tracing/filter: Do not WARN on operand count going below zero

[deliverable/linux.git] / drivers / vfio / vfio.c

/*
 * VFIO core
 *
 * Copyright (C) 2012 Red Hat, Inc.  All rights reserved.
 *     Author: Alex Williamson <alex.williamson@redhat.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:
 * Copyright 2010 Cisco Systems, Inc.  All rights reserved.
 * Author: Tom Lyon, pugs@cisco.com
 */

#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/miscdevice.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/rwsem.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/stat.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 <alex.williamson@redhat.com>"
#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;
        dev_t                           group_devt;
        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 rw_semaphore             group_lock;
        struct vfio_iommu_driver        *iommu_driver;
        void                            *iommu_data;
};

struct vfio_unbound_dev {
        struct device                   *dev;
        struct list_head                unbound_next;
};

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 list_head                unbound_list;
        struct mutex                    unbound_lock;
        atomic_t                        opened;
};

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;
};

/**
 * IOMMU driver registration
 */
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);

/**
 * Group minor allocation/free - both called with vfio.group_lock held
 */
static int vfio_alloc_group_minor(struct vfio_group *group)
{
        return idr_alloc(&vfio.group_idr, group, 0, MINORMASK + 1, GFP_KERNEL);
}

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);

/**
 * Container objects - containers are created when /dev/vfio/vfio is
 * opened, but their lifecycle extends until the last user is done, so
 * it's freed via kref.  Must support container/group/device being
 * closed in any order.
 */
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 void vfio_group_unlock_and_free(struct vfio_group *group)
{
        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);
}

/**
 * Group objects - create, release, get, put, search
 */
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);
        INIT_LIST_HEAD(&group->unbound_list);
        mutex_init(&group->unbound_lock);
        atomic_set(&group->container_users, 0);
        atomic_set(&group->opened, 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);

        /* 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_group_unlock_and_free(group);
                        return tmp;
                }
        }

        minor = vfio_alloc_group_minor(group);
        if (minor < 0) {
                vfio_group_unlock_and_free(group);
                return ERR_PTR(minor);
        }

        dev = device_create(vfio.class, NULL,
                            MKDEV(MAJOR(vfio.group_devt), minor),
                            group, "%d", iommu_group_id(iommu_group));
        if (IS_ERR(dev)) {
                vfio_free_group_minor(minor);
                vfio_group_unlock_and_free(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);
        struct vfio_unbound_dev *unbound, *tmp;
        struct iommu_group *iommu_group = group->iommu_group;

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

        list_for_each_entry_safe(unbound, tmp,
                                 &group->unbound_list, unbound_next) {
                list_del(&unbound->unbound_next);
                kfree(unbound);
        }

        device_destroy(vfio.class, MKDEV(MAJOR(vfio.group_devt), group->minor));
        list_del(&group->vfio_next);
        vfio_free_group_minor(group->minor);
        vfio_group_unlock_and_free(group);
        iommu_group_put(iommu_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;
}

/**
 * Device objects - create, release, get, put, search
 */
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;

        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;
        dev_set_drvdata(dev, device);

        /* 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 */
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);
}
EXPORT_SYMBOL_GPL(vfio_device_put);

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", "pcieport" };

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 in
 * one of the following states:
 *  - driver-less
 *  - bound to a vfio driver
 *  - bound to a whitelisted driver
 *
 * We use two methods to determine whether a device is bound to a vfio
 * driver.  The first is to test whether the device exists in the vfio
 * group.  The second is to test if the device exists on the group
 * unbound_list, indicating it's in the middle of transitioning from
 * a vfio driver to driver-less.
 */
static int vfio_dev_viable(struct device *dev, void *data)
{
        struct vfio_group *group = data;
        struct vfio_device *device;
        struct device_driver *drv = ACCESS_ONCE(dev->driver);
        struct vfio_unbound_dev *unbound;
        int ret = -EINVAL;

        mutex_lock(&group->unbound_lock);
        list_for_each_entry(unbound, &group->unbound_list, unbound_next) {
                if (dev == unbound->dev) {
                        ret = 0;
                        break;
                }
        }
        mutex_unlock(&group->unbound_lock);

        if (!ret || !drv || vfio_whitelisted_driver(drv))
                return 0;

