text: /*
   * mm/mmap.c
   *
   * Written by obz.
   *
   * Address space accounting code	<alan@lxorguk.ukuu.org.uk>
   */
  
  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  
  #include <linux/kernel.h>
  #include <linux/slab.h>
  #include <linux/backing-dev.h>
  #include <linux/mm.h>
  #include <linux/vmacache.h>
  #include <linux/shm.h>
  #include <linux/mman.h>
  #include <linux/pagemap.h>
  #include <linux/swap.h>
  #include <linux/syscalls.h>
  #include <linux/capability.h>
  #include <linux/init.h>
  #include <linux/file.h>
  #include <linux/fs.h>
  #include <linux/personality.h>
  #include <linux/security.h>
  #include <linux/hugetlb.h>
  #include <linux/shmem_fs.h>
  #include <linux/profile.h>
  #include <linux/export.h>
  #include <linux/mount.h>
  #include <linux/mempolicy.h>
  #include <linux/rmap.h>
  #include <linux/mmu_notifier.h>
  #include <linux/mmdebug.h>
  #include <linux/perf_event.h>
  #include <linux/audit.h>
  #include <linux/khugepaged.h>
  #include <linux/uprobes.h>
  #include <linux/rbtree_augmented.h>
  #include <linux/notifier.h>
  #include <linux/memory.h>
  #include <linux/printk.h>
  #include <linux/userfaultfd_k.h>
  #include <linux/moduleparam.h>
  #include <linux/pkeys.h>
  #include <linux/oom.h>
  
  #include <linux/uaccess.h>
  #include <asm/cacheflush.h>
  #include <asm/tlb.h>
  #include <asm/mmu_context.h>
  
  #include "internal.h"
  
  #ifndef arch_mmap_check
  #define arch_mmap_check(addr, len, flags)	(0)
  #endif
  
  #ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS
  const int mmap_rnd_bits_min = CONFIG_ARCH_MMAP_RND_BITS_MIN;
  const int mmap_rnd_bits_max = CONFIG_ARCH_MMAP_RND_BITS_MAX;
  int mmap_rnd_bits __read_mostly = CONFIG_ARCH_MMAP_RND_BITS;
  #endif
  #ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS
  const int mmap_rnd_compat_bits_min = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MIN;
  const int mmap_rnd_compat_bits_max = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MAX;
  int mmap_rnd_compat_bits __read_mostly = CONFIG_ARCH_MMAP_RND_COMPAT_BITS;
  #endif
  
  static bool ignore_rlimit_data;
  core_param(ignore_rlimit_data, ignore_rlimit_data, bool, 0644);
  
  static void unmap_region(struct mm_struct *mm,
  		struct vm_area_struct *vma, struct vm_area_struct *prev,
  		unsigned long start, unsigned long end);
  
  /* description of effects of mapping type and prot in current implementation.
   * this is due to the limited x86 page protection hardware.  The expected
   * behavior is in parens:
   *
   * map_type	prot
   *		PROT_NONE	PROT_READ	PROT_WRITE	PROT_EXEC
   * MAP_SHARED	r: (no) no	r: (yes) yes	r: (no) yes	r: (no) yes
   *		w: (no) no	w: (no) no	w: (yes) yes	w: (no) no
   *		x: (no) no	x: (no) yes	x: (no) yes	x: (yes) yes
   *
   * MAP_PRIVATE	r: (no) no	r: (yes) yes	r: (no) yes	r: (no) yes
   *		w: (no) no	w: (no) no	w: (copy) copy	w: (no) no
   *		x: (no) no	x: (no) yes	x: (no) yes	x: (yes) yes
   *
   * On arm64, PROT_EXEC has the following behaviour for both MAP_SHARED and
   * MAP_PRIVATE:
   *								r: (no) no
   *								w: (no) no
   *								x: (yes) yes
   */
  pgprot_t protection_map[16] __ro_after_init = {
  	__P000, __P001, __P010, __P011, __P100, __P101, __P110, __P111,
  	__S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111
  };
  
  #ifndef CONFIG_ARCH_HAS_FILTER_PGPROT
  static inline pgprot_t arch_filter_pgprot(pgprot_t prot)
  {
  	return prot;
  }
  #endif
  
  pgprot_t vm_get_page_prot(unsigned long vm_flags)
  {
  	pgprot_t ret = __pgprot(pgprot_val(protection_map[vm_flags &
  				(VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]) |
  			pgprot_val(arch_vm_get_page_prot(vm_flags)));
  
  	return arch_filter_pgprot(ret);
  }
  EXPORT_SYMBOL(vm_get_page_prot);
  
  static pgprot_t vm_pgprot_modify(pgprot_t oldprot, unsigned long vm_flags)
  {
  	return pgprot_modify(oldprot, vm_get_page_prot(vm_flags));
  }
  
  /* Update vma->vm_page_prot to reflect vma->vm_flags. */
  void vma_set_page_prot(struct vm_area_struct *vma)
  {
  	unsigned long vm_flags = vma->vm_flags;
  	pgprot_t vm_page_prot;
  
  	vm_page_prot = vm_pgprot_modify(vma->vm_page_prot, vm_flags);
  	if (vma_wants_writenotify(vma, vm_page_prot)) {
  		vm_flags &= ~VM_SHARED;
  		vm_page_prot = vm_pgprot_modify(vm_page_prot, vm_flags);
  	}
  	/* remove_protection_ptes reads vma->vm_page_prot without mmap_sem */
  	WRITE_ONCE(vma->vm_page_prot, vm_page_prot);
  }
  
  /*
   * Requires inode->i_mapping->i_mmap_rwsem
   */
  static void __remove_shared_vm_struct(struct vm_area_struct *vma,
  		struct file *file, struct address_space *mapping)
  {
  	if (vma->vm_flags & VM_DENYWRITE)
  		atomic_inc(&file_inode(file)->i_writecount);
  	if (vma->vm_flags & VM_SHARED)
  		mapping_unmap_writable(mapping);
  
  	flush_dcache_mmap_lock(mapping);
  	vma_interval_tree_remove(vma, &mapping->i_mmap);
  	flush_dcache_mmap_unlock(mapping);
  }
  
  /*
   * Unlink a file-based vm structure from its interval tree, to hide
   * vma from rmap and vmtruncate before freeing its page tables.
   */
  void unlink_file_vma(struct vm_area_struct *vma)
  {
  	struct file *file = vma->vm_file;
  
  	if (file) {
  		struct address_space *mapping = file->f_mapping;
  		i_mmap_lock_write(mapping);
  		__remove_shared_vm_struct(vma, file, mapping);
  		i_mmap_unlock_write(mapping);
  	}
  }
  
  /*
   * Close a vm structure and free it, returning the next.
   */
  static struct vm_area_struct *remove_vma(struct vm_area_struct *vma)
  {
  	struct vm_area_struct *next = vma->vm_next;
  
  	might_sleep();
  	if (vma->vm_ops && vma->vm_ops->close)
  		vma->vm_ops->close(vma);
  	if (vma->vm_file)
  		fput(vma->vm_file);
  	mpol_put(vma_policy(vma));
  	kmem_cache_free(vm_area_cachep, vma);
  	return next;
  }
  
  static int do_brk(unsigned long addr, unsigned long len, struct list_head *uf);
  
  SYSCALL_DEFINE1(brk, unsigned long, brk)
  {
  	unsigned long retval;
  	unsigned long newbrk, oldbrk;
  	struct mm_struct *mm = current->mm;
  	struct vm_area_struct *next;
  	unsigned long min_brk;
  	bool populate;
  	LIST_HEAD(uf);
  
  	if (down_write_killable(&mm->mmap_sem))
  		return -EINTR;
  
  #ifdef CONFIG_COMPAT_BRK
  	/*
  	 * CONFIG_COMPAT_BRK can still be overridden by setting
  	 * randomize_va_space to 2, which will still cause mm->start_brk
  	 * to be arbitrarily shifted
  	 */
  	if (current->brk_randomized)
  		min_brk = mm->start_brk;
  	else
  		min_brk = mm->end_data;
  #else
  	min_brk = mm->start_brk;
  #endif
  	if (brk < min_brk)
  		goto out;
  
  	/*
  	 * Check against rlimit here. If this check is done later after the test
  	 * of oldbrk with newbrk then it can escape the test and let the data
  	 * segment grow beyond its set limit the in case where the limit is
  	 * not page aligned -Ram Gupta
  	 */
  	if (check_data_rlimit(rlimit(RLIMIT_DATA), brk, mm->start_brk,
  			      mm->end_data, mm->start_data))
  		goto out;
  
  	newbrk = PAGE_ALIGN(brk);
  	oldbrk = PAGE_ALIGN(mm->brk);
  	if (oldbrk == newbrk)
  		goto set_brk;
  
  	/* Always allow shrinking brk. */
  	if (brk <= mm->brk) {
  		if (!do_munmap(mm, newbrk, oldbrk-newbrk, &uf))
  			goto set_brk;
  		goto out;
  	}
  
  	/* Check against existing mmap mappings. */
  	next = find_vma(mm, oldbrk);
  	if (next && newbrk + PAGE_SIZE > vm_start_gap(next))
  		goto out;
  
  	/* Ok, looks good - let it rip. */
  	if (do_brk(oldbrk, newbrk-oldbrk, &uf) < 0)
  		goto out;
  
  set_brk:
  	mm->brk = brk;
  	populate = newbrk > oldbrk && (mm->def_flags & VM_LOCKED) != 0;
  	up_write(&mm->mmap_sem);
  	userfaultfd_unmap_complete(mm, &uf);
  	if (populate)
  		mm_populate(oldbrk, newbrk - oldbrk);
  	return brk;
  
  out:
  	retval = mm->brk;
  	up_write(&mm->mmap_sem);
  	return retval;
  }
  
  static long vma_compute_subtree_gap(struct vm_area_struct *vma)
  {
  	unsigned long max, prev_end, subtree_gap;
  
  	/*
  	 * Note: in the rare case of a VM_GROWSDOWN above a VM_GROWSUP, we
  	 * allow two stack_guard_gaps between them here, and when choosing
  	 * an unmapped area; whereas when expanding we only require one.
  	 * That's a little inconsistent, but keeps the code here simpler.
  	 */
  	max = vm_start_gap(vma);
  	if (vma->vm_prev) {
  		prev_end = vm_end_gap(vma->vm_prev);
  		if (max > prev_end)
  			max -= prev_end;
  		else
  			max = 0;
  	}
  	if (vma->vm_rb.rb_left) {
  		subtree_gap = rb_entry(vma->vm_rb.rb_left,
  				struct vm_area_struct, vm_rb)->rb_subtree_gap;
  		if (subtree_gap > max)
  			max = subtree_gap;
  	}
  	if (vma->vm_rb.rb_right) {
  		subtree_gap = rb_entry(vma->vm_rb.rb_right,
  				struct vm_area_struct, vm_rb)->rb_subtree_gap;
  		if (subtree_gap > max)
  			max = subtree_gap;
  	}
  	return max;
  }
  
  #ifdef CONFIG_DEBUG_VM_RB
  static int browse_rb(struct mm_struct *mm)
  {
  	struct rb_root *root = &mm->mm_rb;
  	int i = 0, j, bug = 0;
  	struct rb_node *nd, *pn = NULL;
  	unsigned long prev = 0, pend = 0;
  
  	for (nd = rb_first(root); nd; nd = rb_next(nd)) {
  		struct vm_area_struct *vma;
  		vma = rb_entry(nd, struct vm_area_struct, vm_rb);
  		if (vma->vm_start < prev) {
  			pr_emerg("vm_start %lx < prev %lx\n",
  				  vma->vm_start, prev);
  			bug = 1;
  		}
  		if (vma->vm_start < pend) {
  			pr_emerg("vm_start %lx < pend %lx\n",
  				  vma->vm_start, pend);
  			bug = 1;
  		}
  		if (vma->vm_start > vma->vm_end) {
  			pr_emerg("vm_start %lx > vm_end %lx\n",
  				  vma->vm_start, vma->vm_end);
  			bug = 1;
  		}
  		spin_lock(&mm->page_table_lock);
  		if (vma->rb_subtree_gap != vma_compute_subtree_gap(vma)) {
  			pr_emerg("free gap %lx, correct %lx\n",
  			       vma->rb_subtree_gap,
  			       vma_compute_subtree_gap(vma));
  			bug = 1;
  		}
  		spin_unlock(&mm->page_table_lock);
  		i++;
  		pn = nd;
  		prev = vma->vm_start;
  		pend = vma->vm_end;
  	}
  	j = 0;
  	for (nd = pn; nd; nd = rb_prev(nd))
  		j++;
  	if (i != j) {
  		pr_emerg("backwards %d, forwards %d\n", j, i);
  		bug = 1;
  	}
  	return bug ? -1 : i;
  }
  
  static void validate_mm_rb(struct rb_root *root, struct vm_area_struct *ignore)
  {
  	struct rb_node *nd;
  
  	for (nd = rb_first(root); nd; nd = rb_next(nd)) {
  		struct vm_area_struct *vma;
  		vma = rb_entry(nd, struct vm_area_struct, vm_rb);
  		VM_BUG_ON_VMA(vma != ignore &&
  			vma->rb_subtree_gap != vma_compute_subtree_gap(vma),
  			vma);
  	}
  }
  
  static void validate_mm(struct mm_struct *mm)
  {
  	int bug = 0;
  	int i = 0;
  	unsigned long highest_address = 0;
  	struct vm_area_struct *vma = mm->mmap;
  
  	while (vma) {
  		struct anon_vma *anon_vma = vma->anon_vma;
  		struct anon_vma_chain *avc;
  
  		if (anon_vma) {
  			anon_vma_lock_read(anon_vma);
  			list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
  				anon_vma_interval_tree_verify(avc);
  			anon_vma_unlock_read(anon_vma);
  		}
  
  		highest_address = vm_end_gap(vma);
  		vma = vma->vm_next;
  		i++;
  	}
  	if (i != mm->map_count) {
  		pr_emerg("map_count %d vm_next %d\n", mm->map_count, i);
  		bug = 1;
  	}
  	if (highest_address != mm->highest_vm_end) {
  		pr_emerg("mm->highest_vm_end %lx, found %lx\n",
  			  mm->highest_vm_end, highest_address);
  		bug = 1;
  	}
  	i = browse_rb(mm);
  	if (i != mm->map_count) {
  		if (i != -1)
  			pr_emerg("map_count %d rb %d\n", mm->map_count, i);
  		bug = 1;
  	}
  	VM_BUG_ON_MM(bug, mm);
  }
  #else
  #define validate_mm_rb(root, ignore) do { } while (0)
  #define validate_mm(mm) do { } while (0)
  #endif
  
  RB_DECLARE_CALLBACKS(static, vma_gap_callbacks, struct vm_area_struct, vm_rb,
  		     unsigned long, rb_subtree_gap, vma_compute_subtree_gap)
  
  /*
   * Update augmented rbtree rb_subtree_gap values after vma->vm_start or
   * vma->vm_prev->vm_end values changed, without modifying the vma's position
   * in the rbtree.
   */
  static void vma_gap_update(struct vm_area_struct *vma)
  {
  	/*
  	 * As it turns out, RB_DECLARE_CALLBACKS() already created a callback
  	 * function that does exacltly what we want.
  	 */
  	vma_gap_callbacks_propagate(&vma->vm_rb, NULL);
  }
  
  static inline void vma_rb_insert(struct vm_area_struct *vma,
  				 struct rb_root *root)
  {
  	/* All rb_subtree_gap values must be consistent prior to insertion */
  	validate_mm_rb(root, NULL);
  
  	rb_insert_augmented(&vma->vm_rb, root, &vma_gap_callbacks);
  }
  
  static void __vma_rb_erase(struct vm_area_struct *vma, struct rb_root *root)
  {
  	/*
  	 * Note rb_erase_augmented is a fairly large inline function,
  	 * so make sure we instantiate it only once with our desired
  	 * augmented rbtree callbacks.
  	 */
  	rb_erase_augmented(&vma->vm_rb, root, &vma_gap_callbacks);
  }
  
  static __always_inline void vma_rb_erase_ignore(struct vm_area_struct *vma,
  						struct rb_root *root,
  						struct vm_area_struct *ignore)
  {
  	/*
  	 * All rb_subtree_gap values must be consistent prior to erase,
  	 * with the possible exception of the "next" vma being erased if
  	 * next->vm_start was reduced.
  	 */
  	validate_mm_rb(root, ignore);
  
