Subject: [PATCH v5] Support for dummy vfio iommu driver.

This is primarily required for supporting vfio direct device assignment on platforms
that don't have a hardware IOMMU.

Signed-off-by: Varun Sethi <Varun.Sethi@freescale.com>
Change-Id: Id3e968a7c4110fe392354b053112e2dc083adebd
Reviewed-on: http://git.am.freescale.net:8181/2401
Reviewed-by: Wood Scott-B07421 <scottwood@freescale.com>
Reviewed-by: Yoder Stuart-B08248 <stuart.yoder@freescale.com>
Reviewed-by: Bhushan Bharat-R65777 <Bharat.Bhushan@freescale.com>
Reviewed-by: Fleming Andrew-AFLEMING <AFLEMING@freescale.com>
Tested-by: Fleming Andrew-AFLEMING <AFLEMING@freescale.com>

3 files changed, 712 insertions, 0 deletions

diff --git a/drivers/vfio/Kconfig b/drivers/vfio/Kconfig
index 716536d..aba1d96 100644
--- a/drivers/vfio/Kconfig
+++ b/drivers/vfio/Kconfig
@@ -8,12 +8,17 @@ config VFIO_IOMMU_FSL_PAMU
 	depends on VFIO
 	default n
 
+config VFIO_IOMMU_DUMMY
+	tristate
+	depends on VFIO
+	default n
 
 menuconfig VFIO
 	tristate "VFIO Non-Privileged userspace driver framework"
 	depends on IOMMU_API
 	select VFIO_IOMMU_TYPE1 if X86
 	select VFIO_IOMMU_FSL_PAMU if FSL_PAMU
+	select VFIO_IOMMU_DUMMY if DUMMY_IOMMU
 	help
 	  VFIO provides a framework for secure userspace device drivers.
 	  See Documentation/vfio.txt for more details.
diff --git a/drivers/vfio/Makefile b/drivers/vfio/Makefile
index f68cc94..e4093c5 100644
--- a/drivers/vfio/Makefile
+++ b/drivers/vfio/Makefile
@@ -1,5 +1,6 @@
 obj-$(CONFIG_VFIO) += vfio.o
 obj-$(CONFIG_VFIO_IOMMU_TYPE1) += vfio_iommu_type1.o
 obj-$(CONFIG_VFIO_IOMMU_FSL_PAMU) += vfio_iommu_fsl_pamu.o
+obj-$(CONFIG_VFIO_IOMMU_DUMMY) += vfio_iommu_dummy.o
 obj-$(CONFIG_VFIO_PCI) += pci/
 obj-$(CONFIG_VFIO_FSL_PCI_EP) += fsl_pci_ep/
diff --git a/drivers/vfio/vfio_iommu_dummy.c b/drivers/vfio/vfio_iommu_dummy.c
new file mode 100644
index 0000000..865045a
--- /dev/null
+++ b/drivers/vfio/vfio_iommu_dummy.c
@@ -0,0 +1,706 @@
+/*
+ * VFIO: IOMMU DMA mapping support for systems without IOMMU
+ *
+ * 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.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ * Copyright (C) 2013 Freescale Semiconductor, Inc.
+ *
+ *     Author: Varun Sethi <varun.sethi@freescale.com>
+ *
+ * This file is derived from driver/vfio/vfio_iommu_type1.c and
+ * driver/vfio/vfio_iommu_fsl_pamu.c
+ * This driver is primarily targeted for providing direct device assignment
+ * on platforms that don't have a hardware IOMMU. The driver primarily
+ * pins the pages corresponding to the guest memory. The driver is enabled
+ * via /sys/kernel/vfio_iommu_dummy/enable_iommu_dummy attribute.
