// SPDX-License-Identifier: GPL-2.0

  /*
   *	linux/mm/mlock.c
   *
   *  (C) Copyright 1995 Linus Torvalds
   *  (C) Copyright 2002 Christoph Hellwig
   */

  #include <linux/capability.h>

  #include <linux/mman.h>
  #include <linux/mm.h>

  #include <linux/sched/user.h>

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

  #include <linux/pagevec.h>

  #include <linux/mempolicy.h>
  #include <linux/syscalls.h>

  #include <linux/sched.h>

  #include <linux/export.h>

  #include <linux/rmap.h>
  #include <linux/mmzone.h>
  #include <linux/hugetlb.h>

  #include <linux/memcontrol.h>
  #include <linux/mm_inline.h>

  
  #include "internal.h"

  bool can_do_mlock(void)

  {

  	if (rlimit(RLIMIT_MEMLOCK) != 0)

  		return true;

  	if (capable(CAP_IPC_LOCK))

  		return true;
  	return false;

  }
  EXPORT_SYMBOL(can_do_mlock);

  /*
   * Mlocked pages are marked with PageMlocked() flag for efficient testing
   * in vmscan and, possibly, the fault path; and to support semi-accurate
   * statistics.
   *
   * An mlocked page [PageMlocked(page)] is unevictable.  As such, it will
   * be placed on the LRU "unevictable" list, rather than the [in]active lists.
   * The unevictable list is an LRU sibling list to the [in]active lists.
   * PageUnevictable is set to indicate the unevictable state.
   *
   * When lazy mlocking via vmscan, it is important to ensure that the
   * vma's VM_LOCKED status is not concurrently being modified, otherwise we
   * may have mlocked a page that is being munlocked. So lazy mlock must take
   * the mmap_sem for read, and verify that the vma really is locked
   * (see mm/rmap.c).
   */
  
  /*
   *  LRU accounting for clear_page_mlock()
   */

  void clear_page_mlock(struct page *page)

  {

  	if (!TestClearPageMlocked(page))

  		return;

  	mod_zone_page_state(page_zone(page), NR_MLOCK,
  			    -hpage_nr_pages(page));

  	count_vm_event(UNEVICTABLE_PGCLEARED);

  	/*
  	 * The previous TestClearPageMlocked() corresponds to the smp_mb()
  	 * in __pagevec_lru_add_fn().
  	 *
  	 * See __pagevec_lru_add_fn for more explanation.
  	 */

  	if (!isolate_lru_page(page)) {
  		putback_lru_page(page);
  	} else {
  		/*

  		 * We lost the race. the page already moved to evictable list.

  		 */

  		if (PageUnevictable(page))

  			count_vm_event(UNEVICTABLE_PGSTRANDED);

  	}
  }
  
  /*
   * Mark page as mlocked if not already.
   * If page on LRU, isolate and putback to move to unevictable list.
   */
  void mlock_vma_page(struct page *page)
  {

  	/* Serialize with page migration */

  	BUG_ON(!PageLocked(page));

  	VM_BUG_ON_PAGE(PageTail(page), page);
  	VM_BUG_ON_PAGE(PageCompound(page) && PageDoubleMap(page), page);

  	if (!TestSetPageMlocked(page)) {

  		mod_zone_page_state(page_zone(page), NR_MLOCK,
  				    hpage_nr_pages(page));

  		count_vm_event(UNEVICTABLE_PGMLOCKED);
  		if (!isolate_lru_page(page))
  			putback_lru_page(page);
  	}

  }

  /*

   * Isolate a page from LRU with optional get_page() pin.
   * Assumes lru_lock already held and page already pinned.
   */
  static bool __munlock_isolate_lru_page(struct page *page, bool getpage)
  {
  	if (PageLRU(page)) {
  		struct lruvec *lruvec;

  		lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));

  		if (getpage)
  			get_page(page);
  		ClearPageLRU(page);
  		del_page_from_lru_list(page, lruvec, page_lru(page));
  		return true;
  	}
  
  	return false;
  }
  
  /*

   * Finish munlock after successful page isolation
   *
   * Page must be locked. This is a wrapper for try_to_munlock()
   * and putback_lru_page() with munlock accounting.
   */
  static void __munlock_isolated_page(struct page *page)
  {

