Re: [PATCH v3 3/3] mm/hmm/test: add self tests for HMM

[Jerome Glisse]

On Wed, Oct 23, 2019 at 12:55:15PM -0700, Ralph Campbell wrote:
> Add self tests for HMM.
> 
> Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx>

You can add my signoff

Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx>


> ---
>  MAINTAINERS                            |    3 +
>  drivers/char/Kconfig                   |   11 +
>  drivers/char/Makefile                  |    1 +
>  drivers/char/hmm_dmirror.c             | 1566 ++++++++++++++++++++++++
>  include/Kbuild                         |    1 +
>  include/uapi/linux/hmm_dmirror.h       |   74 ++
>  tools/testing/selftests/vm/.gitignore  |    1 +
>  tools/testing/selftests/vm/Makefile    |    3 +
>  tools/testing/selftests/vm/config      |    3 +
>  tools/testing/selftests/vm/hmm-tests.c | 1311 ++++++++++++++++++++
>  tools/testing/selftests/vm/run_vmtests |   16 +
>  tools/testing/selftests/vm/test_hmm.sh |   97 ++
>  12 files changed, 3087 insertions(+)
>  create mode 100644 drivers/char/hmm_dmirror.c
>  create mode 100644 include/uapi/linux/hmm_dmirror.h
>  create mode 100644 tools/testing/selftests/vm/hmm-tests.c
>  create mode 100755 tools/testing/selftests/vm/test_hmm.sh
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 296de2b51c83..9890b6b8eea0 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -7427,8 +7427,11 @@ M:	Jérôme Glisse <jglisse@xxxxxxxxxx>
>  L:	linux-mm@xxxxxxxxx
>  S:	Maintained
>  F:	mm/hmm*
> +F:	drivers/char/hmm*
>  F:	include/linux/hmm*
> +F:	include/uapi/linux/hmm*
>  F:	Documentation/vm/hmm.rst
> +F:	tools/testing/selftests/vm/*hmm*
>  
>  HOST AP DRIVER
>  M:	Jouni Malinen <j@xxxxx>
> diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
> index df0fc997dc3e..cc8ddb99550d 100644
> --- a/drivers/char/Kconfig
> +++ b/drivers/char/Kconfig
> @@ -535,6 +535,17 @@ config ADI
>  	  and SSM (Silicon Secured Memory).  Intended consumers of this
>  	  driver include crash and makedumpfile.
>  
> +config HMM_DMIRROR
> +	tristate "HMM driver for testing Heterogeneous Memory Management"
> +	depends on HMM_MIRROR
> +	depends on DEVICE_PRIVATE
> +	help
> +	  This is a pseudo device driver solely for testing HMM.
> +	  Say Y here if you want to build the HMM test driver.
> +	  Doing so will allow you to run tools/testing/selftest/vm/hmm-tests.
> +
> +	  If in doubt, say "N".
> +
>  endmenu
>  
>  config RANDOM_TRUST_CPU
> diff --git a/drivers/char/Makefile b/drivers/char/Makefile
> index 7c5ea6f9df14..d4a168c0c138 100644
> --- a/drivers/char/Makefile
> +++ b/drivers/char/Makefile
> @@ -52,3 +52,4 @@ js-rtc-y = rtc.o
>  obj-$(CONFIG_XILLYBUS)		+= xillybus/
>  obj-$(CONFIG_POWERNV_OP_PANEL)	+= powernv-op-panel.o
>  obj-$(CONFIG_ADI)		+= adi.o
> +obj-$(CONFIG_HMM_DMIRROR)	+= hmm_dmirror.o
> diff --git a/drivers/char/hmm_dmirror.c b/drivers/char/hmm_dmirror.c
> new file mode 100644
> index 000000000000..5a1ed34e72e1
> --- /dev/null
> +++ b/drivers/char/hmm_dmirror.c
> @@ -0,0 +1,1566 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright 2013 Red Hat Inc.
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License as
> + * published by the Free Software Foundation; either version 2 of
> + * the License, or (at your option) any later version.
> + *
> + * 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.
> + *
> + * Authors: Jérôme Glisse <jglisse@xxxxxxxxxx>
> + */
> +/*
> + * This is a driver to exercice the HMM (heterogeneous memory management)
> + * mirror and zone device private memory migration APIs of the kernel.
> + * Userspace programs can register with the driver to mirror their own address
> + * space and can use the device to read/write any valid virtual address.
> + *
> + * In some ways it can also serve as an example driver for people wanting to use
> + * HMM inside their own device driver.
> + */
> +#include <linux/init.h>
> +#include <linux/fs.h>
> +#include <linux/mm.h>
> +#include <linux/module.h>
> +#include <linux/kernel.h>
> +#include <linux/cdev.h>
> +#include <linux/device.h>
> +#include <linux/mutex.h>
> +#include <linux/rwsem.h>
> +#include <linux/sched.h>
> +#include <linux/slab.h>
> +#include <linux/highmem.h>
> +#include <linux/delay.h>
> +#include <linux/pagemap.h>
> +#include <linux/hmm.h>
> +#include <linux/vmalloc.h>
> +#include <linux/swap.h>
> +#include <linux/swapops.h>
> +#include <linux/sched/mm.h>
> +#include <linux/platform_device.h>
> +
> +#include <uapi/linux/hmm_dmirror.h>
> +
> +#define DMIRROR_NDEVICES		2
> +#define DMIRROR_RANGE_FAULT_TIMEOUT	1000
> +#define DEVMEM_CHUNK_SIZE		(256 * 1024 * 1024U)
> +#define DEVMEM_CHUNKS_RESERVE		16
> +
> +static const struct dev_pagemap_ops dmirror_devmem_ops;
> +static dev_t dmirror_dev;
> +static struct platform_device *dmirror_platform_devices[DMIRROR_NDEVICES];
> +static struct page *dmirror_zero_page;
> +
> +struct dmirror_device;
> +
> +struct dmirror_bounce {
> +	void			*ptr;
> +	unsigned long		size;
> +	unsigned long		addr;
> +	unsigned long		cpages;
> +};
> +
> +#define DPT_SHIFT PAGE_SHIFT
> +#define DPT_VALID (1UL << 0)
> +#define DPT_WRITE (1UL << 1)
> +#define DPT_DPAGE (1UL << 2)
> +#define DPT_ZPAGE 0x20UL
> +
> +const uint64_t dmirror_hmm_flags[HMM_PFN_FLAG_MAX] = {
> +	[HMM_PFN_VALID] = DPT_VALID,
> +	[HMM_PFN_WRITE] = DPT_WRITE,
> +	[HMM_PFN_DEVICE_PRIVATE] = DPT_DPAGE,
> +};
> +
> +static const uint64_t dmirror_hmm_values[HMM_PFN_VALUE_MAX] = {
> +	[HMM_PFN_NONE]    = 0,
> +	[HMM_PFN_ERROR]   = 0x10,
> +	[HMM_PFN_SPECIAL] = 0x10,
> +};
> +
> +struct dmirror_pt {
> +	u64			pgd[PTRS_PER_PGD];
> +	struct rw_semaphore	lock;
> +};
> +
> +/*
> + * Data attached to the open device file.
> + * Note that it might be shared after a fork().
> + */
> +struct dmirror {
> +	struct hmm_mirror	mirror;
> +	struct dmirror_device	*mdevice;
> +	struct dmirror_pt	pt;
> +	struct mutex		mutex;
> +};
> +
> +/*
> + * ZONE_DEVICE pages for migration and simulating device memory.
> + */
> +struct dmirror_chunk {
> +	struct dev_pagemap	pagemap;
> +	struct dmirror_device	*mdevice;
> +};
> +
> +/*
> + * Per device data.
> + */
> +struct dmirror_device {
> +	struct cdev		cdevice;
> +	struct hmm_devmem	*devmem;
> +	struct platform_device	*pdevice;
> +
> +	unsigned int		devmem_capacity;
> +	unsigned int		devmem_count;
> +	struct dmirror_chunk	**devmem_chunks;
> +	struct mutex		devmem_lock;	/* protects the above */
> +
> +	unsigned long		calloc;
> +	unsigned long		cfree;
> +	struct page		*free_pages;
> +	spinlock_t		lock;		/* protects the above */
> +};
> +
> +static inline unsigned long dmirror_pt_pgd(unsigned long addr)
> +{
> +	return (addr >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1);
> +}
> +
> +static inline unsigned long dmirror_pt_pud(unsigned long addr)
> +{
> +	return (addr >> PUD_SHIFT) & (PTRS_PER_PUD - 1);
> +}
> +
> +static inline unsigned long dmirror_pt_pmd(unsigned long addr)
> +{
> +	return (addr >> PMD_SHIFT) & (PTRS_PER_PMD - 1);
> +}
> +
> +static inline unsigned long dmirror_pt_pte(unsigned long addr)
> +{
> +	return (addr >> PAGE_SHIFT) & (PTRS_PER_PTE - 1);
> +}
> +
> +static inline struct page *dmirror_pt_page(u64 *dptep)
> +{
> +	u64 dpte = *dptep;
> +
> +	if (dpte == DPT_ZPAGE)
> +		return dmirror_zero_page;
> +	if (!(dpte & DPT_VALID))
> +		return NULL;
> +	return pfn_to_page((u64)dpte >> DPT_SHIFT);
> +}
> +
> +static inline struct page *dmirror_pt_page_write(u64 *dptep)
> +{
> +	u64 dpte = *dptep;
> +
> +	if (!(dpte & DPT_VALID) || !(dpte & DPT_WRITE))
> +		return NULL;
> +	return pfn_to_page((u64)dpte >> DPT_SHIFT);
> +}
> +
> +static inline u64 dmirror_pt_from_page(struct page *page)
> +{
> +	if (!page)
> +		return 0;
> +	return (page_to_pfn(page) << DPT_SHIFT) | DPT_VALID;
> +}
> +
> +static struct page *populate_pt(struct dmirror *dmirror, u64 *dptep)
> +{
> +	struct page *page;
> +
> +	/*
> +	 * Since we don't free page tables until the process exits,
> +	 * we can unlock and relock without the page table being freed
> +	 * from under us.
