Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1553 insertions, 0 deletions

diff --git a/lib/test_hmm.c b/lib/test_hmm.c
new file mode 100644
index 0000000000..717dcb8301
--- /dev/null
+++ b/lib/test_hmm.c
@@ -0,0 +1,1553 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * This is a module to test 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.
+ */
+#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/memremap.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 <linux/rmap.h>
+#include <linux/mmu_notifier.h>
+#include <linux/migrate.h>
+
+#include "test_hmm_uapi.h"
+
+#define DMIRROR_NDEVICES		4
+#define DMIRROR_RANGE_FAULT_TIMEOUT	1000
+#define DEVMEM_CHUNK_SIZE		(256 * 1024 * 1024U)
+#define DEVMEM_CHUNKS_RESERVE		16
+
+/*
+ * For device_private pages, dpage is just a dummy struct page
+ * representing a piece of device memory. dmirror_devmem_alloc_page
+ * allocates a real system memory page as backing storage to fake a
+ * real device. zone_device_data points to that backing page. But
+ * for device_coherent memory, the struct page represents real
+ * physical CPU-accessible memory that we can use directly.
+ */
+#define BACKING_PAGE(page) (is_device_private_page((page)) ? \
+			   (page)->zone_device_data : (page))
+
+static unsigned long spm_addr_dev0;
+module_param(spm_addr_dev0, long, 0644);
+MODULE_PARM_DESC(spm_addr_dev0,
+		"Specify start address for SPM (special purpose memory) used for device 0. By setting this Coherent device type will be used. Make sure spm_addr_dev1 is set too. Minimum SPM size should be DEVMEM_CHUNK_SIZE.");
+
+static unsigned long spm_addr_dev1;
+module_param(spm_addr_dev1, long, 0644);
+MODULE_PARM_DESC(spm_addr_dev1,
+		"Specify start address for SPM (special purpose memory) used for device 1. By setting this Coherent device type will be used. Make sure spm_addr_dev0 is set too. Minimum SPM size should be DEVMEM_CHUNK_SIZE.");
+
+static const struct dev_pagemap_ops dmirror_devmem_ops;
+static const struct mmu_interval_notifier_ops dmirror_min_ops;
+static dev_t dmirror_dev;
+
+struct dmirror_device;
+
+struct dmirror_bounce {
+	void			*ptr;
+	unsigned long		size;
+	unsigned long		addr;
+	unsigned long		cpages;
+};
+
+#define DPT_XA_TAG_ATOMIC 1UL
+#define DPT_XA_TAG_WRITE 3UL
+
+/*
+ * Data structure to track address ranges and register for mmu interval
+ * notifier updates.
+ */
+struct dmirror_interval {
+	struct mmu_interval_notifier	notifier;
+	struct dmirror			*dmirror;
+};
+
+/*
+ * Data attached to the open device file.
+ * Note that it might be shared after a fork().
+ */
+struct dmirror {
+	struct dmirror_device		*mdevice;
+	struct xarray			pt;
+	struct mmu_interval_notifier	notifier;
+	struct mutex			mutex;
+};
+
+/*
+ * ZONE_DEVICE pages for migration and simulating device memory.
+ */
+struct dmirror_chunk {
+	struct dev_pagemap	pagemap;
+	struct dmirror_device	*mdevice;
+	bool remove;
+};
+
+/*
+ * Per device data.
+ */
+struct dmirror_device {
+	struct cdev		cdevice;
+	unsigned int            zone_device_type;
+	struct device		device;
+
+	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 struct dmirror_device dmirror_devices[DMIRROR_NDEVICES];
+
+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 bool dmirror_is_private_zone(struct dmirror_device *mdevice)
+{
+	return (mdevice->zone_device_type ==
+		HMM_DMIRROR_MEMORY_DEVICE_PRIVATE) ? true : false;
+}
+
+static enum migrate_vma_direction
+dmirror_select_device(struct dmirror *dmirror)
+{
+	return (dmirror->mdevice->zone_device_type ==
+		HMM_DMIRROR_MEMORY_DEVICE_PRIVATE) ?
+		MIGRATE_VMA_SELECT_DEVICE_PRIVATE :
+		MIGRATE_VMA_SELECT_DEVICE_COHERENT;
+}
+
+static void dmirror_bounce_fini(struct dmirror_bounce *bounce)
+{
+	vfree(bounce->ptr);
+}
+
+static int dmirror_fops_open(struct inode *inode, struct file *filp)
+{
+	struct cdev *cdev = inode->i_cdev;
+	struct dmirror *dmirror;
+	int ret;
+
+	/* Mirror this process address space */
+	dmirror = kzalloc(sizeof(*dmirror), GFP_KERNEL);
+	if (dmirror == NULL)
+		return -ENOMEM;
+
+	dmirror->mdevice = container_of(cdev, struct dmirror_device, cdevice);
+	mutex_init(&dmirror->mutex);
+	xa_init(&dmirror->pt);
+
+	ret = mmu_interval_notifier_insert(&dmirror->notifier, current->mm,
+				0, ULONG_MAX & PAGE_MASK, &dmirror_min_ops);
+	if (ret) {
+		kfree(dmirror);
+		return ret;
+	}
+
+	filp->private_data = dmirror;
+	return 0;
+}
+
+static int dmirror_fops_release(struct inode *inode, struct file *filp)
+{
+	struct dmirror *dmirror = filp->private_data;
+
+	mmu_interval_notifier_remove(&dmirror->notifier);
+	xa_destroy(&dmirror->pt);
+	kfree(dmirror);
+	return 0;
+}
+
+static struct dmirror_chunk *dmirror_page_to_chunk(struct page *page)
+{
+	return container_of(page->pgmap, struct dmirror_chunk, pagemap);
+}
+
+static struct dmirror_device *dmirror_page_to_device(struct page *page)
+
+{
+	return dmirror_page_to_chunk(page)->mdevice;
+}
+
+static int dmirror_do_fault(struct dmirror *dmirror, struct hmm_range *range)
+{
+	unsigned long *pfns = range->hmm_pfns;
+	unsigned long pfn;
+
+	for (pfn = (range->start >> PAGE_SHIFT);
+	     pfn < (range->end >> PAGE_SHIFT);
+	     pfn++, pfns++) {
+		struct page *page;
+		void *entry;
+
+		/*
+		 * Since we asked for hmm_range_fault() to populate pages,
+		 * it shouldn't return an error entry on success.