  	/*
  	 * Optimization: if the page was mapped just once, that's our mapping
  	 * and we don't need to check all the other vmas.
  	 */
  	if (page_mapcount(page) > 1)

  		try_to_munlock(page);

  
  	/* Did try_to_unlock() succeed or punt? */

  	if (!PageMlocked(page))

  		count_vm_event(UNEVICTABLE_PGMUNLOCKED);
  
  	putback_lru_page(page);
  }
  
  /*
   * Accounting for page isolation fail during munlock
   *
   * Performs accounting when page isolation fails in munlock. There is nothing
   * else to do because it means some other task has already removed the page
   * from the LRU. putback_lru_page() will take care of removing the page from
   * the unevictable list, if necessary. vmscan [page_referenced()] will move
   * the page back to the unevictable list if some other vma has it mlocked.
   */
  static void __munlock_isolation_failed(struct page *page)
  {
  	if (PageUnevictable(page))

  		__count_vm_event(UNEVICTABLE_PGSTRANDED);

  	else

  		__count_vm_event(UNEVICTABLE_PGMUNLOCKED);

  }

  /**
   * munlock_vma_page - munlock a vma page

   * @page: page to be unlocked, either a normal page or THP page head

   *
   * returns the size of the page as a page mask (0 for normal page,
   *         HPAGE_PMD_NR - 1 for THP head page)

   *

   * called from munlock()/munmap() path with page supposedly on the LRU.
   * When we munlock a page, because the vma where we found the page is being
   * munlock()ed or munmap()ed, we want to check whether other vmas hold the
   * page locked so that we can leave it on the unevictable lru list and not
   * bother vmscan with it.  However, to walk the page's rmap list in
   * try_to_munlock() we must isolate the page from the LRU.  If some other
   * task has removed the page from the LRU, we won't be able to do that.
   * So we clear the PageMlocked as we might not get another chance.  If we
   * can't isolate the page, we leave it for putback_lru_page() and vmscan
   * [page_referenced()/try_to_unmap()] to deal with.

   */

  unsigned int munlock_vma_page(struct page *page)

  {

  	int nr_pages;

  	struct zone *zone = page_zone(page);

  	/* For try_to_munlock() and to serialize with page migration */

  	BUG_ON(!PageLocked(page));

  	VM_BUG_ON_PAGE(PageTail(page), page);

  	/*

  	 * Serialize with any parallel __split_huge_page_refcount() which
  	 * might otherwise copy PageMlocked to part of the tail pages before
  	 * we clear it in the head page. It also stabilizes hpage_nr_pages().

  	 */

  	spin_lock_irq(zone_lru_lock(zone));

  	if (!TestClearPageMlocked(page)) {
  		/* Potentially, PTE-mapped THP: do not skip the rest PTEs */
  		nr_pages = 1;

  		goto unlock_out;

  	}

  	nr_pages = hpage_nr_pages(page);

  	__mod_zone_page_state(zone, NR_MLOCK, -nr_pages);
  
  	if (__munlock_isolate_lru_page(page, true)) {

  		spin_unlock_irq(zone_lru_lock(zone));

  		__munlock_isolated_page(page);
  		goto out;
  	}
  	__munlock_isolation_failed(page);
  
  unlock_out:

  	spin_unlock_irq(zone_lru_lock(zone));

  
  out:

  	return nr_pages - 1;

  }

  /*
   * convert get_user_pages() return value to posix mlock() error
   */
  static int __mlock_posix_error_return(long retval)
  {
  	if (retval == -EFAULT)
  		retval = -ENOMEM;
  	else if (retval == -ENOMEM)
  		retval = -EAGAIN;
  	return retval;

