Re: [PATCH v9 12/22] s390: vfio-ap: sysfs interfaces to configure control domains

[Tony Krowiak]

On 08/27/2018 04:33 AM, Cornelia Huck wrote:
> On Thu, 23 Aug 2018 10:16:59 -0400
> Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
>
> > On 08/23/2018 06:25 AM, Cornelia Huck wrote:
> > > On Wed, 22 Aug 2018 15:16:19 -0400
> > > Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
> > >   
> > > > One of the things I suggested in a private conversation with Christian
> > > > earlier
> > > > today was to provide an additional rw sysfs attribute - a boolean - that
> > > > indicates
> > > > whether all usage domains should also be control domains. The default
> > > > could be
> > > > true. This would allow one to configure guests with usage-only domains
> > > > as well
> > > > as satisfy the convention.
> > > Would this additional attribute then control "add usage domains to the
> > > list of control domains automatically", or "don't allow to add a usage
> > > domain if it has not already been added as a control domain"?
> > It was just a proposal that wasn't really discussed at all, but this
> > attribute would add usage domains to the list of control domains
> > automatically if set to one. That would be the default behavior which
> > would be turned off by manually setting it to zero.
> If we want to do something like that, having it add the usage domains
> automatically sounds like the more workable alternative. What I like
> about this is that we make it explicit that we change the masks beyond
> what the admin explicitly configured, and provide a knob to turn off
> that behaviour.

So, are you saying I should go ahead and implement this?

> > > One thing I'm still unsure about is how libvirt comes into the picture
> > > here. Will it consume the setting, or actively manipulate it?
> > libvirt is not in the picture. The only thing libvirt does is identify
> > which mediated matrix device (i.e., UUID) is to be used by the guest.
> >
> > > [In general, I'm not very clear about how libvirt will interact with the
> > > whole infrastructure...]
> > The libvirt domain XML will only specify the UUID of the matrix device
> > to be used by the guest. Consequently, libvirt will insert the device
> > statement for the vfio-ap device into the QEMU command line:
> >
> > -device vfio-ap,syfsdev={path-to-mdev}
> >
> > All configuration of the mediated device, including the proposed attribute
> > above, is handled via sysfs attributes.
> So, basically, libvirt will only consume what the admin has already
> configured?

Yes.

>