vfio.c

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/*
 * VFIO core
 *
 * Copyright (C) 2012 Red Hat, Inc.  All rights reserved.
 *     Author: Alex Williamson <[email protected]>
 *
 * 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:
 * Copyright 2010 Cisco Systems, Inc.  All rights reserved.
 * Author: Tom Lyon, [email protected]
 */

#include <linux/cdev.h>
#include <linux/compat.h>
#include <linux/device.h>
#include <linux/file.h>
#include <linux/anon_inodes.h>
#include <linux/fs.h>
#include <linux/idr.h>
#include <linux/iommu.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/uaccess.h>
#include <linux/vfio.h>
#include <linux/wait.h>

#define DRIVER_VERSION  "0.3"
#define DRIVER_AUTHOR   "Alex Williamson <[email protected]>"
#define DRIVER_DESC "VFIO - User Level meta-driver"

static struct vfio {
    struct class            *class;
    struct list_head        iommu_drivers_list;
    struct mutex            iommu_drivers_lock;
    struct list_head        group_list;
    struct idr          group_idr;
    struct mutex            group_lock;
    struct cdev         group_cdev;
    struct device           *dev;
    dev_t               devt;
    struct cdev         cdev;
    wait_queue_head_t       release_q;
} vfio;

struct vfio_iommu_driver {
    const struct vfio_iommu_driver_ops  *ops;
    struct list_head            vfio_next;
};

struct vfio_container {
    struct kref         kref;
    struct list_head        group_list;
    struct mutex            group_lock;
    struct vfio_iommu_driver    *iommu_driver;
    void                *iommu_data;
};

struct vfio_group {
    struct kref         kref;
    int             minor;
    atomic_t            container_users;
    struct iommu_group      *iommu_group;
    struct vfio_container       *container;
    struct list_head        device_list;
    struct mutex            device_lock;
    struct device           *dev;
    struct notifier_block       nb;
    struct list_head        vfio_next;
    struct list_head        container_next;
};

struct vfio_device {
    struct kref         kref;
    struct device           *dev;
    const struct vfio_device_ops    *ops;
    struct vfio_group       *group;
    struct list_head        group_next;
    void                *device_data;
};

int vfio_register_iommu_driver(const struct vfio_iommu_driver_ops *ops)
{
    struct vfio_iommu_driver *driver, *tmp;

    driver = kzalloc(sizeof(*driver), GFP_KERNEL);
    if (!driver)
        return -ENOMEM;

    driver->ops = ops;

    mutex_lock(&vfio.iommu_drivers_lock);

    /* Check for duplicates */
    list_for_each_entry(tmp, &vfio.iommu_drivers_list, vfio_next) {
        if (tmp->ops == ops) {
            mutex_unlock(&vfio.iommu_drivers_lock);
            kfree(driver);
            return -EINVAL;
        }
    }

    list_add(&driver->vfio_next, &vfio.iommu_drivers_list);

    mutex_unlock(&vfio.iommu_drivers_lock);

    return 0;
}
EXPORT_SYMBOL_GPL(vfio_register_iommu_driver);

void vfio_unregister_iommu_driver(const struct vfio_iommu_driver_ops *ops)
{
    struct vfio_iommu_driver *driver;

    mutex_lock(&vfio.iommu_drivers_lock);
    list_for_each_entry(driver, &vfio.iommu_drivers_list, vfio_next) {
        if (driver->ops == ops) {
            list_del(&driver->vfio_next);
            mutex_unlock(&vfio.iommu_drivers_lock);
            kfree(driver);
            return;
        }
    }
    mutex_unlock(&vfio.iommu_drivers_lock);
}
EXPORT_SYMBOL_GPL(vfio_unregister_iommu_driver);

static int vfio_alloc_group_minor(struct vfio_group *group)
{
    int ret, minor;

again:
    if (unlikely(idr_pre_get(&vfio.group_idr, GFP_KERNEL) == 0))
        return -ENOMEM;

    /* index 0 is used by /dev/vfio/vfio */
    ret = idr_get_new_above(&vfio.group_idr, group, 1, &minor);
    if (ret == -EAGAIN)
        goto again;
    if (ret || minor > MINORMASK) {
        if (minor > MINORMASK)
            idr_remove(&vfio.group_idr, minor);
        return -ENOSPC;
    }

    return minor;
}

static void vfio_free_group_minor(int minor)
{
    idr_remove(&vfio.group_idr, minor);
}

static int vfio_iommu_group_notifier(struct notifier_block *nb,
                     unsigned long action, void *data);
static void vfio_group_get(struct vfio_group *group);

static void vfio_container_get(struct vfio_container *container)
{
    kref_get(&container->kref);
}

static void vfio_container_release(struct kref *kref)
{
    struct vfio_container *container;
    container = container_of(kref, struct vfio_container, kref);

    kfree(container);
}

static void vfio_container_put(struct vfio_container *container)
{
    kref_put(&container->kref, vfio_container_release);
}

static struct vfio_group *vfio_create_group(struct iommu_group *iommu_group)
{
    struct vfio_group *group, *tmp;
    struct device *dev;
    int ret, minor;

    group = kzalloc(sizeof(*group), GFP_KERNEL);
    if (!group)
        return ERR_PTR(-ENOMEM);

    kref_init(&group->kref);
    INIT_LIST_HEAD(&group->device_list);
    mutex_init(&group->device_lock);
    atomic_set(&group->container_users, 0);
    group->iommu_group = iommu_group;

    group->nb.notifier_call = vfio_iommu_group_notifier;