> +	 */
> +	mutex_unlock(&dmirror->mutex);
> +	page = alloc_page(GFP_HIGHUSER | __GFP_ZERO);
> +	mutex_lock(&dmirror->mutex);
> +	if (page) {
> +		if (unlikely(*dptep)) {
> +			__free_page(page);
> +			page = dmirror_pt_page(dptep);
> +		} else
> +			*dptep = dmirror_pt_from_page(page);
> +	} else if (*dptep)
> +		page = dmirror_pt_page(dptep);
> +	return page;
> +}
> +
> +static inline unsigned long dmirror_pt_pud_end(unsigned long addr)
> +{
> +	return (addr & PGDIR_MASK) + ((unsigned long)PTRS_PER_PUD << PUD_SHIFT);
> +}
> +
> +static inline unsigned long dmirror_pt_pmd_end(unsigned long addr)
> +{
> +	return (addr & PUD_MASK) + ((unsigned long)PTRS_PER_PMD << PMD_SHIFT);
> +}
> +
> +static inline unsigned long dmirror_pt_pte_end(unsigned long addr)
> +{
> +	return (addr & PMD_MASK) + ((unsigned long)PTRS_PER_PTE << PAGE_SHIFT);
> +}
> +
> +typedef int (*dmirror_walk_cb_t)(struct dmirror *dmirror,
> +				 unsigned long start,
> +				 unsigned long end,
> +				 u64 *dptep,
> +				 void *private);
> +
> +static int dmirror_pt_walk(struct dmirror *dmirror,
> +			   dmirror_walk_cb_t cb,
> +			   unsigned long start,
> +			   unsigned long end,
> +			   void *private,
> +			   bool populate)
> +{
> +	u64 *dpgdp = &dmirror->pt.pgd[dmirror_pt_pgd(start)];
> +	unsigned long addr;
> +	int ret = -ENOENT;
> +
> +	for (addr = start; addr < end; dpgdp++) {
> +		u64 *dpudp;
> +		unsigned long pud_end;
> +		struct page *pud_page;
> +
> +		pud_end = min(end, dmirror_pt_pud_end(addr));
> +		pud_page = dmirror_pt_page(dpgdp);
> +		if (!pud_page) {
> +			if (!populate) {
> +				addr = pud_end;
> +				continue;
> +			}
> +			pud_page = populate_pt(dmirror, dpgdp);
> +			if (!pud_page)
> +				return -ENOMEM;
> +		}
> +		dpudp = kmap(pud_page);
> +		dpudp += dmirror_pt_pud(addr);
> +		for (; addr != pud_end; dpudp++) {
> +			u64 *dpmdp;
> +			unsigned long pmd_end;
> +			struct page *pmd_page;
> +
> +			pmd_end = min(end, dmirror_pt_pmd_end(addr));
> +			pmd_page = dmirror_pt_page(dpudp);
> +			if (!pmd_page) {
> +				if (!populate) {
> +					addr = pmd_end;
> +					continue;
> +				}
> +				pmd_page = populate_pt(dmirror, dpudp);
> +				if (!pmd_page) {
> +					kunmap(pud_page);
> +					return -ENOMEM;
> +				}
> +			}
> +			dpmdp = kmap(pmd_page);
> +			dpmdp += dmirror_pt_pmd(addr);
> +			for (; addr != pmd_end; dpmdp++) {
> +				u64 *dptep;
> +				unsigned long pte_end;
> +				struct page *pte_page;
> +
> +				pte_end = min(end, dmirror_pt_pte_end(addr));
> +				pte_page = dmirror_pt_page(dpmdp);
> +				if (!pte_page) {
> +					if (!populate) {
> +						addr = pte_end;
> +						continue;
> +					}
> +					pte_page = populate_pt(dmirror, dpmdp);
> +					if (!pte_page) {
> +						kunmap(pmd_page);
> +						kunmap(pud_page);
> +						return -ENOMEM;
> +					}
> +				}
> +				if (!cb) {
> +					addr = pte_end;
> +					continue;
> +				}
> +				dptep = kmap(pte_page);
> +				dptep += dmirror_pt_pte(addr);
> +				ret = cb(dmirror, addr, pte_end, dptep,
> +					 private);
> +				kunmap(pte_page);
> +				if (ret) {
> +					kunmap(pmd_page);
> +					kunmap(pud_page);
> +					return ret;
> +				}
> +				addr = pte_end;
> +			}
> +			kunmap(pmd_page);
> +			addr = pmd_end;
> +		}
> +		kunmap(pud_page);
> +		addr = pud_end;
> +	}
> +
> +	return ret;
> +}
> +
> +static void dmirror_pt_free(struct dmirror *dmirror)
> +{
> +	u64 *dpgdp = dmirror->pt.pgd;
> +
> +	for (; dpgdp != dmirror->pt.pgd + PTRS_PER_PGD; dpgdp++) {
> +		u64 *dpudp, *dpudp_orig;
> +		u64 *dpudp_end;
> +		struct page *pud_page;
> +
> +		pud_page = dmirror_pt_page(dpgdp);
> +		if (!pud_page)
> +			continue;
> +
> +		dpudp_orig = kmap_atomic(pud_page);
> +		dpudp = dpudp_orig;
> +		dpudp_end = dpudp + PTRS_PER_PUD;
> +		for (; dpudp != dpudp_end; dpudp++) {
> +			u64 *dpmdp, *dpmdp_orig;
> +			u64 *dpmdp_end;
> +			struct page *pmd_page;
> +
> +			pmd_page = dmirror_pt_page(dpudp);
> +			if (!pmd_page)
> +				continue;
> +
> +			dpmdp_orig = kmap_atomic(pmd_page);
> +			dpmdp = dpmdp_orig;
> +			dpmdp_end = dpmdp + PTRS_PER_PMD;
> +			for (; dpmdp != dpmdp_end; dpmdp++) {
> +				struct page *pte_page;
> +
> +				pte_page = dmirror_pt_page(dpmdp);
> +				if (!pte_page)
> +					continue;
> +
> +				*dpmdp = 0;
> +				__free_page(pte_page);
> +			}
> +			kunmap_atomic(dpmdp_orig);
> +			*dpudp = 0;
> +			__free_page(pmd_page);
> +		}
> +		kunmap_atomic(dpudp_orig);
> +		*dpgdp = 0;
> +		__free_page(pud_page);
> +	}
> +}
> +
> +static int dmirror_bounce_init(struct dmirror_bounce *bounce,
> +			       unsigned long addr,
> +			       unsigned long size)
> +{
> +	bounce->addr = addr;
> +	bounce->size = size;
> +	bounce->cpages = 0;
> +	bounce->ptr = vmalloc(size);
> +	if (!bounce->ptr)
> +		return -ENOMEM;
> +	return 0;
> +}
> +
> +static int dmirror_bounce_copy_from(struct dmirror_bounce *bounce,
> +				    unsigned long addr)
> +{
> +	unsigned long end = addr + bounce->size;
> +	char __user *uptr = (void __user *)addr;
> +	void *ptr = bounce->ptr;
> +
> +	for (; addr < end; addr += PAGE_SIZE, ptr += PAGE_SIZE,
> +					      uptr += PAGE_SIZE) {
> +		int ret;
> +
> +		ret = copy_from_user(ptr, uptr, PAGE_SIZE);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static int dmirror_bounce_copy_to(struct dmirror_bounce *bounce,
> +				  unsigned long addr)
> +{
> +	unsigned long end = addr + bounce->size;
> +	char __user *uptr = (void __user *)addr;
> +	void *ptr = bounce->ptr;
> +
> +	for (; addr < end; addr += PAGE_SIZE, ptr += PAGE_SIZE,
> +					      uptr += PAGE_SIZE) {
> +		int ret;
> +
> +		ret = copy_to_user(uptr, ptr, PAGE_SIZE);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static void dmirror_bounce_fini(struct dmirror_bounce *bounce)
> +{
> +	vfree(bounce->ptr);
> +}
> +
> +static int dmirror_do_update(struct dmirror *dmirror,
> +			     unsigned long addr,
> +			     unsigned long end,
> +			     u64 *dptep,
> +			     void *private)
> +{
> +	/*
> +	 * The page table doesn't hold references to pages since it relies on
> +	 * the mmu notifier to clear pointers when they become stale.
> +	 * Therefore, it is OK to just clear the pte.
> +	 */
> +	for (; addr < end; addr += PAGE_SIZE, ++dptep)
> +		*dptep = 0;
> +
> +	return 0;
> +}
> +
> +static int dmirror_update(struct hmm_mirror *mirror,
> +			  const struct mmu_notifier_range *update)
> +{
> +	struct dmirror *dmirror = container_of(mirror, struct dmirror, mirror);
> +
> +	if (mmu_notifier_range_blockable(update))
> +		mutex_lock(&dmirror->mutex);
> +	else if (!mutex_trylock(&dmirror->mutex))
> +		return -EAGAIN;
> +
> +	dmirror_pt_walk(dmirror, dmirror_do_update, update->start,
> +			update->end, NULL, false);
> +	mutex_unlock(&dmirror->mutex);
> +	return 0;
> +}
> +
> +static const struct hmm_mirror_ops dmirror_ops = {
> +	.sync_cpu_device_pagetables	= &dmirror_update,
> +};
> +
> +/*
> + * dmirror_new() - allocate and initialize dmirror struct.
> + *
> + * @mdevice: The device this mirror is associated with.
> + * @filp: The active device file descriptor this mirror is associated with.
> + */
> +static struct dmirror *dmirror_new(struct dmirror_device *mdevice)
> +{
> +	struct mm_struct *mm = get_task_mm(current);
> +	struct dmirror *dmirror;
> +	int ret;
> +
> +	if (!mm)
> +		goto err;
> +
> +	/* Mirror this process address space */
> +	dmirror = kzalloc(sizeof(*dmirror), GFP_KERNEL);
> +	if (dmirror == NULL)
> +		goto err_mmput;
> +
> +	dmirror->mdevice = mdevice;
> +	dmirror->mirror.ops = &dmirror_ops;
> +	mutex_init(&dmirror->mutex);
> +
> +	down_write(&mm->mmap_sem);
> +	ret = hmm_mirror_register(&dmirror->mirror, mm);
> +	up_write(&mm->mmap_sem);
> +	if (ret)
> +		goto err_free;
> +
> +	mmput(mm);
> +	return dmirror;
> +
> +err_free:
> +	kfree(dmirror);
> +err_mmput:
> +	mmput(mm);
> +err:
> +	return NULL;
> +}
> +
> +static void dmirror_del(struct dmirror *dmirror)
> +{
> +	hmm_mirror_unregister(&dmirror->mirror);
> +	dmirror_pt_free(dmirror);
> +	kfree(dmirror);
> +}
> +
> +/*
> + * Below are the file operation for the dmirror device file. Only ioctl matters.
> + *
> + * Note this is highly specific to the dmirror device driver and should not be
> + * construed as an example on how to design the API a real device driver would
> + * expose to userspace.
> + */
> +static ssize_t dmirror_fops_read(struct file *filp,
> +			       char __user *buf,
> +			       size_t count,
> +			       loff_t *ppos)
> +{
> +	return -EINVAL;
> +}
> +
> +static ssize_t dmirror_fops_write(struct file *filp,
> +				const char __user *buf,
> +				size_t count,
> +				loff_t *ppos)
> +{
> +	return -EINVAL;
> +}
> +
> +static int dmirror_fops_mmap(struct file *filp, struct vm_area_struct *vma)
> +{
> +	/* Forbid mmap of the dmirror device file. */
> +	return -EINVAL;
> +}
> +
> +static int dmirror_fops_open(struct inode *inode, struct file *filp)
> +{
> +	struct cdev *cdev = inode->i_cdev;
> +	struct dmirror_device *mdevice;
> +	struct dmirror *dmirror;
> +
> +	/* No exclusive opens. */
> +	if (filp->f_flags & O_EXCL)
> +		return -EINVAL;
> +
> +	mdevice = container_of(cdev, struct dmirror_device, cdevice);
> +	dmirror = dmirror_new(mdevice);
> +	if (!dmirror)
> +		return -ENOMEM;
> +
> +	/* Only the first open registers the address space. */
> +	mutex_lock(&mdevice->devmem_lock);
> +	if (filp->private_data)
> +		goto err_busy;
> +	filp->private_data = dmirror;
> +	mutex_unlock(&mdevice->devmem_lock);
> +
> +	return 0;
> +
> +err_busy:
> +	mutex_unlock(&mdevice->devmem_lock);
> +	dmirror_del(dmirror);
> +	return -EBUSY;
> +}
> +
> +static int dmirror_fops_release(struct inode *inode, struct file *filp)
> +{
> +	struct dmirror *dmirror = filp->private_data;
> +
> +	if (!dmirror)
> +		return 0;
> +
> +	dmirror_del(dmirror);
> +	filp->private_data = NULL;
> +
> +	return 0;
> +}
> +
> +static inline struct dmirror_device *dmirror_page_to_device(struct page *page)
> +
> +{
> +	struct dmirror_chunk *devmem;
> +
> +	devmem = container_of(page->pgmap, struct dmirror_chunk, pagemap);
> +	return devmem->mdevice;
> +}
> +
> +static bool dmirror_device_is_mine(struct dmirror_device *mdevice,
> +				   struct page *page)
> +{
> +	if (!is_zone_device_page(page))
> +		return false;
> +	return page->pgmap->ops == &dmirror_devmem_ops &&
> +		dmirror_page_to_device(page) == mdevice;
> +}
> +
> +static int dmirror_do_fault(struct dmirror *dmirror,
> +			    unsigned long addr,
> +			    unsigned long end,
> +			    u64 *dptep,
> +			    void *private)
> +{
> +	struct hmm_range *range = private;
> +	unsigned long idx = (addr - range->start) >> PAGE_SHIFT;
> +	uint64_t *pfns = range->pfns;
> +
> +	for (; addr < end; addr += PAGE_SIZE, ++dptep, ++idx) {
> +		struct page *page;
> +		u64 dpte;
> +
> +		/*
> +		 * HMM_PFN_ERROR is returned if it is accessing invalid memory
> +		 * either because of memory error (hardware detected memory
> +		 * corruption) or more likely because of truncate on mmap
> +		 * file.
> +		 */
> +		if (pfns[idx] == range->values[HMM_PFN_ERROR])
> +			return -EFAULT;
> +		/*
> +		 * The only special PFN HMM returns is the read-only zero page
> +		 * which doesn't have a matching struct page.
