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Date:   Tue, 9 Jul 2019 12:49:20 +0200
From:   Cornelia Huck <cohuck@redhat.com>
To:     Tony Krowiak <akrowiak@linux.ibm.com>
Cc:     linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
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        alex.williamson@redhat.com, kwankhede@nvidia.com
Subject: Re: [PATCH v4 3/7] s390: zcrypt: driver callback to indicate
 resource in use
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On Mon, 8 Jul 2019 10:27:11 -0400
Tony Krowiak <akrowiak@linux.ibm.com> wrote:

> On 7/1/19 3:26 PM, Cornelia Huck wrote:
> > On Wed, 19 Jun 2019 09:04:18 -0400
> > Tony Krowiak <akrowiak@linux.ibm.com> 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.