    /*
     * blocking notifiers acquire a rwsem around registering and hold
     * it around callback.  Therefore, need to register outside of
     * vfio.group_lock to avoid A-B/B-A contention.  Our callback won't
     * do anything unless it can find the group in vfio.group_list, so
     * no harm in registering early.
     */
    ret = iommu_group_register_notifier(iommu_group, &group->nb);
    if (ret) {
        kfree(group);
        return ERR_PTR(ret);
    }

    mutex_lock(&vfio.group_lock);

    minor = vfio_alloc_group_minor(group);
    if (minor < 0) {
        mutex_unlock(&vfio.group_lock);
        kfree(group);
        return ERR_PTR(minor);
    }

    /* Did we race creating this group? */
    list_for_each_entry(tmp, &vfio.group_list, vfio_next) {
        if (tmp->iommu_group == iommu_group) {
            vfio_group_get(tmp);
            vfio_free_group_minor(minor);
            mutex_unlock(&vfio.group_lock);
            kfree(group);
            return tmp;
        }
    }

    dev = device_create(vfio.class, NULL, MKDEV(MAJOR(vfio.devt), minor),
                group, "%d", iommu_group_id(iommu_group));
    if (IS_ERR(dev)) {
        vfio_free_group_minor(minor);
        mutex_unlock(&vfio.group_lock);
        kfree(group);
        return (struct vfio_group *)dev; /* ERR_PTR */
    }

    group->minor = minor;
    group->dev = dev;

    list_add(&group->vfio_next, &vfio.group_list);

    mutex_unlock(&vfio.group_lock);

    return group;
}

/* called with vfio.group_lock held */
static void vfio_group_release(struct kref *kref)
{
    struct vfio_group *group = container_of(kref, struct vfio_group, kref);

    WARN_ON(!list_empty(&group->device_list));

    device_destroy(vfio.class, MKDEV(MAJOR(vfio.devt), group->minor));
    list_del(&group->vfio_next);
    vfio_free_group_minor(group->minor);

    mutex_unlock(&vfio.group_lock);

    /*
     * Unregister outside of lock.  A spurious callback is harmless now
     * that the group is no longer in vfio.group_list.
     */
    iommu_group_unregister_notifier(group->iommu_group, &group->nb);

    kfree(group);
}

static void vfio_group_put(struct vfio_group *group)
{
    kref_put_mutex(&group->kref, vfio_group_release, &vfio.group_lock);
}

/* Assume group_lock or group reference is held */
static void vfio_group_get(struct vfio_group *group)
{
    kref_get(&group->kref);
}

/*
 * Not really a try as we will sleep for mutex, but we need to make
 * sure the group pointer is valid under lock and get a reference.
 */
static struct vfio_group *vfio_group_try_get(struct vfio_group *group)
{
    struct vfio_group *target = group;

    mutex_lock(&vfio.group_lock);
    list_for_each_entry(group, &vfio.group_list, vfio_next) {
        if (group == target) {
            vfio_group_get(group);
            mutex_unlock(&vfio.group_lock);
            return group;
        }
    }
    mutex_unlock(&vfio.group_lock);

    return NULL;
}

static
struct vfio_group *vfio_group_get_from_iommu(struct iommu_group *iommu_group)
{
    struct vfio_group *group;

    mutex_lock(&vfio.group_lock);
    list_for_each_entry(group, &vfio.group_list, vfio_next) {
        if (group->iommu_group == iommu_group) {
            vfio_group_get(group);
            mutex_unlock(&vfio.group_lock);
            return group;
        }
    }
    mutex_unlock(&vfio.group_lock);

    return NULL;
}

static struct vfio_group *vfio_group_get_from_minor(int minor)
{
    struct vfio_group *group;

    mutex_lock(&vfio.group_lock);
    group = idr_find(&vfio.group_idr, minor);
    if (!group) {
        mutex_unlock(&vfio.group_lock);
        return NULL;
    }
    vfio_group_get(group);
    mutex_unlock(&vfio.group_lock);

    return group;
}

static
struct vfio_device *vfio_group_create_device(struct vfio_group *group,
                         struct device *dev,
                         const struct vfio_device_ops *ops,
                         void *device_data)
{
    struct vfio_device *device;
    int ret;

    device = kzalloc(sizeof(*device), GFP_KERNEL);
    if (!device)
        return ERR_PTR(-ENOMEM);

    kref_init(&device->kref);
    device->dev = dev;
    device->group = group;
    device->ops = ops;
    device->device_data = device_data;

    ret = dev_set_drvdata(dev, device);
    if (ret) {
        kfree(device);
        return ERR_PTR(ret);
    }