  }

  /*

   * Prepare page for fast batched LRU putback via putback_lru_evictable_pagevec()
   *
   * The fast path is available only for evictable pages with single mapping.
   * Then we can bypass the per-cpu pvec and get better performance.
   * when mapcount > 1 we need try_to_munlock() which can fail.
   * when !page_evictable(), we need the full redo logic of putback_lru_page to
   * avoid leaving evictable page in unevictable list.
   *
   * In case of success, @page is added to @pvec and @pgrescued is incremented
   * in case that the page was previously unevictable. @page is also unlocked.
   */
  static bool __putback_lru_fast_prepare(struct page *page, struct pagevec *pvec,
  		int *pgrescued)
  {

  	VM_BUG_ON_PAGE(PageLRU(page), page);
  	VM_BUG_ON_PAGE(!PageLocked(page), page);

  
  	if (page_mapcount(page) <= 1 && page_evictable(page)) {
  		pagevec_add(pvec, page);
  		if (TestClearPageUnevictable(page))
  			(*pgrescued)++;
  		unlock_page(page);
  		return true;
  	}
  
  	return false;
  }
  
  /*
   * Putback multiple evictable pages to the LRU
   *
   * Batched putback of evictable pages that bypasses the per-cpu pvec. Some of
   * the pages might have meanwhile become unevictable but that is OK.
   */
  static void __putback_lru_fast(struct pagevec *pvec, int pgrescued)
  {
  	count_vm_events(UNEVICTABLE_PGMUNLOCKED, pagevec_count(pvec));
  	/*
  	 *__pagevec_lru_add() calls release_pages() so we don't call
  	 * put_page() explicitly
  	 */
  	__pagevec_lru_add(pvec);
  	count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
  }
  
  /*

   * Munlock a batch of pages from the same zone
   *
   * The work is split to two main phases. First phase clears the Mlocked flag
   * and attempts to isolate the pages, all under a single zone lru lock.
   * The second phase finishes the munlock only for pages where isolation
   * succeeded.
   *

   * Note that the pagevec may be modified during the process.

   */
  static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
  {
  	int i;
  	int nr = pagevec_count(pvec);

  	int delta_munlocked = -nr;

  	struct pagevec pvec_putback;
  	int pgrescued = 0;

  	pagevec_init(&pvec_putback);

  	/* Phase 1: page isolation */

  	spin_lock_irq(zone_lru_lock(zone));

  	for (i = 0; i < nr; i++) {
  		struct page *page = pvec->pages[i];
  
  		if (TestClearPageMlocked(page)) {

  			/*

  			 * We already have pin from follow_page_mask()
  			 * so we can spare the get_page() here.

  			 */

  			if (__munlock_isolate_lru_page(page, false))
  				continue;
  			else
  				__munlock_isolation_failed(page);

  		} else {
  			delta_munlocked++;

  		}

  
  		/*
  		 * We won't be munlocking this page in the next phase
  		 * but we still need to release the follow_page_mask()
  		 * pin. We cannot do it under lru_lock however. If it's
  		 * the last pin, __page_cache_release() would deadlock.
  		 */
  		pagevec_add(&pvec_putback, pvec->pages[i]);
  		pvec->pages[i] = NULL;

  	}

  	__mod_zone_page_state(zone, NR_MLOCK, delta_munlocked);

  	spin_unlock_irq(zone_lru_lock(zone));

  	/* Now we can release pins of pages that we are not munlocking */
  	pagevec_release(&pvec_putback);

  	/* Phase 2: page munlock */

  	for (i = 0; i < nr; i++) {
  		struct page *page = pvec->pages[i];
  
  		if (page) {
  			lock_page(page);

  			if (!__putback_lru_fast_prepare(page, &pvec_putback,
  					&pgrescued)) {

  				/*
  				 * Slow path. We don't want to lose the last
  				 * pin before unlock_page()
  				 */
  				get_page(page); /* for putback_lru_page() */

