// SPDX-License-Identifier: GPL-2.0

  /*
   *	linux/mm/madvise.c
   *
   * Copyright (C) 1999  Linus Torvalds
   * Copyright (C) 2002  Christoph Hellwig
   */
  
  #include <linux/mman.h>
  #include <linux/pagemap.h>
  #include <linux/syscalls.h>

  #include <linux/mempolicy.h>

  #include <linux/page-isolation.h>

  #include <linux/page_idle.h>

  #include <linux/userfaultfd_k.h>

  #include <linux/hugetlb.h>

  #include <linux/falloc.h>

  #include <linux/fadvise.h>

  #include <linux/sched.h>

  #include <linux/ksm.h>

  #include <linux/fs.h>

  #include <linux/file.h>

  #include <linux/blkdev.h>

  #include <linux/backing-dev.h>

  #include <linux/pagewalk.h>

  #include <linux/swap.h>
  #include <linux/swapops.h>

  #include <linux/shmem_fs.h>

  #include <linux/mmu_notifier.h>
  
  #include <asm/tlb.h>

  #include "internal.h"

  struct madvise_walk_private {
  	struct mmu_gather *tlb;
  	bool pageout;
  };

  /*

   * Any behaviour which results in changes to the vma->vm_flags needs to
   * take mmap_sem for writing. Others, which simply traverse vmas, need
   * to only take it for reading.
   */
  static int madvise_need_mmap_write(int behavior)
  {
  	switch (behavior) {
  	case MADV_REMOVE:
  	case MADV_WILLNEED:
  	case MADV_DONTNEED:

  	case MADV_COLD:

  	case MADV_PAGEOUT:

  	case MADV_FREE:

  		return 0;
  	default:
  		/* be safe, default to 1. list exceptions explicitly */
  		return 1;
  	}
  }
  
  /*

   * We can potentially split a vm area into separate
   * areas, each area with its own behavior.
   */

  static long madvise_behavior(struct vm_area_struct *vma,

  		     struct vm_area_struct **prev,
  		     unsigned long start, unsigned long end, int behavior)

  {

  	struct mm_struct *mm = vma->vm_mm;

  	int error = 0;

  	pgoff_t pgoff;

  	unsigned long new_flags = vma->vm_flags;

  
  	switch (behavior) {

  	case MADV_NORMAL:
  		new_flags = new_flags & ~VM_RAND_READ & ~VM_SEQ_READ;
  		break;

  	case MADV_SEQUENTIAL:

  		new_flags = (new_flags & ~VM_RAND_READ) | VM_SEQ_READ;

  		break;
  	case MADV_RANDOM:

  		new_flags = (new_flags & ~VM_SEQ_READ) | VM_RAND_READ;

  		break;

  	case MADV_DONTFORK:
  		new_flags |= VM_DONTCOPY;
  		break;
  	case MADV_DOFORK:

  		if (vma->vm_flags & VM_IO) {
  			error = -EINVAL;
  			goto out;
  		}

  		new_flags &= ~VM_DONTCOPY;

  		break;

  	case MADV_WIPEONFORK:
  		/* MADV_WIPEONFORK is only supported on anonymous memory. */
  		if (vma->vm_file || vma->vm_flags & VM_SHARED) {
  			error = -EINVAL;
  			goto out;
  		}
  		new_flags |= VM_WIPEONFORK;
  		break;
  	case MADV_KEEPONFORK:
  		new_flags &= ~VM_WIPEONFORK;
  		break;

  	case MADV_DONTDUMP:

  		new_flags |= VM_DONTDUMP;

  		break;
  	case MADV_DODUMP:

  		if (!is_vm_hugetlb_page(vma) && new_flags & VM_SPECIAL) {

  			error = -EINVAL;
  			goto out;
  		}
  		new_flags &= ~VM_DONTDUMP;

  		break;

  	case MADV_MERGEABLE:
  	case MADV_UNMERGEABLE:
  		error = ksm_madvise(vma, start, end, behavior, &new_flags);

  		if (error)
  			goto out_convert_errno;

  		break;

  	case MADV_HUGEPAGE:

  	case MADV_NOHUGEPAGE:

  		error = hugepage_madvise(vma, &new_flags, behavior);

  		if (error)
  			goto out_convert_errno;

  		break;

  	}

  	if (new_flags == vma->vm_flags) {
  		*prev = vma;

  		goto out;

  	}
  
  	pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
  	*prev = vma_merge(mm, *prev, start, end, new_flags, vma->anon_vma,

  			  vma->vm_file, pgoff, vma_policy(vma),
  			  vma->vm_userfaultfd_ctx);

  	if (*prev) {
  		vma = *prev;
  		goto success;
  	}
  
  	*prev = vma;

  
  	if (start != vma->vm_start) {

  		if (unlikely(mm->map_count >= sysctl_max_map_count)) {
  			error = -ENOMEM;

  			goto out;