+ *
+ */
+
+#include <linux/compat.h>
+#include <linux/device.h>
+#include <linux/fs.h>
+#include <linux/iommu.h>
+#include <linux/module.h>
+#include <linux/mm.h>
+#include <linux/pci.h>		/* pci_bus_type */
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <linux/vfio.h>
+#include <linux/workqueue.h>
+#include <linux/hugetlb.h>
+
+struct vfio_iommu {
+	struct mutex		lock;
+	struct list_head	dma_list;
+	struct list_head	group_list;
+};
+
+struct vfio_dma {
+	struct list_head	next;
+	dma_addr_t		iova;		/* Device address */
+	unsigned long		vaddr;		/* Process virtual addr */
+	long			npage;		/* Number of pages */
+	int			prot;		/* IOMMU_READ/WRITE */
+};
+
+struct vfio_group {
+	struct iommu_group	*iommu_group;
+	struct list_head	next;
+};
+
+#define NPAGE_TO_SIZE(npage)	((size_t)(npage) << PAGE_SHIFT)
+
+struct vwork {
+	struct mm_struct	*mm;
+	long			npage;
+	struct work_struct	work;
+};
+
+static int enable_iommu_dummy;
+
+/* delayed decrement/increment for locked_vm */
+static void vfio_lock_acct_bg(struct work_struct *work)
+{
+	struct vwork *vwork = container_of(work, struct vwork, work);
+	struct mm_struct *mm;
+
+	mm = vwork->mm;
+	down_write(&mm->mmap_sem);
+	mm->locked_vm += vwork->npage;
+	up_write(&mm->mmap_sem);
+	mmput(mm);
+	kfree(vwork);
+}
+
+static void vfio_lock_acct(long npage)
+{
+	struct vwork *vwork;
+	struct mm_struct *mm;
+
+	if (!current->mm)
+		return; /* process exited */
+
+	if (down_write_trylock(&current->mm->mmap_sem)) {
+		current->mm->locked_vm += npage;
+		up_write(&current->mm->mmap_sem);
+		return;
+	}
+
+	/*
+	 * Couldn't get mmap_sem lock, so must setup to update
+	 * mm->locked_vm later. If locked_vm were atomic, we
+	 * wouldn't need this silliness
+	 */
+	vwork = kmalloc(sizeof(struct vwork), GFP_KERNEL);
+	if (!vwork)
+		return;
+	mm = get_task_mm(current);
+	if (!mm) {
+		kfree(vwork);
+		return;
+	}
+	INIT_WORK(&vwork->work, vfio_lock_acct_bg);
+	vwork->mm = mm;
+	vwork->npage = npage;
+	schedule_work(&vwork->work);
+}
+
+/*
+ * Some mappings aren't backed by a struct page, for example an mmap'd
+ * MMIO range for our own or another device.  These use a different
+ * pfn conversion and shouldn't be tracked as locked pages.
+ */
+static bool is_invalid_reserved_pfn(unsigned long pfn)
+{
+	if (pfn_valid(pfn)) {
+		bool reserved;
+		struct page *tail = pfn_to_page(pfn);
+		struct page *head = compound_trans_head(tail);
+		reserved = !!(PageReserved(head));
+		if (head != tail) {
+			/*
+			 * "head" is not a dangling pointer
+			 * (compound_trans_head takes care of that)
+			 * but the hugepage may have been split
+			 * from under us (and we may not hold a
+			 * reference count on the head page so it can
+			 * be reused before we run PageReferenced), so
+			 * we've to check PageTail before returning
+			 * what we just read.
+			 */
+			smp_rmb();
+			if (PageTail(tail))
+				return reserved;
+		}
+		return PageReserved(tail);
+	}
+
+	return true;
+}
+
+static int put_pfn(unsigned long pfn, int prot)
+{
+	if (!is_invalid_reserved_pfn(pfn)) {
+		struct page *page = pfn_to_page(pfn);
+		if (prot & IOMMU_WRITE)
+			SetPageDirty(page);
+		put_page(page);
+		return 1;
+	}
+	return 0;
+}
+
+static int vaddr_get_pfn(unsigned long vaddr, int prot, unsigned int nr_pages)
+{
+	struct page **pages;
+	int i, ret;
+	long locked = 0;
+
+	pages = kzalloc(sizeof(*pages) * nr_pages, GFP_KERNEL | __GFP_ZERO);
+	ret = get_user_pages_fast(vaddr, nr_pages, !!(prot & IOMMU_WRITE), pages);
+	if (ret != nr_pages)
+		goto error;
+
+	/* All Pages should be contiguous */
+	for (i = 1; i < nr_pages; i++) {
+		if (page_to_pfn(pages[i]) != page_to_pfn(pages[i - 1]) + 1)
+			goto error;
+		if (!is_invalid_reserved_pfn(page_to_pfn(pages[i])))
+			locked++;
+	}
+
+	vfio_lock_acct(locked);
+
+	kfree(pages);
+	return 0;
+error:
+	for (i = 0; i < nr_pages; i++)
+		if (pages[i])
