// SPDX-License-Identifier: GPL-2.0-or-later

  /*
   * Copyright 2013 Red Hat Inc.
   *

   * Authors: Jérôme Glisse <jglisse@redhat.com>

   */
  /*
   * Refer to include/linux/hmm.h for information about heterogeneous memory
   * management or HMM for short.
   */

  #include <linux/pagewalk.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/sched/mm.h>

  #include <linux/jump_label.h>

  #include <linux/dma-mapping.h>

  #include <linux/mmu_notifier.h>

  #include <linux/memory_hotplug.h>

  static struct mmu_notifier *hmm_alloc_notifier(struct mm_struct *mm)

  {

  	struct hmm *hmm;

  	hmm = kzalloc(sizeof(*hmm), GFP_KERNEL);

  	if (!hmm)

  		return ERR_PTR(-ENOMEM);

  	init_waitqueue_head(&hmm->wq);

  	INIT_LIST_HEAD(&hmm->mirrors);
  	init_rwsem(&hmm->mirrors_sem);

  	INIT_LIST_HEAD(&hmm->ranges);

  	spin_lock_init(&hmm->ranges_lock);

  	hmm->notifiers = 0;

  	return &hmm->mmu_notifier;

  }

  static void hmm_free_notifier(struct mmu_notifier *mn)

  {

  	struct hmm *hmm = container_of(mn, struct hmm, mmu_notifier);

  	WARN_ON(!list_empty(&hmm->ranges));
  	WARN_ON(!list_empty(&hmm->mirrors));

  	kfree(hmm);

  }

  static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm)

  {

  	struct hmm *hmm = container_of(mn, struct hmm, mmu_notifier);

  	struct hmm_mirror *mirror;

  	/*
  	 * Since hmm_range_register() holds the mmget() lock hmm_release() is
  	 * prevented as long as a range exists.
  	 */
  	WARN_ON(!list_empty_careful(&hmm->ranges));

  	down_read(&hmm->mirrors_sem);
  	list_for_each_entry(mirror, &hmm->mirrors, list) {
  		/*
  		 * Note: The driver is not allowed to trigger
  		 * hmm_mirror_unregister() from this thread.
  		 */
  		if (mirror->ops->release)

  			mirror->ops->release(mirror);

  	}

  	up_read(&hmm->mirrors_sem);

  }

  static void notifiers_decrement(struct hmm *hmm)

  {

  	unsigned long flags;

  	spin_lock_irqsave(&hmm->ranges_lock, flags);
  	hmm->notifiers--;
  	if (!hmm->notifiers) {
  		struct hmm_range *range;

  		list_for_each_entry(range, &hmm->ranges, list) {
  			if (range->valid)
  				continue;
  			range->valid = true;

  		}

  		wake_up_all(&hmm->wq);

  	}

  	spin_unlock_irqrestore(&hmm->ranges_lock, flags);

  }

  static int hmm_invalidate_range_start(struct mmu_notifier *mn,

  			const struct mmu_notifier_range *nrange)

  {

  	struct hmm *hmm = container_of(mn, struct hmm, mmu_notifier);

  	struct hmm_mirror *mirror;

  	struct hmm_range *range;

  	unsigned long flags;

  	int ret = 0;

  	spin_lock_irqsave(&hmm->ranges_lock, flags);

  	hmm->notifiers++;
  	list_for_each_entry(range, &hmm->ranges, list) {

  		if (nrange->end < range->start || nrange->start >= range->end)

  			continue;
  
  		range->valid = false;
  	}

  	spin_unlock_irqrestore(&hmm->ranges_lock, flags);

  	if (mmu_notifier_range_blockable(nrange))

  		down_read(&hmm->mirrors_sem);
  	else if (!down_read_trylock(&hmm->mirrors_sem)) {
  		ret = -EAGAIN;
  		goto out;
  	}

  	list_for_each_entry(mirror, &hmm->mirrors, list) {

  		int rc;

  		rc = mirror->ops->sync_cpu_device_pagetables(mirror, nrange);

  		if (rc) {

  			if (WARN_ON(mmu_notifier_range_blockable(nrange) ||
  			    rc != -EAGAIN))

  				continue;

  			ret = -EAGAIN;

  			break;

