linux-kernel - Re: [PATCH v11 26/26] s390: doc: detailed specifications for AP virtualization

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Date:   Thu, 27 Sep 2018 13:59:23 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>,
        Halil Pasic <pasic@...ux.ibm.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        Tony Krowiak <akrowiak@...ux.vnet.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, freude@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, kwankhede@...dia.com,
        bjsdjshi@...ux.vnet.ibm.com, pbonzini@...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,
        frankja@...ux.ibm.com, Tony Krowiak <akrowiak@...ux.ibm.com>
Subject: Re: [PATCH v11 26/26] s390: doc: detailed specifications for AP
 virtualization



On 09/27/2018 01:51 PM, Cornelia Huck wrote:
> On Thu, 27 Sep 2018 13:29:43 +0200
> Halil Pasic <pasic@...ux.ibm.com> wrote:
> 
>> On 09/27/2018 12:42 AM, Alex Williamson wrote:
>>> On Tue, 25 Sep 2018 19:16:41 -0400
>>> Tony Krowiak <akrowiak@...ux.vnet.ibm.com> wrote:
>>>> +   This is how the matrix is configured for Guest2:
>>>> +
>>>> +      echo 5 > assign_adapter
>>>> +      echo 0x47 > assign_domain
>>>> +      echo 0xff > assign_domain
>>>> +
>>>> +   This is how the matrix is configured for Guest3:
>>>> +
>>>> +      echo 6 > assign_adapter
>>>> +      echo 0x47 > assign_domain
>>>> +      echo 0xff > assign_domain
>>>> +  
>>>
>>> I'm curious why this interface didn't adopt the +/- notation invented
>>> above for consistency.  Too difficult to do rollbacks with a string on
>>> entries?
>>>   
>>
>> I remember that we did discuss that possibility around v9, but I can't
>> tell why did we decide to not implement it. Maybe Tony has an answer.
> 
> IIRC, that was a discussion on the base ap driver interfaces rather
> than vfio-ap.
> 
>>
>> Anyway, if we were to do that, we would use different attribute names
>> (e.g. just domain_mask, or something similar instead of
>> (assign|unassign)_xxx). So I think such an interface can still be added
>> on top of the existing one. Having that said having multiple interfaces
>> for the very same thing is usually not so nice IMHO.
> 
> Nod to all of your points.
> 
> As we do the configuration while the guest is not running anyway, the
> different interfaces probably do not make that much difference in
> practice. It should be fine to stick to the current interface for now
> and only add a new one if we really think it is significantly better.

Tony, can you maybe provide a quick on-top patch that clarifies Alex
comments regarding the documentation? (State that is is big endian,
fixup the small things etc).
I can then either fold it in or provide it as an on top patch depending
on how much has changed.