Message-ID: <20200116142418.6ca1b6b2@w520.home>
Date:   Thu, 16 Jan 2020 14:24:18 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>
Cc:     "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Subject: Re: [PATCH v4 11/12] samples: add vfio-mdev-pci driver

On Thu, 16 Jan 2020 12:33:06 +0000
"Liu, Yi L" <yi.l.liu@...el.com> wrote:

> > From: Alex Williamson [mailto:alex.williamson@...hat.com]
> > Sent: Friday, January 10, 2020 6:49 AM
> > To: Liu, Yi L <yi.l.liu@...el.com>
> > Subject: Re: [PATCH v4 11/12] samples: add vfio-mdev-pci driver
> > 
> > On Tue,  7 Jan 2020 20:01:48 +0800
> > Liu Yi L <yi.l.liu@...el.com> wrote:
> >   
> > > This patch adds sample driver named vfio-mdev-pci. It is to wrap
> > > a PCI device as a mediated device. For a pci device, once bound
> > > to vfio-mdev-pci driver, user space access of this device will
> > > go through vfio mdev framework. The usage of the device follows
> > > mdev management method. e.g. user should create a mdev before
> > > exposing the device to user-space.
> > >
> > > Benefit of this new driver would be acting as a sample driver
> > > for recent changes from "vfio/mdev: IOMMU aware mediated device"
> > > patchset. Also it could be a good experiment driver for future
> > > device specific mdev migration support. This sample driver only
> > > supports singleton iommu groups, for non-singleton iommu groups,
> > > this sample driver doesn't work. It will fail when trying to assign
> > > the non-singleton iommu group to VMs.
> > >
> > > To use this driver:
> > > a) build and load vfio-mdev-pci.ko module
> > >    execute "make menuconfig" and config CONFIG_SAMPLE_VFIO_MDEV_PCI
> > >    then load it with following command:  
> > >    > sudo modprobe vfio
> > >    > sudo modprobe vfio-pci
> > >    > sudo insmod samples/vfio-mdev-pci/vfio-mdev-pci.ko  
> > >
> > > b) unbind original device driver
> > >    e.g. use following command to unbind its original driver  
> > >    > echo $dev_bdf > /sys/bus/pci/devices/$dev_bdf/driver/unbind  
> > >
> > > c) bind vfio-mdev-pci driver to the physical device  
> > >    > echo $vend_id $dev_id > /sys/bus/pci/drivers/vfio-mdev-pci/new_id  
> > >
> > > d) check the supported mdev instances  
> > >    > ls /sys/bus/pci/devices/$dev_bdf/mdev_supported_types/  
> > >      vfio-mdev-pci-type_name  
> > >    > ls /sys/bus/pci/devices/$dev_bdf/mdev_supported_types/\  
> > >      vfio-mdev-pci-type_name/
> > >      available_instances  create  device_api  devices  name
> > >
> > > e)  create mdev on this physical device (only 1 instance)  
> > >    > echo "83b8f4f2-509f-382f-3c1e-e6bfe0fa1003" > \  
> > >      /sys/bus/pci/devices/$dev_bdf/mdev_supported_types/\
> > >      vfio-mdev-pci-type_name/create
> > >
> > > f) passthru the mdev to guest
> > >    add the following line in QEMU boot command
> > >     -device vfio-pci,\
> > >      sysfsdev=/sys/bus/mdev/devices/83b8f4f2-509f-382f-3c1e-e6bfe0fa1003
> > >
> > > g) destroy mdev  
> > >    > echo 1 > /sys/bus/mdev/devices/83b8f4f2-509f-382f-3c1e-e6bfe0fa1003/\  
> > >      remove
> > >
> > > Cc: Kevin Tian <kevin.tian@...el.com>
> > > Cc: Lu Baolu <baolu.lu@...ux.intel.com>
> > > Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>
> > > Suggested-by: Alex Williamson <alex.williamson@...hat.com>
> > > Signed-off-by: Liu Yi L <yi.l.liu@...el.com>
> > > ---
> > >  samples/Kconfig                       |  10 +
> > >  samples/Makefile                      |   1 +
> > >  samples/vfio-mdev-pci/Makefile        |   4 +
> > >  samples/vfio-mdev-pci/vfio_mdev_pci.c | 397  
> > ++++++++++++++++++++++++++++++++++  
> > >  4 files changed, 412 insertions(+)
> > >  create mode 100644 samples/vfio-mdev-pci/Makefile
> > >  create mode 100644 samples/vfio-mdev-pci/vfio_mdev_pci.c
> > >
> > > diff --git a/samples/Kconfig b/samples/Kconfig
> > > index 9d236c3..50d207c 100644
> > > --- a/samples/Kconfig
> > > +++ b/samples/Kconfig
> > > @@ -190,5 +190,15 @@ config SAMPLE_INTEL_MEI
> > >  	help
> > >  	  Build a sample program to work with mei device.
