linux-kernel - Re: [PATCH v5 05/13] s390: vfio-ap: register matrix device with VFIO mdev framework

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Date:   Fri, 11 May 2018 19:18:38 +0200
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.vnet.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     freude@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, borntraeger@...ibm.com,
        cohuck@...hat.com, kwankhede@...dia.com,
        bjsdjshi@...ux.vnet.ibm.com, pbonzini@...hat.com,
        alex.williamson@...hat.com, pmorel@...ux.vnet.ibm.com,
        alifm@...ux.vnet.ibm.com, mjrosato@...ux.vnet.ibm.com,
        jjherne@...ux.vnet.ibm.com, thuth@...hat.com,
        pasic@...ux.vnet.ibm.com, berrange@...hat.com,
        fiuczy@...ux.vnet.ibm.com, buendgen@...ibm.com
Subject: Re: [PATCH v5 05/13] s390: vfio-ap: register matrix device with VFIO
 mdev framework



On 05/07/2018 05:11 PM, Tony Krowiak wrote:
> Registers the matrix device created by the VFIO AP device
> driver with the VFIO mediated device framework.
> Registering the matrix device will create the sysfs
> structures needed to create mediated matrix devices
> each of which will be used to configure the AP matrix
> for a guest and connect it to the VFIO AP device driver.
> 
[..]
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> new file mode 100644
> index 0000000..d7d36fb
> --- /dev/null
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -0,0 +1,106 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Adjunct processor matrix VFIO device driver callbacks.
> + *
> + * Copyright IBM Corp. 2017
> + * Author(s): Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
> + *
> + */
> +#include <linux/string.h>
> +#include <linux/vfio.h>
> +#include <linux/device.h>
> +#include <linux/list.h>
> +#include <linux/ctype.h>
> +
> +#include "vfio_ap_private.h"
> +
> +#define VFOP_AP_MDEV_TYPE_HWVIRT "passthrough"
> +#define VFIO_AP_MDEV_NAME_HWVIRT "VFIO AP Passthrough Device"
> +
> +static int vfio_ap_mdev_create(struct kobject *kobj, struct mdev_device *mdev)
> +{
> +	struct ap_matrix *ap_matrix = to_ap_matrix(mdev_parent_dev(mdev));
> +
> +	ap_matrix->available_instances--;
> +
> +	return 0;
> +}
> +
> +static int vfio_ap_mdev_remove(struct mdev_device *mdev)
> +{
> +	struct ap_matrix *ap_matrix = to_ap_matrix(mdev_parent_dev(mdev));
> +
> +	ap_matrix->available_instances++;
> +
> +	return 0;
> +}
> +

The above functions seem to be called with the lock of this auto-generated
mdev parent device held. That's why we don't have to care about synchronization
ourselves, right?

A small comment in the code could be helpful for mdev non-experts. Hell, I would
even consider documenting it for all mdev -- took me some time to figure out.

[..]


> +int vfio_ap_mdev_register(struct ap_matrix *ap_matrix)
> +{
> +	int ret;
> +
> +	ret = mdev_register_device(&ap_matrix->device, &vfio_ap_matrix_ops);
> +	if (ret)
> +		return ret;
> +
> +	ap_matrix->available_instances = AP_MATRIX_MAX_AVAILABLE_INSTANCES;
> +
> +	return 0;
> +}
> +
> +void vfio_ap_mdev_unregister(struct ap_matrix *ap_matrix)
> +{
> +	ap_matrix->available_instances--;

What is this for? I don't understand.

Regards,
Halil

> +	mdev_unregister_device(&ap_matrix->device);
> +}