// SPDX-License-Identifier: GPL-2.0

  #include <linux/pagewalk.h>

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

  #include <linux/hugetlb.h>

  /*
   * We want to know the real level where a entry is located ignoring any
   * folding of levels which may be happening. For example if p4d is folded then
   * a missing entry found at level 1 (p4d) is actually at level 0 (pgd).
   */
  static int real_depth(int depth)
  {
  	if (depth == 3 && PTRS_PER_PMD == 1)
  		depth = 2;
  	if (depth == 2 && PTRS_PER_PUD == 1)
  		depth = 1;
  	if (depth == 1 && PTRS_PER_P4D == 1)
  		depth = 0;
  	return depth;
  }

  static int walk_pte_range_inner(pte_t *pte, unsigned long addr,
  				unsigned long end, struct mm_walk *walk)

  {

  	const struct mm_walk_ops *ops = walk->ops;

  	int err = 0;

  	for (;;) {

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

  		if (err)
  		       break;

  		if (addr >= end - PAGE_SIZE)

  			break;

  		addr += PAGE_SIZE;

  		pte++;
  	}

  	return err;
  }
  
  static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
  			  struct mm_walk *walk)
  {
  	pte_t *pte;
  	int err = 0;
  	spinlock_t *ptl;
  
  	if (walk->no_vma) {
  		pte = pte_offset_map(pmd, addr);
  		err = walk_pte_range_inner(pte, addr, end, walk);
  		pte_unmap(pte);
  	} else {
  		pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
  		err = walk_pte_range_inner(pte, addr, end, walk);
  		pte_unmap_unlock(pte, ptl);
  	}

  	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;

  	const struct mm_walk_ops *ops = walk->ops;

  	int err = 0;

  	int depth = real_depth(3);

  
  	pmd = pmd_offset(pud, addr);
  	do {

  again:

  		next = pmd_addr_end(addr, end);

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

  			if (ops->pte_hole)

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

  			if (err)
  				break;
  			continue;
  		}

  
  		walk->action = ACTION_SUBTREE;

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

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

  		if (err)
  			break;

  		if (walk->action == ACTION_AGAIN)
  			goto again;

  		/*
  		 * Check this here so we only break down trans_huge
  		 * pages when we _need_ to
  		 */

  		if ((!walk->vma && (pmd_leaf(*pmd) || !pmd_present(*pmd))) ||
  		    walk->action == ACTION_CONTINUE ||

  		    !(ops->pte_entry))

  			continue;

  		if (walk->vma) {
  			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(p4d_t *p4d, unsigned long addr, unsigned long end,

  			  struct mm_walk *walk)

  {
  	pud_t *pud;
  	unsigned long next;

  	const struct mm_walk_ops *ops = walk->ops;

  	int err = 0;

  	int depth = real_depth(2);

  	pud = pud_offset(p4d, addr);

  	do {

   again:

  		next = pud_addr_end(addr, end);

  		if (pud_none(*pud) || (!walk->vma && !walk->no_vma)) {

  			if (ops->pte_hole)

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

  			if (err)
  				break;
  			continue;
  		}

  		walk->action = ACTION_SUBTREE;

  		if (ops->pud_entry)
  			err = ops->pud_entry(pud, addr, next, walk);
  		if (err)
  			break;
  
  		if (walk->action == ACTION_AGAIN)
  			goto again;

  		if ((!walk->vma && (pud_leaf(*pud) || !pud_present(*pud))) ||
  		    walk->action == ACTION_CONTINUE ||

  		    !(ops->pmd_entry || ops->pte_entry))
  			continue;

  		if (walk->vma)
  			split_huge_pud(walk->vma, pud, addr);

  		if (pud_none(*pud))
  			goto again;

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

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

  static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,
  			  struct mm_walk *walk)
  {
  	p4d_t *p4d;
  	unsigned long next;

  	const struct mm_walk_ops *ops = walk->ops;

  	int err = 0;

  	int depth = real_depth(1);

  
  	p4d = p4d_offset(pgd, addr);
  	do {
  		next = p4d_addr_end(addr, end);
  		if (p4d_none_or_clear_bad(p4d)) {

  			if (ops->pte_hole)