  	__vma_rb_erase(vma, root);
  }
  
  static __always_inline void vma_rb_erase(struct vm_area_struct *vma,
  					 struct rb_root *root)
  {
  	/*
  	 * All rb_subtree_gap values must be consistent prior to erase,
  	 * with the possible exception of the vma being erased.
  	 */
  	validate_mm_rb(root, vma);
  
  	__vma_rb_erase(vma, root);
  }
  
  /*
   * vma has some anon_vma assigned, and is already inserted on that
   * anon_vma's interval trees.
   *
   * Before updating the vma's vm_start / vm_end / vm_pgoff fields, the
   * vma must be removed from the anon_vma's interval trees using
   * anon_vma_interval_tree_pre_update_vma().
   *
   * After the update, the vma will be reinserted using
   * anon_vma_interval_tree_post_update_vma().
   *
   * The entire update must be protected by exclusive mmap_sem and by
   * the root anon_vma's mutex.
   */
  static inline void
  anon_vma_interval_tree_pre_update_vma(struct vm_area_struct *vma)
  {
  	struct anon_vma_chain *avc;
  
  	list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
  		anon_vma_interval_tree_remove(avc, &avc->anon_vma->rb_root);
  }
  
  static inline void
  anon_vma_interval_tree_post_update_vma(struct vm_area_struct *vma)
  {
  	struct anon_vma_chain *avc;
  
  	list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
  		anon_vma_interval_tree_insert(avc, &avc->anon_vma->rb_root);
  }
  
  static int find_vma_links(struct mm_struct *mm, unsigned long addr,
  		unsigned long end, struct vm_area_struct **pprev,
  		struct rb_node ***rb_link, struct rb_node **rb_parent)
  {
  	struct rb_node **__rb_link, *__rb_parent, *rb_prev;
  
  	__rb_link = &mm->mm_rb.rb_node;
  	rb_prev = __rb_parent = NULL;
  
  	while (*__rb_link) {
  		struct vm_area_struct *vma_tmp;
  
  		__rb_parent = *__rb_link;
  		vma_tmp = rb_entry(__rb_parent, struct vm_area_struct, vm_rb);
  
  		if (vma_tmp->vm_end > addr) {
  			/* Fail if an existing vma overlaps the area */
  			if (vma_tmp->vm_start < end)
  				return -ENOMEM;
  			__rb_link = &__rb_parent->rb_left;
  		} else {
  			rb_prev = __rb_parent;
  			__rb_link = &__rb_parent->rb_right;
  		}
  	}
  
  	*pprev = NULL;
  	if (rb_prev)
  		*pprev = rb_entry(rb_prev, struct vm_area_struct, vm_rb);
  	*rb_link = __rb_link;
  	*rb_parent = __rb_parent;
  	return 0;
  }
  
  static unsigned long count_vma_pages_range(struct mm_struct *mm,
  		unsigned long addr, unsigned long end)
  {
  	unsigned long nr_pages = 0;
  	struct vm_area_struct *vma;
  
  	/* Find first overlaping mapping */
  	vma = find_vma_intersection(mm, addr, end);
  	if (!vma)
  		return 0;
  
  	nr_pages = (min(end, vma->vm_end) -
  		max(addr, vma->vm_start)) >> PAGE_SHIFT;
  
  	/* Iterate over the rest of the overlaps */
  	for (vma = vma->vm_next; vma; vma = vma->vm_next) {
  		unsigned long overlap_len;
  
  		if (vma->vm_start > end)
  			break;
  
  		overlap_len = min(end, vma->vm_end) - vma->vm_start;
  		nr_pages += overlap_len >> PAGE_SHIFT;
  	}
  
  	return nr_pages;
  }
  
  void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma,
  		struct rb_node **rb_link, struct rb_node *rb_parent)
  {
  	/* Update tracking information for the gap following the new vma. */
  	if (vma->vm_next)
  		vma_gap_update(vma->vm_next);
  	else
  		mm->highest_vm_end = vm_end_gap(vma);
  
  	/*
  	 * vma->vm_prev wasn't known when we followed the rbtree to find the
  	 * correct insertion point for that vma. As a result, we could not
  	 * update the vma vm_rb parents rb_subtree_gap values on the way down.
  	 * So, we first insert the vma with a zero rb_subtree_gap value
  	 * (to be consistent with what we did on the way down), and then
  	 * immediately update the gap to the correct value. Finally we
  	 * rebalance the rbtree after all augmented values have been set.
  	 */
  	rb_link_node(&vma->vm_rb, rb_parent, rb_link);
  	vma->rb_subtree_gap = 0;
  	vma_gap_update(vma);
  	vma_rb_insert(vma, &mm->mm_rb);
  }
  
  static void __vma_link_file(struct vm_area_struct *vma)
  {
  	struct file *file;
  
  	file = vma->vm_file;
  	if (file) {
  		struct address_space *mapping = file->f_mapping;
  
  		if (vma->vm_flags & VM_DENYWRITE)
  			atomic_dec(&file_inode(file)->i_writecount);
  		if (vma->vm_flags & VM_SHARED)
  			atomic_inc(&mapping->i_mmap_writable);
  
  		flush_dcache_mmap_lock(mapping);
  		vma_interval_tree_insert(vma, &mapping->i_mmap);
  		flush_dcache_mmap_unlock(mapping);
  	}
  }
  
  static void
  __vma_link(struct mm_struct *mm, struct vm_area_struct *vma,
  	struct vm_area_struct *prev, struct rb_node **rb_link,
  	struct rb_node *rb_parent)
  {
  	__vma_link_list(mm, vma, prev, rb_parent);
  	__vma_link_rb(mm, vma, rb_link, rb_parent);
  }
  
  static void vma_link(struct mm_struct *mm, struct vm_area_struct *vma,
  			struct vm_area_struct *prev, struct rb_node **rb_link,
  			struct rb_node *rb_parent)
  {
  	struct address_space *mapping = NULL;
  
  	if (vma->vm_file) {
  		mapping = vma->vm_file->f_mapping;
  		i_mmap_lock_write(mapping);
  	}
  
  	__vma_link(mm, vma, prev, rb_link, rb_parent);
  	__vma_link_file(vma);
  
  	if (mapping)
  		i_mmap_unlock_write(mapping);
  
  	mm->map_count++;
  	validate_mm(mm);
  }
  
  /*
   * Helper for vma_adjust() in the split_vma insert case: insert a vma into the
   * mm's list and rbtree.  It has already been inserted into the interval tree.
   */
  static void __insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
  {
  	struct vm_area_struct *prev;
  	struct rb_node **rb_link, *rb_parent;
  
  	if (find_vma_links(mm, vma->vm_start, vma->vm_end,
  			   &prev, &rb_link, &rb_parent))
  		BUG();
  	__vma_link(mm, vma, prev, rb_link, rb_parent);
  	mm->map_count++;
  }
  
  static __always_inline void __vma_unlink_common(struct mm_struct *mm,
  						struct vm_area_struct *vma,
  						struct vm_area_struct *prev,
  						bool has_prev,
  						struct vm_area_struct *ignore)
  {
  	struct vm_area_struct *next;
  
  	vma_rb_erase_ignore(vma, &mm->mm_rb, ignore);
  	next = vma->vm_next;
  	if (has_prev)
  		prev->vm_next = next;
  	else {
  		prev = vma->vm_prev;
  		if (prev)
  			prev->vm_next = next;
  		else
  			mm->mmap = next;
  	}
  	if (next)
  		next->vm_prev = prev;
  
  	/* Kill the cache */
  	vmacache_invalidate(mm);
  }
  
  static inline void __vma_unlink_prev(struct mm_struct *mm,
  				     struct vm_area_struct *vma,
  				     struct vm_area_struct *prev)
  {
  	__vma_unlink_common(mm, vma, prev, true, vma);
  }
  
  /*
   * We cannot adjust vm_start, vm_end, vm_pgoff fields of a vma that
   * is already present in an i_mmap tree without adjusting the tree.
   * The following helper function should be used when such adjustments
   * are necessary.  The "insert" vma (if any) is to be inserted
   * before we drop the necessary locks.
   */
  int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
  	unsigned long end, pgoff_t pgoff, struct vm_area_struct *insert,
  	struct vm_area_struct *expand)
  {
  	struct mm_struct *mm = vma->vm_mm;
  	struct vm_area_struct *next = vma->vm_next, *orig_vma = vma;
  	struct address_space *mapping = NULL;
  	struct rb_root_cached *root = NULL;
  	struct anon_vma *anon_vma = NULL;
  	struct file *file = vma->vm_file;
  	bool start_changed = false, end_changed = false;
  	long adjust_next = 0;
  	int remove_next = 0;
  
  	if (next && !insert) {
  		struct vm_area_struct *exporter = NULL, *importer = NULL;
  
  		if (end >= next->vm_end) {
  			/*
  			 * vma expands, overlapping all the next, and
  			 * perhaps the one after too (mprotect case 6).
  			 * The only other cases that gets here are
  			 * case 1, case 7 and case 8.
  			 */
  			if (next == expand) {
  				/*
  				 * The only case where we don't expand "vma"
  				 * and we expand "next" instead is case 8.
  				 */
  				VM_WARN_ON(end != next->vm_end);
  				/*
  				 * remove_next == 3 means we're
  				 * removing "vma" and that to do so we
  				 * swapped "vma" and "next".
  				 */
  				remove_next = 3;
  				VM_WARN_ON(file != next->vm_file);
  				swap(vma, next);
  			} else {
  				VM_WARN_ON(expand != vma);
  				/*
  				 * case 1, 6, 7, remove_next == 2 is case 6,
  				 * remove_next == 1 is case 1 or 7.
  				 */
  				remove_next = 1 + (end > next->vm_end);
  				VM_WARN_ON(remove_next == 2 &&
  					   end != next->vm_next->vm_end);
  				VM_WARN_ON(remove_next == 1 &&
  					   end != next->vm_end);
  				/* trim end to next, for case 6 first pass */
  				end = next->vm_end;
  			}
  
  			exporter = next;
  			importer = vma;
  
  			/*
  			 * If next doesn't have anon_vma, import from vma after
  			 * next, if the vma overlaps with it.
  			 */
  			if (remove_next == 2 && !next->anon_vma)
  				exporter = next->vm_next;
  
  		} else if (end > next->vm_start) {
  			/*
  			 * vma expands, overlapping part of the next:
  			 * mprotect case 5 shifting the boundary up.
  			 */
  			adjust_next = (end - next->vm_start) >> PAGE_SHIFT;
  			exporter = next;
  			importer = vma;
  			VM_WARN_ON(expand != importer);
  		} else if (end < vma->vm_end) {
  			/*
  			 * vma shrinks, and !insert tells it's not
  			 * split_vma inserting another: so it must be
  			 * mprotect case 4 shifting the boundary down.
  			 */
  			adjust_next = -((vma->vm_end - end) >> PAGE_SHIFT);
  			exporter = vma;
  			importer = next;
  			VM_WARN_ON(expand != importer);
  		}
  
  		/*
  		 * Easily overlooked: when mprotect shifts the boundary,
  		 * make sure the expanding vma has anon_vma set if the
  		 * shrinking vma had, to cover any anon pages imported.
  		 */
  		if (exporter && exporter->anon_vma && !importer->anon_vma) {
  			int error;
  
  			importer->anon_vma = exporter->anon_vma;
  			error = anon_vma_clone(importer, exporter);
  			if (error)
  				return error;
  		}
  	}
  again:
  	vma_adjust_trans_huge(orig_vma, start, end, adjust_next);
  
  	if (file) {
  		mapping = file->f_mapping;
  		root = &mapping->i_mmap;
  		uprobe_munmap(vma, vma->vm_start, vma->vm_end);
  
  		if (adjust_next)
  			uprobe_munmap(next, next->vm_start, next->vm_end);
  
  		i_mmap_lock_write(mapping);
  		if (insert) {
  			/*
  			 * Put into interval tree now, so instantiated pages
  			 * are visible to arm/parisc __flush_dcache_page
  			 * throughout; but we cannot insert into address
  			 * space until vma start or end is updated.
  			 */
  			__vma_link_file(insert);
  		}
  	}
  
  	anon_vma = vma->anon_vma;
  	if (!anon_vma && adjust_next)
  		anon_vma = next->anon_vma;
  	if (anon_vma) {
  		VM_WARN_ON(adjust_next && next->anon_vma &&
  			   anon_vma != next->anon_vma);
  		anon_vma_lock_write(anon_vma);
  		anon_vma_interval_tree_pre_update_vma(vma);
  		if (adjust_next)
  			anon_vma_interval_tree_pre_update_vma(next);
  	}
  
  	if (root) {
  		flush_dcache_mmap_lock(mapping);
  		vma_interval_tree_remove(vma, root);
  		if (adjust_next)
  			vma_interval_tree_remove(next, root);
  	}
  
  	if (start != vma->vm_start) {
  		vma->vm_start = start;
  		start_changed = true;
  	}
  	if (end != vma->vm_end) {
  		vma->vm_end = end;
  		end_changed = true;
  	}
  	vma->vm_pgoff = pgoff;
  	if (adjust_next) {
  		next->vm_start += adjust_next << PAGE_SHIFT;
  		next->vm_pgoff += adjust_next;
  	}
  
  	if (root) {
  		if (adjust_next)
  			vma_interval_tree_insert(next, root);
  		vma_interval_tree_insert(vma, root);
  		flush_dcache_mmap_unlock(mapping);
  	}
  
  	if (remove_next) {
  		/*
  		 * vma_merge has merged next into vma, and needs
  		 * us to remove next before dropping the locks.
  		 */
  		if (remove_next != 3)
  			__vma_unlink_prev(mm, next, vma);
  		else
  			/*
  			 * vma is not before next if they've been
  			 * swapped.
  			 *
  			 * pre-swap() next->vm_start was reduced so
  			 * tell validate_mm_rb to ignore pre-swap()
  			 * "next" (which is stored in post-swap()
  			 * "vma").
  			 */
  			__vma_unlink_common(mm, next, NULL, false, vma);
  		if (file)
  			__remove_shared_vm_struct(next, file, mapping);
  	} else if (insert) {
  		/*
  		 * split_vma has split insert from vma, and needs
  		 * us to insert it before dropping the locks
  		 * (it may either follow vma or precede it).
  		 */
  		__insert_vm_struct(mm, insert);
  	} else {
  		if (start_changed)
  			vma_gap_update(vma);
  		if (end_changed) {
  			if (!next)
  				mm->highest_vm_end = vm_end_gap(vma);
  			else if (!adjust_next)
  				vma_gap_update(next);
  		}
  	}
  
  	if (anon_vma) {
  		anon_vma_interval_tree_post_update_vma(vma);
  		if (adjust_next)
  			anon_vma_interval_tree_post_update_vma(next);
  		anon_vma_unlock_write(anon_vma);
  	}
  	if (mapping)
  		i_mmap_unlock_write(mapping);
  
  	if (root) {
  		uprobe_mmap(vma);
  