  		}
  		error = __split_vma(mm, vma, start, 1);

  		if (error)
  			goto out_convert_errno;

  	}
  
  	if (end != vma->vm_end) {

  		if (unlikely(mm->map_count >= sysctl_max_map_count)) {
  			error = -ENOMEM;

  			goto out;

  		}
  		error = __split_vma(mm, vma, end, 0);

  		if (error)
  			goto out_convert_errno;

  	}

  success:

  	/*
  	 * vm_flags is protected by the mmap_sem held in write mode.
  	 */

  	vma->vm_flags = new_flags;

  
  out_convert_errno:
  	/*
  	 * madvise() returns EAGAIN if kernel resources, such as
  	 * slab, are temporarily unavailable.
  	 */
  	if (error == -ENOMEM)
  		error = -EAGAIN;

  out:

  	return error;
  }

  #ifdef CONFIG_SWAP
  static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,
  	unsigned long end, struct mm_walk *walk)
  {
  	pte_t *orig_pte;
  	struct vm_area_struct *vma = walk->private;
  	unsigned long index;
  
  	if (pmd_none_or_trans_huge_or_clear_bad(pmd))
  		return 0;
  
  	for (index = start; index != end; index += PAGE_SIZE) {
  		pte_t pte;
  		swp_entry_t entry;
  		struct page *page;
  		spinlock_t *ptl;
  
  		orig_pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl);
  		pte = *(orig_pte + ((index - start) / PAGE_SIZE));
  		pte_unmap_unlock(orig_pte, ptl);

  		if (pte_present(pte) || pte_none(pte))

  			continue;
  		entry = pte_to_swp_entry(pte);
  		if (unlikely(non_swap_entry(entry)))
  			continue;
  
  		page = read_swap_cache_async(entry, GFP_HIGHUSER_MOVABLE,

  							vma, index, false);

  		if (page)

  			put_page(page);

  	}
  
  	return 0;
  }

  static const struct mm_walk_ops swapin_walk_ops = {
  	.pmd_entry		= swapin_walk_pmd_entry,
  };

  
  static void force_shm_swapin_readahead(struct vm_area_struct *vma,
  		unsigned long start, unsigned long end,
  		struct address_space *mapping)
  {
  	pgoff_t index;
  	struct page *page;
  	swp_entry_t swap;
  
  	for (; start < end; start += PAGE_SIZE) {
  		index = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;

  		page = find_get_entry(mapping, index);

  		if (!xa_is_value(page)) {

  			if (page)

  				put_page(page);

  			continue;
  		}
  		swap = radix_to_swp_entry(page);
  		page = read_swap_cache_async(swap, GFP_HIGHUSER_MOVABLE,

  							NULL, 0, false);

  		if (page)

  			put_page(page);

  	}
  
  	lru_add_drain();	/* Push any new pages onto the LRU now */
  }
  #endif		/* CONFIG_SWAP */

  /*
   * Schedule all required I/O operations.  Do not wait for completion.
   */

  static long madvise_willneed(struct vm_area_struct *vma,
  			     struct vm_area_struct **prev,

  			     unsigned long start, unsigned long end)
  {
  	struct file *file = vma->vm_file;

  	loff_t offset;

  	*prev = vma;

  #ifdef CONFIG_SWAP

  	if (!file) {

  		walk_page_range(vma->vm_mm, start, end, &swapin_walk_ops, vma);
  		lru_add_drain(); /* Push any new pages onto the LRU now */

  		return 0;
  	}

  	if (shmem_mapping(file->f_mapping)) {

  		force_shm_swapin_readahead(vma, start, end,
  					file->f_mapping);
  		return 0;
  	}
  #else

  	if (!file)
  		return -EBADF;

  #endif

  	if (IS_DAX(file_inode(file))) {

  		/* no bad return value, but ignore advice */
  		return 0;
  	}

  	/*
  	 * Filesystem's fadvise may need to take various locks.  We need to
  	 * explicitly grab a reference because the vma (and hence the
  	 * vma's reference to the file) can go away as soon as we drop
  	 * mmap_sem.
  	 */
  	*prev = NULL;	/* tell sys_madvise we drop mmap_sem */
  	get_file(file);
  	up_read(&current->mm->mmap_sem);
  	offset = (loff_t)(start - vma->vm_start)
  			+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
  	vfs_fadvise(file, offset, end - start, POSIX_FADV_WILLNEED);
  	fput(file);
  	down_read(&current->mm->mmap_sem);

  	return 0;
  }

  static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
  				unsigned long addr, unsigned long end,
  				struct mm_walk *walk)

