Re: [PATCH v3 6/9] vfio: ap: register IOMMU VFIO notifier

[Tony Krowiak]

On 2/19/19 4:59 AM, Halil Pasic wrote:
> On Fri, 15 Feb 2019 17:55:35 -0500
> Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
>
> > On 2/14/19 8:51 AM, Pierre Morel wrote:
> > > To be able to use the VFIO interface to facilitate the
> > > mediated device memory pining/unpining we need to register
> > > a notifier for IOMMU.
> > >
> > > Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
> > > ---
> > >    drivers/s390/crypto/vfio_ap_ops.c     | 64 +++++++++++++++++++++++++++++++----
> > >    drivers/s390/crypto/vfio_ap_private.h |  2 ++
> > >    2 files changed, 60 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> > > index 1851b24..6eddc2c 100644
> > > --- a/drivers/s390/crypto/vfio_ap_ops.c
> > > +++ b/drivers/s390/crypto/vfio_ap_ops.c
>
> [..]
>    	struct vfio_ap_queue *q;
> > > @@ -967,12 +996,32 @@ static int vfio_ap_mdev_open(struct mdev_device *mdev)
> > >    
> > >    	ret = vfio_register_notifier(mdev_dev(mdev), VFIO_GROUP_NOTIFY,
> > >    				     &events, &matrix_mdev->group_notifier);
> > > -	if (ret) {
> > > -		module_put(THIS_MODULE);
> > > -		return ret;
> > > -	}
> > > +	if (ret)
> > > +		goto err_group;
> > > +
> > > +	matrix_mdev->iommu_notifier.notifier_call = vfio_ap_mdev_iommu_notifier;
> > > +	events = VFIO_IOMMU_NOTIFY_DMA_UNMAP;
> > > +
> > > +	ret = vfio_register_notifier(mdev_dev(mdev), VFIO_IOMMU_NOTIFY,
> > > +				     &events, &matrix_mdev->iommu_notifier);
> > > +	if (ret)
> > > +		goto err_iommu;
> > > +
> > > +	ret = vfio_ap_associate_queues(matrix_mdev);
> > > +	if (ret)
> > > +		goto err_associate;
> >
> > I think the matrix_mdev should be associated with queues when an
> > assignment of an adapter or domain is made to the mdev device via its
> > sysfs interfaces. I say this because assigning an adapter or domain to
> > an mdev device effectively grants ownership of any additional AP queues
> > added to the mdev device's AP matrix as a result of the assignment. It
> > only makes sense to assign ownership to the vfio_ap_queue objects
> > representing the queues at that time. If an adapter or domain is
> > dynamically assigned while a guest is using the affected queues, then
> > the associations will have to be made at that time and this code will
> > likely go bye bye.
>
>
> Actually, we need the stuff in vfio_ap_queues only if the guest is
> offered to  decides to use AP adaper interrupts. I would prefer to have
> it around only when needed: as long as we have the nib pinned for any
> given queue. Is there a reason why not to do so?

Even if we keep the vfio_ap_queue around for the life of a guest,
association/dissociation will have to be done when an adapter or domain
is dynamically assigned.

> Regards,
> Halil
>   
> [..]