  				__munlock_isolated_page(page);
  				unlock_page(page);

  				put_page(page); /* from follow_page_mask() */

  			}

  		}
  	}

  	/*
  	 * Phase 3: page putback for pages that qualified for the fast path
  	 * This will also call put_page() to return pin from follow_page_mask()
  	 */

  	if (pagevec_count(&pvec_putback))
  		__putback_lru_fast(&pvec_putback, pgrescued);

  }
  
  /*
   * Fill up pagevec for __munlock_pagevec using pte walk
   *
   * The function expects that the struct page corresponding to @start address is
   * a non-TPH page already pinned and in the @pvec, and that it belongs to @zone.
   *
   * The rest of @pvec is filled by subsequent pages within the same pmd and same
   * zone, as long as the pte's are present and vm_normal_page() succeeds. These
   * pages also get pinned.
   *
   * Returns the address of the next page that should be scanned. This equals
   * @start + PAGE_SIZE when no page could be added by the pte walk.
   */
  static unsigned long __munlock_pagevec_fill(struct pagevec *pvec,

  			struct vm_area_struct *vma, struct zone *zone,
  			unsigned long start, unsigned long end)

  {
  	pte_t *pte;
  	spinlock_t *ptl;
  
  	/*
  	 * Initialize pte walk starting at the already pinned page where we

  	 * are sure that there is a pte, as it was pinned under the same
  	 * mmap_sem write op.

  	 */
  	pte = get_locked_pte(vma->vm_mm, start,	&ptl);

  	/* Make sure we do not cross the page table boundary */
  	end = pgd_addr_end(start, end);

  	end = p4d_addr_end(start, end);

  	end = pud_addr_end(start, end);
  	end = pmd_addr_end(start, end);

  
  	/* The page next to the pinned page is the first we will try to get */
  	start += PAGE_SIZE;
  	while (start < end) {
  		struct page *page = NULL;
  		pte++;
  		if (pte_present(*pte))
  			page = vm_normal_page(vma, start, *pte);
  		/*
  		 * Break if page could not be obtained or the page's node+zone does not
  		 * match
  		 */

  		if (!page || page_zone(page) != zone)

  			break;

  		/*
  		 * Do not use pagevec for PTE-mapped THP,
  		 * munlock_vma_pages_range() will handle them.
  		 */
  		if (PageTransCompound(page))
  			break;

  		get_page(page);
  		/*
  		 * Increase the address that will be returned *before* the
  		 * eventual break due to pvec becoming full by adding the page
  		 */
  		start += PAGE_SIZE;
  		if (pagevec_add(pvec, page) == 0)
  			break;
  	}
  	pte_unmap_unlock(pte, ptl);
  	return start;

  }
  
  /*

   * munlock_vma_pages_range() - munlock all pages in the vma range.'
   * @vma - vma containing range to be munlock()ed.
   * @start - start address in @vma of the range
   * @end - end of range in @vma.
   *
   *  For mremap(), munmap() and exit().
   *
   * Called with @vma VM_LOCKED.
   *
   * Returns with VM_LOCKED cleared.  Callers must be prepared to
   * deal with this.
   *
   * We don't save and restore VM_LOCKED here because pages are
   * still on lru.  In unmap path, pages might be scanned by reclaim
   * and re-mlocked by try_to_{munlock|unmap} before we unmap and
   * free them.  This will result in freeing mlocked pages.

   */

  void munlock_vma_pages_range(struct vm_area_struct *vma,

  			     unsigned long start, unsigned long end)

  {

  	vma->vm_flags &= VM_LOCKED_CLEAR_MASK;

  	while (start < end) {

  		struct page *page;

  		unsigned int page_mask = 0;

  		unsigned long page_increm;

  		struct pagevec pvec;
  		struct zone *zone;

  		pagevec_init(&pvec);

