diff --git a/src/kernel/linux/v4.19/mm/hmm.c b/src/kernel/linux/v4.19/mm/hmm.c
new file mode 100644
index 0000000..57f0d2a
--- /dev/null
+++ b/src/kernel/linux/v4.19/mm/hmm.c
@@ -0,0 +1,1348 @@
+/*
+ * 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: JÃ©rÃ´me Glisse <jglisse@redhat.com>
+ */
+/*
+ * Refer to include/linux/hmm.h for information about heterogeneous memory
+ * management or HMM for short.
+ */
+#include <linux/mm.h>
+#include <linux/hmm.h>
+#include <linux/init.h>
+#include <linux/rmap.h>
+#include <linux/swap.h>
+#include <linux/slab.h>
+#include <linux/sched.h>
+#include <linux/mmzone.h>
+#include <linux/pagemap.h>
+#include <linux/swapops.h>
+#include <linux/hugetlb.h>
+#include <linux/memremap.h>
+#include <linux/jump_label.h>
+#include <linux/mmu_notifier.h>
+#include <linux/memory_hotplug.h>
+
+#define PA_SECTION_SIZE (1UL << PA_SECTION_SHIFT)
+
+#if IS_ENABLED(CONFIG_HMM_MIRROR)
+static const struct mmu_notifier_ops hmm_mmu_notifier_ops;
+
+/*
+ * struct hmm - HMM per mm struct
+ *
+ * @mm: mm struct this HMM struct is bound to
+ * @lock: lock protecting ranges list
+ * @sequence: we track updates to the CPU page table with a sequence number
+ * @ranges: list of range being snapshotted
+ * @mirrors: list of mirrors for this mm
+ * @mmu_notifier: mmu notifier to track updates to CPU page table
+ * @mirrors_sem: read/write semaphore protecting the mirrors list
+ */
+struct hmm {
+	struct mm_struct	*mm;
+	spinlock_t		lock;
+	atomic_t		sequence;
+	struct list_head	ranges;
+	struct list_head	mirrors;
+	struct mmu_notifier	mmu_notifier;
+	struct rw_semaphore	mirrors_sem;
+};
+
+/*
+ * hmm_register - register HMM against an mm (HMM internal)
+ *
+ * @mm: mm struct to attach to
+ *
+ * This is not intended to be used directly by device drivers. It allocates an
+ * HMM struct if mm does not have one, and initializes it.
+ */
+static struct hmm *hmm_register(struct mm_struct *mm)
+{
+	struct hmm *hmm = READ_ONCE(mm->hmm);
+	bool cleanup = false;
+
+	/*
+	 * The hmm struct can only be freed once the mm_struct goes away,
+	 * hence we should always have pre-allocated an new hmm struct
+	 * above.
+	 */
+	if (hmm)
+		return hmm;
+
+	hmm = kmalloc(sizeof(*hmm), GFP_KERNEL);
+	if (!hmm)
+		return NULL;
+	INIT_LIST_HEAD(&hmm->mirrors);
+	init_rwsem(&hmm->mirrors_sem);
+	atomic_set(&hmm->sequence, 0);
+	hmm->mmu_notifier.ops = NULL;
+	INIT_LIST_HEAD(&hmm->ranges);
+	spin_lock_init(&hmm->lock);
+	hmm->mm = mm;
+
+	spin_lock(&mm->page_table_lock);
+	if (!mm->hmm)
+		mm->hmm = hmm;
+	else
+		cleanup = true;
+	spin_unlock(&mm->page_table_lock);
+
+	if (cleanup)
+		goto error;
+
+	/*
+	 * We should only get here if hold the mmap_sem in write mode ie on
+	 * registration of first mirror through hmm_mirror_register()
+	 */
+	hmm->mmu_notifier.ops = &hmm_mmu_notifier_ops;
+	if (__mmu_notifier_register(&hmm->mmu_notifier, mm))
+		goto error_mm;
+
+	return mm->hmm;
+
+error_mm:
+	spin_lock(&mm->page_table_lock);
+	if (mm->hmm == hmm)
+		mm->hmm = NULL;
+	spin_unlock(&mm->page_table_lock);
+error:
+	kfree(hmm);
+	return NULL;
+}
+
+void hmm_mm_destroy(struct mm_struct *mm)
+{
+	kfree(mm->hmm);
+}
+
+static void hmm_invalidate_range(struct hmm *hmm,
+				 enum hmm_update_type action,
+				 unsigned long start,
+				 unsigned long end)
+{
+	struct hmm_mirror *mirror;
+	struct hmm_range *range;
+
+	spin_lock(&hmm->lock);
+	list_for_each_entry(range, &hmm->ranges, list) {
+		unsigned long addr, idx, npages;
+
+		if (end < range->start || start >= range->end)
+			continue;
+
+		range->valid = false;
+		addr = max(start, range->start);
+		idx = (addr - range->start) >> PAGE_SHIFT;
+		npages = (min(range->end, end) - addr) >> PAGE_SHIFT;
+		memset(&range->pfns[idx], 0, sizeof(*range->pfns) * npages);
+	}
+	spin_unlock(&hmm->lock);
+
+	down_read(&hmm->mirrors_sem);
+	list_for_each_entry(mirror, &hmm->mirrors, list)
+		mirror->ops->sync_cpu_device_pagetables(mirror, action,
+							start, end);
+	up_read(&hmm->mirrors_sem);
+}
+
+static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+	struct hmm_mirror *mirror;
+	struct hmm *hmm = mm->hmm;
+
+	down_write(&hmm->mirrors_sem);
+	mirror = list_first_entry_or_null(&hmm->mirrors, struct hmm_mirror,
+					  list);
+	while (mirror) {
+		list_del_init(&mirror->list);
+		if (mirror->ops->release) {
+			/*
+			 * Drop mirrors_sem so callback can wait on any pending
+			 * work that might itself trigger mmu_notifier callback
+			 * and thus would deadlock with us.