  		}
  	}
  	up_read(&hmm->mirrors_sem);
  
  out:

  	if (ret)
  		notifiers_decrement(hmm);

  	return ret;

  }
  
  static void hmm_invalidate_range_end(struct mmu_notifier *mn,

  			const struct mmu_notifier_range *nrange)

  {

  	struct hmm *hmm = container_of(mn, struct hmm, mmu_notifier);

  	notifiers_decrement(hmm);

  }
  
  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,

  	.alloc_notifier		= hmm_alloc_notifier,
  	.free_notifier		= hmm_free_notifier,

  };
  
  /*
   * hmm_mirror_register() - register a mirror against an mm
   *
   * @mirror: new mirror struct to register
   * @mm: mm to register against

   * Return: 0 on success, -ENOMEM if no memory, -EINVAL if invalid arguments

   *
   * To start mirroring a process address space, the device driver must register
   * an HMM mirror struct.

   *
   * The caller cannot unregister the hmm_mirror while any ranges are
   * registered.
   *
   * Callers using this function must put a call to mmu_notifier_synchronize()
   * in their module exit functions.

   */
  int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm)
  {

  	struct mmu_notifier *mn;

  	lockdep_assert_held_write(&mm->mmap_sem);

  	/* Sanity check */
  	if (!mm || !mirror || !mirror->ops)
  		return -EINVAL;

  	mn = mmu_notifier_get_locked(&hmm_mmu_notifier_ops, mm);
  	if (IS_ERR(mn))
  		return PTR_ERR(mn);
  	mirror->hmm = container_of(mn, struct hmm, mmu_notifier);

  
  	down_write(&mirror->hmm->mirrors_sem);

  	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: mirror struct to unregister

   *
   * Stop mirroring a process address space, and cleanup.
   */
  void hmm_mirror_unregister(struct hmm_mirror *mirror)
  {

  	struct hmm *hmm = mirror->hmm;

  
  	down_write(&hmm->mirrors_sem);

  	list_del(&mirror->list);

  	up_write(&hmm->mirrors_sem);

  	mmu_notifier_put(&hmm->mmu_notifier);

  }
  EXPORT_SYMBOL(hmm_mirror_unregister);

  struct hmm_vma_walk {
  	struct hmm_range	*range;

  	struct dev_pagemap	*pgmap;

  	unsigned long		last;

  	unsigned int		flags;

  };

  static int hmm_vma_do_fault(struct mm_walk *walk, unsigned long addr,
  			    bool write_fault, uint64_t *pfn)

  {

  	unsigned int flags = 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;

  	if (!vma)
  		goto err;

  	if (hmm_vma_walk->flags & HMM_FAULT_ALLOW_RETRY)
  		flags |= FAULT_FLAG_ALLOW_RETRY;
  	if (write_fault)
  		flags |= FAULT_FLAG_WRITE;

  	ret = handle_mm_fault(vma, addr, flags);

  	if (ret & VM_FAULT_RETRY) {
  		/* Note, handle_mm_fault did up_read(&mm->mmap_sem)) */

  		return -EAGAIN;

  	}

  	if (ret & VM_FAULT_ERROR)
  		goto err;

  	return -EBUSY;

  
  err:
  	*pfn = range->values[HMM_PFN_ERROR];
  	return -EFAULT;

  }

  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)
   * @addr: 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

   * Return: 0 on success, -EBUSY 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;

  	if (write_fault && walk->vma && !(walk->vma->vm_flags & VM_WRITE))
  		return -EPERM;

  	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 != -EBUSY)

  				return ret;
  		}
  	}

  	return (fault || write_fault) ? -EBUSY : 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;

  	if (hmm_vma_walk->flags & HMM_FAULT_SNAPSHOT)

  		return;

  	/*
  	 * So we not only consider the individual per page request we also
  	 * consider the default flags requested for the range. The API can

  	 * be used 2 ways. The first one where the HMM user coalesces
  	 * multiple page faults into one request and sets flags per pfn for
  	 * those faults. The second one where the HMM user wants to pre-

  	 * fault a range with specific flags. For the latter one it is a
  	 * waste to have the user pre-fill the pfn arrays with a default
  	 * flags value.
  	 */
  	pfns = (pfns & range->pfn_flags_mask) | range->default_flags;

