Subject: Re: [RFC PATCH 3/4] virtio: introudce a mdev based transport

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 10 Sep 2019 06:01:16 -0400

On Tue, Sep 10, 2019 at 04:19:34PM +0800, Jason Wang wrote:
> This path introduces a new mdev transport for virtio. This is used to
> use kernel virtio driver to drive the mediated device that is capable
> of populating virtqueue directly.
> 
> A new virtio-mdev driver will be registered to the mdev bus, when a
> new virtio-mdev device is probed, it will register the device with
> mdev based config ops. This means, unlike the exist hardware
> transport, this is a software transport between mdev driver and mdev
> device. The transport was implemented through:
> 
> - configuration access was implemented through parent_ops->read()/write()
> - vq/config callback was implemented through parent_ops->ioctl()
> 
> This transport is derived from virtio MMIO protocol and was wrote for
> kernel driver. But for the transport itself, but the design goal is to
> be generic enough to support userspace driver (this part will be added
> in the future).
> 
> Note:
> - current mdev assume all the parameter of parent_ops was from
>   userspace. This prevents us from implementing the kernel mdev
>   driver. For a quick POC, this patch just abuse those parameter and
>   assume the mdev device implementation will treat them as kernel
>   pointer. This should be addressed in the formal series by extending
>   mdev_parent_ops.
> - for a quick POC, I just drive the transport from MMIO, I'm pretty
>   there's lot of optimization space for this.
> 
> Signed-off-by: Jason Wang <[email-masked]>
> ---
>  drivers/vfio/mdev/Kconfig        |   7 +
>  drivers/vfio/mdev/Makefile       |   1 +
>  drivers/vfio/mdev/virtio_mdev.c  | 500 +++++++++++++++++++++++++++++++
>  include/uapi/linux/virtio_mdev.h | 131 ++++++++
>  4 files changed, 639 insertions(+)
>  create mode 100644 drivers/vfio/mdev/virtio_mdev.c
>  create mode 100644 include/uapi/linux/virtio_mdev.h
> 
> diff --git a/drivers/vfio/mdev/Kconfig b/drivers/vfio/mdev/Kconfig
> index 5da27f2100f9..c488c31fc137 100644
> --- a/drivers/vfio/mdev/Kconfig
> +++ b/drivers/vfio/mdev/Kconfig
> @@ -16,3 +16,10 @@ config VFIO_MDEV_DEVICE
>  	default n
>  	help
>  	  VFIO based driver for Mediated devices.
> +
> +config VIRTIO_MDEV_DEVICE
> +	tristate "VIRTIO driver for Mediated devices"
> +	depends on VFIO_MDEV && VIRTIO
> +	default n
> +	help
> +	  VIRTIO based driver for Mediated devices.
> diff --git a/drivers/vfio/mdev/Makefile b/drivers/vfio/mdev/Makefile
> index 101516fdf375..99d31e29c23e 100644
> --- a/drivers/vfio/mdev/Makefile
> +++ b/drivers/vfio/mdev/Makefile
> @@ -4,3 +4,4 @@ mdev-y := mdev_core.o mdev_sysfs.o mdev_driver.o
>  
>  obj-$(CONFIG_VFIO_MDEV) += mdev.o
>  obj-$(CONFIG_VFIO_MDEV_DEVICE) += vfio_mdev.o
> +obj-$(CONFIG_VIRTIO_MDEV_DEVICE) += virtio_mdev.o
> diff --git a/drivers/vfio/mdev/virtio_mdev.c b/drivers/vfio/mdev/virtio_mdev.c
> new file mode 100644
> index 000000000000..5ff09089297e
> --- /dev/null
> +++ b/drivers/vfio/mdev/virtio_mdev.c
> @@ -0,0 +1,500 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * VIRTIO based driver for Mediated device
> + *
> + * Copyright (c) 2019, Red Hat. All rights reserved.
> + *     Author: Jason Wang <[email-masked]>
> + *
> + * Based on Virtio MMIO driver.
