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Subject: Re: [PATCH v6 21/21] s390: doc: detailed specifications for AP
 virtualization
To:     pmorel@linux.ibm.com, Tony Krowiak <akrowiak@linux.vnet.ibm.com>,
        linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     freude@de.ibm.com, schwidefsky@de.ibm.com,
        heiko.carstens@de.ibm.com, borntraeger@de.ibm.com,
        cohuck@redhat.com, kwankhede@nvidia.com,
        bjsdjshi@linux.vnet.ibm.com, pbonzini@redhat.com,
        alex.williamson@redhat.com, pmorel@linux.vnet.ibm.com,
        alifm@linux.vnet.ibm.com, mjrosato@linux.vnet.ibm.com,
        jjherne@linux.vnet.ibm.com, thuth@redhat.com,
        pasic@linux.vnet.ibm.com, berrange@redhat.com,
        fiuczy@linux.vnet.ibm.com, buendgen@de.ibm.com,
        Tony Krowiak <akrowiak@linux.ibm.com>
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From:   Halil Pasic <pasic@linux.ibm.com>
Date:   Mon, 9 Jul 2018 11:50:00 -0400
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On 07/09/2018 05:21 AM, Pierre Morel wrote:
> On 03/07/2018 01:10, Halil Pasic wrote:
>>
>>
>> On 06/29/2018 11:11 PM, Tony Krowiak wrote:
>>> This patch provides documentation describing the AP architecture and
>>> design concepts behind the virtualization of AP devices. It also
>>> includes an example of how to configure AP devices for exclusive
>>> use of KVM guests.
>>>
>>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
>>
>> I don't like the design of external interfaces except for:
>> * cpu model features, and
>> * reset handling.
>>
>> In particular:
>>
>>
> ...snip...
> 
>> 4) If I were to act out the role of the administrator, I would prefer to think of
>> specifying or changing the access controls of a guest in respect to AP (that is
>> setting the AP matrix) as a single atomic operation -- which either succeeds or fails.
>>
>> The operation should succeed for any valid configuration, and fail for any invalid
>> on.
>>
>> The current piecemeal approach seems even less fitting if we consider changing the
>> access controls of a running guest. AFAIK changing access controls for a running
>> guest is possible, and I don't see a reason why should we artificially prohibit this.
>>
>> I think the current sysfs interface for manipulating the matrix is good for
>> manual playing around, but I would prefer having an interface that is better
>> suited for programs (e.g. ioctl).
> 
> I disagree with using ioctl.

Why? What speaks against ioctl?

> I agree that the current implementation is not right.
> The configuration of APM and AQM should always be guarantied as coherent
> within the host but it can be done doing the right checks when using the sysfs.
> 

I'm glad we agree on this one at least.

Regards,
Halil