    /* No need to get group_lock, caller has group reference */
    vfio_group_get(group);

    mutex_lock(&group->device_lock);
    list_add(&device->group_next, &group->device_list);
    mutex_unlock(&group->device_lock);

    return device;
}

static void vfio_device_release(struct kref *kref)
{
    struct vfio_device *device = container_of(kref,
                          struct vfio_device, kref);
    struct vfio_group *group = device->group;

    list_del(&device->group_next);
    mutex_unlock(&group->device_lock);

    dev_set_drvdata(device->dev, NULL);

    kfree(device);

    /* vfio_del_group_dev may be waiting for this device */
    wake_up(&vfio.release_q);
}

/* Device reference always implies a group reference */
static void vfio_device_put(struct vfio_device *device)
{
    struct vfio_group *group = device->group;
    kref_put_mutex(&device->kref, vfio_device_release, &group->device_lock);
    vfio_group_put(group);
}

static void vfio_device_get(struct vfio_device *device)
{
    vfio_group_get(device->group);
    kref_get(&device->kref);
}

static struct vfio_device *vfio_group_get_device(struct vfio_group *group,
                         struct device *dev)
{
    struct vfio_device *device;

    mutex_lock(&group->device_lock);
    list_for_each_entry(device, &group->device_list, group_next) {
        if (device->dev == dev) {
            vfio_device_get(device);
            mutex_unlock(&group->device_lock);
            return device;
        }
    }
    mutex_unlock(&group->device_lock);
    return NULL;
}

/*
 * Whitelist some drivers that we know are safe (no dma) or just sit on
 * a device.  It's not always practical to leave a device within a group
 * driverless as it could get re-bound to something unsafe.
 */
static const char * const vfio_driver_whitelist[] = { "pci-stub" };

static bool vfio_whitelisted_driver(struct device_driver *drv)
{
    int i;

    for (i = 0; i < ARRAY_SIZE(vfio_driver_whitelist); i++) {
        if (!strcmp(drv->name, vfio_driver_whitelist[i]))
            return true;
    }

    return false;
}

/*
 * A vfio group is viable for use by userspace if all devices are either
 * driver-less or bound to a vfio or whitelisted driver.  We test the
 * latter by the existence of a struct vfio_device matching the dev.
 */
static int vfio_dev_viable(struct device *dev, void *data)
{
    struct vfio_group *group = data;
    struct vfio_device *device;

    if (!dev->driver || vfio_whitelisted_driver(dev->driver))
        return 0;

    device = vfio_group_get_device(group, dev);
    if (device) {
        vfio_device_put(device);
        return 0;
    }

    return -EINVAL;
}

static int vfio_group_nb_add_dev(struct vfio_group *group, struct device *dev)
{
    struct vfio_device *device;

    /* Do we already know about it?  We shouldn't */
    device = vfio_group_get_device(group, dev);
    if (WARN_ON_ONCE(device)) {
        vfio_device_put(device);
        return 0;
    }

    /* Nothing to do for idle groups */
    if (!atomic_read(&group->container_users))
        return 0;

    /* TODO Prevent device auto probing */
    WARN("Device %s added to live group %d!\n", dev_name(dev),
         iommu_group_id(group->iommu_group));

    return 0;
}

static int vfio_group_nb_del_dev(struct vfio_group *group, struct device *dev)
{
    struct vfio_device *device;

    /*
     * Expect to fall out here.  If a device was in use, it would
     * have been bound to a vfio sub-driver, which would have blocked
     * in .remove at vfio_del_group_dev.  Sanity check that we no
     * longer track the device, so it's safe to remove.
     */
    device = vfio_group_get_device(group, dev);
    if (likely(!device))
        return 0;

    WARN("Device %s removed from live group %d!\n", dev_name(dev),
         iommu_group_id(group->iommu_group));

    vfio_device_put(device);
    return 0;
}

static int vfio_group_nb_verify(struct vfio_group *group, struct device *dev)
{
    /* We don't care what happens when the group isn't in use */
    if (!atomic_read(&group->container_users))
        return 0;

    return vfio_dev_viable(dev, group);
}

static int vfio_iommu_group_notifier(struct notifier_block *nb,
                     unsigned long action, void *data)
{
    struct vfio_group *group = container_of(nb, struct vfio_group, nb);
    struct device *dev = data;