+		 */
+		WARN_ON(*pfns & HMM_PFN_ERROR);
+		WARN_ON(!(*pfns & HMM_PFN_VALID));
+
+		page = hmm_pfn_to_page(*pfns);
+		WARN_ON(!page);
+
+		entry = page;
+		if (*pfns & HMM_PFN_WRITE)
+			entry = xa_tag_pointer(entry, DPT_XA_TAG_WRITE);
+		else if (WARN_ON(range->default_flags & HMM_PFN_WRITE))
+			return -EFAULT;
+		entry = xa_store(&dmirror->pt, pfn, entry, GFP_ATOMIC);
+		if (xa_is_err(entry))
+			return xa_err(entry);
+	}
+
+	return 0;
+}
+
+static void dmirror_do_update(struct dmirror *dmirror, unsigned long start,
+			      unsigned long end)
+{
+	unsigned long pfn;
+	void *entry;
+
+	/*
+	 * The XArray doesn't hold references to pages since it relies on
+	 * the mmu notifier to clear page pointers when they become stale.
+	 * Therefore, it is OK to just clear the entry.
+	 */
+	xa_for_each_range(&dmirror->pt, pfn, entry, start >> PAGE_SHIFT,
+			  end >> PAGE_SHIFT)
+		xa_erase(&dmirror->pt, pfn);
+}
+
+static bool dmirror_interval_invalidate(struct mmu_interval_notifier *mni,
+				const struct mmu_notifier_range *range,
+				unsigned long cur_seq)
+{
+	struct dmirror *dmirror = container_of(mni, struct dmirror, notifier);
+
+	/*
+	 * Ignore invalidation callbacks for device private pages since
+	 * the invalidation is handled as part of the migration process.
+	 */
+	if (range->event == MMU_NOTIFY_MIGRATE &&
+	    range->owner == dmirror->mdevice)
+		return true;
+
+	if (mmu_notifier_range_blockable(range))
+		mutex_lock(&dmirror->mutex);
+	else if (!mutex_trylock(&dmirror->mutex))
+		return false;
+
+	mmu_interval_set_seq(mni, cur_seq);
+	dmirror_do_update(dmirror, range->start, range->end);
+
+	mutex_unlock(&dmirror->mutex);
+	return true;
+}
+
+static const struct mmu_interval_notifier_ops dmirror_min_ops = {
+	.invalidate = dmirror_interval_invalidate,
+};
+
+static int dmirror_range_fault(struct dmirror *dmirror,
+				struct hmm_range *range)
+{
+	struct mm_struct *mm = dmirror->notifier.mm;
+	unsigned long timeout =
+		jiffies + msecs_to_jiffies(HMM_RANGE_DEFAULT_TIMEOUT);
+	int ret;
+
+	while (true) {
+		if (time_after(jiffies, timeout)) {
+			ret = -EBUSY;
+			goto out;
+		}
+
+		range->notifier_seq = mmu_interval_read_begin(range->notifier);
+		mmap_read_lock(mm);
+		ret = hmm_range_fault(range);
+		mmap_read_unlock(mm);
+		if (ret) {
+			if (ret == -EBUSY)
+				continue;
+			goto out;
+		}
+
+		mutex_lock(&dmirror->mutex);
+		if (mmu_interval_read_retry(range->notifier,
+					    range->notifier_seq)) {
+			mutex_unlock(&dmirror->mutex);
+			continue;
+		}
+		break;
+	}
+
+	ret = dmirror_do_fault(dmirror, range);
+
+	mutex_unlock(&dmirror->mutex);
+out:
+	return ret;
+}
+
+static int dmirror_fault(struct dmirror *dmirror, unsigned long start,
+			 unsigned long end, bool write)
+{
+	struct mm_struct *mm = dmirror->notifier.mm;
+	unsigned long addr;
+	unsigned long pfns[64];
+	struct hmm_range range = {
+		.notifier = &dmirror->notifier,
+		.hmm_pfns = pfns,
+		.pfn_flags_mask = 0,
+		.default_flags =
+			HMM_PFN_REQ_FAULT | (write ? HMM_PFN_REQ_WRITE : 0),
+		.dev_private_owner = dmirror->mdevice,
+	};
+	int ret = 0;
+
+	/* Since the mm is for the mirrored process, get a reference first. */
+	if (!mmget_not_zero(mm))
+		return 0;
+
+	for (addr = start; addr < end; addr = range.end) {
+		range.start = addr;
+		range.end = min(addr + (ARRAY_SIZE(pfns) << PAGE_SHIFT), end);
+
+		ret = dmirror_range_fault(dmirror, &range);
+		if (ret)
+			break;
+	}
+
+	mmput(mm);
+	return ret;
+}
+
+static int dmirror_do_read(struct dmirror *dmirror, unsigned long start,
+			   unsigned long end, struct dmirror_bounce *bounce)
+{
+	unsigned long pfn;
+	void *ptr;
+
+	ptr = bounce->ptr + ((start - bounce->addr) & PAGE_MASK);
+
+	for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++) {
+		void *entry;
+		struct page *page;
+
+		entry = xa_load(&dmirror->pt, pfn);
+		page = xa_untag_pointer(entry);
+		if (!page)
+			return -ENOENT;
+
+		memcpy_from_page(ptr, page, 0, PAGE_SIZE);
+
