linux-kernel - Re: [PATCH v11 08/14] s390/vfio-ap: hot plug/unplug queues on bind/unbind of queue device

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Message-ID: <20201104142310.15f9d73b.pasic@linux.ibm.com>
Date:   Wed, 4 Nov 2020 14:23:10 +0100
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, 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, frankja@...ux.ibm.com, david@...hat.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com
Subject: Re: [PATCH v11 08/14] s390/vfio-ap: hot plug/unplug queues on
 bind/unbind of queue device

On Tue, 3 Nov 2020 17:49:21 -0500
Tony Krowiak <akrowiak@...ux.ibm.com> wrote:

> > We do this to show the no queues but bits set output in show? We could
> > get rid of some code if we were to not z  

Managed to delete "eroize" fro "zeroize"

> 
> I'm not sure what you are saying/asking here. The reason for this
> is because there is no point in setting bits in the APCB if no queues
> will be made available to the guest which is the case if the APM or
> AQM are cleared.

Exactly my train of thought! There is no point doing work (here
zeroizing) that has no effect.

Also I'm leaning towards incremental updates to the shadow_apcb (instead
of basically recomputing it from the scratch each time). One thing I'm
particularly worried abut is that because of the third argument of
vfio_ap_mdev_filter_guest_matrix() called filter_apid, we could end up
with different filtering decision than previously. E.g. we decided to
filter the card on e.g. removal of a single queueu, but then somebody
does an assign domain, and suddenly we unplug the domain and plug the
card. With incremental changes the shadow_apcb, we could do less work
(revise only what needs to be), and it would be more straight forward
to reason about the absence of inconsistent filtering.

Regards,
Halil