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

[Tony Krowiak]

On 1/12/22 06:52, Halil Pasic wrote:
> On Tue, 11 Jan 2022 16:19:06 -0500
> Tony Krowiak <akrowiak@xxxxxxxxxxxxx> 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.