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

  			if (err)
  				break;
  			continue;
  		}

  		if (ops->p4d_entry) {
  			err = ops->p4d_entry(p4d, addr, next, walk);
  			if (err)
  				break;
  		}
  		if (ops->pud_entry || ops->pmd_entry || ops->pte_entry)

  			err = walk_pud_range(p4d, addr, next, walk);
  		if (err)
  			break;
  	} while (p4d++, 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;

  	const struct mm_walk_ops *ops = walk->ops;

  	int err = 0;

  	if (walk->pgd)
  		pgd = walk->pgd + pgd_index(addr);
  	else
  		pgd = pgd_offset(walk->mm, addr);

  	do {
  		next = pgd_addr_end(addr, end);
  		if (pgd_none_or_clear_bad(pgd)) {

  			if (ops->pte_hole)

  				err = ops->pte_hole(addr, next, 0, walk);

  			if (err)
  				break;
  			continue;
  		}

  		if (ops->pgd_entry) {
  			err = ops->pgd_entry(pgd, addr, next, walk);
  			if (err)
  				break;
  		}
  		if (ops->p4d_entry || ops->pud_entry || ops->pmd_entry ||
  		    ops->pte_entry)

  			err = walk_p4d_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);

  	unsigned long sz = huge_page_size(h);

  	pte_t *pte;

  	const struct mm_walk_ops *ops = walk->ops;

  	int err = 0;
  
  	do {
  		next = hugetlb_entry_end(h, addr, end);

  		pte = huge_pte_offset(walk->mm, addr & hmask, sz);

  
  		if (pte)

  			err = ops->hugetlb_entry(pte, hmask, addr, next, walk);
  		else if (ops->pte_hole)

  			err = ops->pte_hole(addr, next, -1, 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;

  	const struct mm_walk_ops *ops = walk->ops;

  	if (ops->test_walk)
  		return ops->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 (ops->pte_hole)

  			err = ops->pte_hole(start, end, -1, 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;

  	const struct mm_walk_ops *ops = walk->ops;
  
  	if (vma && ops->pre_vma) {
  		err = ops->pre_vma(start, end, walk);
  		if (err)
  			return err;
  	}

  
  	if (vma && is_vm_hugetlb_page(vma)) {

  		if (ops->hugetlb_entry)

  			err = walk_hugetlb_range(start, end, walk);
  	} else
  		err = walk_pgd_range(start, end, walk);

  	if (vma && ops->post_vma)
  		ops->post_vma(walk);

  	return err;
  }

  /**

   * walk_page_range - walk page table with caller specific callbacks

   * @mm:		mm_struct representing the target process of page table walk
   * @start:	start address of the virtual address range
   * @end:	end address of the virtual address range
   * @ops:	operation to call during the walk
   * @private:	private data for callbacks' usage

   *

   * Recursively walk the page table tree of the process represented by @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 @ops->test_walk() are used for this

   * purpose.

   *

   * If operations need to be staged before and committed after a vma is walked,
   * there are two callbacks, pre_vma() and post_vma(). Note that post_vma(),
   * since it is intended to handle commit-type operations, can't return any
   * errors.
   *

   * 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, @private should be helpful.

   *

   * Locking:

   *   Callers of walk_page_range() and walk_page_vma() should hold @mm->mmap_lock,

   *   because these function traverse vma list and/or access to vma's data.

   */

  int walk_page_range(struct mm_struct *mm, unsigned long start,
  		unsigned long end, const struct mm_walk_ops *ops,
  		void *private)

  {

  	int err = 0;

  	unsigned long next;
  	struct vm_area_struct *vma;

  	struct mm_walk walk = {
  		.ops		= ops,
  		.mm		= mm,
  		.private	= private,
  	};

  	if (start >= end)
  		return -EINVAL;

  	if (!walk.mm)

  		return -EINVAL;

  	mmap_assert_locked(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.ops->pte_hole)
  			err = __walk_page_range(start, next, &walk);

  		if (err)
  			break;

