linux-kernel - Re: [PATCH v12 10/17] s390/vfio-ap: initialize the guest apcb

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Message-ID: <20201129020923.6c470310.pasic@linux.ibm.com>
Date:   Sun, 29 Nov 2020 02:09:23 +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 v12 10/17] s390/vfio-ap: initialize the guest apcb

On Tue, 24 Nov 2020 16:40:09 -0500
Tony Krowiak <akrowiak@...ux.ibm.com> wrote:

> The APCB is a control block containing the masks that specify the adapters,
> domains and control domains to which a KVM guest is granted access. When
> the vfio_ap device driver is notified that the KVM pointer has been set,
> the guest's APCB is initialized from the AP configuration of adapters,
> domains and control domains assigned to the matrix mdev. The linux device
> model, however, precludes passing through to a guest any devices that
> are not bound to the device driver facilitating the pass-through.
> Consequently, APQNs assigned to the matrix mdev that do not reference
> AP queue devices must be filtered before assigning them to the KVM guest's
> APCB; however, the AP architecture precludes filtering individual APQNs, so
> the APQNs will be filtered by APID. That is, if a given APQN does not
> reference a queue device bound to the vfio_ap driver, its APID will not
> get assigned to the guest's APCB. For example:
> 
> Queues bound to vfio_ap:
> 04.0004
> 04.0022
> 04.0035
> 05.0004
> 05.0022
> 
> Adapters/domains assigned to the matrix mdev:
> 04 0004
>    0022
>    0035
> 05 0004
>    0022
>    0035
> 
> APQNs assigned to APCB:
> 04.0004
> 04.0022
> 04.0035
> 
> The APID 05 was filtered from the matrix mdev's matrix because
> queue device 05.0035 is not bound to the vfio_ap device driver.
> 
> Signed-off-by: Tony Krowiak <akrowiak@...ux.ibm.com>

This adds filtering. So from here guest_matrix may be different
than matrix also for an mdev that is associated with a guest. I'm still
grappling with the big picture. Have you thought about testability?
How is a testcase supposed to figure out which behavior is
to be deemed correct?

I don't like the title line. It implies that guest apcb was
uninitialized before. Which is not the case.