  {

  	struct madvise_walk_private *private = walk->private;
  	struct mmu_gather *tlb = private->tlb;
  	bool pageout = private->pageout;

  	struct mm_struct *mm = tlb->mm;
  	struct vm_area_struct *vma = walk->vma;
  	pte_t *orig_pte, *pte, ptent;
  	spinlock_t *ptl;

  	struct page *page = NULL;
  	LIST_HEAD(page_list);
  
  	if (fatal_signal_pending(current))
  		return -EINTR;

  
  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
  	if (pmd_trans_huge(*pmd)) {
  		pmd_t orig_pmd;
  		unsigned long next = pmd_addr_end(addr, end);
  
  		tlb_change_page_size(tlb, HPAGE_PMD_SIZE);
  		ptl = pmd_trans_huge_lock(pmd, vma);
  		if (!ptl)
  			return 0;
  
  		orig_pmd = *pmd;
  		if (is_huge_zero_pmd(orig_pmd))
  			goto huge_unlock;
  
  		if (unlikely(!pmd_present(orig_pmd))) {
  			VM_BUG_ON(thp_migration_supported() &&
  					!is_pmd_migration_entry(orig_pmd));
  			goto huge_unlock;
  		}
  
  		page = pmd_page(orig_pmd);
  		if (next - addr != HPAGE_PMD_SIZE) {
  			int err;
  
  			if (page_mapcount(page) != 1)
  				goto huge_unlock;
  
  			get_page(page);
  			spin_unlock(ptl);
  			lock_page(page);
  			err = split_huge_page(page);
  			unlock_page(page);
  			put_page(page);
  			if (!err)
  				goto regular_page;
  			return 0;
  		}
  
  		if (pmd_young(orig_pmd)) {
  			pmdp_invalidate(vma, addr, pmd);
  			orig_pmd = pmd_mkold(orig_pmd);
  
  			set_pmd_at(mm, addr, pmd, orig_pmd);
  			tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
  		}

  		ClearPageReferenced(page);

  		test_and_clear_page_young(page);

  		if (pageout) {

  			if (!isolate_lru_page(page)) {
  				if (PageUnevictable(page))
  					putback_lru_page(page);
  				else
  					list_add(&page->lru, &page_list);
  			}

  		} else
  			deactivate_page(page);

  huge_unlock:
  		spin_unlock(ptl);

  		if (pageout)
  			reclaim_pages(&page_list);

  		return 0;
  	}
  
  	if (pmd_trans_unstable(pmd))
  		return 0;
  regular_page:
  #endif
  	tlb_change_page_size(tlb, PAGE_SIZE);
  	orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
  	flush_tlb_batched_pending(mm);
  	arch_enter_lazy_mmu_mode();
  	for (; addr < end; pte++, addr += PAGE_SIZE) {
  		ptent = *pte;
  
  		if (pte_none(ptent))
  			continue;
  
  		if (!pte_present(ptent))
  			continue;
  
  		page = vm_normal_page(vma, addr, ptent);
  		if (!page)
  			continue;
  
  		/*
  		 * Creating a THP page is expensive so split it only if we
  		 * are sure it's worth. Split it if we are only owner.
  		 */
  		if (PageTransCompound(page)) {
  			if (page_mapcount(page) != 1)
  				break;
  			get_page(page);
  			if (!trylock_page(page)) {
  				put_page(page);
  				break;
  			}
  			pte_unmap_unlock(orig_pte, ptl);
  			if (split_huge_page(page)) {
  				unlock_page(page);
  				put_page(page);
  				pte_offset_map_lock(mm, pmd, addr, &ptl);
  				break;
  			}
  			unlock_page(page);
  			put_page(page);
  			pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
  			pte--;
  			addr -= PAGE_SIZE;
  			continue;
  		}
  
  		VM_BUG_ON_PAGE(PageTransCompound(page), page);
  
  		if (pte_young(ptent)) {
  			ptent = ptep_get_and_clear_full(mm, addr, pte,
  							tlb->fullmm);
  			ptent = pte_mkold(ptent);
  			set_pte_at(mm, addr, pte, ptent);
  			tlb_remove_tlb_entry(tlb, pte, addr);
  		}
  
  		/*
  		 * We are deactivating a page for accelerating reclaiming.
  		 * VM couldn't reclaim the page unless we clear PG_young.
  		 * As a side effect, it makes confuse idle-page tracking
  		 * because they will miss recent referenced history.
  		 */

  		ClearPageReferenced(page);

  		test_and_clear_page_young(page);

  		if (pageout) {

  			if (!isolate_lru_page(page)) {
  				if (PageUnevictable(page))
  					putback_lru_page(page);
  				else
  					list_add(&page->lru, &page_list);
  			}