    /*
     * Need to go through a group_lock lookup to get a reference or
     * we risk racing a group being removed.  Leave a WARN_ON for
     * debuging, but if the group no longer exists, a spurious notify
     * is harmless.
     */
    group = vfio_group_try_get(group);
    if (WARN_ON(!group))
        return NOTIFY_OK;

    switch (action) {
    case IOMMU_GROUP_NOTIFY_ADD_DEVICE:
        vfio_group_nb_add_dev(group, dev);
        break;
    case IOMMU_GROUP_NOTIFY_DEL_DEVICE:
        vfio_group_nb_del_dev(group, dev);
        break;
    case IOMMU_GROUP_NOTIFY_BIND_DRIVER:
        pr_debug("%s: Device %s, group %d binding to driver\n",
             __func__, dev_name(dev),
             iommu_group_id(group->iommu_group));
        break;
    case IOMMU_GROUP_NOTIFY_BOUND_DRIVER:
        pr_debug("%s: Device %s, group %d bound to driver %s\n",
             __func__, dev_name(dev),
             iommu_group_id(group->iommu_group), dev->driver->name);
        BUG_ON(vfio_group_nb_verify(group, dev));
        break;
    case IOMMU_GROUP_NOTIFY_UNBIND_DRIVER:
        pr_debug("%s: Device %s, group %d unbinding from driver %s\n",
             __func__, dev_name(dev),
             iommu_group_id(group->iommu_group), dev->driver->name);
        break;
    case IOMMU_GROUP_NOTIFY_UNBOUND_DRIVER:
        pr_debug("%s: Device %s, group %d unbound from driver\n",
             __func__, dev_name(dev),
             iommu_group_id(group->iommu_group));
        /*
         * XXX An unbound device in a live group is ok, but we'd
         * really like to avoid the above BUG_ON by preventing other
         * drivers from binding to it.  Once that occurs, we have to
         * stop the system to maintain isolation.  At a minimum, we'd
         * want a toggle to disable driver auto probe for this device.
         */
        break;
    }

    vfio_group_put(group);
    return NOTIFY_OK;
}

int vfio_add_group_dev(struct device *dev,
               const struct vfio_device_ops *ops, void *device_data)
{
    struct iommu_group *iommu_group;
    struct vfio_group *group;
    struct vfio_device *device;

    iommu_group = iommu_group_get(dev);
    if (!iommu_group)
        return -EINVAL;

    group = vfio_group_get_from_iommu(iommu_group);
    if (!group) {
        group = vfio_create_group(iommu_group);
        if (IS_ERR(group)) {
            iommu_group_put(iommu_group);
            return PTR_ERR(group);
        }
    }

    device = vfio_group_get_device(group, dev);
    if (device) {
        WARN(1, "Device %s already exists on group %d\n",
             dev_name(dev), iommu_group_id(iommu_group));
        vfio_device_put(device);
        vfio_group_put(group);
        iommu_group_put(iommu_group);
        return -EBUSY;
    }

    device = vfio_group_create_device(group, dev, ops, device_data);
    if (IS_ERR(device)) {
        vfio_group_put(group);
        iommu_group_put(iommu_group);
        return PTR_ERR(device);
    }

    /*
     * Added device holds reference to iommu_group and vfio_device
     * (which in turn holds reference to vfio_group).  Drop extra
     * group reference used while acquiring device.
     */
    vfio_group_put(group);

    return 0;
}
EXPORT_SYMBOL_GPL(vfio_add_group_dev);

/* Test whether a struct device is present in our tracking */
static bool vfio_dev_present(struct device *dev)
{
    struct iommu_group *iommu_group;
    struct vfio_group *group;
    struct vfio_device *device;

    iommu_group = iommu_group_get(dev);
    if (!iommu_group)
        return false;

    group = vfio_group_get_from_iommu(iommu_group);
    if (!group) {
        iommu_group_put(iommu_group);
        return false;
    }

    device = vfio_group_get_device(group, dev);
    if (!device) {
        vfio_group_put(group);
        iommu_group_put(iommu_group);
        return false;
    }

    vfio_device_put(device);
    vfio_group_put(group);
    iommu_group_put(iommu_group);
    return true;
}

/*
 * Decrement the device reference count and wait for the device to be
 * removed.  Open file descriptors for the device... */
void *vfio_del_group_dev(struct device *dev)
{
    struct vfio_device *device = dev_get_drvdata(dev);
    struct vfio_group *group = device->group;
    struct iommu_group *iommu_group = group->iommu_group;
    void *device_data = device->device_data;

    vfio_device_put(device);

