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

[Pierre Morel]

On 12/03/2019 22:39, Tony Krowiak wrote:
> 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)
> > > +{
> > > +ÂÂÂ int apqi, apqn;
> > > +ÂÂÂ int ret = 0;
> > > +ÂÂÂ struct vfio_ap_queue *q;
> > > +ÂÂÂ struct list_head q_list;
> > > +
> > > +ÂÂÂ INIT_LIST_HEAD(&q_list);
> > > +
> > > +ÂÂÂ for_each_set_bit_inv(apqi, matrix_mdev->matrix.aqm, AP_DOMAINS) {
> > > +ÂÂÂÂÂÂÂ apqn = AP_MKQID(apid, apqi);
> > > +ÂÂÂÂÂÂÂ q = vfio_ap_get_queue(apqn, &matrix_dev->free_list);
> > > +ÂÂÂÂÂÂÂ if (!q) {
> > > +ÂÂÂÂÂÂÂÂÂÂÂ ret = -EADDRNOTAVAIL;
> > > +ÂÂÂÂÂÂÂÂÂÂÂ goto rewind;
> > > +ÂÂÂÂÂÂÂ }
> > > +ÂÂÂÂÂÂÂ if (q->matrix_mdev) {
> > > +ÂÂÂÂÂÂÂÂÂÂÂ 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).
>
> It is necessary to determine if the queue is in use by another mdev, so
> it will still be necessary to traverse all of the matrix_mdev structs to
> see if q is in matrix_mdev->qlist. It seems that maintaining the qlist
> does not buy us much.

Tony, Halil already pointed out this issue and I already answered.
Please, no need to duplicate the remarks.

Pierre

--
Pierre Morel
Linux/KVM/QEMU in BÃblingen - Germany