  	/* We aren't ask to do anything ... */

  	if (!(pfns & range->flags[HMM_PFN_VALID]))

  		return;

  	/* If this is device memory then 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->flags & HMM_FAULT_SNAPSHOT) {

  		*fault = *write_fault = false;
  		return;
  	}

  	*fault = *write_fault = false;

  	for (i = 0; i < npages; ++i) {
  		hmm_pte_need_fault(hmm_vma_walk, pfns[i], cpu_flags,
  				   fault, write_fault);

  		if ((*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];

  }

  #ifdef CONFIG_TRANSPARENT_HUGEPAGE

  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) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);

  	for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++) {
  		if (pmd_devmap(pmd)) {
  			hmm_vma_walk->pgmap = get_dev_pagemap(pfn,
  					      hmm_vma_walk->pgmap);
  			if (unlikely(!hmm_vma_walk->pgmap))
  				return -EBUSY;
  		}

  		pfns[i] = hmm_device_entry_from_pfn(range, pfn) | cpu_flags;

  	}
  	if (hmm_vma_walk->pgmap) {
  		put_dev_pagemap(hmm_vma_walk->pgmap);
  		hmm_vma_walk->pgmap = NULL;
  	}

  	hmm_vma_walk->last = end;
  	return 0;
  }

  #else /* CONFIG_TRANSPARENT_HUGEPAGE */
  /* stub to allow the code below to compile */
  int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr,
  		unsigned long end, uint64_t *pfns, pmd_t pmd);
  #endif /* CONFIG_TRANSPARENT_HUGEPAGE */

  static inline uint64_t pte_to_hmm_pfn_flags(struct hmm_range *range, pte_t pte)

  {

  	if (pte_none(pte) || !pte_present(pte) || pte_protnone(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;

  	bool fault, write_fault;
  	uint64_t cpu_flags;

  	pte_t pte = *ptep;

  	uint64_t orig_pfn = *pfn;

  	*pfn = range->values[HMM_PFN_NONE];

  	fault = write_fault = false;

  
  	if (pte_none(pte)) {

  		hmm_pte_need_fault(hmm_vma_walk, orig_pfn, 0,
  				   &fault, &write_fault);

  		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)) {

  			cpu_flags = pte_to_hmm_pfn_flags(range, pte);
  			hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags,
  					   &fault, &write_fault);

  			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_device_entry_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(walk->mm, pmdp, addr);

  				return -EBUSY;

  			}
  			return 0;
  		}
  
  		/* Report error for everything else */

  		*pfn = range->values[HMM_PFN_ERROR];

  		return -EFAULT;

  	} else {
  		cpu_flags = pte_to_hmm_pfn_flags(range, pte);
  		hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags,
  				   &fault, &write_fault);

  	}

  	if (fault || write_fault)

  		goto fault;

  	if (pte_devmap(pte)) {
  		hmm_vma_walk->pgmap = get_dev_pagemap(pte_pfn(pte),
  					      hmm_vma_walk->pgmap);
  		if (unlikely(!hmm_vma_walk->pgmap))
  			return -EBUSY;
  	} else if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL) && pte_special(pte)) {
  		*pfn = range->values[HMM_PFN_SPECIAL];
  		return -EFAULT;
  	}

  	*pfn = hmm_device_entry_from_pfn(range, pte_pfn(pte)) | cpu_flags;

  	return 0;
  
  fault:

  	if (hmm_vma_walk->pgmap) {
  		put_dev_pagemap(hmm_vma_walk->pgmap);
  		hmm_vma_walk->pgmap = NULL;
  	}

  	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;

  	pmd_t pmd;

  again:

  	pmd = READ_ONCE(*pmdp);
  	if (pmd_none(pmd))

  		return hmm_vma_walk_hole(start, end, walk);

  	if (thp_migration_supported() && is_pmd_migration_entry(pmd)) {
  		bool fault, write_fault;
  		unsigned long 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);
  		if (fault || write_fault) {
  			hmm_vma_walk->last = addr;

  			pmd_migration_entry_wait(walk->mm, pmdp);

  			return -EBUSY;