+			 */
+			up_write(&hmm->mirrors_sem);
+			mirror->ops->release(mirror);
+			down_write(&hmm->mirrors_sem);
+		}
+		mirror = list_first_entry_or_null(&hmm->mirrors,
+						  struct hmm_mirror, list);
+	}
+	up_write(&hmm->mirrors_sem);
+}
+
+static int hmm_invalidate_range_start(struct mmu_notifier *mn,
+				       struct mm_struct *mm,
+				       unsigned long start,
+				       unsigned long end,
+				       bool blockable)
+{
+	struct hmm *hmm = mm->hmm;
+
+	VM_BUG_ON(!hmm);
+
+	atomic_inc(&hmm->sequence);
+
+	return 0;
+}
+
+static void hmm_invalidate_range_end(struct mmu_notifier *mn,
+				     struct mm_struct *mm,
+				     unsigned long start,
+				     unsigned long end)
+{
+	struct hmm *hmm = mm->hmm;
+
+	VM_BUG_ON(!hmm);
+
+	hmm_invalidate_range(mm->hmm, HMM_UPDATE_INVALIDATE, start, end);
+}
+
+static const struct mmu_notifier_ops hmm_mmu_notifier_ops = {
+	.release		= hmm_release,
+	.invalidate_range_start	= hmm_invalidate_range_start,
+	.invalidate_range_end	= hmm_invalidate_range_end,
+};
+
+/*
+ * hmm_mirror_register() - register a mirror against an mm
+ *
+ * @mirror: new mirror struct to register
+ * @mm: mm to register against
+ *
+ * To start mirroring a process address space, the device driver must register
+ * an HMM mirror struct.
+ *
+ * THE mm->mmap_sem MUST BE HELD IN WRITE MODE !
+ */
+int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm)
+{
+	/* Sanity check */
+	if (!mm || !mirror || !mirror->ops)
+		return -EINVAL;
+
+again:
+	mirror->hmm = hmm_register(mm);
+	if (!mirror->hmm)
+		return -ENOMEM;
+
+	down_write(&mirror->hmm->mirrors_sem);
+	if (mirror->hmm->mm == NULL) {
+		/*
+		 * A racing hmm_mirror_unregister() is about to destroy the hmm
+		 * struct. Try again to allocate a new one.
+		 */
+		up_write(&mirror->hmm->mirrors_sem);
+		mirror->hmm = NULL;
+		goto again;
+	} else {
+		list_add(&mirror->list, &mirror->hmm->mirrors);
+		up_write(&mirror->hmm->mirrors_sem);
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(hmm_mirror_register);
+
+/*
+ * hmm_mirror_unregister() - unregister a mirror
+ *
+ * @mirror: new mirror struct to register
+ *
+ * Stop mirroring a process address space, and cleanup.
+ */
+void hmm_mirror_unregister(struct hmm_mirror *mirror)
+{
+	bool should_unregister = false;
+	struct mm_struct *mm;
+	struct hmm *hmm;
+
+	if (mirror->hmm == NULL)
+		return;
+
+	hmm = mirror->hmm;
+	down_write(&hmm->mirrors_sem);
+	list_del_init(&mirror->list);
+	should_unregister = list_empty(&hmm->mirrors);
+	mirror->hmm = NULL;
+	mm = hmm->mm;
+	hmm->mm = NULL;
+	up_write(&hmm->mirrors_sem);
+
+	if (!should_unregister || mm == NULL)
+		return;
+
+	mmu_notifier_unregister_no_release(&hmm->mmu_notifier, mm);
+
+	spin_lock(&mm->page_table_lock);
+	if (mm->hmm == hmm)
+		mm->hmm = NULL;
+	spin_unlock(&mm->page_table_lock);
+
+	kfree(hmm);
+}
+EXPORT_SYMBOL(hmm_mirror_unregister);
+
+struct hmm_vma_walk {
+	struct hmm_range	*range;
+	unsigned long		last;
+	bool			fault;
+	bool			block;
+};
+
+static int hmm_vma_do_fault(struct mm_walk *walk, unsigned long addr,
+			    bool write_fault, uint64_t *pfn)
+{
+	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_REMOTE;
+	struct hmm_vma_walk *hmm_vma_walk = walk->private;
+	struct hmm_range *range = hmm_vma_walk->range;
+	struct vm_area_struct *vma = walk->vma;
+	vm_fault_t ret;
+
+	flags |= hmm_vma_walk->block ? 0 : FAULT_FLAG_ALLOW_RETRY;
+	flags |= write_fault ? FAULT_FLAG_WRITE : 0;
+	ret = handle_mm_fault(vma, addr, flags);
+	if (ret & VM_FAULT_RETRY)
+		return -EBUSY;
+	if (ret & VM_FAULT_ERROR) {
+		*pfn = range->values[HMM_PFN_ERROR];
+		return -EFAULT;
+	}
+
+	return -EAGAIN;
+}
+
+static int hmm_pfns_bad(unsigned long addr,
+			unsigned long end,
+			struct mm_walk *walk)
+{
+	struct hmm_vma_walk *hmm_vma_walk = walk->private;
+	struct hmm_range *range = hmm_vma_walk->range;
+	uint64_t *pfns = range->pfns;
+	unsigned long i;
+
+	i = (addr - range->start) >> PAGE_SHIFT;
+	for (; addr < end; addr += PAGE_SIZE, i++)
+		pfns[i] = range->values[HMM_PFN_ERROR];
+
+	return 0;
+}
+
+/*
+ * hmm_vma_walk_hole() - handle a range lacking valid pmd or pte(s)
+ * @start: range virtual start address (inclusive)
+ * @end: range virtual end address (exclusive)
+ * @fault: should we fault or not ?
+ * @write_fault: write fault ?
+ * @walk: mm_walk structure
+ * Returns: 0 on success, -EAGAIN after page fault, or page fault error
+ *
+ * This function will be called whenever pmd_none() or pte_none() returns true,
+ * or whenever there is no page directory covering the virtual address range.