+			put_page(pages[i]);
+	kfree(pages);
+	return -EFAULT;
+}
+
+/* Unmap DMA region */
+static long __vfio_dma_do_unmap(struct vfio_iommu *iommu, dma_addr_t iova,
+			     long npage, int prot)
+{
+	long unlocked = 0;
+	unsigned long size;
+	unsigned long pfn;
+	int i;
+
+	/* currently we support at most one huge page mapping */
+	size = npage << PAGE_SHIFT;
+	/* Release the pinned pages */
+	/* one is to one mapping iova = host physical*/
+	pfn = iova >> PAGE_SHIFT;
+	if (pfn) {
+		for (i = 0; i < npage; i++, pfn++)
+			unlocked += put_pfn(pfn, prot);
+	}
+
+
+	return unlocked;
+}
+
+static void vfio_dma_unmap(struct vfio_iommu *iommu, dma_addr_t iova,
+			   long npage, int prot)
+{
+	long unlocked;
+
+	unlocked = __vfio_dma_do_unmap(iommu, iova, npage, prot);
+	vfio_lock_acct(-unlocked);
+}
+
+static inline bool ranges_overlap(dma_addr_t start1, size_t size1,
+				  dma_addr_t start2, size_t size2)
+{
+	if (start1 < start2)
+		return (start2 - start1 < size1);
+	else if (start2 < start1)
+		return (start1 - start2 < size2);
+	return (size1 > 0 && size2 > 0);
+}
+
+static struct vfio_dma *vfio_find_dma(struct vfio_iommu *iommu,
+				      dma_addr_t start, size_t size)
+{
+	struct vfio_dma *dma;
+
+	list_for_each_entry(dma, &iommu->dma_list, next) {
+		if (ranges_overlap(dma->iova, NPAGE_TO_SIZE(dma->npage),
+				   start, size))
+			return dma;
+	}
+	return NULL;
+}
+
+static long vfio_remove_dma_overlap(struct vfio_iommu *iommu, dma_addr_t start,
+				    size_t size, struct vfio_dma *dma)
+{
+	struct vfio_dma *split;
+	long npage_lo, npage_hi;
+
+	/* Existing dma region is completely covered, unmap all */
+	if (start <= dma->iova &&
+	    start + size >= dma->iova + NPAGE_TO_SIZE(dma->npage)) {
+		vfio_dma_unmap(iommu, dma->iova, dma->npage, dma->prot);
+		list_del(&dma->next);
+		npage_lo = dma->npage;
+		kfree(dma);
+		return npage_lo;
+	}
+
+	/* Overlap low address of existing range */
+	if (start <= dma->iova) {
+		size_t overlap;
+
+		overlap = start + size - dma->iova;
+		npage_lo = overlap >> PAGE_SHIFT;
+
+		vfio_dma_unmap(iommu, dma->iova, npage_lo, dma->prot);
+		dma->iova += overlap;
+		dma->vaddr += overlap;
+		dma->npage -= npage_lo;
+		return npage_lo;
+	}
+
+	/* Overlap high address of existing range */
+	if (start + size >= dma->iova + NPAGE_TO_SIZE(dma->npage)) {
+		size_t overlap;
+
+		overlap = dma->iova + NPAGE_TO_SIZE(dma->npage) - start;
+		npage_hi = overlap >> PAGE_SHIFT;
+
+		vfio_dma_unmap(iommu, start, npage_hi, dma->prot);
+		dma->npage -= npage_hi;
+		return npage_hi;
+	}
+
+	/* Split existing */
+	npage_lo = (start - dma->iova) >> PAGE_SHIFT;
+	npage_hi = dma->npage - (size >> PAGE_SHIFT) - npage_lo;
+
+	split = kzalloc(sizeof(*split), GFP_KERNEL);
+	if (!split)
+		return -ENOMEM;
+
+	vfio_dma_unmap(iommu, start, size >> PAGE_SHIFT, dma->prot);
+
+	dma->npage = npage_lo;
+
+	split->npage = npage_hi;
+	split->iova = start + size;
+	split->vaddr = dma->vaddr + NPAGE_TO_SIZE(npage_lo) + size;
+	split->prot = dma->prot;
+	list_add(&split->next, &iommu->dma_list);
+	return size >> PAGE_SHIFT;
+}
+
+/* Map DMA region */
+static int __vfio_dma_map(struct vfio_iommu *iommu, dma_addr_t iova,
+			  unsigned long vaddr, long npage, int prot)
+{
+	int ret;
+
+	/*
+	 * XXX We break mappings into pages and use get_user_pages_fast to
+	 * pin the pages in memory.  It's been suggested that mlock might
+	 * provide a more efficient mechanism, but nothing prevents the
+	 * user from munlocking the pages, which could then allow the user
+	 * access to random host memory.  We also have no guarantee from the
+	 * IOMMU API that the iommu driver can unmap sub-pages of previous
+	 * mappings.  This means we might lose an entire range if a single
+	 * page within it is unmapped.  Single page mappings are inefficient,
+	 * but provide the most flexibility for now.
