Re: [PATCH v4] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated

[Tony Krowiak]

On 12/21/20 11:05 PM, Halil Pasic wrote:
> On Mon, 21 Dec 2020 13:56:25 -0500
> Tony Krowiak <akrowiak@xxxxxxxxxxxxx> 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 takes the
> > following actions:
> > 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state
> >     of the mediated device.
> > 2. Calls the kvm_get_kvm() function to increment its reference counter.
> > 3. Sets the function pointer to the function that handles interception of
> >     the instruction that enables/disables interrupt processing.
> > 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to
> >     the guest.
> >
> > In order to avoid memory leaks, when the notifier is called to receive
> > notification that the KVM pointer has been set to NULL, the vfio_ap device
> > driver should reverse the actions taken when the KVM pointer was set.
> >
> > Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>
> > Reviewed-by: Halil Pasic <pasic@xxxxxxxxxxxxx>
> > Reviewed-by: Cornelia Huck <cohuck@xxxxxxxxxx>
> [..]
>
> >   static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
> >   				       unsigned long action, void *data)
> >   {
> > -	int ret;
> > +	int ret, notify_rc = NOTIFY_DONE;
> >   	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);
> > +	mutex_lock(&matrix_dev->lock);
> >   
> >   	if (!data) {
> > -		matrix_mdev->kvm = NULL;
> > -		return NOTIFY_OK;
> > +		if (matrix_mdev->kvm)
> > +			vfio_ap_mdev_unset_kvm(matrix_mdev);
> > +		notify_rc = NOTIFY_OK;
> > +		goto notify_done;
> >   	}
> >   
> >   	ret = vfio_ap_mdev_set_kvm(matrix_mdev, data);
> >   	if (ret)
> > -		return NOTIFY_DONE;
> > +		goto notify_done;
> >   
> >   	/* If there is no CRYCB pointer, then we can't copy the masks */
> >   	if (!matrix_mdev->kvm->arch.crypto.crycbd)
> > -		return NOTIFY_DONE;
> > +		goto notify_done;
> >   
> >   	kvm_arch_crypto_set_masks(matrix_mdev->kvm, matrix_mdev->matrix.apm,
> >   				  matrix_mdev->matrix.aqm,
> >   				  matrix_mdev->matrix.adm);
> >   
> > -	return NOTIFY_OK;
> Shouldn't there be an
>   +	notify_rc = NOTIFY_OK;
> here? I mean you initialize notify_rc to NOTIFY_DONE, in the !data branch
> on success you set notify_rc to NOTIFY_OK, but in the !!data branch it
> just stays NOTIFY_DONE. Or am I missing something?

I don't think it matters much since NOTIFY_OK and NOTIFY_DONE have
no further effect on processing of the notification queue, but I believe
you are correct, this is a change from what we originally had. I can
restore the original return values if you'd prefer.

> Otherwise LGTM!
>
> Regards,
> Halil
>
> > +notify_done:
> > +	mutex_unlock(&matrix_dev->lock);
> > +	return notify_rc;
> >   }
> [..]