+ */
+static int hmm_vma_walk_hole_(unsigned long addr, unsigned long end,
+			      bool fault, bool write_fault,
+			      struct mm_walk *walk)
+{
+	struct hmm_vma_walk *hmm_vma_walk = walk->private;
+	struct hmm_range *range = hmm_vma_walk->range;
+	uint64_t *pfns = range->pfns;
+	unsigned long i;
+
+	hmm_vma_walk->last = addr;
+	i = (addr - range->start) >> PAGE_SHIFT;
+	for (; addr < end; addr += PAGE_SIZE, i++) {
+		pfns[i] = range->values[HMM_PFN_NONE];
+		if (fault || write_fault) {
+			int ret;
+
+			ret = hmm_vma_do_fault(walk, addr, write_fault,
+					       &pfns[i]);
+			if (ret != -EAGAIN)
+				return ret;
+		}
+	}
+
+	return (fault || write_fault) ? -EAGAIN : 0;
+}
+
+static inline void hmm_pte_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
+				      uint64_t pfns, uint64_t cpu_flags,
+				      bool *fault, bool *write_fault)
+{
+	struct hmm_range *range = hmm_vma_walk->range;
+
+	*fault = *write_fault = false;
+	if (!hmm_vma_walk->fault)
+		return;
+
+	/* We aren't ask to do anything ... */
+	if (!(pfns & range->flags[HMM_PFN_VALID]))
+		return;
+	/* If this is device memory than only fault if explicitly requested */
+	if ((cpu_flags & range->flags[HMM_PFN_DEVICE_PRIVATE])) {
+		/* Do we fault on device memory ? */
+		if (pfns & range->flags[HMM_PFN_DEVICE_PRIVATE]) {
+			*write_fault = pfns & range->flags[HMM_PFN_WRITE];
+			*fault = true;
+		}
+		return;
+	}
+
+	/* If CPU page table is not valid then we need to fault */
+	*fault = !(cpu_flags & range->flags[HMM_PFN_VALID]);
+	/* Need to write fault ? */
+	if ((pfns & range->flags[HMM_PFN_WRITE]) &&
+	    !(cpu_flags & range->flags[HMM_PFN_WRITE])) {
+		*write_fault = true;
+		*fault = true;
+	}
+}
+
+static void hmm_range_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
+				 const uint64_t *pfns, unsigned long npages,
+				 uint64_t cpu_flags, bool *fault,
+				 bool *write_fault)
+{
+	unsigned long i;
+
+	if (!hmm_vma_walk->fault) {
+		*fault = *write_fault = false;
+		return;
+	}
+
+	for (i = 0; i < npages; ++i) {
+		hmm_pte_need_fault(hmm_vma_walk, pfns[i], cpu_flags,
+				   fault, write_fault);
+		if ((*fault) || (*write_fault))
+			return;
+	}
+}
+
+static int hmm_vma_walk_hole(unsigned long addr, unsigned long end,
+			     struct mm_walk *walk)
+{
+	struct hmm_vma_walk *hmm_vma_walk = walk->private;
+	struct hmm_range *range = hmm_vma_walk->range;
+	bool fault, write_fault;
+	unsigned long i, npages;
+	uint64_t *pfns;
+
+	i = (addr - range->start) >> PAGE_SHIFT;
+	npages = (end - addr) >> PAGE_SHIFT;
+	pfns = &range->pfns[i];
+	hmm_range_need_fault(hmm_vma_walk, pfns, npages,
+			     0, &fault, &write_fault);
+	return hmm_vma_walk_hole_(addr, end, fault, write_fault, walk);
+}
+
+static inline uint64_t pmd_to_hmm_pfn_flags(struct hmm_range *range, pmd_t pmd)
+{
+	if (pmd_protnone(pmd))
+		return 0;
+	return pmd_write(pmd) ? range->flags[HMM_PFN_VALID] |
+				range->flags[HMM_PFN_WRITE] :
+				range->flags[HMM_PFN_VALID];
+}
+
+static int hmm_vma_handle_pmd(struct mm_walk *walk,
+			      unsigned long addr,
+			      unsigned long end,
+			      uint64_t *pfns,
+			      pmd_t pmd)
+{
+	struct hmm_vma_walk *hmm_vma_walk = walk->private;
+	struct hmm_range *range = hmm_vma_walk->range;
+	unsigned long pfn, npages, i;
+	bool fault, write_fault;
+	uint64_t cpu_flags;
+
+	npages = (end - addr) >> PAGE_SHIFT;
+	cpu_flags = pmd_to_hmm_pfn_flags(range, pmd);
+	hmm_range_need_fault(hmm_vma_walk, pfns, npages, cpu_flags,
+			     &fault, &write_fault);
+
+	if (pmd_protnone(pmd) || fault || write_fault)
+		return hmm_vma_walk_hole_(addr, end, fault, write_fault, walk);
+
+	pfn = pmd_pfn(pmd) + pte_index(addr);
+	for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++)
+		pfns[i] = hmm_pfn_from_pfn(range, pfn) | cpu_flags;
+	hmm_vma_walk->last = end;
+	return 0;
+}
+
+static inline uint64_t pte_to_hmm_pfn_flags(struct hmm_range *range, pte_t pte)
+{
+	if (pte_none(pte) || !pte_present(pte))
+		return 0;
+	return pte_write(pte) ? range->flags[HMM_PFN_VALID] |
+				range->flags[HMM_PFN_WRITE] :
+				range->flags[HMM_PFN_VALID];
+}
+
+static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
+			      unsigned long end, pmd_t *pmdp, pte_t *ptep,
+			      uint64_t *pfn)
+{
+	struct hmm_vma_walk *hmm_vma_walk = walk->private;
+	struct hmm_range *range = hmm_vma_walk->range;
+	struct vm_area_struct *vma = walk->vma;
+	bool fault, write_fault;
+	uint64_t cpu_flags;
+	pte_t pte = *ptep;
+	uint64_t orig_pfn = *pfn;
+
+	*pfn = range->values[HMM_PFN_NONE];
+	cpu_flags = pte_to_hmm_pfn_flags(range, pte);
+	hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags,
+			   &fault, &write_fault);
+
+	if (pte_none(pte)) {
+		if (fault || write_fault)
+			goto fault;
+		return 0;
+	}
+
+	if (!pte_present(pte)) {
+		swp_entry_t entry = pte_to_swp_entry(pte);
+
+		if (!non_swap_entry(entry)) {
+			if (fault || write_fault)
+				goto fault;
+			return 0;
+		}
+
+		/*
+		 * This is a special swap entry, ignore migration, use
+		 * device and report anything else as error.