> +		 */
> +		if (pfns[idx] == range->values[HMM_PFN_SPECIAL]) {
> +			*dptep = DPT_ZPAGE;
> +			continue;
> +		}
> +		if (!(pfns[idx] & range->flags[HMM_PFN_VALID]))
> +			return -EFAULT;
> +		page = hmm_device_entry_to_page(range, pfns[idx]);
> +		/* We asked for pages to be populated but check anyway. */
> +		if (!page)
> +			return -EFAULT;
> +		dpte = dmirror_pt_from_page(page);
> +		if (is_zone_device_page(page)) {
> +			if (!dmirror_device_is_mine(dmirror->mdevice, page))
> +				continue;
> +			dpte |= DPT_DPAGE;
> +		}
> +		if (pfns[idx] & range->flags[HMM_PFN_WRITE])
> +			dpte |= DPT_WRITE;
> +		else if (range->default_flags & range->flags[HMM_PFN_WRITE])
> +			return -EFAULT;
> +		*dptep = dpte;
> +	}
> +
> +	return 0;
> +}
> +
> +static int dmirror_fault(struct dmirror *dmirror,
> +			 unsigned long start,
> +			 unsigned long end,
> +			 bool write)
> +{
> +	struct mm_struct *mm = dmirror->mirror.hmm->mmu_notifier.mm;
> +	unsigned long addr;
> +	unsigned long next;
> +	uint64_t pfns[64];
> +	struct hmm_range range = {
> +		.pfns = pfns,
> +		.flags = dmirror_hmm_flags,
> +		.values = dmirror_hmm_values,
> +		.pfn_shift = DPT_SHIFT,
> +		.pfn_flags_mask = ~(dmirror_hmm_flags[HMM_PFN_VALID] |
> +				    dmirror_hmm_flags[HMM_PFN_WRITE]),
> +		.default_flags = dmirror_hmm_flags[HMM_PFN_VALID] |
> +				(write ? dmirror_hmm_flags[HMM_PFN_WRITE] : 0),
> +	};
> +	int ret = 0;
> +
> +	for (addr = start; addr < end; ) {
> +		long count;
> +
> +		next = min(addr + (ARRAY_SIZE(pfns) << PAGE_SHIFT), end);
> +		range.start = addr;
> +		range.end = next;
> +
> +		down_read(&mm->mmap_sem);
> +
> +		ret = hmm_range_register(&range, &dmirror->mirror);
> +		if (ret) {
> +			up_read(&mm->mmap_sem);
> +			break;
> +		}
> +
> +		if (!hmm_range_wait_until_valid(&range,
> +						DMIRROR_RANGE_FAULT_TIMEOUT)) {
> +			hmm_range_unregister(&range);
> +			up_read(&mm->mmap_sem);
> +			continue;
> +		}
> +
> +		count = hmm_range_fault(&range, 0);
> +		if (count < 0) {
> +			ret = count;
> +			hmm_range_unregister(&range);
> +			up_read(&mm->mmap_sem);
> +			break;
> +		}
> +
> +		if (!hmm_range_valid(&range)) {
> +			hmm_range_unregister(&range);
> +			up_read(&mm->mmap_sem);
> +			continue;
> +		}
> +		mutex_lock(&dmirror->mutex);
> +		ret = dmirror_pt_walk(dmirror, dmirror_do_fault,
> +				      addr, next, &range, true);
> +		mutex_unlock(&dmirror->mutex);
> +		hmm_range_unregister(&range);
> +		up_read(&mm->mmap_sem);
> +		if (ret)
> +			break;
> +
> +		addr = next;
> +	}
> +
> +	return ret;
> +}
> +
> +static int dmirror_do_read(struct dmirror *dmirror,
> +			   unsigned long addr,
> +			   unsigned long end,
> +			   u64 *dptep,
> +			   void *private)
> +{
> +	struct dmirror_bounce *bounce = private;
> +	void *ptr;
> +
> +	ptr = bounce->ptr + ((addr - bounce->addr) & PAGE_MASK);
> +
> +	for (; addr < end; addr += PAGE_SIZE, ++dptep) {
> +		struct page *page;
> +		void *tmp;
> +
> +		page = dmirror_pt_page(dptep);
> +		if (!page)
> +			return -ENOENT;
> +
> +		tmp = kmap(page);
> +		memcpy(ptr, tmp, PAGE_SIZE);
> +		kunmap(page);
> +
> +		ptr += PAGE_SIZE;
> +		bounce->cpages++;
> +	}
> +
> +	return 0;
> +}
> +
> +static int dmirror_read(struct dmirror *dmirror,
> +			struct hmm_dmirror_cmd *cmd)
> +{
> +	struct dmirror_bounce bounce;
> +	unsigned long start, end;
> +	unsigned long size = cmd->npages << PAGE_SHIFT;
> +	int ret;
> +
> +	start = cmd->addr;
> +	end = start + size;
> +	if (end < start)
> +		return -EINVAL;
> +
> +	ret = dmirror_bounce_init(&bounce, start, size);
> +	if (ret)
> +		return ret;
> +
> +again:
> +	mutex_lock(&dmirror->mutex);
> +	ret = dmirror_pt_walk(dmirror, dmirror_do_read, start, end, &bounce,
> +				false);
> +	mutex_unlock(&dmirror->mutex);
> +	if (ret == 0)
> +		ret = dmirror_bounce_copy_to(&bounce, cmd->ptr);
> +	else if (ret == -ENOENT) {
> +		start = cmd->addr + (bounce.cpages << PAGE_SHIFT);
> +		ret = dmirror_fault(dmirror, start, end, false);
> +		if (ret == 0) {
> +			cmd->faults++;
> +			goto again;
> +		}
> +	}
> +
> +	cmd->cpages = bounce.cpages;
> +	dmirror_bounce_fini(&bounce);
> +	return ret;
> +}
> +
> +static int dmirror_do_write(struct dmirror *dmirror,
> +			    unsigned long addr,
> +			    unsigned long end,
> +			    u64 *dptep,
> +			    void *private)
> +{
> +	struct dmirror_bounce *bounce = private;
> +	void *ptr;
> +
> +	ptr = bounce->ptr + ((addr - bounce->addr) & PAGE_MASK);
> +
> +	for (; addr < end; addr += PAGE_SIZE, ++dptep) {
> +		struct page *page;
> +		void *tmp;
> +
> +		page = dmirror_pt_page_write(dptep);
> +		if (!page)
> +			return -ENOENT;
> +
> +		tmp = kmap(page);
> +		memcpy(tmp, ptr, PAGE_SIZE);
> +		kunmap(page);
> +
> +		ptr += PAGE_SIZE;
> +		bounce->cpages++;
> +	}
> +
> +	return 0;
> +}
> +
> +static int dmirror_write(struct dmirror *dmirror,
> +			 struct hmm_dmirror_cmd *cmd)
> +{
> +	struct dmirror_bounce bounce;
> +	unsigned long start, end;
> +	unsigned long size = cmd->npages << PAGE_SHIFT;
> +	int ret;
> +
> +	start = cmd->addr;
> +	end = start + size;
> +	if (end < start)
> +		return -EINVAL;
> +
> +	ret = dmirror_bounce_init(&bounce, start, size);
> +	if (ret)
> +		return ret;
> +	ret = dmirror_bounce_copy_from(&bounce, cmd->ptr);
> +	if (ret)
> +		return ret;
> +
> +again:
> +	mutex_lock(&dmirror->mutex);
> +	ret = dmirror_pt_walk(dmirror, dmirror_do_write,
> +			      start, end, &bounce, false);
> +	mutex_unlock(&dmirror->mutex);
> +	if (ret == -ENOENT) {
> +		start = cmd->addr + (bounce.cpages << PAGE_SHIFT);
> +		ret = dmirror_fault(dmirror, start, end, true);
> +		if (ret == 0) {
> +			cmd->faults++;
> +			goto again;
> +		}
> +	}
> +
> +	cmd->cpages = bounce.cpages;
> +	dmirror_bounce_fini(&bounce);
> +	return ret;
> +}
> +
> +static bool dmirror_allocate_chunk(struct dmirror_device *mdevice,
> +				   struct page **ppage)
> +{
> +	struct dmirror_chunk *devmem;
> +	struct resource *res;
> +	unsigned long pfn;
> +	unsigned long pfn_first;
> +	unsigned long pfn_last;
> +	void *ptr;
> +
> +	mutex_lock(&mdevice->devmem_lock);
> +
> +	if (mdevice->devmem_count == mdevice->devmem_capacity) {
> +		struct dmirror_chunk **new_chunks;
> +		unsigned int new_capacity;
> +
> +		new_capacity = mdevice->devmem_capacity +
> +				DEVMEM_CHUNKS_RESERVE;
> +		new_chunks = krealloc(mdevice->devmem_chunks,
> +				sizeof(new_chunks[0]) * new_capacity,
> +				GFP_KERNEL);
> +		if (!new_chunks)
> +			goto err;
> +		mdevice->devmem_capacity = new_capacity;
> +		mdevice->devmem_chunks = new_chunks;
> +	}
> +
> +	res = devm_request_free_mem_region(&mdevice->pdevice->dev,
> +					&iomem_resource, DEVMEM_CHUNK_SIZE);
> +	if (IS_ERR(res))
> +		goto err;
> +
> +	devmem = kzalloc(sizeof(*devmem), GFP_KERNEL);
> +	if (!devmem)
> +		goto err;
> +
> +	devmem->pagemap.type = MEMORY_DEVICE_PRIVATE;
> +	devmem->pagemap.res = *res;
> +	devmem->pagemap.ops = &dmirror_devmem_ops;
> +	ptr = devm_memremap_pages(&mdevice->pdevice->dev, &devmem->pagemap);
> +	if (IS_ERR(ptr))
> +		goto err_free;
> +
> +	devmem->mdevice = mdevice;
> +	pfn_first = devmem->pagemap.res.start >> PAGE_SHIFT;
> +	pfn_last = pfn_first +
> +		(resource_size(&devmem->pagemap.res) >> PAGE_SHIFT);
> +	mdevice->devmem_chunks[mdevice->devmem_count++] = devmem;
> +
> +	mutex_unlock(&mdevice->devmem_lock);
> +
> +	pr_info("added new %u MB chunk (total %u chunks, %u MB) PFNs [0x%lx 0x%lx)\n",
> +		DEVMEM_CHUNK_SIZE / (1024 * 1024),
> +		mdevice->devmem_count,
> +		mdevice->devmem_count * (DEVMEM_CHUNK_SIZE / (1024 * 1024)),
> +		pfn_first, pfn_last);
> +
> +	spin_lock(&mdevice->lock);
> +	for (pfn = pfn_first; pfn < pfn_last; pfn++) {
> +		struct page *page = pfn_to_page(pfn);
> +
> +		page->zone_device_data = mdevice->free_pages;
> +		mdevice->free_pages = page;
> +	}
> +	if (ppage) {
> +		*ppage = mdevice->free_pages;
> +		mdevice->free_pages = (*ppage)->zone_device_data;
> +		mdevice->calloc++;
> +	}
> +	spin_unlock(&mdevice->lock);
> +
> +	return true;
> +
> +err_free:
> +	kfree(devmem);
> +err:
> +	mutex_unlock(&mdevice->devmem_lock);
> +	return false;
> +}
> +
> +static struct page *dmirror_devmem_alloc_page(struct dmirror_device *mdevice)
> +{
> +	struct page *dpage = NULL;
> +	struct page *rpage;
> +
> +	/*
> +	 * This is a fake device so we alloc real system memory to store
> +	 * our device memory.
> +	 */
> +	rpage = alloc_page(GFP_HIGHUSER);
> +	if (!rpage)
> +		return NULL;
> +
> +	spin_lock(&mdevice->lock);
> +
> +	if (mdevice->free_pages) {
> +		dpage = mdevice->free_pages;
> +		mdevice->free_pages = dpage->zone_device_data;
> +		mdevice->calloc++;
> +		spin_unlock(&mdevice->lock);
> +	} else {
> +		spin_unlock(&mdevice->lock);
> +		if (!dmirror_allocate_chunk(mdevice, &dpage))
> +			goto error;
> +	}
> +
> +	dpage->zone_device_data = rpage;
> +	get_page(dpage);
> +	lock_page(dpage);
> +	return dpage;
> +
> +error:
> +	__free_page(rpage);
> +	return NULL;
> +}
> +
> +static void dmirror_migrate_alloc_and_copy(struct migrate_vma *args,
> +					   struct dmirror *dmirror)
> +{
> +	struct dmirror_device *mdevice = dmirror->mdevice;
> +	const unsigned long *src = args->src;
> +	unsigned long *dst = args->dst;
> +	unsigned long addr;
> +
> +	for (addr = args->start; addr < args->end; addr += PAGE_SIZE,
> +						   src++, dst++) {
> +		struct page *spage;
> +		struct page *dpage;
> +		struct page *rpage;
> +
> +		if (!(*src & MIGRATE_PFN_MIGRATE))
> +			continue;
> +
> +		/*
> +		 * Note that spage might be NULL which is OK since it is an
> +		 * unallocated pte_none() or read-only zero page.
> +		 */
> +		spage = migrate_pfn_to_page(*src);
> +
> +		/*
> +		 * Don't migrate device private pages from our own driver or
> +		 * others. For our own we would do a device private memory copy
> +		 * not a migration and for others, we would need to fault the
> +		 * other device's page into system memory first.
> +		 */
> +		if (spage && is_zone_device_page(spage))
> +			continue;
> +
> +		dpage = dmirror_devmem_alloc_page(mdevice);
> +		if (!dpage)
> +			continue;
> +
> +		rpage = dpage->zone_device_data;
> +		if (spage)
> +			copy_highpage(rpage, spage);
> +		else
> +			clear_highpage(rpage);
> +
> +		/*
> +		 * Normally, a device would use the page->zone_device_data to
> +		 * point to the mirror but here we use it to hold the page for
> +		 * the simulated device memory and that page holds the pointer
> +		 * to the mirror.
> +		 */
> +		rpage->zone_device_data = dmirror;
> +
> +		*dst = migrate_pfn(page_to_pfn(dpage)) |
> +			    MIGRATE_PFN_LOCKED;
> +		if ((*src & MIGRATE_PFN_WRITE) ||
> +		    (!spage && args->vma->vm_flags & VM_WRITE))
> +			*dst |= MIGRATE_PFN_WRITE;
> +	}
> +	/* Try to pre-allocate page tables. */
> +	mutex_lock(&dmirror->mutex);
> +	dmirror_pt_walk(dmirror, NULL, args->start, args->end, NULL, true);
> +	mutex_unlock(&dmirror->mutex);
> +}
> +
> +struct dmirror_migrate {
> +	struct hmm_dmirror_cmd		*cmd;
> +	const unsigned long		*src;
> +	const unsigned long		*dst;
> +	unsigned long			start;
> +};
> +
> +static int dmirror_do_migrate(struct dmirror *dmirror,
> +			      unsigned long addr,
> +			      unsigned long end,
> +			      u64 *dptep,
> +			      void *private)
> +{
> +	struct dmirror_migrate *migrate = private;
> +	const unsigned long *src = migrate->src;
> +	const unsigned long *dst = migrate->dst;
> +	unsigned long idx = (addr - migrate->start) >> PAGE_SHIFT;
> +
> +	for (; addr < end; addr += PAGE_SIZE, ++dptep, ++idx) {
> +		struct page *page;
> +		u64 dpte;
> +
> +		if (!(src[idx] & MIGRATE_PFN_MIGRATE))
> +			continue;
> +
> +		page = migrate_pfn_to_page(dst[idx]);
> +		if (!page)
> +			continue;
> +
> +		/*
> +		 * Map the page that holds the data so dmirror_pt_walk()
> +		 * doesn't have to deal with ZONE_DEVICE private pages.