  		}
  		return 0;
  	} else if (!pmd_present(pmd))
  		return hmm_pfns_bad(start, end, walk);

  	if (pmd_devmap(pmd) || pmd_trans_huge(pmd)) {

  		/*

  		 * No need to take pmd_lock here, even if some other thread

  		 * is splitting the huge pmd we will get that event through
  		 * mmu_notifier callback.
  		 *

  		 * So just read pmd value and check again it's 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;

  		i = (addr - range->start) >> PAGE_SHIFT;

  		return hmm_vma_handle_pmd(walk, addr, end, &pfns[i], pmd);

  	}

  	/*

  	 * We have handled all the valid cases above ie either none, migration,

  	 * huge or transparent huge. At this point either it is a valid pmd
  	 * entry pointing to pte directory or it is a bad pmd that will not
  	 * recover.
  	 */
  	if (pmd_bad(pmd))

  		return hmm_pfns_bad(start, end, walk);
  
  	ptep = pte_offset_map(pmdp, addr);

  	i = (addr - range->start) >> PAGE_SHIFT;

  	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;

  		}

  	}

  	if (hmm_vma_walk->pgmap) {
  		/*
  		 * We do put_dev_pagemap() here and not in hmm_vma_handle_pte()
  		 * so that we can leverage get_dev_pagemap() optimization which
  		 * will not re-take a reference on a pgmap if we already have
  		 * one.
  		 */
  		put_dev_pagemap(hmm_vma_walk->pgmap);
  		hmm_vma_walk->pgmap = NULL;
  	}

  	pte_unmap(ptep - 1);

  	hmm_vma_walk->last = addr;

  	return 0;
  }

  #if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && \
      defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
  static inline uint64_t pud_to_hmm_pfn_flags(struct hmm_range *range, pud_t pud)
  {
  	if (!pud_present(pud))
  		return 0;
  	return pud_write(pud) ? range->flags[HMM_PFN_VALID] |
  				range->flags[HMM_PFN_WRITE] :
  				range->flags[HMM_PFN_VALID];
  }
  
  static int hmm_vma_walk_pud(pud_t *pudp, 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;
  	unsigned long addr = start, next;
  	pmd_t *pmdp;
  	pud_t pud;
  	int ret;
  
  again:
  	pud = READ_ONCE(*pudp);
  	if (pud_none(pud))
  		return hmm_vma_walk_hole(start, end, walk);
  
  	if (pud_huge(pud) && pud_devmap(pud)) {
  		unsigned long i, npages, pfn;
  		uint64_t *pfns, cpu_flags;
  		bool fault, write_fault;
  
  		if (!pud_present(pud))
  			return hmm_vma_walk_hole(start, end, walk);
  
  		i = (addr - range->start) >> PAGE_SHIFT;
  		npages = (end - addr) >> PAGE_SHIFT;
  		pfns = &range->pfns[i];
  
  		cpu_flags = pud_to_hmm_pfn_flags(range, pud);
  		hmm_range_need_fault(hmm_vma_walk, pfns, npages,
  				     cpu_flags, &fault, &write_fault);
  		if (fault || write_fault)
  			return hmm_vma_walk_hole_(addr, end, fault,
  						write_fault, walk);

  		pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
  		for (i = 0; i < npages; ++i, ++pfn) {
  			hmm_vma_walk->pgmap = get_dev_pagemap(pfn,
  					      hmm_vma_walk->pgmap);
  			if (unlikely(!hmm_vma_walk->pgmap))
  				return -EBUSY;

  			pfns[i] = hmm_device_entry_from_pfn(range, pfn) |
  				  cpu_flags;

  		}
  		if (hmm_vma_walk->pgmap) {
  			put_dev_pagemap(hmm_vma_walk->pgmap);
  			hmm_vma_walk->pgmap = NULL;
  		}
  		hmm_vma_walk->last = end;
  		return 0;