> > >
> > > +config SAMPLE_VFIO_MDEV_PCI
> > > +	tristate "Sample driver for wrapping PCI device as a mdev"
> > > +	select VFIO_PCI_COMMON
> > > +	select VFIO_PCI
> > > +	depends on VFIO_MDEV && VFIO_MDEV_DEVICE
> > > +	help
> > > +	  Sample driver for wrapping a PCI device as a mdev. Once bound to
> > > +	  this driver, device passthru should through mdev path.
> > > +
> > > +	  If you don't know what to do here, say N.
> > >
> > >  endif # SAMPLES
> > > diff --git a/samples/Makefile b/samples/Makefile
> > > index 5ce50ef..84faced 100644
> > > --- a/samples/Makefile
> > > +++ b/samples/Makefile
> > > @@ -21,5 +21,6 @@ obj-$(CONFIG_SAMPLE_FTRACE_DIRECT)	+= ftrace/
> > >  obj-$(CONFIG_SAMPLE_TRACE_ARRAY)	+= ftrace/
> > >  obj-$(CONFIG_VIDEO_PCI_SKELETON)	+= v4l/
> > >  obj-y					+= vfio-mdev/
> > > +obj-y					+= vfio-mdev-pci/  
> > 
> > I think we could just lump this into vfio-mdev rather than making
> > another directory.  
> 
> sure. will move it. :-)
> 
> >   
> > >  subdir-$(CONFIG_SAMPLE_VFS)		+= vfs
> > >  obj-$(CONFIG_SAMPLE_INTEL_MEI)		+= mei/
> > > diff --git a/samples/vfio-mdev-pci/Makefile b/samples/vfio-mdev-pci/Makefile
> > > new file mode 100644
> > > index 0000000..41b2139
> > > --- /dev/null
> > > +++ b/samples/vfio-mdev-pci/Makefile
> > > @@ -0,0 +1,4 @@
> > > +# SPDX-License-Identifier: GPL-2.0-only
> > > +vfio-mdev-pci-y := vfio_mdev_pci.o
> > > +
> > > +obj-$(CONFIG_SAMPLE_VFIO_MDEV_PCI) += vfio-mdev-pci.o
> > > diff --git a/samples/vfio-mdev-pci/vfio_mdev_pci.c b/samples/vfio-mdev-  
> > pci/vfio_mdev_pci.c  
> > > new file mode 100644
> > > index 0000000..b180356
> > > --- /dev/null
> > > +++ b/samples/vfio-mdev-pci/vfio_mdev_pci.c
> > > @@ -0,0 +1,397 @@
> > > +/*
> > > + * Copyright © 2020 Intel Corporation.
> > > + *     Author: Liu Yi L <yi.l.liu@...el.com>
> > > + *
> > > + * This program is free software; you can redistribute it and/or modify
> > > + * it under the terms of the GNU General Public License version 2 as
> > > + * published by the Free Software Foundation.
> > > + *
> > > + * Derived from original vfio_pci.c:
> > > + * Copyright (C) 2012 Red Hat, Inc.  All rights reserved.
> > > + *     Author: Alex Williamson <alex.williamson@...hat.com>
> > > + *
> > > + * Derived from original vfio:
> > > + * Copyright 2010 Cisco Systems, Inc.  All rights reserved.