  		} else
  			deactivate_page(page);

  	}
  
  	arch_leave_lazy_mmu_mode();
  	pte_unmap_unlock(orig_pte, ptl);

  	if (pageout)
  		reclaim_pages(&page_list);

  	cond_resched();
  
  	return 0;
  }
  
  static const struct mm_walk_ops cold_walk_ops = {

  	.pmd_entry = madvise_cold_or_pageout_pte_range,

  };
  
  static void madvise_cold_page_range(struct mmu_gather *tlb,
  			     struct vm_area_struct *vma,
  			     unsigned long addr, unsigned long end)
  {

  	struct madvise_walk_private walk_private = {
  		.pageout = false,
  		.tlb = tlb,
  	};

  	tlb_start_vma(tlb, vma);

  	walk_page_range(vma->vm_mm, addr, end, &cold_walk_ops, &walk_private);

  	tlb_end_vma(tlb, vma);
  }
  
  static long madvise_cold(struct vm_area_struct *vma,
  			struct vm_area_struct **prev,
  			unsigned long start_addr, unsigned long end_addr)
  {
  	struct mm_struct *mm = vma->vm_mm;
  	struct mmu_gather tlb;
  
  	*prev = vma;
  	if (!can_madv_lru_vma(vma))
  		return -EINVAL;
  
  	lru_add_drain();
  	tlb_gather_mmu(&tlb, mm, start_addr, end_addr);
  	madvise_cold_page_range(&tlb, vma, start_addr, end_addr);
  	tlb_finish_mmu(&tlb, start_addr, end_addr);
  
  	return 0;
  }

  static void madvise_pageout_page_range(struct mmu_gather *tlb,
  			     struct vm_area_struct *vma,
  			     unsigned long addr, unsigned long end)
  {

  	struct madvise_walk_private walk_private = {
  		.pageout = true,
  		.tlb = tlb,
  	};

  	tlb_start_vma(tlb, vma);

  	walk_page_range(vma->vm_mm, addr, end, &cold_walk_ops, &walk_private);

  	tlb_end_vma(tlb, vma);
  }
  
  static inline bool can_do_pageout(struct vm_area_struct *vma)
  {
  	if (vma_is_anonymous(vma))
  		return true;
  	if (!vma->vm_file)
  		return false;
  	/*
  	 * paging out pagecache only for non-anonymous mappings that correspond
  	 * to the files the calling process could (if tried) open for writing;
  	 * otherwise we'd be including shared non-exclusive mappings, which
  	 * opens a side channel.
  	 */
  	return inode_owner_or_capable(file_inode(vma->vm_file)) ||
  		inode_permission(file_inode(vma->vm_file), MAY_WRITE) == 0;
  }
  
  static long madvise_pageout(struct vm_area_struct *vma,
  			struct vm_area_struct **prev,
  			unsigned long start_addr, unsigned long end_addr)
  {
  	struct mm_struct *mm = vma->vm_mm;
  	struct mmu_gather tlb;
  
  	*prev = vma;
  	if (!can_madv_lru_vma(vma))
  		return -EINVAL;
  
  	if (!can_do_pageout(vma))
  		return 0;
  
  	lru_add_drain();
  	tlb_gather_mmu(&tlb, mm, start_addr, end_addr);
  	madvise_pageout_page_range(&tlb, vma, start_addr, end_addr);
  	tlb_finish_mmu(&tlb, start_addr, end_addr);
  
  	return 0;
  }

  static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
  				unsigned long end, struct mm_walk *walk)
  
  {
  	struct mmu_gather *tlb = walk->private;
  	struct mm_struct *mm = tlb->mm;
  	struct vm_area_struct *vma = walk->vma;
  	spinlock_t *ptl;
  	pte_t *orig_pte, *pte, ptent;
  	struct page *page;

  	int nr_swap = 0;

  	unsigned long next;
  
  	next = pmd_addr_end(addr, end);
  	if (pmd_trans_huge(*pmd))
  		if (madvise_free_huge_pmd(tlb, vma, pmd, addr, next))
  			goto next;

  	if (pmd_trans_unstable(pmd))
  		return 0;

  	tlb_change_page_size(tlb, PAGE_SIZE);

  	orig_pte = pte = pte_offset_map_lock(mm, pmd, addr, &ptl);

  	flush_tlb_batched_pending(mm);

  	arch_enter_lazy_mmu_mode();
  	for (; addr != end; pte++, addr += PAGE_SIZE) {
  		ptent = *pte;

  		if (pte_none(ptent))

  			continue;