> +		 */
> +		page = page->zone_device_data;
> +		dpte = dmirror_pt_from_page(page) | DPT_DPAGE;
> +		if (dst[idx] & MIGRATE_PFN_WRITE)
> +			dpte |= DPT_WRITE;
> +		*dptep = dpte;
> +	}
> +
> +	return 0;
> +}
> +
> +static void dmirror_migrate_finalize_and_map(struct migrate_vma *args,
> +					     struct dmirror *dmirror,
> +					     struct hmm_dmirror_cmd *cmd)
> +{
> +	struct dmirror_migrate migrate;
> +
> +	migrate.cmd = cmd;
> +	migrate.src = args->src;
> +	migrate.dst = args->dst;
> +	migrate.start = args->start;
> +
> +	/* Map the migrated pages into the device's page tables. */
> +	mutex_lock(&dmirror->mutex);
> +	dmirror_pt_walk(dmirror, dmirror_do_migrate, args->start, args->end,
> +			&migrate, true);
> +	mutex_unlock(&dmirror->mutex);
> +}
> +
> +static int dmirror_migrate(struct dmirror *dmirror,
> +			   struct hmm_dmirror_cmd *cmd)
> +{
> +	unsigned long start, end, addr;
> +	unsigned long size = cmd->npages << PAGE_SHIFT;
> +	struct mm_struct *mm = dmirror->mirror.hmm->mmu_notifier.mm;
> +	struct vm_area_struct *vma;
> +	unsigned long src_pfns[64];
> +	unsigned long dst_pfns[64];
> +	struct dmirror_bounce bounce;
> +	struct migrate_vma args;
> +	unsigned long next;
> +	int ret;
> +
> +	start = cmd->addr;
> +	end = start + size;
> +	if (end < start)
> +		return -EINVAL;
> +
> +	down_read(&mm->mmap_sem);
> +	for (addr = start; addr < end; addr = next) {
> +		next = min(end, addr + (ARRAY_SIZE(src_pfns) << PAGE_SHIFT));
> +
> +		vma = find_vma(mm, addr);
> +		if (!vma || addr < vma->vm_start) {
> +			ret = -EINVAL;
> +			goto out;
> +		}
> +		if (next > vma->vm_end)
> +			next = vma->vm_end;
> +
> +		args.vma = vma;
> +		args.src = src_pfns;
> +		args.dst = dst_pfns;
> +		args.start = addr;
> +		args.end = next;
> +		ret = migrate_vma_setup(&args);
> +		if (ret)
> +			goto out;
> +
> +		dmirror_migrate_alloc_and_copy(&args, dmirror);
> +		migrate_vma_pages(&args);
> +		dmirror_migrate_finalize_and_map(&args, dmirror, cmd);
> +		migrate_vma_finalize(&args);
> +	}
> +	up_read(&mm->mmap_sem);
> +
> +	/* Return the migrated data for verification. */
> +	ret = dmirror_bounce_init(&bounce, start, size);
> +	if (ret)
> +		return ret;
> +	mutex_lock(&dmirror->mutex);
> +	ret = dmirror_pt_walk(dmirror, dmirror_do_read, start, end, &bounce,
> +				false);
> +	mutex_unlock(&dmirror->mutex);
> +	if (ret == 0)
> +		ret = dmirror_bounce_copy_to(&bounce, cmd->ptr);
> +	cmd->cpages = bounce.cpages;
> +	dmirror_bounce_fini(&bounce);
> +	return ret;
> +
> +out:
> +	up_read(&mm->mmap_sem);
> +	return ret;
> +}
> +
> +static void dmirror_mkentry(struct dmirror *dmirror,
> +			    struct hmm_range *range,
> +			    unsigned char *perm,
> +			    uint64_t entry)
> +{
> +	struct page *page;
> +
> +	if (entry == range->values[HMM_PFN_ERROR]) {
> +		*perm = HMM_DMIRROR_PROT_ERROR;
> +		return;
> +	}
> +	page = hmm_device_entry_to_page(range, entry);
> +	if (!page) {
> +		*perm = HMM_DMIRROR_PROT_NONE;
> +		return;
> +	}
> +	if (entry & range->flags[HMM_PFN_DEVICE_PRIVATE]) {
> +		/* Is the page migrated to this device or some other? */
> +		if (dmirror->mdevice == dmirror_page_to_device(page))
> +			*perm = HMM_DMIRROR_PROT_DEV_PRIVATE_LOCAL;
> +		else
> +			*perm = HMM_DMIRROR_PROT_DEV_PRIVATE_REMOTE;
> +	} else if (is_zero_pfn(page_to_pfn(page)))
> +		*perm = HMM_DMIRROR_PROT_ZERO;
> +	else
> +		*perm = HMM_DMIRROR_PROT_NONE;
> +	if (entry & range->flags[HMM_PFN_WRITE])
> +		*perm |= HMM_DMIRROR_PROT_WRITE;
> +	else
> +		*perm |= HMM_DMIRROR_PROT_READ;
> +}
> +
> +static int dmirror_snapshot(struct dmirror *dmirror,
> +			    struct hmm_dmirror_cmd *cmd)
> +{
> +	struct mm_struct *mm = dmirror->mirror.hmm->mmu_notifier.mm;
> +	unsigned long start, end;
> +	unsigned long size = cmd->npages << PAGE_SHIFT;
> +	unsigned long addr;
> +	unsigned long next;
> +	uint64_t pfns[64];
> +	unsigned char perm[64];
> +	char __user *uptr;
> +	struct hmm_range range = {
> +		.pfns = pfns,
> +		.flags = dmirror_hmm_flags,
> +		.values = dmirror_hmm_values,
> +		.pfn_shift = DPT_SHIFT,
> +		.pfn_flags_mask = ~0ULL,
> +	};
> +	int ret = 0;
> +
> +	start = cmd->addr;
> +	end = start + size;
> +	uptr = (void __user *)cmd->ptr;
> +
> +	for (addr = start; addr < end; ) {
> +		long count;
> +		unsigned long i;
> +		unsigned long n;
> +
> +		next = min(addr + (ARRAY_SIZE(pfns) << PAGE_SHIFT), end);
> +		range.start = addr;
> +		range.end = next;
> +
> +		down_read(&mm->mmap_sem);
> +
> +		ret = hmm_range_register(&range, &dmirror->mirror);
> +		if (ret) {
> +			up_read(&mm->mmap_sem);
> +			break;
> +		}
> +
> +		if (!hmm_range_wait_until_valid(&range,
> +						DMIRROR_RANGE_FAULT_TIMEOUT)) {
> +			hmm_range_unregister(&range);
> +			up_read(&mm->mmap_sem);
> +			continue;
> +		}
> +
> +		count = hmm_range_fault(&range, HMM_FAULT_SNAPSHOT);
> +		if (count < 0) {
> +			ret = count;
> +			hmm_range_unregister(&range);
> +			up_read(&mm->mmap_sem);
> +			if (ret == -EBUSY)
> +				continue;
> +			break;
> +		}
> +
> +		if (!hmm_range_valid(&range)) {
> +			hmm_range_unregister(&range);
> +			up_read(&mm->mmap_sem);
> +			continue;
> +		}
> +
> +		n = (next - addr) >> PAGE_SHIFT;
> +		for (i = 0; i < n; i++)
> +			dmirror_mkentry(dmirror, &range, perm + i, pfns[i]);
> +		hmm_range_unregister(&range);
> +		up_read(&mm->mmap_sem);
> +
> +		ret = copy_to_user(uptr, perm, n);
> +		if (ret)
> +			break;
> +
> +		cmd->cpages += n;
> +		uptr += n;
> +		addr = next;
> +	}
> +
> +	return ret;
> +}
> +
> +static long dmirror_fops_unlocked_ioctl(struct file *filp,
> +					unsigned int command,
> +					unsigned long arg)
> +{
> +	void __user *uarg = (void __user *)arg;
> +	struct hmm_dmirror_cmd cmd;
> +	struct dmirror *dmirror;
> +	int ret;
> +
> +	dmirror = filp->private_data;
> +	if (!dmirror)
> +		return -EINVAL;
> +
> +	ret = copy_from_user(&cmd, uarg, sizeof(cmd));
> +	if (ret)
> +		return ret;
> +
> +	if (cmd.addr & ~PAGE_MASK)
> +		return -EINVAL;
> +	if (cmd.addr >= (cmd.addr + (cmd.npages << PAGE_SHIFT)))
> +		return -EINVAL;
> +
> +	cmd.cpages = 0;
> +	cmd.faults = 0;
> +
> +	switch (command) {
> +	case HMM_DMIRROR_READ:
> +		ret = dmirror_read(dmirror, &cmd);
> +		break;
> +
> +	case HMM_DMIRROR_WRITE:
> +		ret = dmirror_write(dmirror, &cmd);
> +		break;
> +
> +	case HMM_DMIRROR_MIGRATE:
> +		ret = dmirror_migrate(dmirror, &cmd);
> +		break;
> +
> +	case HMM_DMIRROR_SNAPSHOT:
> +		ret = dmirror_snapshot(dmirror, &cmd);
> +		break;
> +
> +	default:
> +		return -EINVAL;
> +	}
> +	if (ret)
> +		return ret;
> +
> +	return copy_to_user(uarg, &cmd, sizeof(cmd));
> +}
> +
> +static const struct file_operations dmirror_fops = {
> +	.read		= dmirror_fops_read,
> +	.write		= dmirror_fops_write,
> +	.mmap		= dmirror_fops_mmap,
> +	.open		= dmirror_fops_open,
> +	.release	= dmirror_fops_release,
> +	.unlocked_ioctl = dmirror_fops_unlocked_ioctl,
> +	.llseek		= default_llseek,
> +	.owner		= THIS_MODULE,
> +};
> +
> +static void dmirror_devmem_free(struct page *page)
> +{
> +	struct page *rpage = page->zone_device_data;
> +	struct dmirror_device *mdevice;
> +
> +	if (rpage)
> +		__free_page(rpage);
> +
> +	mdevice = dmirror_page_to_device(page);
> +
> +	spin_lock(&mdevice->lock);
> +	mdevice->cfree++;
> +	page->zone_device_data = mdevice->free_pages;
> +	mdevice->free_pages = page;
> +	spin_unlock(&mdevice->lock);
> +}
> +
> +static vm_fault_t dmirror_devmem_fault_alloc_and_copy(struct migrate_vma *args,
> +						struct dmirror_device *mdevice)
> +{
> +	struct vm_area_struct *vma = args->vma;
> +	const unsigned long *src = args->src;
> +	unsigned long *dst = args->dst;
> +	unsigned long start = args->start;
> +	unsigned long end = args->end;
> +	unsigned long addr;
> +
> +	for (addr = start; addr < end; addr += PAGE_SIZE,
> +				       src++, dst++) {
> +		struct page *dpage, *spage;
> +
> +		spage = migrate_pfn_to_page(*src);
> +		if (!spage || !(*src & MIGRATE_PFN_MIGRATE))
> +			continue;
> +		if (!dmirror_device_is_mine(mdevice, spage))
> +			continue;
> +		spage = spage->zone_device_data;
> +
> +		dpage = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, addr);
> +		if (!dpage)
> +			continue;
> +
> +		lock_page(dpage);
> +		copy_highpage(dpage, spage);
> +		*dst = migrate_pfn(page_to_pfn(dpage)) |
> +			    MIGRATE_PFN_LOCKED;
> +		if (*src & MIGRATE_PFN_WRITE)
> +			*dst |= MIGRATE_PFN_WRITE;
> +	}
> +	return 0;
> +}
> +
> +static void dmirror_devmem_fault_finalize_and_map(struct migrate_vma *args,
> +						  struct dmirror *dmirror)
> +{
> +	/* Invalidate the device's page table mapping. */
> +	mutex_lock(&dmirror->mutex);
> +	dmirror_pt_walk(dmirror, dmirror_do_update, args->start, args->end,
> +			NULL, false);
> +	mutex_unlock(&dmirror->mutex);
> +}
> +
> +static vm_fault_t dmirror_devmem_fault(struct vm_fault *vmf)
> +{
> +	struct migrate_vma args;
> +	unsigned long src_pfns;
> +	unsigned long dst_pfns;
> +	struct page *rpage;
> +	struct dmirror *dmirror;
> +	vm_fault_t ret;
> +
> +	/* FIXME demonstrate how we can adjust migrate range */
> +	args.vma = vmf->vma;
> +	args.start = vmf->address;
> +	args.end = args.start + PAGE_SIZE;
> +	args.src = &src_pfns;
> +	args.dst = &dst_pfns;
> +
> +	if (migrate_vma_setup(&args))
> +		return VM_FAULT_SIGBUS;
> +
> +	/*
> +	 * Normally, a device would use the page->zone_device_data to point to
> +	 * the mirror but here we use it to hold the page for the simulated
> +	 * device memory and that page holds the pointer to the mirror.
> +	 */
> +	rpage = vmf->page->zone_device_data;
> +	dmirror = rpage->zone_device_data;
> +
> +	ret = dmirror_devmem_fault_alloc_and_copy(&args, dmirror->mdevice);
> +	if (ret)
> +		return ret;
> +	migrate_vma_pages(&args);
> +	dmirror_devmem_fault_finalize_and_map(&args, dmirror);
> +	migrate_vma_finalize(&args);
> +	return 0;
> +}
> +
> +static const struct dev_pagemap_ops dmirror_devmem_ops = {
> +	.page_free	= dmirror_devmem_free,
> +	.migrate_to_ram	= dmirror_devmem_fault,
> +};
> +
> +static void dmirror_pdev_del(void *arg)
> +{
> +	struct dmirror_device *mdevice = arg;
> +	unsigned int i;
> +
> +	if (mdevice->devmem_chunks) {
> +		for (i = 0; i < mdevice->devmem_count; i++)
> +			kfree(mdevice->devmem_chunks[i]);
> +		kfree(mdevice->devmem_chunks);
> +	}
> +
> +	cdev_del(&mdevice->cdevice);
> +	kfree(mdevice);
> +}
> +
> +static int dmirror_probe(struct platform_device *pdev)
> +{
> +	struct dmirror_device *mdevice;
> +	int ret;
> +
> +	mdevice = kzalloc(sizeof(*mdevice), GFP_KERNEL);
> +	if (!mdevice)
> +		return -ENOMEM;
> +
> +	mdevice->pdevice = pdev;
> +	mutex_init(&mdevice->devmem_lock);
> +	spin_lock_init(&mdevice->lock);
> +
> +	cdev_init(&mdevice->cdevice, &dmirror_fops);
> +	ret = cdev_add(&mdevice->cdevice, pdev->dev.devt, 1);
> +	if (ret) {
> +		kfree(mdevice);
> +		return ret;
> +	}
> +
> +	platform_set_drvdata(pdev, mdevice);
> +	ret = devm_add_action_or_reset(&pdev->dev, dmirror_pdev_del, mdevice);
> +	if (ret)
> +		return ret;
> +
> +	/* Build list of free struct page */
> +	dmirror_allocate_chunk(mdevice, NULL);
> +
> +	return 0;
> +}
> +
> +static int dmirror_remove(struct platform_device *pdev)
> +{
> +	/* all probe actions are unwound by devm */
> +	return 0;
> +}
> +
> +static struct platform_driver dmirror_device_driver = {
> +	.probe		= dmirror_probe,
> +	.remove		= dmirror_remove,
> +	.driver		= {
> +		.name	= "HMM_DMIRROR",
> +	},
> +};
> +
> +static int __init hmm_dmirror_init(void)
> +{
> +	int ret;
> +	int id;
> +
> +	ret = platform_driver_register(&dmirror_device_driver);
> +	if (ret)
> +		return ret;
> +
> +	ret = alloc_chrdev_region(&dmirror_dev, 0, DMIRROR_NDEVICES,
> +				  "HMM_DMIRROR");
> +	if (ret)
> +		goto err_unreg;
> +
> +	for (id = 0; id < DMIRROR_NDEVICES; id++) {
> +		struct platform_device *pd;
> +
> +		pd = platform_device_alloc("HMM_DMIRROR", id);
> +		if (!pd) {
> +			ret = -ENOMEM;
> +			goto err_chrdev;
> +		}
> +		pd->dev.devt = MKDEV(MAJOR(dmirror_dev), id);
> +		ret = platform_device_add(pd);
> +		if (ret) {
> +			platform_device_put(pd);
> +			goto err_chrdev;
> +		}
> +		dmirror_platform_devices[id] = pd;
> +	}
> +
> +	/*
> +	 * Allocate a zero page to simulate a reserved page of device private
> +	 * memory which is always zero. The zero_pfn page isn't used just to
> +	 * make the code here simpler (i.e., we need a struct page for it).