> + */
> +
> +#include <linux/init.h>
> +#include <linux/module.h>
> +#include <linux/device.h>
> +#include <linux/kernel.h>
> +#include <linux/slab.h>
> +#include <linux/uuid.h>
> +#include <linux/mdev.h>
> +#include <linux/virtio.h>
> +#include <linux/virtio_config.h>
> +#include <linux/virtio_ring.h>
> +#include <uapi/linux/virtio_mdev.h>
> +#include "mdev_private.h"
> +
> +#define DRIVER_VERSION  "0.1"
> +#define DRIVER_AUTHOR   "Red Hat Corporation"
> +#define DRIVER_DESC     "VIRTIO based driver for Mediated device"
> +
> +#define to_virtio_mdev_device(dev) \
> +	container_of(dev, struct virtio_mdev_device, vdev)
> +
> +struct virtio_mdev_device {
> +	struct virtio_device vdev;
> +	struct mdev_device *mdev;
> +	unsigned long version;
> +
> +	struct virtqueue **vqs;
> +	spinlock_t lock;
> +};
> +
> +struct virtio_mdev_vq_info {
> +	/* the actual virtqueue */
> +	struct virtqueue *vq;
> +
> +	/* the list node for the virtqueues list */
> +	struct list_head node;
> +};
> +
> +static u32 virtio_mdev_readl(struct mdev_device *mdev,
> +			     loff_t off)
> +{
> +	struct mdev_parent *parent = mdev->parent;
> +	ssize_t len;
> +	u32 val;
> +
> +	if (unlikely(!parent->ops->read))
> +		return 0xFFFFFFFF;
> +
> +	len = parent->ops->read(mdev, (char *)&val, 4, &off);
> +	if (len != 4)
> +		return 0xFFFFFFFF;
> +
> +	return val;
> +}
> +
> +static void virtio_mdev_writel(struct mdev_device *mdev,
> +			       loff_t off, u32 val)
> +{
> +	struct mdev_parent *parent = mdev->parent;
> +
> +	if (unlikely(!parent->ops->write))
> +		return;
> +
> +	parent->ops->write(mdev, (char *)&val, 4, &off);
> +
> +	return;
> +}
> +
> +static void virtio_mdev_get(struct virtio_device *vdev, unsigned offset,
> +			    void *buf, unsigned len)
> +{
> +	struct virtio_mdev_device *vm_dev = to_virtio_mdev_device(vdev);
> +	struct mdev_device *mdev = vm_dev->mdev;
> +	struct mdev_parent *parent = mdev->parent;
> +
> +	loff_t off = offset + VIRTIO_MDEV_CONFIG;
> +
> +	switch (len) {
> +	case 1:
> +		*(u8 *)buf = parent->ops->read(mdev, buf, 1, &off);
> +		break;
> +	case 2:
> +		*(u16 *)buf = parent->ops->read(mdev, buf, 2, &off);
> +		break;
> +	case 4:
> +		*(u32 *)buf = parent->ops->read(mdev, buf, 4, &off);
> +		break;
> +	case 8:
> +		*(u32 *)buf = parent->ops->read(mdev, buf, 4, &off);
> +		*((u32 *)buf + 1) = parent->ops->read(mdev, buf, 4, &off);
> +		break;
> +	default:
> +		BUG();
> +	}
> +
> +	return;
> +}
> +
> +static void virtio_mdev_set(struct virtio_device *vdev, unsigned offset,
> +			    const void *buf, unsigned len)
> +{
> +	struct virtio_mdev_device *vm_dev = to_virtio_mdev_device(vdev);
> +	struct mdev_device *mdev = vm_dev->mdev;
> +	struct mdev_parent *parent = mdev->parent;
> +	loff_t off = offset + VIRTIO_MDEV_CONFIG;
> +
> +	switch (len) {
> +	case 1:
> +	case 2:
> +	case 4:
> +	case 8:
> +		break;
> +	default:
> +		BUG();
> +	}
> +
> +	parent->ops->write(mdev, buf, len, &off);
> +
> +	return;
> +}
> +
> +static u32 virtio_mdev_generation(struct virtio_device *vdev)
> +{
> +	struct virtio_mdev_device *vm_dev = to_virtio_mdev_device(vdev);