  		/*
  		 * Although FOLL_DUMP is intended for get_dump_page(),
  		 * it just so happens that its special treatment of the
  		 * ZERO_PAGE (returning an error instead of doing get_page)
  		 * suits munlock very well (and if somehow an abnormal page
  		 * has sneaked into the range, we won't oops here: great).
  		 */

  		page = follow_page(vma, start, FOLL_GET | FOLL_DUMP);

  		if (page && !IS_ERR(page)) {
  			if (PageTransTail(page)) {
  				VM_BUG_ON_PAGE(PageMlocked(page), page);
  				put_page(page); /* follow_page_mask() */
  			} else if (PageTransHuge(page)) {
  				lock_page(page);
  				/*
  				 * Any THP page found by follow_page_mask() may
  				 * have gotten split before reaching

  				 * munlock_vma_page(), so we need to compute
  				 * the page_mask here instead.

  				 */
  				page_mask = munlock_vma_page(page);
  				unlock_page(page);
  				put_page(page); /* follow_page_mask() */
  			} else {
  				/*
  				 * Non-huge pages are handled in batches via
  				 * pagevec. The pin from follow_page_mask()
  				 * prevents them from collapsing by THP.
  				 */
  				pagevec_add(&pvec, page);
  				zone = page_zone(page);

  				/*
  				 * Try to fill the rest of pagevec using fast
  				 * pte walk. This will also update start to
  				 * the next page to process. Then munlock the
  				 * pagevec.
  				 */
  				start = __munlock_pagevec_fill(&pvec, vma,

  						zone, start, end);

  				__munlock_pagevec(&pvec, zone);
  				goto next;
  			}

  		}

  		page_increm = 1 + page_mask;

  		start += page_increm * PAGE_SIZE;

  next:

  		cond_resched();
  	}

  }
  
  /*
   * mlock_fixup  - handle mlock[all]/munlock[all] requests.
   *
   * Filters out "special" vmas -- VM_LOCKED never gets set for these, and
   * munlock is a no-op.  However, for some special vmas, we go ahead and

   * populate the ptes.

   *
   * For vmas that pass the filters, merge/split as appropriate.
   */

  static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,

  	unsigned long start, unsigned long end, vm_flags_t newflags)

  {

  	struct mm_struct *mm = vma->vm_mm;

  	pgoff_t pgoff;

  	int nr_pages;

  	int ret = 0;

  	int lock = !!(newflags & VM_LOCKED);

  	vm_flags_t old_flags = vma->vm_flags;

  	if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||

  	    is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm) ||
  	    vma_is_dax(vma))

  		/* don't set VM_LOCKED or VM_LOCKONFAULT and don't count */
  		goto out;

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

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

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

  	if (start != vma->vm_start) {
  		ret = split_vma(mm, vma, start, 1);
  		if (ret)
  			goto out;
  	}
  
  	if (end != vma->vm_end) {
  		ret = split_vma(mm, vma, end, 0);
  		if (ret)
  			goto out;
  	}
  
  success:
  	/*

  	 * Keep track of amount of locked VM.
  	 */
  	nr_pages = (end - start) >> PAGE_SHIFT;
  	if (!lock)
  		nr_pages = -nr_pages;

  	else if (old_flags & VM_LOCKED)
  		nr_pages = 0;

  	mm->locked_vm += nr_pages;
  
  	/*

  	 * vm_flags is protected by the mmap_sem held in write mode.
  	 * It's okay if try_to_unmap_one unmaps a page just after we

  	 * set VM_LOCKED, populate_vma_page_range will bring it back.

  	 */

  	if (lock)

  		vma->vm_flags = newflags;

  	else

  		munlock_vma_pages_range(vma, start, end);

  out:

  	*prev = vma;

  	return ret;
  }

  static int apply_vma_lock_flags(unsigned long start, size_t len,
  				vm_flags_t flags)

  {
  	unsigned long nstart, end, tmp;
  	struct vm_area_struct * vma, * prev;
  	int error;

  	VM_BUG_ON(offset_in_page(start));