> > > + * Author: Tom Lyon, pugs@...co.com
> > > + */
> > > +
> > > +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> > > +
> > > +#include <linux/device.h>
> > > +#include <linux/eventfd.h>
> > > +#include <linux/file.h>
> > > +#include <linux/interrupt.h>
> > > +#include <linux/iommu.h>
> > > +#include <linux/module.h>
> > > +#include <linux/mutex.h>
> > > +#include <linux/notifier.h>
> > > +#include <linux/pci.h>
> > > +#include <linux/pm_runtime.h>
> > > +#include <linux/slab.h>
> > > +#include <linux/types.h>
> > > +#include <linux/uaccess.h>
> > > +#include <linux/vfio.h>
> > > +#include <linux/vgaarb.h>
> > > +#include <linux/nospec.h>
> > > +#include <linux/mdev.h>
> > > +#include <linux/vfio_pci_common.h>
> > > +
> > > +#define DRIVER_VERSION  "0.1"
> > > +#define DRIVER_AUTHOR   "Liu Yi L <yi.l.liu@...el.com>"
> > > +#define DRIVER_DESC     "VFIO Mdev PCI - Sample driver for PCI device as a  
> > mdev"  
> > > +
> > > +#define VFIO_MDEV_PCI_NAME  "vfio-mdev-pci"
> > > +
> > > +static char ids[1024] __initdata;
> > > +module_param_string(ids, ids, sizeof(ids), 0);
> > > +MODULE_PARM_DESC(ids, "Initial PCI IDs to add to the vfio-mdev-pci driver,  
> > format is \"vendor:device[:subvendor[:subdevice[:class[:class_mask]]]]\" and
> > multiple comma separated entries can be specified");  
> > > +
> > > +static bool nointxmask;
> > > +module_param_named(nointxmask, nointxmask, bool, S_IRUGO | S_IWUSR);
> > > +MODULE_PARM_DESC(nointxmask,
> > > +		  "Disable support for PCI 2.3 style INTx masking.  If this resolves  
> > problems for specific devices, report lspci -vvvxxx to linux-pci@...r.kernel.org so
> > the device can be fixed automatically via the broken_intx_masking flag.");  
> > > +
> > > +#ifdef CONFIG_VFIO_PCI_VGA
> > > +static bool disable_vga;
> > > +module_param(disable_vga, bool, S_IRUGO);
> > > +MODULE_PARM_DESC(disable_vga, "Disable VGA resource access through vfio-  
> > mdev-pci");  
> > > +#endif
> > > +
> > > +static bool disable_idle_d3;
> > > +module_param(disable_idle_d3, bool, S_IRUGO | S_IWUSR);
> > > +MODULE_PARM_DESC(disable_idle_d3,
> > > +		 "Disable using the PCI D3 low power state for idle, unused devices");
> > > +
> > > +static struct pci_driver vfio_mdev_pci_driver;
> > > +
> > > +static ssize_t
> > > +name_show(struct kobject *kobj, struct device *dev, char *buf)
> > > +{
> > > +	return sprintf(buf, "%s-type1\n", dev_name(dev));
> > > +}
> > > +
> > > +MDEV_TYPE_ATTR_RO(name);
> > > +
> > > +static ssize_t
> > > +available_instances_show(struct kobject *kobj, struct device *dev, char *buf)
> > > +{
> > > +	return sprintf(buf, "%d\n", 1);
> > > +}
> > > +
> > > +MDEV_TYPE_ATTR_RO(available_instances);
> > > +
> > > +static ssize_t device_api_show(struct kobject *kobj, struct device *dev,
> > > +		char *buf)
> > > +{
> > > +	return sprintf(buf, "%s\n", VFIO_DEVICE_API_PCI_STRING);
> > > +}
> > > +
> > > +MDEV_TYPE_ATTR_RO(device_api);
> > > +
> > > +static struct attribute *vfio_mdev_pci_types_attrs[] = {
> > > +	&mdev_type_attr_name.attr,
> > > +	&mdev_type_attr_device_api.attr,
> > > +	&mdev_type_attr_available_instances.attr,
> > > +	NULL,
> > > +};
> > > +
> > > +static struct attribute_group vfio_mdev_pci_type_group1 = {
> > > +	.name  = "type1",
> > > +	.attrs = vfio_mdev_pci_types_attrs,
> > > +};
> > > +
> > > +struct attribute_group *vfio_mdev_pci_type_groups[] = {