> +
> +	if (vm_dev->version == 1)
> +		return 0;
> +	else
> +		return virtio_mdev_readl(vm_dev->mdev,
> +					 VIRTIO_MDEV_CONFIG_GENERATION);
> +}
> +
> +static u8 virtio_mdev_get_status(struct virtio_device *vdev)
> +{
> +	struct virtio_mdev_device *vm_dev = to_virtio_mdev_device(vdev);
> +
> +	return virtio_mdev_readl(vm_dev->mdev, VIRTIO_MDEV_STATUS) & 0xff;
> +}
> +
> +static void virtio_mdev_set_status(struct virtio_device *vdev, u8 status)
> +{
> +	struct virtio_mdev_device *vm_dev = to_virtio_mdev_device(vdev);
> +
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_STATUS, status);
> +}
> +
> +static void virtio_mdev_reset(struct virtio_device *vdev)
> +{
> +	struct virtio_mdev_device *vm_dev = to_virtio_mdev_device(vdev);
> +
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_STATUS, 0);
> +}
> +
> +static bool virtio_mdev_notify(struct virtqueue *vq)
> +{
> +	struct virtio_mdev_device *vm_dev = to_virtio_mdev_device(vq->vdev);
> +
> +	/* We write the queue's selector into the notification register to
> +	 * signal the other end */
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_QUEUE_NOTIFY,
> +			   vq->index);
> +	return true;
> +}
> +
> +static irqreturn_t virtio_mdev_config_cb(void *private)
> +{
> +	struct virtio_mdev_device *vm_dev = private;
> +
> +	virtio_config_changed(&vm_dev->vdev);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static irqreturn_t virtio_mdev_virtqueue_cb(void *private)
> +{
> +	struct virtio_mdev_vq_info *info = private;
> +
> +	return vring_interrupt(0, info->vq);
> +}
> +
> +static struct virtqueue *
> +virtio_mdev_setup_vq(struct virtio_device *vdev, unsigned index,
> +		     void (*callback)(struct virtqueue *vq),
> +		     const char *name, bool ctx)
> +{
> +	struct virtio_mdev_device *vm_dev = to_virtio_mdev_device(vdev);
> +	struct mdev_device *mdev= vm_dev->mdev;
> +	struct mdev_parent *parent = mdev->parent;
> +	struct virtio_mdev_vq_info *info;
> +	struct virtio_mdev_callback cb;
> +	struct virtqueue *vq;
> +	unsigned long flags;
> +	u32 align, num;
> +	u64 addr;
> +	int err;
> +
> +	if (!name)
> +		return NULL;
> +
> +	/* Select the queue we're interested in */
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_QUEUE_SEL, index);
> +
> +	/* Queue shouldn't already be set up. */
> +	if (virtio_mdev_readl(vm_dev->mdev, VIRTIO_MDEV_QUEUE_READY)) {
> +		err = -ENOENT;
> +		goto error_available;
> +	}
> +
> +	/* Allocate and fill out our active queue description */
> +	info = kmalloc(sizeof(*info), GFP_KERNEL);
> +	if (!info) {
> +		err = -ENOMEM;
> +		goto error_kmalloc;
> +	}
> +
> +	num = virtio_mdev_readl(vm_dev->mdev, VIRTIO_MDEV_QUEUE_NUM_MAX);
> +	if (num == 0) {
> +		err = -ENOENT;
> +		goto error_new_virtqueue;
> +	}
> +
> +	/* Create the vring */
> +	align = virtio_mdev_readl(vm_dev->mdev, VIRTIO_MDEV_QUEUE_ALIGN);
> +	vq = vring_create_virtqueue(index, num, align, vdev,
> +				    true, true, ctx,
> +				    virtio_mdev_notify, callback, name);
> +	if (!vq) {
> +		err = -ENOMEM;
> +		goto error_new_virtqueue;
> +	}
> +