+		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;
+
+	while (1) {
+		mutex_lock(&dmirror->mutex);
+		ret = dmirror_do_read(dmirror, start, end, &bounce);
+		mutex_unlock(&dmirror->mutex);
+		if (ret != -ENOENT)
+			break;
+
+		start = cmd->addr + (bounce.cpages << PAGE_SHIFT);
+		ret = dmirror_fault(dmirror, start, end, false);
+		if (ret)
+			break;
+		cmd->faults++;
+	}
+
+	if (ret == 0) {
+		if (copy_to_user(u64_to_user_ptr(cmd->ptr), bounce.ptr,
+				 bounce.size))
+			ret = -EFAULT;
+	}
+	cmd->cpages = bounce.cpages;
+	dmirror_bounce_fini(&bounce);
+	return ret;
+}
+
+static int dmirror_do_write(struct dmirror *dmirror, unsigned long start,
+			    unsigned long end, struct dmirror_bounce *bounce)
+{
+	unsigned long pfn;
+	void *ptr;
+
+	ptr = bounce->ptr + ((start - bounce->addr) & PAGE_MASK);
+
+	for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++) {
+		void *entry;
+		struct page *page;
+
+		entry = xa_load(&dmirror->pt, pfn);
+		page = xa_untag_pointer(entry);
+		if (!page || xa_pointer_tag(entry) != DPT_XA_TAG_WRITE)
+			return -ENOENT;
+
+		memcpy_to_page(page, 0, ptr, PAGE_SIZE);
+
+		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;
+	if (copy_from_user(bounce.ptr, u64_to_user_ptr(cmd->ptr),
+			   bounce.size)) {
+		ret = -EFAULT;
+		goto fini;
+	}
+
+	while (1) {
+		mutex_lock(&dmirror->mutex);
+		ret = dmirror_do_write(dmirror, start, end, &bounce);
+		mutex_unlock(&dmirror->mutex);
+		if (ret != -ENOENT)
+			break;
+
+		start = cmd->addr + (bounce.cpages << PAGE_SHIFT);
+		ret = dmirror_fault(dmirror, start, end, true);
+		if (ret)
+			break;
+		cmd->faults++;
+	}
+
+fini:
+	cmd->cpages = bounce.cpages;
+	dmirror_bounce_fini(&bounce);
+	return ret;
+}
+
+static int dmirror_allocate_chunk(struct dmirror_device *mdevice,
+				   struct page **ppage)
+{
+	struct dmirror_chunk *devmem;
+	struct resource *res = NULL;
+	unsigned long pfn;
+	unsigned long pfn_first;
+	unsigned long pfn_last;
+	void *ptr;
+	int ret = -ENOMEM;
+
+	devmem = kzalloc(sizeof(*devmem), GFP_KERNEL);
+	if (!devmem)
+		return ret;
+
+	switch (mdevice->zone_device_type) {
+	case HMM_DMIRROR_MEMORY_DEVICE_PRIVATE:
+		res = request_free_mem_region(&iomem_resource, DEVMEM_CHUNK_SIZE,
+					      "hmm_dmirror");
+		if (IS_ERR_OR_NULL(res))
+			goto err_devmem;
+		devmem->pagemap.range.start = res->start;
+		devmem->pagemap.range.end = res->end;
+		devmem->pagemap.type = MEMORY_DEVICE_PRIVATE;
+		break;
+	case HMM_DMIRROR_MEMORY_DEVICE_COHERENT:
+		devmem->pagemap.range.start = (MINOR(mdevice->cdevice.dev) - 2) ?
+							spm_addr_dev0 :
+							spm_addr_dev1;
+		devmem->pagemap.range.end = devmem->pagemap.range.start +
+					    DEVMEM_CHUNK_SIZE - 1;
+		devmem->pagemap.type = MEMORY_DEVICE_COHERENT;
+		break;
+	default:
+		ret = -EINVAL;
+		goto err_devmem;
+	}
+
+	devmem->pagemap.nr_range = 1;
+	devmem->pagemap.ops = &dmirror_devmem_ops;
+	devmem->pagemap.owner = mdevice;
+
+	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_release;
+		mdevice->devmem_capacity = new_capacity;
+		mdevice->devmem_chunks = new_chunks;
+	}
+	ptr = memremap_pages(&devmem->pagemap, numa_node_id());
+	if (IS_ERR_OR_NULL(ptr)) {
+		if (ptr)
+			ret = PTR_ERR(ptr);
+		else
+			ret = -EFAULT;
+		goto err_release;
+	}
+
+	devmem->mdevice = mdevice;
+	pfn_first = devmem->pagemap.range.start >> PAGE_SHIFT;
+	pfn_last = pfn_first + (range_len(&devmem->pagemap.range) >> 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 0;
+
+err_release:
+	mutex_unlock(&mdevice->devmem_lock);
+	if (res && devmem->pagemap.type == MEMORY_DEVICE_PRIVATE)
+		release_mem_region(devmem->pagemap.range.start,
+				   range_len(&devmem->pagemap.range));
+err_devmem:
+	kfree(devmem);
+
+	return ret;
+}
+
+static struct page *dmirror_devmem_alloc_page(struct dmirror_device *mdevice)
+{
+	struct page *dpage = NULL;
+	struct page *rpage = NULL;
+
+	/*
+	 * For ZONE_DEVICE private type, this is a fake device so we allocate
+	 * real system memory to store our device memory.