+		 */
+		if (is_device_private_entry(entry)) {
+			cpu_flags = range->flags[HMM_PFN_VALID] |
+				range->flags[HMM_PFN_DEVICE_PRIVATE];
+			cpu_flags |= is_write_device_private_entry(entry) ?
+				range->flags[HMM_PFN_WRITE] : 0;
+			hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags,
+					   &fault, &write_fault);
+			if (fault || write_fault)
+				goto fault;
+			*pfn = hmm_pfn_from_pfn(range, swp_offset(entry));
+			*pfn |= cpu_flags;
+			return 0;
+		}
+
+		if (is_migration_entry(entry)) {
+			if (fault || write_fault) {
+				pte_unmap(ptep);
+				hmm_vma_walk->last = addr;
+				migration_entry_wait(vma->vm_mm,
+						     pmdp, addr);
+				return -EAGAIN;
+			}
+			return 0;
+		}
+
+		/* Report error for everything else */
+		*pfn = range->values[HMM_PFN_ERROR];
+		return -EFAULT;
+	}
+
+	if (fault || write_fault)
+		goto fault;
+
+	*pfn = hmm_pfn_from_pfn(range, pte_pfn(pte)) | cpu_flags;
+	return 0;
+
+fault:
+	pte_unmap(ptep);
+	/* Fault any virtual address we were asked to fault */
+	return hmm_vma_walk_hole_(addr, end, fault, write_fault, walk);
+}
+
+static int hmm_vma_walk_pmd(pmd_t *pmdp,
+			    unsigned long start,
+			    unsigned long end,
+			    struct mm_walk *walk)
+{
+	struct hmm_vma_walk *hmm_vma_walk = walk->private;
+	struct hmm_range *range = hmm_vma_walk->range;
+	uint64_t *pfns = range->pfns;
+	unsigned long addr = start, i;
+	pte_t *ptep;
+
+	i = (addr - range->start) >> PAGE_SHIFT;
+
+again:
+	if (pmd_none(*pmdp))
+		return hmm_vma_walk_hole(start, end, walk);
+
+	if (pmd_huge(*pmdp) && (range->vma->vm_flags & VM_HUGETLB))
+		return hmm_pfns_bad(start, end, walk);
+
+	if (pmd_devmap(*pmdp) || pmd_trans_huge(*pmdp)) {
+		pmd_t pmd;
+
+		/*
+		 * No need to take pmd_lock here, even if some other threads
+		 * is splitting the huge pmd we will get that event through
+		 * mmu_notifier callback.
+		 *
+		 * So just read pmd value and check again its a transparent
+		 * huge or device mapping one and compute corresponding pfn
+		 * values.
+		 */
+		pmd = pmd_read_atomic(pmdp);
+		barrier();
+		if (!pmd_devmap(pmd) && !pmd_trans_huge(pmd))
+			goto again;
+
+		return hmm_vma_handle_pmd(walk, addr, end, &pfns[i], pmd);
+	}
+
+	if (pmd_bad(*pmdp))
+		return hmm_pfns_bad(start, end, walk);
+
+	ptep = pte_offset_map(pmdp, addr);
+	for (; addr < end; addr += PAGE_SIZE, ptep++, i++) {
+		int r;
+
+		r = hmm_vma_handle_pte(walk, addr, end, pmdp, ptep, &pfns[i]);
+		if (r) {
+			/* hmm_vma_handle_pte() did unmap pte directory */
+			hmm_vma_walk->last = addr;
+			return r;
+		}
+	}
+	pte_unmap(ptep - 1);
+
+	hmm_vma_walk->last = addr;
+	return 0;
+}
+
+static void hmm_pfns_clear(struct hmm_range *range,
+			   uint64_t *pfns,
+			   unsigned long addr,
+			   unsigned long end)
+{
+	for (; addr < end; addr += PAGE_SIZE, pfns++)
+		*pfns = range->values[HMM_PFN_NONE];
+}
+
+static void hmm_pfns_special(struct hmm_range *range)
+{
+	unsigned long addr = range->start, i = 0;
+
+	for (; addr < range->end; addr += PAGE_SIZE, i++)
+		range->pfns[i] = range->values[HMM_PFN_SPECIAL];
+}
+
+/*
+ * hmm_vma_get_pfns() - snapshot CPU page table for a range of virtual addresses
+ * @range: range being snapshotted
+ * Returns: -EINVAL if invalid argument, -ENOMEM out of memory, -EPERM invalid
+ *          vma permission, 0 success
+ *
+ * This snapshots the CPU page table for a range of virtual addresses. Snapshot
+ * validity is tracked by range struct. See hmm_vma_range_done() for further
+ * information.
+ *
+ * The range struct is initialized here. It tracks the CPU page table, but only
+ * if the function returns success (0), in which case the caller must then call
+ * hmm_vma_range_done() to stop CPU page table update tracking on this range.
+ *
+ * NOT CALLING hmm_vma_range_done() IF FUNCTION RETURNS 0 WILL LEAD TO SERIOUS
+ * MEMORY CORRUPTION ! YOU HAVE BEEN WARNED !
+ */
+int hmm_vma_get_pfns(struct hmm_range *range)
+{
+	struct vm_area_struct *vma = range->vma;
+	struct hmm_vma_walk hmm_vma_walk;
+	struct mm_walk mm_walk;
+	struct hmm *hmm;
+
+	/* Sanity check, this really should not happen ! */
+	if (range->start < vma->vm_start || range->start >= vma->vm_end)
+		return -EINVAL;
+	if (range->end < vma->vm_start || range->end > vma->vm_end)
+		return -EINVAL;
+
+	hmm = hmm_register(vma->vm_mm);
+	if (!hmm)
+		return -ENOMEM;
+	/* Caller must have registered a mirror, via hmm_mirror_register() ! */
+	if (!hmm->mmu_notifier.ops)
+		return -EINVAL;
+
+	/* FIXME support hugetlb fs */
+	if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL) ||
+			vma_is_dax(vma)) {
+		hmm_pfns_special(range);
+		return -EINVAL;
+	}
+
+	if (!(vma->vm_flags & VM_READ)) {
+		/*
+		 * If vma do not allow read access, then assume that it does
+		 * not allow write access, either. Architecture that allow
+		 * write without read access are not supported by HMM, because
+		 * operations such has atomic access would not work.