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

        return ret;
}

/**
 * Async device support
 */
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_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;
        struct vfio_unbound_dev *unbound;

        /*
         * Need to go through a group_lock lookup to get a reference or we
         * risk racing a group being removed.  Ignore spurious notifies.
         */
        group = vfio_group_try_get(group);
        if (!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:
                /*
                 * Nothing to do here.  If the device is in use, then the
                 * vfio sub-driver should block the remove callback until
                 * it is unused.  If the device is unused or attached to a
                 * stub driver, then it should be released and we don't
                 * care that it will be going away.
                 */
                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.
                 */

                mutex_lock(&group->unbound_lock);
                list_for_each_entry(unbound,
                                    &group->unbound_list, unbound_next) {
                        if (dev == unbound->dev) {
                                list_del(&unbound->unbound_next);
                                kfree(unbound);
                                break;
                        }
                }
                mutex_unlock(&group->unbound_lock);
                break;
        }

        vfio_group_put(group);
        return NOTIFY_OK;
}

/**
 * VFIO driver API
 */
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);
                }
        } else {
                /*
                 * A found vfio_group already holds a reference to the
                 * iommu_group.  A created vfio_group keeps the reference.
                 */
                iommu_group_put(iommu_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);
                return -EBUSY;
        }

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

        /*
         * Drop all but the vfio_device reference.  The vfio_device holds
         * a reference to the vfio_group, which holds a reference to the
         * iommu_group.
         */
        vfio_group_put(group);

        return 0;
}
EXPORT_SYMBOL_GPL(vfio_add_group_dev);

/**
 * Get a reference to the vfio_device for a device that is known to
 * be bound to a vfio driver.  The driver implicitly holds a
 * vfio_device reference between vfio_add_group_dev and
 * vfio_del_group_dev.  We can therefore use drvdata to increment
 * that reference from the struct device.  This additional
 * reference must be released by calling vfio_device_put.
 */
struct vfio_device *vfio_device_get_from_dev(struct device *dev)
{
        struct vfio_device *device = dev_get_drvdata(dev);

        vfio_device_get(device);

        return device;
}
EXPORT_SYMBOL_GPL(vfio_device_get_from_dev);

/*
 * Caller must hold a reference to the vfio_device
 */
void *vfio_device_data(struct vfio_device *device)
{
        return device->device_data;
}
EXPORT_SYMBOL_GPL(vfio_device_data);

/* Given a referenced group, check if it contains the device */
static bool vfio_dev_present(struct vfio_group *group, struct device *dev)
{
        struct vfio_device *device;

        device = vfio_group_get_device(group, dev);
        if (!device)
                return false;

        vfio_device_put(device);
        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;
        void *device_data = device->device_data;
        struct vfio_unbound_dev *unbound;
        unsigned int i = 0;
        long ret;
        bool interrupted = false;

        /*
         * The group exists so long as we have a device reference.  Get
         * a group reference and use it to scan for the device going away.
         */
        vfio_group_get(group);

        /*
         * When the device is removed from the group, the group suddenly
         * becomes non-viable; the device has a driver (until the unbind
         * completes), but it's not present in the group.  This is bad news
         * for any external users that need to re-acquire a group reference
         * in order to match and release their existing reference.  To
         * solve this, we track such devices on the unbound_list to bridge
         * the gap until they're fully unbound.
         */
        unbound = kzalloc(sizeof(*unbound), GFP_KERNEL);
        if (unbound) {
                unbound->dev = dev;
                mutex_lock(&group->unbound_lock);
                list_add(&unbound->unbound_next, &group->unbound_list);
                mutex_unlock(&group->unbound_lock);
        }
        WARN_ON(!unbound);

        vfio_device_put(device);