  		if (adjust_next)
  			uprobe_mmap(next);
  	}
  
  	if (remove_next) {
  		if (file) {
  			uprobe_munmap(next, next->vm_start, next->vm_end);
  			fput(file);
  		}
  		if (next->anon_vma)
  			anon_vma_merge(vma, next);
  		mm->map_count--;
  		mpol_put(vma_policy(next));
  		kmem_cache_free(vm_area_cachep, next);
  		/*
  		 * In mprotect's case 6 (see comments on vma_merge),
  		 * we must remove another next too. It would clutter
  		 * up the code too much to do both in one go.
  		 */
  		if (remove_next != 3) {
  			/*
  			 * If "next" was removed and vma->vm_end was
  			 * expanded (up) over it, in turn
  			 * "next->vm_prev->vm_end" changed and the
  			 * "vma->vm_next" gap must be updated.
  			 */
  			next = vma->vm_next;
  		} else {
  			/*
  			 * For the scope of the comment "next" and
  			 * "vma" considered pre-swap(): if "vma" was
  			 * removed, next->vm_start was expanded (down)
  			 * over it and the "next" gap must be updated.
  			 * Because of the swap() the post-swap() "vma"
  			 * actually points to pre-swap() "next"
  			 * (post-swap() "next" as opposed is now a
  			 * dangling pointer).
  			 */
  			next = vma;
  		}
  		if (remove_next == 2) {
  			remove_next = 1;
  			end = next->vm_end;
  			goto again;
  		}
  		else if (next)
  			vma_gap_update(next);
  		else {
  			/*
  			 * If remove_next == 2 we obviously can't
  			 * reach this path.
  			 *
  			 * If remove_next == 3 we can't reach this
  			 * path because pre-swap() next is always not
  			 * NULL. pre-swap() "next" is not being
  			 * removed and its next->vm_end is not altered
  			 * (and furthermore "end" already matches
  			 * next->vm_end in remove_next == 3).
  			 *
  			 * We reach this only in the remove_next == 1
  			 * case if the "next" vma that was removed was
  			 * the highest vma of the mm. However in such
  			 * case next->vm_end == "end" and the extended
  			 * "vma" has vma->vm_end == next->vm_end so
  			 * mm->highest_vm_end doesn't need any update
  			 * in remove_next == 1 case.
  			 */
  			VM_WARN_ON(mm->highest_vm_end != vm_end_gap(vma));
  		}
  	}
  	if (insert && file)
  		uprobe_mmap(insert);
  
  	validate_mm(mm);
  
  	return 0;
  }
  
  /*
   * If the vma has a ->close operation then the driver probably needs to release
   * per-vma resources, so we don't attempt to merge those.
   */
  static inline int is_mergeable_vma(struct vm_area_struct *vma,
  				struct file *file, unsigned long vm_flags,
  				struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
  {
  	/*
  	 * VM_SOFTDIRTY should not prevent from VMA merging, if we
  	 * match the flags but dirty bit -- the caller should mark
  	 * merged VMA as dirty. If dirty bit won't be excluded from
  	 * comparison, we increase pressue on the memory system forcing
  	 * the kernel to generate new VMAs when old one could be
  	 * extended instead.
  	 */
  	if ((vma->vm_flags ^ vm_flags) & ~VM_SOFTDIRTY)
  		return 0;
  	if (vma->vm_file != file)
  		return 0;
  	if (vma->vm_ops && vma->vm_ops->close)
  		return 0;
  	if (!is_mergeable_vm_userfaultfd_ctx(vma, vm_userfaultfd_ctx))
  		return 0;
  	return 1;
  }
  
  static inline int is_mergeable_anon_vma(struct anon_vma *anon_vma1,
  					struct anon_vma *anon_vma2,
  					struct vm_area_struct *vma)
  {
  	/*
  	 * The list_is_singular() test is to avoid merging VMA cloned from
  	 * parents. This can improve scalability caused by anon_vma lock.
  	 */
  	if ((!anon_vma1 || !anon_vma2) && (!vma ||
  		list_is_singular(&vma->anon_vma_chain)))
  		return 1;
  	return anon_vma1 == anon_vma2;
  }
  
  /*
   * Return true if we can merge this (vm_flags,anon_vma,file,vm_pgoff)
   * in front of (at a lower virtual address and file offset than) the vma.
   *
   * We cannot merge two vmas if they have differently assigned (non-NULL)
   * anon_vmas, nor if same anon_vma is assigned but offsets incompatible.
   *
   * We don't check here for the merged mmap wrapping around the end of pagecache
   * indices (16TB on ia32) because do_mmap_pgoff() does not permit mmap's which
   * wrap, nor mmaps which cover the final page at index -1UL.
   */
  static int
  can_vma_merge_before(struct vm_area_struct *vma, unsigned long vm_flags,
  		     struct anon_vma *anon_vma, struct file *file,
  		     pgoff_t vm_pgoff,
  		     struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
  {
  	if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx) &&
  	    is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
  		if (vma->vm_pgoff == vm_pgoff)
  			return 1;
  	}
  	return 0;
  }
  
  /*
   * Return true if we can merge this (vm_flags,anon_vma,file,vm_pgoff)
   * beyond (at a higher virtual address and file offset than) the vma.
   *
   * We cannot merge two vmas if they have differently assigned (non-NULL)
   * anon_vmas, nor if same anon_vma is assigned but offsets incompatible.
   */
  static int
  can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
  		    struct anon_vma *anon_vma, struct file *file,
  		    pgoff_t vm_pgoff,
  		    struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
  {
  	if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx) &&
  	    is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
  		pgoff_t vm_pglen;
  		vm_pglen = vma_pages(vma);
  		if (vma->vm_pgoff + vm_pglen == vm_pgoff)
  			return 1;
  	}
  	return 0;
  }
  
  /*
   * Given a mapping request (addr,end,vm_flags,file,pgoff), figure out
   * whether that can be merged with its predecessor or its successor.
   * Or both (it neatly fills a hole).
   *
   * In most cases - when called for mmap, brk or mremap - [addr,end) is
   * certain not to be mapped by the time vma_merge is called; but when
   * called for mprotect, it is certain to be already mapped (either at
   * an offset within prev, or at the start of next), and the flags of
   * this area are about to be changed to vm_flags - and the no-change
   * case has already been eliminated.
   *
   * The following mprotect cases have to be considered, where AAAA is
   * the area passed down from mprotect_fixup, never extending beyond one
   * vma, PPPPPP is the prev vma specified, and NNNNNN the next vma after:
   *
   *     AAAA             AAAA                AAAA          AAAA
   *    PPPPPPNNNNNN    PPPPPPNNNNNN    PPPPPPNNNNNN    PPPPNNNNXXXX
   *    cannot merge    might become    might become    might become
   *                    PPNNNNNNNNNN    PPPPPPPPPPNN    PPPPPPPPPPPP 6 or
   *    mmap, brk or    case 4 below    case 5 below    PPPPPPPPXXXX 7 or
   *    mremap move:                                    PPPPXXXXXXXX 8
   *        AAAA
   *    PPPP    NNNN    PPPPPPPPPPPP    PPPPPPPPNNNN    PPPPNNNNNNNN
   *    might become    case 1 below    case 2 below    case 3 below
   *
   * It is important for case 8 that the the vma NNNN overlapping the
   * region AAAA is never going to extended over XXXX. Instead XXXX must
   * be extended in region AAAA and NNNN must be removed. This way in
   * all cases where vma_merge succeeds, the moment vma_adjust drops the
   * rmap_locks, the properties of the merged vma will be already
   * correct for the whole merged range. Some of those properties like
   * vm_page_prot/vm_flags may be accessed by rmap_walks and they must
   * be correct for the whole merged range immediately after the
   * rmap_locks are released. Otherwise if XXXX would be removed and
   * NNNN would be extended over the XXXX range, remove_migration_ptes
   * or other rmap walkers (if working on addresses beyond the "end"
   * parameter) may establish ptes with the wrong permissions of NNNN
   * instead of the right permissions of XXXX.
   */
  struct vm_area_struct *vma_merge(struct mm_struct *mm,
  			struct vm_area_struct *prev, unsigned long addr,
  			unsigned long end, unsigned long vm_flags,
  			struct anon_vma *anon_vma, struct file *file,
  			pgoff_t pgoff, struct mempolicy *policy,
  			struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
  {
  	pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
  	struct vm_area_struct *area, *next;
  	int err;
  
  	/*
  	 * We later require that vma->vm_flags == vm_flags,
  	 * so this tests vma->vm_flags & VM_SPECIAL, too.
  	 */
  	if (vm_flags & VM_SPECIAL)
  		return NULL;
  
  	if (prev)
  		next = prev->vm_next;
  	else
  		next = mm->mmap;
  	area = next;
  	if (area && area->vm_end == end)		/* cases 6, 7, 8 */
  		next = next->vm_next;
  
  	/* verify some invariant that must be enforced by the caller */
  	VM_WARN_ON(prev && addr <= prev->vm_start);
  	VM_WARN_ON(area && end > area->vm_end);
  	VM_WARN_ON(addr >= end);
  
  	/*
  	 * Can it merge with the predecessor?
  	 */
  	if (prev && prev->vm_end == addr &&
  			mpol_equal(vma_policy(prev), policy) &&
  			can_vma_merge_after(prev, vm_flags,
  					    anon_vma, file, pgoff,
  					    vm_userfaultfd_ctx)) {
  		/*
  		 * OK, it can.  Can we now merge in the successor as well?
  		 */
  		if (next && end == next->vm_start &&
  				mpol_equal(policy, vma_policy(next)) &&
  				can_vma_merge_before(next, vm_flags,
  						     anon_vma, file,
  						     pgoff+pglen,
  						     vm_userfaultfd_ctx) &&
  				is_mergeable_anon_vma(prev->anon_vma,
  						      next->anon_vma, NULL)) {
  							/* cases 1, 6 */
  			err = __vma_adjust(prev, prev->vm_start,
  					 next->vm_end, prev->vm_pgoff, NULL,
  					 prev);
  		} else					/* cases 2, 5, 7 */
  			err = __vma_adjust(prev, prev->vm_start,
  					 end, prev->vm_pgoff, NULL, prev);
  		if (err)
  			return NULL;
  		khugepaged_enter_vma_merge(prev, vm_flags);
  		return prev;
  	}
  
  	/*
  	 * Can this new request be merged in front of next?
  	 */
  	if (next && end == next->vm_start &&
  			mpol_equal(policy, vma_policy(next)) &&
  			can_vma_merge_before(next, vm_flags,
  					     anon_vma, file, pgoff+pglen,
  					     vm_userfaultfd_ctx)) {
  		if (prev && addr < prev->vm_end)	/* case 4 */
  			err = __vma_adjust(prev, prev->vm_start,
  					 addr, prev->vm_pgoff, NULL, next);
  		else {					/* cases 3, 8 */
  			err = __vma_adjust(area, addr, next->vm_end,
  					 next->vm_pgoff - pglen, NULL, next);
  			/*
  			 * In case 3 area is already equal to next and
  			 * this is a noop, but in case 8 "area" has
  			 * been removed and next was expanded over it.
  			 */
  			area = next;
  		}
  		if (err)
  			return NULL;
  		khugepaged_enter_vma_merge(area, vm_flags);
  		return area;
  	}
  
  	return NULL;
  }
  
  /*
   * Rough compatbility check to quickly see if it's even worth looking
   * at sharing an anon_vma.
   *
   * They need to have the same vm_file, and the flags can only differ
   * in things that mprotect may change.
   *
   * NOTE! The fact that we share an anon_vma doesn't _have_ to mean that
   * we can merge the two vma's. For example, we refuse to merge a vma if
   * there is a vm_ops->close() function, because that indicates that the
   * driver is doing some kind of reference counting. But that doesn't
   * really matter for the anon_vma sharing case.
   */
  static int anon_vma_compatible(struct vm_area_struct *a, struct vm_area_struct *b)
  {
  	return a->vm_end == b->vm_start &&
  		mpol_equal(vma_policy(a), vma_policy(b)) &&
  		a->vm_file == b->vm_file &&
  		!((a->vm_flags ^ b->vm_flags) & ~(VM_READ|VM_WRITE|VM_EXEC|VM_SOFTDIRTY)) &&
  		b->vm_pgoff == a->vm_pgoff + ((b->vm_start - a->vm_start) >> PAGE_SHIFT);
  }
  
  /*
   * Do some basic sanity checking to see if we can re-use the anon_vma
   * from 'old'. The 'a'/'b' vma's are in VM order - one of them will be
   * the same as 'old', the other will be the new one that is trying
   * to share the anon_vma.
   *
   * NOTE! This runs with mm_sem held for reading, so it is possible that
   * the anon_vma of 'old' is concurrently in the process of being set up
   * by another page fault trying to merge _that_. But that's ok: if it
   * is being set up, that automatically means that it will be a singleton
   * acceptable for merging, so we can do all of this optimistically. But
   * we do that READ_ONCE() to make sure that we never re-load the pointer.
   *
   * IOW: that the "list_is_singular()" test on the anon_vma_chain only
   * matters for the 'stable anon_vma' case (ie the thing we want to avoid
   * is to return an anon_vma that is "complex" due to having gone through
   * a fork).
   *
   * We also make sure that the two vma's are compatible (adjacent,
   * and with the same memory policies). That's all stable, even with just
   * a read lock on the mm_sem.
   */
  static struct anon_vma *reusable_anon_vma(struct vm_area_struct *old, struct vm_area_struct *a, struct vm_area_struct *b)
  {
  	if (anon_vma_compatible(a, b)) {
  		struct anon_vma *anon_vma = READ_ONCE(old->anon_vma);
  
  		if (anon_vma && list_is_singular(&old->anon_vma_chain))
  			return anon_vma;
  	}
  	return NULL;
  }
  
  /*
   * find_mergeable_anon_vma is used by anon_vma_prepare, to check
   * neighbouring vmas for a suitable anon_vma, before it goes off
   * to allocate a new anon_vma.  It checks because a repetitive
   * sequence of mprotects and faults may otherwise lead to distinct
   * anon_vmas being allocated, preventing vma merge in subsequent
   * mprotect.
   */
  struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *vma)
  {
  	struct anon_vma *anon_vma;
  	struct vm_area_struct *near;
  
  	near = vma->vm_next;
  	if (!near)
  		goto try_prev;
  
  	anon_vma = reusable_anon_vma(near, vma, near);
  	if (anon_vma)
  		return anon_vma;
  try_prev:
  	near = vma->vm_prev;
  	if (!near)
  		goto none;
  
  	anon_vma = reusable_anon_vma(near, near, vma);
  	if (anon_vma)
  		return anon_vma;
  none:
  	/*
  	 * There's no absolute need to look only at touching neighbours:
  	 * we could search further afield for "compatible" anon_vmas.
  	 * But it would probably just be a waste of time searching,
  	 * or lead to too many vmas hanging off the same anon_vma.
  	 * We're trying to allow mprotect remerging later on,
  	 * not trying to minimize memory used for anon_vmas.
  	 */
  	return NULL;
  }
  
  /*
   * If a hint addr is less than mmap_min_addr change hint to be as
   * low as possible but still greater than mmap_min_addr
   */
  static inline unsigned long round_hint_to_min(unsigned long hint)
  {
  	hint &= PAGE_MASK;
  	if (((void *)hint != NULL) &&
  	    (hint < mmap_min_addr))
  		return PAGE_ALIGN(mmap_min_addr);
  	return hint;
  }
  
  static inline int mlock_future_check(struct mm_struct *mm,
  				     unsigned long flags,
  				     unsigned long len)
  {
  	unsigned long locked, lock_limit;
  
  	/*  mlock MCL_FUTURE? */
  	if (flags & VM_LOCKED) {
  		locked = len >> PAGE_SHIFT;
  		locked += mm->locked_vm;
  		lock_limit = rlimit(RLIMIT_MEMLOCK);
  		lock_limit >>= PAGE_SHIFT;
  		if (locked > lock_limit && !capable(CAP_IPC_LOCK))
  			return -EAGAIN;
  	}
  	return 0;
  }
  
  static inline u64 file_mmap_size_max(struct file *file, struct inode *inode)
  {
  	if (S_ISREG(inode->i_mode))
  		return MAX_LFS_FILESIZE;
  
  	if (S_ISBLK(inode->i_mode))
  		return MAX_LFS_FILESIZE;
  
  	/* Special "we do even unsigned file positions" case */
  	if (file->f_mode & FMODE_UNSIGNED_OFFSET)
  		return 0;
  
  	/* Yes, random drivers might want more. But I'm tired of buggy drivers */
  	return ULONG_MAX;
  }
  
  static inline bool file_mmap_ok(struct file *file, struct inode *inode,
  				unsigned long pgoff, unsigned long len)
  {
  	u64 maxsize = file_mmap_size_max(file, inode);
  
  	if (maxsize && len > maxsize)
  		return false;
  	maxsize -= len;
  	if (pgoff > maxsize >> PAGE_SHIFT)
  		return false;
  	return true;
  }
  