> > > +	&vfio_mdev_pci_type_group1,
> > > +	NULL,
> > > +};
> > > +
> > > +struct vfio_mdev_pci {
> > > +	struct vfio_pci_device *vdev;
> > > +	struct mdev_device *mdev;
> > > +	unsigned long handle;
> > > +};
> > > +
> > > +static int vfio_mdev_pci_create(struct kobject *kobj, struct mdev_device *mdev)
> > > +{
> > > +	struct device *pdev;
> > > +	struct vfio_pci_device *vdev;
> > > +	struct vfio_mdev_pci *pmdev;
> > > +	int ret;
> > > +
> > > +	pdev = mdev_parent_dev(mdev);
> > > +	vdev = dev_get_drvdata(pdev);
> > > +	pmdev = kzalloc(sizeof(struct vfio_mdev_pci), GFP_KERNEL);
> > > +	if (pmdev == NULL) {
> > > +		ret = -EBUSY;
> > > +		goto out;
> > > +	}
> > > +
> > > +	pmdev->mdev = mdev;
> > > +	pmdev->vdev = vdev;
> > > +	mdev_set_drvdata(mdev, pmdev);
> > > +	ret = mdev_set_iommu_device(mdev_dev(mdev), pdev);
> > > +	if (ret) {
> > > +		pr_info("%s, failed to config iommu isolation for mdev: %s on  
> > pf: %s\n",  
> > > +			__func__, dev_name(mdev_dev(mdev)), dev_name(pdev));
> > > +		goto out;
> > > +	}
> > > +
> > > +	pr_info("%s, creation succeeded for mdev: %s\n", __func__,
> > > +		     dev_name(mdev_dev(mdev)));
> > > +out:
> > > +	return ret;
> > > +}
> > > +
> > > +static int vfio_mdev_pci_remove(struct mdev_device *mdev)
> > > +{
> > > +	struct vfio_mdev_pci *pmdev = mdev_get_drvdata(mdev);
> > > +
> > > +	kfree(pmdev);
> > > +	pr_info("%s, succeeded for mdev: %s\n", __func__,
> > > +		     dev_name(mdev_dev(mdev)));
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static int vfio_mdev_pci_open(struct mdev_device *mdev)
> > > +{
> > > +	struct vfio_mdev_pci *pmdev = mdev_get_drvdata(mdev);
> > > +	struct vfio_pci_device *vdev = pmdev->vdev;
> > > +	int ret = 0;
> > > +
> > > +	if (!try_module_get(THIS_MODULE))
> > > +		return -ENODEV;
> > > +
> > > +	vfio_pci_refresh_config(vdev, nointxmask, disable_idle_d3);
> > > +
> > > +	mutex_lock(&vdev->reflck->lock);
> > > +
> > > +	if (!vdev->refcnt) {
> > > +		ret = vfio_pci_enable(vdev);
> > > +		if (ret)
> > > +			goto error;
> > > +
> > > +		vfio_spapr_pci_eeh_open(vdev->pdev);
> > > +	}
> > > +	vdev->refcnt++;
> > > +error:
> > > +	mutex_unlock(&vdev->reflck->lock);
> > > +	if (!ret)
> > > +		pr_info("Succeeded to open mdev: %s on pf: %s\n",
> > > +		dev_name(mdev_dev(mdev)), dev_name(&pmdev->vdev->pdev-
> > >dev));
> > > +	else {
> > > +		pr_info("Failed to open mdev: %s on pf: %s\n",
> > > +		dev_name(mdev_dev(mdev)), dev_name(&pmdev->vdev->pdev-
> > >dev));
> > > +		module_put(THIS_MODULE);
> > > +	}
> > > +	return ret;
> > > +}
> > > +
> > > +static void vfio_mdev_pci_release(struct mdev_device *mdev)
> > > +{
> > > +	struct vfio_mdev_pci *pmdev = mdev_get_drvdata(mdev);
> > > +	struct vfio_pci_device *vdev = pmdev->vdev;
> > > +
> > > +	pr_info("Release mdev: %s on pf: %s\n",
> > > +		dev_name(mdev_dev(mdev)), dev_name(&pmdev->vdev->pdev-
> > >dev));
> > > +
> > > +	mutex_lock(&vdev->reflck->lock);
> > > +
> > > +	if (!(--vdev->refcnt)) {
> > > +		vfio_spapr_pci_eeh_release(vdev->pdev);
> > > +		vfio_pci_disable(vdev);
> > > +	}
> > > +
> > > +	mutex_unlock(&vdev->reflck->lock);
> > > +
> > > +	module_put(THIS_MODULE);
> > > +}  
> > 
> > open() and release() here are almost identical between vfio_pci and
> > vfio_mdev_pci, which suggests maybe there should be common functions to
> > call into like we do for the below.  