        /*
         * If the device is still present in the group after the above
         * 'put', then it is in use and we need to request it from the
         * bus driver.  The driver may in turn need to request the
         * device from the user.  We send the request on an arbitrary
         * interval with counter to allow the driver to take escalating
         * measures to release the device if it has the ability to do so.
         */
        do {
                device = vfio_group_get_device(group, dev);
                if (!device)
                        break;

                if (device->ops->request)
                        device->ops->request(device_data, i++);

                vfio_device_put(device);

                if (interrupted) {
                        ret = wait_event_timeout(vfio.release_q,
                                        !vfio_dev_present(group, dev), HZ * 10);
                } else {
                        ret = wait_event_interruptible_timeout(vfio.release_q,
                                        !vfio_dev_present(group, dev), HZ * 10);
                        if (ret == -ERESTARTSYS) {
                                interrupted = true;
                                dev_warn(dev,
                                         "Device is currently in use, task"
                                         " \"%s\" (%d) "
                                         "blocked until device is released",
                                         current->comm, task_pid_nr(current));
                        }
                }
        } while (ret <= 0);

        vfio_group_put(group);

        return device_data;
}
EXPORT_SYMBOL_GPL(vfio_del_group_dev);

/**
 * VFIO base fd, /dev/vfio/vfio
 */
static long vfio_ioctl_check_extension(struct vfio_container *container,
                                       unsigned long arg)
{
        struct vfio_iommu_driver *driver;
        long ret = 0;

        down_read(&container->group_lock);

        driver = container->iommu_driver;

        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);
        }

        up_read(&container->group_lock);

        return ret;
}

/* hold write lock on 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;

        down_write(&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) {
                up_write(&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:
        up_write(&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;

        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:
                down_read(&container->group_lock);

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

                if (driver) /* passthrough all unrecognized ioctls */
                        ret = driver->ops->ioctl(data, cmd, arg);

                up_read(&container->group_lock);
        }

        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);
        init_rwsem(&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;
        ssize_t ret = -EINVAL;

        down_read(&container->group_lock);

        driver = container->iommu_driver;
        if (likely(driver && driver->ops->read))
                ret = driver->ops->read(container->iommu_data,
                                        buf, count, ppos);

        up_read(&container->group_lock);

        return ret;
}

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;
        ssize_t ret = -EINVAL;

        down_read(&container->group_lock);

        driver = container->iommu_driver;
        if (likely(driver && driver->ops->write))
                ret = driver->ops->write(container->iommu_data,
                                         buf, count, ppos);

        up_read(&container->group_lock);

        return ret;
}

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;
        int ret = -EINVAL;

        down_read(&container->group_lock);

        driver = container->iommu_driver;
        if (likely(driver && driver->ops->mmap))
                ret = driver->ops->mmap(container->iommu_data, vma);

        up_read(&container->group_lock);

        return ret;
}

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,
};

/**
 * VFIO Group fd, /dev/vfio/$GROUP
 */
static void __vfio_group_unset_container(struct vfio_group *group)
{
        struct vfio_container *container = group->container;
        struct vfio_iommu_driver *driver;

        down_write(&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;
        }

        up_write(&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 */

        down_write(&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:
        up_write(&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_flags(O_CLOEXEC);
                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;
        int opened;

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

        /* Do we need multiple instances of the group open?  Seems not. */
        opened = atomic_cmpxchg(&group->opened, 0, 1);
        if (opened) {
                vfio_group_put(group);
                return -EBUSY;
        }

        /* Is something still in use from a previous open? */
        if (group->container) {
                atomic_dec(&group->opened);
                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);

        atomic_dec(&group->opened);

        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,
};

/**
 * VFIO Device fd
 */
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,
};

