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Subject: Re: [PATCH v9 12/22] s390: vfio-ap: sysfs interfaces to configure
 control domains
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From:   Christian Borntraeger <borntraeger@de.ibm.com>
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Date:   Wed, 22 Aug 2018 17:48:28 +0200
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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.
>>>>
>>>>> IMHO this quote is quite a half-full half-empty cup one:
>>>>> * it mandates the set of usage domains is a subset of the set
>>>>> of the control domains, but
>>>>> * it speaks of independent controls, namely about the 'usage domain index'
>>>>> and the 'control domain index list' and makes the enforcement of the rule
>>>>> a job of the administrator (instead of codifying it in the controls).
>>>> I'm wondering if a configuration with a usage domain that is not also a
>>>> control domain is rejected outright? Anybody tried that? :)
>>>
>>> Yes, and no it is not.
>>> We can use a queue (usage domain) to a AP card for SHA-512 or RSA without
>>> having to define the queue as a control domain.
>>
>> Huh? My HMC allows to add a domain as
>> - control only domain
>> - control and usage domain.
>>
>> But I am not able to configure a usage-only domain for my LPAR. That seems to match
>> the current code, no?
>>
> 
> Yes, it may not be configurable by the HMC but if we start a guest with no control domain it is not a problem to access the hardware through the usage domain.
> 
> I tested this a long time ago, but tested again today to be sure on my LPAR.
> 
> AFAIU adding a control only domain and a control and usage domain
> allows say:
> control and usage domain 1
> control only domain 2
> 
> Allow to send a message to domain 2 using queue 1
> 
> Allow also to send a domain modifying message to domain 1 using queue 1
> 
> control domain are domain which are controlled

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?
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.


> It seems that the HMC enforce the LPARs to have access to their usage domain (AFAIU from Harald)