+	 * For ZONE_DEVICE coherent type we use the actual dpage to store the
+	 * data and ignore rpage.
+	 */
+	if (dmirror_is_private_zone(mdevice)) {
+		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;
+	}
+
+	zone_device_page_init(dpage);
+	dpage->zone_device_data = rpage;
+	return dpage;
+
+error:
+	if (rpage)
+		__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);
+		if (WARN(spage && is_zone_device_page(spage),
+		     "page already in device spage pfn: 0x%lx\n",
+		     page_to_pfn(spage)))
+			continue;
+
+		dpage = dmirror_devmem_alloc_page(mdevice);
+		if (!dpage)
+			continue;
+
+		rpage = BACKING_PAGE(dpage);
+		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;
+
+		pr_debug("migrating from sys to dev pfn src: 0x%lx pfn dst: 0x%lx\n",
+			 page_to_pfn(spage), page_to_pfn(dpage));
+		*dst = migrate_pfn(page_to_pfn(dpage));
+		if ((*src & MIGRATE_PFN_WRITE) ||
+		    (!spage && args->vma->vm_flags & VM_WRITE))
+			*dst |= MIGRATE_PFN_WRITE;
+	}
+}
+
+static int dmirror_check_atomic(struct dmirror *dmirror, unsigned long start,
+			     unsigned long end)
+{
+	unsigned long pfn;
+
+	for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++) {
+		void *entry;
+
+		entry = xa_load(&dmirror->pt, pfn);
+		if (xa_pointer_tag(entry) == DPT_XA_TAG_ATOMIC)
+			return -EPERM;
+	}
+
+	return 0;
+}
+
+static int dmirror_atomic_map(unsigned long start, unsigned long end,
+			      struct page **pages, struct dmirror *dmirror)
+{
+	unsigned long pfn, mapped = 0;
+	int i;
+
+	/* Map the migrated pages into the device's page tables. */
+	mutex_lock(&dmirror->mutex);
+
+	for (i = 0, pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++, i++) {
+		void *entry;
+
+		if (!pages[i])
+			continue;
+
+		entry = pages[i];
+		entry = xa_tag_pointer(entry, DPT_XA_TAG_ATOMIC);
+		entry = xa_store(&dmirror->pt, pfn, entry, GFP_ATOMIC);
+		if (xa_is_err(entry)) {
+			mutex_unlock(&dmirror->mutex);
+			return xa_err(entry);
+		}
+
+		mapped++;
+	}
+
+	mutex_unlock(&dmirror->mutex);
+	return mapped;
+}
+
+static int dmirror_migrate_finalize_and_map(struct migrate_vma *args,
+					    struct dmirror *dmirror)
+{
+	unsigned long start = args->start;
+	unsigned long end = args->end;
+	const unsigned long *src = args->src;
+	const unsigned long *dst = args->dst;
+	unsigned long pfn;
+
+	/* Map the migrated pages into the device's page tables. */
+	mutex_lock(&dmirror->mutex);
+
+	for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++,
+								src++, dst++) {
+		struct page *dpage;
+		void *entry;
+
+		if (!(*src & MIGRATE_PFN_MIGRATE))
+			continue;
+
+		dpage = migrate_pfn_to_page(*dst);
+		if (!dpage)
+			continue;
+
+		entry = BACKING_PAGE(dpage);
+		if (*dst & MIGRATE_PFN_WRITE)
+			entry = xa_tag_pointer(entry, DPT_XA_TAG_WRITE);
+		entry = xa_store(&dmirror->pt, pfn, entry, GFP_ATOMIC);
+		if (xa_is_err(entry)) {
+			mutex_unlock(&dmirror->mutex);
+			return xa_err(entry);
+		}
+	}
+
+	mutex_unlock(&dmirror->mutex);
+	return 0;
+}
+
+static int dmirror_exclusive(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->notifier.mm;
+	struct page *pages[64];
+	struct dmirror_bounce bounce;
+	unsigned long next;
+	int ret;
+
+	start = cmd->addr;
+	end = start + size;
+	if (end < start)
+		return -EINVAL;
+
+	/* Since the mm is for the mirrored process, get a reference first. */
+	if (!mmget_not_zero(mm))
+		return -EINVAL;
+
+	mmap_read_lock(mm);
+	for (addr = start; addr < end; addr = next) {
+		unsigned long mapped = 0;
+		int i;
+
+		if (end < addr + (ARRAY_SIZE(pages) << PAGE_SHIFT))
+			next = end;
+		else
+			next = addr + (ARRAY_SIZE(pages) << PAGE_SHIFT);
+
+		ret = make_device_exclusive_range(mm, addr, next, pages, NULL);
+		/*
+		 * Do dmirror_atomic_map() iff all pages are marked for
+		 * exclusive access to avoid accessing uninitialized
+		 * fields of pages.