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

  	return err;
  }

  /*
   * Similar to walk_page_range() but can walk any page tables even if they are
   * not backed by VMAs. Because 'unusual' entries may be walked this function
   * will also not lock the PTEs for the pte_entry() callback. This is useful for
   * walking the kernel pages tables or page tables for firmware.
   */

  int walk_page_range_novma(struct mm_struct *mm, unsigned long start,
  			  unsigned long end, const struct mm_walk_ops *ops,

  			  pgd_t *pgd,

  			  void *private)
  {
  	struct mm_walk walk = {
  		.ops		= ops,
  		.mm		= mm,

  		.pgd		= pgd,

  		.private	= private,
  		.no_vma		= true
  	};
  
  	if (start >= end || !walk.mm)
  		return -EINVAL;

  	mmap_assert_locked(walk.mm);

  
  	return __walk_page_range(start, end, &walk);
  }

  int walk_page_vma(struct vm_area_struct *vma, const struct mm_walk_ops *ops,
  		void *private)

  {

  	struct mm_walk walk = {
  		.ops		= ops,
  		.mm		= vma->vm_mm,
  		.vma		= vma,
  		.private	= private,
  	};

  	int err;

  	if (!walk.mm)

  		return -EINVAL;

  	mmap_assert_locked(walk.mm);

  
  	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);

  }

  
  /**
   * walk_page_mapping - walk all memory areas mapped into a struct address_space.
   * @mapping: Pointer to the struct address_space
   * @first_index: First page offset in the address_space
   * @nr: Number of incremental page offsets to cover
   * @ops:	operation to call during the walk
   * @private:	private data for callbacks' usage
   *
   * This function walks all memory areas mapped into a struct address_space.
   * The walk is limited to only the given page-size index range, but if
   * the index boundaries cross a huge page-table entry, that entry will be
   * included.
   *
   * Also see walk_page_range() for additional information.
   *
   * Locking:

   *   This function can't require that the struct mm_struct::mmap_lock is held,

   *   since @mapping may be mapped by multiple processes. Instead
   *   @mapping->i_mmap_rwsem must be held. This might have implications in the
   *   callbacks, and it's up tho the caller to ensure that the

   *   struct mm_struct::mmap_lock is not needed.

   *
   *   Also this means that a caller can't rely on the struct
   *   vm_area_struct::vm_flags to be constant across a call,
   *   except for immutable flags. Callers requiring this shouldn't use
   *   this function.
   *
   * Return: 0 on success, negative error code on failure, positive number on
   * caller defined premature termination.
   */
  int walk_page_mapping(struct address_space *mapping, pgoff_t first_index,
  		      pgoff_t nr, const struct mm_walk_ops *ops,
  		      void *private)
  {
  	struct mm_walk walk = {
  		.ops		= ops,
  		.private	= private,
  	};
  	struct vm_area_struct *vma;
  	pgoff_t vba, vea, cba, cea;
  	unsigned long start_addr, end_addr;
  	int err = 0;
  
  	lockdep_assert_held(&mapping->i_mmap_rwsem);
  	vma_interval_tree_foreach(vma, &mapping->i_mmap, first_index,
  				  first_index + nr - 1) {
  		/* Clip to the vma */
  		vba = vma->vm_pgoff;
  		vea = vba + vma_pages(vma);
  		cba = first_index;
  		cba = max(cba, vba);
  		cea = first_index + nr;
  		cea = min(cea, vea);
  
  		start_addr = ((cba - vba) << PAGE_SHIFT) + vma->vm_start;
  		end_addr = ((cea - vba) << PAGE_SHIFT) + vma->vm_start;
  		if (start_addr >= end_addr)
  			continue;
  
  		walk.vma = vma;
  		walk.mm = vma->vm_mm;
  
  		err = walk_page_test(vma->vm_start, vma->vm_end, &walk);
  		if (err > 0) {
  			err = 0;
  			break;
  		} else if (err < 0)
  			break;
  
  		err = __walk_page_range(start_addr, end_addr, &walk);
  		if (err)
  			break;
  	}
  
  	return err;
  }