> 
> yes, let me have more study and do better abstract in next version. :-)
> 
> > > +static long vfio_mdev_pci_ioctl(struct mdev_device *mdev, unsigned int cmd,
> > > +			     unsigned long arg)
> > > +{
> > > +	struct vfio_mdev_pci *pmdev = mdev_get_drvdata(mdev);
> > > +
> > > +	return vfio_pci_ioctl(pmdev->vdev, cmd, arg);
> > > +}
> > > +
> > > +static int vfio_mdev_pci_mmap(struct mdev_device *mdev,
> > > +				struct vm_area_struct *vma)
> > > +{
> > > +	struct vfio_mdev_pci *pmdev = mdev_get_drvdata(mdev);
> > > +
> > > +	return vfio_pci_mmap(pmdev->vdev, vma);
> > > +}
> > > +
> > > +static ssize_t vfio_mdev_pci_read(struct mdev_device *mdev, char __user *buf,
> > > +			size_t count, loff_t *ppos)
> > > +{
> > > +	struct vfio_mdev_pci *pmdev = mdev_get_drvdata(mdev);
> > > +
> > > +	return vfio_pci_read(pmdev->vdev, buf, count, ppos);
> > > +}
> > > +
> > > +static ssize_t vfio_mdev_pci_write(struct mdev_device *mdev,
> > > +				const char __user *buf,
> > > +				size_t count, loff_t *ppos)
> > > +{
> > > +	struct vfio_mdev_pci *pmdev = mdev_get_drvdata(mdev);
> > > +
> > > +	return vfio_pci_write(pmdev->vdev, (char __user *)buf, count, ppos);
> > > +}
> > > +
> > > +static const struct mdev_parent_ops vfio_mdev_pci_ops = {
> > > +	.supported_type_groups	= vfio_mdev_pci_type_groups,
> > > +	.create			= vfio_mdev_pci_create,
> > > +	.remove			= vfio_mdev_pci_remove,
> > > +
> > > +	.open			= vfio_mdev_pci_open,
> > > +	.release		= vfio_mdev_pci_release,
> > > +
> > > +	.read			= vfio_mdev_pci_read,
> > > +	.write			= vfio_mdev_pci_write,
> > > +	.mmap			= vfio_mdev_pci_mmap,
> > > +	.ioctl			= vfio_mdev_pci_ioctl,
> > > +};
> > > +
> > > +static int vfio_mdev_pci_driver_probe(struct pci_dev *pdev,
> > > +				       const struct pci_device_id *id)
> > > +{
> > > +	struct vfio_pci_device *vdev;
> > > +	int ret;
> > > +
> > > +	if (pdev->hdr_type != PCI_HEADER_TYPE_NORMAL)
> > > +		return -EINVAL;
> > > +
> > > +	/*
> > > +	 * Prevent binding to PFs with VFs enabled, this too easily allows
> > > +	 * userspace instance with VFs and PFs from the same device, which
> > > +	 * cannot work.  Disabling SR-IOV here would initiate removing the
> > > +	 * VFs, which would unbind the driver, which is prone to blocking
> > > +	 * if that VF is also in use by vfio-pci or vfio-mdev-pci. Just
> > > +	 * reject these PFs and let the user sort it out.