  /*
   * The caller must hold down_write(&current->mm->mmap_sem).
   */
  unsigned long do_mmap(struct file *file, unsigned long addr,
  			unsigned long len, unsigned long prot,
  			unsigned long flags, vm_flags_t vm_flags,
  			unsigned long pgoff, unsigned long *populate,
  			struct list_head *uf)
  {
  	struct mm_struct *mm = current->mm;
  	int pkey = 0;
  
  	*populate = 0;
  
  	if (!len)
  		return -EINVAL;
  
  	/*
  	 * Does the application expect PROT_READ to imply PROT_EXEC?
  	 *
  	 * (the exception is when the underlying filesystem is noexec
  	 *  mounted, in which case we dont add PROT_EXEC.)
  	 */
  	if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
  		if (!(file && path_noexec(&file->f_path)))
  			prot |= PROT_EXEC;
  
  	/* force arch specific MAP_FIXED handling in get_unmapped_area */
  	if (flags & MAP_FIXED_NOREPLACE)
  		flags |= MAP_FIXED;
  
  	if (!(flags & MAP_FIXED))
  		addr = round_hint_to_min(addr);
  
  	/* Careful about overflows.. */
  	len = PAGE_ALIGN(len);
  	if (!len)
  		return -ENOMEM;
  
  	/* offset overflow? */
  	if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
  		return -EOVERFLOW;
  
  	/* Too many mappings? */
  	if (mm->map_count > sysctl_max_map_count)
  		return -ENOMEM;
  
  	/* Obtain the address to map to. we verify (or select) it and ensure
  	 * that it represents a valid section of the address space.
  	 */
  	addr = get_unmapped_area(file, addr, len, pgoff, flags);
  	if (offset_in_page(addr))
  		return addr;
  
  	if (flags & MAP_FIXED_NOREPLACE) {
  		struct vm_area_struct *vma = find_vma(mm, addr);
  
  		if (vma && vma->vm_start <= addr)
  			return -EEXIST;
  	}
  
  	if (prot == PROT_EXEC) {
  		pkey = execute_only_pkey(mm);
  		if (pkey < 0)
  			pkey = 0;
  	}
  
  	/* Do simple checking here so the lower-level routines won't have
  	 * to. we assume access permissions have been handled by the open
  	 * of the memory object, so we don't do any here.
  	 */
  	vm_flags |= calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
  			mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
  
  	if (flags & MAP_LOCKED)
  		if (!can_do_mlock())
  			return -EPERM;
  
  	if (mlock_future_check(mm, vm_flags, len))
  		return -EAGAIN;
  
  	if (file) {
  		struct inode *inode = file_inode(file);
  		unsigned long flags_mask;
  
  		if (!file_mmap_ok(file, inode, pgoff, len))
  			return -EOVERFLOW;
  
  		flags_mask = LEGACY_MAP_MASK | file->f_op->mmap_supported_flags;
  
  		switch (flags & MAP_TYPE) {
  		case MAP_SHARED:
  			/*
  			 * Force use of MAP_SHARED_VALIDATE with non-legacy
  			 * flags. E.g. MAP_SYNC is dangerous to use with
  			 * MAP_SHARED as you don't know which consistency model
  			 * you will get. We silently ignore unsupported flags
  			 * with MAP_SHARED to preserve backward compatibility.
  			 */
  			flags &= LEGACY_MAP_MASK;
  			/* fall through */
  		case MAP_SHARED_VALIDATE:
  			if (flags & ~flags_mask)
  				return -EOPNOTSUPP;
  			if ((prot&PROT_WRITE) && !(file->f_mode&FMODE_WRITE))
  				return -EACCES;
  
  			/*
  			 * Make sure we don't allow writing to an append-only
  			 * file..
  			 */
  			if (IS_APPEND(inode) && (file->f_mode & FMODE_WRITE))
  				return -EACCES;
  
  			/*
  			 * Make sure there are no mandatory locks on the file.
  			 */
  			if (locks_verify_locked(file))
  				return -EAGAIN;
  
  			vm_flags |= VM_SHARED | VM_MAYSHARE;
  			if (!(file->f_mode & FMODE_WRITE))
  				vm_flags &= ~(VM_MAYWRITE | VM_SHARED);
  
  			/* fall through */
  		case MAP_PRIVATE:
  			if (!(file->f_mode & FMODE_READ))
  				return -EACCES;
  			if (path_noexec(&file->f_path)) {
  				if (vm_flags & VM_EXEC)
  					return -EPERM;
  				vm_flags &= ~VM_MAYEXEC;
  			}
  
  			if (!file->f_op->mmap)
  				return -ENODEV;
  			if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
  				return -EINVAL;
  			break;
  
  		default:
  			return -EINVAL;
  		}
  	} else {
  		switch (flags & MAP_TYPE) {
  		case MAP_SHARED:
  			if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
  				return -EINVAL;
  			/*
  			 * Ignore pgoff.
  			 */
  			pgoff = 0;
  			vm_flags |= VM_SHARED | VM_MAYSHARE;
  			break;
  		case MAP_PRIVATE:
  			/*
  			 * Set pgoff according to addr for anon_vma.
  			 */
  			pgoff = addr >> PAGE_SHIFT;
  			break;
  		default:
  			return -EINVAL;
  		}
  	}
  
  	/*
  	 * Set 'VM_NORESERVE' if we should not account for the
  	 * memory use of this mapping.
  	 */
  	if (flags & MAP_NORESERVE) {
  		/* We honor MAP_NORESERVE if allowed to overcommit */
  		if (sysctl_overcommit_memory != OVERCOMMIT_NEVER)
  			vm_flags |= VM_NORESERVE;
  
  		/* hugetlb applies strict overcommit unless MAP_NORESERVE */
  		if (file && is_file_hugepages(file))
  			vm_flags |= VM_NORESERVE;
  	}
  
  	addr = mmap_region(file, addr, len, vm_flags, pgoff, uf);
  	if (!IS_ERR_VALUE(addr) &&
  	    ((vm_flags & VM_LOCKED) ||
  	     (flags & (MAP_POPULATE | MAP_NONBLOCK)) == MAP_POPULATE))
  		*populate = len;
  	return addr;
  }
  
  unsigned long ksys_mmap_pgoff(unsigned long addr, unsigned long len,
  			      unsigned long prot, unsigned long flags,
  			      unsigned long fd, unsigned long pgoff)
  {
  	struct file *file = NULL;
  	unsigned long retval;
  
  	if (!(flags & MAP_ANONYMOUS)) {
  		audit_mmap_fd(fd, flags);
  		file = fget(fd);
  		if (!file)
  			return -EBADF;
  		if (is_file_hugepages(file))
  			len = ALIGN(len, huge_page_size(hstate_file(file)));
  		retval = -EINVAL;
  		if (unlikely(flags & MAP_HUGETLB && !is_file_hugepages(file)))
  			goto out_fput;
  	} else if (flags & MAP_HUGETLB) {
  		struct user_struct *user = NULL;
  		struct hstate *hs;
  
  		hs = hstate_sizelog((flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK);
  		if (!hs)
  			return -EINVAL;
  
  		len = ALIGN(len, huge_page_size(hs));
  		/*
  		 * VM_NORESERVE is used because the reservations will be
  		 * taken when vm_ops->mmap() is called
  		 * A dummy user value is used because we are not locking
  		 * memory so no accounting is necessary
  		 */
  		file = hugetlb_file_setup(HUGETLB_ANON_FILE, len,
  				VM_NORESERVE,
  				&user, HUGETLB_ANONHUGE_INODE,
  				(flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK);
  		if (IS_ERR(file))
  			return PTR_ERR(file);
  	}
  
  	flags &= ~(MAP_EXECUTABLE | MAP_DENYWRITE);
  
  	retval = vm_mmap_pgoff(file, addr, len, prot, flags, pgoff);
  out_fput:
  	if (file)
  		fput(file);
  	return retval;
  }
  
  SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len,
  		unsigned long, prot, unsigned long, flags,
  		unsigned long, fd, unsigned long, pgoff)
  {
  	return ksys_mmap_pgoff(addr, len, prot, flags, fd, pgoff);
  }
  
  #ifdef __ARCH_WANT_SYS_OLD_MMAP
  struct mmap_arg_struct {
  	unsigned long addr;
  	unsigned long len;
  	unsigned long prot;
  	unsigned long flags;
  	unsigned long fd;
  	unsigned long offset;
  };
  
  SYSCALL_DEFINE1(old_mmap, struct mmap_arg_struct __user *, arg)
  {
  	struct mmap_arg_struct a;
  
  	if (copy_from_user(&a, arg, sizeof(a)))
  		return -EFAULT;
  	if (offset_in_page(a.offset))
  		return -EINVAL;
  
  	return ksys_mmap_pgoff(a.addr, a.len, a.prot, a.flags, a.fd,
  			       a.offset >> PAGE_SHIFT);
  }
  #endif /* __ARCH_WANT_SYS_OLD_MMAP */
  
  /*
   * Some shared mappigns will want the pages marked read-only
   * to track write events. If so, we'll downgrade vm_page_prot
   * to the private version (using protection_map[] without the
   * VM_SHARED bit).
   */
  int vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot)
  {
  	vm_flags_t vm_flags = vma->vm_flags;
  	const struct vm_operations_struct *vm_ops = vma->vm_ops;
  
  	/* If it was private or non-writable, the write bit is already clear */
  	if ((vm_flags & (VM_WRITE|VM_SHARED)) != ((VM_WRITE|VM_SHARED)))
  		return 0;
  
  	/* The backer wishes to know when pages are first written to? */
  	if (vm_ops && (vm_ops->page_mkwrite || vm_ops->pfn_mkwrite))
  		return 1;
  
  	/* The open routine did something to the protections that pgprot_modify
  	 * won't preserve? */
  	if (pgprot_val(vm_page_prot) !=
  	    pgprot_val(vm_pgprot_modify(vm_page_prot, vm_flags)))
  		return 0;
  
  	/* Do we need to track softdirty? */
  	if (IS_ENABLED(CONFIG_MEM_SOFT_DIRTY) && !(vm_flags & VM_SOFTDIRTY))
  		return 1;
  
  	/* Specialty mapping? */
  	if (vm_flags & VM_PFNMAP)
  		return 0;
  
  	/* Can the mapping track the dirty pages? */
  	return vma->vm_file && vma->vm_file->f_mapping &&
  		mapping_cap_account_dirty(vma->vm_file->f_mapping);
  }
  
  /*
   * We account for memory if it's a private writeable mapping,
   * not hugepages and VM_NORESERVE wasn't set.
   */
  static inline int accountable_mapping(struct file *file, vm_flags_t vm_flags)
  {
  	/*
  	 * hugetlb has its own accounting separate from the core VM
  	 * VM_HUGETLB may not be set yet so we cannot check for that flag.
  	 */
  	if (file && is_file_hugepages(file))
  		return 0;
  
  	return (vm_flags & (VM_NORESERVE | VM_SHARED | VM_WRITE)) == VM_WRITE;
  }
  
  unsigned long mmap_region(struct file *file, unsigned long addr,
  		unsigned long len, vm_flags_t vm_flags, unsigned long pgoff,
  		struct list_head *uf)
  {
  	struct mm_struct *mm = current->mm;
  	struct vm_area_struct *vma, *prev;
  	int error;
  	struct rb_node **rb_link, *rb_parent;
  	unsigned long charged = 0;
  
  	/* Check against address space limit. */
  	if (!may_expand_vm(mm, vm_flags, len >> PAGE_SHIFT)) {
  		unsigned long nr_pages;
  
  		/*
  		 * MAP_FIXED may remove pages of mappings that intersects with
  		 * requested mapping. Account for the pages it would unmap.
  		 */
  		nr_pages = count_vma_pages_range(mm, addr, addr + len);
  
  		if (!may_expand_vm(mm, vm_flags,
  					(len >> PAGE_SHIFT) - nr_pages))
  			return -ENOMEM;
  	}
  
  	/* Clear old maps */
  	while (find_vma_links(mm, addr, addr + len, &prev, &rb_link,
  			      &rb_parent)) {
  		if (do_munmap(mm, addr, len, uf))
  			return -ENOMEM;
  	}
  
  	/*
  	 * Private writable mapping: check memory availability
  	 */
  	if (accountable_mapping(file, vm_flags)) {
  		charged = len >> PAGE_SHIFT;
  		if (security_vm_enough_memory_mm(mm, charged))
  			return -ENOMEM;
  		vm_flags |= VM_ACCOUNT;
  	}
  
  	/*
  	 * Can we just expand an old mapping?
  	 */
  	vma = vma_merge(mm, prev, addr, addr + len, vm_flags,
  			NULL, file, pgoff, NULL, NULL_VM_UFFD_CTX);
  	if (vma)
  		goto out;
  
  	/*
  	 * Determine the object being mapped and call the appropriate
  	 * specific mapper. the address has already been validated, but
  	 * not unmapped, but the maps are removed from the list.
  	 */
  	vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
  	if (!vma) {
  		error = -ENOMEM;
  		goto unacct_error;
  	}
  
  	vma->vm_mm = mm;
  	vma->vm_start = addr;
  	vma->vm_end = addr + len;
  	vma->vm_flags = vm_flags;
  	vma->vm_page_prot = vm_get_page_prot(vm_flags);
  	vma->vm_pgoff = pgoff;
  	INIT_LIST_HEAD(&vma->anon_vma_chain);
  
  	if (file) {
  		if (vm_flags & VM_DENYWRITE) {
  			error = deny_write_access(file);
  			if (error)
  				goto free_vma;
  		}
  		if (vm_flags & VM_SHARED) {
  			error = mapping_map_writable(file->f_mapping);
  			if (error)
  				goto allow_write_and_free_vma;
  		}
  
  		/* ->mmap() can change vma->vm_file, but must guarantee that
  		 * vma_link() below can deny write-access if VM_DENYWRITE is set
  		 * and map writably if VM_SHARED is set. This usually means the
  		 * new file must not have been exposed to user-space, yet.
  		 */
  		vma->vm_file = get_file(file);
  		error = call_mmap(file, vma);
  		if (error)
  			goto unmap_and_free_vma;
  
  		/* Can addr have changed??
  		 *
  		 * Answer: Yes, several device drivers can do it in their
  		 *         f_op->mmap method. -DaveM
  		 * Bug: If addr is changed, prev, rb_link, rb_parent should
  		 *      be updated for vma_link()
  		 */
  		WARN_ON_ONCE(addr != vma->vm_start);
  
  		addr = vma->vm_start;
  		vm_flags = vma->vm_flags;
  	} else if (vm_flags & VM_SHARED) {
  		error = shmem_zero_setup(vma);
  		if (error)
  			goto free_vma;
  	}
  
  	vma_link(mm, vma, prev, rb_link, rb_parent);
  	/* Once vma denies write, undo our temporary denial count */
  	if (file) {
  		if (vm_flags & VM_SHARED)
  			mapping_unmap_writable(file->f_mapping);
  		if (vm_flags & VM_DENYWRITE)
  			allow_write_access(file);
  	}
  	file = vma->vm_file;
  out:
  	perf_event_mmap(vma);
  
  	vm_stat_account(mm, vm_flags, len >> PAGE_SHIFT);
  	if (vm_flags & VM_LOCKED) {
  		if (!((vm_flags & VM_SPECIAL) || is_vm_hugetlb_page(vma) ||
  					vma == get_gate_vma(current->mm)))
  			mm->locked_vm += (len >> PAGE_SHIFT);
  		else
  			vma->vm_flags &= VM_LOCKED_CLEAR_MASK;
  	}
  
  	if (file)
  		uprobe_mmap(vma);
  
  	/*
  	 * New (or expanded) vma always get soft dirty status.
  	 * Otherwise user-space soft-dirty page tracker won't
  	 * be able to distinguish situation when vma area unmapped,
  	 * then new mapped in-place (which must be aimed as
  	 * a completely new data area).
  	 */
  	vma->vm_flags |= VM_SOFTDIRTY;
  
  	vma_set_page_prot(vma);
  
  	return addr;
  
  unmap_and_free_vma:
  	vma->vm_file = NULL;
  	fput(file);
  