  	}
  
  	split_huge_pud(walk->vma, pudp, addr);
  	if (pud_none(*pudp))
  		goto again;
  
  	pmdp = pmd_offset(pudp, addr);
  	do {
  		next = pmd_addr_end(addr, end);
  		ret = hmm_vma_walk_pmd(pmdp, addr, next, walk);
  		if (ret)
  			return ret;
  	} while (pmdp++, addr = next, addr != end);
  
  	return 0;
  }

  #else
  #define hmm_vma_walk_pud	NULL
  #endif

  #ifdef CONFIG_HUGETLB_PAGE

  static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
  				      unsigned long start, unsigned long end,
  				      struct mm_walk *walk)
  {

  	unsigned long addr = start, i, 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;

  	uint64_t orig_pfn, cpu_flags;
  	bool fault, write_fault;
  	spinlock_t *ptl;
  	pte_t entry;
  	int ret = 0;

  	ptl = huge_pte_lock(hstate_vma(vma), walk->mm, pte);

  	entry = huge_ptep_get(pte);

  	i = (start - range->start) >> PAGE_SHIFT;

  	orig_pfn = range->pfns[i];
  	range->pfns[i] = range->values[HMM_PFN_NONE];
  	cpu_flags = pte_to_hmm_pfn_flags(range, entry);
  	fault = write_fault = false;
  	hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags,
  			   &fault, &write_fault);
  	if (fault || write_fault) {
  		ret = -ENOENT;
  		goto unlock;
  	}

  	pfn = pte_pfn(entry) + ((start & ~hmask) >> PAGE_SHIFT);

  	for (; addr < end; addr += PAGE_SIZE, i++, pfn++)

  		range->pfns[i] = hmm_device_entry_from_pfn(range, pfn) |
  				 cpu_flags;

  	hmm_vma_walk->last = end;
  
  unlock:
  	spin_unlock(ptl);
  
  	if (ret == -ENOENT)
  		return hmm_vma_walk_hole_(addr, end, fault, write_fault, walk);
  
  	return ret;

  }

  #else
  #define hmm_vma_walk_hugetlb_entry NULL
  #endif /* CONFIG_HUGETLB_PAGE */

  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];

  }

  /*

   * hmm_range_register() - start tracking change to CPU page table over a range

   * @range: range

   * @mm: the mm struct for the range of virtual address

   *

   * Return: 0 on success, -EFAULT if the address space is no longer valid

   *

   * Track updates to the CPU page table see include/linux/hmm.h

   */

  int hmm_range_register(struct hmm_range *range, struct hmm_mirror *mirror)

  {

  	struct hmm *hmm = mirror->hmm;

  	unsigned long flags;

  	range->valid = false;

  	range->hmm = NULL;

  	if ((range->start & (PAGE_SIZE - 1)) || (range->end & (PAGE_SIZE - 1)))

  		return -EINVAL;

  	if (range->start >= range->end)

  		return -EINVAL;

  	/* Prevent hmm_release() from running while the range is valid */

  	if (!mmget_not_zero(hmm->mmu_notifier.mm))

  		return -EFAULT;

  	/* Initialize range to track CPU page table updates. */

  	spin_lock_irqsave(&hmm->ranges_lock, flags);

  	range->hmm = hmm;

  	list_add(&range->list, &hmm->ranges);

  	/*

  	 * If there are any concurrent notifiers we have to wait for them for
  	 * the range to be valid (see hmm_range_wait_until_valid()).

  	 */

  	if (!hmm->notifiers)

  		range->valid = true;

  	spin_unlock_irqrestore(&hmm->ranges_lock, flags);

  
  	return 0;

  }

  EXPORT_SYMBOL(hmm_range_register);

  
  /*

   * hmm_range_unregister() - stop tracking change to CPU page table over a range
   * @range: range

   *
   * Range struct is used to track updates to the CPU page table after a call to

   * hmm_range_register(). See include/linux/hmm.h for how to use it.

   */

  void hmm_range_unregister(struct hmm_range *range)

  {

  	struct hmm *hmm = range->hmm;

  	unsigned long flags;

  	spin_lock_irqsave(&hmm->ranges_lock, flags);

  	list_del_init(&range->list);

  	spin_unlock_irqrestore(&hmm->ranges_lock, flags);

  	/* Drop reference taken by hmm_range_register() */

  	mmput(hmm->mmu_notifier.mm);

  
  	/*
  	 * The range is now invalid and the ref on the hmm is dropped, so
  	 * poison the pointer.  Leave other fields in place, for the caller's
  	 * use.
  	 */

  	range->valid = false;

  	memset(&range->hmm, POISON_INUSE, sizeof(range->hmm));

