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

[Pierre Morel <pmorel@linux.ibm.com>]

On 06/06/2018 16:24, Tony Krowiak wrote:
> On 06/05/2018 08:40 AM, Pierre Morel wrote:
>> 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
>
> I am not certain what you mean by this. Are you suggesting we display the
> actual mask? For example, the APM:
>
> 08000000000000001000000000000c0000000030000000000800000000000001
>
> If that is the case, I completely disagree as that would be worthless 
> from
> a user perspective. Trying to figure out which APs are configured 
> would be
> ridiculously complicated.

- It is compatible with what the AP BUS shows
- a cut and past is easy
- you can use a userland script to translate to another format

>
> Or, are you suggesting something like this:
>
> 4,67,116,117,154,155,255

- this is not compatible with what the AP BUS shows
- as in the first case this is easy to parse

Both propositions look better to me.

>
> Personally, I found viewing the queues to be much more valuable when
> configuring the mediated device's matrix. I originally displayed the
> individual adapter and domain attributes and found it cumbersome to
> mentally configure what the matrix looked like. If you think of the
> lszcrypt command, it outputs the adapters and queues which is the model
> I used for this.

what is the point of seeing what the matrix looks like ?
It is interesting for the developer not for the administrator.
What the administrator needs is:
- To assign AP and to see what has been assigned
- To assign domains and to see what has been assigned

>
>> 2) As I said above, what you show is not the effective mask used by 
>> the guest
>
> Why would a sysfs attribute for the mediated matrix device show the 
> effective
> mask used by the guest?

OK, bad word, "effective", replace with "really".

We do not implement any kind of provisioning nor do we implement update
of the CRYCB at any point after the first mediated device open.

Binding a queue and updating the mask can be done at any time (may be we 
should change this ?)

What is the point of showing a matrix which will never be used by the guest?



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