  	/* Undo any partial mapping done by a device driver. */
  	unmap_region(mm, vma, prev, vma->vm_start, vma->vm_end);
  	charged = 0;
  	if (vm_flags & VM_SHARED)
  		mapping_unmap_writable(file->f_mapping);
  allow_write_and_free_vma:
  	if (vm_flags & VM_DENYWRITE)
  		allow_write_access(file);
  free_vma:
  	kmem_cache_free(vm_area_cachep, vma);
  unacct_error:
  	if (charged)
  		vm_unacct_memory(charged);
  	return error;
  }
  
  unsigned long unmapped_area(struct vm_unmapped_area_info *info)
  {
  	/*
  	 * We implement the search by looking for an rbtree node that
  	 * immediately follows a suitable gap. That is,
  	 * - gap_start = vma->vm_prev->vm_end <= info->high_limit - length;
  	 * - gap_end   = vma->vm_start        >= info->low_limit  + length;
  	 * - gap_end - gap_start >= length
  	 */
  
  	struct mm_struct *mm = current->mm;
  	struct vm_area_struct *vma;
  	unsigned long length, low_limit, high_limit, gap_start, gap_end;
  
  	/* Adjust search length to account for worst case alignment overhead */
  	length = info->length + info->align_mask;
  	if (length < info->length)
  		return -ENOMEM;
  
  	/* Adjust search limits by the desired length */
  	if (info->high_limit < length)
  		return -ENOMEM;
  	high_limit = info->high_limit - length;
  
  	if (info->low_limit > high_limit)
  		return -ENOMEM;
  	low_limit = info->low_limit + length;
  
  	/* Check if rbtree root looks promising */
  	if (RB_EMPTY_ROOT(&mm->mm_rb))
  		goto check_highest;
  	vma = rb_entry(mm->mm_rb.rb_node, struct vm_area_struct, vm_rb);
  	if (vma->rb_subtree_gap < length)
  		goto check_highest;
  
  	while (true) {
  		/* Visit left subtree if it looks promising */
  		gap_end = vm_start_gap(vma);
  		if (gap_end >= low_limit && vma->vm_rb.rb_left) {
  			struct vm_area_struct *left =
  				rb_entry(vma->vm_rb.rb_left,
  					 struct vm_area_struct, vm_rb);
  			if (left->rb_subtree_gap >= length) {
  				vma = left;
  				continue;
  			}
  		}
  
  		gap_start = vma->vm_prev ? vm_end_gap(vma->vm_prev) : 0;
  check_current:
  		/* Check if current node has a suitable gap */
  		if (gap_start > high_limit)
  			return -ENOMEM;
  		if (gap_end >= low_limit &&
  		    gap_end > gap_start && gap_end - gap_start >= length)
  			goto found;
  
  		/* Visit right subtree if it looks promising */
  		if (vma->vm_rb.rb_right) {
  			struct vm_area_struct *right =
  				rb_entry(vma->vm_rb.rb_right,
  					 struct vm_area_struct, vm_rb);
  			if (right->rb_subtree_gap >= length) {
  				vma = right;
  				continue;
  			}
  		}
  
  		/* Go back up the rbtree to find next candidate node */
  		while (true) {
  			struct rb_node *prev = &vma->vm_rb;
  			if (!rb_parent(prev))
  				goto check_highest;
  			vma = rb_entry(rb_parent(prev),
  				       struct vm_area_struct, vm_rb);
  			if (prev == vma->vm_rb.rb_left) {
  				gap_start = vm_end_gap(vma->vm_prev);
  				gap_end = vm_start_gap(vma);
  				goto check_current;
  			}
  		}
  	}
  
  check_highest:
  	/* Check highest gap, which does not precede any rbtree node */
  	gap_start = mm->highest_vm_end;
  	gap_end = ULONG_MAX;  /* Only for VM_BUG_ON below */
  	if (gap_start > high_limit)
  		return -ENOMEM;
  
  found:
  	/* We found a suitable gap. Clip it with the original low_limit. */
  	if (gap_start < info->low_limit)
  		gap_start = info->low_limit;
  
  	/* Adjust gap address to the desired alignment */
  	gap_start += (info->align_offset - gap_start) & info->align_mask;
  
  	VM_BUG_ON(gap_start + info->length > info->high_limit);
  	VM_BUG_ON(gap_start + info->length > gap_end);
  	return gap_start;
  }
  
  unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
  {
  	struct mm_struct *mm = current->mm;
  	struct vm_area_struct *vma;
  	unsigned long length, low_limit, high_limit, gap_start, gap_end;
  
  	/* Adjust search length to account for worst case alignment overhead */
  	length = info->length + info->align_mask;
  	if (length < info->length)
  		return -ENOMEM;
  
  	/*
  	 * Adjust search limits by the desired length.
  	 * See implementation comment at top of unmapped_area().
  	 */
  	gap_end = info->high_limit;
  	if (gap_end < length)
  		return -ENOMEM;
  	high_limit = gap_end - length;
  
  	if (info->low_limit > high_limit)
  		return -ENOMEM;
  	low_limit = info->low_limit + length;
  
  	/* Check highest gap, which does not precede any rbtree node */
  	gap_start = mm->highest_vm_end;
  	if (gap_start <= high_limit)
  		goto found_highest;
  
  	/* Check if rbtree root looks promising */
  	if (RB_EMPTY_ROOT(&mm->mm_rb))
  		return -ENOMEM;
  	vma = rb_entry(mm->mm_rb.rb_node, struct vm_area_struct, vm_rb);
  	if (vma->rb_subtree_gap < length)
  		return -ENOMEM;
  
  	while (true) {
  		/* Visit right subtree if it looks promising */
  		gap_start = vma->vm_prev ? vm_end_gap(vma->vm_prev) : 0;
  		if (gap_start <= high_limit && vma->vm_rb.rb_right) {
  			struct vm_area_struct *right =
  				rb_entry(vma->vm_rb.rb_right,
  					 struct vm_area_struct, vm_rb);
  			if (right->rb_subtree_gap >= length) {
  				vma = right;
  				continue;
  			}
  		}
  
  check_current:
  		/* Check if current node has a suitable gap */
  		gap_end = vm_start_gap(vma);
  		if (gap_end < low_limit)
  			return -ENOMEM;
  		if (gap_start <= high_limit &&
  		    gap_end > gap_start && gap_end - gap_start >= length)
  			goto found;
  
  		/* Visit left subtree if it looks promising */
  		if (vma->vm_rb.rb_left) {
  			struct vm_area_struct *left =
  				rb_entry(vma->vm_rb.rb_left,
  					 struct vm_area_struct, vm_rb);
  			if (left->rb_subtree_gap >= length) {
  				vma = left;
  				continue;
  			}
  		}
  
  		/* Go back up the rbtree to find next candidate node */
  		while (true) {
  			struct rb_node *prev = &vma->vm_rb;
  			if (!rb_parent(prev))
  				return -ENOMEM;
  			vma = rb_entry(rb_parent(prev),
  				       struct vm_area_struct, vm_rb);
  			if (prev == vma->vm_rb.rb_right) {
  				gap_start = vma->vm_prev ?
  					vm_end_gap(vma->vm_prev) : 0;
  				goto check_current;
  			}
  		}
  	}
  
  found:
  	/* We found a suitable gap. Clip it with the original high_limit. */
  	if (gap_end > info->high_limit)
  		gap_end = info->high_limit;
  
  found_highest:
  	/* Compute highest gap address at the desired alignment */
  	gap_end -= info->length;
  	gap_end -= (gap_end - info->align_offset) & info->align_mask;
  
  	VM_BUG_ON(gap_end < info->low_limit);
  	VM_BUG_ON(gap_end < gap_start);
  	return gap_end;
  }
  
  /* Get an address range which is currently unmapped.
   * For shmat() with addr=0.
   *
   * Ugly calling convention alert:
   * Return value with the low bits set means error value,
   * ie
   *	if (ret & ~PAGE_MASK)
   *		error = ret;
   *
   * This function "knows" that -ENOMEM has the bits set.
   */
  #ifndef HAVE_ARCH_UNMAPPED_AREA
  unsigned long
  arch_get_unmapped_area(struct file *filp, unsigned long addr,
  		unsigned long len, unsigned long pgoff, unsigned long flags)
  {
  	struct mm_struct *mm = current->mm;
  	struct vm_area_struct *vma, *prev;
  	struct vm_unmapped_area_info info;
  
  	if (len > TASK_SIZE - mmap_min_addr)
  		return -ENOMEM;
  
  	if (flags & MAP_FIXED)
  		return addr;
  
  	if (addr) {
  		addr = PAGE_ALIGN(addr);
  		vma = find_vma_prev(mm, addr, &prev);
  		if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
  		    (!vma || addr + len <= vm_start_gap(vma)) &&
  		    (!prev || addr >= vm_end_gap(prev)))
  			return addr;
  	}
  
  	info.flags = 0;
  	info.length = len;
  	info.low_limit = mm->mmap_base;
  	info.high_limit = TASK_SIZE;
  	info.align_mask = 0;
  	return vm_unmapped_area(&info);
  }
  #endif
  
  /*
   * This mmap-allocator allocates new areas top-down from below the
   * stack's low limit (the base):
   */
  #ifndef HAVE_ARCH_UNMAPPED_AREA_TOPDOWN
  unsigned long
  arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
  			  const unsigned long len, const unsigned long pgoff,
  			  const unsigned long flags)
  {
  	struct vm_area_struct *vma, *prev;
  	struct mm_struct *mm = current->mm;
  	unsigned long addr = addr0;
  	struct vm_unmapped_area_info info;
  
  	/* requested length too big for entire address space */
  	if (len > TASK_SIZE - mmap_min_addr)
  		return -ENOMEM;
  
  	if (flags & MAP_FIXED)
  		return addr;
  
  	/* requesting a specific address */
  	if (addr) {
  		addr = PAGE_ALIGN(addr);
  		vma = find_vma_prev(mm, addr, &prev);
  		if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
  				(!vma || addr + len <= vm_start_gap(vma)) &&
  				(!prev || addr >= vm_end_gap(prev)))
  			return addr;
  	}
  
  	info.flags = VM_UNMAPPED_AREA_TOPDOWN;
  	info.length = len;
  	info.low_limit = max(PAGE_SIZE, mmap_min_addr);
  	info.high_limit = mm->mmap_base;
  	info.align_mask = 0;
  	addr = vm_unmapped_area(&info);
  
  	/*
  	 * A failed mmap() very likely causes application failure,
  	 * so fall back to the bottom-up function here. This scenario
  	 * can happen with large stack limits and large mmap()
  	 * allocations.
  	 */
  	if (offset_in_page(addr)) {
  		VM_BUG_ON(addr != -ENOMEM);
  		info.flags = 0;
  		info.low_limit = TASK_UNMAPPED_BASE;
  		info.high_limit = TASK_SIZE;
  		addr = vm_unmapped_area(&info);
  	}
  
  	return addr;
  }
  #endif
  
  unsigned long
  get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
  		unsigned long pgoff, unsigned long flags)
  {
  	unsigned long (*get_area)(struct file *, unsigned long,
  				  unsigned long, unsigned long, unsigned long);
  
  	unsigned long error = arch_mmap_check(addr, len, flags);
  	if (error)
  		return error;
  
  	/* Careful about overflows.. */
  	if (len > TASK_SIZE)
  		return -ENOMEM;
  
  	get_area = current->mm->get_unmapped_area;
  	if (file) {
  		if (file->f_op->get_unmapped_area)
  			get_area = file->f_op->get_unmapped_area;
  	} else if (flags & MAP_SHARED) {
  		/*
  		 * mmap_region() will call shmem_zero_setup() to create a file,
  		 * so use shmem's get_unmapped_area in case it can be huge.
  		 * do_mmap_pgoff() will clear pgoff, so match alignment.
  		 */
  		pgoff = 0;
  		get_area = shmem_get_unmapped_area;
  	}
  
  	addr = get_area(file, addr, len, pgoff, flags);
  	if (IS_ERR_VALUE(addr))
  		return addr;
  
  	if (addr > TASK_SIZE - len)
  		return -ENOMEM;
  	if (offset_in_page(addr))
  		return -EINVAL;
  
  	error = security_mmap_addr(addr);
  	return error ? error : addr;
  }
  
  EXPORT_SYMBOL(get_unmapped_area);
  
  /* Look up the first VMA which satisfies  addr < vm_end,  NULL if none. */
  struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
  {
  	struct rb_node *rb_node;
  	struct vm_area_struct *vma;
  
  	/* Check the cache first. */
  	vma = vmacache_find(mm, addr);
  	if (likely(vma))
  		return vma;
  
  	rb_node = mm->mm_rb.rb_node;
  
  	while (rb_node) {
  		struct vm_area_struct *tmp;
  
  		tmp = rb_entry(rb_node, struct vm_area_struct, vm_rb);
  
  		if (tmp->vm_end > addr) {
  			vma = tmp;
  			if (tmp->vm_start <= addr)
  				break;
  			rb_node = rb_node->rb_left;
  		} else
  			rb_node = rb_node->rb_right;
  	}
  
  	if (vma)
  		vmacache_update(addr, vma);
  	return vma;
  }
  
  EXPORT_SYMBOL(find_vma);
  
  /*
   * Same as find_vma, but also return a pointer to the previous VMA in *pprev.
   */
  struct vm_area_struct *
  find_vma_prev(struct mm_struct *mm, unsigned long addr,
  			struct vm_area_struct **pprev)
  {
  	struct vm_area_struct *vma;
  
  	vma = find_vma(mm, addr);
  	if (vma) {
  		*pprev = vma->vm_prev;
  	} else {
  		struct rb_node *rb_node = mm->mm_rb.rb_node;
  		*pprev = NULL;
  		while (rb_node) {
  			*pprev = rb_entry(rb_node, struct vm_area_struct, vm_rb);
  			rb_node = rb_node->rb_right;
  		}
  	}
  	return vma;
  }
  
  /*
   * Verify that the stack growth is acceptable and
   * update accounting. This is shared with both the
   * grow-up and grow-down cases.
   */
  static int acct_stack_growth(struct vm_area_struct *vma,
  			     unsigned long size, unsigned long grow)
  {
  	struct mm_struct *mm = vma->vm_mm;
  	unsigned long new_start;
  
  	/* address space limit tests */
  	if (!may_expand_vm(mm, vma->vm_flags, grow))
  		return -ENOMEM;
  
  	/* Stack limit test */
  	if (size > rlimit(RLIMIT_STACK))
  		return -ENOMEM;
  
  	/* mlock limit tests */
  	if (vma->vm_flags & VM_LOCKED) {
  		unsigned long locked;
  		unsigned long limit;
  		locked = mm->locked_vm + grow;
  		limit = rlimit(RLIMIT_MEMLOCK);
  		limit >>= PAGE_SHIFT;
  		if (locked > limit && !capable(CAP_IPC_LOCK))
  			return -ENOMEM;
  	}
  
  	/* Check to ensure the stack will not grow into a hugetlb-only region */
  	new_start = (vma->vm_flags & VM_GROWSUP) ? vma->vm_start :
  			vma->vm_end - size;
  	if (is_hugepage_only_range(vma->vm_mm, new_start, size))
  		return -EFAULT;
  
  	/*
  	 * Overcommit..  This must be the final test, as it will
  	 * update security statistics.
  	 */
  	if (security_vm_enough_memory_mm(mm, grow))
  		return -ENOMEM;
  
  	return 0;
  }
  
  #if defined(CONFIG_STACK_GROWSUP) || defined(CONFIG_IA64)
  /*
   * PA-RISC uses this for its stack; IA64 for its Register Backing Store.
   * vma is the last one with address > vma->vm_end.  Have to extend vma.
   */
  int expand_upwards(struct vm_area_struct *vma, unsigned long address)
  {
  	struct mm_struct *mm = vma->vm_mm;
  	struct vm_area_struct *next;
  	unsigned long gap_addr;
  	int error = 0;
  
  	if (!(vma->vm_flags & VM_GROWSUP))
  		return -EFAULT;
  
  	/* Guard against exceeding limits of the address space. */
  	address &= PAGE_MASK;
  	if (address >= (TASK_SIZE & PAGE_MASK))
  		return -ENOMEM;
  	address += PAGE_SIZE;
  
  	/* Enforce stack_guard_gap */
  	gap_addr = address + stack_guard_gap;
  