+		 */
+		hmm_pfns_clear(range, range->pfns, range->start, range->end);
+		return -EPERM;
+	}
+
+	/* Initialize range to track CPU page table update */
+	spin_lock(&hmm->lock);
+	range->valid = true;
+	list_add_rcu(&range->list, &hmm->ranges);
+	spin_unlock(&hmm->lock);
+
+	hmm_vma_walk.fault = false;
+	hmm_vma_walk.range = range;
+	mm_walk.private = &hmm_vma_walk;
+
+	mm_walk.vma = vma;
+	mm_walk.mm = vma->vm_mm;
+	mm_walk.pte_entry = NULL;
+	mm_walk.test_walk = NULL;
+	mm_walk.hugetlb_entry = NULL;
+	mm_walk.pmd_entry = hmm_vma_walk_pmd;
+	mm_walk.pte_hole = hmm_vma_walk_hole;
+
+	walk_page_range(range->start, range->end, &mm_walk);
+	return 0;
+}
+EXPORT_SYMBOL(hmm_vma_get_pfns);
+
+/*
+ * hmm_vma_range_done() - stop tracking change to CPU page table over a range
+ * @range: range being tracked
+ * Returns: false if range data has been invalidated, true otherwise
+ *
+ * Range struct is used to track updates to the CPU page table after a call to
+ * either hmm_vma_get_pfns() or hmm_vma_fault(). Once the device driver is done
+ * using the data,  or wants to lock updates to the data it got from those
+ * functions, it must call the hmm_vma_range_done() function, which will then
+ * stop tracking CPU page table updates.
+ *
+ * Note that device driver must still implement general CPU page table update
+ * tracking either by using hmm_mirror (see hmm_mirror_register()) or by using
+ * the mmu_notifier API directly.
+ *
+ * CPU page table update tracking done through hmm_range is only temporary and
+ * to be used while trying to duplicate CPU page table contents for a range of
+ * virtual addresses.
+ *
+ * There are two ways to use this :
+ * again:
+ *   hmm_vma_get_pfns(range); or hmm_vma_fault(...);
+ *   trans = device_build_page_table_update_transaction(pfns);
+ *   device_page_table_lock();
+ *   if (!hmm_vma_range_done(range)) {
+ *     device_page_table_unlock();
+ *     goto again;
+ *   }
+ *   device_commit_transaction(trans);
+ *   device_page_table_unlock();
+ *
+ * Or:
+ *   hmm_vma_get_pfns(range); or hmm_vma_fault(...);
+ *   device_page_table_lock();
+ *   hmm_vma_range_done(range);
+ *   device_update_page_table(range->pfns);
+ *   device_page_table_unlock();
+ */
+bool hmm_vma_range_done(struct hmm_range *range)
+{
+	unsigned long npages = (range->end - range->start) >> PAGE_SHIFT;
+	struct hmm *hmm;
+
+	if (range->end <= range->start) {
+		BUG();
+		return false;
+	}
+
+	hmm = hmm_register(range->vma->vm_mm);
+	if (!hmm) {
+		memset(range->pfns, 0, sizeof(*range->pfns) * npages);
+		return false;
+	}
+
+	spin_lock(&hmm->lock);
+	list_del_rcu(&range->list);
+	spin_unlock(&hmm->lock);
+
+	return range->valid;
+}
+EXPORT_SYMBOL(hmm_vma_range_done);
+
+/*
+ * hmm_vma_fault() - try to fault some address in a virtual address range
+ * @range: range being faulted
+ * @block: allow blocking on fault (if true it sleeps and do not drop mmap_sem)
+ * Returns: 0 success, error otherwise (-EAGAIN means mmap_sem have been drop)
+ *
+ * This is similar to a regular CPU page fault except that it will not trigger
+ * any memory migration if the memory being faulted is not accessible by CPUs.
+ *
+ * On error, for one virtual address in the range, the function will mark the
+ * corresponding HMM pfn entry with an error flag.
+ *
+ * Expected use pattern:
+ * retry:
+ *   down_read(&mm->mmap_sem);
+ *   // Find vma and address device wants to fault, initialize hmm_pfn_t
+ *   // array accordingly
+ *   ret = hmm_vma_fault(range, write, block);
+ *   switch (ret) {
+ *   case -EAGAIN:
+ *     hmm_vma_range_done(range);
+ *     // You might want to rate limit or yield to play nicely, you may
+ *     // also commit any valid pfn in the array assuming that you are
+ *     // getting true from hmm_vma_range_monitor_end()
+ *     goto retry;
+ *   case 0:
+ *     break;
+ *   case -ENOMEM:
+ *   case -EINVAL:
+ *   case -EPERM:
+ *   default:
+ *     // Handle error !
+ *     up_read(&mm->mmap_sem)
+ *     return;
+ *   }
+ *   // Take device driver lock that serialize device page table update
+ *   driver_lock_device_page_table_update();
+ *   hmm_vma_range_done(range);
+ *   // Commit pfns we got from hmm_vma_fault()
+ *   driver_unlock_device_page_table_update();
+ *   up_read(&mm->mmap_sem)
+ *
+ * YOU MUST CALL hmm_vma_range_done() AFTER THIS FUNCTION RETURN SUCCESS (0)
+ * BEFORE FREEING THE range struct OR YOU WILL HAVE SERIOUS MEMORY CORRUPTION !
+ *
+ * YOU HAVE BEEN WARNED !