> +	 */
> +	dmirror_zero_page = alloc_page(GFP_HIGHUSER | __GFP_ZERO);
> +	if (!dmirror_zero_page)
> +		goto err_chrdev;
> +
> +	pr_info("hmm_dmirror loaded. This is only for testing HMM.\n");
> +	return 0;
> +
> +err_chrdev:
> +	while (--id >= 0) {
> +		platform_device_unregister(dmirror_platform_devices[id]);
> +		dmirror_platform_devices[id] = NULL;
> +	}
> +	unregister_chrdev_region(dmirror_dev, 1);
> +err_unreg:
> +	platform_driver_unregister(&dmirror_device_driver);
> +	return ret;
> +}
> +
> +static void __exit hmm_dmirror_exit(void)
> +{
> +	int id;
> +
> +	if (dmirror_zero_page)
> +		__free_page(dmirror_zero_page);
> +	for (id = 0; id < DMIRROR_NDEVICES; id++)
> +		platform_device_unregister(dmirror_platform_devices[id]);
> +	unregister_chrdev_region(dmirror_dev, DMIRROR_NDEVICES);
> +	platform_driver_unregister(&dmirror_device_driver);
> +	mmu_notifier_synchronize();
> +}
> +
> +module_init(hmm_dmirror_init);
> +module_exit(hmm_dmirror_exit);
> +MODULE_LICENSE("GPL");
> diff --git a/include/Kbuild b/include/Kbuild
> index ffba79483cc5..6ffb44a45957 100644
> --- a/include/Kbuild
> +++ b/include/Kbuild
> @@ -1063,6 +1063,7 @@ header-test-			+= uapi/linux/coda_psdev.h
>  header-test-			+= uapi/linux/errqueue.h
>  header-test-			+= uapi/linux/eventpoll.h
>  header-test-			+= uapi/linux/hdlc/ioctl.h
> +header-test-			+= uapi/linux/hmm_dmirror.h
>  header-test-			+= uapi/linux/input.h
>  header-test-			+= uapi/linux/kvm.h
>  header-test-			+= uapi/linux/kvm_para.h
> diff --git a/include/uapi/linux/hmm_dmirror.h b/include/uapi/linux/hmm_dmirror.h
> new file mode 100644
> index 000000000000..61d3643aff95
> --- /dev/null
> +++ b/include/uapi/linux/hmm_dmirror.h
> @@ -0,0 +1,74 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +/*
> + * Copyright 2013 Red Hat Inc.
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License as
> + * published by the Free Software Foundation; either version 2 of
> + * the License, or (at your option) any later version.
> + *
> + * 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.
> + *
> + * Authors: Jérôme Glisse <jglisse@xxxxxxxxxx>
> + */
> +/*
> + * This is a dummy driver to exercise the HMM (heterogeneous memory management)
> + * API of the kernel. It allows a userspace program to expose its entire address
> + * space through the HMM dummy driver file.
> + */
> +#ifndef _UAPI_LINUX_HMM_DMIRROR_H
> +#define _UAPI_LINUX_HMM_DMIRROR_H
> +
> +#include <linux/types.h>
> +#include <linux/ioctl.h>
> +
> +/*
> + * Structure to pass to the HMM test driver to mimic a device accessing
> + * system memory and ZONE_DEVICE private memory through device page tables.
> + *
> + * @addr: (in) user address the device will read/write
> + * @ptr: (in) user address where device data is copied to/from
> + * @npages: (in) number of pages to read/write
> + * @cpages: (out) number of pages copied
> + * @faults: (out) number of device page faults seen
> + */
> +struct hmm_dmirror_cmd {
> +	__u64		addr;
> +	__u64		ptr;
> +	__u64		npages;
> +	__u64		cpages;
> +	__u64		faults;
> +};
> +
> +/* Expose the address space of the calling process through hmm dummy dev file */
> +#define HMM_DMIRROR_READ		_IOWR('H', 0x00, struct hmm_dmirror_cmd)
> +#define HMM_DMIRROR_WRITE		_IOWR('H', 0x01, struct hmm_dmirror_cmd)
> +#define HMM_DMIRROR_MIGRATE		_IOWR('H', 0x02, struct hmm_dmirror_cmd)
> +#define HMM_DMIRROR_SNAPSHOT		_IOWR('H', 0x03, struct hmm_dmirror_cmd)
> +
> +/*
> + * Values returned in hmm_dmirror_cmd.ptr for HMM_DMIRROR_SNAPSHOT.
> + * HMM_DMIRROR_PROT_ERROR: no valid mirror PTE for this page
> + * HMM_DMIRROR_PROT_NONE: unpopulated PTE or PTE with no access
> + * HMM_DMIRROR_PROT_READ: read-only PTE
> + * HMM_DMIRROR_PROT_WRITE: read/write PTE
> + * HMM_DMIRROR_PROT_ZERO: special read-only zero page
> + * HMM_DMIRROR_PROT_DEV_PRIVATE_LOCAL: Migrated device private page on the
> + *					device the ioctl() is made
> + * HMM_DMIRROR_PROT_DEV_PRIVATE_REMOTE: Migrated device private page on some
> + *					other device
> + */
> +enum {
> +	HMM_DMIRROR_PROT_ERROR			= 0xFF,
> +	HMM_DMIRROR_PROT_NONE			= 0x00,
> +	HMM_DMIRROR_PROT_READ			= 0x01,
> +	HMM_DMIRROR_PROT_WRITE			= 0x02,
> +	HMM_DMIRROR_PROT_ZERO			= 0x10,
> +	HMM_DMIRROR_PROT_DEV_PRIVATE_LOCAL	= 0x20,
> +	HMM_DMIRROR_PROT_DEV_PRIVATE_REMOTE	= 0x30,
> +};
> +
> +#endif /* _UAPI_LINUX_HMM_DMIRROR_H */
> diff --git a/tools/testing/selftests/vm/.gitignore b/tools/testing/selftests/vm/.gitignore
> index 31b3c98b6d34..3054565b3f07 100644
> --- a/tools/testing/selftests/vm/.gitignore
> +++ b/tools/testing/selftests/vm/.gitignore
> @@ -14,3 +14,4 @@ virtual_address_range
>  gup_benchmark
>  va_128TBswitch
>  map_fixed_noreplace
> +hmm-tests
> diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile
> index 9534dc2bc929..5643cfb5e3d6 100644
> --- a/tools/testing/selftests/vm/Makefile
> +++ b/tools/testing/selftests/vm/Makefile
> @@ -5,6 +5,7 @@ CFLAGS = -Wall -I ../../../../usr/include $(EXTRA_CFLAGS)
>  LDLIBS = -lrt
>  TEST_GEN_FILES = compaction_test
>  TEST_GEN_FILES += gup_benchmark
> +TEST_GEN_FILES += hmm-tests
>  TEST_GEN_FILES += hugepage-mmap
>  TEST_GEN_FILES += hugepage-shm
>  TEST_GEN_FILES += map_hugetlb
> @@ -26,6 +27,8 @@ TEST_FILES := test_vmalloc.sh
>  KSFT_KHDR_INSTALL := 1
>  include ../lib.mk
>  
> +$(OUTPUT)/hmm-tests: LDLIBS += -lhugetlbfs -lpthread
> +
>  $(OUTPUT)/userfaultfd: LDLIBS += -lpthread
>  
>  $(OUTPUT)/mlock-random-test: LDLIBS += -lcap
> diff --git a/tools/testing/selftests/vm/config b/tools/testing/selftests/vm/config
> index 1c0d76cb5adf..34cfab18e737 100644
> --- a/tools/testing/selftests/vm/config
> +++ b/tools/testing/selftests/vm/config
> @@ -1,2 +1,5 @@
>  CONFIG_SYSVIPC=y
>  CONFIG_USERFAULTFD=y
> +CONFIG_HMM_MIRROR=y
> +CONFIG_DEVICE_PRIVATE=y
> +CONFIG_HMM_DMIRROR=m
> diff --git a/tools/testing/selftests/vm/hmm-tests.c b/tools/testing/selftests/vm/hmm-tests.c
> new file mode 100644
> index 000000000000..f4ae6188fd0e
> --- /dev/null
> +++ b/tools/testing/selftests/vm/hmm-tests.c
> @@ -0,0 +1,1311 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright 2013 Red Hat Inc.
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License as
> + * published by the Free Software Foundation; either version 2 of
> + * the License, or (at your option) any later version.
> + *
> + * 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.
> + *
> + * Authors: Jérôme Glisse <jglisse@xxxxxxxxxx>
> + */
> +
> +/*
> + * HMM stands for Heterogeneous Memory Management, it is a helper layer inside
> + * the linux kernel to help device drivers mirror a process address space in
> + * the device. This allows the device to use the same address space which
> + * makes communication and data exchange a lot easier.
> + *
> + * This framework's sole purpose is to exercise various code paths inside
> + * the kernel to make sure that HMM performs as expected and to flush out any
> + * bugs.
> + */
> +
> +#include "../kselftest_harness.h"
> +
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <stdint.h>
> +#include <unistd.h>
> +#include <strings.h>
> +#include <time.h>
> +#include <pthread.h>
> +#include <hugetlbfs.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +#include <sys/mman.h>
> +#include <sys/ioctl.h>
> +#include <linux/hmm_dmirror.h>
> +
> +struct hmm_buffer {
> +	void		*ptr;
> +	void		*mirror;
> +	unsigned long	size;
> +	int		fd;
> +	uint64_t	cpages;
> +	uint64_t	faults;
> +};
> +
> +#define TWOMEG		(1 << 21)
> +#define HMM_BUFFER_SIZE (1024 << 12)
> +#define HMM_PATH_MAX    64
> +#define NTIMES		256
> +
> +#define ALIGN(x, a) (((x) + (a - 1)) & (~((a) - 1)))
> +
> +FIXTURE(hmm)
> +{
> +	int		fd;
> +	unsigned int	page_size;
> +	unsigned int	page_shift;
> +};
> +
> +FIXTURE(hmm2)
> +{
> +	int		fd0;
> +	int		fd1;
> +	unsigned int	page_size;
> +	unsigned int	page_shift;
> +};
> +
> +static int hmm_open(int unit)
> +{
> +	char pathname[HMM_PATH_MAX];
> +	int fd;
> +
> +	snprintf(pathname, sizeof(pathname), "/dev/hmm_dmirror%d", unit);
> +	fd = open(pathname, O_RDWR, 0);
> +	if (fd < 0)
> +		fprintf(stderr, "could not open hmm dmirror driver (%s)\n",
> +			pathname);
> +	return fd;
> +}
> +
> +FIXTURE_SETUP(hmm)
> +{
> +	self->page_size = sysconf(_SC_PAGE_SIZE);
> +	self->page_shift = ffs(self->page_size) - 1;
> +
> +	self->fd = hmm_open(0);
> +	ASSERT_GE(self->fd, 0);
> +}
> +
> +FIXTURE_SETUP(hmm2)
> +{
> +	self->page_size = sysconf(_SC_PAGE_SIZE);
> +	self->page_shift = ffs(self->page_size) - 1;
> +
> +	self->fd0 = hmm_open(0);
> +	ASSERT_GE(self->fd0, 0);
> +	self->fd1 = hmm_open(1);
> +	ASSERT_GE(self->fd1, 0);
> +}
> +
> +FIXTURE_TEARDOWN(hmm)
> +{
> +	int ret = close(self->fd);
> +
> +	ASSERT_EQ(ret, 0);
> +	self->fd = -1;
> +}
> +
> +FIXTURE_TEARDOWN(hmm2)
> +{
> +	int ret = close(self->fd0);
> +
> +	ASSERT_EQ(ret, 0);
> +	self->fd0 = -1;
> +
> +	ret = close(self->fd1);
> +	ASSERT_EQ(ret, 0);
> +	self->fd1 = -1;
> +}
> +
> +static int hmm_dmirror_cmd(int fd,
> +			   unsigned long request,
> +			   struct hmm_buffer *buffer,
> +			   unsigned long npages)
> +{
> +	struct hmm_dmirror_cmd cmd;
> +	int ret;
> +
> +	/* Simulate a device reading system memory. */
> +	cmd.addr = (__u64)buffer->ptr;
> +	cmd.ptr = (__u64)buffer->mirror;
> +	cmd.npages = npages;
> +
> +	for (;;) {
> +		ret = ioctl(fd, request, &cmd);
> +		if (ret == 0)
> +			break;
> +		if (errno == EINTR)
> +			continue;
> +		return -errno;
> +	}
> +	buffer->cpages = cmd.cpages;
> +	buffer->faults = cmd.faults;
> +
> +	return 0;
> +}
> +
> +static void hmm_buffer_free(struct hmm_buffer *buffer)
> +{
> +	if (buffer == NULL)
> +		return;
> +
> +	if (buffer->ptr)
> +		munmap(buffer->ptr, buffer->size);
> +	free(buffer->mirror);
> +	free(buffer);
> +}
> +
> +/*
> + * Create a temporary file that will be deleted on close.
