// SPDX-License-Identifier: GPL-2.0

  #include <linux/mm.h>
  #include <linux/rmap.h>
  #include <linux/hugetlb.h>
  #include <linux/swap.h>
  #include <linux/swapops.h>
  
  #include "internal.h"

  static inline bool not_found(struct page_vma_mapped_walk *pvmw)
  {
  	page_vma_mapped_walk_done(pvmw);
  	return false;
  }
  
  static bool map_pte(struct page_vma_mapped_walk *pvmw)
  {
  	pvmw->pte = pte_offset_map(pvmw->pmd, pvmw->address);
  	if (!(pvmw->flags & PVMW_SYNC)) {
  		if (pvmw->flags & PVMW_MIGRATION) {
  			if (!is_swap_pte(*pvmw->pte))
  				return false;
  		} else {

  			/*
  			 * We get here when we are trying to unmap a private
  			 * device page from the process address space. Such
  			 * page is not CPU accessible and thus is mapped as
  			 * a special swap entry, nonetheless it still does
  			 * count as a valid regular mapping for the page (and
  			 * is accounted as such in page maps count).
  			 *
  			 * So handle this special case as if it was a normal
  			 * page mapping ie lock CPU page table and returns
  			 * true.
  			 *
  			 * For more details on device private memory see HMM
  			 * (include/linux/hmm.h or mm/hmm.c).
  			 */
  			if (is_swap_pte(*pvmw->pte)) {
  				swp_entry_t entry;
  
  				/* Handle un-addressable ZONE_DEVICE memory */
  				entry = pte_to_swp_entry(*pvmw->pte);

  				if (!is_device_private_entry(entry) &&
  				    !is_device_exclusive_entry(entry))

  					return false;
  			} else if (!pte_present(*pvmw->pte))

  				return false;
  		}
  	}
  	pvmw->ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
  	spin_lock(pvmw->ptl);
  	return true;
  }

  static inline bool pfn_is_match(struct page *page, unsigned long pfn)

  {

  	unsigned long page_pfn = page_to_pfn(page);
  
  	/* normal page and hugetlbfs page */
  	if (!PageTransCompound(page) || PageHuge(page))
  		return page_pfn == pfn;

  
  	/* THP can be referenced by any subpage */

  	return pfn >= page_pfn && pfn - page_pfn < thp_nr_pages(page);

  }

  /**
   * check_pte - check if @pvmw->page is mapped at the @pvmw->pte

   * @pvmw: page_vma_mapped_walk struct, includes a pair pte and page for checking

   *
   * page_vma_mapped_walk() found a place where @pvmw->page is *potentially*
   * mapped. check_pte() has to validate this.
   *

   * pvmw->pte may point to empty PTE, swap PTE or PTE pointing to
   * arbitrary page.

   *
   * If PVMW_MIGRATION flag is set, returns true if @pvmw->pte contains migration
   * entry that points to @pvmw->page or any subpage in case of THP.
   *

   * If PVMW_MIGRATION flag is not set, returns true if pvmw->pte points to
   * pvmw->page or any subpage in case of THP.

   *
   * Otherwise, return false.
   *
   */

  static bool check_pte(struct page_vma_mapped_walk *pvmw)
  {

  	unsigned long pfn;

  	if (pvmw->flags & PVMW_MIGRATION) {

  		swp_entry_t entry;
  		if (!is_swap_pte(*pvmw->pte))
  			return false;
  		entry = pte_to_swp_entry(*pvmw->pte);

  		if (!is_migration_entry(entry) &&
  		    !is_device_exclusive_entry(entry))

  			return false;

  		pfn = swp_offset(entry);

  	} else if (is_swap_pte(*pvmw->pte)) {
  		swp_entry_t entry;

  		/* Handle un-addressable ZONE_DEVICE memory */
  		entry = pte_to_swp_entry(*pvmw->pte);

  		if (!is_device_private_entry(entry) &&
  		    !is_device_exclusive_entry(entry))

  			return false;

  		pfn = swp_offset(entry);

  	} else {
  		if (!pte_present(*pvmw->pte))

  			return false;

  
  		pfn = pte_pfn(*pvmw->pte);

  	}

  	return pfn_is_match(pvmw->page, pfn);

  }

  static void step_forward(struct page_vma_mapped_walk *pvmw, unsigned long size)
  {
  	pvmw->address = (pvmw->address + size) & ~(size - 1);
  	if (!pvmw->address)
  		pvmw->address = ULONG_MAX;
  }

  /**
   * page_vma_mapped_walk - check if @pvmw->page is mapped in @pvmw->vma at
   * @pvmw->address
   * @pvmw: pointer to struct page_vma_mapped_walk. page, vma, address and flags
   * must be set. pmd, pte and ptl must be NULL.
   *
   * Returns true if the page is mapped in the vma. @pvmw->pmd and @pvmw->pte point
   * to relevant page table entries. @pvmw->ptl is locked. @pvmw->address is
   * adjusted if needed (for PTE-mapped THPs).
   *
   * If @pvmw->pmd is set but @pvmw->pte is not, you have found PMD-mapped page
   * (usually THP). For PTE-mapped THP, you should run page_vma_mapped_walk() in
   * a loop to find all PTEs that map the THP.
   *
   * For HugeTLB pages, @pvmw->pte is set to the relevant page table entry
   * regardless of which page table level the page is mapped at. @pvmw->pmd is
   * NULL.
   *

   * Returns false if there are no more page table entries for the page in

   * the vma. @pvmw->ptl is unlocked and @pvmw->pte is unmapped.
   *
   * If you need to stop the walk before page_vma_mapped_walk() returned false,
   * use page_vma_mapped_walk_done(). It will do the housekeeping.
   */
  bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
  {
  	struct mm_struct *mm = pvmw->vma->vm_mm;
  	struct page *page = pvmw->page;

  	unsigned long end;

  	pgd_t *pgd;

  	p4d_t *p4d;

  	pud_t *pud;

  	pmd_t pmde;