+ */
+int hmm_vma_fault(struct hmm_range *range, bool block)
+{
+	struct vm_area_struct *vma = range->vma;
+	unsigned long start = range->start;
+	struct hmm_vma_walk hmm_vma_walk;
+	struct mm_walk mm_walk;
+	struct hmm *hmm;
+	int ret;
+
+	/* Sanity check, this really should not happen ! */
+	if (range->start < vma->vm_start || range->start >= vma->vm_end)
+		return -EINVAL;
+	if (range->end < vma->vm_start || range->end > vma->vm_end)
+		return -EINVAL;
+
+	hmm = hmm_register(vma->vm_mm);
+	if (!hmm) {
+		hmm_pfns_clear(range, range->pfns, range->start, range->end);
+		return -ENOMEM;
+	}
+	/* Caller must have registered a mirror using hmm_mirror_register() */
+	if (!hmm->mmu_notifier.ops)
+		return -EINVAL;
+
+	/* FIXME support hugetlb fs */
+	if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL) ||
+			vma_is_dax(vma)) {
+		hmm_pfns_special(range);
+		return -EINVAL;
+	}
+
+	if (!(vma->vm_flags & VM_READ)) {
+		/*
+		 * If vma do not allow read access, then assume that it does
+		 * not allow write access, either. Architecture that allow
+		 * write without read access are not supported by HMM, because
+		 * operations such has atomic access would not work.
+		 */
+		hmm_pfns_clear(range, range->pfns, range->start, range->end);
+		return -EPERM;
+	}
+
+	/* Initialize range to track CPU page table update */
+	spin_lock(&hmm->lock);
+	range->valid = true;
+	list_add_rcu(&range->list, &hmm->ranges);
+	spin_unlock(&hmm->lock);
+
+	hmm_vma_walk.fault = true;
+	hmm_vma_walk.block = block;
+	hmm_vma_walk.range = range;
+	mm_walk.private = &hmm_vma_walk;
+	hmm_vma_walk.last = range->start;
+
+	mm_walk.vma = vma;
+	mm_walk.mm = vma->vm_mm;
+	mm_walk.pte_entry = NULL;
+	mm_walk.test_walk = NULL;
+	mm_walk.hugetlb_entry = NULL;
+	mm_walk.pmd_entry = hmm_vma_walk_pmd;
+	mm_walk.pte_hole = hmm_vma_walk_hole;
+
+	do {
+		ret = walk_page_range(start, range->end, &mm_walk);
+		start = hmm_vma_walk.last;
+	} while (ret == -EAGAIN);
+
+	if (ret) {
+		unsigned long i;
+
+		i = (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;
+		hmm_pfns_clear(range, &range->pfns[i], hmm_vma_walk.last,
+			       range->end);
+		hmm_vma_range_done(range);
+	}
+	return ret;
+}
+EXPORT_SYMBOL(hmm_vma_fault);
+#endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */
+
+
+#if IS_ENABLED(CONFIG_DEVICE_PRIVATE) ||  IS_ENABLED(CONFIG_DEVICE_PUBLIC)
+struct page *hmm_vma_alloc_locked_page(struct vm_area_struct *vma,
+				       unsigned long addr)
+{
+	struct page *page;
+
+	page = alloc_page_vma(GFP_HIGHUSER, vma, addr);
+	if (!page)
+		return NULL;
+	lock_page(page);
+	return page;
+}
+EXPORT_SYMBOL(hmm_vma_alloc_locked_page);
+
+
+static void hmm_devmem_ref_release(struct percpu_ref *ref)
+{
+	struct hmm_devmem *devmem;
+
+	devmem = container_of(ref, struct hmm_devmem, ref);
+	complete(&devmem->completion);
+}
+
+static void hmm_devmem_ref_exit(void *data)
+{
+	struct percpu_ref *ref = data;
+	struct hmm_devmem *devmem;
+
+	devmem = container_of(ref, struct hmm_devmem, ref);
+	percpu_ref_exit(ref);
+}
+
+static void hmm_devmem_ref_kill(void *data)
+{
+	struct percpu_ref *ref = data;
+	struct hmm_devmem *devmem;
+
+	devmem = container_of(ref, struct hmm_devmem, ref);
+	percpu_ref_kill(ref);
+	wait_for_completion(&devmem->completion);
+}
+
+static int hmm_devmem_fault(struct vm_area_struct *vma,
+			    unsigned long addr,
+			    const struct page *page,
+			    unsigned int flags,
+			    pmd_t *pmdp)
+{
+	struct hmm_devmem *devmem = page->pgmap->data;
+
+	return devmem->ops->fault(devmem, vma, addr, page, flags, pmdp);
+}
+
+static void hmm_devmem_free(struct page *page, void *data)
+{
+	struct hmm_devmem *devmem = data;
+
+	page->mapping = NULL;
+
+	devmem->ops->free(devmem, page);
+}
+
+static DEFINE_MUTEX(hmm_devmem_lock);
+static RADIX_TREE(hmm_devmem_radix, GFP_KERNEL);
+
+static void hmm_devmem_radix_release(struct resource *resource)
+{
+	resource_size_t key;
+
+	mutex_lock(&hmm_devmem_lock);
+	for (key = resource->start;
+	     key <= resource->end;
+	     key += PA_SECTION_SIZE)
+		radix_tree_delete(&hmm_devmem_radix, key >> PA_SECTION_SHIFT);
+	mutex_unlock(&hmm_devmem_lock);
+}
+
+static void hmm_devmem_release(void *data)
+{
+	struct hmm_devmem *devmem = data;
+	struct resource *resource = devmem->resource;
+	unsigned long start_pfn, npages;
+	struct zone *zone;
+	struct page *page;
+
+	/* pages are dead and unused, undo the arch mapping */
+	start_pfn = (resource->start & ~(PA_SECTION_SIZE - 1)) >> PAGE_SHIFT;
+	npages = ALIGN(resource_size(resource), PA_SECTION_SIZE) >> PAGE_SHIFT;
+
+	page = pfn_to_page(start_pfn);
+	zone = page_zone(page);
+
+	mem_hotplug_begin();
+	if (resource->desc == IORES_DESC_DEVICE_PRIVATE_MEMORY)
+		__remove_pages(zone, start_pfn, npages, NULL);
+	else
+		arch_remove_memory(start_pfn << PAGE_SHIFT,
+				   npages << PAGE_SHIFT, NULL);
+	mem_hotplug_done();
+
+	hmm_devmem_radix_release(resource);
+}
+
+static int hmm_devmem_pages_create(struct hmm_devmem *devmem)
