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Subject: Re: [PATCH v9 12/22] s390: vfio-ap: sysfs interfaces to configure
 control domains
To:     Halil Pasic <pasic@linux.ibm.com>,
        Tony Krowiak <akrowiak@linux.ibm.com>,
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From:   Pierre Morel <pmorel@linux.ibm.com>
Date:   Thu, 23 Aug 2018 12:41:11 +0200
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On 23/08/2018 11:26, Halil Pasic wrote:
> 
> 
> On 08/22/2018 09:16 PM, Tony Krowiak wrote:
>> On 08/22/2018 01:11 PM, Halil Pasic wrote:
>>>
>>>
>>> On 08/22/2018 05:48 PM, Christian Borntraeger wrote:
>>>> On 08/22/2018 05:34 PM, Pierre Morel wrote:
>>>>> On 22/08/2018 17:11, Christian Borntraeger wrote:
>>>>>>
>>>>>>
>>>>>> On 08/22/2018 01:03 PM, Pierre Morel wrote:
>>>>>>>> That's interesting.
>>>>>>>>
...
>>>>
>>>> So you have changed the code to not automatically make a usage domain a
>>>> control domain in the bitfield (and you could still use it as a usage
>>>> domain). Correct?

Yes.

>>>
>>> I tested basically the same yesterday, with the same results.
>>>
>>>> I think this is probably expected. the "usage implies control" seems to
>>>> be a convention implemented by HMC (lpar) and z/VM but millicode offers
>>>> the bits to have usage-only domains. As LPAR and z/VM will always 
>>>> enable
>>>> any usage-domain to also be a control domain we should do the same.

I think it is the reasonable thing to do.

>>>
>>> I'm fine either way, but slightly prefer higher level management 
>>> software
>>> and not the kernel accommodating this convention.

Please, we do not need this in a first version just make it easy
stick with what HMC does.

>>> with read access to, let's say a regular file. For me, all options 
>>> (rw, r, and w)
>>> do make sense, and if I had to pick the one that makes the least 
>>> sense I would
>>> pick write only. The convention is in these terms making read-only 
>>> illegal. But
>>> should 'usage only domains' ever get identified as something somebody 
>>> wants to do
>>> we can just add an attribute for that. So I'm fine either way.

We do not need to introduce new features now.

regards,
Pierre


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