Re: [PATCH v5 06/13] KVM: s390: interfaces to manage guest's AP matrix

[Tony Krowiak]

On 05/16/2018 03:48 AM, Pierre Morel wrote:
> On 15/05/2018 18:07, Tony Krowiak wrote:
> > On 05/15/2018 10:55 AM, Pierre Morel wrote:
> > > On 07/05/2018 17:11, Tony Krowiak wrote:
> > > > Provides interfaces to manage the AP adapters, usage domains
> > > > and control domains assigned to a KVM guest.
> > > >
> > > > The guest's SIE state description has a satellite structure called the
> > > > Crypto Control Block (CRYCB) containing three bitmask fields
> > > > identifying the adapters, queues (domains) and control domains
> > > > assigned to the KVM guest:
> ...snip...
> > > > +}
> > >
> > > This function (ap_validate_queue_sharing) only verifies that VM 
> > > don't share queues.
> > > What about the queues used by a host application?
> >
> > How can that be verified from this function? I suppose I could put a 
> > check in here to
> > verify that the queues are reserved by the vfio_ap device driver, but 
> > that would
> > be redundant because an AP queue can not be assigned to a mediated 
> > matrix device
> > via its sysfs attributes unless it is reserved by the vfio_ap device 
> > driver (see
> > patches 7, 8 and 9).
> >
> > > I understand that you want to implement  these checks within KVM but 
> > > this is
> > > related to which queue devices are bound to the matrix and which one 
> > > are not.
> >
> > See my comments above and below about AP queue assignment to the 
> > mediated matrix
> > device. The one verification we can't do when the devices are 
> > assigned is whether
> > another guest is using the queue because assignment occurs before the 
> > guest using
> > the queue is started in which case we have no access to KVM. It makes 
> > no sense to
> > do so at assignment time anyway because it doesn't matter until the 
> > guest using
> > the mediated matrix device is started, so that check is done in KVM.
> >
> > > I think that this should be related somehow to the bounded queue 
> > > devices and
> > > therefor implemented inside the matrix driver.
> >
> > As I stated above, when an AP queue is assigned to the mediated 
> > matrix device via
> > its sysfs attributes, a check is done to verify that it is bound to 
> > the vfio_ap
> > device driver (see patches 7, 8 and 9). If not, then assignment will 
> > be rejected;
> > therefore, it will not be possible to configure a CRYCB with AP 
> > queues that are
> > not bound to the device driver.
>
> This patch and te followed patches take care that the queues are bound 
> to the
> matrix driver when they are assigned to the matrix using the sysfs 
> entries.
>
> But they do not take care that the queue can not be unbound before you 
> start
> the guest, and they are not in the path if the admin decide to unbind 
> a queue
> at some later time.

That is a good point. I need to put a check in the device driver at the time
the mediated device fd is opened to verify that the queues being 
configured in
the guest's CRYCB are bound to the driver.

> > > Regards,
> > >
> > > Pierre