Re: [PATCH] s390/vfio-ap: Clean up vfio_ap resources when KVM pointer invalidated

[Halil Pasic <pasic@linux.ibm.com>]

On Mon, 7 Dec 2020 14:05:55 -0500
Tony Krowiak <akrowiak@linux.ibm.com> wrote:

> 
> 
> On 12/2/20 6:41 PM, Tony Krowiak wrote:
> > The vfio_ap device driver registers a group notifier with VFIO when the
> > file descriptor for a VFIO mediated device for a KVM guest is opened to
> > receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM
> > event). When the KVM pointer is set, the vfio_ap driver stashes the pointer
> > and calls the kvm_get_kvm() function to increment its reference counter.
> > When the notifier is called to make notification that the KVM pointer has
> > been set to NULL, the driver should clean up any resources associated with
> > the KVM pointer and decrement its reference counter. The current
> > implementation does not take care of this clean up.
> >
> > Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> > ---
> >   drivers/s390/crypto/vfio_ap_ops.c | 21 +++++++++++++--------
> >   1 file changed, 13 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> > index e0bde8518745..eeb9c9130756 100644
> > --- a/drivers/s390/crypto/vfio_ap_ops.c
> > +++ b/drivers/s390/crypto/vfio_ap_ops.c
> > @@ -1083,6 +1083,17 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb,
> >   	return NOTIFY_DONE;
> >   }
> >   
> > +static void vfio_ap_mdev_put_kvm(struct ap_matrix_mdev *matrix_mdev)
> > +{
> > +	if (matrix_mdev->kvm) {
> > +		kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
> > +		matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
> > +		vfio_ap_mdev_reset_queues(matrix_mdev->mdev);
> 
> This reset probably does not belong here since there is no
> reason to reset the queues in the group notifier (see below).

What about kvm_s390_gisc_unregister()? That needs a valid kvm
pointer, or? Or is it OK to not pair a kvm_s390_gisc_register()
with an kvm_s390_gisc_unregister()?

Regards,
Halil

> The reset should be done in the release callback only regardless
> of whether the KVM pointer exists or not.
> 
> > +		kvm_put_kvm(matrix_mdev->kvm);
> > +		matrix_mdev->kvm = NULL;
> > +	}
> > +}
> > +
> >   static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
> >   				       unsigned long action, void *data)
> >   {
> > @@ -1095,7 +1106,7 @@ static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
> >   	matrix_mdev = container_of(nb, struct ap_matrix_mdev, group_notifier);
> >   
> >   	if (!data) {
> > -		matrix_mdev->kvm = NULL;
> > +		vfio_ap_mdev_put_kvm(matrix_mdev);
> >   		return NOTIFY_OK;
> >   	}
> >   
> > @@ -1222,13 +1233,7 @@ static void vfio_ap_mdev_release(struct mdev_device *mdev)
> >   	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
> >   
> >   	mutex_lock(&matrix_dev->lock);
> > -	if (matrix_mdev->kvm) {
> > -		kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
> > -		matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
> > -		vfio_ap_mdev_reset_queues(mdev);
> 
> This release should be moved outside of the block and
> performed regardless of whether the KVM pointer exists or
> not.
> 
> > -		kvm_put_kvm(matrix_mdev->kvm);
> > -		matrix_mdev->kvm = NULL;
> > -	}
> > +	vfio_ap_mdev_put_kvm(matrix_mdev);
> >   	mutex_unlock(&matrix_dev->lock);
> >   
> >   	vfio_unregister_notifier(mdev_dev(mdev), VFIO_IOMMU_NOTIFY,
>