+		 */
+		if (ret == (next - addr) >> PAGE_SHIFT)
+			mapped = dmirror_atomic_map(addr, next, pages, dmirror);
+		for (i = 0; i < ret; i++) {
+			if (pages[i]) {
+				unlock_page(pages[i]);
+				put_page(pages[i]);
+			}
+		}
+
+		if (addr + (mapped << PAGE_SHIFT) < next) {
+			mmap_read_unlock(mm);
+			mmput(mm);
+			return -EBUSY;
+		}
+	}
+	mmap_read_unlock(mm);
+	mmput(mm);
+
+	/* Return the migrated data for verification. */
+	ret = dmirror_bounce_init(&bounce, start, size);
+	if (ret)
+		return ret;
+	mutex_lock(&dmirror->mutex);
+	ret = dmirror_do_read(dmirror, start, end, &bounce);
+	mutex_unlock(&dmirror->mutex);
+	if (ret == 0) {
+		if (copy_to_user(u64_to_user_ptr(cmd->ptr), bounce.ptr,
+				 bounce.size))
+			ret = -EFAULT;
+	}
+
+	cmd->cpages = bounce.cpages;
+	dmirror_bounce_fini(&bounce);
+	return ret;
+}
+
+static vm_fault_t dmirror_devmem_fault_alloc_and_copy(struct migrate_vma *args,
+						      struct dmirror *dmirror)
+{
+	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 (WARN_ON(!is_device_private_page(spage) &&
+			    !is_device_coherent_page(spage)))
+			continue;
+		spage = BACKING_PAGE(spage);
+		dpage = alloc_page_vma(GFP_HIGHUSER_MOVABLE, args->vma, addr);
+		if (!dpage)
+			continue;
+		pr_debug("migrating from dev to sys pfn src: 0x%lx pfn dst: 0x%lx\n",
+			 page_to_pfn(spage), page_to_pfn(dpage));
+
+		lock_page(dpage);
+		xa_erase(&dmirror->pt, addr >> PAGE_SHIFT);
+		copy_highpage(dpage, spage);
+		*dst = migrate_pfn(page_to_pfn(dpage));
+		if (*src & MIGRATE_PFN_WRITE)
+			*dst |= MIGRATE_PFN_WRITE;
+	}
+	return 0;
+}
+
+static unsigned long
+dmirror_successful_migrated_pages(struct migrate_vma *migrate)
+{
+	unsigned long cpages = 0;
+	unsigned long i;
+
+	for (i = 0; i < migrate->npages; i++) {
+		if (migrate->src[i] & MIGRATE_PFN_VALID &&
+		    migrate->src[i] & MIGRATE_PFN_MIGRATE)
+			cpages++;
+	}
+	return cpages;
+}
+
+static int dmirror_migrate_to_system(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->notifier.mm;
+	struct vm_area_struct *vma;
+	unsigned long src_pfns[64] = { 0 };
+	unsigned long dst_pfns[64] = { 0 };
+	struct migrate_vma args = { 0 };
+	unsigned long next;
+	int ret;
+
+	start = cmd->addr;
+	end = start + size;
+	if (end < start)
+		return -EINVAL;
+
+	/* Since the mm is for the mirrored process, get a reference first. */
+	if (!mmget_not_zero(mm))
+		return -EINVAL;
+
+	cmd->cpages = 0;
+	mmap_read_lock(mm);
+	for (addr = start; addr < end; addr = next) {
+		vma = vma_lookup(mm, addr);
+		if (!vma || !(vma->vm_flags & VM_READ)) {
+			ret = -EINVAL;
+			goto out;
+		}
+		next = min(end, addr + (ARRAY_SIZE(src_pfns) << PAGE_SHIFT));
+		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;
+		args.pgmap_owner = dmirror->mdevice;
+		args.flags = dmirror_select_device(dmirror);
+
+		ret = migrate_vma_setup(&args);
+		if (ret)
+			goto out;
+
+		pr_debug("Migrating from device mem to sys mem\n");
+		dmirror_devmem_fault_alloc_and_copy(&args, dmirror);
+
+		migrate_vma_pages(&args);
+		cmd->cpages += dmirror_successful_migrated_pages(&args);
+		migrate_vma_finalize(&args);
+	}
+out:
+	mmap_read_unlock(mm);
+	mmput(mm);
+
+	return ret;
+}
+
+static int dmirror_migrate_to_device(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->notifier.mm;
+	struct vm_area_struct *vma;
+	unsigned long src_pfns[64] = { 0 };
+	unsigned long dst_pfns[64] = { 0 };
+	struct dmirror_bounce bounce;
+	struct migrate_vma args = { 0 };
+	unsigned long next;
+	int ret;
+
+	start = cmd->addr;
+	end = start + size;
+	if (end < start)
+		return -EINVAL;
+
+	/* Since the mm is for the mirrored process, get a reference first. */
+	if (!mmget_not_zero(mm))
+		return -EINVAL;
+
+	mmap_read_lock(mm);
+	for (addr = start; addr < end; addr = next) {
+		vma = vma_lookup(mm, addr);
+		if (!vma || !(vma->vm_flags & VM_READ)) {
+			ret = -EINVAL;
+			goto out;
+		}
+		next = min(end, addr + (ARRAY_SIZE(src_pfns) << PAGE_SHIFT));
+		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;
+		args.pgmap_owner = dmirror->mdevice;
+		args.flags = MIGRATE_VMA_SELECT_SYSTEM;
+		ret = migrate_vma_setup(&args);
+		if (ret)
+			goto out;
+
+		pr_debug("Migrating from sys mem to device mem\n");
+		dmirror_migrate_alloc_and_copy(&args, dmirror);
+		migrate_vma_pages(&args);
+		dmirror_migrate_finalize_and_map(&args, dmirror);
+		migrate_vma_finalize(&args);
+	}
+	mmap_read_unlock(mm);
+	mmput(mm);
+
+	/*
+	 * Return the migrated data for verification.