  	/* Guard against overflow */
  	if (gap_addr < address || gap_addr > TASK_SIZE)
  		gap_addr = TASK_SIZE;
  
  	next = vma->vm_next;
  	if (next && next->vm_start < gap_addr &&
  			(next->vm_flags & (VM_WRITE|VM_READ|VM_EXEC))) {
  		if (!(next->vm_flags & VM_GROWSUP))
  			return -ENOMEM;
  		/* Check that both stack segments have the same anon_vma? */
  	}
  
  	/* We must make sure the anon_vma is allocated. */
  	if (unlikely(anon_vma_prepare(vma)))
  		return -ENOMEM;
  
  	/*
  	 * vma->vm_start/vm_end cannot change under us because the caller
  	 * is required to hold the mmap_sem in read mode.  We need the
  	 * anon_vma lock to serialize against concurrent expand_stacks.
  	 */
  	anon_vma_lock_write(vma->anon_vma);
  
  	/* Somebody else might have raced and expanded it already */
  	if (address > vma->vm_end) {
  		unsigned long size, grow;
  
  		size = address - vma->vm_start;
  		grow = (address - vma->vm_end) >> PAGE_SHIFT;
  
  		error = -ENOMEM;
  		if (vma->vm_pgoff + (size >> PAGE_SHIFT) >= vma->vm_pgoff) {
  			error = acct_stack_growth(vma, size, grow);
  			if (!error) {
  				/*
  				 * vma_gap_update() doesn't support concurrent
  				 * updates, but we only hold a shared mmap_sem
  				 * lock here, so we need to protect against
  				 * concurrent vma expansions.
  				 * anon_vma_lock_write() doesn't help here, as
  				 * we don't guarantee that all growable vmas
  				 * in a mm share the same root anon vma.
  				 * So, we reuse mm->page_table_lock to guard
  				 * against concurrent vma expansions.
  				 */
  				spin_lock(&mm->page_table_lock);
  				if (vma->vm_flags & VM_LOCKED)
  					mm->locked_vm += grow;
  				vm_stat_account(mm, vma->vm_flags, grow);
  				anon_vma_interval_tree_pre_update_vma(vma);
  				vma->vm_end = address;
  				anon_vma_interval_tree_post_update_vma(vma);
  				if (vma->vm_next)
  					vma_gap_update(vma->vm_next);
  				else
  					mm->highest_vm_end = vm_end_gap(vma);
  				spin_unlock(&mm->page_table_lock);
  
  				perf_event_mmap(vma);
  			}
  		}
  	}
  	anon_vma_unlock_write(vma->anon_vma);
  	khugepaged_enter_vma_merge(vma, vma->vm_flags);
  	validate_mm(mm);
  	return error;
  }
  #endif /* CONFIG_STACK_GROWSUP || CONFIG_IA64 */
  
  /*
   * vma is the first one with address < vma->vm_start.  Have to extend vma.
   */
  int expand_downwards(struct vm_area_struct *vma,
  				   unsigned long address)
  {
  	struct mm_struct *mm = vma->vm_mm;
  	struct vm_area_struct *prev;
  	int error;
  
  	address &= PAGE_MASK;
  	error = security_mmap_addr(address);
  	if (error)
  		return error;
  
  	/* Enforce stack_guard_gap */
  	prev = vma->vm_prev;
  	/* Check that both stack segments have the same anon_vma? */
  	if (prev && !(prev->vm_flags & VM_GROWSDOWN) &&
  			(prev->vm_flags & (VM_WRITE|VM_READ|VM_EXEC))) {
  		if (address - prev->vm_end < stack_guard_gap)
  			return -ENOMEM;
  	}
  
  	/* We must make sure the anon_vma is allocated. */
  	if (unlikely(anon_vma_prepare(vma)))
  		return -ENOMEM;
  
  	/*
  	 * vma->vm_start/vm_end cannot change under us because the caller
  	 * is required to hold the mmap_sem in read mode.  We need the
  	 * anon_vma lock to serialize against concurrent expand_stacks.
  	 */
  	anon_vma_lock_write(vma->anon_vma);
  
  	/* Somebody else might have raced and expanded it already */
  	if (address < vma->vm_start) {
  		unsigned long size, grow;
  
  		size = vma->vm_end - address;
  		grow = (vma->vm_start - address) >> PAGE_SHIFT;
  
  		error = -ENOMEM;
  		if (grow <= vma->vm_pgoff) {
  			error = acct_stack_growth(vma, size, grow);
  			if (!error) {
  				/*
  				 * vma_gap_update() doesn't support concurrent
  				 * updates, but we only hold a shared mmap_sem
  				 * lock here, so we need to protect against
  				 * concurrent vma expansions.
  				 * anon_vma_lock_write() doesn't help here, as
  				 * we don't guarantee that all growable vmas
  				 * in a mm share the same root anon vma.
  				 * So, we reuse mm->page_table_lock to guard
  				 * against concurrent vma expansions.
  				 */
  				spin_lock(&mm->page_table_lock);
  				if (vma->vm_flags & VM_LOCKED)
  					mm->locked_vm += grow;
  				vm_stat_account(mm, vma->vm_flags, grow);
  				anon_vma_interval_tree_pre_update_vma(vma);
  				vma->vm_start = address;
  				vma->vm_pgoff -= grow;
  				anon_vma_interval_tree_post_update_vma(vma);
  				vma_gap_update(vma);
  				spin_unlock(&mm->page_table_lock);
  
  				perf_event_mmap(vma);
  			}
  		}
  	}
  	anon_vma_unlock_write(vma->anon_vma);
  	khugepaged_enter_vma_merge(vma, vma->vm_flags);
  	validate_mm(mm);
  	return error;
  }
  
  /* enforced gap between the expanding stack and other mappings. */
  unsigned long stack_guard_gap = 256UL<<PAGE_SHIFT;
  
  static int __init cmdline_parse_stack_guard_gap(char *p)
  {
  	unsigned long val;
  	char *endptr;
  
  	val = simple_strtoul(p, &endptr, 10);
  	if (!*endptr)
  		stack_guard_gap = val << PAGE_SHIFT;
  
  	return 0;
  }
  __setup("stack_guard_gap=", cmdline_parse_stack_guard_gap);
  
  #ifdef CONFIG_STACK_GROWSUP
  int expand_stack(struct vm_area_struct *vma, unsigned long address)
  {
  	return expand_upwards(vma, address);
  }
  
  struct vm_area_struct *
  find_extend_vma(struct mm_struct *mm, unsigned long addr)
  {
  	struct vm_area_struct *vma, *prev;
  
  	addr &= PAGE_MASK;
  	vma = find_vma_prev(mm, addr, &prev);
  	if (vma && (vma->vm_start <= addr))
  		return vma;
  	if (!prev || expand_stack(prev, addr))
  		return NULL;
  	if (prev->vm_flags & VM_LOCKED)
  		populate_vma_page_range(prev, addr, prev->vm_end, NULL);
  	return prev;
  }
  #else
  int expand_stack(struct vm_area_struct *vma, unsigned long address)
  {
  	return expand_downwards(vma, address);
  }
  
  struct vm_area_struct *
  find_extend_vma(struct mm_struct *mm, unsigned long addr)
  {
  	struct vm_area_struct *vma;
  	unsigned long start;
  
  	addr &= PAGE_MASK;
  	vma = find_vma(mm, addr);
  	if (!vma)
  		return NULL;
  	if (vma->vm_start <= addr)
  		return vma;
  	if (!(vma->vm_flags & VM_GROWSDOWN))
  		return NULL;
  	start = vma->vm_start;
  	if (expand_stack(vma, addr))
  		return NULL;
  	if (vma->vm_flags & VM_LOCKED)
  		populate_vma_page_range(vma, addr, start, NULL);
  	return vma;
  }
  #endif
  
  EXPORT_SYMBOL_GPL(find_extend_vma);
  
  /*
   * Ok - we have the memory areas we should free on the vma list,
   * so release them, and do the vma updates.
   *
   * Called with the mm semaphore held.
   */
  static void remove_vma_list(struct mm_struct *mm, struct vm_area_struct *vma)
  {
  	unsigned long nr_accounted = 0;
  
  	/* Update high watermark before we lower total_vm */
  	update_hiwater_vm(mm);
  	do {
  		long nrpages = vma_pages(vma);
  
  		if (vma->vm_flags & VM_ACCOUNT)
  			nr_accounted += nrpages;
  		vm_stat_account(mm, vma->vm_flags, -nrpages);
  		vma = remove_vma(vma);
  	} while (vma);
  	vm_unacct_memory(nr_accounted);
  	validate_mm(mm);
  }
  
  /*
   * Get rid of page table information in the indicated region.
   *
   * Called with the mm semaphore held.
   */
  static void unmap_region(struct mm_struct *mm,
  		struct vm_area_struct *vma, struct vm_area_struct *prev,
  		unsigned long start, unsigned long end)
  {
  	struct vm_area_struct *next = prev ? prev->vm_next : mm->mmap;
  	struct mmu_gather tlb;
  
  	lru_add_drain();
  	tlb_gather_mmu(&tlb, mm, start, end);
  	update_hiwater_rss(mm);
  	unmap_vmas(&tlb, vma, start, end);
  	free_pgtables(&tlb, vma, prev ? prev->vm_end : FIRST_USER_ADDRESS,
  				 next ? next->vm_start : USER_PGTABLES_CEILING);
  	tlb_finish_mmu(&tlb, start, end);
  }
  
  /*
   * Create a list of vma's touched by the unmap, removing them from the mm's
   * vma list as we go..
   */
  static void
  detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma,
  	struct vm_area_struct *prev, unsigned long end)
  {
  	struct vm_area_struct **insertion_point;
  	struct vm_area_struct *tail_vma = NULL;
  
  	insertion_point = (prev ? &prev->vm_next : &mm->mmap);
  	vma->vm_prev = NULL;
  	do {
  		vma_rb_erase(vma, &mm->mm_rb);
  		mm->map_count--;
  		tail_vma = vma;
  		vma = vma->vm_next;
  	} while (vma && vma->vm_start < end);
  	*insertion_point = vma;
  	if (vma) {
  		vma->vm_prev = prev;
  		vma_gap_update(vma);
  	} else
  		mm->highest_vm_end = prev ? vm_end_gap(prev) : 0;
  	tail_vma->vm_next = NULL;
  
  	/* Kill the cache */
  	vmacache_invalidate(mm);
  }
  
  /*
   * __split_vma() bypasses sysctl_max_map_count checking.  We use this where it
   * has already been checked or doesn't make sense to fail.
   */
  int __split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
  		unsigned long addr, int new_below)
  {
  	struct vm_area_struct *new;
  	int err;
  
  	if (vma->vm_ops && vma->vm_ops->split) {
  		err = vma->vm_ops->split(vma, addr);
  		if (err)
  			return err;
  	}
  
  	new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
  	if (!new)
  		return -ENOMEM;
  
  	/* most fields are the same, copy all, and then fixup */
  	*new = *vma;
  
  	INIT_LIST_HEAD(&new->anon_vma_chain);
  
  	if (new_below)
  		new->vm_end = addr;
  	else {
  		new->vm_start = addr;
  		new->vm_pgoff += ((addr - vma->vm_start) >> PAGE_SHIFT);
  	}
  
  	err = vma_dup_policy(vma, new);
  	if (err)
  		goto out_free_vma;
  
  	err = anon_vma_clone(new, vma);
  	if (err)
  		goto out_free_mpol;
  
  	if (new->vm_file)
  		get_file(new->vm_file);
  
  	if (new->vm_ops && new->vm_ops->open)
  		new->vm_ops->open(new);
  
  	if (new_below)
  		err = vma_adjust(vma, addr, vma->vm_end, vma->vm_pgoff +
  			((addr - new->vm_start) >> PAGE_SHIFT), new);
  	else
  		err = vma_adjust(vma, vma->vm_start, addr, vma->vm_pgoff, new);
  
  	/* Success. */
  	if (!err)
  		return 0;
  
  	/* Clean everything up if vma_adjust failed. */
  	if (new->vm_ops && new->vm_ops->close)
  		new->vm_ops->close(new);
  	if (new->vm_file)
  		fput(new->vm_file);
  	unlink_anon_vmas(new);
   out_free_mpol:
  	mpol_put(vma_policy(new));
   out_free_vma:
  	kmem_cache_free(vm_area_cachep, new);
  	return err;
  }
  
  /*
   * Split a vma into two pieces at address 'addr', a new vma is allocated
   * either for the first part or the tail.
   */
  int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
  	      unsigned long addr, int new_below)
  {
  	if (mm->map_count >= sysctl_max_map_count)
  		return -ENOMEM;
  
  	return __split_vma(mm, vma, addr, new_below);
  }
  
  /* Munmap is split into 2 main parts -- this part which finds
   * what needs doing, and the areas themselves, which do the
   * work.  This now handles partial unmappings.
   * Jeremy Fitzhardinge <jeremy@goop.org>
   */
  int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
  	      struct list_head *uf)
  {
  	unsigned long end;
  	struct vm_area_struct *vma, *prev, *last;
  
  	if ((offset_in_page(start)) || start > TASK_SIZE || len > TASK_SIZE-start)
  		return -EINVAL;
  
  	len = PAGE_ALIGN(len);
  	if (len == 0)
  		return -EINVAL;
  
  	/* Find the first overlapping VMA */
  	vma = find_vma(mm, start);
  	if (!vma)
  		return 0;
  	prev = vma->vm_prev;
  	/* we have  start < vma->vm_end  */
  
  	/* if it doesn't overlap, we have nothing.. */
  	end = start + len;
  	if (vma->vm_start >= end)
  		return 0;
  
  	/*
  	 * If we need to split any vma, do it now to save pain later.
  	 *
  	 * Note: mremap's move_vma VM_ACCOUNT handling assumes a partially
  	 * unmapped vm_area_struct will remain in use: so lower split_vma
  	 * places tmp vma above, and higher split_vma places tmp vma below.
  	 */
  	if (start > vma->vm_start) {
  		int error;
  
  		/*
  		 * Make sure that map_count on return from munmap() will
  		 * not exceed its limit; but let map_count go just above
  		 * its limit temporarily, to help free resources as expected.
  		 */
  		if (end < vma->vm_end && mm->map_count >= sysctl_max_map_count)
  			return -ENOMEM;
  
  		error = __split_vma(mm, vma, start, 0);
  		if (error)
  			return error;
  		prev = vma;
  	}
  
  	/* Does it split the last one? */
  	last = find_vma(mm, end);
  	if (last && end > last->vm_start) {
  		int error = __split_vma(mm, last, end, 1);
  		if (error)
  			return error;
  	}
  	vma = prev ? prev->vm_next : mm->mmap;
  
  	if (unlikely(uf)) {
  		/*
  		 * If userfaultfd_unmap_prep returns an error the vmas
  		 * will remain splitted, but userland will get a
  		 * highly unexpected error anyway. This is no
  		 * different than the case where the first of the two
  		 * __split_vma fails, but we don't undo the first
  		 * split, despite we could. This is unlikely enough
  		 * failure that it's not worth optimizing it for.
  		 */
  		int error = userfaultfd_unmap_prep(vma, start, end, uf);
  		if (error)
  			return error;
  	}
  
  	/*
  	 * unlock any mlock()ed ranges before detaching vmas
  	 */
  	if (mm->locked_vm) {
  		struct vm_area_struct *tmp = vma;
  		while (tmp && tmp->vm_start < end) {
  			if (tmp->vm_flags & VM_LOCKED) {
  				mm->locked_vm -= vma_pages(tmp);
  				munlock_vma_pages_all(tmp);
  			}
  			tmp = tmp->vm_next;
  		}
  	}
  
  	/*
  	 * Remove the vma's, and unmap the actual pages
  	 */
  	detach_vmas_to_be_unmapped(mm, vma, prev, end);
  	unmap_region(mm, vma, prev, start, end);
  
  	arch_unmap(mm, vma, start, end);
  
  	/* Fix up all other VM information */
  	remove_vma_list(mm, vma);
  
  	return 0;
  }
  
  int vm_munmap(unsigned long start, size_t len)
  {
  	int ret;
  	struct mm_struct *mm = current->mm;
  	LIST_HEAD(uf);
  
  	if (down_write_killable(&mm->mmap_sem))
  		return -EINTR;
  
  	ret = do_munmap(mm, start, len, &uf);
  	up_write(&mm->mmap_sem);
  	userfaultfd_unmap_complete(mm, &uf);
  	return ret;
  }
  EXPORT_SYMBOL(vm_munmap);
  
