Re: [PATCH v4 3/7] s390: zcrypt: driver callback to indicate resource in use

[Tony Krowiak]

On 7/9/19 6:49 AM, Cornelia Huck wrote:
> On Mon, 8 Jul 2019 10:27:11 -0400
> Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
>
> > On 7/1/19 3:26 PM, Cornelia Huck wrote:
> > > On Wed, 19 Jun 2019 09:04:18 -0400
> > > Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
>
> > > > Allow me to first address your fear that a bad actor can hog
> > > > resources that can't be removed by root. With this enhancement,
> > > > there is nothing preventing a root user from taking resources
> > > > from a matrix mdev, it simply forces him/her to follow the
> > > > proper procedure. The resources to be removed must first be
> > > > unassigned from the matrix mdev to which they are assigned.
> > > > The AP bus's /sys/bus/ap/apmask and /sys/bus/ap/aqmask
> > > > sysfs attributes can then be edited to transfer ownership
> > > > of the resources to zcrypt.
> > >
> > > What is the suggested procedure when root wants to unbind a queue
> > > device? Find the mdev using the queue (is that easy enough?), unassign
> > > it, then unbind? Failing to unbind is a bit unexpected; can we point
> > > the admin to the correct mdev from which the queue has to be removed
> > > first?
> >
> > The proper procedure is to first unassign the adapter, domain, or both
> > from the mdev to which the APQN is assigned. The difficulty in finding
> > the queue depends upon how many mdevs have been created. I would expect
> > that an admin would keep records of who owns what, but in the case he or
> > she doesn't, it would be a matter of printing out the matrix attribute
> > of each mdev until you find the mdev to which the APQN is assigned.
>
> Ok, so the information is basically available, if needed.
>
> > The only means I know of for informing the admin to which mdev a given
> > APQN is assigned is to log the error when it occurs.
>
> That might be helpful, if it's easy to do.
>
> > I think Matt is
> > also looking to provide query functions in the management tool on which
> > he is currently working.
>
> That also sounds helpful.
>
> (...)
>
> > > > * It forces the use of the proper procedure to change ownership of AP
> > > >      queues.
> > >
> > > This needs to be properly documented, and the admin needs to have a
> > > chance to find out why unbinding didn't work and what needs to be done
> > > (see my comments above).
> >
> > I will create a section in the vfio-ap.txt document that comes with this
> > patch set describing the proper procedure for unbinding queues. Of
> > course, we'll make sure the official IBM doc also more thoroughly
> > describes this.
>
> +1 for good documentation.
>
> With that, I don't really object to this change.

Then I will make the suggested changes and post v5 to the list.

>