Re: [PATCH v9 15/22] s390: vfio-ap: implement mediated device open callback

[Tony Krowiak]

On 08/15/2018 12:08 PM, Cornelia Huck wrote:
> On Mon, 13 Aug 2018 17:48:12 -0400
> Tony Krowiak <akrowiak@xxxxxxxxxxxxxxxxxx> wrote:
>
> > From: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>
> >
> > Implements the open callback on the mediated matrix device.
> > The function registers a group notifier to receive notification
> > of the VFIO_GROUP_NOTIFY_SET_KVM event. When notified,
> > the vfio_ap device driver will get access to the guest's
> > kvm structure. The open callback must ensure that only one
> > mediated device shall be opened per guest.
> >
> > Signed-off-by: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>
> > Acked-by: Halil Pasic <pasic@xxxxxxxxxxxxx>
> > Tested-by: Michael Mueller <mimu@xxxxxxxxxxxxx>
> > Tested-by: Farhan Ali <alifm@xxxxxxxxxxxxx>
> > Tested-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
> > Acked-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
> > Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> > ---
> >   drivers/s390/crypto/vfio_ap_ops.c     |  174 ++++++++++++++++++++++++++++++++-
> >   drivers/s390/crypto/vfio_ap_private.h |    2 +
> >   2 files changed, 175 insertions(+), 1 deletions(-)
> > @@ -602,7 +633,6 @@ static ssize_t matrix_show(struct device *dev, struct device_attribute *attr,
> >   }
> >   DEVICE_ATTR_RO(matrix);
> >   
> > -
> Nit: whitespace change

A nit, but somebody else will point it out too, so I will fix it.

> >   static struct attribute *vfio_ap_mdev_attrs[] = {
> >   	&dev_attr_assign_adapter.attr,
> >   	&dev_attr_unassign_adapter.attr,
> (...)
>
> > +/**
> > + * vfio_ap_mdev_open_once
> > + *
> > + * @matrix_mdev: a mediated matrix device
> > + *
> > + * Return 0 if no other mediated matrix device has been opened for the
> > + * KVM guest assigned to @matrix_mdev; otherwise, returns an error.
> > + */
> > +static int vfio_ap_mdev_open_once(struct ap_matrix_mdev *matrix_mdev,
> > +				  struct kvm *kvm)
> You're passing kvm in here, but do not use it.

I'll fix it.

> > +{
> > +	struct ap_matrix_mdev *m;
> > +
> > +	mutex_lock(&matrix_dev.lock);
> > +
> > +	list_for_each_entry(m, &matrix_dev.mdev_list, list) {
> > +		if ((m != matrix_mdev) && (m->kvm == matrix_mdev->kvm)) {
> If you used it here instead of matrix_mdev->kvm...

I believe that was the case in a previous patch, but for some reason the 
code
was changed. I'll rework this so it uses the kvm param instead.

> > +			mutex_unlock(&matrix_dev.lock);
> > +			return -EPERM;
> > +		}
> > +	}
> > +
> > +	mutex_unlock(&matrix_dev.lock);
> > +
> > +	return 0;
> > +}
> > +
> > +static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
> > +				       unsigned long action, void *data)
> > +{
> > +	int ret;
> > +	struct ap_matrix_mdev *matrix_mdev;
> > +
> > +	if (action != VFIO_GROUP_NOTIFY_SET_KVM)
> > +		return NOTIFY_OK;
> > +
> > +	matrix_mdev = container_of(nb, struct ap_matrix_mdev, group_notifier);
> > +
> > +	matrix_mdev->kvm = data;
> > +	if (data == NULL)
> > +		return NOTIFY_OK;
> > +
> > +	ret = vfio_ap_mdev_open_once(matrix_mdev, data);
> ...you could move this up to before overwriting matrix_mdev->kvm and
> bailing out when the check failed, which makes more sense to me.

That makes more sense to me too. Don't set matrix_mdev->kvm until we
know it is okay to do so.

> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = kvm_ap_validate_crypto_setup(matrix_mdev->kvm);
> > +	if (ret)
> > +		return ret;
> It probably makes more sense to return NOTIFY_DONE in the error case
> (NOTIFY_BAD does not sound like a good idea as it would stop processing
> the notifier chain).

Will do.

> > +
> > +	vfio_ap_mdev_copy_masks(matrix_mdev);
> > +
> > +	return NOTIFY_OK;
> > +}
> Otherwise, looks sane.

Good!!!

>