  		/*
  		 * If the pte has swp_entry, just clear page table to
  		 * prevent swap-in which is more expensive rather than
  		 * (page allocation + zeroing).
  		 */
  		if (!pte_present(ptent)) {
  			swp_entry_t entry;
  
  			entry = pte_to_swp_entry(ptent);
  			if (non_swap_entry(entry))
  				continue;
  			nr_swap--;
  			free_swap_and_cache(entry);
  			pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
  			continue;
  		}

  		page = vm_normal_page(vma, addr, ptent);

  		if (!page)
  			continue;
  
  		/*
  		 * If pmd isn't transhuge but the page is THP and
  		 * is owned by only this process, split it and
  		 * deactivate all pages.
  		 */
  		if (PageTransCompound(page)) {
  			if (page_mapcount(page) != 1)
  				goto out;
  			get_page(page);
  			if (!trylock_page(page)) {
  				put_page(page);
  				goto out;
  			}
  			pte_unmap_unlock(orig_pte, ptl);
  			if (split_huge_page(page)) {
  				unlock_page(page);
  				put_page(page);
  				pte_offset_map_lock(mm, pmd, addr, &ptl);
  				goto out;
  			}

  			unlock_page(page);

  			put_page(page);

  			pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
  			pte--;
  			addr -= PAGE_SIZE;
  			continue;
  		}
  
  		VM_BUG_ON_PAGE(PageTransCompound(page), page);
  
  		if (PageSwapCache(page) || PageDirty(page)) {
  			if (!trylock_page(page))
  				continue;
  			/*
  			 * If page is shared with others, we couldn't clear
  			 * PG_dirty of the page.
  			 */
  			if (page_mapcount(page) != 1) {
  				unlock_page(page);
  				continue;
  			}
  
  			if (PageSwapCache(page) && !try_to_free_swap(page)) {
  				unlock_page(page);
  				continue;
  			}
  
  			ClearPageDirty(page);
  			unlock_page(page);
  		}
  
  		if (pte_young(ptent) || pte_dirty(ptent)) {
  			/*
  			 * Some of architecture(ex, PPC) don't update TLB
  			 * with set_pte_at and tlb_remove_tlb_entry so for
  			 * the portability, remap the pte with old|clean
  			 * after pte clearing.
  			 */
  			ptent = ptep_get_and_clear_full(mm, addr, pte,
  							tlb->fullmm);
  
  			ptent = pte_mkold(ptent);
  			ptent = pte_mkclean(ptent);
  			set_pte_at(mm, addr, pte, ptent);
  			tlb_remove_tlb_entry(tlb, pte, addr);
  		}

  		mark_page_lazyfree(page);

  	}
  out:

  	if (nr_swap) {
  		if (current->mm == mm)
  			sync_mm_rss(mm);
  
  		add_mm_counter(mm, MM_SWAPENTS, nr_swap);
  	}

  	arch_leave_lazy_mmu_mode();
  	pte_unmap_unlock(orig_pte, ptl);
  	cond_resched();

  next:

  	return 0;
  }

  static const struct mm_walk_ops madvise_free_walk_ops = {
  	.pmd_entry		= madvise_free_pte_range,
  };

  
  static int madvise_free_single_vma(struct vm_area_struct *vma,
  			unsigned long start_addr, unsigned long end_addr)
  {

  	struct mm_struct *mm = vma->vm_mm;

  	struct mmu_notifier_range range;

  	struct mmu_gather tlb;

  	/* MADV_FREE works for only anon vma at the moment */
  	if (!vma_is_anonymous(vma))
  		return -EINVAL;

  	range.start = max(vma->vm_start, start_addr);
  	if (range.start >= vma->vm_end)

  		return -EINVAL;

  	range.end = min(vma->vm_end, end_addr);
  	if (range.end <= vma->vm_start)

  		return -EINVAL;

  	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm,

  				range.start, range.end);

  
  	lru_add_drain();

  	tlb_gather_mmu(&tlb, mm, range.start, range.end);

  	update_hiwater_rss(mm);

  	mmu_notifier_invalidate_range_start(&range);

  	tlb_start_vma(&tlb, vma);
  	walk_page_range(vma->vm_mm, range.start, range.end,
  			&madvise_free_walk_ops, &tlb);
  	tlb_end_vma(&tlb, vma);

  	mmu_notifier_invalidate_range_end(&range);
  	tlb_finish_mmu(&tlb, range.start, range.end);

  
  	return 0;
  }

  /*
   * Application no longer needs these pages.  If the pages are dirty,
   * it's OK to just throw them away.  The app will be more careful about
   * data it wants to keep.  Be sure to free swap resources too.  The

   * zap_page_range call sets things up for shrink_active_list to actually free

   * these pages later if no one else has touched them in the meantime,
   * although we could add these pages to a global reuse list for

   * shrink_active_list to pick up before reclaiming other pages.