    /* TODO send a signal to encourage this to be released */
    wait_event(vfio.release_q, !vfio_dev_present(dev));

    iommu_group_put(iommu_group);

    return device_data;
}
EXPORT_SYMBOL_GPL(vfio_del_group_dev);

static long vfio_ioctl_check_extension(struct vfio_container *container,
                       unsigned long arg)
{
    struct vfio_iommu_driver *driver = container->iommu_driver;
    long ret = 0;

    switch (arg) {
        /* No base extensions yet */
    default:
        /*
         * If no driver is set, poll all registered drivers for
         * extensions and return the first positive result.  If
         * a driver is already set, further queries will be passed
         * only to that driver.
         */
        if (!driver) {
            mutex_lock(&vfio.iommu_drivers_lock);
            list_for_each_entry(driver, &vfio.iommu_drivers_list,
                        vfio_next) {
                if (!try_module_get(driver->ops->owner))
                    continue;

                ret = driver->ops->ioctl(NULL,
                             VFIO_CHECK_EXTENSION,
                             arg);
                module_put(driver->ops->owner);
                if (ret > 0)
                    break;
            }
            mutex_unlock(&vfio.iommu_drivers_lock);
        } else
            ret = driver->ops->ioctl(container->iommu_data,
                         VFIO_CHECK_EXTENSION, arg);
    }

    return ret;
}

/* hold container->group_lock */
static int __vfio_container_attach_groups(struct vfio_container *container,
                      struct vfio_iommu_driver *driver,
                      void *data)
{
    struct vfio_group *group;
    int ret = -ENODEV;

    list_for_each_entry(group, &container->group_list, container_next) {
        ret = driver->ops->attach_group(data, group->iommu_group);
        if (ret)
            goto unwind;
    }

    return ret;

unwind:
    list_for_each_entry_continue_reverse(group, &container->group_list,
                         container_next) {
        driver->ops->detach_group(data, group->iommu_group);
    }

    return ret;
}

static long vfio_ioctl_set_iommu(struct vfio_container *container,
                 unsigned long arg)
{
    struct vfio_iommu_driver *driver;
    long ret = -ENODEV;

    mutex_lock(&container->group_lock);

    /*
     * The container is designed to be an unprivileged interface while
     * the group can be assigned to specific users.  Therefore, only by
     * adding a group to a container does the user get the privilege of
     * enabling the iommu, which may allocate finite resources.  There
     * is no unset_iommu, but by removing all the groups from a container,
     * the container is deprivileged and returns to an unset state.
     */
    if (list_empty(&container->group_list) || container->iommu_driver) {
        mutex_unlock(&container->group_lock);
        return -EINVAL;
    }

    mutex_lock(&vfio.iommu_drivers_lock);
    list_for_each_entry(driver, &vfio.iommu_drivers_list, vfio_next) {
        void *data;

        if (!try_module_get(driver->ops->owner))
            continue;

        /*
         * The arg magic for SET_IOMMU is the same as CHECK_EXTENSION,
         * so test which iommu driver reported support for this
         * extension and call open on them.  We also pass them the
         * magic, allowing a single driver to support multiple
         * interfaces if they'd like.
         */
        if (driver->ops->ioctl(NULL, VFIO_CHECK_EXTENSION, arg) <= 0) {
            module_put(driver->ops->owner);
            continue;
        }

        /* module reference holds the driver we're working on */
        mutex_unlock(&vfio.iommu_drivers_lock);

        data = driver->ops->open(arg);
        if (IS_ERR(data)) {
            ret = PTR_ERR(data);
            module_put(driver->ops->owner);
            goto skip_drivers_unlock;
        }

        ret = __vfio_container_attach_groups(container, driver, data);
        if (!ret) {
            container->iommu_driver = driver;
            container->iommu_data = data;
        } else {
            driver->ops->release(data);
            module_put(driver->ops->owner);
        }

        goto skip_drivers_unlock;
    }

    mutex_unlock(&vfio.iommu_drivers_lock);
skip_drivers_unlock:
    mutex_unlock(&container->group_lock);

    return ret;
}

static long vfio_fops_unl_ioctl(struct file *filep,
                unsigned int cmd, unsigned long arg)
{
    struct vfio_container *container = filep->private_data;
    struct vfio_iommu_driver *driver;
    void *data;
    long ret = -EINVAL;

    if (!container)
        return ret;

    driver = container->iommu_driver;
    data = container->iommu_data;

    switch (cmd) {
    case VFIO_GET_API_VERSION:
        ret = VFIO_API_VERSION;
        break;
    case VFIO_CHECK_EXTENSION:
        ret = vfio_ioctl_check_extension(container, arg);
        break;
    case VFIO_SET_IOMMU:
        ret = vfio_ioctl_set_iommu(container, arg);
        break;
    default:
        if (driver) /* passthrough all unrecognized ioctls */
            ret = driver->ops->ioctl(data, cmd, arg);
    }

    return ret;
}

#ifdef CONFIG_COMPAT
static long vfio_fops_compat_ioctl(struct file *filep,
                   unsigned int cmd, unsigned long arg)
{
    arg = (unsigned long)compat_ptr(arg);
    return vfio_fops_unl_ioctl(filep, cmd, arg);
}
#endif  /* CONFIG_COMPAT */

static int vfio_fops_open(struct inode *inode, struct file *filep)
{
    struct vfio_container *container;

    container = kzalloc(sizeof(*container), GFP_KERNEL);
    if (!container)
        return -ENOMEM;