  }

  EXPORT_SYMBOL(hmm_range_unregister);

  static const struct mm_walk_ops hmm_walk_ops = {
  	.pud_entry	= hmm_vma_walk_pud,
  	.pmd_entry	= hmm_vma_walk_pmd,
  	.pte_hole	= hmm_vma_walk_hole,
  	.hugetlb_entry	= hmm_vma_walk_hugetlb_entry,
  };

  /**
   * hmm_range_fault - try to fault some address in a virtual address range
   * @range:	range being faulted
   * @flags:	HMM_FAULT_* flags
   *
   * Return: the number of valid pages in range->pfns[] (from range start
   * address), which may be zero.  On error one of the following status codes
   * can be returned:

   *

   * -EINVAL:	Invalid arguments or mm or virtual address is in an invalid vma
   *		(e.g., device file vma).
   * -ENOMEM:	Out of memory.
   * -EPERM:	Invalid permission (e.g., asking for write and range is read
   *		only).
   * -EAGAIN:	A page fault needs to be retried and mmap_sem was dropped.
   * -EBUSY:	The range has been invalidated and the caller needs to wait for
   *		the invalidation to finish.
   * -EFAULT:	Invalid (i.e., either no valid vma or it is illegal to access
   *		that range) number of valid pages in range->pfns[] (from
   *              range start address).

   *
   * 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
   * and caller does not ask for migration.

   *

   * On error, for one virtual address in the range, the function will mark the
   * corresponding HMM pfn entry with an error flag.

   */

  long hmm_range_fault(struct hmm_range *range, unsigned int flags)

  {

  	const unsigned long device_vma = VM_IO | VM_PFNMAP | VM_MIXEDMAP;

  	unsigned long start = range->start, end;

  	struct hmm_vma_walk hmm_vma_walk;

  	struct hmm *hmm = range->hmm;
  	struct vm_area_struct *vma;

  	int ret;

  	lockdep_assert_held(&hmm->mmu_notifier.mm->mmap_sem);

  	do {
  		/* If range is no longer valid force retry. */

  		if (!range->valid)
  			return -EBUSY;

  		vma = find_vma(hmm->mmu_notifier.mm, start);

  		if (vma == NULL || (vma->vm_flags & device_vma))

  			return -EFAULT;

  		if (!(vma->vm_flags & VM_READ)) {
  			/*
  			 * If vma do not allow read access, then assume that it
  			 * does not allow write access, either. HMM does not
  			 * support architecture that allow write without read.
  			 */
  			hmm_pfns_clear(range, range->pfns,
  				range->start, range->end);
  			return -EPERM;
  		}

  		hmm_vma_walk.pgmap = NULL;

  		hmm_vma_walk.last = start;

  		hmm_vma_walk.flags = flags;

  		hmm_vma_walk.range = range;

  		end = min(range->end, vma->vm_end);

  		walk_page_range(vma->vm_mm, start, end, &hmm_walk_ops,
  				&hmm_vma_walk);

  
  		do {

  			ret = walk_page_range(vma->vm_mm, start, end,
  					&hmm_walk_ops, &hmm_vma_walk);

  			start = hmm_vma_walk.last;
  
  			/* Keep trying while the range is valid. */
  		} while (ret == -EBUSY && range->valid);
  
  		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);
  			return ret;
  		}
  		start = end;

  	} while (start < range->end);

  	return (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;

  }

  EXPORT_SYMBOL(hmm_range_fault);

  
  /**

   * hmm_range_dma_map - hmm_range_fault() and dma map page all in one.
   * @range:	range being faulted
   * @device:	device to map page to
   * @daddrs:	array of dma addresses for the mapped pages
   * @flags:	HMM_FAULT_*

   *

   * Return: the number of pages mapped on success (including zero), or any
   * status return from hmm_range_fault() otherwise.

