linux-kernel - Re: [PATCH v3 1/9] s390: vfio_ap: link the vfio_ap devices to the vfio

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Date:   Wed, 20 Feb 2019 10:05:03 +0100
From:   Cornelia Huck <cohuck@...hat.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>
Cc:     pmorel@...ux.ibm.com, borntraeger@...ibm.com,
        alex.williamson@...hat.com, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, kvm@...r.kernel.org,
        frankja@...ux.ibm.com, pasic@...ux.ibm.com, david@...hat.com,
        schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
        freude@...ux.ibm.com, mimu@...ux.ibm.com
Subject: Re: [PATCH v3 1/9] s390: vfio_ap: link the vfio_ap devices to the
 vfio_ap bus subsystem

On Tue, 19 Feb 2019 17:27:05 -0500
Tony Krowiak <akrowiak@...ux.ibm.com> wrote:

> On 2/18/19 11:57 AM, Cornelia Huck wrote:
> > On Mon, 18 Feb 2019 11:35:45 -0500
> > Tony Krowiak <akrowiak@...ux.ibm.com> wrote:
> >   
> >> On 2/18/19 7:01 AM, Cornelia Huck wrote:  
> >>> On Fri, 15 Feb 2019 16:59:33 -0500
> >>> Tony Krowiak <akrowiak@...ux.ibm.com> wrote:
> >>>      
> >>>> On 2/15/19 4:11 AM, Cornelia Huck wrote:  
> >>>>> On Thu, 14 Feb 2019 13:30:59 -0500
> >>>>> Tony Krowiak <akrowiak@...ux.ibm.com> wrote:
> >>>>>         
> >>>>>> On 2/14/19 12:36 PM, Pierre Morel wrote:  
> >>>>>>> On 14/02/2019 17:57, Cornelia Huck wrote:  
> >>>      
> >>>>>>>> (And reading further in the current code, it seems we clear that
> >>>>>>>> structure _after_ the matrix device had been setup, so how can that
> >>>>>>>> even work? Where am I confused?)  
> >>>>>>>
> >>>>>>> On device_register there were no bus, so the core just do not look for a
> >>>>>>> driver and this field was nor tested nor overwritten.  
> >>>>>
> >>>>> Hm... so has the callback in driver_for_each_device() in
> >>>>> vfio_ap_verify_queue_reserved() ever been invoked at all? It seems this
> >>>>> patch fixes more than just libudev issues...  
> >>>>
> >>>> It is this patch that rendered the driver_for_each_device() in
> >>>> vfio_ap_verify_queue_reserved() erroneous. That function gets called
> >>>> every time an adapter or domain is assigned to the mdev. This patch
> >>>> introduced the problem with driver_for_each_device().  
> >>>
> >>> So, does this function need to be removed or called from another place,
> >>> then? (It looks like it was dead code before.)  
> >>
> >> I don't see why you think it's dead code:
> >>
> >> assign_adapter_store  
> >> ==> vfio_ap_mdev_verify_queues_reserved_for_apid
> >>       ==> vfio_ap_verify_queue_reserved
> >>           ==> driver_for_each_device  
> >>
> >> The only way that the vfio_ap_verify_queue_reserved - the function that
> >> calls driver_for_each_device - does not get called is if no bits have
> >> yet been set in matrix_mdev->matrix.aqm.  
> > 
> > What I don't see is how this can be called if no device has been, in
> > fact, bound to the driver in the driver core...  
> 
> Let's start with the fact that one can create an mdev device regardless
> of whether a queue has been bound to the vfio_ap driver. Once an mdev
> device is created, one can start assigning adapters, domains and control
> domains to it. Let's say the admin now attempts to assign an adapter, in
> which case the assign_adapter_store() function is invoked. After
> verifying that the APID passed in is a valid adapter number, the
> vfio_ap_mdev_verify_queues_reserved_for_apid() function is called.
> This function first checks if any domains have been assigned and if not,
> calls vfio_ap_verify_queue_reserved(&apid, NULL). It is in this function
> that the driver_for_each_device() function is called. Since there are
> no devices bound to the vfio_ap device driver, the callback passed in to
> the driver_for_each_device() function will never get called, so the
> vfio_ap_mdev_verify_queues_reserved_for_apid() function will return
> -EADDRNOTAVAIL. A similar flow will occur if the first assignment is for
> a domain. The bottom line is, the driver_for_each_device() function is
> called every time an adapter or domain is assigned.

Indeed. I just got lost with the various drivers and devices in play
here :(