+	 * Only for pages in device zone
+	 */
+	ret = dmirror_bounce_init(&bounce, start, size);
+	if (ret)
+		return ret;
+	mutex_lock(&dmirror->mutex);
+	ret = dmirror_do_read(dmirror, start, end, &bounce);
+	mutex_unlock(&dmirror->mutex);
+	if (ret == 0) {
+		if (copy_to_user(u64_to_user_ptr(cmd->ptr), bounce.ptr,
+				 bounce.size))
+			ret = -EFAULT;
+	}
+	cmd->cpages = bounce.cpages;
+	dmirror_bounce_fini(&bounce);
+	return ret;
+
+out:
+	mmap_read_unlock(mm);
+	mmput(mm);
+	return ret;
+}
+
+static void dmirror_mkentry(struct dmirror *dmirror, struct hmm_range *range,
+			    unsigned char *perm, unsigned long entry)
+{
+	struct page *page;
+
+	if (entry & HMM_PFN_ERROR) {
+		*perm = HMM_DMIRROR_PROT_ERROR;
+		return;
+	}
+	if (!(entry & HMM_PFN_VALID)) {
+		*perm = HMM_DMIRROR_PROT_NONE;
+		return;
+	}
+
+	page = hmm_pfn_to_page(entry);
+	if (is_device_private_page(page)) {
+		/* 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_device_coherent_page(page)) {
+		/* Is the page migrated to this device or some other? */
+		if (dmirror->mdevice == dmirror_page_to_device(page))
+			*perm = HMM_DMIRROR_PROT_DEV_COHERENT_LOCAL;
+		else
+			*perm = HMM_DMIRROR_PROT_DEV_COHERENT_REMOTE;
+	} else if (is_zero_pfn(page_to_pfn(page)))
+		*perm = HMM_DMIRROR_PROT_ZERO;
+	else
+		*perm = HMM_DMIRROR_PROT_NONE;
+	if (entry & HMM_PFN_WRITE)
+		*perm |= HMM_DMIRROR_PROT_WRITE;
+	else
+		*perm |= HMM_DMIRROR_PROT_READ;
+	if (hmm_pfn_to_map_order(entry) + PAGE_SHIFT == PMD_SHIFT)
+		*perm |= HMM_DMIRROR_PROT_PMD;
+	else if (hmm_pfn_to_map_order(entry) + PAGE_SHIFT == PUD_SHIFT)
+		*perm |= HMM_DMIRROR_PROT_PUD;
+}
+
+static bool dmirror_snapshot_invalidate(struct mmu_interval_notifier *mni,
+				const struct mmu_notifier_range *range,
+				unsigned long cur_seq)
+{
+	struct dmirror_interval *dmi =
+		container_of(mni, struct dmirror_interval, notifier);
+	struct dmirror *dmirror = dmi->dmirror;
+
+	if (mmu_notifier_range_blockable(range))
+		mutex_lock(&dmirror->mutex);
+	else if (!mutex_trylock(&dmirror->mutex))
+		return false;
+
+	/*
+	 * Snapshots only need to set the sequence number since any
+	 * invalidation in the interval invalidates the whole snapshot.
+	 */
+	mmu_interval_set_seq(mni, cur_seq);
+
+	mutex_unlock(&dmirror->mutex);
+	return true;
+}
+
+static const struct mmu_interval_notifier_ops dmirror_mrn_ops = {
+	.invalidate = dmirror_snapshot_invalidate,
+};
+
+static int dmirror_range_snapshot(struct dmirror *dmirror,
+				  struct hmm_range *range,
+				  unsigned char *perm)
+{
+	struct mm_struct *mm = dmirror->notifier.mm;
+	struct dmirror_interval notifier;
+	unsigned long timeout =
+		jiffies + msecs_to_jiffies(HMM_RANGE_DEFAULT_TIMEOUT);
+	unsigned long i;
+	unsigned long n;
+	int ret = 0;
+
+	notifier.dmirror = dmirror;
+	range->notifier = &notifier.notifier;
+
+	ret = mmu_interval_notifier_insert(range->notifier, mm,
+			range->start, range->end - range->start,
+			&dmirror_mrn_ops);
+	if (ret)
+		return ret;
+
+	while (true) {
+		if (time_after(jiffies, timeout)) {
+			ret = -EBUSY;
+			goto out;
+		}
+
+		range->notifier_seq = mmu_interval_read_begin(range->notifier);
+
+		mmap_read_lock(mm);
+		ret = hmm_range_fault(range);
+		mmap_read_unlock(mm);
+		if (ret) {
+			if (ret == -EBUSY)
+				continue;
+			goto out;
+		}
+
+		mutex_lock(&dmirror->mutex);
+		if (mmu_interval_read_retry(range->notifier,
+					    range->notifier_seq)) {
+			mutex_unlock(&dmirror->mutex);
+			continue;
+		}
+		break;
+	}
+
+	n = (range->end - range->start) >> PAGE_SHIFT;
+	for (i = 0; i < n; i++)
+		dmirror_mkentry(dmirror, range, perm + i, range->hmm_pfns[i]);
+
+	mutex_unlock(&dmirror->mutex);
+out:
+	mmu_interval_notifier_remove(range->notifier);
+	return ret;
+}
+
+static int dmirror_snapshot(struct dmirror *dmirror,
+			    struct hmm_dmirror_cmd *cmd)
+{
+	struct mm_struct *mm = dmirror->notifier.mm;
+	unsigned long start, end;
+	unsigned long size = cmd->npages << PAGE_SHIFT;
+	unsigned long addr;
+	unsigned long next;
+	unsigned long pfns[64];
+	unsigned char perm[64];
+	char __user *uptr;
+	struct hmm_range range = {
+		.hmm_pfns = pfns,
+		.dev_private_owner = dmirror->mdevice,
+	};
+	int ret = 0;
+
+	start = cmd->addr;
+	end = start + size;
+	if (end < start)
+		return -EINVAL;
+
+	/* Since the mm is for the mirrored process, get a reference first. */
+	if (!mmget_not_zero(mm))
+		return -EINVAL;
+
+	/*
+	 * Register a temporary notifier to detect invalidations even if it
+	 * overlaps with other mmu_interval_notifiers.
