linux-kernel - Re: [PATCH v9 12/22] s390: vfio-ap: sysfs interfaces to configure control domains

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Date:   Wed, 22 Aug 2018 17:53:37 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Halil Pasic <pasic@...ux.ibm.com>
Cc:     Tony Krowiak <akrowiak@...ux.ibm.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,
        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,
        frankja@...ux.ibm.com
Subject: Re: [PATCH v9 12/22] s390: vfio-ap: sysfs interfaces to configure
 control domains

On 22/08/2018 17:48, 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.
>>>>>
>>>>>> 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?

yes
and I used Harald's libica tests to verify it in the guest.

> 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)


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