+{
+	resource_size_t key, align_start, align_size, align_end;
+	struct device *device = devmem->device;
+	int ret, nid, is_ram;
+	unsigned long pfn;
+
+	align_start = devmem->resource->start & ~(PA_SECTION_SIZE - 1);
+	align_size = ALIGN(devmem->resource->start +
+			   resource_size(devmem->resource),
+			   PA_SECTION_SIZE) - align_start;
+
+	is_ram = region_intersects(align_start, align_size,
+				   IORESOURCE_SYSTEM_RAM,
+				   IORES_DESC_NONE);
+	if (is_ram == REGION_MIXED) {
+		WARN_ONCE(1, "%s attempted on mixed region %pr\n",
+				__func__, devmem->resource);
+		return -ENXIO;
+	}
+	if (is_ram == REGION_INTERSECTS)
+		return -ENXIO;
+
+	if (devmem->resource->desc == IORES_DESC_DEVICE_PUBLIC_MEMORY)
+		devmem->pagemap.type = MEMORY_DEVICE_PUBLIC;
+	else
+		devmem->pagemap.type = MEMORY_DEVICE_PRIVATE;
+
+	devmem->pagemap.res = *devmem->resource;
+	devmem->pagemap.page_fault = hmm_devmem_fault;
+	devmem->pagemap.page_free = hmm_devmem_free;
+	devmem->pagemap.dev = devmem->device;
+	devmem->pagemap.ref = &devmem->ref;
+	devmem->pagemap.data = devmem;
+
+	mutex_lock(&hmm_devmem_lock);
+	align_end = align_start + align_size - 1;
+	for (key = align_start; key <= align_end; key += PA_SECTION_SIZE) {
+		struct hmm_devmem *dup;
+
+		dup = radix_tree_lookup(&hmm_devmem_radix,
+					key >> PA_SECTION_SHIFT);
+		if (dup) {
+			dev_err(device, "%s: collides with mapping for %s\n",
+				__func__, dev_name(dup->device));
+			mutex_unlock(&hmm_devmem_lock);
+			ret = -EBUSY;
+			goto error;
+		}
+		ret = radix_tree_insert(&hmm_devmem_radix,
+					key >> PA_SECTION_SHIFT,
+					devmem);
+		if (ret) {
+			dev_err(device, "%s: failed: %d\n", __func__, ret);
+			mutex_unlock(&hmm_devmem_lock);
+			goto error_radix;
+		}
+	}
+	mutex_unlock(&hmm_devmem_lock);
+
+	nid = dev_to_node(device);
+	if (nid < 0)
+		nid = numa_mem_id();
+
+	mem_hotplug_begin();
+	/*
+	 * For device private memory we call add_pages() as we only need to
+	 * allocate and initialize struct page for the device memory. More-
+	 * over the device memory is un-accessible thus we do not want to
+	 * create a linear mapping for the memory like arch_add_memory()
+	 * would do.
+	 *
+	 * For device public memory, which is accesible by the CPU, we do
+	 * want the linear mapping and thus use arch_add_memory().
+	 */
+	if (devmem->pagemap.type == MEMORY_DEVICE_PUBLIC)
+		ret = arch_add_memory(nid, align_start, align_size, NULL,
+				false);
+	else
+		ret = add_pages(nid, align_start >> PAGE_SHIFT,
+				align_size >> PAGE_SHIFT, NULL, false);
+	if (ret) {
+		mem_hotplug_done();
+		goto error_add_memory;
+	}
+	move_pfn_range_to_zone(&NODE_DATA(nid)->node_zones[ZONE_DEVICE],
+				align_start >> PAGE_SHIFT,
+				align_size >> PAGE_SHIFT, NULL);
+	mem_hotplug_done();
+
+	for (pfn = devmem->pfn_first; pfn < devmem->pfn_last; pfn++) {
+		struct page *page = pfn_to_page(pfn);
+
+		page->pgmap = &devmem->pagemap;
+	}
+	return 0;
+
+error_add_memory:
+	untrack_pfn(NULL, PHYS_PFN(align_start), align_size);
+error_radix:
+	hmm_devmem_radix_release(devmem->resource);
+error:
+	return ret;
+}
+
+/*
+ * hmm_devmem_add() - hotplug ZONE_DEVICE memory for device memory
+ *
+ * @ops: memory event device driver callback (see struct hmm_devmem_ops)
+ * @device: device struct to bind the resource too
+ * @size: size in bytes of the device memory to add
+ * Returns: pointer to new hmm_devmem struct ERR_PTR otherwise
+ *
+ * This function first finds an empty range of physical address big enough to
+ * contain the new resource, and then hotplugs it as ZONE_DEVICE memory, which
+ * in turn allocates struct pages. It does not do anything beyond that; all
+ * events affecting the memory will go through the various callbacks provided
+ * by hmm_devmem_ops struct.
+ *
+ * Device driver should call this function during device initialization and
+ * is then responsible of memory management. HMM only provides helpers.
+ */
+struct hmm_devmem *hmm_devmem_add(const struct hmm_devmem_ops *ops,
+				  struct device *device,
+				  unsigned long size)
+{
+	struct hmm_devmem *devmem;
+	resource_size_t addr;
+	int ret;
+
+	dev_pagemap_get_ops();
+
+	devmem = devm_kzalloc(device, sizeof(*devmem), GFP_KERNEL);
+	if (!devmem)
+		return ERR_PTR(-ENOMEM);
+
+	init_completion(&devmem->completion);
+	devmem->pfn_first = -1UL;
+	devmem->pfn_last = -1UL;
+	devmem->resource = NULL;
+	devmem->device = device;
+	devmem->ops = ops;
+
+	ret = percpu_ref_init(&devmem->ref, &hmm_devmem_ref_release,
+			      0, GFP_KERNEL);
+	if (ret)
+		return ERR_PTR(ret);
+
+	ret = devm_add_action_or_reset(device, hmm_devmem_ref_exit, &devmem->ref);
+	if (ret)
+		return ERR_PTR(ret);
+
+	size = ALIGN(size, PA_SECTION_SIZE);
+	addr = min((unsigned long)iomem_resource.end,
+		   (1UL << MAX_PHYSMEM_BITS) - 1);
+	addr = addr - size + 1UL;
+
+	/*
+	 * FIXME add a new helper to quickly walk resource tree and find free
+	 * range
+	 *
+	 * FIXME what about ioport_resource resource ?