    INIT_LIST_HEAD(&container->group_list);
    mutex_init(&container->group_lock);
    kref_init(&container->kref);

    filep->private_data = container;

    return 0;
}

static int vfio_fops_release(struct inode *inode, struct file *filep)
{
    struct vfio_container *container = filep->private_data;

    filep->private_data = NULL;

    vfio_container_put(container);

    return 0;
}

/*
 * Once an iommu driver is set, we optionally pass read/write/mmap
 * on to the driver, allowing management interfaces beyond ioctl.
 */
static ssize_t vfio_fops_read(struct file *filep, char __user *buf,
                  size_t count, loff_t *ppos)
{
    struct vfio_container *container = filep->private_data;
    struct vfio_iommu_driver *driver = container->iommu_driver;

    if (unlikely(!driver || !driver->ops->read))
        return -EINVAL;

    return driver->ops->read(container->iommu_data, buf, count, ppos);
}

static ssize_t vfio_fops_write(struct file *filep, const char __user *buf,
                   size_t count, loff_t *ppos)
{
    struct vfio_container *container = filep->private_data;
    struct vfio_iommu_driver *driver = container->iommu_driver;

    if (unlikely(!driver || !driver->ops->write))
        return -EINVAL;

    return driver->ops->write(container->iommu_data, buf, count, ppos);
}

static int vfio_fops_mmap(struct file *filep, struct vm_area_struct *vma)
{
    struct vfio_container *container = filep->private_data;
    struct vfio_iommu_driver *driver = container->iommu_driver;

    if (unlikely(!driver || !driver->ops->mmap))
        return -EINVAL;

    return driver->ops->mmap(container->iommu_data, vma);
}

static const struct file_operations vfio_fops = {
    .owner      = THIS_MODULE,
    .open       = vfio_fops_open,
    .release    = vfio_fops_release,
    .read       = vfio_fops_read,
    .write      = vfio_fops_write,
    .unlocked_ioctl = vfio_fops_unl_ioctl,
#ifdef CONFIG_COMPAT
    .compat_ioctl   = vfio_fops_compat_ioctl,
#endif
    .mmap       = vfio_fops_mmap,
};

static void __vfio_group_unset_container(struct vfio_group *group)
{
    struct vfio_container *container = group->container;
    struct vfio_iommu_driver *driver;

    mutex_lock(&container->group_lock);

    driver = container->iommu_driver;
    if (driver)
        driver->ops->detach_group(container->iommu_data,
                      group->iommu_group);

    group->container = NULL;
    list_del(&group->container_next);

    /* Detaching the last group deprivileges a container, remove iommu */
    if (driver && list_empty(&container->group_list)) {
        driver->ops->release(container->iommu_data);
        module_put(driver->ops->owner);
        container->iommu_driver = NULL;
        container->iommu_data = NULL;
    }

    mutex_unlock(&container->group_lock);

    vfio_container_put(container);
}

/*
 * VFIO_GROUP_UNSET_CONTAINER should fail if there are other users or
 * if there was no container to unset.  Since the ioctl is called on
 * the group, we know that still exists, therefore the only valid
 * transition here is 1->0.
 */
static int vfio_group_unset_container(struct vfio_group *group)
{
    int users = atomic_cmpxchg(&group->container_users, 1, 0);

    if (!users)
        return -EINVAL;
    if (users != 1)
        return -EBUSY;

    __vfio_group_unset_container(group);

    return 0;
}

/*
 * When removing container users, anything that removes the last user
 * implicitly removes the group from the container.  That is, if the
 * group file descriptor is closed, as well as any device file descriptors,
 * the group is free.
 */
static void vfio_group_try_dissolve_container(struct vfio_group *group)
{
    if (0 == atomic_dec_if_positive(&group->container_users))
        __vfio_group_unset_container(group);
}

static int vfio_group_set_container(struct vfio_group *group, int container_fd)
{
    struct fd f;
    struct vfio_container *container;
    struct vfio_iommu_driver *driver;
    int ret = 0;

    if (atomic_read(&group->container_users))
        return -EINVAL;

    f = fdget(container_fd);
    if (!f.file)
        return -EBADF;

    /* Sanity check, is this really our fd? */
    if (f.file->f_op != &vfio_fops) {
        fdput(f);
        return -EINVAL;
    }

    container = f.file->private_data;
    WARN_ON(!container); /* fget ensures we don't race vfio_release */

    mutex_lock(&container->group_lock);

    driver = container->iommu_driver;
    if (driver) {
        ret = driver->ops->attach_group(container->iommu_data,
                        group->iommu_group);
        if (ret)
            goto unlock_out;
    }

    group->container = container;
    list_add(&group->container_next, &container->group_list);

