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

  #include <linux/hugetlb.h>

  
  static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,

  			  struct mm_walk *walk)

  {
  	pte_t *pte;
  	int err = 0;
  
  	pte = pte_offset_map(pmd, addr);

  	for (;;) {

  		err = walk->pte_entry(pte, addr, addr + PAGE_SIZE, walk);

  		if (err)
  		       break;

  		addr += PAGE_SIZE;
  		if (addr == end)
  			break;
  		pte++;
  	}

  
  	pte_unmap(pte);
  	return err;
  }
  
  static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,

  			  struct mm_walk *walk)

  {
  	pmd_t *pmd;
  	unsigned long next;
  	int err = 0;
  
  	pmd = pmd_offset(pud, addr);
  	do {

  again:

  		next = pmd_addr_end(addr, end);

  		if (pmd_none(*pmd) || !walk->vma) {

  			if (walk->pte_hole)

  				err = walk->pte_hole(addr, next, walk);

  			if (err)
  				break;
  			continue;
  		}

  		/*
  		 * This implies that each ->pmd_entry() handler
  		 * needs to know about pmd_trans_huge() pmds
  		 */

  		if (walk->pmd_entry)

  			err = walk->pmd_entry(pmd, addr, next, walk);

  		if (err)
  			break;
  
  		/*
  		 * Check this here so we only break down trans_huge
  		 * pages when we _need_ to
  		 */
  		if (!walk->pte_entry)
  			continue;

  		split_huge_pmd(walk->vma, pmd, addr);

  		if (pmd_trans_unstable(pmd))

  			goto again;
  		err = walk_pte_range(pmd, addr, next, walk);

  		if (err)
  			break;
  	} while (pmd++, addr = next, addr != end);
  
  	return err;
  }
  
  static int walk_pud_range(pgd_t *pgd, unsigned long addr, unsigned long end,

  			  struct mm_walk *walk)

  {
  	pud_t *pud;
  	unsigned long next;
  	int err = 0;
  
  	pud = pud_offset(pgd, addr);
  	do {
  		next = pud_addr_end(addr, end);
  		if (pud_none_or_clear_bad(pud)) {
  			if (walk->pte_hole)

  				err = walk->pte_hole(addr, next, walk);

  			if (err)
  				break;
  			continue;
  		}

  		if (walk->pmd_entry || walk->pte_entry)

  			err = walk_pmd_range(pud, addr, next, walk);

  		if (err)
  			break;
  	} while (pud++, addr = next, addr != end);
  
  	return err;
  }

  static int walk_pgd_range(unsigned long addr, unsigned long end,
  			  struct mm_walk *walk)
  {
  	pgd_t *pgd;
  	unsigned long next;
  	int err = 0;
  
  	pgd = pgd_offset(walk->mm, addr);
  	do {
  		next = pgd_addr_end(addr, end);
  		if (pgd_none_or_clear_bad(pgd)) {
  			if (walk->pte_hole)
  				err = walk->pte_hole(addr, next, walk);
  			if (err)
  				break;
  			continue;
  		}
  		if (walk->pmd_entry || walk->pte_entry)
  			err = walk_pud_range(pgd, addr, next, walk);
  		if (err)
  			break;
  	} while (pgd++, addr = next, addr != end);
  
  	return err;
  }

  #ifdef CONFIG_HUGETLB_PAGE
  static unsigned long hugetlb_entry_end(struct hstate *h, unsigned long addr,
  				       unsigned long end)
  {
  	unsigned long boundary = (addr & huge_page_mask(h)) + huge_page_size(h);
  	return boundary < end ? boundary : end;
  }

  static int walk_hugetlb_range(unsigned long addr, unsigned long end,

  			      struct mm_walk *walk)
  {

  	struct vm_area_struct *vma = walk->vma;

  	struct hstate *h = hstate_vma(vma);
  	unsigned long next;
  	unsigned long hmask = huge_page_mask(h);
  	pte_t *pte;
  	int err = 0;
  
  	do {
  		next = hugetlb_entry_end(h, addr, end);
  		pte = huge_pte_offset(walk->mm, addr & hmask);
  		if (pte && walk->hugetlb_entry)
  			err = walk->hugetlb_entry(pte, hmask, addr, next, walk);
  		if (err)

  			break;

  	} while (addr = next, addr != end);

  	return err;

  }

  #else /* CONFIG_HUGETLB_PAGE */

  static int walk_hugetlb_range(unsigned long addr, unsigned long end,

  			      struct mm_walk *walk)
  {
  	return 0;
  }
  
  #endif /* CONFIG_HUGETLB_PAGE */

  /*
   * Decide whether we really walk over the current vma on [@start, @end)
   * or skip it via the returned value. Return 0 if we do walk over the
   * current vma, and return 1 if we skip the vma. Negative values means
   * error, where we abort the current walk.