> +	/* Setup virtqueue callback */
> +	cb.callback = virtio_mdev_virtqueue_cb;
> +	cb.private = info;
> +	err = parent->ops->ioctl(mdev, VIRTIO_MDEV_SET_VQ_CALLBACK,
> +				 (unsigned long)&cb);
> +	if (err) {
> +		err = -EINVAL;
> +		goto error_callback;
> +	}
> +
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_QUEUE_NUM,
> +			   virtqueue_get_vring_size(vq));
> +	addr = virtqueue_get_desc_addr(vq);
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_QUEUE_DESC_LOW, (u32)addr);
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_QUEUE_DESC_HIGH,
> +			   (u32)(addr >> 32));
> +
> +	addr = virtqueue_get_avail_addr(vq);
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_QUEUE_AVAIL_LOW, (u32)addr);
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_QUEUE_AVAIL_HIGH,
> +			   (u32)(addr >> 32));
> +
> +	addr = virtqueue_get_used_addr(vq);
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_QUEUE_USED_LOW, (u32)addr);
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_QUEUE_USED_HIGH, (u32)(addr >> 32));
> +
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_QUEUE_READY, 1);
> +
> +	vq->priv = info;
> +	info->vq = vq;
> +
> +	return vq;
> +
> +error_callback:
> +	vring_del_virtqueue(vq);
> +error_new_virtqueue:
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_QUEUE_READY, 0);
> +	WARN_ON(virtio_mdev_readl(vm_dev->mdev, VIRTIO_MDEV_QUEUE_READY));
> +	kfree(info);
> +error_kmalloc:
> +error_available:
> +	return ERR_PTR(err);
> +
> +}
> +
> +static void virtio_mdev_del_vq(struct virtqueue *vq)
> +{
> +	struct virtio_mdev_device *vm_dev = to_virtio_mdev_device(vq->vdev);
> +	struct virtio_mdev_vq_info *info = vq->priv;
> +	unsigned long flags;
> +	unsigned int index = vq->index;
> +
> +	/* Select and deactivate the queue */
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_QUEUE_SEL, index);
> +	virtio_mdev_writel(vm_dev->mdev,VIRTIO_MDEV_QUEUE_READY, 0);
> +	WARN_ON(virtio_mdev_readl(vm_dev->mdev, VIRTIO_MDEV_QUEUE_READY));
> +
> +	vring_del_virtqueue(vq);
> +
> +	kfree(info);
> +}
> +
> +static void virtio_mdev_del_vqs(struct virtio_device *vdev)
> +{
> +	struct virtqueue *vq, *n;
> +
> +	list_for_each_entry_safe(vq, n, &vdev->vqs, list)
> +		virtio_mdev_del_vq(vq);
> +
> +	return;
> +}
> +
> +static int virtio_mdev_find_vqs(struct virtio_device *vdev, unsigned nvqs,
> +				struct virtqueue *vqs[],
> +				vq_callback_t *callbacks[],
> +				const char * const names[],
> +				const bool *ctx,
> +				struct irq_affinity *desc)
> +{
> +	struct virtio_mdev_device *vm_dev = to_virtio_mdev_device(vdev);
> +	struct mdev_device *mdev = vm_dev->mdev;
> +	struct mdev_parent *parent = mdev->parent;
> +	struct virtio_mdev_callback cb;
> +	int i, err, queue_idx = 0;
> +	vm_dev->vqs = kmalloc_array(queue_idx, sizeof(*vm_dev->vqs),
> +				    GFP_KERNEL);
> +	if (!vm_dev->vqs)
> +		return -ENOMEM;
> +
> +	for (i = 0; i < nvqs; ++i) {
> +		if (!names[i]) {
> +			vqs[i] = NULL;
> +			continue;
> +		}
> +
> +		vqs[i] = virtio_mdev_setup_vq(vdev, queue_idx++,
> +					      callbacks[i], names[i], ctx ?