> + */
> +static int hmm_create_file(unsigned long size)
> +{
> +	char path[HMM_PATH_MAX];
> +	int fd;
> +
> +	strcpy(path, "/tmp");
> +	fd = open(path, O_TMPFILE | O_EXCL | O_RDWR, 0600);
> +	if (fd >= 0) {
> +		int r;
> +
> +		do {
> +			r = ftruncate(fd, size);
> +		} while (r == -1 && errno == EINTR);
> +		if (!r)
> +			return fd;
> +		close(fd);
> +	}
> +	return -1;
> +}
> +
> +/*
> + * Return a random unsigned number.
> + */
> +static unsigned int hmm_random(void)
> +{
> +	static int fd = -1;
> +	unsigned int r;
> +
> +	if (fd < 0) {
> +		fd = open("/dev/urandom", O_RDONLY);
> +		if (fd < 0) {
> +			fprintf(stderr, "%s:%d failed to open /dev/urandom\n",
> +					__FILE__, __LINE__);
> +			return ~0U;
> +		}
> +	}
> +	read(fd, &r, sizeof(r));
> +	return r;
> +}
> +
> +static void hmm_nanosleep(unsigned int n)
> +{
> +	struct timespec t;
> +
> +	t.tv_sec = 0;
> +	t.tv_nsec = n;
> +	nanosleep(&t, NULL);
> +}
> +
> +/*
> + * Simple NULL test of device open/close.
> + */
> +TEST_F(hmm, open_close)
> +{
> +}
> +
> +/*
> + * Read private anonymous memory.
> + */
> +TEST_F(hmm, anon_read)
> +{
> +	struct hmm_buffer *buffer;
> +	unsigned long npages;
> +	unsigned long size;
> +	unsigned long i;
> +	int *ptr;
> +	int ret;
> +	int val;
> +
> +	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
> +	ASSERT_NE(npages, 0);
> +	size = npages << self->page_shift;
> +
> +	buffer = malloc(sizeof(*buffer));
> +	ASSERT_NE(buffer, NULL);
> +
> +	buffer->fd = -1;
> +	buffer->size = size;
> +	buffer->mirror = malloc(size);
> +	ASSERT_NE(buffer->mirror, NULL);
> +
> +	buffer->ptr = mmap(NULL, size,
> +			   PROT_READ | PROT_WRITE,
> +			   MAP_PRIVATE | MAP_ANONYMOUS,
> +			   buffer->fd, 0);
> +	ASSERT_NE(buffer->ptr, MAP_FAILED);
> +
> +	/*
> +	 * Initialize buffer in system memory but leave the first two pages
> +	 * zero (pte_none and pfn_zero).
> +	 */
> +	i = 2 * self->page_size / sizeof(*ptr);
> +	for (ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +		ptr[i] = i;
> +
> +	/* Set buffer permission to read-only. */
> +	ret = mprotect(buffer->ptr, size, PROT_READ);
> +	ASSERT_EQ(ret, 0);
> +
> +	/* Populate the CPU page table with a special zero page. */
> +	val = *(int *)(buffer->ptr + self->page_size);
> +	ASSERT_EQ(val, 0);
> +
> +	/* Simulate a device reading system memory. */
> +	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_READ, buffer, npages);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(buffer->cpages, npages);
> +	ASSERT_EQ(buffer->faults, 1);
> +
> +	/* Check what the device read. */
> +	ptr = buffer->mirror;
> +	for (i = 0; i < 2 * self->page_size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], 0);
> +	for (; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], i);
> +
> +	hmm_buffer_free(buffer);
> +}
> +
> +/*
> + * Read private anonymous memory which has been protected with
> + * mprotect() PROT_NONE.
> + */
> +TEST_F(hmm, anon_read_prot)
> +{
> +	struct hmm_buffer *buffer;
> +	unsigned long npages;
> +	unsigned long size;
> +	unsigned long i;
> +	int *ptr;
> +	int ret;
> +
> +	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
> +	ASSERT_NE(npages, 0);
> +	size = npages << self->page_shift;
> +
> +	buffer = malloc(sizeof(*buffer));
> +	ASSERT_NE(buffer, NULL);
> +
> +	buffer->fd = -1;
> +	buffer->size = size;
> +	buffer->mirror = malloc(size);
> +	ASSERT_NE(buffer->mirror, NULL);
> +
> +	buffer->ptr = mmap(NULL, size,
> +			   PROT_READ | PROT_WRITE,
> +			   MAP_PRIVATE | MAP_ANONYMOUS,
> +			   buffer->fd, 0);
> +	ASSERT_NE(buffer->ptr, MAP_FAILED);
> +
> +	/* Initialize buffer in system memory. */
> +	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +		ptr[i] = i;
> +
> +	/* Initialize mirror buffer so we can verify it isn't written. */
> +	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> +		ptr[i] = -i;
> +
> +	/* Protect buffer from reading. */
> +	ret = mprotect(buffer->ptr, size, PROT_NONE);
> +	ASSERT_EQ(ret, 0);
> +
> +	/* Simulate a device reading system memory. */
> +	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_READ, buffer, npages);
> +	ASSERT_EQ(ret, -EFAULT);
> +
> +	/* Allow CPU to read the buffer so we can check it. */
> +	ret = mprotect(buffer->ptr, size, PROT_READ);
> +	ASSERT_EQ(ret, 0);
> +	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], i);
> +
> +	/* Check what the device read. */
> +	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], -i);
> +
> +	hmm_buffer_free(buffer);
> +}
> +
> +/*
> + * Write private anonymous memory.
> + */
> +TEST_F(hmm, anon_write)
> +{
> +	struct hmm_buffer *buffer;
> +	unsigned long npages;
> +	unsigned long size;
> +	unsigned long i;
> +	int *ptr;
> +	int ret;
> +
> +	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
> +	ASSERT_NE(npages, 0);
> +	size = npages << self->page_shift;
> +
> +	buffer = malloc(sizeof(*buffer));
> +	ASSERT_NE(buffer, NULL);
> +
> +	buffer->fd = -1;
> +	buffer->size = size;
> +	buffer->mirror = malloc(size);
> +	ASSERT_NE(buffer->mirror, NULL);
> +
> +	buffer->ptr = mmap(NULL, size,
> +			   PROT_READ | PROT_WRITE,
> +			   MAP_PRIVATE | MAP_ANONYMOUS,
> +			   buffer->fd, 0);
> +	ASSERT_NE(buffer->ptr, MAP_FAILED);
> +
> +	/* Initialize data that the device will write to buffer->ptr. */
> +	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> +		ptr[i] = i;
> +
> +	/* Simulate a device writing system memory. */
> +	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_WRITE, buffer, npages);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(buffer->cpages, npages);
> +	ASSERT_EQ(buffer->faults, 1);
> +
> +	/* Check what the device wrote. */
> +	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], i);
> +
> +	hmm_buffer_free(buffer);
> +}
> +
> +/*
> + * Write private anonymous memory which has been protected with
> + * mprotect() PROT_READ.
> + */
> +TEST_F(hmm, anon_write_prot)
> +{
> +	struct hmm_buffer *buffer;
> +	unsigned long npages;
> +	unsigned long size;
> +	unsigned long i;
> +	int *ptr;
> +	int ret;
> +
> +	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
> +	ASSERT_NE(npages, 0);
> +	size = npages << self->page_shift;
> +
> +	buffer = malloc(sizeof(*buffer));
> +	ASSERT_NE(buffer, NULL);
> +
> +	buffer->fd = -1;
> +	buffer->size = size;
> +	buffer->mirror = malloc(size);
> +	ASSERT_NE(buffer->mirror, NULL);
> +
> +	buffer->ptr = mmap(NULL, size,
> +			   PROT_READ,
> +			   MAP_PRIVATE | MAP_ANONYMOUS,
> +			   buffer->fd, 0);
> +	ASSERT_NE(buffer->ptr, MAP_FAILED);
> +
> +	/* Simulate a device reading a zero page of memory. */
> +	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_READ, buffer, 1);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(buffer->cpages, 1);
> +	ASSERT_EQ(buffer->faults, 1);
> +
> +	/* Initialize data that the device will write to buffer->ptr. */
> +	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> +		ptr[i] = i;
> +
> +	/* Simulate a device writing system memory. */
> +	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_WRITE, buffer, npages);
> +	ASSERT_EQ(ret, -EPERM);
> +
> +	/* Check what the device wrote. */
> +	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], 0);
> +
> +	/* Now allow writing and see that the zero page is replaced. */
> +	ret = mprotect(buffer->ptr, size, PROT_WRITE | PROT_READ);
> +	ASSERT_EQ(ret, 0);
> +
> +	/* Simulate a device writing system memory. */
> +	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_WRITE, buffer, npages);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(buffer->cpages, npages);
> +	ASSERT_EQ(buffer->faults, 1);
> +
> +	/* Check what the device wrote. */
> +	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], i);
> +
> +	hmm_buffer_free(buffer);
> +}
> +
> +/*
> + * Check that a device writing an anonymous private mapping
> + * will copy-on-write if a child process inherits the mapping.
> + */
> +TEST_F(hmm, anon_write_child)
> +{
> +	struct hmm_buffer *buffer;
> +	unsigned long npages;
> +	unsigned long size;
> +	unsigned long i;
> +	int *ptr;
> +	pid_t pid;
> +	int child_fd;
> +	int ret;
> +
> +	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
> +	ASSERT_NE(npages, 0);
> +	size = npages << self->page_shift;
> +
> +	buffer = malloc(sizeof(*buffer));
> +	ASSERT_NE(buffer, NULL);
> +
> +	buffer->fd = -1;
> +	buffer->size = size;
> +	buffer->mirror = malloc(size);
> +	ASSERT_NE(buffer->mirror, NULL);
> +
> +	buffer->ptr = mmap(NULL, size,
> +			   PROT_READ | PROT_WRITE,
> +			   MAP_PRIVATE | MAP_ANONYMOUS,
> +			   buffer->fd, 0);
> +	ASSERT_NE(buffer->ptr, MAP_FAILED);
> +
> +	/* Initialize buffer->ptr so we can tell if it is written. */
> +	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +		ptr[i] = i;
> +
> +	/* Initialize data that the device will write to buffer->ptr. */
> +	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> +		ptr[i] = -i;
> +
> +	pid = fork();
> +	if (pid == -1)
> +		ASSERT_EQ(pid, 0);
> +	if (pid != 0) {
> +		waitpid(pid, &ret, 0);
> +		ASSERT_EQ(WIFEXITED(ret), 1);
> +
> +		/* Check that the parent's buffer did not change. */
> +		for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +			ASSERT_EQ(ptr[i], i);
> +		return;
> +	}
> +
> +	/* Check that we see the parent's values. */
> +	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], i);
> +	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], -i);
> +
> +	/* The child process needs its own mirror to its own mm. */
> +	child_fd = hmm_open(0);
> +	ASSERT_GE(child_fd, 0);
> +
> +	/* Simulate a device writing system memory. */
> +	ret = hmm_dmirror_cmd(child_fd, HMM_DMIRROR_WRITE, buffer, npages);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(buffer->cpages, npages);
> +	ASSERT_EQ(buffer->faults, 1);
> +
> +	/* Check what the device wrote. */
> +	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], -i);
> +
> +	close(child_fd);
> +	exit(0);
> +}
> +
> +/*
> + * Check that a device writing an anonymous shared mapping
> + * will not copy-on-write if a child process inherits the mapping.
> + */
> +TEST_F(hmm, anon_write_child_shared)
> +{
> +	struct hmm_buffer *buffer;
> +	unsigned long npages;
> +	unsigned long size;
> +	unsigned long i;
> +	int *ptr;
> +	pid_t pid;
> +	int child_fd;
> +	int ret;
> +
> +	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
> +	ASSERT_NE(npages, 0);
> +	size = npages << self->page_shift;
> +
> +	buffer = malloc(sizeof(*buffer));
> +	ASSERT_NE(buffer, NULL);
> +
> +	buffer->fd = -1;
> +	buffer->size = size;
> +	buffer->mirror = malloc(size);
> +	ASSERT_NE(buffer->mirror, NULL);
> +
> +	buffer->ptr = mmap(NULL, size,
> +			   PROT_READ | PROT_WRITE,
> +			   MAP_SHARED | MAP_ANONYMOUS,
> +			   buffer->fd, 0);
> +	ASSERT_NE(buffer->ptr, MAP_FAILED);
> +
> +	/* Initialize buffer->ptr so we can tell if it is written. */
> +	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +		ptr[i] = i;
> +
> +	/* Initialize data that the device will write to buffer->ptr. */
> +	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> +		ptr[i] = -i;
> +
> +	pid = fork();
> +	if (pid == -1)
> +		ASSERT_EQ(pid, 0);
> +	if (pid != 0) {
> +		waitpid(pid, &ret, 0);
> +		ASSERT_EQ(WIFEXITED(ret), 1);
> +
> +		/* Check that the parent's buffer did change. */
> +		for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +			ASSERT_EQ(ptr[i], -i);
> +		return;
> +	}
> +
> +	/* Check that we see the parent's values. */
> +	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], i);
> +	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], -i);
> +
> +	/* The child process needs its own mirror to its own mm. */
> +	child_fd = hmm_open(0);
> +	ASSERT_GE(child_fd, 0);
> +
> +	/* Simulate a device writing system memory. */
> +	ret = hmm_dmirror_cmd(child_fd, HMM_DMIRROR_WRITE, buffer, npages);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(buffer->cpages, npages);
> +	ASSERT_EQ(buffer->faults, 1);
> +
> +	/* Check what the device wrote. */
> +	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], -i);
> +
> +	close(child_fd);
> +	exit(0);
> +}
> +
> +/*
> + * Write private anonymous huge page.