> > > +	 */
> > > +	if (pci_num_vf(pdev)) {
> > > +		pci_warn(pdev, "Cannot bind to PF with SR-IOV enabled\n");
> > > +		return -EBUSY;
> > > +	}
> > > +
> > > +	vdev = kzalloc(sizeof(*vdev), GFP_KERNEL);
> > > +	if (!vdev)
> > > +		return -ENOMEM;
> > > +
> > > +	vdev->pdev = pdev;
> > > +	vdev->irq_type = VFIO_PCI_NUM_IRQS;
> > > +	mutex_init(&vdev->igate);
> > > +	spin_lock_init(&vdev->irqlock);
> > > +	mutex_init(&vdev->ioeventfds_lock);
> > > +	INIT_LIST_HEAD(&vdev->ioeventfds_list);
> > > +	vdev->nointxmask = nointxmask;
> > > +#ifdef CONFIG_VFIO_PCI_VGA
> > > +	vdev->disable_vga = disable_vga;
> > > +#endif
> > > +	vdev->disable_idle_d3 = disable_idle_d3;
> > > +
> > > +	pci_set_drvdata(pdev, vdev);
> > > +
> > > +	ret = vfio_pci_reflck_attach(vdev);
> > > +	if (ret) {
> > > +		pci_set_drvdata(pdev, NULL);
> > > +		kfree(vdev);
> > > +		return ret;
> > > +	}
> > > +
> > > +	if (vfio_pci_is_vga(pdev)) {
> > > +		vga_client_register(pdev, vdev, NULL, vfio_pci_set_vga_decode);
> > > +		vga_set_legacy_decoding(pdev,
> > > +					vfio_pci_set_vga_decode(vdev, false));
> > > +	}
> > > +
> > > +	vfio_pci_probe_power_state(vdev);
> > > +
> > > +	if (!vdev->disable_idle_d3) {
> > > +		/*
> > > +		 * pci-core sets the device power state to an unknown value at
> > > +		 * bootup and after being removed from a driver.  The only
> > > +		 * transition it allows from this unknown state is to D0, which
> > > +		 * typically happens when a driver calls pci_enable_device().
> > > +		 * We're not ready to enable the device yet, but we do want to
> > > +		 * be able to get to D3.  Therefore first do a D0 transition
> > > +		 * before going to D3.
> > > +		 */
> > > +		vfio_pci_set_power_state(vdev, PCI_D0);
> > > +		vfio_pci_set_power_state(vdev, PCI_D3hot);
> > > +	}  
> > 
> > Ditto here and remove below, this seems like boilerplate that shouldn't
> > be duplicated per leaf module.  Thanks,  
> 
> Sure, the code snippet above may also be abstracted to be a common API
> provided by vfio-pci-common.ko. :-)
> 
> I have a confusion which may need confirm with you. Do you also want the
> below code snippet be placed in the vfio-pci-common.ko and exposed out
> as a wrapped API? Thus it can be used by sample driver and other future
> drivers which want to wrap PCI device as a mdev. May be I misundstood
> your comment. :-(


I think some sort of vfio_pci_common_{probe,remove}() would be a
reasonable starting point where the respective module _{probe,remove}
functions would call into these and add their module specific code
around it.  That would at least give us a point to cleanup things that
are only used by the common code in the common code.

I'm still struggling how we make this user consumable should we accept
this and progress beyond a proof of concept sample driver though.  For
example, if a vendor actually implements an mdev wrapper driver or even
just a device specific vfio-pci wrapper, to enable for example
migration support, how does a user know which driver to use for each
particular feature?  The best I can come up with so far is something
like was done for vfio-platform reset modules.  For instance a module
that extends features for a given device in vfio-pci might register an
ops structure and id table with vfio-pci, along with creating a module
alias (or aliases) for the devices it supports.  When a device is
probed by vfio-pci it could try to match against registered id tables
to find a device specific ops structure, if one is not found it could
do a request_module using the PCI vendor and device IDs and some unique
vfio-pci string, check again, and use the default ops if device
specific ops are still not present.  That would solve the problem on
the vfio-pci side.  For mdevs, I tend to assume that this vfio-mdev-pci
meta driver is an anomaly only for the purpose of creating a generic
test device for IOMMU backed mdevs and that "real" mdev vendor drivers
will just be mdev enlightened host drivers, like i915 and nvidia are
now.  Thanks,

Alex

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