> +					      ctx[i] : false);
> +		if (IS_ERR(vqs[i])) {
> +			err = PTR_ERR(vqs[i]);
> +			goto err_setup_vq;
> +		}
> +	}
> +
> +	cb.callback = virtio_mdev_config_cb;
> +	cb.private = vm_dev;
> +	err = parent->ops->ioctl(mdev, VIRTIO_MDEV_SET_CONFIG_CALLBACK,
> +				 (unsigned long)&cb);
> +	if (err)
> +		goto err_setup_vq;
> +
> +	return 0;
> +
> +err_setup_vq:
> +	kfree(vm_dev->vqs);
> +	virtio_mdev_del_vqs(vdev);
> +	return err;
> +}
> +
> +static u64 virtio_mdev_get_features(struct virtio_device *vdev)
> +{
> +	struct virtio_mdev_device *vm_dev = to_virtio_mdev_device(vdev);
> +	u64 features;
> +
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_DEVICE_FEATURES_SEL, 1);
> +	features = virtio_mdev_readl(vm_dev->mdev, VIRTIO_MDEV_DEVICE_FEATURES);
> +	features <<= 32;
> +
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_DEVICE_FEATURES_SEL, 0);
> +	features |= virtio_mdev_readl(vm_dev->mdev, VIRTIO_MDEV_DEVICE_FEATURES);
> +
> +	return features;
> +}
> +
> +static int virtio_mdev_finalize_features(struct virtio_device *vdev)
> +{
> +	struct virtio_mdev_device *vm_dev = to_virtio_mdev_device(vdev);
> +
> +	/* Give virtio_ring a chance to accept features. */
> +	vring_transport_features(vdev);
> +
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_DRIVER_FEATURES_SEL, 1);
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_DRIVER_FEATURES,
> +			   (u32)(vdev->features >> 32));
> +
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_DRIVER_FEATURES_SEL, 0);
> +	virtio_mdev_writel(vm_dev->mdev, VIRTIO_MDEV_DRIVER_FEATURES,
> +			   (u32)vdev->features);
> +
> +	return 0;
> +}
> +
> +static const char *virtio_mdev_bus_name(struct virtio_device *vdev)
> +{
> +	struct virtio_mdev_device *vm_dev = to_virtio_mdev_device(vdev);
> +	struct mdev_device *mdev = vm_dev->mdev;
> +
> +	return dev_name(&mdev->dev);
> +}
> +
> +static const struct virtio_config_ops virtio_mdev_config_ops = {
> +	.get		= virtio_mdev_get,
> +	.set		= virtio_mdev_set,
> +	.generation	= virtio_mdev_generation,
> +	.get_status	= virtio_mdev_get_status,
> +	.set_status	= virtio_mdev_set_status,
> +	.reset		= virtio_mdev_reset,
> +	.find_vqs	= virtio_mdev_find_vqs,
> +	.del_vqs	= virtio_mdev_del_vqs,
> +	.get_features	= virtio_mdev_get_features,
> +	.finalize_features = virtio_mdev_finalize_features,
> +	.bus_name	= virtio_mdev_bus_name,
> +};
> +
> +static void virtio_mdev_release_dev(struct device *_d)
> +{
> +	struct virtio_device *vdev =
> +	       container_of(_d, struct virtio_device, dev);
> +	struct virtio_mdev_device *vm_dev =
> +	       container_of(vdev, struct virtio_mdev_device, vdev);
> +
> +	devm_kfree(_d, vm_dev);
> +}
> +
> +static int virtio_mdev_probe(struct device *dev)
> +{
> +	struct mdev_device *mdev = to_mdev_device(dev);
> +	struct virtio_mdev_device *vm_dev;
> +	unsigned long magic;
> +	int rc;
> +
> +	magic = virtio_mdev_readl(mdev, VIRTIO_MDEV_MAGIC_VALUE);
> +	if (magic != ('v' | 'i' << 8 | 'r' << 16 | 't' << 24)) {
> +		dev_warn(dev, "Wrong magic value 0x%08lx!\n", magic);
> +		return -ENODEV;
> +	}
> +
> +	vm_dev = devm_kzalloc(dev, sizeof(*vm_dev), GFP_KERNEL);
> +	if (!vm_dev)
> +		return -ENOMEM;
> +
> +	vm_dev->vdev.dev.parent = dev;
> +	vm_dev->vdev.dev.release = virtio_mdev_release_dev;
> +	vm_dev->vdev.config = &virtio_mdev_config_ops;
> +	vm_dev->mdev = mdev;
> +	vm_dev->vqs = NULL;
> +	spin_lock_init(&vm_dev->lock);
> +
> +	vm_dev->version = virtio_mdev_readl(mdev, VIRTIO_MDEV_VERSION);