    /* Get a reference on the container and mark a user within the group */
    vfio_container_get(container);
    atomic_inc(&group->container_users);

unlock_out:
    mutex_unlock(&container->group_lock);
    fdput(f);
    return ret;
}

static bool vfio_group_viable(struct vfio_group *group)
{
    return (iommu_group_for_each_dev(group->iommu_group,
                     group, vfio_dev_viable) == 0);
}

static const struct file_operations vfio_device_fops;

static int vfio_group_get_device_fd(struct vfio_group *group, char *buf)
{
    struct vfio_device *device;
    struct file *filep;
    int ret = -ENODEV;

    if (0 == atomic_read(&group->container_users) ||
        !group->container->iommu_driver || !vfio_group_viable(group))
        return -EINVAL;

    mutex_lock(&group->device_lock);
    list_for_each_entry(device, &group->device_list, group_next) {
        if (strcmp(dev_name(device->dev), buf))
            continue;

        ret = device->ops->open(device->device_data);
        if (ret)
            break;
        /*
         * We can't use anon_inode_getfd() because we need to modify
         * the f_mode flags directly to allow more than just ioctls
         */
        ret = get_unused_fd();
        if (ret < 0) {
            device->ops->release(device->device_data);
            break;
        }

        filep = anon_inode_getfile("[vfio-device]", &vfio_device_fops,
                       device, O_RDWR);
        if (IS_ERR(filep)) {
            put_unused_fd(ret);
            ret = PTR_ERR(filep);
            device->ops->release(device->device_data);
            break;
        }

        /*
         * TODO: add an anon_inode interface to do this.
         * Appears to be missing by lack of need rather than
         * explicitly prevented.  Now there's need.
         */
        filep->f_mode |= (FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE);

        vfio_device_get(device);
        atomic_inc(&group->container_users);

        fd_install(ret, filep);
        break;
    }
    mutex_unlock(&group->device_lock);

    return ret;
}

static long vfio_group_fops_unl_ioctl(struct file *filep,
                      unsigned int cmd, unsigned long arg)
{
    struct vfio_group *group = filep->private_data;
    long ret = -ENOTTY;

    switch (cmd) {
    case VFIO_GROUP_GET_STATUS:
    {
        struct vfio_group_status status;
        unsigned long minsz;

        minsz = offsetofend(struct vfio_group_status, flags);

        if (copy_from_user(&status, (void __user *)arg, minsz))
            return -EFAULT;

        if (status.argsz < minsz)
            return -EINVAL;

        status.flags = 0;

        if (vfio_group_viable(group))
            status.flags |= VFIO_GROUP_FLAGS_VIABLE;

        if (group->container)
            status.flags |= VFIO_GROUP_FLAGS_CONTAINER_SET;

        if (copy_to_user((void __user *)arg, &status, minsz))
            return -EFAULT;

        ret = 0;
        break;
    }
    case VFIO_GROUP_SET_CONTAINER:
    {
        int fd;

        if (get_user(fd, (int __user *)arg))
            return -EFAULT;

        if (fd < 0)
            return -EINVAL;

        ret = vfio_group_set_container(group, fd);
        break;
    }
    case VFIO_GROUP_UNSET_CONTAINER:
        ret = vfio_group_unset_container(group);
        break;
    case VFIO_GROUP_GET_DEVICE_FD:
    {
        char *buf;

        buf = strndup_user((const char __user *)arg, PAGE_SIZE);
        if (IS_ERR(buf))
            return PTR_ERR(buf);

        ret = vfio_group_get_device_fd(group, buf);
        kfree(buf);
        break;
    }
    }

    return ret;
}

#ifdef CONFIG_COMPAT
static long vfio_group_fops_compat_ioctl(struct file *filep,
                     unsigned int cmd, unsigned long arg)
{
    arg = (unsigned long)compat_ptr(arg);
    return vfio_group_fops_unl_ioctl(filep, cmd, arg);
}
#endif  /* CONFIG_COMPAT */

static int vfio_group_fops_open(struct inode *inode, struct file *filep)
{
    struct vfio_group *group;

    group = vfio_group_get_from_minor(iminor(inode));
    if (!group)
        return -ENODEV;

    if (group->container) {
        vfio_group_put(group);
        return -EBUSY;
    }

    filep->private_data = group;

    return 0;
}

static int vfio_group_fops_release(struct inode *inode, struct file *filep)
{
    struct vfio_group *group = filep->private_data;

    filep->private_data = NULL;

    vfio_group_try_dissolve_container(group);

    vfio_group_put(group);

    return 0;
}

static const struct file_operations vfio_group_fops = {
    .owner      = THIS_MODULE,
    .unlocked_ioctl = vfio_group_fops_unl_ioctl,
#ifdef CONFIG_COMPAT
    .compat_ioctl   = vfio_group_fops_compat_ioctl,
#endif
    .open       = vfio_group_fops_open,
    .release    = vfio_group_fops_release,
};

static int vfio_device_fops_release(struct inode *inode, struct file *filep)
{
    struct vfio_device *device = filep->private_data;

    device->ops->release(device->device_data);

    vfio_group_try_dissolve_container(device->group);

    vfio_device_put(device);

    return 0;
}

static long vfio_device_fops_unl_ioctl(struct file *filep,
                       unsigned int cmd, unsigned long arg)
{
    struct vfio_device *device = filep->private_data;