  SYSCALL_DEFINE2(munmap, unsigned long, addr, size_t, len)
  {
  	profile_munmap(addr);
  	return vm_munmap(addr, len);
  }
  
  
  /*
   * Emulation of deprecated remap_file_pages() syscall.
   */
  SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
  		unsigned long, prot, unsigned long, pgoff, unsigned long, flags)
  {
  
  	struct mm_struct *mm = current->mm;
  	struct vm_area_struct *vma;
  	unsigned long populate = 0;
  	unsigned long ret = -EINVAL;
  	struct file *file;
  
  	pr_warn_once("%s (%d) uses deprecated remap_file_pages() syscall. See Documentation/vm/remap_file_pages.rst.\n",
  		     current->comm, current->pid);
  
  	if (prot)
  		return ret;
  	start = start & PAGE_MASK;
  	size = size & PAGE_MASK;
  
  	if (start + size <= start)
  		return ret;
  
  	/* Does pgoff wrap? */
  	if (pgoff + (size >> PAGE_SHIFT) < pgoff)
  		return ret;
  
  	if (down_write_killable(&mm->mmap_sem))
  		return -EINTR;
  
  	vma = find_vma(mm, start);
  
  	if (!vma || !(vma->vm_flags & VM_SHARED))
  		goto out;
  
  	if (start < vma->vm_start)
  		goto out;
  
  	if (start + size > vma->vm_end) {
  		struct vm_area_struct *next;
  
  		for (next = vma->vm_next; next; next = next->vm_next) {
  			/* hole between vmas ? */
  			if (next->vm_start != next->vm_prev->vm_end)
  				goto out;
  
  			if (next->vm_file != vma->vm_file)
  				goto out;
  
  			if (next->vm_flags != vma->vm_flags)
  				goto out;
  
  			if (start + size <= next->vm_end)
  				break;
  		}
  
  		if (!next)
  			goto out;
  	}
  
  	prot |= vma->vm_flags & VM_READ ? PROT_READ : 0;
  	prot |= vma->vm_flags & VM_WRITE ? PROT_WRITE : 0;
  	prot |= vma->vm_flags & VM_EXEC ? PROT_EXEC : 0;
  
  	flags &= MAP_NONBLOCK;
  	flags |= MAP_SHARED | MAP_FIXED | MAP_POPULATE;
  	if (vma->vm_flags & VM_LOCKED) {
  		struct vm_area_struct *tmp;
  		flags |= MAP_LOCKED;
  
  		/* drop PG_Mlocked flag for over-mapped range */
  		for (tmp = vma; tmp->vm_start >= start + size;
  				tmp = tmp->vm_next) {
  			/*
  			 * Split pmd and munlock page on the border
  			 * of the range.
  			 */
  			vma_adjust_trans_huge(tmp, start, start + size, 0);
  
  			munlock_vma_pages_range(tmp,
  					max(tmp->vm_start, start),
  					min(tmp->vm_end, start + size));
  		}
  	}
  
  	file = get_file(vma->vm_file);
  	ret = do_mmap_pgoff(vma->vm_file, start, size,
  			prot, flags, pgoff, &populate, NULL);
  	fput(file);
  out:
  	up_write(&mm->mmap_sem);
  	if (populate)
  		mm_populate(ret, populate);
  	if (!IS_ERR_VALUE(ret))
  		ret = 0;
  	return ret;
  }
  
  static inline void verify_mm_writelocked(struct mm_struct *mm)
  {
  #ifdef CONFIG_DEBUG_VM
  	if (unlikely(down_read_trylock(&mm->mmap_sem))) {
  		WARN_ON(1);
  		up_read(&mm->mmap_sem);
  	}
  #endif
  }
  
  /*
   *  this is really a simplified "do_mmap".  it only handles
   *  anonymous maps.  eventually we may be able to do some
   *  brk-specific accounting here.
   */
  static int do_brk_flags(unsigned long addr, unsigned long request, unsigned long flags, struct list_head *uf)
  {
  	struct mm_struct *mm = current->mm;
  	struct vm_area_struct *vma, *prev;
  	unsigned long len;
  	struct rb_node **rb_link, *rb_parent;
  	pgoff_t pgoff = addr >> PAGE_SHIFT;
  	int error;
  
  	len = PAGE_ALIGN(request);
  	if (len < request)
  		return -ENOMEM;
  	if (!len)
  		return 0;
  
  	/* Until we need other flags, refuse anything except VM_EXEC. */
  	if ((flags & (~VM_EXEC)) != 0)
  		return -EINVAL;
  	flags |= VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;
  
  	error = get_unmapped_area(NULL, addr, len, 0, MAP_FIXED);
  	if (offset_in_page(error))
  		return error;
  
  	error = mlock_future_check(mm, mm->def_flags, len);
  	if (error)
  		return error;
  
  	/*
  	 * mm->mmap_sem is required to protect against another thread
  	 * changing the mappings in case we sleep.
  	 */
  	verify_mm_writelocked(mm);
  
  	/*
  	 * Clear old maps.  this also does some error checking for us
  	 */
  	while (find_vma_links(mm, addr, addr + len, &prev, &rb_link,
  			      &rb_parent)) {
  		if (do_munmap(mm, addr, len, uf))
  			return -ENOMEM;
  	}
  
  	/* Check against address space limits *after* clearing old maps... */
  	if (!may_expand_vm(mm, flags, len >> PAGE_SHIFT))
  		return -ENOMEM;
  
  	if (mm->map_count > sysctl_max_map_count)
  		return -ENOMEM;
  
  	if (security_vm_enough_memory_mm(mm, len >> PAGE_SHIFT))
  		return -ENOMEM;
  
  	/* Can we just expand an old private anonymous mapping? */
  	vma = vma_merge(mm, prev, addr, addr + len, flags,
  			NULL, NULL, pgoff, NULL, NULL_VM_UFFD_CTX);
  	if (vma)
  		goto out;
  
  	/*
  	 * create a vma struct for an anonymous mapping
  	 */
  	vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
  	if (!vma) {
  		vm_unacct_memory(len >> PAGE_SHIFT);
  		return -ENOMEM;
  	}
  
  	INIT_LIST_HEAD(&vma->anon_vma_chain);
  	vma->vm_mm = mm;
  	vma->vm_start = addr;
  	vma->vm_end = addr + len;
  	vma->vm_pgoff = pgoff;
  	vma->vm_flags = flags;
  	vma->vm_page_prot = vm_get_page_prot(flags);
  	vma_link(mm, vma, prev, rb_link, rb_parent);
  out:
  	perf_event_mmap(vma);
  	mm->total_vm += len >> PAGE_SHIFT;
  	mm->data_vm += len >> PAGE_SHIFT;
  	if (flags & VM_LOCKED)
  		mm->locked_vm += (len >> PAGE_SHIFT);
  	vma->vm_flags |= VM_SOFTDIRTY;
  	return 0;
  }
  
  static int do_brk(unsigned long addr, unsigned long len, struct list_head *uf)
  {
  	return do_brk_flags(addr, len, 0, uf);
  }
  
  int vm_brk_flags(unsigned long addr, unsigned long len, unsigned long flags)
  {
  	struct mm_struct *mm = current->mm;
  	int ret;
  	bool populate;
  	LIST_HEAD(uf);
  
  	if (down_write_killable(&mm->mmap_sem))
  		return -EINTR;
  
  	ret = do_brk_flags(addr, len, flags, &uf);
  	populate = ((mm->def_flags & VM_LOCKED) != 0);
  	up_write(&mm->mmap_sem);
  	userfaultfd_unmap_complete(mm, &uf);
  	if (populate && !ret)
  		mm_populate(addr, len);
  	return ret;
  }
  EXPORT_SYMBOL(vm_brk_flags);
  
  int vm_brk(unsigned long addr, unsigned long len)
  {
  	return vm_brk_flags(addr, len, 0);
  }
  EXPORT_SYMBOL(vm_brk);
  
  /* Release all mmaps. */
  void exit_mmap(struct mm_struct *mm)
  {
  	struct mmu_gather tlb;
  	struct vm_area_struct *vma;
  	unsigned long nr_accounted = 0;
  
  	/* mm's last user has gone, and its about to be pulled down */
  	mmu_notifier_release(mm);
  
  	if (unlikely(mm_is_oom_victim(mm))) {
  		/*
  		 * Manually reap the mm to free as much memory as possible.
  		 * Then, as the oom reaper does, set MMF_OOM_SKIP to disregard
  		 * this mm from further consideration.  Taking mm->mmap_sem for
  		 * write after setting MMF_OOM_SKIP will guarantee that the oom
  		 * reaper will not run on this mm again after mmap_sem is
  		 * dropped.
  		 *
  		 * Nothing can be holding mm->mmap_sem here and the above call
  		 * to mmu_notifier_release(mm) ensures mmu notifier callbacks in
  		 * __oom_reap_task_mm() will not block.
  		 *
  		 * This needs to be done before calling munlock_vma_pages_all(),
  		 * which clears VM_LOCKED, otherwise the oom reaper cannot
  		 * reliably test it.
  		 */
  		mutex_lock(&oom_lock);
  		__oom_reap_task_mm(mm);
  		mutex_unlock(&oom_lock);
  
  		set_bit(MMF_OOM_SKIP, &mm->flags);
  		down_write(&mm->mmap_sem);
  		up_write(&mm->mmap_sem);
  	}
  
  	if (mm->locked_vm) {
  		vma = mm->mmap;
  		while (vma) {
  			if (vma->vm_flags & VM_LOCKED)
  				munlock_vma_pages_all(vma);
  			vma = vma->vm_next;
  		}
  	}
  
  	arch_exit_mmap(mm);
  
  	vma = mm->mmap;
  	if (!vma)	/* Can happen if dup_mmap() received an OOM */
  		return;
  
  	lru_add_drain();
  	flush_cache_mm(mm);
  	tlb_gather_mmu(&tlb, mm, 0, -1);
  	/* update_hiwater_rss(mm) here? but nobody should be looking */
  	/* Use -1 here to ensure all VMAs in the mm are unmapped */
  	unmap_vmas(&tlb, vma, 0, -1);
  	free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, USER_PGTABLES_CEILING);
  	tlb_finish_mmu(&tlb, 0, -1);
  
  	/*
  	 * Walk the list again, actually closing and freeing it,
  	 * with preemption enabled, without holding any MM locks.
  	 */
  	while (vma) {
  		if (vma->vm_flags & VM_ACCOUNT)
  			nr_accounted += vma_pages(vma);
  		vma = remove_vma(vma);
  	}
  	vm_unacct_memory(nr_accounted);
  }
  
  /* Insert vm structure into process list sorted by address
   * and into the inode's i_mmap tree.  If vm_file is non-NULL
   * then i_mmap_rwsem is taken here.
   */
  int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
  {
  	struct vm_area_struct *prev;
  	struct rb_node **rb_link, *rb_parent;
  
  	if (find_vma_links(mm, vma->vm_start, vma->vm_end,
  			   &prev, &rb_link, &rb_parent))
  		return -ENOMEM;
  	if ((vma->vm_flags & VM_ACCOUNT) &&
  	     security_vm_enough_memory_mm(mm, vma_pages(vma)))
  		return -ENOMEM;
  
  	/*
  	 * The vm_pgoff of a purely anonymous vma should be irrelevant
  	 * until its first write fault, when page's anon_vma and index
  	 * are set.  But now set the vm_pgoff it will almost certainly
  	 * end up with (unless mremap moves it elsewhere before that
  	 * first wfault), so /proc/pid/maps tells a consistent story.
  	 *
  	 * By setting it to reflect the virtual start address of the
  	 * vma, merges and splits can happen in a seamless way, just
  	 * using the existing file pgoff checks and manipulations.
  	 * Similarly in do_mmap_pgoff and in do_brk.
  	 */
  	if (vma_is_anonymous(vma)) {
  		BUG_ON(vma->anon_vma);
  		vma->vm_pgoff = vma->vm_start >> PAGE_SHIFT;
  	}
  
  	vma_link(mm, vma, prev, rb_link, rb_parent);
  	return 0;
  }
  
  /*
   * Copy the vma structure to a new location in the same mm,
   * prior to moving page table entries, to effect an mremap move.
   */
  struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
  	unsigned long addr, unsigned long len, pgoff_t pgoff,
  	bool *need_rmap_locks)
  {
  	struct vm_area_struct *vma = *vmap;
  	unsigned long vma_start = vma->vm_start;
  	struct mm_struct *mm = vma->vm_mm;
  	struct vm_area_struct *new_vma, *prev;
  	struct rb_node **rb_link, *rb_parent;
  	bool faulted_in_anon_vma = true;
  
  	/*
  	 * If anonymous vma has not yet been faulted, update new pgoff
  	 * to match new location, to increase its chance of merging.
  	 */
  	if (unlikely(vma_is_anonymous(vma) && !vma->anon_vma)) {
  		pgoff = addr >> PAGE_SHIFT;
  		faulted_in_anon_vma = false;
  	}
  
  	if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent))
  		return NULL;	/* should never get here */
  	new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags,
  			    vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
  			    vma->vm_userfaultfd_ctx);
  	if (new_vma) {
  		/*
  		 * Source vma may have been merged into new_vma
  		 */
  		if (unlikely(vma_start >= new_vma->vm_start &&
  			     vma_start < new_vma->vm_end)) {
  			/*
  			 * The only way we can get a vma_merge with
  			 * self during an mremap is if the vma hasn't
  			 * been faulted in yet and we were allowed to
  			 * reset the dst vma->vm_pgoff to the
  			 * destination address of the mremap to allow
  			 * the merge to happen. mremap must change the
  			 * vm_pgoff linearity between src and dst vmas
  			 * (in turn preventing a vma_merge) to be
  			 * safe. It is only safe to keep the vm_pgoff
  			 * linear if there are no pages mapped yet.
  			 */
  			VM_BUG_ON_VMA(faulted_in_anon_vma, new_vma);
  			*vmap = vma = new_vma;
  		}
  		*need_rmap_locks = (new_vma->vm_pgoff <= vma->vm_pgoff);
  	} else {
  		new_vma = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
  		if (!new_vma)
  			goto out;
  		*new_vma = *vma;
  		new_vma->vm_start = addr;
  		new_vma->vm_end = addr + len;
  		new_vma->vm_pgoff = pgoff;
  		if (vma_dup_policy(vma, new_vma))
  			goto out_free_vma;
  		INIT_LIST_HEAD(&new_vma->anon_vma_chain);
  		if (anon_vma_clone(new_vma, vma))
  			goto out_free_mempol;
  		if (new_vma->vm_file)
  			get_file(new_vma->vm_file);
  		if (new_vma->vm_ops && new_vma->vm_ops->open)
  			new_vma->vm_ops->open(new_vma);
  		vma_link(mm, new_vma, prev, rb_link, rb_parent);
  		*need_rmap_locks = false;
  	}
  	return new_vma;
  
  out_free_mempol:
  	mpol_put(vma_policy(new_vma));
  out_free_vma:
  	kmem_cache_free(vm_area_cachep, new_vma);
  out:
  	return NULL;
  }
  
  /*
   * Return true if the calling process may expand its vm space by the passed
   * number of pages
   */
  bool may_expand_vm(struct mm_struct *mm, vm_flags_t flags, unsigned long npages)
  {
  	if (mm->total_vm + npages > rlimit(RLIMIT_AS) >> PAGE_SHIFT)
  		return false;
  
  	if (is_data_mapping(flags) &&
  	    mm->data_vm + npages > rlimit(RLIMIT_DATA) >> PAGE_SHIFT) {
  		/* Workaround for Valgrind */
  		if (rlimit(RLIMIT_DATA) == 0 &&
  		    mm->data_vm + npages <= rlimit_max(RLIMIT_DATA) >> PAGE_SHIFT)
  			return true;
  
  		pr_warn_once("%s (%d): VmData %lu exceed data ulimit %lu. Update limits%s.\n",
  			     current->comm, current->pid,
  			     (mm->data_vm + npages) << PAGE_SHIFT,
  			     rlimit(RLIMIT_DATA),
  			     ignore_rlimit_data ? "" : " or use boot option ignore_rlimit_data");
  
  		if (!ignore_rlimit_data)
  			return false;
  	}
  
  	return true;
  }
  
  void vm_stat_account(struct mm_struct *mm, vm_flags_t flags, long npages)
  {
  	mm->total_vm += npages;
  
  	if (is_exec_mapping(flags))
  		mm->exec_vm += npages;
  	else if (is_stack_mapping(flags))
  		mm->stack_vm += npages;
  	else if (is_data_mapping(flags))
  		mm->data_vm += npages;
  }
  
  static vm_fault_t special_mapping_fault(struct vm_fault *vmf);
  