+	 */
+	ret = vaddr_get_pfn(vaddr, prot, npage);
+	if (ret) {
+		pr_err("%s unable to map vaddr = %lx\n",
+			__func__, vaddr);
+		__vfio_dma_do_unmap(iommu, iova, npage, prot);
+		return ret;
+	}
+
+	return 0;
+}
+
+static int vfio_dma_do_map(struct vfio_iommu *iommu,
+			   struct vfio_iommu_type1_dma_map *map)
+{
+	struct vfio_dma *dma, *pdma = NULL;
+	dma_addr_t iova = map->iova;
+	unsigned long locked, lock_limit, vaddr = map->vaddr;
+	size_t size = map->size;
+	int ret = 0, prot = 0;
+	long npage;
+
+	/* READ/WRITE from device perspective */
+	if (map->flags & VFIO_DMA_MAP_FLAG_WRITE)
+		prot |= IOMMU_WRITE;
+	if (map->flags & VFIO_DMA_MAP_FLAG_READ)
+		prot |= IOMMU_READ;
+
+	if (!prot)
+		return -EINVAL; /* No READ/WRITE? */
+
+	/* Don't allow IOVA wrap */
+	if (iova + size && iova + size < iova)
+		return -EINVAL;
+
+	/* Don't allow virtual address wrap */
+	if (vaddr + size && vaddr + size < vaddr)
+		return -EINVAL;
+
+	npage = size >> PAGE_SHIFT;
+	if (!npage)
+		return -EINVAL;
+
+	mutex_lock(&iommu->lock);
+
+	if (vfio_find_dma(iommu, iova, size)) {
+		ret = -EBUSY;
+		goto out_lock;
+	}
+
+	/* account for locked pages */
+	locked = current->mm->locked_vm + npage;
+	lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+	if (locked > lock_limit && !capable(CAP_IPC_LOCK)) {
+		pr_warn("%s: RLIMIT_MEMLOCK (%ld) exceeded\n",
+			__func__, rlimit(RLIMIT_MEMLOCK));
+		ret = -ENOMEM;
+		goto out_lock;
+	}
+
+	ret = __vfio_dma_map(iommu, iova, vaddr, npage, prot);
+	if (ret)
+		goto out_lock;
+
+	/* Check if we about a region below - nothing below 0 */
+	if (iova) {
+		dma = vfio_find_dma(iommu, iova - 1, 1);
+		if (dma && dma->prot == prot &&
+		    dma->vaddr + NPAGE_TO_SIZE(dma->npage) == vaddr) {
+
+			dma->npage += npage;
+			iova = dma->iova;
+			vaddr = dma->vaddr;
+			npage = dma->npage;
+			size = NPAGE_TO_SIZE(npage);
+
+			pdma = dma;
+		}
+	}
+
+	/* Check if we abut a region above - nothing above ~0 + 1 */
+	if (iova + size) {
+		dma = vfio_find_dma(iommu, iova + size, 1);
+		if (dma && dma->prot == prot &&
+		    dma->vaddr == vaddr + size) {
+
+			dma->npage += npage;
+			dma->iova = iova;
+			dma->vaddr = vaddr;
+
+			/*
+			 * If merged above and below, remove previously
+			 * merged entry.  New entry covers it.
