vfio.c

/*
 * VFIO-KVM bridge pseudo device
 *
 * Copyright (C) 2013 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.
 */

#include <linux/errno.h>
#include <linux/file.h>
#include <linux/kvm_host.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/vfio.h>

struct kvm_vfio_group {
	struct list_head node;
	struct vfio_group *vfio_group;
};

struct kvm_vfio {
	struct list_head group_list;
	struct mutex lock;
	bool noncoherent;
};

static struct vfio_group *kvm_vfio_group_get_external_user(struct file *filep)
{
	struct vfio_group *vfio_group;
	struct vfio_group *(*fn)(struct file *);

	fn = symbol_get(vfio_group_get_external_user);
	if (!fn)
		return ERR_PTR(-EINVAL);

	vfio_group = fn(filep);

	symbol_put(vfio_group_get_external_user);

	return vfio_group;
}

static void kvm_vfio_group_put_external_user(struct vfio_group *vfio_group)
{
	void (*fn)(struct vfio_group *);

	fn = symbol_get(vfio_group_put_external_user);
	if (!fn)
		return;

	fn(vfio_group);

	symbol_put(vfio_group_put_external_user);
}

/*
 * Groups can use the same or different IOMMU domains.  If the same then
 * adding a new group may change the coherency of groups we've previously
 * been told about.  We don't want to care about any of that so we retest
 * each group and bail as soon as we find one that's noncoherent.  This
 * means we only ever [un]register_noncoherent_dma once for the whole device.
 */
static void kvm_vfio_update_coherency(struct kvm_device *dev)
{
	struct kvm_vfio *kv = dev->private;
	bool noncoherent = false;
	struct kvm_vfio_group *kvg;

	mutex_lock(&kv->lock);

	list_for_each_entry(kvg, &kv->group_list, node) {
		/*
		 * TODO: We need an interface to check the coherency of
		 * the IOMMU domain this group is using.  For now, assume
		 * it's always noncoherent.
		 */
		noncoherent = true;
		break;
	}

	if (noncoherent != kv->noncoherent) {
		kv->noncoherent = noncoherent;

		if (kv->noncoherent)
			kvm_arch_register_noncoherent_dma(dev->kvm);
		else
			kvm_arch_unregister_noncoherent_dma(dev->kvm);
	}

	mutex_unlock(&kv->lock);
}

static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
{
	struct kvm_vfio *kv = dev->private;
	struct vfio_group *vfio_group;
	struct kvm_vfio_group *kvg;
	void __user *argp = (void __user *)arg;
	struct fd f;
	int32_t fd;
	int ret;

	switch (attr) {
	case KVM_DEV_VFIO_GROUP_ADD:
		if (get_user(fd, (int32_t __user *)argp))
			return -EFAULT;

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

		vfio_group = kvm_vfio_group_get_external_user(f.file);
		fdput(f);

		if (IS_ERR(vfio_group))
			return PTR_ERR(vfio_group);

		mutex_lock(&kv->lock);

		list_for_each_entry(kvg, &kv->group_list, node) {
			if (kvg->vfio_group == vfio_group) {
				mutex_unlock(&kv->lock);
				kvm_vfio_group_put_external_user(vfio_group);
				return -EEXIST;
			}
		}

		kvg = kzalloc(sizeof(*kvg), GFP_KERNEL);
		if (!kvg) {
			mutex_unlock(&kv->lock);
			kvm_vfio_group_put_external_user(vfio_group);
			return -ENOMEM;
		}

		list_add_tail(&kvg->node, &kv->group_list);
		kvg->vfio_group = vfio_group;

		mutex_unlock(&kv->lock);

		kvm_vfio_update_coherency(dev);

		return 0;

	case KVM_DEV_VFIO_GROUP_DEL:
		if (get_user(fd, (int32_t __user *)argp))
			return -EFAULT;

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

		vfio_group = kvm_vfio_group_get_external_user(f.file);
		fdput(f);

		if (IS_ERR(vfio_group))
			return PTR_ERR(vfio_group);

		ret = -ENOENT;

		mutex_lock(&kv->lock);

		list_for_each_entry(kvg, &kv->group_list, node) {
			if (kvg->vfio_group != vfio_group)
				continue;

			list_del(&kvg->node);
			kvm_vfio_group_put_external_user(kvg->vfio_group);
			kfree(kvg);
			ret = 0;
			break;
		}

		mutex_unlock(&kv->lock);

		kvm_vfio_group_put_external_user(vfio_group);

		kvm_vfio_update_coherency(dev);

		return ret;
	}

	return -ENXIO;
}

static int kvm_vfio_set_attr(struct kvm_device *dev,
			     struct kvm_device_attr *attr)
{
	switch (attr->group) {
	case KVM_DEV_VFIO_GROUP:
		return kvm_vfio_set_group(dev, attr->attr, attr->addr);
	}

	return -ENXIO;
}

static int kvm_vfio_has_attr(struct kvm_device *dev,
			     struct kvm_device_attr *attr)
{
	switch (attr->group) {
	case KVM_DEV_VFIO_GROUP:
		switch (attr->attr) {
		case KVM_DEV_VFIO_GROUP_ADD:
		case KVM_DEV_VFIO_GROUP_DEL:
			return 0;
		}

		break;
	}

	return -ENXIO;
}

static void kvm_vfio_destroy(struct kvm_device *dev)
{
	struct kvm_vfio *kv = dev->private;
	struct kvm_vfio_group *kvg, *tmp;

	list_for_each_entry_safe(kvg, tmp, &kv->group_list, node) {
		kvm_vfio_group_put_external_user(kvg->vfio_group);
		list_del(&kvg->node);
		kfree(kvg);
	}

	kvm_vfio_update_coherency(dev);

	kfree(kv);
	kfree(dev); /* alloc by kvm_ioctl_create_device, free by .destroy */
}

static int kvm_vfio_create(struct kvm_device *dev, u32 type)
{
	struct kvm_device *tmp;
	struct kvm_vfio *kv;

	/* Only one VFIO "device" per VM */
	list_for_each_entry(tmp, &dev->kvm->devices, vm_node)
		if (tmp->ops == &kvm_vfio_ops)
			return -EBUSY;

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

	INIT_LIST_HEAD(&kv->group_list);
	mutex_init(&kv->lock);

	dev->private = kv;

	return 0;
}

struct kvm_device_ops kvm_vfio_ops = {
	.name = "kvm-vfio",
	.create = kvm_vfio_create,
	.destroy = kvm_vfio_destroy,
	.set_attr = kvm_vfio_set_attr,
	.has_attr = kvm_vfio_has_attr,
};