdev *lstdev;
> > -	DECLARE_BITMAP(apm, AP_DEVICES);
> > -	DECLARE_BITMAP(aqm, AP_DOMAINS);
> > -
> > -	list_for_each_entry(lstdev, &matrix_dev->mdev_list, node) {
> > -		if (matrix_mdev == lstdev)
> > -			continue;
> > -
> > -		memset(apm, 0, sizeof(apm));
> > -		memset(aqm, 0, sizeof(aqm));
> > -
> > -		/*
> > -		 * We work on full longs, as we can only exclude the leftover
> > -		 * bits in non-inverse order. The leftover is all zeros.
> > -		 */
> > -		if (!bitmap_and(apm, matrix_mdev->matrix.apm,
> > -				lstdev->matrix.apm, AP_DEVICES))
> > -			continue;
> > -
> > -		if (!bitmap_and(aqm, matrix_mdev->matrix.aqm,
> > -				lstdev->matrix.aqm, AP_DOMAINS))
> > -			continue;
> > -
> > -		return -EADDRINUSE;
> > +	int apid, apqn;
> > +	int ret = 0;
> > +	struct vfio_ap_queue *q;
> > +	struct list_head q_list;
> > +	struct ap_matrix_mdev *tmp = NULL;
> > +
> > +	INIT_LIST_HEAD(&q_list);
> > +
> > +	for_each_set_bit_inv(apid, matrix_mdev->matrix.apm, AP_DEVICES) {
> > +		apqn = AP_MKQID(apid, apqi);
> > +		q = vfio_ap_get_queue(apqn, &matrix_dev->free_list);
> > +		if (!q) {
> > +			ret = -EADDRNOTAVAIL;
> > +			goto rewind;
> > +		}
> > +		if (q->matrix_mdev) {
> > +			ret = -EADDRINUSE;
>
> Same here!
>
> Regards,
> Halil
>
> > +			goto rewind;
> > +		}
> > +		list_move(&q->list, &q_list);
> >   	}
>
> [..]