  /*
   * Having a close hook prevents vma merging regardless of flags.
   */
  static void special_mapping_close(struct vm_area_struct *vma)
  {
  }
  
  static const char *special_mapping_name(struct vm_area_struct *vma)
  {
  	return ((struct vm_special_mapping *)vma->vm_private_data)->name;
  }
  
  static int special_mapping_mremap(struct vm_area_struct *new_vma)
  {
  	struct vm_special_mapping *sm = new_vma->vm_private_data;
  
  	if (WARN_ON_ONCE(current->mm != new_vma->vm_mm))
  		return -EFAULT;
  
  	if (sm->mremap)
  		return sm->mremap(sm, new_vma);
  
  	return 0;
  }
  
  static const struct vm_operations_struct special_mapping_vmops = {
  	.close = special_mapping_close,
  	.fault = special_mapping_fault,
  	.mremap = special_mapping_mremap,
  	.name = special_mapping_name,
  };
  
  static const struct vm_operations_struct legacy_special_mapping_vmops = {
  	.close = special_mapping_close,
  	.fault = special_mapping_fault,
  };
  
  static vm_fault_t special_mapping_fault(struct vm_fault *vmf)
  {
  	struct vm_area_struct *vma = vmf->vma;
  	pgoff_t pgoff;
  	struct page **pages;
  
  	if (vma->vm_ops == &legacy_special_mapping_vmops) {
  		pages = vma->vm_private_data;
  	} else {
  		struct vm_special_mapping *sm = vma->vm_private_data;
  
  		if (sm->fault)
  			return sm->fault(sm, vmf->vma, vmf);
  
  		pages = sm->pages;
  	}
  
  	for (pgoff = vmf->pgoff; pgoff && *pages; ++pages)
  		pgoff--;
  
  	if (*pages) {
  		struct page *page = *pages;
  		get_page(page);
  		vmf->page = page;
  		return 0;
  	}
  
  	return VM_FAULT_SIGBUS;
  }
  
  static struct vm_area_struct *__install_special_mapping(
  	struct mm_struct *mm,
  	unsigned long addr, unsigned long len,
  	unsigned long vm_flags, void *priv,
  	const struct vm_operations_struct *ops)
  {
  	int ret;
  	struct vm_area_struct *vma;
  
  	vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
  	if (unlikely(vma == NULL))
  		return ERR_PTR(-ENOMEM);
  
  	INIT_LIST_HEAD(&vma->anon_vma_chain);
  	vma->vm_mm = mm;
  	vma->vm_start = addr;
  	vma->vm_end = addr + len;
  
  	vma->vm_flags = vm_flags | mm->def_flags | VM_DONTEXPAND | VM_SOFTDIRTY;
  	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
  
  	vma->vm_ops = ops;
  	vma->vm_private_data = priv;
  
  	ret = insert_vm_struct(mm, vma);
  	if (ret)
  		goto out;
  
  	vm_stat_account(mm, vma->vm_flags, len >> PAGE_SHIFT);
  
  	perf_event_mmap(vma);
  
  	return vma;
  
  out:
  	kmem_cache_free(vm_area_cachep, vma);
  	return ERR_PTR(ret);
  }
  
  bool vma_is_special_mapping(const struct vm_area_struct *vma,
  	const struct vm_special_mapping *sm)
  {
  	return vma->vm_private_data == sm &&
  		(vma->vm_ops == &special_mapping_vmops ||
  		 vma->vm_ops == &legacy_special_mapping_vmops);
  }
  
  /*
   * Called with mm->mmap_sem held for writing.
   * Insert a new vma covering the given region, with the given flags.
   * Its pages are supplied by the given array of struct page *.
   * The array can be shorter than len >> PAGE_SHIFT if it's null-terminated.
   * The region past the last page supplied will always produce SIGBUS.
   * The array pointer and the pages it points to are assumed to stay alive
   * for as long as this mapping might exist.
   */
  struct vm_area_struct *_install_special_mapping(
  	struct mm_struct *mm,
  	unsigned long addr, unsigned long len,
  	unsigned long vm_flags, const struct vm_special_mapping *spec)
  {
  	return __install_special_mapping(mm, addr, len, vm_flags, (void *)spec,
  					&special_mapping_vmops);
  }
  
  int install_special_mapping(struct mm_struct *mm,
  			    unsigned long addr, unsigned long len,
  			    unsigned long vm_flags, struct page **pages)
  {
  	struct vm_area_struct *vma = __install_special_mapping(
  		mm, addr, len, vm_flags, (void *)pages,
  		&legacy_special_mapping_vmops);
  
  	return PTR_ERR_OR_ZERO(vma);
  }
  
  static DEFINE_MUTEX(mm_all_locks_mutex);
  
  static void vm_lock_anon_vma(struct mm_struct *mm, struct anon_vma *anon_vma)
  {
  	if (!test_bit(0, (unsigned long *) &anon_vma->root->rb_root.rb_root.rb_node)) {
  		/*
  		 * The LSB of head.next can't change from under us
  		 * because we hold the mm_all_locks_mutex.
  		 */
  		down_write_nest_lock(&anon_vma->root->rwsem, &mm->mmap_sem);
  		/*
  		 * We can safely modify head.next after taking the
  		 * anon_vma->root->rwsem. If some other vma in this mm shares
  		 * the same anon_vma we won't take it again.
  		 *
  		 * No need of atomic instructions here, head.next
  		 * can't change from under us thanks to the
  		 * anon_vma->root->rwsem.
  		 */
  		if (__test_and_set_bit(0, (unsigned long *)
  				       &anon_vma->root->rb_root.rb_root.rb_node))
  			BUG();
  	}
  }
  
  static void vm_lock_mapping(struct mm_struct *mm, struct address_space *mapping)
  {
  	if (!test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
  		/*
  		 * AS_MM_ALL_LOCKS can't change from under us because
  		 * we hold the mm_all_locks_mutex.
  		 *
  		 * Operations on ->flags have to be atomic because
  		 * even if AS_MM_ALL_LOCKS is stable thanks to the
  		 * mm_all_locks_mutex, there may be other cpus
  		 * changing other bitflags in parallel to us.
  		 */
  		if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags))
  			BUG();
  		down_write_nest_lock(&mapping->i_mmap_rwsem, &mm->mmap_sem);
  	}
  }
  
  /*
   * This operation locks against the VM for all pte/vma/mm related
   * operations that could ever happen on a certain mm. This includes
   * vmtruncate, try_to_unmap, and all page faults.
   *
   * The caller must take the mmap_sem in write mode before calling
   * mm_take_all_locks(). The caller isn't allowed to release the
   * mmap_sem until mm_drop_all_locks() returns.
   *
   * mmap_sem in write mode is required in order to block all operations
   * that could modify pagetables and free pages without need of
   * altering the vma layout. It's also needed in write mode to avoid new
   * anon_vmas to be associated with existing vmas.
   *
   * A single task can't take more than one mm_take_all_locks() in a row
   * or it would deadlock.
   *
   * The LSB in anon_vma->rb_root.rb_node and the AS_MM_ALL_LOCKS bitflag in
   * mapping->flags avoid to take the same lock twice, if more than one
   * vma in this mm is backed by the same anon_vma or address_space.
   *
   * We take locks in following order, accordingly to comment at beginning
   * of mm/rmap.c:
   *   - all hugetlbfs_i_mmap_rwsem_key locks (aka mapping->i_mmap_rwsem for
   *     hugetlb mapping);
   *   - all i_mmap_rwsem locks;
   *   - all anon_vma->rwseml
   *
   * We can take all locks within these types randomly because the VM code
   * doesn't nest them and we protected from parallel mm_take_all_locks() by
   * mm_all_locks_mutex.
   *
   * mm_take_all_locks() and mm_drop_all_locks are expensive operations
   * that may have to take thousand of locks.
   *
   * mm_take_all_locks() can fail if it's interrupted by signals.
   */
  int mm_take_all_locks(struct mm_struct *mm)
  {
  	struct vm_area_struct *vma;
  	struct anon_vma_chain *avc;
  
  	BUG_ON(down_read_trylock(&mm->mmap_sem));
  
  	mutex_lock(&mm_all_locks_mutex);
  
  	for (vma = mm->mmap; vma; vma = vma->vm_next) {
  		if (signal_pending(current))
  			goto out_unlock;
  		if (vma->vm_file && vma->vm_file->f_mapping &&
  				is_vm_hugetlb_page(vma))
  			vm_lock_mapping(mm, vma->vm_file->f_mapping);
  	}
  
  	for (vma = mm->mmap; vma; vma = vma->vm_next) {
  		if (signal_pending(current))
  			goto out_unlock;
  		if (vma->vm_file && vma->vm_file->f_mapping &&
  				!is_vm_hugetlb_page(vma))
  			vm_lock_mapping(mm, vma->vm_file->f_mapping);
  	}
  
  	for (vma = mm->mmap; vma; vma = vma->vm_next) {
  		if (signal_pending(current))
  			goto out_unlock;
  		if (vma->anon_vma)
  			list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
  				vm_lock_anon_vma(mm, avc->anon_vma);
  	}
  
  	return 0;
  
  out_unlock:
  	mm_drop_all_locks(mm);
  	return -EINTR;
  }
  
  static void vm_unlock_anon_vma(struct anon_vma *anon_vma)
  {
  	if (test_bit(0, (unsigned long *) &anon_vma->root->rb_root.rb_root.rb_node)) {
  		/*
  		 * The LSB of head.next can't change to 0 from under
  		 * us because we hold the mm_all_locks_mutex.
  		 *
  		 * We must however clear the bitflag before unlocking
  		 * the vma so the users using the anon_vma->rb_root will
  		 * never see our bitflag.
  		 *
  		 * No need of atomic instructions here, head.next
  		 * can't change from under us until we release the
  		 * anon_vma->root->rwsem.
  		 */
  		if (!__test_and_clear_bit(0, (unsigned long *)
  					  &anon_vma->root->rb_root.rb_root.rb_node))
  			BUG();
  		anon_vma_unlock_write(anon_vma);
  	}
  }
  
  static void vm_unlock_mapping(struct address_space *mapping)
  {
  	if (test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
  		/*
  		 * AS_MM_ALL_LOCKS can't change to 0 from under us
  		 * because we hold the mm_all_locks_mutex.
  		 */
  		i_mmap_unlock_write(mapping);
  		if (!test_and_clear_bit(AS_MM_ALL_LOCKS,
  					&mapping->flags))
  			BUG();
  	}
  }
  
  /*
   * The mmap_sem cannot be released by the caller until
   * mm_drop_all_locks() returns.
   */
  void mm_drop_all_locks(struct mm_struct *mm)
  {
  	struct vm_area_struct *vma;
  	struct anon_vma_chain *avc;
  
  	BUG_ON(down_read_trylock(&mm->mmap_sem));
  	BUG_ON(!mutex_is_locked(&mm_all_locks_mutex));
  
  	for (vma = mm->mmap; vma; vma = vma->vm_next) {
  		if (vma->anon_vma)
  			list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
  				vm_unlock_anon_vma(avc->anon_vma);
  		if (vma->vm_file && vma->vm_file->f_mapping)
  			vm_unlock_mapping(vma->vm_file->f_mapping);
  	}
  
  	mutex_unlock(&mm_all_locks_mutex);
  }
  
  /*
   * initialise the percpu counter for VM
   */
  void __init mmap_init(void)
  {
  	int ret;
  
  	ret = percpu_counter_init(&vm_committed_as, 0, GFP_KERNEL);
  	VM_BUG_ON(ret);
  }
  
  /*
   * Initialise sysctl_user_reserve_kbytes.
   *
   * This is intended to prevent a user from starting a single memory hogging
   * process, such that they cannot recover (kill the hog) in OVERCOMMIT_NEVER
   * mode.
   *
   * The default value is min(3% of free memory, 128MB)
   * 128MB is enough to recover with sshd/login, bash, and top/kill.
   */
  static int init_user_reserve(void)
  {
  	unsigned long free_kbytes;
  
  	free_kbytes = global_zone_page_state(NR_FREE_PAGES) << (PAGE_SHIFT - 10);
  
  	sysctl_user_reserve_kbytes = min(free_kbytes / 32, 1UL << 17);
  	return 0;
  }
  subsys_initcall(init_user_reserve);
  
  /*
   * Initialise sysctl_admin_reserve_kbytes.
   *
   * The purpose of sysctl_admin_reserve_kbytes is to allow the sys admin
   * to log in and kill a memory hogging process.
   *
   * Systems with more than 256MB will reserve 8MB, enough to recover
   * with sshd, bash, and top in OVERCOMMIT_GUESS. Smaller systems will
   * only reserve 3% of free pages by default.
   */
  static int init_admin_reserve(void)
  {
  	unsigned long free_kbytes;
  
  	free_kbytes = global_zone_page_state(NR_FREE_PAGES) << (PAGE_SHIFT - 10);
  
  	sysctl_admin_reserve_kbytes = min(free_kbytes / 32, 1UL << 13);
  	return 0;
  }
  subsys_initcall(init_admin_reserve);
  
  /*
   * Reinititalise user and admin reserves if memory is added or removed.
   *
   * The default user reserve max is 128MB, and the default max for the
   * admin reserve is 8MB. These are usually, but not always, enough to
   * enable recovery from a memory hogging process using login/sshd, a shell,
   * and tools like top. It may make sense to increase or even disable the
   * reserve depending on the existence of swap or variations in the recovery
   * tools. So, the admin may have changed them.
   *
   * If memory is added and the reserves have been eliminated or increased above
   * the default max, then we'll trust the admin.
   *
   * If memory is removed and there isn't enough free memory, then we
   * need to reset the reserves.
   *
   * Otherwise keep the reserve set by the admin.
   */
  static int reserve_mem_notifier(struct notifier_block *nb,
  			     unsigned long action, void *data)
  {
  	unsigned long tmp, free_kbytes;
  
  	switch (action) {
  	case MEM_ONLINE:
  		/* Default max is 128MB. Leave alone if modified by operator. */
  		tmp = sysctl_user_reserve_kbytes;
  		if (0 < tmp && tmp < (1UL << 17))
  			init_user_reserve();
  
  		/* Default max is 8MB.  Leave alone if modified by operator. */
  		tmp = sysctl_admin_reserve_kbytes;
  		if (0 < tmp && tmp < (1UL << 13))
  			init_admin_reserve();
  
  		break;
  	case MEM_OFFLINE:
  		free_kbytes = global_zone_page_state(NR_FREE_PAGES) << (PAGE_SHIFT - 10);
  
  		if (sysctl_user_reserve_kbytes > free_kbytes) {
  			init_user_reserve();
  			pr_info("vm.user_reserve_kbytes reset to %lu\n",
  				sysctl_user_reserve_kbytes);
  		}
  
  		if (sysctl_admin_reserve_kbytes > free_kbytes) {
  			init_admin_reserve();
  			pr_info("vm.admin_reserve_kbytes reset to %lu\n",
  				sysctl_admin_reserve_kbytes);
  		}
  		break;
  	default:
  		break;
  	}
  	return NOTIFY_OK;
  }
  
  static struct notifier_block reserve_mem_nb = {
  	.notifier_call = reserve_mem_notifier,
  };
  
  static int __meminit init_reserve_notifier(void)
  {
  	if (register_hotmemory_notifier(&reserve_mem_nb))
  		pr_err("Failed registering memory add/remove notifier for admin reserve\n");
  
  	return 0;
  }
  subsys_initcall(init_reserve_notifier);
  