  
  	/* The only possible pmd mapping has been handled on last iteration */
  	if (pvmw->pmd && !pvmw->pte)
  		return not_found(pvmw);

  	if (unlikely(PageHuge(page))) {

  		/* The only possible mapping was handled on last iteration */
  		if (pvmw->pte)
  			return not_found(pvmw);

  		/* when pud is not present, pte will be NULL */

  		pvmw->pte = huge_pte_offset(mm, pvmw->address, page_size(page));

  		if (!pvmw->pte)
  			return false;
  
  		pvmw->ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte);
  		spin_lock(pvmw->ptl);
  		if (!check_pte(pvmw))
  			return not_found(pvmw);
  		return true;
  	}

  	/*
  	 * Seek to next pte only makes sense for THP.
  	 * But more important than that optimization, is to filter out
  	 * any PageKsm page: whose page->index misleads vma_address()
  	 * and vma_address_end() to disaster.
  	 */
  	end = PageTransCompound(page) ?
  		vma_address_end(page, pvmw->vma) :
  		pvmw->address + PAGE_SIZE;

  	if (pvmw->pte)
  		goto next_pte;

  restart:

  	do {

  		pgd = pgd_offset(mm, pvmw->address);

  		if (!pgd_present(*pgd)) {
  			step_forward(pvmw, PGDIR_SIZE);
  			continue;
  		}

  		p4d = p4d_offset(pgd, pvmw->address);

  		if (!p4d_present(*p4d)) {
  			step_forward(pvmw, P4D_SIZE);
  			continue;
  		}

  		pud = pud_offset(p4d, pvmw->address);

  		if (!pud_present(*pud)) {
  			step_forward(pvmw, PUD_SIZE);
  			continue;
  		}

  		pvmw->pmd = pmd_offset(pud, pvmw->address);

  		/*

  		 * Make sure the pmd value isn't cached in a register by the
  		 * compiler and used as a stale value after we've observed a
  		 * subsequent update.

  		 */

  		pmde = READ_ONCE(*pvmw->pmd);
  
  		if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) {
  			pvmw->ptl = pmd_lock(mm, pvmw->pmd);
  			pmde = *pvmw->pmd;
  			if (likely(pmd_trans_huge(pmde))) {
  				if (pvmw->flags & PVMW_MIGRATION)
  					return not_found(pvmw);
  				if (pmd_page(pmde) != page)
  					return not_found(pvmw);
  				return true;
  			}
  			if (!pmd_present(pmde)) {
  				swp_entry_t entry;
  
  				if (!thp_migration_supported() ||
  				    !(pvmw->flags & PVMW_MIGRATION))
  					return not_found(pvmw);
  				entry = pmd_to_swp_entry(pmde);
  				if (!is_migration_entry(entry) ||

  				    pfn_swap_entry_to_page(entry) != page)

  					return not_found(pvmw);
  				return true;
  			}
  			/* THP pmd was split under us: handle on pte level */
  			spin_unlock(pvmw->ptl);
  			pvmw->ptl = NULL;
  		} else if (!pmd_present(pmde)) {
  			/*
  			 * If PVMW_SYNC, take and drop THP pmd lock so that we
  			 * cannot return prematurely, while zap_huge_pmd() has
  			 * cleared *pmd but not decremented compound_mapcount().
  			 */
  			if ((pvmw->flags & PVMW_SYNC) &&
  			    PageTransCompound(page)) {
  				spinlock_t *ptl = pmd_lock(mm, pvmw->pmd);

  				spin_unlock(ptl);
  			}

  			step_forward(pvmw, PMD_SIZE);
  			continue;

  		}

  		if (!map_pte(pvmw))
  			goto next_pte;

  this_pte:

  		if (check_pte(pvmw))
  			return true;

  next_pte:

  		do {

  			pvmw->address += PAGE_SIZE;

  			if (pvmw->address >= end)

  				return not_found(pvmw);
  			/* Did we cross page table boundary? */

  			if ((pvmw->address & (PMD_SIZE - PAGE_SIZE)) == 0) {

  				if (pvmw->ptl) {
  					spin_unlock(pvmw->ptl);
  					pvmw->ptl = NULL;
  				}

  				pte_unmap(pvmw->pte);
  				pvmw->pte = NULL;

  				goto restart;

  			}

  			pvmw->pte++;

  			if ((pvmw->flags & PVMW_SYNC) && !pvmw->ptl) {
  				pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
  				spin_lock(pvmw->ptl);
  			}

  		} while (pte_none(*pvmw->pte));
  
  		if (!pvmw->ptl) {
  			pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
  			spin_lock(pvmw->ptl);
  		}

  		goto this_pte;

  	} while (pvmw->address < end);
  
  	return false;

  }

  
  /**
   * page_mapped_in_vma - check whether a page is really mapped in a VMA
   * @page: the page to test
   * @vma: the VMA to test
   *
   * Returns 1 if the page is mapped into the page tables of the VMA, 0
   * if the page is not mapped into the page tables of this VMA.  Only
   * valid for normal file or anonymous VMAs.
   */
  int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
  {
  	struct page_vma_mapped_walk pvmw = {
  		.page = page,
  		.vma = vma,
  		.flags = PVMW_SYNC,
  	};

  	pvmw.address = vma_address(page, vma);
  	if (pvmw.address == -EFAULT)

  		return 0;

  	if (!page_vma_mapped_walk(&pvmw))
  		return 0;
  	page_vma_mapped_walk_done(&pvmw);
  	return 1;
  }