  	VM_BUG_ON(len != PAGE_ALIGN(len));

  	end = start + len;
  	if (end < start)
  		return -EINVAL;
  	if (end == start)
  		return 0;

  	vma = find_vma(current->mm, start);

  	if (!vma || vma->vm_start > start)
  		return -ENOMEM;

  	prev = vma->vm_prev;

  	if (start > vma->vm_start)
  		prev = vma;
  
  	for (nstart = start ; ; ) {

  		vm_flags_t newflags = vma->vm_flags & VM_LOCKED_CLEAR_MASK;

  		newflags |= flags;

  		/* Here we know that  vma->vm_start <= nstart < vma->vm_end. */

  		tmp = vma->vm_end;
  		if (tmp > end)
  			tmp = end;
  		error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
  		if (error)
  			break;
  		nstart = tmp;
  		if (nstart < prev->vm_end)
  			nstart = prev->vm_end;
  		if (nstart >= end)
  			break;
  
  		vma = prev->vm_next;
  		if (!vma || vma->vm_start != nstart) {
  			error = -ENOMEM;
  			break;
  		}
  	}
  	return error;
  }

  /*
   * Go through vma areas and sum size of mlocked
   * vma pages, as return value.
   * Note deferred memory locking case(mlock2(,,MLOCK_ONFAULT)
   * is also counted.
   * Return value: previously mlocked page counts
   */
  static int count_mm_mlocked_page_nr(struct mm_struct *mm,
  		unsigned long start, size_t len)
  {
  	struct vm_area_struct *vma;
  	int count = 0;
  
  	if (mm == NULL)
  		mm = current->mm;
  
  	vma = find_vma(mm, start);
  	if (vma == NULL)
  		vma = mm->mmap;
  
  	for (; vma ; vma = vma->vm_next) {
  		if (start >= vma->vm_end)
  			continue;
  		if (start + len <=  vma->vm_start)
  			break;
  		if (vma->vm_flags & VM_LOCKED) {
  			if (start > vma->vm_start)
  				count -= (start - vma->vm_start);
  			if (start + len < vma->vm_end) {
  				count += start + len - vma->vm_start;
  				break;
  			}
  			count += vma->vm_end - vma->vm_start;
  		}
  	}
  
  	return count >> PAGE_SHIFT;
  }

  static __must_check int do_mlock(unsigned long start, size_t len, vm_flags_t flags)

  {
  	unsigned long locked;
  	unsigned long lock_limit;
  	int error = -ENOMEM;
  
  	if (!can_do_mlock())
  		return -EPERM;

  	len = PAGE_ALIGN(len + (offset_in_page(start)));

  	start &= PAGE_MASK;

  	lock_limit = rlimit(RLIMIT_MEMLOCK);

  	lock_limit >>= PAGE_SHIFT;

  	locked = len >> PAGE_SHIFT;

  	if (down_write_killable(&current->mm->mmap_sem))
  		return -EINTR;

  
  	locked += current->mm->locked_vm;

  	if ((locked > lock_limit) && (!capable(CAP_IPC_LOCK))) {
  		/*
  		 * It is possible that the regions requested intersect with
  		 * previously mlocked areas, that part area in "mm->locked_vm"
  		 * should not be counted to new mlock increment count. So check
  		 * and adjust locked count if necessary.
  		 */
  		locked -= count_mm_mlocked_page_nr(current->mm,
  				start, len);
  	}

  
  	/* check against resource limits */
  	if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))

  		error = apply_vma_lock_flags(start, len, flags);

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

  	if (error)
  		return error;
  
  	error = __mm_populate(start, len, 0);
  	if (error)
  		return __mlock_posix_error_return(error);
  	return 0;

  }

  SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
  {
  	return do_mlock(start, len, VM_LOCKED);
  }

  SYSCALL_DEFINE3(mlock2, unsigned long, start, size_t, len, int, flags)
  {

  	vm_flags_t vm_flags = VM_LOCKED;
  
  	if (flags & ~MLOCK_ONFAULT)

  		return -EINVAL;

  	if (flags & MLOCK_ONFAULT)
  		vm_flags |= VM_LOCKONFAULT;
  
  	return do_mlock(start, len, vm_flags);

