#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)) {
  			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_page_pmd_mm(walk->mm, addr, pmd);
  		if (pmd_none_or_trans_huge_or_clear_bad(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->pud_entry)
  			err = walk->pud_entry(pud, addr, next, walk);
  		if (!err && (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;
  }
  
  #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(struct vm_area_struct *vma,
  			      unsigned long addr, unsigned long end,
  			      struct mm_walk *walk)
  {
  	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)
  			return err;
  	} while (addr = next, addr != end);
  
  	return 0;
  }
  
  #else /* CONFIG_HUGETLB_PAGE */
  static int walk_hugetlb_range(struct vm_area_struct *vma,
  			      unsigned long addr, unsigned long end,
  			      struct mm_walk *walk)
  {
  	return 0;
  }
  
  #endif /* CONFIG_HUGETLB_PAGE */
  
  
  
  /**
   * walk_page_range - walk a memory map's page tables with a callback
   * @addr: starting address
   * @end: ending address
   * @walk: set of callbacks to invoke for each level of the tree
   *
   * Recursively walk the page table for the memory area in a VMA,
   * calling supplied callbacks. Callbacks are called in-order (first
   * PGD, first PUD, first PMD, first PTE, second PTE... second PMD,
   * etc.). If lower-level callbacks are omitted, walking depth is reduced.
   *
   * Each callback receives an entry pointer and the start and end of the
   * associated range, and a copy of the original mm_walk for access to
   * the ->private or ->mm fields.
   *
   * Usually no locks are taken, but splitting transparent huge page may
   * take page table lock. And the bottom level iterator will map PTE
   * directories from highmem if necessary.
   *
   * If any callback returns a non-zero value, the walk is aborted and
   * the return value is propagated back to the caller. Otherwise 0 is returned.
   *
   * walk->mm->mmap_sem must be held for at least read if walk->hugetlb_entry
   * is !NULL.
   */
  int walk_page_range(unsigned long addr, unsigned long end,
  		    struct mm_walk *walk)
  {
  	pgd_t *pgd;
  	unsigned long next;
  	int err = 0;
  
  	if (addr >= end)
  		return err;
  
  	if (!walk->mm)
  		return -EINVAL;
  
  	VM_BUG_ON(!rwsem_is_locked(&walk->mm->mmap_sem));
  
  	pgd = pgd_offset(walk->mm, addr);
  	do {
  		struct vm_area_struct *vma = NULL;
  
  		next = pgd_addr_end(addr, end);
  
  		/*
  		 * This function was not intended to be vma based.
  		 * But there are vma special cases to be handled:
  		 * - hugetlb vma's
  		 * - VM_PFNMAP vma's
  		 */
  		vma = find_vma(walk->mm, addr);
  		if (vma) {
  			/*
  			 * There are no page structures backing a VM_PFNMAP
  			 * range, so do not allow split_huge_page_pmd().
  			 */
  			if ((vma->vm_start <= addr) &&
  			    (vma->vm_flags & VM_PFNMAP)) {
  				next = vma->vm_end;
  				pgd = pgd_offset(walk->mm, next);
  				continue;
  			}
  			/*
  			 * Handle hugetlb vma individually because pagetable
  			 * walk for the hugetlb page is dependent on the
  			 * architecture and we can't handled it in the same
  			 * manner as non-huge pages.
  			 */
  			if (walk->hugetlb_entry && (vma->vm_start <= addr) &&
  			    is_vm_hugetlb_page(vma)) {
  				if (vma->vm_end < next)
  					next = vma->vm_end;
  				/*
  				 * Hugepage is very tightly coupled with vma,
  				 * so walk through hugetlb entries within a
  				 * given vma.
  				 */
  				err = walk_hugetlb_range(vma, addr, next, walk);
  				if (err)
  					break;
  				pgd = pgd_offset(walk->mm, next);
  				continue;
  			}
  		}
  
  		if (pgd_none_or_clear_bad(pgd)) {
  			if (walk->pte_hole)
  				err = walk->pte_hole(addr, next, walk);
  			if (err)
  				break;
  			pgd++;
  			continue;
  		}
  		if (walk->pgd_entry)
  			err = walk->pgd_entry(pgd, addr, next, walk);
  		if (!err &&
  		    (walk->pud_entry || walk->pmd_entry || walk->pte_entry))
  			err = walk_pud_range(pgd, addr, next, walk);
  		if (err)
  			break;
  		pgd++;
  	} while (addr = next, addr < end);
  
  	return err;
  }