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

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Date:   Tue, 9 Jul 2019 17:11:20 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, freude@...ux.ibm.com, borntraeger@...ibm.com,
        frankja@...ux.ibm.com, david@...hat.com, mjrosato@...ux.ibm.com,
        schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
        pmorel@...ux.ibm.com, pasic@...ux.ibm.com,
        alex.williamson@...hat.com, kwankhede@...dia.com
Subject: Re: [PATCH v4 3/7] s390: zcrypt: driver callback to indicate resource
 in use

On 7/9/19 6:49 AM, Cornelia Huck wrote:
> On Mon, 8 Jul 2019 10:27:11 -0400
> Tony Krowiak <akrowiak@...ux.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@...ux.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.

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

>