linux-kernel - Re: [PATCH v5 10/13] s390: vfio-ap: sysfs interface to view matrix mdev matrix

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Date:   Tue, 5 Jun 2018 14:40:44 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.vnet.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     freude@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, borntraeger@...ibm.com,
        cohuck@...hat.com, kwankhede@...dia.com,
        bjsdjshi@...ux.vnet.ibm.com, pbonzini@...hat.com,
        alex.williamson@...hat.com, pmorel@...ux.vnet.ibm.com,
        alifm@...ux.vnet.ibm.com, mjrosato@...ux.vnet.ibm.com,
        jjherne@...ux.vnet.ibm.com, thuth@...hat.com,
        pasic@...ux.vnet.ibm.com, berrange@...hat.com,
        fiuczy@...ux.vnet.ibm.com, buendgen@...ibm.com
Subject: Re: [PATCH v5 10/13] s390: vfio-ap: sysfs interface to view matrix
 mdev matrix

On 30/05/2018 16:28, Tony Krowiak wrote:
> On 05/24/2018 05:10 AM, Pierre Morel wrote:
>> On 23/05/2018 16:38, Tony Krowiak wrote:
>>> On 05/16/2018 03:55 AM, Pierre Morel wrote:
>>>> On 07/05/2018 17:11, Tony Krowiak wrote:
>>>>> Provides a sysfs interface to view the AP matrix configured for the
>>>>> mediated matrix device.
>>>>>
>>>>> The relevant sysfs structures are:
>>>>>
>>>>> /sys/devices/vfio_ap
>>>>> ... [matrix]
>>>>> ...... [mdev_supported_types]
>>>>> ......... [vfio_ap-passthrough]
>>>>> ............ [devices]
>>>>> ...............[$uuid]
>>>>> .................. matrix
>>>>>
>>>>> To view the matrix configured for the mediated matrix device,
>>>>> print the matrix file:
>>>>
>>>> This is the configured matrix, not the one used by the guest.
>>>> Nothing in the patches protect against binding a queue and assigning
>>>> a new AP when the guest runs.
>>>> The card and queue will be showed by this entry.
>>>
>>> Of course, as stated above, this is the matrix configured for the
>>> mediated matrix device. Are you suggesting here that the driver
>>> should prevent assigning a new adapter or domain while a guest is
>>> running? Couldn't this be a step in the process for hot (un)plugging
>>> AP queues?
>>
>> No, I mean what is the point to show this?
>> It is not what the guest sees.
>> Has it any use case?
>
> The point is to display the matrix so one can view the AP queues that
> have been assigned to the mediated matrix device. This is the only way
> to view the matrix. Do you not find value in being able to see what
> has been assigned to the mediated matrix device?

Two things:
1) I think it is better to retrieve the individual masks
2) As I said above, what you show is not the effective mask used by the 
guest




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