+	 */
+	uptr = u64_to_user_ptr(cmd->ptr);
+	for (addr = start; addr < end; addr = next) {
+		unsigned long n;
+
+		next = min(addr + (ARRAY_SIZE(pfns) << PAGE_SHIFT), end);
+		range.start = addr;
+		range.end = next;
+
+		ret = dmirror_range_snapshot(dmirror, &range, perm);
+		if (ret)
+			break;
+
+		n = (range.end - range.start) >> PAGE_SHIFT;
+		if (copy_to_user(uptr, perm, n)) {
+			ret = -EFAULT;
+			break;
+		}
+
+		cmd->cpages += n;
+		uptr += n;
+	}
+	mmput(mm);
+
+	return ret;
+}
+
+static void dmirror_device_evict_chunk(struct dmirror_chunk *chunk)
+{
+	unsigned long start_pfn = chunk->pagemap.range.start >> PAGE_SHIFT;
+	unsigned long end_pfn = chunk->pagemap.range.end >> PAGE_SHIFT;
+	unsigned long npages = end_pfn - start_pfn + 1;
+	unsigned long i;
+	unsigned long *src_pfns;
+	unsigned long *dst_pfns;
+
+	src_pfns = kcalloc(npages, sizeof(*src_pfns), GFP_KERNEL);
+	dst_pfns = kcalloc(npages, sizeof(*dst_pfns), GFP_KERNEL);
+
+	migrate_device_range(src_pfns, start_pfn, npages);
+	for (i = 0; i < npages; i++) {
+		struct page *dpage, *spage;
+
+		spage = migrate_pfn_to_page(src_pfns[i]);
+		if (!spage || !(src_pfns[i] & MIGRATE_PFN_MIGRATE))
+			continue;
+
+		if (WARN_ON(!is_device_private_page(spage) &&
+			    !is_device_coherent_page(spage)))
+			continue;
+		spage = BACKING_PAGE(spage);
+		dpage = alloc_page(GFP_HIGHUSER_MOVABLE | __GFP_NOFAIL);
+		lock_page(dpage);
+		copy_highpage(dpage, spage);
+		dst_pfns[i] = migrate_pfn(page_to_pfn(dpage));
+		if (src_pfns[i] & MIGRATE_PFN_WRITE)
+			dst_pfns[i] |= MIGRATE_PFN_WRITE;
+	}
+	migrate_device_pages(src_pfns, dst_pfns, npages);
+	migrate_device_finalize(src_pfns, dst_pfns, npages);
+	kfree(src_pfns);
+	kfree(dst_pfns);
+}
+
+/* Removes free pages from the free list so they can't be re-allocated */
+static void dmirror_remove_free_pages(struct dmirror_chunk *devmem)
+{
+	struct dmirror_device *mdevice = devmem->mdevice;
+	struct page *page;
+
+	for (page = mdevice->free_pages; page; page = page->zone_device_data)
+		if (dmirror_page_to_chunk(page) == devmem)
+			mdevice->free_pages = page->zone_device_data;
+}
+
+static void dmirror_device_remove_chunks(struct dmirror_device *mdevice)
+{
+	unsigned int i;
+
+	mutex_lock(&mdevice->devmem_lock);
+	if (mdevice->devmem_chunks) {
+		for (i = 0; i < mdevice->devmem_count; i++) {
+			struct dmirror_chunk *devmem =
+				mdevice->devmem_chunks[i];
+
+			spin_lock(&mdevice->lock);
+			devmem->remove = true;
+			dmirror_remove_free_pages(devmem);
+			spin_unlock(&mdevice->lock);
+
+			dmirror_device_evict_chunk(devmem);
+			memunmap_pages(&devmem->pagemap);
+			if (devmem->pagemap.type == MEMORY_DEVICE_PRIVATE)
+				release_mem_region(devmem->pagemap.range.start,
+						   range_len(&devmem->pagemap.range));
+			kfree(devmem);
+		}
+		mdevice->devmem_count = 0;
+		mdevice->devmem_capacity = 0;
+		mdevice->free_pages = NULL;
+		kfree(mdevice->devmem_chunks);
+		mdevice->devmem_chunks = NULL;
+	}
+	mutex_unlock(&mdevice->devmem_lock);
+}
+
+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;
+
+	if (copy_from_user(&cmd, uarg, sizeof(cmd)))
+		return -EFAULT;
+
+	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_TO_DEV:
+		ret = dmirror_migrate_to_device(dmirror, &cmd);
+		break;
+
+	case HMM_DMIRROR_MIGRATE_TO_SYS:
+		ret = dmirror_migrate_to_system(dmirror, &cmd);
+		break;
+
+	case HMM_DMIRROR_EXCLUSIVE:
+		ret = dmirror_exclusive(dmirror, &cmd);
+		break;
+
+	case HMM_DMIRROR_CHECK_EXCLUSIVE:
+		ret = dmirror_check_atomic(dmirror, cmd.addr,
+					cmd.addr + (cmd.npages << PAGE_SHIFT));
+		break;
+
+	case HMM_DMIRROR_SNAPSHOT:
+		ret = dmirror_snapshot(dmirror, &cmd);
+		break;
+
+	case HMM_DMIRROR_RELEASE:
+		dmirror_device_remove_chunks(dmirror->mdevice);
+		ret = 0;
+		break;
+
+	default:
+		return -EINVAL;
+	}
+	if (ret)
+		return ret;
+
+	if (copy_to_user(uarg, &cmd, sizeof(cmd)))
+		return -EFAULT;
+
+	return 0;
+}
+
+static int dmirror_fops_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	unsigned long addr;
+
+	for (addr = vma->vm_start; addr < vma->vm_end; addr += PAGE_SIZE) {
+		struct page *page;