    if (unlikely(!device->ops->ioctl))
        return -EINVAL;

    return device->ops->ioctl(device->device_data, cmd, arg);
}

static ssize_t vfio_device_fops_read(struct file *filep, char __user *buf,
                     size_t count, loff_t *ppos)
{
    struct vfio_device *device = filep->private_data;

    if (unlikely(!device->ops->read))
        return -EINVAL;

    return device->ops->read(device->device_data, buf, count, ppos);
}

static ssize_t vfio_device_fops_write(struct file *filep,
                      const char __user *buf,
                      size_t count, loff_t *ppos)
{
    struct vfio_device *device = filep->private_data;

    if (unlikely(!device->ops->write))
        return -EINVAL;

    return device->ops->write(device->device_data, buf, count, ppos);
}

static int vfio_device_fops_mmap(struct file *filep, struct vm_area_struct *vma)
{
    struct vfio_device *device = filep->private_data;

    if (unlikely(!device->ops->mmap))
        return -EINVAL;

    return device->ops->mmap(device->device_data, vma);
}

#ifdef CONFIG_COMPAT
static long vfio_device_fops_compat_ioctl(struct file *filep,
                      unsigned int cmd, unsigned long arg)
{
    arg = (unsigned long)compat_ptr(arg);
    return vfio_device_fops_unl_ioctl(filep, cmd, arg);
}
#endif  /* CONFIG_COMPAT */

static const struct file_operations vfio_device_fops = {
    .owner      = THIS_MODULE,
    .release    = vfio_device_fops_release,
    .read       = vfio_device_fops_read,
    .write      = vfio_device_fops_write,
    .unlocked_ioctl = vfio_device_fops_unl_ioctl,
#ifdef CONFIG_COMPAT
    .compat_ioctl   = vfio_device_fops_compat_ioctl,
#endif
    .mmap       = vfio_device_fops_mmap,
};

static char *vfio_devnode(struct device *dev, umode_t *mode)
{
    return kasprintf(GFP_KERNEL, "vfio/%s", dev_name(dev));
}

static int __init vfio_init(void)
{
    int ret;

    idr_init(&vfio.group_idr);
    mutex_init(&vfio.group_lock);
    mutex_init(&vfio.iommu_drivers_lock);
    INIT_LIST_HEAD(&vfio.group_list);
    INIT_LIST_HEAD(&vfio.iommu_drivers_list);
    init_waitqueue_head(&vfio.release_q);

    vfio.class = class_create(THIS_MODULE, "vfio");
    if (IS_ERR(vfio.class)) {
        ret = PTR_ERR(vfio.class);
        goto err_class;
    }

    vfio.class->devnode = vfio_devnode;

    ret = alloc_chrdev_region(&vfio.devt, 0, MINORMASK, "vfio");
    if (ret)
        goto err_base_chrdev;

    cdev_init(&vfio.cdev, &vfio_fops);
    ret = cdev_add(&vfio.cdev, vfio.devt, 1);
    if (ret)
        goto err_base_cdev;

    vfio.dev = device_create(vfio.class, NULL, vfio.devt, NULL, "vfio");
    if (IS_ERR(vfio.dev)) {
        ret = PTR_ERR(vfio.dev);
        goto err_base_dev;
    }

    /* /dev/vfio/$GROUP */
    cdev_init(&vfio.group_cdev, &vfio_group_fops);
    ret = cdev_add(&vfio.group_cdev,
               MKDEV(MAJOR(vfio.devt), 1), MINORMASK - 1);
    if (ret)
        goto err_groups_cdev;

    pr_info(DRIVER_DESC " version: " DRIVER_VERSION "\n");

    /*
     * Attempt to load known iommu-drivers.  This gives us a working
     * environment without the user needing to explicitly load iommu
     * drivers.
     */
    request_module_nowait("vfio_iommu_type1");

    return 0;

err_groups_cdev:
    device_destroy(vfio.class, vfio.devt);
err_base_dev:
    cdev_del(&vfio.cdev);
err_base_cdev:
    unregister_chrdev_region(vfio.devt, MINORMASK);
err_base_chrdev:
    class_destroy(vfio.class);
    vfio.class = NULL;
err_class:
    return ret;
}

static void __exit vfio_cleanup(void)
{
    WARN_ON(!list_empty(&vfio.group_list));

    idr_destroy(&vfio.group_idr);
    cdev_del(&vfio.group_cdev);
    device_destroy(vfio.class, vfio.devt);
    cdev_del(&vfio.cdev);
    unregister_chrdev_region(vfio.devt, MINORMASK);
    class_destroy(vfio.class);
    vfio.class = NULL;
}

module_init(vfio_init);
module_exit(vfio_cleanup);

MODULE_VERSION(DRIVER_VERSION);
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR(DRIVER_AUTHOR);
MODULE_DESCRIPTION(DRIVER_DESC);