  }

  SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)

  {
  	int ret;

  	len = PAGE_ALIGN(len + (offset_in_page(start)));

  	start &= PAGE_MASK;

  	if (down_write_killable(&current->mm->mmap_sem))
  		return -EINTR;

  	ret = apply_vma_lock_flags(start, len, 0);

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

  	return ret;
  }

  /*
   * Take the MCL_* flags passed into mlockall (or 0 if called from munlockall)
   * and translate into the appropriate modifications to mm->def_flags and/or the
   * flags for all current VMAs.
   *
   * There are a couple of subtleties with this.  If mlockall() is called multiple
   * times with different flags, the values do not necessarily stack.  If mlockall
   * is called once including the MCL_FUTURE flag and then a second time without
   * it, VM_LOCKED and VM_LOCKONFAULT will be cleared from mm->def_flags.
   */

  static int apply_mlockall_flags(int flags)

  {
  	struct vm_area_struct * vma, * prev = NULL;

  	vm_flags_t to_add = 0;

  	current->mm->def_flags &= VM_LOCKED_CLEAR_MASK;
  	if (flags & MCL_FUTURE) {

  		current->mm->def_flags |= VM_LOCKED;

  		if (flags & MCL_ONFAULT)
  			current->mm->def_flags |= VM_LOCKONFAULT;
  
  		if (!(flags & MCL_CURRENT))
  			goto out;
  	}
  
  	if (flags & MCL_CURRENT) {
  		to_add |= VM_LOCKED;
  		if (flags & MCL_ONFAULT)
  			to_add |= VM_LOCKONFAULT;
  	}

  
  	for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {

  		vm_flags_t newflags;

  		newflags = vma->vm_flags & VM_LOCKED_CLEAR_MASK;
  		newflags |= to_add;

  
  		/* Ignore errors */
  		mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);

  		cond_resched();

  	}
  out:
  	return 0;
  }

  SYSCALL_DEFINE1(mlockall, int, flags)

  {
  	unsigned long lock_limit;

  	int ret;

  	if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE | MCL_ONFAULT)))

  		return -EINVAL;

  	if (!can_do_mlock())

  		return -EPERM;

  	lock_limit = rlimit(RLIMIT_MEMLOCK);

  	lock_limit >>= PAGE_SHIFT;

  	if (down_write_killable(&current->mm->mmap_sem))
  		return -EINTR;

  	ret = -ENOMEM;

  	if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
  	    capable(CAP_IPC_LOCK))

  		ret = apply_mlockall_flags(flags);

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

  	if (!ret && (flags & MCL_CURRENT))
  		mm_populate(0, TASK_SIZE);

  	return ret;
  }

  SYSCALL_DEFINE0(munlockall)

  {
  	int ret;

  	if (down_write_killable(&current->mm->mmap_sem))
  		return -EINTR;

  	ret = apply_mlockall_flags(0);

  	up_write(&current->mm->mmap_sem);
  	return ret;
  }
  
  /*
   * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
   * shm segments) get accounted against the user_struct instead.
   */
  static DEFINE_SPINLOCK(shmlock_user_lock);
  
  int user_shm_lock(size_t size, struct user_struct *user)
  {
  	unsigned long lock_limit, locked;
  	int allowed = 0;
  
  	locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;

  	lock_limit = rlimit(RLIMIT_MEMLOCK);

  	if (lock_limit == RLIM_INFINITY)
  		allowed = 1;

  	lock_limit >>= PAGE_SHIFT;
  	spin_lock(&shmlock_user_lock);

  	if (!allowed &&
  	    locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))

  		goto out;
  	get_uid(user);
  	user->locked_shm += locked;
  	allowed = 1;
  out:
  	spin_unlock(&shmlock_user_lock);
  	return allowed;
  }
  
  void user_shm_unlock(size_t size, struct user_struct *user)
  {
  	spin_lock(&shmlock_user_lock);
  	user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
  	spin_unlock(&shmlock_user_lock);
  	free_uid(user);
  }