> +	if (vm_dev->version != 1) {
> +		dev_err(dev, "Version %ld not supported!\n",
> +			vm_dev->version);
> +		return -ENXIO;
> +	}
> +
> +	vm_dev->vdev.id.device = virtio_mdev_readl(mdev, VIRTIO_MDEV_DEVICE_ID);
> +	if (vm_dev->vdev.id.device == 0)
> +		return -ENODEV;
> +
> +	vm_dev->vdev.id.vendor = virtio_mdev_readl(mdev, VIRTIO_MDEV_VENDOR_ID);
> +	rc = register_virtio_device(&vm_dev->vdev);
> +	if (rc)
> +		put_device(dev);
> +
> +	dev_set_drvdata(dev, vm_dev);
> +
> +	return rc;
> +
> +}
> +
> +static void virtio_mdev_remove(struct device *dev)
> +{
> +	struct virtio_mdev_device *vm_dev = dev_get_drvdata(dev);
> +
> +	unregister_virtio_device(&vm_dev->vdev);
> +}
> +
> +static struct mdev_driver virtio_mdev_driver = {
> +	.name	= "virtio_mdev",
> +	.probe	= virtio_mdev_probe,
> +	.remove	= virtio_mdev_remove,
> +};
> +
> +static int __init virtio_mdev_init(void)
> +{
> +	return mdev_register_driver(&virtio_mdev_driver, THIS_MODULE);
> +}
> +
> +static void __exit virtio_mdev_exit(void)
> +{
> +	mdev_unregister_driver(&virtio_mdev_driver);
> +}
> +
> +module_init(virtio_mdev_init)
> +module_exit(virtio_mdev_exit)
> +
> +MODULE_VERSION(DRIVER_VERSION);
> +MODULE_LICENSE("GPL v2");
> +MODULE_AUTHOR(DRIVER_AUTHOR);
> +MODULE_DESCRIPTION(DRIVER_DESC);
> diff --git a/include/uapi/linux/virtio_mdev.h b/include/uapi/linux/virtio_mdev.h
> new file mode 100644
> index 000000000000..8040de6b960a
> --- /dev/null
> +++ b/include/uapi/linux/virtio_mdev.h
> @@ -0,0 +1,131 @@
> +/*
> + * Virtio mediated device driver
> + *
> + * Copyright 2019, Red Hat Corp.
> + *
> + * Based on Virtio MMIO driver by ARM Ltd, copyright ARM Ltd. 2011
> + *
> + * This header is BSD licensed so anyone can use the definitions to implement
> + * compatible drivers/servers.
> + *
> + * Redistribution and use in source and binary forms, with or without
> + * modification, are permitted provided that the following conditions
> + * are met:
> + * 1. Redistributions of source code must retain the above copyright
> + *    notice, this list of conditions and the following disclaimer.
> + * 2. Redistributions in binary form must reproduce the above copyright
> + *    notice, this list of conditions and the following disclaimer in the
> + *    documentation and/or other materials provided with the distribution.
> + * 3. Neither the name of IBM nor the names of its contributors
> + *    may be used to endorse or promote products derived from this software
> + *    without specific prior written permission.
> + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS'' AND
> + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
> + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
> + * ARE DISCLAIMED.  IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
> + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
> + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
> + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
> + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
> + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
> + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
> + * SUCH DAMAGE.
> + */
> +#ifndef _LINUX_VIRTIO_MDEV_H
> +#define _LINUX_VIRTIO_MDEV_H
> +
> +#include <linux/interrupt.h>
> +#include <linux/vringh.h>
> +#include <uapi/linux/virtio_net.h>
> +
> +/*
> + * Ioctls
> + */

Pls add a bit more content here. It's redundant to state these
are ioctls. Much better to document what does each one do.

