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

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Message-Id: <20190219105946.29e510a6@oc2783563651>
Date:   Tue, 19 Feb 2019 10:59:46 +0100
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>
Cc:     Pierre Morel <pmorel@...ux.ibm.com>, borntraeger@...ibm.com,
        alex.williamson@...hat.com, cohuck@...hat.com,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, frankja@...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 6/9] vfio: ap: register IOMMU VFIO notifier

On Fri, 15 Feb 2019 17:55:35 -0500
Tony Krowiak <akrowiak@...ux.ibm.com> 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@...ux.ibm.com>
> > ---
> >   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? 

Regards,
Halil
 
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