> + */
> +TEST_F(hmm, anon_write_huge)
> +{
> +	struct hmm_buffer *buffer;
> +	unsigned long npages;
> +	unsigned long size;
> +	unsigned long i;
> +	void *old_ptr;
> +	void *map;
> +	int *ptr;
> +	int ret;
> +
> +	size = 2 * TWOMEG;
> +
> +	buffer = malloc(sizeof(*buffer));
> +	ASSERT_NE(buffer, NULL);
> +
> +	buffer->fd = -1;
> +	buffer->size = size;
> +	buffer->mirror = malloc(size);
> +	ASSERT_NE(buffer->mirror, NULL);
> +
> +	buffer->ptr = mmap(NULL, size,
> +			   PROT_READ | PROT_WRITE,
> +			   MAP_PRIVATE | MAP_ANONYMOUS,
> +			   buffer->fd, 0);
> +	ASSERT_NE(buffer->ptr, MAP_FAILED);
> +
> +	size = TWOMEG;
> +	npages = size >> self->page_shift;
> +	map = (void *)ALIGN((uintptr_t)buffer->ptr, size);
> +	ret = madvise(map, size, MADV_HUGEPAGE);
> +	ASSERT_EQ(ret, 0);
> +	old_ptr = buffer->ptr;
> +	buffer->ptr = map;
> +
> +	/* Initialize data that the device will write to buffer->ptr. */
> +	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> +		ptr[i] = i;
> +
> +	/* Simulate a device writing system memory. */
> +	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_WRITE, buffer, npages);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(buffer->cpages, npages);
> +	ASSERT_EQ(buffer->faults, 1);
> +
> +	/* Check what the device wrote. */
> +	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], i);
> +
> +	buffer->ptr = old_ptr;
> +	hmm_buffer_free(buffer);
> +}
> +
> +/*
> + * Write huge TLBFS page.
> + */
> +TEST_F(hmm, anon_write_hugetlbfs)
> +{
> +	struct hmm_buffer *buffer;
> +	unsigned long npages;
> +	unsigned long size;
> +	unsigned long i;
> +	int *ptr;
> +	int ret;
> +	long pagesizes[4];
> +	int n, idx;
> +
> +	/* Skip test if we can't allocate a hugetlbfs page. */
> +
> +	n = gethugepagesizes(pagesizes, 4);
> +	if (n <= 0)
> +		return;
> +	for (idx = 0; --n > 0; ) {
> +		if (pagesizes[n] < pagesizes[idx])
> +			idx = n;
> +	}
> +	size = ALIGN(TWOMEG, pagesizes[idx]);
> +	npages = size >> self->page_shift;
> +
> +	buffer = malloc(sizeof(*buffer));
> +	ASSERT_NE(buffer, NULL);
> +
> +	buffer->ptr = get_hugepage_region(size, GHR_STRICT);
> +	if (buffer->ptr == NULL) {
> +		free(buffer);
> +		return;
> +	}
> +
> +	buffer->fd = -1;
> +	buffer->size = size;
> +	buffer->mirror = malloc(size);
> +	ASSERT_NE(buffer->mirror, NULL);
> +
> +	/* Initialize data that the device will write to buffer->ptr. */
> +	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> +		ptr[i] = i;
> +
> +	/* Simulate a device writing system memory. */
> +	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_WRITE, buffer, npages);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(buffer->cpages, npages);
> +	ASSERT_EQ(buffer->faults, 1);
> +
> +	/* Check what the device wrote. */
> +	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], i);
> +
> +	free_hugepage_region(buffer->ptr);
> +	buffer->ptr = NULL;
> +	hmm_buffer_free(buffer);
> +}
> +
> +/*
> + * Read mmap'ed file memory.
> + */
> +TEST_F(hmm, file_read)
> +{
> +	struct hmm_buffer *buffer;
> +	unsigned long npages;
> +	unsigned long size;
> +	unsigned long i;
> +	int *ptr;
> +	int ret;
> +	int fd;
> +	off_t off;
> +	ssize_t len;
> +
> +	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
> +	ASSERT_NE(npages, 0);
> +	size = npages << self->page_shift;
> +
> +	fd = hmm_create_file(size);
> +	ASSERT_GE(fd, 0);
> +
> +	buffer = malloc(sizeof(*buffer));
> +	ASSERT_NE(buffer, NULL);
> +
> +	buffer->fd = fd;
> +	buffer->size = size;
> +	buffer->mirror = malloc(size);
> +	ASSERT_NE(buffer->mirror, NULL);
> +
> +	/* Write initial contents of the file. */
> +	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> +		ptr[i] = i;
> +	off = lseek(fd, 0, SEEK_SET);
> +	ASSERT_EQ(off, 0);
> +	len = write(fd, buffer->mirror, size);
> +	ASSERT_EQ(len, size);
> +	memset(buffer->mirror, 0, size);
> +
> +	buffer->ptr = mmap(NULL, size,
> +			   PROT_READ,
> +			   MAP_SHARED,
> +			   buffer->fd, 0);
> +	ASSERT_NE(buffer->ptr, MAP_FAILED);
> +
> +	/* Simulate a device reading system memory. */
> +	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_READ, buffer, npages);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(buffer->cpages, npages);
> +	ASSERT_EQ(buffer->faults, 1);
> +
> +	/* Check what the device read. */
> +	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], i);
> +
> +	hmm_buffer_free(buffer);
> +}
> +
> +/*
> + * Write mmap'ed file memory.
> + */
> +TEST_F(hmm, file_write)
> +{
> +	struct hmm_buffer *buffer;
> +	unsigned long npages;
> +	unsigned long size;
> +	unsigned long i;
> +	int *ptr;
> +	int ret;
> +	int fd;
> +	off_t off;
> +	ssize_t len;
> +
> +	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
> +	ASSERT_NE(npages, 0);
> +	size = npages << self->page_shift;
> +
> +	fd = hmm_create_file(size);
> +	ASSERT_GE(fd, 0);
> +
> +	buffer = malloc(sizeof(*buffer));
> +	ASSERT_NE(buffer, NULL);
> +
> +	buffer->fd = fd;
> +	buffer->size = size;
> +	buffer->mirror = malloc(size);
> +	ASSERT_NE(buffer->mirror, NULL);
> +
> +	buffer->ptr = mmap(NULL, size,
> +			   PROT_READ | PROT_WRITE,
> +			   MAP_SHARED,
> +			   buffer->fd, 0);
> +	ASSERT_NE(buffer->ptr, MAP_FAILED);
> +
> +	/* Initialize data that the device will write to buffer->ptr. */
> +	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> +		ptr[i] = i;
> +
> +	/* Simulate a device writing system memory. */
> +	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_WRITE, buffer, npages);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(buffer->cpages, npages);
> +	ASSERT_EQ(buffer->faults, 1);
> +
> +	/* Check what the device wrote. */
> +	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], i);
> +
> +	/* Check that the device also wrote the file. */
> +	off = lseek(fd, 0, SEEK_SET);
> +	ASSERT_EQ(off, 0);
> +	len = read(fd, buffer->mirror, size);
> +	ASSERT_EQ(len, size);
> +	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], i);
> +
> +	hmm_buffer_free(buffer);
> +}
> +
> +/*
> + * Migrate anonymous memory to device private memory.
> + */
> +TEST_F(hmm, migrate)
> +{
> +	struct hmm_buffer *buffer;
> +	unsigned long npages;
> +	unsigned long size;
> +	unsigned long i;
> +	int *ptr;
> +	int ret;
> +
> +	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
> +	ASSERT_NE(npages, 0);
> +	size = npages << self->page_shift;
> +
> +	buffer = malloc(sizeof(*buffer));
> +	ASSERT_NE(buffer, NULL);
> +
> +	buffer->fd = -1;
> +	buffer->size = size;
> +	buffer->mirror = malloc(size);
> +	ASSERT_NE(buffer->mirror, NULL);
> +
> +	buffer->ptr = mmap(NULL, size,
> +			   PROT_READ | PROT_WRITE,
> +			   MAP_PRIVATE | MAP_ANONYMOUS,
> +			   buffer->fd, 0);
> +	ASSERT_NE(buffer->ptr, MAP_FAILED);
> +
> +	/* Initialize buffer in system memory. */
> +	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +		ptr[i] = i;
> +
> +	/* Migrate memory to device. */
> +	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_MIGRATE, buffer, npages);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(buffer->cpages, npages);
> +
> +	/* Check what the device read. */
> +	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], i);
> +
> +	hmm_buffer_free(buffer);
> +}
> +
> +/*
> + * Migrate anonymous memory to device private memory and fault it back to system
> + * memory.
> + */
> +TEST_F(hmm, migrate_fault)
> +{
> +	struct hmm_buffer *buffer;
> +	unsigned long npages;
> +	unsigned long size;
> +	unsigned long i;
> +	int *ptr;
> +	int ret;
> +
> +	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
> +	ASSERT_NE(npages, 0);
> +	size = npages << self->page_shift;
> +
> +	buffer = malloc(sizeof(*buffer));
> +	ASSERT_NE(buffer, NULL);
> +
> +	buffer->fd = -1;
> +	buffer->size = size;
> +	buffer->mirror = malloc(size);
> +	ASSERT_NE(buffer->mirror, NULL);
> +
> +	buffer->ptr = mmap(NULL, size,
> +			   PROT_READ | PROT_WRITE,
> +			   MAP_PRIVATE | MAP_ANONYMOUS,
> +			   buffer->fd, 0);
> +	ASSERT_NE(buffer->ptr, MAP_FAILED);
> +
> +	/* Initialize buffer in system memory. */
> +	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +		ptr[i] = i;
> +
> +	/* Migrate memory to device. */
> +	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_MIGRATE, buffer, npages);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(buffer->cpages, npages);
> +
> +	/* Check what the device read. */
> +	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], i);
> +
> +	/* Fault pages back to system memory and check them. */
> +	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], i);
> +
> +	hmm_buffer_free(buffer);
> +}
> +
> +/*
> + * Try to migrate various memory types to device private memory.
> + */
> +TEST_F(hmm2, migrate_mixed)
> +{
> +	struct hmm_buffer *buffer;
> +	unsigned long npages;
> +	unsigned long size;
> +	int *ptr;
> +	unsigned char *p;
> +	int ret;
> +	int val;
> +
> +	npages = 6;
> +	size = npages << self->page_shift;
> +
> +	buffer = malloc(sizeof(*buffer));
> +	ASSERT_NE(buffer, NULL);
> +
> +	buffer->fd = -1;
> +	buffer->size = size;
> +	buffer->mirror = malloc(size);
> +	ASSERT_NE(buffer->mirror, NULL);
> +
> +	/* Reserve a range of addresses. */
> +	buffer->ptr = mmap(NULL, size,
> +			   PROT_NONE,
> +			   MAP_PRIVATE | MAP_ANONYMOUS,
> +			   buffer->fd, 0);
> +	ASSERT_NE(buffer->ptr, MAP_FAILED);
> +	p = buffer->ptr;
> +
> +	/* Now try to migrate everything to device 1. */
> +	ret = hmm_dmirror_cmd(self->fd1, HMM_DMIRROR_MIGRATE, buffer, npages);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(buffer->cpages, 6);
> +
> +	/* Punch a hole after the first page address. */
> +	ret = munmap(buffer->ptr + self->page_size, self->page_size);
> +	ASSERT_EQ(ret, 0);
> +
> +	/* We expect an error if the vma doesn't cover the range. */
> +	ret = hmm_dmirror_cmd(self->fd1, HMM_DMIRROR_MIGRATE, buffer, 3);
> +	ASSERT_EQ(ret, -EINVAL);
> +
> +	/* Page 2 will be a read-only zero page. */
> +	ret = mprotect(buffer->ptr + 2 * self->page_size, self->page_size,
> +				PROT_READ);
> +	ASSERT_EQ(ret, 0);
> +	ptr = (int *)(buffer->ptr + 2 * self->page_size);
> +	val = *ptr + 3;
> +	ASSERT_EQ(val, 3);
> +
> +	/* Page 3 will be read-only. */
> +	ret = mprotect(buffer->ptr + 3 * self->page_size, self->page_size,
> +				PROT_READ | PROT_WRITE);
> +	ASSERT_EQ(ret, 0);
> +	ptr = (int *)(buffer->ptr + 3 * self->page_size);
> +	*ptr = val;
> +	ret = mprotect(buffer->ptr + 3 * self->page_size, self->page_size,
> +				PROT_READ);
> +	ASSERT_EQ(ret, 0);
> +
> +	/* Page 4 will be read-write. */
> +	ret = mprotect(buffer->ptr + 4 * self->page_size, self->page_size,
> +				PROT_READ | PROT_WRITE);
> +	ASSERT_EQ(ret, 0);
> +	ptr = (int *)(buffer->ptr + 4 * self->page_size);
> +	*ptr = val;
> +
> +	/* Page 5 won't be migrated to device 0 because it's on device 1. */
> +	buffer->ptr = p + 5 * self->page_size;
> +	ret = hmm_dmirror_cmd(self->fd0, HMM_DMIRROR_MIGRATE, buffer, 1);
> +	ASSERT_EQ(ret, -ENOENT);
> +	buffer->ptr = p;
> +
> +	/* Now try to migrate pages 2-3 to device 1. */
> +	buffer->ptr = p + 2 * self->page_size;
> +	ret = hmm_dmirror_cmd(self->fd1, HMM_DMIRROR_MIGRATE, buffer, 2);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(buffer->cpages, 2);
> +	buffer->ptr = p;
> +
> +	hmm_buffer_free(buffer);
> +}
> +
> +/*
> + * Migrate anonymous memory to device private memory and fault it back to system
> + * memory multiple times.