   */

  long hmm_range_dma_map(struct hmm_range *range, struct device *device,
  		dma_addr_t *daddrs, unsigned int flags)

  {
  	unsigned long i, npages, mapped;
  	long ret;

  	ret = hmm_range_fault(range, flags);

  	if (ret <= 0)
  		return ret ? ret : -EBUSY;
  
  	npages = (range->end - range->start) >> PAGE_SHIFT;
  	for (i = 0, mapped = 0; i < npages; ++i) {
  		enum dma_data_direction dir = DMA_TO_DEVICE;
  		struct page *page;
  
  		/*
  		 * FIXME need to update DMA API to provide invalid DMA address
  		 * value instead of a function to test dma address value. This
  		 * would remove lot of dumb code duplicated accross many arch.
  		 *
  		 * For now setting it to 0 here is good enough as the pfns[]
  		 * value is what is use to check what is valid and what isn't.
  		 */
  		daddrs[i] = 0;

  		page = hmm_device_entry_to_page(range, range->pfns[i]);

  		if (page == NULL)
  			continue;
  
  		/* Check if range is being invalidated */
  		if (!range->valid) {
  			ret = -EBUSY;
  			goto unmap;
  		}
  
  		/* If it is read and write than map bi-directional. */
  		if (range->pfns[i] & range->flags[HMM_PFN_WRITE])
  			dir = DMA_BIDIRECTIONAL;
  
  		daddrs[i] = dma_map_page(device, page, 0, PAGE_SIZE, dir);
  		if (dma_mapping_error(device, daddrs[i])) {
  			ret = -EFAULT;
  			goto unmap;
  		}
  
  		mapped++;
  	}
  
  	return mapped;
  
  unmap:
  	for (npages = i, i = 0; (i < npages) && mapped; ++i) {
  		enum dma_data_direction dir = DMA_TO_DEVICE;
  		struct page *page;

  		page = hmm_device_entry_to_page(range, range->pfns[i]);

  		if (page == NULL)
  			continue;
  
  		if (dma_mapping_error(device, daddrs[i]))
  			continue;
  
  		/* If it is read and write than map bi-directional. */
  		if (range->pfns[i] & range->flags[HMM_PFN_WRITE])
  			dir = DMA_BIDIRECTIONAL;
  
  		dma_unmap_page(device, daddrs[i], PAGE_SIZE, dir);
  		mapped--;
  	}
  
  	return ret;
  }
  EXPORT_SYMBOL(hmm_range_dma_map);
  
  /**
   * hmm_range_dma_unmap() - unmap range of that was map with hmm_range_dma_map()
   * @range: range being unmapped

   * @device: device against which dma map was done
   * @daddrs: dma address of mapped pages
   * @dirty: dirty page if it had the write flag set

   * Return: number of page unmapped on success, -EINVAL otherwise

   *
   * Note that caller MUST abide by mmu notifier or use HMM mirror and abide
   * to the sync_cpu_device_pagetables() callback so that it is safe here to
   * call set_page_dirty(). Caller must also take appropriate locks to avoid
   * concurrent mmu notifier or sync_cpu_device_pagetables() to make progress.
   */
  long hmm_range_dma_unmap(struct hmm_range *range,

  			 struct device *device,
  			 dma_addr_t *daddrs,
  			 bool dirty)
  {
  	unsigned long i, npages;
  	long cpages = 0;
  
  	/* Sanity check. */
  	if (range->end <= range->start)
  		return -EINVAL;
  	if (!daddrs)
  		return -EINVAL;
  	if (!range->pfns)
  		return -EINVAL;
  
  	npages = (range->end - range->start) >> PAGE_SHIFT;
  	for (i = 0; i < npages; ++i) {
  		enum dma_data_direction dir = DMA_TO_DEVICE;
  		struct page *page;

  		page = hmm_device_entry_to_page(range, range->pfns[i]);

  		if (page == NULL)
  			continue;
  
  		/* If it is read and write than map bi-directional. */
  		if (range->pfns[i] & range->flags[HMM_PFN_WRITE]) {
  			dir = DMA_BIDIRECTIONAL;
  
  			/*
  			 * See comments in function description on why it is
  			 * safe here to call set_page_dirty()
  			 */
  			if (dirty)
  				set_page_dirty(page);
  		}
  
  		/* Unmap and clear pfns/dma address */
  		dma_unmap_page(device, daddrs[i], PAGE_SIZE, dir);
  		range->pfns[i] = range->values[HMM_PFN_NONE];
  		/* FIXME see comments in hmm_vma_dma_map() */
  		daddrs[i] = 0;
  		cpages++;
  	}
  
  	return cpages;
  }
  EXPORT_SYMBOL(hmm_range_dma_unmap);