   *
   * NB: This interface discards data rather than pushes it out to swap,
   * as some implementations do.  This has performance implications for
   * applications like large transactional databases which want to discard
   * pages in anonymous maps after committing to backing store the data
   * that was kept in them.  There is no reason to write this data out to
   * the swap area if the application is discarding it.
   *
   * An interface that causes the system to free clean pages and flush
   * dirty pages is already available as msync(MS_INVALIDATE).
   */

  static long madvise_dontneed_single_vma(struct vm_area_struct *vma,
  					unsigned long start, unsigned long end)
  {
  	zap_page_range(vma, start, end - start);
  	return 0;
  }
  
  static long madvise_dontneed_free(struct vm_area_struct *vma,
  				  struct vm_area_struct **prev,
  				  unsigned long start, unsigned long end,
  				  int behavior)

  {

  	*prev = vma;

  	if (!can_madv_lru_vma(vma))

  		return -EINVAL;

  	if (!userfaultfd_remove(vma, start, end)) {
  		*prev = NULL; /* mmap_sem has been dropped, prev is stale */
  
  		down_read(&current->mm->mmap_sem);
  		vma = find_vma(current->mm, start);
  		if (!vma)
  			return -ENOMEM;
  		if (start < vma->vm_start) {
  			/*
  			 * This "vma" under revalidation is the one
  			 * with the lowest vma->vm_start where start
  			 * is also < vma->vm_end. If start <
  			 * vma->vm_start it means an hole materialized
  			 * in the user address space within the

  			 * virtual range passed to MADV_DONTNEED
  			 * or MADV_FREE.

  			 */
  			return -ENOMEM;
  		}

  		if (!can_madv_lru_vma(vma))

  			return -EINVAL;
  		if (end > vma->vm_end) {
  			/*
  			 * Don't fail if end > vma->vm_end. If the old
  			 * vma was splitted while the mmap_sem was
  			 * released the effect of the concurrent

  			 * operation may not cause madvise() to

  			 * have an undefined result. There may be an
  			 * adjacent next vma that we'll walk
  			 * next. userfaultfd_remove() will generate an
  			 * UFFD_EVENT_REMOVE repetition on the
  			 * end-vma->vm_end range, but the manager can
  			 * handle a repetition fine.
  			 */
  			end = vma->vm_end;
  		}
  		VM_WARN_ON(start >= end);
  	}

  
  	if (behavior == MADV_DONTNEED)
  		return madvise_dontneed_single_vma(vma, start, end);
  	else if (behavior == MADV_FREE)
  		return madvise_free_single_vma(vma, start, end);
  	else
  		return -EINVAL;

  }

  /*
   * Application wants to free up the pages and associated backing store.
   * This is effectively punching a hole into the middle of a file.

   */
  static long madvise_remove(struct vm_area_struct *vma,

  				struct vm_area_struct **prev,

  				unsigned long start, unsigned long end)
  {

  	loff_t offset;

  	int error;

  	struct file *f;

  	*prev = NULL;	/* tell sys_madvise we drop mmap_sem */

  	if (vma->vm_flags & VM_LOCKED)

  		return -EINVAL;

  	f = vma->vm_file;
  
  	if (!f || !f->f_mapping || !f->f_mapping->host) {

  			return -EINVAL;
  	}

  	if ((vma->vm_flags & (VM_SHARED|VM_WRITE)) != (VM_SHARED|VM_WRITE))
  		return -EACCES;

  	offset = (loff_t)(start - vma->vm_start)
  			+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);

  	/*
  	 * Filesystem's fallocate may need to take i_mutex.  We need to
  	 * explicitly grab a reference because the vma (and hence the
  	 * vma's reference to the file) can go away as soon as we drop
  	 * mmap_sem.
  	 */
  	get_file(f);

  	if (userfaultfd_remove(vma, start, end)) {
  		/* mmap_sem was not released by userfaultfd_remove() */
  		up_read(&current->mm->mmap_sem);
  	}

  	error = vfs_fallocate(f,

  				FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
  				offset, end - start);

  	fput(f);

  	down_read(&current->mm->mmap_sem);

  	return error;

  }

  #ifdef CONFIG_MEMORY_FAILURE
  /*
   * Error injection support for memory error handling.
   */

  static int madvise_inject_error(int behavior,
  		unsigned long start, unsigned long end)

  {

  	struct page *page;

  	struct zone *zone;

  	unsigned int order;

  	if (!capable(CAP_SYS_ADMIN))
  		return -EPERM;

  
  	for (; start < end; start += PAGE_SIZE << order) {

  		unsigned long pfn;

  		int ret;

  		ret = get_user_pages_fast(start, 1, 0, &page);

  		if (ret != 1)
  			return ret;

  		pfn = page_to_pfn(page);