/**
 * External user API, exported by symbols to be linked dynamically.
 *
 * The protocol includes:
 *  1. do normal VFIO init operation:
 *      - opening a new container;
 *      - attaching group(s) to it;
 *      - setting an IOMMU driver for a container.
 * When IOMMU is set for a container, all groups in it are
 * considered ready to use by an external user.
 *
 * 2. User space passes a group fd to an external user.
 * The external user calls vfio_group_get_external_user()
 * to verify that:
 *      - the group is initialized;
 *      - IOMMU is set for it.
 * If both checks passed, vfio_group_get_external_user()
 * increments the container user counter to prevent
 * the VFIO group from disposal before KVM exits.
 *
 * 3. The external user calls vfio_external_user_iommu_id()
 * to know an IOMMU ID.
 *
 * 4. When the external KVM finishes, it calls
 * vfio_group_put_external_user() to release the VFIO group.
 * This call decrements the container user counter.
 */
struct vfio_group *vfio_group_get_external_user(struct file *filep)
{
        struct vfio_group *group = filep->private_data;

        if (filep->f_op != &vfio_group_fops)
                return ERR_PTR(-EINVAL);

        if (!atomic_inc_not_zero(&group->container_users))
                return ERR_PTR(-EINVAL);

        if (!group->container->iommu_driver ||
                        !vfio_group_viable(group)) {
                atomic_dec(&group->container_users);
                return ERR_PTR(-EINVAL);
        }

        vfio_group_get(group);

        return group;
}
EXPORT_SYMBOL_GPL(vfio_group_get_external_user);

void vfio_group_put_external_user(struct vfio_group *group)
{
        vfio_group_put(group);
        vfio_group_try_dissolve_container(group);
}
EXPORT_SYMBOL_GPL(vfio_group_put_external_user);

int vfio_external_user_iommu_id(struct vfio_group *group)
{
        return iommu_group_id(group->iommu_group);
}
EXPORT_SYMBOL_GPL(vfio_external_user_iommu_id);

long vfio_external_check_extension(struct vfio_group *group, unsigned long arg)
{
        return vfio_ioctl_check_extension(group->container, arg);
}
EXPORT_SYMBOL_GPL(vfio_external_check_extension);

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

static struct miscdevice vfio_dev = {
        .minor = VFIO_MINOR,
        .name = "vfio",
        .fops = &vfio_fops,
        .nodename = "vfio/vfio",
        .mode = S_IRUGO | S_IWUGO,
};

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);

        ret = misc_register(&vfio_dev);
        if (ret) {
                pr_err("vfio: misc device register failed\n");
                return ret;
        }

        /* /dev/vfio/$GROUP */
        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.group_devt, 0, MINORMASK, "vfio");
        if (ret)
                goto err_alloc_chrdev;

        cdev_init(&vfio.group_cdev, &vfio_group_fops);
        ret = cdev_add(&vfio.group_cdev, vfio.group_devt, MINORMASK);
        if (ret)
                goto err_cdev_add;

        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");
        request_module_nowait("vfio_iommu_spapr_tce");

        return 0;

err_cdev_add:
        unregister_chrdev_region(vfio.group_devt, MINORMASK);
err_alloc_chrdev:
        class_destroy(vfio.class);
        vfio.class = NULL;
err_class:
        misc_deregister(&vfio_dev);
        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);
        unregister_chrdev_region(vfio.group_devt, MINORMASK);
        class_destroy(vfio.class);
        vfio.class = NULL;
        misc_deregister(&vfio_dev);
}

module_init(vfio_init);
module_exit(vfio_cleanup);

MODULE_VERSION(DRIVER_VERSION);
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR(DRIVER_AUTHOR);
MODULE_DESCRIPTION(DRIVER_DESC);
MODULE_ALIAS_MISCDEV(VFIO_MINOR);
MODULE_ALIAS("devname:vfio/vfio");