Re: [PATCH v5 10/13] s390: vfio-ap: sysfs interface to view matrix mdev matrix

[Tony Krowiak]

On 06/06/2018 11:10 AM, Pierre Morel wrote:
> On 06/06/2018 16:24, Tony Krowiak wrote:
> > On 06/05/2018 08:40 AM, Pierre Morel wrote:
> > > On 30/05/2018 16:28, Tony Krowiak wrote:
> > > > On 05/24/2018 05:10 AM, Pierre Morel wrote:
> > > > > On 23/05/2018 16:38, Tony Krowiak wrote:
> > > > > > On 05/16/2018 03:55 AM, Pierre Morel wrote:
> > > > > > > On 07/05/2018 17:11, Tony Krowiak wrote:
> > > > > > > > Provides a sysfs interface to view the AP matrix configured for 
> > > > > > > > the
> > > > > > > > mediated matrix device.
> > > > > > > >
> > > > > > > > The relevant sysfs structures are:
> > > > > > > >
> > > > > > > > /sys/devices/vfio_ap
> > > > > > > > ... [matrix]
> > > > > > > > ...... [mdev_supported_types]
> > > > > > > > ......... [vfio_ap-passthrough]
> > > > > > > > ............ [devices]
> > > > > > > > ...............[$uuid]
> > > > > > > > .................. matrix
> > > > > > > >
> > > > > > > > To view the matrix configured for the mediated matrix device,
> > > > > > > > print the matrix file:
> > > > > > >
> > > > > > > This is the configured matrix, not the one used by the guest.
> > > > > > > Nothing in the patches protect against binding a queue and 
> > > > > > > assigning
> > > > > > > a new AP when the guest runs.
> > > > > > > The card and queue will be showed by this entry.
> > > > > >
> > > > > > Of course, as stated above, this is the matrix configured for the
> > > > > > mediated matrix device. Are you suggesting here that the driver
> > > > > > should prevent assigning a new adapter or domain while a guest is
> > > > > > running? Couldn't this be a step in the process for hot (un)plugging
> > > > > > AP queues?
> > > > >
> > > > > No, I mean what is the point to show this?
> > > > > It is not what the guest sees.
> > > > > Has it any use case?
> > > >
> > > > The point is to display the matrix so one can view the AP queues that
> > > > have been assigned to the mediated matrix device. This is the only way
> > > > to view the matrix. Do you not find value in being able to see what
> > > > has been assigned to the mediated matrix device?
> > >
> > > Two things:
> > > 1) I think it is better to retrieve the individual masks
> >
> > I am not certain what you mean by this. Are you suggesting we display 
> > the
> > actual mask? For example, the APM:
> >
> > 08000000000000001000000000000c0000000030000000000800000000000001
> >
> > If that is the case, I completely disagree as that would be worthless 
> > from
> > a user perspective. Trying to figure out which APs are configured 
> > would be
> > ridiculously complicated.
>
> - It is compatible with what the AP BUS shows
> - a cut and past is easy
> - you can use a userland script to translate to another format
>
> > Or, are you suggesting something like this:
> >
> > 4,67,116,117,154,155,255
>
> - this is not compatible with what the AP BUS shows
> - as in the first case this is easy to parse
>
> Both propositions look better to me.
>
> > Personally, I found viewing the queues to be much more valuable when
> > configuring the mediated device's matrix. I originally displayed the
> > individual adapter and domain attributes and found it cumbersome to
> > mentally configure what the matrix looked like. If you think of the
> > lszcrypt command, it outputs the adapters and queues which is the model
> > I used for this.
>
> what is the point of seeing what the matrix looks like ?
> It is interesting for the developer not for the administrator.
> What the administrator needs is:
> - To assign AP and to see what has been assigned
> - To assign domains and to see what has been assigned
>
> > > 2) As I said above, what you show is not the effective mask used by 
> > > the guest
> >
> > Why would a sysfs attribute for the mediated matrix device show the 
> > effective
> > mask used by the guest?
>
> OK, bad word, "effective", replace with "really".
>
> We do not implement any kind of provisioning nor do we implement update
> of the CRYCB at any point after the first mediated device open.

I think this is a way we might be able to hot plug/unplug devices.

> Binding a queue and updating the mask can be done at any time (may be 
> we should change this ?)

As I said above, I think we can utilize this as a means of hot 
plugging/unplugging AP
adapters and domains. If the guest is running when an adapter or domain 
is assigned,
we can update the guest's CRYCB at that time.

> What is the point of showing a matrix which will never be used by the 
> guest?

That is simply not true. The matrix WILL be used by a guest the next time a
guest is configured with a vfio-ap device referencing the path to the
mediated matrix device - i.e., -device vfio-ap,sysfsdev=$PATH. The point
is to show the matrix assigned to the mediated matrix device. In my 
mind, the
mediated matrix device is a separate object from the guest. Sure it is used
to configure a guest's matrix when the guest is started, but it could be 
used
to configure the matrix for any guest; it has no direct connection to a
particular guest until a guest using the device is started. IMHO the sysfs
attributes for the mediated matrix device reflect only the attributes of
the device, not the attributes of a guest.

> > >