  		/*
  		 * When soft offlining hugepages, after migrating the page
  		 * we dissolve it, therefore in the second loop "page" will
  		 * no longer be a compound page, and order will be 0.
  		 */
  		order = compound_order(compound_head(page));

  		if (PageHWPoison(page)) {
  			put_page(page);

  			continue;
  		}

  
  		if (behavior == MADV_SOFT_OFFLINE) {
  			pr_info("Soft offlining pfn %#lx at process virtual address %#lx
  ",

  					pfn, start);

  
  			ret = soft_offline_page(page, MF_COUNT_INCREASED);

  			if (ret)

  				return ret;

  			continue;
  		}

  		pr_info("Injecting memory failure for pfn %#lx at process virtual address %#lx
  ",

  				pfn, start);

  		/*
  		 * Drop the page reference taken by get_user_pages_fast(). In
  		 * the absence of MF_COUNT_INCREASED the memory_failure()
  		 * routine is responsible for pinning the page to prevent it
  		 * from being released back to the page allocator.
  		 */
  		put_page(page);
  		ret = memory_failure(pfn, 0);

  		if (ret)
  			return ret;

  	}

  
  	/* Ensure that all poisoned pages are removed from per-cpu lists */
  	for_each_populated_zone(zone)
  		drain_all_pages(zone);

  	return 0;

  }
  #endif

  static long
  madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
  		unsigned long start, unsigned long end, int behavior)

  {

  	switch (behavior) {

  	case MADV_REMOVE:

  		return madvise_remove(vma, prev, start, end);

  	case MADV_WILLNEED:

  		return madvise_willneed(vma, prev, start, end);

  	case MADV_COLD:
  		return madvise_cold(vma, prev, start, end);

  	case MADV_PAGEOUT:
  		return madvise_pageout(vma, prev, start, end);

  	case MADV_FREE:

  	case MADV_DONTNEED:

  		return madvise_dontneed_free(vma, prev, start, end, behavior);

  	default:

  		return madvise_behavior(vma, prev, start, end, behavior);

  	}

  }

  static bool

  madvise_behavior_valid(int behavior)
  {
  	switch (behavior) {
  	case MADV_DOFORK:
  	case MADV_DONTFORK:
  	case MADV_NORMAL:
  	case MADV_SEQUENTIAL:
  	case MADV_RANDOM:
  	case MADV_REMOVE:
  	case MADV_WILLNEED:
  	case MADV_DONTNEED:

  	case MADV_FREE:

  	case MADV_COLD:

  	case MADV_PAGEOUT:

  #ifdef CONFIG_KSM
  	case MADV_MERGEABLE:
  	case MADV_UNMERGEABLE:
  #endif

  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
  	case MADV_HUGEPAGE:

  	case MADV_NOHUGEPAGE:

  #endif

  	case MADV_DONTDUMP:
  	case MADV_DODUMP:

  	case MADV_WIPEONFORK:
  	case MADV_KEEPONFORK:

  #ifdef CONFIG_MEMORY_FAILURE
  	case MADV_SOFT_OFFLINE:
  	case MADV_HWPOISON:
  #endif

  		return true;

  
  	default:

  		return false;

  	}
  }

  /*
   * The madvise(2) system call.
   *
   * Applications can use madvise() to advise the kernel how it should
   * handle paging I/O in this VM area.  The idea is to help the kernel
   * use appropriate read-ahead and caching techniques.  The information
   * provided is advisory only, and can be safely disregarded by the
   * kernel without affecting the correct operation of the application.
   *
   * behavior values:
   *  MADV_NORMAL - the default behavior is to read clusters.  This
   *		results in some read-ahead and read-behind.
   *  MADV_RANDOM - the system should read the minimum amount of data
   *		on any access, since it is unlikely that the appli-
   *		cation will need more than what it asks for.
   *  MADV_SEQUENTIAL - pages in the given range will probably be accessed
   *		once, so they can be aggressively read ahead, and
   *		can be freed soon after they are accessed.
   *  MADV_WILLNEED - the application is notifying the system to read
   *		some pages ahead.
   *  MADV_DONTNEED - the application is finished with the given range,
   *		so the kernel can free resources associated with it.

   *  MADV_FREE - the application marks pages in the given range as lazy free,
   *		where actual purges are postponed until memory pressure happens.

   *  MADV_REMOVE - the application wants to free up the given range of
   *		pages and associated backing store.

   *  MADV_DONTFORK - omit this area from child's address space when forking:
   *		typically, to avoid COWing pages pinned by get_user_pages().
   *  MADV_DOFORK - cancel MADV_DONTFORK: no longer omit this area when forking.