> + */
> +TEST_F(hmm, migrate_multiple)
> +{
> +	struct hmm_buffer *buffer;
> +	unsigned long npages;
> +	unsigned long size;
> +	unsigned long i;
> +	unsigned long c;
> +	int *ptr;
> +	int ret;
> +
> +	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
> +	ASSERT_NE(npages, 0);
> +	size = npages << self->page_shift;
> +
> +	for (c = 0; c < NTIMES; c++) {
> +		buffer = malloc(sizeof(*buffer));
> +		ASSERT_NE(buffer, NULL);
> +
> +		buffer->fd = -1;
> +		buffer->size = size;
> +		buffer->mirror = malloc(size);
> +		ASSERT_NE(buffer->mirror, NULL);
> +
> +		buffer->ptr = mmap(NULL, size,
> +				   PROT_READ | PROT_WRITE,
> +				   MAP_PRIVATE | MAP_ANONYMOUS,
> +				   buffer->fd, 0);
> +		ASSERT_NE(buffer->ptr, MAP_FAILED);
> +
> +		/* Initialize buffer in system memory. */
> +		for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +			ptr[i] = i;
> +
> +		/* Migrate memory to device. */
> +		ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_MIGRATE, buffer,
> +				      npages);
> +		ASSERT_EQ(ret, 0);
> +		ASSERT_EQ(buffer->cpages, npages);
> +
> +		/* Check what the device read. */
> +		for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> +			ASSERT_EQ(ptr[i], i);
> +
> +		/* Fault pages back to system memory and check them. */
> +		for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +			ASSERT_EQ(ptr[i], i);
> +
> +		hmm_buffer_free(buffer);
> +	}
> +}
> +
> +/*
> + * Read anonymous memory multiple times.
> + */
> +TEST_F(hmm, anon_read_multiple)
> +{
> +	struct hmm_buffer *buffer;
> +	unsigned long npages;
> +	unsigned long size;
> +	unsigned long i;
> +	unsigned long c;
> +	int *ptr;
> +	int ret;
> +
> +	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
> +	ASSERT_NE(npages, 0);
> +	size = npages << self->page_shift;
> +
> +	for (c = 0; c < NTIMES; c++) {
> +		buffer = malloc(sizeof(*buffer));
> +		ASSERT_NE(buffer, NULL);
> +
> +		buffer->fd = -1;
> +		buffer->size = size;
> +		buffer->mirror = malloc(size);
> +		ASSERT_NE(buffer->mirror, NULL);
> +
> +		buffer->ptr = mmap(NULL, size,
> +				   PROT_READ | PROT_WRITE,
> +				   MAP_PRIVATE | MAP_ANONYMOUS,
> +				   buffer->fd, 0);
> +		ASSERT_NE(buffer->ptr, MAP_FAILED);
> +
> +		/* Initialize buffer in system memory. */
> +		for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +			ptr[i] = i + c;
> +
> +		/* Simulate a device reading system memory. */
> +		ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_READ, buffer,
> +				      npages);
> +		ASSERT_EQ(ret, 0);
> +		ASSERT_EQ(buffer->cpages, npages);
> +		ASSERT_EQ(buffer->faults, 1);
> +
> +		/* Check what the device read. */
> +		for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> +			ASSERT_EQ(ptr[i], i + c);
> +
> +		hmm_buffer_free(buffer);
> +	}
> +}
> +
> +void *unmap_buffer(void *p)
> +{
> +	struct hmm_buffer *buffer = p;
> +
> +	/* Delay for a bit and then unmap buffer while it is being read. */
> +	hmm_nanosleep(hmm_random() % 32000);
> +	munmap(buffer->ptr + buffer->size / 2, buffer->size / 2);
> +	buffer->ptr = NULL;
> +
> +	return NULL;
> +}
> +
> +/*
> + * Try reading anonymous memory while it is being unmapped.
> + */
> +TEST_F(hmm, anon_teardown)
> +{
> +	unsigned long npages;
> +	unsigned long size;
> +	unsigned long c;
> +	void *ret;
> +
> +	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
> +	ASSERT_NE(npages, 0);
> +	size = npages << self->page_shift;
> +
> +	for (c = 0; c < NTIMES; ++c) {
> +		pthread_t thread;
> +		struct hmm_buffer *buffer;
> +		unsigned long i;
> +		int *ptr;
> +		int rc;
> +
> +		buffer = malloc(sizeof(*buffer));
> +		ASSERT_NE(buffer, NULL);
> +
> +		buffer->fd = -1;
> +		buffer->size = size;
> +		buffer->mirror = malloc(size);
> +		ASSERT_NE(buffer->mirror, NULL);
> +
> +		buffer->ptr = mmap(NULL, size,
> +				   PROT_READ | PROT_WRITE,
> +				   MAP_PRIVATE | MAP_ANONYMOUS,
> +				   buffer->fd, 0);
> +		ASSERT_NE(buffer->ptr, MAP_FAILED);
> +
> +		/* Initialize buffer in system memory. */
> +		for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +			ptr[i] = i + c;
> +
> +		rc = pthread_create(&thread, NULL, unmap_buffer, buffer);
> +		ASSERT_EQ(rc, 0);
> +
> +		/* Simulate a device reading system memory. */
> +		rc = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_READ, buffer,
> +				     npages);
> +		if (rc == 0) {
> +			ASSERT_EQ(buffer->cpages, npages);
> +			ASSERT_EQ(buffer->faults, 1);
> +
> +			/* Check what the device read. */
> +			for (i = 0, ptr = buffer->mirror;
> +			     i < size / sizeof(*ptr);
> +			     ++i)
> +				ASSERT_EQ(ptr[i], i + c);
> +		}
> +
> +		pthread_join(thread, &ret);
> +		hmm_buffer_free(buffer);
> +	}
> +}
> +
> +/*
> + * Test memory snapshot without faulting in pages accessed by the device.
> + */
> +TEST_F(hmm2, snapshot)
> +{
> +	struct hmm_buffer *buffer;
> +	unsigned long npages;
> +	unsigned long size;
> +	int *ptr;
> +	unsigned char *p;
> +	unsigned char *m;
> +	int ret;
> +	int val;
> +
> +	npages = 7;
> +	size = npages << self->page_shift;
> +
> +	buffer = malloc(sizeof(*buffer));
> +	ASSERT_NE(buffer, NULL);
> +
> +	buffer->fd = -1;
> +	buffer->size = size;
> +	buffer->mirror = malloc(npages);
> +	ASSERT_NE(buffer->mirror, NULL);
> +
> +	/* Reserve a range of addresses. */
> +	buffer->ptr = mmap(NULL, size,
> +			   PROT_NONE,
> +			   MAP_PRIVATE | MAP_ANONYMOUS,
> +			   buffer->fd, 0);
> +	ASSERT_NE(buffer->ptr, MAP_FAILED);
> +	p = buffer->ptr;
> +
> +	/* Punch a hole after the first page address. */
> +	ret = munmap(buffer->ptr + self->page_size, self->page_size);
> +	ASSERT_EQ(ret, 0);
> +
> +	/* Page 2 will be read-only zero page. */
> +	ret = mprotect(buffer->ptr + 2 * self->page_size, self->page_size,
> +				PROT_READ);
> +	ASSERT_EQ(ret, 0);
> +	ptr = (int *)(buffer->ptr + 2 * self->page_size);
> +	val = *ptr + 3;
> +	ASSERT_EQ(val, 3);
> +
> +	/* Page 3 will be read-only. */
> +	ret = mprotect(buffer->ptr + 3 * self->page_size, self->page_size,
> +				PROT_READ | PROT_WRITE);
> +	ASSERT_EQ(ret, 0);
> +	ptr = (int *)(buffer->ptr + 3 * self->page_size);
> +	*ptr = val;
> +	ret = mprotect(buffer->ptr + 3 * self->page_size, self->page_size,
> +				PROT_READ);
> +	ASSERT_EQ(ret, 0);
> +
> +	/* Page 4-6 will be read-write. */
> +	ret = mprotect(buffer->ptr + 4 * self->page_size, 3 * self->page_size,
> +				PROT_READ | PROT_WRITE);
> +	ASSERT_EQ(ret, 0);
> +	ptr = (int *)(buffer->ptr + 4 * self->page_size);
> +	*ptr = val;
> +
> +	/* Page 5 will be migrated to device 0. */
> +	buffer->ptr = p + 5 * self->page_size;
> +	ret = hmm_dmirror_cmd(self->fd0, HMM_DMIRROR_MIGRATE, buffer, 1);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(buffer->cpages, 1);
> +
> +	/* Page 6 will be migrated to device 1. */
> +	buffer->ptr = p + 6 * self->page_size;
> +	ret = hmm_dmirror_cmd(self->fd1, HMM_DMIRROR_MIGRATE, buffer, 1);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(buffer->cpages, 1);
> +
> +	/* Simulate a device snapshotting CPU pagetables. */
> +	buffer->ptr = p;
> +	ret = hmm_dmirror_cmd(self->fd0, HMM_DMIRROR_SNAPSHOT, buffer, npages);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(buffer->cpages, npages);
> +
> +	/* Check what the device saw. */
> +	m = buffer->mirror;
> +	ASSERT_EQ(m[0], HMM_DMIRROR_PROT_NONE);
> +	ASSERT_EQ(m[1], HMM_DMIRROR_PROT_NONE);
> +	ASSERT_EQ(m[2], HMM_DMIRROR_PROT_ZERO | HMM_DMIRROR_PROT_READ);
> +	ASSERT_EQ(m[3], HMM_DMIRROR_PROT_READ);
> +	ASSERT_EQ(m[4], HMM_DMIRROR_PROT_WRITE);
> +	ASSERT_EQ(m[5], HMM_DMIRROR_PROT_DEV_PRIVATE_LOCAL |
> +			HMM_DMIRROR_PROT_WRITE);
> +	ASSERT_EQ(m[6], HMM_DMIRROR_PROT_DEV_PRIVATE_REMOTE |
> +			HMM_DMIRROR_PROT_WRITE);
> +
> +	hmm_buffer_free(buffer);
> +}
> +
> +TEST_HARNESS_MAIN
> diff --git a/tools/testing/selftests/vm/run_vmtests b/tools/testing/selftests/vm/run_vmtests
> index 951c507a27f7..634cfefdaffd 100755
> --- a/tools/testing/selftests/vm/run_vmtests
> +++ b/tools/testing/selftests/vm/run_vmtests
> @@ -227,4 +227,20 @@ else
>  	exitcode=1
>  fi
>  
> +echo "------------------------------------"
> +echo "running HMM smoke test"
> +echo "------------------------------------"
> +./test_hmm.sh smoke
> +ret_val=$?
> +
> +if [ $ret_val -eq 0 ]; then
> +	echo "[PASS]"
> +elif [ $ret_val -eq $ksft_skip ]; then
> +	echo "[SKIP]"
> +	exitcode=$ksft_skip
> +else
> +	echo "[FAIL]"
> +	exitcode=1
> +fi
> +
>  exit $exitcode
> diff --git a/tools/testing/selftests/vm/test_hmm.sh b/tools/testing/selftests/vm/test_hmm.sh
> new file mode 100755
> index 000000000000..268d32752045
> --- /dev/null
> +++ b/tools/testing/selftests/vm/test_hmm.sh
> @@ -0,0 +1,97 @@
> +#!/bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +#
> +# Copyright (C) 2018 Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
> +#
> +# This is a test script for the kernel test driver to analyse vmalloc
> +# allocator. Therefore it is just a kernel module loader. You can specify
> +# and pass different parameters in order to:
> +#     a) analyse performance of vmalloc allocations;
> +#     b) stressing and stability check of vmalloc subsystem.
> +
> +TEST_NAME="test_hmm"
> +DRIVER="hmm_dmirror"
> +
> +# 1 if fails
> +exitcode=1
> +
> +# Kselftest framework requirement - SKIP code is 4.
> +ksft_skip=4
> +
> +check_test_requirements()
> +{
> +	uid=$(id -u)
> +	if [ $uid -ne 0 ]; then
> +		echo "$0: Must be run as root"
> +		exit $ksft_skip
> +	fi
> +
> +	if ! which modprobe > /dev/null 2>&1; then
> +		echo "$0: You need modprobe installed"
> +		exit $ksft_skip
> +	fi
> +
> +	if ! modinfo $DRIVER > /dev/null 2>&1; then
> +		echo "$0: You must have the following enabled in your kernel:"
> +		echo "CONFIG_HMM_DMIRROR=m"
> +		exit $ksft_skip
> +	fi
> +}
> +
> +load_driver()
> +{
> +	modprobe $DRIVER > /dev/null 2>&1
> +	if [ $? == 0 ]; then
> +		major=$(awk "\$2==\"HMM_DMIRROR\" {print \$1}" /proc/devices)
> +		mknod /dev/hmm_dmirror0 c $major 0
> +		mknod /dev/hmm_dmirror1 c $major 1
> +	fi
> +}
> +
> +unload_driver()
> +{
> +	modprobe -r $DRIVER > /dev/null 2>&1
> +	rm -f /dev/hmm_dmirror?
> +}
> +
> +run_smoke()
> +{
> +	echo "Running smoke test. Note, this test provides basic coverage."
> +
> +	load_driver
> +	./hmm-tests
> +	unload_driver
> +}
> +
> +usage()
> +{
> +	echo -n "Usage: $0"
> +	echo
> +	echo "Example usage:"
> +	echo
> +	echo "# Shows help message"
> +	echo "./${TEST_NAME}.sh"
> +	echo
> +	echo "# Smoke testing"
> +	echo "./${TEST_NAME}.sh smoke"
> +	echo
> +	exit 0
> +}
> +
> +function run_test()
> +{
> +	if [ $# -eq 0 ]; then
> +		usage
> +	else
> +		if [ "$1" = "smoke" ]; then
> +			run_smoke
> +		else
> +			usage
> +		fi
> +	fi
> +}
> +
> +check_test_requirements
> +run_test $@
> +
> +exit 0
> -- 
> 2.20.1
>