+		int ret;
+
+		page = alloc_page(GFP_KERNEL | __GFP_ZERO);
+		if (!page)
+			return -ENOMEM;
+
+		ret = vm_insert_page(vma, addr, page);
+		if (ret) {
+			__free_page(page);
+			return ret;
+		}
+		put_page(page);
+	}
+
+	return 0;
+}
+
+static const struct file_operations dmirror_fops = {
+	.open		= dmirror_fops_open,
+	.release	= dmirror_fops_release,
+	.mmap		= dmirror_fops_mmap,
+	.unlocked_ioctl = dmirror_fops_unlocked_ioctl,
+	.llseek		= default_llseek,
+	.owner		= THIS_MODULE,
+};
+
+static void dmirror_devmem_free(struct page *page)
+{
+	struct page *rpage = BACKING_PAGE(page);
+	struct dmirror_device *mdevice;
+
+	if (rpage != page)
+		__free_page(rpage);
+
+	mdevice = dmirror_page_to_device(page);
+	spin_lock(&mdevice->lock);
+
+	/* Return page to our allocator if not freeing the chunk */
+	if (!dmirror_page_to_chunk(page)->remove) {
+		mdevice->cfree++;
+		page->zone_device_data = mdevice->free_pages;
+		mdevice->free_pages = page;
+	}
+	spin_unlock(&mdevice->lock);
+}
+
+static vm_fault_t dmirror_devmem_fault(struct vm_fault *vmf)
+{
+	struct migrate_vma args = { 0 };
+	unsigned long src_pfns = 0;
+	unsigned long dst_pfns = 0;
+	struct page *rpage;
+	struct dmirror *dmirror;
+	vm_fault_t ret;
+
+	/*
+	 * 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;
+
+	/* 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;
+	args.pgmap_owner = dmirror->mdevice;
+	args.flags = dmirror_select_device(dmirror);
+	args.fault_page = vmf->page;
+
+	if (migrate_vma_setup(&args))
+		return VM_FAULT_SIGBUS;
+
+	ret = dmirror_devmem_fault_alloc_and_copy(&args, dmirror);
+	if (ret)
+		return ret;
+	migrate_vma_pages(&args);
+	/*
+	 * No device finalize step is needed since
+	 * dmirror_devmem_fault_alloc_and_copy() will have already
+	 * invalidated the device page table.
+	 */
+	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 int dmirror_device_init(struct dmirror_device *mdevice, int id)
+{
+	dev_t dev;
+	int ret;
+
+	dev = MKDEV(MAJOR(dmirror_dev), id);
+	mutex_init(&mdevice->devmem_lock);
+	spin_lock_init(&mdevice->lock);
+
+	cdev_init(&mdevice->cdevice, &dmirror_fops);
+	mdevice->cdevice.owner = THIS_MODULE;
+	device_initialize(&mdevice->device);
+	mdevice->device.devt = dev;
+
+	ret = dev_set_name(&mdevice->device, "hmm_dmirror%u", id);
+	if (ret)
+		return ret;
+
+	ret = cdev_device_add(&mdevice->cdevice, &mdevice->device);
+	if (ret)
+		return ret;
+
+	/* Build a list of free ZONE_DEVICE struct pages */
+	return dmirror_allocate_chunk(mdevice, NULL);
+}
+
+static void dmirror_device_remove(struct dmirror_device *mdevice)
+{
+	dmirror_device_remove_chunks(mdevice);
+	cdev_device_del(&mdevice->cdevice, &mdevice->device);
+}
+
+static int __init hmm_dmirror_init(void)
+{
+	int ret;
+	int id = 0;
+	int ndevices = 0;
+
+	ret = alloc_chrdev_region(&dmirror_dev, 0, DMIRROR_NDEVICES,
+				  "HMM_DMIRROR");
+	if (ret)
+		goto err_unreg;
+
+	memset(dmirror_devices, 0, DMIRROR_NDEVICES * sizeof(dmirror_devices[0]));
+	dmirror_devices[ndevices++].zone_device_type =
+				HMM_DMIRROR_MEMORY_DEVICE_PRIVATE;
+	dmirror_devices[ndevices++].zone_device_type =
+				HMM_DMIRROR_MEMORY_DEVICE_PRIVATE;
+	if (spm_addr_dev0 && spm_addr_dev1) {
+		dmirror_devices[ndevices++].zone_device_type =
+					HMM_DMIRROR_MEMORY_DEVICE_COHERENT;
+		dmirror_devices[ndevices++].zone_device_type =
+					HMM_DMIRROR_MEMORY_DEVICE_COHERENT;
+	}
+	for (id = 0; id < ndevices; id++) {
+		ret = dmirror_device_init(dmirror_devices + id, id);
+		if (ret)
+			goto err_chrdev;
+	}
+
+	pr_info("HMM test module loaded. This is only for testing HMM.\n");
+	return 0;
+
+err_chrdev:
+	while (--id >= 0)
+		dmirror_device_remove(dmirror_devices + id);
+	unregister_chrdev_region(dmirror_dev, DMIRROR_NDEVICES);
+err_unreg:
+	return ret;
+}
+
+static void __exit hmm_dmirror_exit(void)
+{
+	int id;
+
+	for (id = 0; id < DMIRROR_NDEVICES; id++)
+		if (dmirror_devices[id].zone_device_type)
+			dmirror_device_remove(dmirror_devices + id);
+	unregister_chrdev_region(dmirror_dev, DMIRROR_NDEVICES);
+}
+
+module_init(hmm_dmirror_init);
+module_exit(hmm_dmirror_exit);
+MODULE_LICENSE("GPL");