+	 */
+	for (; addr > size && addr >= iomem_resource.start; addr -= size) {
+		ret = region_intersects(addr, size, 0, IORES_DESC_NONE);
+		if (ret != REGION_DISJOINT)
+			continue;
+
+		devmem->resource = devm_request_mem_region(device, addr, size,
+							   dev_name(device));
+		if (!devmem->resource)
+			return ERR_PTR(-ENOMEM);
+		break;
+	}
+	if (!devmem->resource)
+		return ERR_PTR(-ERANGE);
+
+	devmem->resource->desc = IORES_DESC_DEVICE_PRIVATE_MEMORY;
+	devmem->pfn_first = devmem->resource->start >> PAGE_SHIFT;
+	devmem->pfn_last = devmem->pfn_first +
+			   (resource_size(devmem->resource) >> PAGE_SHIFT);
+
+	ret = hmm_devmem_pages_create(devmem);
+	if (ret)
+		return ERR_PTR(ret);
+
+	ret = devm_add_action_or_reset(device, hmm_devmem_release, devmem);
+	if (ret)
+		return ERR_PTR(ret);
+
+	return devmem;
+}
+EXPORT_SYMBOL_GPL(hmm_devmem_add);
+
+struct hmm_devmem *hmm_devmem_add_resource(const struct hmm_devmem_ops *ops,
+					   struct device *device,
+					   struct resource *res)
+{
+	struct hmm_devmem *devmem;
+	int ret;
+
+	if (res->desc != IORES_DESC_DEVICE_PUBLIC_MEMORY)
+		return ERR_PTR(-EINVAL);
+
+	dev_pagemap_get_ops();
+
+	devmem = devm_kzalloc(device, sizeof(*devmem), GFP_KERNEL);
+	if (!devmem)
+		return ERR_PTR(-ENOMEM);
+
+	init_completion(&devmem->completion);
+	devmem->pfn_first = -1UL;
+	devmem->pfn_last = -1UL;
+	devmem->resource = res;
+	devmem->device = device;
+	devmem->ops = ops;
+
+	ret = percpu_ref_init(&devmem->ref, &hmm_devmem_ref_release,
+			      0, GFP_KERNEL);
+	if (ret)
+		return ERR_PTR(ret);
+
+	ret = devm_add_action_or_reset(device, hmm_devmem_ref_exit,
+			&devmem->ref);
+	if (ret)
+		return ERR_PTR(ret);
+
+	devmem->pfn_first = devmem->resource->start >> PAGE_SHIFT;
+	devmem->pfn_last = devmem->pfn_first +
+			   (resource_size(devmem->resource) >> PAGE_SHIFT);
+
+	ret = hmm_devmem_pages_create(devmem);
+	if (ret)
+		return ERR_PTR(ret);
+
+	ret = devm_add_action_or_reset(device, hmm_devmem_release, devmem);
+	if (ret)
+		return ERR_PTR(ret);
+
+	ret = devm_add_action_or_reset(device, hmm_devmem_ref_kill,
+			&devmem->ref);
+	if (ret)
+		return ERR_PTR(ret);
+
+	return devmem;
+}
+EXPORT_SYMBOL_GPL(hmm_devmem_add_resource);
+
+/*
+ * A device driver that wants to handle multiple devices memory through a
+ * single fake device can use hmm_device to do so. This is purely a helper
+ * and it is not needed to make use of any HMM functionality.
+ */
+#define HMM_DEVICE_MAX 256
+
+static DECLARE_BITMAP(hmm_device_mask, HMM_DEVICE_MAX);
+static DEFINE_SPINLOCK(hmm_device_lock);
+static struct class *hmm_device_class;
+static dev_t hmm_device_devt;
+
+static void hmm_device_release(struct device *device)
+{
+	struct hmm_device *hmm_device;
+
+	hmm_device = container_of(device, struct hmm_device, device);
+	spin_lock(&hmm_device_lock);
+	clear_bit(hmm_device->minor, hmm_device_mask);
+	spin_unlock(&hmm_device_lock);
+
+	kfree(hmm_device);
+}
+
+struct hmm_device *hmm_device_new(void *drvdata)
+{
+	struct hmm_device *hmm_device;
+
+	hmm_device = kzalloc(sizeof(*hmm_device), GFP_KERNEL);
+	if (!hmm_device)
+		return ERR_PTR(-ENOMEM);
+
+	spin_lock(&hmm_device_lock);
+	hmm_device->minor = find_first_zero_bit(hmm_device_mask, HMM_DEVICE_MAX);
+	if (hmm_device->minor >= HMM_DEVICE_MAX) {
+		spin_unlock(&hmm_device_lock);
+		kfree(hmm_device);
+		return ERR_PTR(-EBUSY);
+	}
+	set_bit(hmm_device->minor, hmm_device_mask);
+	spin_unlock(&hmm_device_lock);
+
+	dev_set_name(&hmm_device->device, "hmm_device%d", hmm_device->minor);
+	hmm_device->device.devt = MKDEV(MAJOR(hmm_device_devt),
+					hmm_device->minor);
+	hmm_device->device.release = hmm_device_release;
+	dev_set_drvdata(&hmm_device->device, drvdata);
+	hmm_device->device.class = hmm_device_class;
+	device_initialize(&hmm_device->device);
+
+	return hmm_device;
+}
+EXPORT_SYMBOL(hmm_device_new);
+
+void hmm_device_put(struct hmm_device *hmm_device)
+{
+	put_device(&hmm_device->device);
+}
+EXPORT_SYMBOL(hmm_device_put);
+
+static int __init hmm_init(void)
+{
+	int ret;
+
+	ret = alloc_chrdev_region(&hmm_device_devt, 0,
+				  HMM_DEVICE_MAX,
+				  "hmm_device");
+	if (ret)
+		return ret;
+
+	hmm_device_class = class_create(THIS_MODULE, "hmm_device");
+	if (IS_ERR(hmm_device_class)) {
+		unregister_chrdev_region(hmm_device_devt, HMM_DEVICE_MAX);
+		return PTR_ERR(hmm_device_class);
+	}
+	return 0;
+}
+
+device_initcall(hmm_init);
+#endif /* CONFIG_DEVICE_PRIVATE || CONFIG_DEVICE_PUBLIC */