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Date:   Mon, 20 Aug 2018 16:23:17 +0200
From:   Cornelia Huck <cohuck@redhat.com>
To:     Tony Krowiak <akrowiak@linux.vnet.ibm.com>
Cc:     linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, freude@de.ibm.com, schwidefsky@de.ibm.com,
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        fiuczy@linux.vnet.ibm.com, buendgen@de.ibm.com,
        frankja@linux.ibm.com, Tony Krowiak <akrowiak@linux.ibm.com>
Subject: Re: [PATCH v9 12/22] s390: vfio-ap: sysfs interfaces to configure
 control domains
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On Mon, 13 Aug 2018 17:48:09 -0400
Tony Krowiak <akrowiak@linux.vnet.ibm.com> wrote:

> From: Tony Krowiak <akrowiak@linux.ibm.com>
> 
> Provides the sysfs interfaces for:
> 
> 1. Assigning AP control domains to the mediated matrix device
> 
> 2. Unassigning AP control domains from a mediated matrix device
> 
> 3. Displaying the control domains assigned to a mediated matrix
>    device
> 
> The IDs of the AP control domains assigned to the mediated matrix
> device are stored in an AP domain mask (ADM). The bits in the ADM,
> from most significant to least significant bit, correspond to
> AP domain numbers 0 to 255. On some systems, the maximum allowable
> domain number may be less than 255 - depending upon the host's
> AP configuration - and assignment may be rejected if the input
> domain ID exceeds the limit.

Please remind me of the relationship between control domains and usage
domains... IIRC, usage domains allow both requests and configuration,
while control domains allow only configuration, and are by convention a
superset of usage domains.

Is there a hard requirement somewhere in there, or can the admin
cheerfully use different masks for usage domains and control domains
without the SIE choking on it?