linux-kernel - Re: [PATCH v17 06/15] s390/vfio-ap: refresh guest's APCB by filtering APQNs assigned to mdev

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Message-ID: <1cbbe637-b04b-dcea-8773-39c56cf0664d@linux.ibm.com>
Date:   Fri, 14 Jan 2022 19:31:22 -0500
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Halil Pasic <pasic@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, jjherne@...ux.ibm.com, freude@...ux.ibm.com,
        borntraeger@...ibm.com, cohuck@...hat.com, mjrosato@...ux.ibm.com,
        alex.williamson@...hat.com, kwankhede@...dia.com,
        fiuczy@...ux.ibm.com
Subject: Re: [PATCH v17 06/15] s390/vfio-ap: refresh guest's APCB by filtering
 APQNs assigned to mdev



On 1/12/22 06:52, Halil Pasic wrote:
> On Tue, 11 Jan 2022 16:19:06 -0500
> Tony Krowiak <akrowiak@...ux.ibm.com> wrote:
>
>>> Also we could probably do the filtering incrementally. In a sense that
>>> at a time only so much changes, and we know that the invariant was
>>> preserved without that change. But that would probably end up trading
>>> complexity for cycles. I will trust your judgment and your tests on this
>>> matter.
>> I am not entirely clear on what you are suggesting. I think you are
>> suggesting that there may not be a need to look at every APQN
>> assigned to the mdev when an adapter or domain is assigned or
>> unassigned or a queue is probed or removed. Maybe you can clarify
>> what you are suggesting here.
> Exactly. For example if we have the following assigned
> adapters:
> 1, 2, 3
> domains:
> 1, 2, 3
> and the operation we are trying to perform is assign domain 4, then it
> is sufficient to have a look at the queues with the APQNs (1,4), (2,4)
> and (3, 4). We don't have to examine all the 14 queues.
>
> When an unassign dapter is performed, there is no need to do the
> re-filtering, because there is nothing that can pop-back or go away. And
> on unassign domain is performed, then all we care about are the queues
> of that domain on the filtered adapters.
>
> Similarly if after that successful assign the queue (3,4) gets removed
> (from vfio_ap) and then added back again and probed, we only have to
> look at the queues (3, 1), (3, 2), (3, 3).
>
> But I'm OK with the current design of this. It is certainly conceptually
> simpler to say we have a master-copy and we filter that master-copy based
> on the very same rules every time something changes. I'm really fine
> either way as log as it works well. :D
>
> Regards,
> Halil

I spent a day messing with this and was able to make it work, so
the next implementation will incorporate your idea here.