text: /*
   *	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/hugetlb.h>
  #include <linux/falloc.h>
  #include <linux/sched.h>
  #include <linux/ksm.h>
  #include <linux/fs.h>
  #include <linux/file.h>
  #include <linux/blkdev.h>
  #include <linux/swap.h>
  #include <linux/swapops.h>
  
  /*
   * 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:
  		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_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;
  		break;
  	case MADV_HUGEPAGE:
  	case MADV_NOHUGEPAGE:
  		error = hugepage_madvise(vma, &new_flags, behavior);
  		if (error)
  			goto out;
  		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_get_anon_name(vma));
  	if (*prev) {
  		vma = *prev;
  		goto success;
  	}
  
  	*prev = vma;
  
  	if (start != vma->vm_start) {
  		error = split_vma(mm, vma, start, 1);
  		if (error)
  			goto out;
  	}
  
  	if (end != vma->vm_end) {
  		error = split_vma(mm, vma, end, 0);
  		if (error)
  			goto out;
  	}
  
  success:
  	/*
  	 * vm_flags is protected by the mmap_sem held in write mode.
  	 */
  	vma->vm_flags = new_flags;
  
  out:
  	if (error == -ENOMEM)
  		error = -EAGAIN;
  	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) || pte_file(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);
  		if (page)
  			page_cache_release(page);
  	}
  
  	return 0;
  }
  
  static void force_swapin_readahead(struct vm_area_struct *vma,
  		unsigned long start, unsigned long end)
  {
  	struct mm_walk walk = {
  		.mm = vma->vm_mm,
  		.pmd_entry = swapin_walk_pmd_entry,
  		.private = vma,
  	};
  
  	walk_page_range(start, end, &walk);
  
  	lru_add_drain();	/* Push any new pages onto the LRU now */
  }
  
  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 (!radix_tree_exceptional_entry(page)) {
  			if (page)
  				page_cache_release(page);
  			continue;
  		}
  		swap = radix_to_swp_entry(page);
  		page = read_swap_cache_async(swap, GFP_HIGHUSER_MOVABLE,
  								NULL, 0);
  		if (page)
  			page_cache_release(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;
  
  	*prev = vma;
  #ifdef CONFIG_SWAP
  	if (!file || mapping_cap_swap_backed(file->f_mapping)) {
  		if (!file)
  			force_swapin_readahead(vma, start, end);
  		else
  			force_shm_swapin_readahead(vma, start, end,
  						file->f_mapping);
  		return 0;
  	}
  #endif
  
  	if (!file)
  		return -EBADF;
  
  	if (file->f_mapping->a_ops->get_xip_mem) {
  		/* no bad return value, but ignore advice */
  		return 0;
  	}
  
  	start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
  	if (end > vma->vm_end)
  		end = vma->vm_end;
  	end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
  
  	force_page_cache_readahead(file->f_mapping, file, start, end - start);
  	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(struct vm_area_struct *vma,
  			     struct vm_area_struct **prev,
  			     unsigned long start, unsigned long end)
  {
  	*prev = vma;
  	if (vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP))
  		return -EINVAL;
  
  	if (unlikely(vma->vm_flags & VM_NONLINEAR)) {
  		struct zap_details details = {
  			.nonlinear_vma = vma,
  			.last_index = ULONG_MAX,
  		};
  		zap_page_range(vma, start, end - start, &details);
  	} else
  		zap_page_range(vma, start, end - start, NULL);
  	return 0;
  }
  
  /*
   * 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|VM_NONLINEAR|VM_HUGETLB))
  		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);
  	up_read(&current->mm->mmap_sem);
  	error = do_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_hwpoison(int bhv, unsigned long start, unsigned long end)
  {
  	struct page *p;
  	if (!capable(CAP_SYS_ADMIN))
  		return -EPERM;
  	for (; start < end; start += PAGE_SIZE <<
  				compound_order(compound_head(p))) {
  		int ret;
  
  		ret = get_user_pages_fast(start, 1, 0, &p);
  		if (ret != 1)
  			return ret;
  
  		if (PageHWPoison(p)) {
  			put_page(p);
  			continue;
  		}
  		if (bhv == MADV_SOFT_OFFLINE) {
  			pr_info("Soft offlining page %#lx at %#lx\n",
  				page_to_pfn(p), start);
  			ret = soft_offline_page(p, MF_COUNT_INCREASED);
  			if (ret)
  				return ret;
  			continue;
  		}
  		pr_info("Injecting memory failure for page %#lx at %#lx\n",
  		       page_to_pfn(p), start);
  		/* Ignore return value for now */
  		memory_failure(page_to_pfn(p), 0, MF_COUNT_INCREASED);
  	}
  	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_DONTNEED:
  		return madvise_dontneed(vma, prev, start, end);
  	default:
  		return madvise_behavior(vma, prev, start, end, behavior);
  	}
  }
  
  static int
  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:
  #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:
  		return 1;
  
  	default:
  		return 0;
  	}
  }
  
  /*
   * 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_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_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.
   *
   * 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.
   *  -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;
  
  #ifdef CONFIG_MEMORY_FAILURE
  	if (behavior == MADV_HWPOISON || behavior == MADV_SOFT_OFFLINE)
  		return madvise_hwpoison(behavior, start, start+len_in);
  #endif
  	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;
  
  	write = madvise_need_mmap_write(behavior);
  	if (write)
  		down_write(&current->mm->mmap_sem);
  	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;
  }
  