/*
   * Copyright 2013 Red Hat Inc.
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License as published by
   * the Free Software Foundation; either version 2 of the License, or
   * (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * Authors: Jérôme Glisse <jglisse@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;
  
  	/*
  	 * 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)) {
  		kfree(hmm);
  		return NULL;
  	}
  
  	spin_lock(&mm->page_table_lock);
  	if (!mm->hmm)
  		mm->hmm = hmm;
  	else
  		cleanup = true;
  	spin_unlock(&mm->page_table_lock);
  
  	if (cleanup) {
  		mmu_notifier_unregister(&hmm->mmu_notifier, mm);
  		kfree(hmm);
  	}

  	return mm->hmm;
  }
  
  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 void hmm_invalidate_range_start(struct mmu_notifier *mn,
  				       struct mm_struct *mm,
  				       unsigned long start,
  				       unsigned long end)
  {
  	struct hmm *hmm = mm->hmm;
  
  	VM_BUG_ON(!hmm);
  
  	atomic_inc(&hmm->sequence);
  }
  
  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;
  
  	spin_lock(&mm->page_table_lock);
  	if (mm->hmm == hmm)
  		mm->hmm = NULL;
  	spin_unlock(&mm->page_table_lock);
  
  	mmu_notifier_unregister_no_release(&hmm->mmu_notifier, mm);
  	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;
  	int r;
  
  	flags |= hmm_vma_walk->block ? 0 : FAULT_FLAG_ALLOW_RETRY;

  	flags |= write_fault ? FAULT_FLAG_WRITE : 0;

  	r = handle_mm_fault(vma, addr, flags);
  	if (r & VM_FAULT_RETRY)
  		return -EBUSY;
  	if (r & 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)) {
  		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)) {
  		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);
  	devm_remove_action(devmem->device, &hmm_devmem_ref_exit, data);
  }
  
  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);
  	devm_remove_action(devmem->device, &hmm_devmem_ref_kill, data);
  }
  
  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;
  
  	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, align_start, align_size;

  
  	align_start = resource->start & ~(PA_SECTION_SIZE - 1);
  	align_size = ALIGN(resource_size(resource), PA_SECTION_SIZE);

  
  	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(struct device *dev, void *data)
  {
  	struct hmm_devmem *devmem = data;
  	struct resource *resource = devmem->resource;
  	unsigned long start_pfn, npages;
  	struct zone *zone;
  	struct page *page;
  
  	if (percpu_ref_tryget_live(&devmem->ref)) {
  		dev_WARN(dev, "%s: page mapping is still live!
  ", __func__);
  		percpu_ref_put(&devmem->ref);
  	}
  
  	/* 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
  ",
  				__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
  ",
  				__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
  ", __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;
  }
  
  static int hmm_devmem_match(struct device *dev, void *data, void *match_data)
  {
  	struct hmm_devmem *devmem = data;
  
  	return devmem->resource == match_data;
  }
  
  static void hmm_devmem_pages_remove(struct hmm_devmem *devmem)
  {
  	devres_release(devmem->device, &hmm_devmem_release,
  		       &hmm_devmem_match, devmem->resource);
  }
  
  /*
   * 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 = devres_alloc_node(&hmm_devmem_release, sizeof(*devmem),
  				   GFP_KERNEL, dev_to_node(device));
  	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)
  		goto error_percpu_ref;
  
  	ret = devm_add_action(device, hmm_devmem_ref_exit, &devmem->ref);
  	if (ret)
  		goto error_devm_add_action;
  
  	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) {
  			ret = -ENOMEM;
  			goto error_no_resource;
  		}
  		break;
  	}
  	if (!devmem->resource) {
  		ret = -ERANGE;
  		goto error_no_resource;
  	}
  
  	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)
  		goto error_pages;
  
  	devres_add(device, devmem);
  
  	ret = devm_add_action(device, hmm_devmem_ref_kill, &devmem->ref);
  	if (ret) {
  		hmm_devmem_remove(devmem);
  		return ERR_PTR(ret);
  	}
  
  	return devmem;
  
  error_pages:
  	devm_release_mem_region(device, devmem->resource->start,
  				resource_size(devmem->resource));
  error_no_resource:
  error_devm_add_action:
  	hmm_devmem_ref_kill(&devmem->ref);
  	hmm_devmem_ref_exit(&devmem->ref);
  error_percpu_ref:
  	devres_free(devmem);
  	return ERR_PTR(ret);
  }
  EXPORT_SYMBOL(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 = devres_alloc_node(&hmm_devmem_release, sizeof(*devmem),
  				   GFP_KERNEL, dev_to_node(device));
  	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)
  		goto error_percpu_ref;
  
  	ret = devm_add_action(device, hmm_devmem_ref_exit, &devmem->ref);
  	if (ret)
  		goto error_devm_add_action;
  
  
  	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)
  		goto error_devm_add_action;
  
  	devres_add(device, devmem);
  
  	ret = devm_add_action(device, hmm_devmem_ref_kill, &devmem->ref);
  	if (ret) {
  		hmm_devmem_remove(devmem);
  		return ERR_PTR(ret);
  	}
  
  	return devmem;
  
  error_devm_add_action:
  	hmm_devmem_ref_kill(&devmem->ref);
  	hmm_devmem_ref_exit(&devmem->ref);
  error_percpu_ref:
  	devres_free(devmem);
  	return ERR_PTR(ret);
  }
  EXPORT_SYMBOL(hmm_devmem_add_resource);

  /*
   * hmm_devmem_remove() - remove device memory (kill and free ZONE_DEVICE)
   *
   * @devmem: hmm_devmem struct use to track and manage the ZONE_DEVICE memory
   *
   * This will hot-unplug memory that was hotplugged by hmm_devmem_add on behalf
   * of the device driver. It will free struct page and remove the resource that
   * reserved the physical address range for this device memory.
   */
  void hmm_devmem_remove(struct hmm_devmem *devmem)
  {
  	resource_size_t start, size;
  	struct device *device;

  	bool cdm = false;

  
  	if (!devmem)
  		return;
  
  	device = devmem->device;
  	start = devmem->resource->start;
  	size = resource_size(devmem->resource);

  	cdm = devmem->resource->desc == IORES_DESC_DEVICE_PUBLIC_MEMORY;

  	hmm_devmem_ref_kill(&devmem->ref);
  	hmm_devmem_ref_exit(&devmem->ref);
  	hmm_devmem_pages_remove(devmem);

  	if (!cdm)
  		devm_release_mem_region(device, start, size);

  }
  EXPORT_SYMBOL(hmm_devmem_remove);

  
  /*
   * 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 */