+			 */
+			if (pdma) {
+				list_del(&pdma->next);
+				kfree(pdma);
+			}
+			pdma = dma;
+		}
+	}
+
+	/* Isolated, new region */
+	if (!pdma) {
+		dma = kzalloc(sizeof(*dma), GFP_KERNEL);
+		if (!dma) {
+			ret = -ENOMEM;
+			vfio_dma_unmap(iommu, iova, npage, prot);
+			goto out_lock;
+		}
+
+		dma->npage = npage;
+		dma->iova = iova;
+		dma->vaddr = vaddr;
+		dma->prot = prot;
+		list_add(&dma->next, &iommu->dma_list);
+	}
+
+out_lock:
+	mutex_unlock(&iommu->lock);
+	return ret;
+}
+
+static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
+			     struct vfio_iommu_type1_dma_unmap *unmap)
+{
+	long ret = 0, npage = unmap->size >> PAGE_SHIFT;
+	struct vfio_dma *dma, *tmp;
+
+	mutex_lock(&iommu->lock);
+
+	list_for_each_entry_safe(dma, tmp, &iommu->dma_list, next) {
+		if (ranges_overlap(dma->iova, NPAGE_TO_SIZE(dma->npage),
+				   unmap->iova, unmap->size)) {
+			ret = vfio_remove_dma_overlap(iommu, unmap->iova,
+						      unmap->size, dma);
+			if (ret > 0)
+				npage -= ret;
+			if (ret < 0 || npage == 0)
+				break;
+		}
+	}
+
+	mutex_unlock(&iommu->lock);
+	return ret > 0 ? 0 : (int)ret;
+}
+
+static void *vfio_iommu_dummy_open(unsigned long arg)
+{
+	struct vfio_iommu *iommu;
+
+	if (arg != VFIO_IOMMU_DUMMY)
+		return ERR_PTR(-EINVAL);
+
+	iommu = kzalloc(sizeof(*iommu), GFP_KERNEL);
+	if (!iommu)
+		return ERR_PTR(-ENOMEM);
+
+	INIT_LIST_HEAD(&iommu->group_list);
+	INIT_LIST_HEAD(&iommu->dma_list);
+	mutex_init(&iommu->lock);
+
+	return iommu;
+}
+
+static void vfio_iommu_dummy_release(void *iommu_data)
+{
+	struct vfio_iommu *iommu = iommu_data;
+	struct vfio_group *group, *group_tmp;
+	struct vfio_dma *dma, *dma_tmp;
+
+	list_for_each_entry_safe(group, group_tmp, &iommu->group_list, next) {
+		list_del(&group->next);
+		kfree(group);
+	}
+
+	list_for_each_entry_safe(dma, dma_tmp, &iommu->dma_list, next) {
+		vfio_dma_unmap(iommu, dma->iova, dma->npage, dma->prot);
+		list_del(&dma->next);
+		kfree(dma);
+	}
+
+	kfree(iommu);
+}
+
+static long vfio_iommu_dummy_ioctl(void *iommu_data,
+				   unsigned int cmd, unsigned long arg)
+{
+	struct vfio_iommu *iommu = iommu_data;
+	unsigned long minsz;
+
+	if (cmd == VFIO_CHECK_EXTENSION) {
+		switch (arg) {
+		case VFIO_IOMMU_DUMMY:
+			return 1;
+		default:
+			return 0;
+		}
+	} else if (cmd == VFIO_IOMMU_MAP_DMA) {
+		struct vfio_iommu_type1_dma_map map;
+		uint32_t mask = VFIO_DMA_MAP_FLAG_READ |
+				VFIO_DMA_MAP_FLAG_WRITE;
+
+		minsz = offsetofend(struct vfio_iommu_type1_dma_map, size);
+
+		if (copy_from_user(&map, (void __user *)arg, minsz))
+			return -EFAULT;
+
+		if (map.argsz < minsz || map.flags & ~mask)
+			return -EINVAL;
+
+		return vfio_dma_do_map(iommu, &map);
+
+	} else if (cmd == VFIO_IOMMU_UNMAP_DMA) {
+		struct vfio_iommu_type1_dma_unmap unmap;
+
+		minsz = offsetofend(struct vfio_iommu_type1_dma_unmap, size);
+
+		if (copy_from_user(&unmap, (void __user *)arg, minsz))
+			return -EFAULT;
+
+		if (unmap.argsz < minsz || unmap.flags)
+			return -EINVAL;
+
+		return vfio_dma_do_unmap(iommu, &unmap);
+	}
+
+	return -ENOTTY;
+}
+
+static int vfio_iommu_dummy_attach_group(void *iommu_data,
+					 struct iommu_group *iommu_group)
+{
+	struct vfio_iommu *iommu = iommu_data;
+	struct vfio_group *group, *tmp;
+
+	group = kzalloc(sizeof(*group), GFP_KERNEL);
+	if (!group)
+		return -ENOMEM;