   */
  static int walk_page_test(unsigned long start, unsigned long end,
  			struct mm_walk *walk)
  {
  	struct vm_area_struct *vma = walk->vma;

  	if (walk->test_walk)
  		return walk->test_walk(start, end, walk);
  
  	/*

  	 * vma(VM_PFNMAP) doesn't have any valid struct pages behind VM_PFNMAP
  	 * range, so we don't walk over it as we do for normal vmas. However,
  	 * Some callers are interested in handling hole range and they don't
  	 * want to just ignore any single address range. Such users certainly
  	 * define their ->pte_hole() callbacks, so let's delegate them to handle
  	 * vma(VM_PFNMAP).

  	 */

  	if (vma->vm_flags & VM_PFNMAP) {
  		int err = 1;
  		if (walk->pte_hole)
  			err = walk->pte_hole(start, end, walk);
  		return err ? err : 1;
  	}

  	return 0;
  }
  
  static int __walk_page_range(unsigned long start, unsigned long end,
  			struct mm_walk *walk)
  {
  	int err = 0;
  	struct vm_area_struct *vma = walk->vma;
  
  	if (vma && is_vm_hugetlb_page(vma)) {
  		if (walk->hugetlb_entry)
  			err = walk_hugetlb_range(start, end, walk);
  	} else
  		err = walk_pgd_range(start, end, walk);
  
  	return err;
  }

  /**

   * walk_page_range - walk page table with caller specific callbacks

   *

   * Recursively walk the page table tree of the process represented by @walk->mm
   * within the virtual address range [@start, @end). During walking, we can do
   * some caller-specific works for each entry, by setting up pmd_entry(),
   * pte_entry(), and/or hugetlb_entry(). If you don't set up for some of these
   * callbacks, the associated entries/pages are just ignored.
   * The return values of these callbacks are commonly defined like below:
   *  - 0  : succeeded to handle the current entry, and if you don't reach the
   *         end address yet, continue to walk.
   *  - >0 : succeeded to handle the current entry, and return to the caller
   *         with caller specific value.
   *  - <0 : failed to handle the current entry, and return to the caller
   *         with error code.

   *

   * Before starting to walk page table, some callers want to check whether
   * they really want to walk over the current vma, typically by checking
   * its vm_flags. walk_page_test() and @walk->test_walk() are used for this
   * purpose.

   *

   * struct mm_walk keeps current values of some common data like vma and pmd,
   * which are useful for the access from callbacks. If you want to pass some
   * caller-specific data to callbacks, @walk->private should be helpful.

   *

   * Locking:
   *   Callers of walk_page_range() and walk_page_vma() should hold
   *   @walk->mm->mmap_sem, because these function traverse vma list and/or
   *   access to vma's data.

   */

  int walk_page_range(unsigned long start, unsigned long end,

  		    struct mm_walk *walk)

  {

  	int err = 0;

  	unsigned long next;
  	struct vm_area_struct *vma;

  	if (start >= end)
  		return -EINVAL;

  	if (!walk->mm)
  		return -EINVAL;

  	VM_BUG_ON_MM(!rwsem_is_locked(&walk->mm->mmap_sem), walk->mm);

  	vma = find_vma(walk->mm, start);

  	do {

  		if (!vma) { /* after the last vma */
  			walk->vma = NULL;
  			next = end;
  		} else if (start < vma->vm_start) { /* outside vma */
  			walk->vma = NULL;
  			next = min(end, vma->vm_start);
  		} else { /* inside vma */
  			walk->vma = vma;
  			next = min(end, vma->vm_end);
  			vma = vma->vm_next;

  			err = walk_page_test(start, next, walk);

  			if (err > 0) {
  				/*
  				 * positive return values are purely for
  				 * controlling the pagewalk, so should never
  				 * be passed to the callers.
  				 */
  				err = 0;

  				continue;

  			}

  			if (err < 0)

  				break;

  		}

  		if (walk->vma || walk->pte_hole)
  			err = __walk_page_range(start, next, walk);

  		if (err)
  			break;

  	} while (start = next, start < end);

  	return err;
  }

  
  int walk_page_vma(struct vm_area_struct *vma, struct mm_walk *walk)
  {
  	int err;
  
  	if (!walk->mm)
  		return -EINVAL;
  
  	VM_BUG_ON(!rwsem_is_locked(&walk->mm->mmap_sem));
  	VM_BUG_ON(!vma);
  	walk->vma = vma;
  	err = walk_page_test(vma->vm_start, vma->vm_end, walk);
  	if (err > 0)
  		return 0;
  	if (err < 0)
  		return err;
  	return __walk_page_range(vma->vm_start, vma->vm_end, walk);
  }