> +
> +struct virtio_mdev_callback {
> +	irqreturn_t (*callback)(void *);
> +	void *private;
> +};
> +
> +#define VIRTIO_MDEV 0xAF
> +#define VIRTIO_MDEV_SET_VQ_CALLBACK _IOW(VIRTIO_MDEV, 0x00, \
> +					 struct virtio_mdev_callback)
> +#define VIRTIO_MDEV_SET_CONFIG_CALLBACK _IOW(VIRTIO_MDEV, 0x01, \
> +					struct virtio_mdev_callback)

Function pointer in an ioctl parameter? How does this ever make sense?
And can't we use a couple of registers for this, and avoid ioctls?

> +
> +#define VIRTIO_MDEV_DEVICE_API_STRING		"virtio-mdev"
> +
> +/*
> + * Control registers
> + */
> +
> +/* Magic value ("virt" string) - Read Only */
> +#define VIRTIO_MDEV_MAGIC_VALUE		0x000
> +
> +/* Virtio device version - Read Only */
> +#define VIRTIO_MDEV_VERSION		0x004
> +
> +/* Virtio device ID - Read Only */
> +#define VIRTIO_MDEV_DEVICE_ID		0x008
> +
> +/* Virtio vendor ID - Read Only */
> +#define VIRTIO_MDEV_VENDOR_ID		0x00c
> +
> +/* Bitmask of the features supported by the device (host)
> + * (32 bits per set) - Read Only */
> +#define VIRTIO_MDEV_DEVICE_FEATURES	0x010
> +
> +/* Device (host) features set selector - Write Only */
> +#define VIRTIO_MDEV_DEVICE_FEATURES_SEL	0x014
> +
> +/* Bitmask of features activated by the driver (guest)
> + * (32 bits per set) - Write Only */
> +#define VIRTIO_MDEV_DRIVER_FEATURES	0x020
> +
> +/* Activated features set selector - Write Only */
> +#define VIRTIO_MDEV_DRIVER_FEATURES_SEL	0x024
> +
> +/* Queue selector - Write Only */
> +#define VIRTIO_MDEV_QUEUE_SEL		0x030
> +
> +/* Maximum size of the currently selected queue - Read Only */
> +#define VIRTIO_MDEV_QUEUE_NUM_MAX	0x034
> +
> +/* Queue size for the currently selected queue - Write Only */
> +#define VIRTIO_MDEV_QUEUE_NUM		0x038
> +
> +/* Ready bit for the currently selected queue - Read Write */
> +#define VIRTIO_MDEV_QUEUE_READY		0x044

Is this same as started?

> +
> +/* Alignment of virtqueue - Read Only */
> +#define VIRTIO_MDEV_QUEUE_ALIGN		0x048
> +
> +/* Queue notifier - Write Only */
> +#define VIRTIO_MDEV_QUEUE_NOTIFY	0x050
> +
> +/* Device status register - Read Write */
> +#define VIRTIO_MDEV_STATUS		0x060
> +
> +/* Selected queue's Descriptor Table address, 64 bits in two halves */
> +#define VIRTIO_MDEV_QUEUE_DESC_LOW	0x080
> +#define VIRTIO_MDEV_QUEUE_DESC_HIGH	0x084
> +
> +/* Selected queue's Available Ring address, 64 bits in two halves */
> +#define VIRTIO_MDEV_QUEUE_AVAIL_LOW	0x090
> +#define VIRTIO_MDEV_QUEUE_AVAIL_HIGH	0x094
> +
> +/* Selected queue's Used Ring address, 64 bits in two halves */
> +#define VIRTIO_MDEV_QUEUE_USED_LOW	0x0a0
> +#define VIRTIO_MDEV_QUEUE_USED_HIGH	0x0a4
> +
> +/* Configuration atomicity value */
> +#define VIRTIO_MDEV_CONFIG_GENERATION	0x0fc
> +
> +/* The config space is defined by each driver as
> + * the per-driver configuration space - Read Write */
> +#define VIRTIO_MDEV_CONFIG		0x100

Mixing device and generic config space is what virtio pci did,
caused lots of problems with extensions.
It would be better to reserve much more space.

> +
> +#endif
> +
> +
> +/* Ready bit for the currently selected queue - Read Write */
> -- 
> 2.19.1