+
+	mutex_lock(&iommu->lock);
+
+	list_for_each_entry(tmp, &iommu->group_list, next) {
+		if (tmp->iommu_group == iommu_group) {
+			mutex_unlock(&iommu->lock);
+			kfree(group);
+			return -EINVAL;
+		}
+	}
+
+	group->iommu_group = iommu_group;
+	list_add(&group->next, &iommu->group_list);
+
+	mutex_unlock(&iommu->lock);
+
+	return 0;
+}
+
+static void vfio_iommu_dummy_detach_group(void *iommu_data,
+					  struct iommu_group *iommu_group)
+{
+	struct vfio_iommu *iommu = iommu_data;
+	struct vfio_group *group;
+
+	mutex_lock(&iommu->lock);
+
+	list_for_each_entry(group, &iommu->group_list, next) {
+		if (group->iommu_group == iommu_group) {
+			list_del(&group->next);
+			kfree(group);
+			break;
+		}
+	}
+
+	mutex_unlock(&iommu->lock);
+
+}
+
+static const struct vfio_iommu_driver_ops vfio_iommu_driver_ops_dummy = {
+	.name		= "vfio-iommu-dummy",
+	.owner		= THIS_MODULE,
+	.open		= vfio_iommu_dummy_open,
+	.release	= vfio_iommu_dummy_release,
+	.ioctl		= vfio_iommu_dummy_ioctl,
+	.attach_group	= vfio_iommu_dummy_attach_group,
+	.detach_group	= vfio_iommu_dummy_detach_group,
+};
+
+static int iommu_dummy_add_device(struct device *dev)
+{
+	struct iommu_group *group;
+	int ret;
+
+	group = iommu_group_get(dev);
+	if (!group) {
+		group = iommu_group_alloc();
+		if (IS_ERR(group))
+			return PTR_ERR(group);
+	}
+
+	ret = iommu_group_add_device(group, dev);
+	iommu_group_put(group);
+
+	return ret;
+}
+
+static struct iommu_ops iommu_dummy_ops = {
+	.add_device = iommu_dummy_add_device,
+};
+
+static ssize_t enable_iommu_dummy_show(struct kobject *kobj,
+				      struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%d\n", enable_iommu_dummy);
+}
+
+static ssize_t enable_iommu_dummy_store(struct kobject *kobj,
+				       struct kobj_attribute *attr,
+				       const char *buf, size_t count)
+{
+	int val;
+
+	sscanf(buf, "%du", &val);
+
+	if (!enable_iommu_dummy && val) {
+		pr_warn("Enabling vfio_iommu_dummy driver, can't be disabled\n");
+		bus_set_iommu(&pci_bus_type, &iommu_dummy_ops);
+		vfio_register_iommu_driver(&vfio_iommu_driver_ops_dummy);
+		enable_iommu_dummy = 1;
+	}
+
+	return count;
+}
+
+static struct kobj_attribute enable_iommu_dummy_attribute =
+	__ATTR(enable_iommu_dummy, 0666, enable_iommu_dummy_show, enable_iommu_dummy_store);
+
+static struct attribute *attrs[] = {
+	&enable_iommu_dummy_attribute.attr,
+	NULL,
+};
+
+static struct attribute_group attr_group = {
+	.attrs = attrs,
+};
+
+static struct kobject *vfio_iommu_dummy_kobj;
+
+static int __init vfio_iommu_dummy_init(void)
+{
+	int retval;
+
+	vfio_iommu_dummy_kobj = kobject_create_and_add("vfio_iommu_dummy", kernel_kobj);
+	if (!vfio_iommu_dummy_kobj)
+		return -ENOMEM;
+
+	/* Create the files associated with vfio_iommu_dummy kobject */
+	retval = sysfs_create_group(vfio_iommu_dummy_kobj, &attr_group);
+	if (retval)
+		kobject_put(vfio_iommu_dummy_kobj);
+
+	return retval;
+}
+
+static void __exit vfio_iommu_dummy_cleanup(void)
+{
+	if (enable_iommu_dummy)
+		vfio_unregister_iommu_driver(&vfio_iommu_driver_ops_dummy);
+
+	kobject_put(vfio_iommu_dummy_kobj);
+}
+
+module_init(vfio_iommu_dummy_init);
+module_exit(vfio_iommu_dummy_cleanup);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Varun Sethi <Varun.Sethi@freescale.com>");
+MODULE_DESCRIPTION("Dummy IOMMU driver for VFIO");