linux-kernel - Re: [PATCH v12 11/17] s390/vfio-ap: allow assignment of unavailable AP queues to mdev device

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Date:   Wed, 16 Dec 2020 23:09:14 +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 11/17] s390/vfio-ap: allow assignment of unavailable
 AP queues to mdev device

On Wed, 16 Dec 2020 15:14:47 -0500
Tony Krowiak <akrowiak@...ux.ibm.com> wrote:

> 
> 
> On 11/28/20 8:17 PM, Halil Pasic wrote:
> > On Tue, 24 Nov 2020 16:40:10 -0500
> > Tony Krowiak <akrowiak@...ux.ibm.com> wrote:
> >
> >> The current implementation does not allow assignment of an AP adapter or
> >> domain to an mdev device if each APQN resulting from the assignment
> >> does not reference an AP queue device that is bound to the vfio_ap device
> >> driver. This patch allows assignment of AP resources to the matrix mdev as
> >> long as the APQNs resulting from the assignment:
> >>     1. Are not reserved by the AP BUS for use by the zcrypt device drivers.
> >>     2. Are not assigned to another matrix mdev.
> >>
> >> The rationale behind this is twofold:
> >>     1. The AP architecture does not preclude assignment of APQNs to an AP
> >>        configuration that are not available to the system.
> >>     2. APQNs that do not reference a queue device bound to the vfio_ap
> >>        device driver will not be assigned to the guest's CRYCB, so the
> >>        guest will not get access to queues not bound to the vfio_ap driver.
> >>
> >> Signed-off-by: Tony Krowiak <akrowiak@...ux.ibm.com>
> > Again code looks good. I'm still worried about all the incremental
> > changes (good for review) and their testability.
> 
> I'm not sure what your concern is here. Is there an expectation
> that each patch needs to be testable by itself, or whether the
> functionality in each patch can be easily tested en masse?

I was referring to the testability of each patch in the following
sense: can you (at least theoretically) write a testsuite, that has
perfect coverage, and no false positives for each prefix of the
series applied. 

BTW I don't consider this a showstopper. 

> 
> I'm not sure some of these changes can be tested with an
> automated test because the test code would have to be able to
> dynamically change the host's AP configuration and I don't know
> if there is currently a way to do this programmatically. In order to
> test the effects of dynamic host crypto configuration manually, one
> needs access to an SE or HMC with DPM.
> 

Nested should also give you this: you can change G2 which is a host
to G3.

Regards,
Halil