   *  MADV_WIPEONFORK - present the child process with zero-filled memory in this
   *              range after a fork.
   *  MADV_KEEPONFORK - undo the effect of MADV_WIPEONFORK

   *  MADV_HWPOISON - trigger memory error handler as if the given memory range
   *		were corrupted by unrecoverable hardware memory failure.
   *  MADV_SOFT_OFFLINE - try to soft-offline the given range of memory.

   *  MADV_MERGEABLE - the application recommends that KSM try to merge pages in
   *		this area with pages of identical content from other such areas.
   *  MADV_UNMERGEABLE- cancel MADV_MERGEABLE: no longer merge pages with others.

   *  MADV_HUGEPAGE - the application wants to back the given range by transparent
   *		huge pages in the future. Existing pages might be coalesced and
   *		new pages might be allocated as THP.
   *  MADV_NOHUGEPAGE - mark the given range as not worth being backed by
   *		transparent huge pages so the existing pages will not be
   *		coalesced into THP and new pages will not be allocated as THP.
   *  MADV_DONTDUMP - the application wants to prevent pages in the given range
   *		from being included in its core dump.
   *  MADV_DODUMP - cancel MADV_DONTDUMP: no longer exclude from core dump.

   *
   * return values:
   *  zero    - success
   *  -EINVAL - start + len < 0, start is not page-aligned,
   *		"behavior" is not a valid value, or application

   *		is attempting to release locked or shared pages,
   *		or the specified address range includes file, Huge TLB,
   *		MAP_SHARED or VMPFNMAP range.

   *  -ENOMEM - addresses in the specified range are not currently
   *		mapped, or are outside the AS of the process.
   *  -EIO    - an I/O error occurred while paging in data.
   *  -EBADF  - map exists, but area maps something that isn't a file.
   *  -EAGAIN - a kernel resource was temporarily unavailable.
   */

  SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)

  {

  	unsigned long end, tmp;

  	struct vm_area_struct *vma, *prev;

  	int unmapped_error = 0;
  	int error = -EINVAL;

  	int write;

  	size_t len;

  	struct blk_plug plug;

  	start = untagged_addr(start);

  	if (!madvise_behavior_valid(behavior))
  		return error;

  	if (start & ~PAGE_MASK)

  		return error;

  	len = (len_in + ~PAGE_MASK) & PAGE_MASK;
  
  	/* Check to see whether len was rounded up from small -ve to zero */
  	if (len_in && !len)

  		return error;

  
  	end = start + len;
  	if (end < start)

  		return error;

  
  	error = 0;
  	if (end == start)

  		return error;

  #ifdef CONFIG_MEMORY_FAILURE
  	if (behavior == MADV_HWPOISON || behavior == MADV_SOFT_OFFLINE)
  		return madvise_inject_error(behavior, start, start + len_in);
  #endif

  	write = madvise_need_mmap_write(behavior);

  	if (write) {
  		if (down_write_killable(&current->mm->mmap_sem))
  			return -EINTR;
  	} else {

  		down_read(&current->mm->mmap_sem);

  	}

  
  	/*
  	 * If the interval [start,end) covers some unmapped address
  	 * ranges, just ignore them, but return -ENOMEM at the end.

  	 * - different from the way of handling in mlock etc.

  	 */

  	vma = find_vma_prev(current->mm, start, &prev);

  	if (vma && start > vma->vm_start)
  		prev = vma;

  	blk_start_plug(&plug);

  	for (;;) {
  		/* Still start < end. */
  		error = -ENOMEM;
  		if (!vma)

  			goto out;

  		/* Here start < (end|vma->vm_end). */

  		if (start < vma->vm_start) {
  			unmapped_error = -ENOMEM;
  			start = vma->vm_start;

  			if (start >= end)

  				goto out;

  		}

  		/* Here vma->vm_start <= start < (end|vma->vm_end) */
  		tmp = vma->vm_end;
  		if (end < tmp)
  			tmp = end;

  		/* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
  		error = madvise_vma(vma, &prev, start, tmp, behavior);

  		if (error)

  			goto out;

  		start = tmp;

  		if (prev && start < prev->vm_end)

  			start = prev->vm_end;
  		error = unmapped_error;
  		if (start >= end)

  			goto out;

  		if (prev)
  			vma = prev->vm_next;
  		else	/* madvise_remove dropped mmap_sem */
  			vma = find_vma(current->mm, start);

  	}

  out:

  	blk_finish_plug(&plug);

  	if (write)

  		up_write(&current->mm->mmap_sem);
  	else
  		up_read(&current->mm->mmap_sem);

  	return error;
  }