// SPDX-License-Identifier: GPL-2.0

  /*
   *	mm/mremap.c
   *
   *	(C) Copyright 1996 Linus Torvalds
   *

   *	Address space accounting code	<alan@lxorguk.ukuu.org.uk>

   *	(C) Copyright 2002 Red Hat Inc, All Rights Reserved
   */
  
  #include <linux/mm.h>
  #include <linux/hugetlb.h>

  #include <linux/shm.h>

  #include <linux/ksm.h>

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

  #include <linux/capability.h>

  #include <linux/fs.h>

  #include <linux/swapops.h>

  #include <linux/highmem.h>
  #include <linux/security.h>
  #include <linux/syscalls.h>

  #include <linux/mmu_notifier.h>

  #include <linux/uaccess.h>

  #include <linux/mm-arch-hooks.h>

  #include <linux/userfaultfd_k.h>

  #include <asm/cacheflush.h>
  #include <asm/tlbflush.h>

  #include "internal.h"

  static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)

  {
  	pgd_t *pgd;

  	p4d_t *p4d;

  	pud_t *pud;
  	pmd_t *pmd;
  
  	pgd = pgd_offset(mm, addr);
  	if (pgd_none_or_clear_bad(pgd))
  		return NULL;

  	p4d = p4d_offset(pgd, addr);
  	if (p4d_none_or_clear_bad(p4d))
  		return NULL;
  
  	pud = pud_offset(p4d, addr);

  	if (pud_none_or_clear_bad(pud))
  		return NULL;
  
  	pmd = pmd_offset(pud, addr);

  	if (pmd_none(*pmd))

  		return NULL;

  	return pmd;

  }

  static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
  			    unsigned long addr)

  {
  	pgd_t *pgd;

  	p4d_t *p4d;

  	pud_t *pud;

  	pmd_t *pmd;

  
  	pgd = pgd_offset(mm, addr);

  	p4d = p4d_alloc(mm, pgd, addr);
  	if (!p4d)
  		return NULL;
  	pud = pud_alloc(mm, p4d, addr);

  	if (!pud)

  		return NULL;

  	pmd = pmd_alloc(mm, pud, addr);

  	if (!pmd)

  		return NULL;

  	VM_BUG_ON(pmd_trans_huge(*pmd));

  	return pmd;

  }

  static void take_rmap_locks(struct vm_area_struct *vma)
  {
  	if (vma->vm_file)
  		i_mmap_lock_write(vma->vm_file->f_mapping);
  	if (vma->anon_vma)
  		anon_vma_lock_write(vma->anon_vma);
  }
  
  static void drop_rmap_locks(struct vm_area_struct *vma)
  {
  	if (vma->anon_vma)
  		anon_vma_unlock_write(vma->anon_vma);
  	if (vma->vm_file)
  		i_mmap_unlock_write(vma->vm_file->f_mapping);
  }

  static pte_t move_soft_dirty_pte(pte_t pte)
  {
  	/*
  	 * Set soft dirty bit so we can notice
  	 * in userspace the ptes were moved.
  	 */
  #ifdef CONFIG_MEM_SOFT_DIRTY
  	if (pte_present(pte))
  		pte = pte_mksoft_dirty(pte);
  	else if (is_swap_pte(pte))
  		pte = pte_swp_mksoft_dirty(pte);

  #endif
  	return pte;
  }

  static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
  		unsigned long old_addr, unsigned long old_end,
  		struct vm_area_struct *new_vma, pmd_t *new_pmd,

  		unsigned long new_addr, bool need_rmap_locks)

  {

  	struct mm_struct *mm = vma->vm_mm;

  	pte_t *old_pte, *new_pte, pte;

  	spinlock_t *old_ptl, *new_ptl;

  	bool force_flush = false;
  	unsigned long len = old_end - old_addr;

  	/*

  	 * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma

  	 * locks to ensure that rmap will always observe either the old or the
  	 * new ptes. This is the easiest way to avoid races with
  	 * truncate_pagecache(), page migration, etc...
  	 *
  	 * When need_rmap_locks is false, we use other ways to avoid
  	 * such races:
  	 *
  	 * - During exec() shift_arg_pages(), we use a specially tagged vma

  	 *   which rmap call sites look for using vma_is_temporary_stack().

  	 *
  	 * - During mremap(), new_vma is often known to be placed after vma
  	 *   in rmap traversal order. This ensures rmap will always observe
  	 *   either the old pte, or the new pte, or both (the page table locks
  	 *   serialize access to individual ptes, but only rmap traversal
  	 *   order guarantees that we won't miss both the old and new ptes).
  	 */

  	if (need_rmap_locks)
  		take_rmap_locks(vma);

  	/*
  	 * We don't have to worry about the ordering of src and dst

  	 * pte locks because exclusive mmap_lock prevents deadlock.

  	 */

  	old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);

  	new_pte = pte_offset_map(new_pmd, new_addr);

  	new_ptl = pte_lockptr(mm, new_pmd);
  	if (new_ptl != old_ptl)

  		spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);

  	flush_tlb_batched_pending(vma->vm_mm);

  	arch_enter_lazy_mmu_mode();

  
  	for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
  				   new_pte++, new_addr += PAGE_SIZE) {
  		if (pte_none(*old_pte))
  			continue;

  		pte = ptep_get_and_clear(mm, old_addr, old_pte);

  		/*

  		 * If we are remapping a valid PTE, make sure

  		 * to flush TLB before we drop the PTL for the

  		 * PTE.

  		 *

  		 * NOTE! Both old and new PTL matter: the old one
  		 * for racing with page_mkclean(), the new one to
  		 * make sure the physical page stays valid until
  		 * the TLB entry for the old mapping has been
  		 * flushed.

  		 */

  		if (pte_present(pte))

  			force_flush = true;

  		pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);

  		pte = move_soft_dirty_pte(pte);
  		set_pte_at(mm, new_addr, new_pte, pte);

  	}

  	arch_leave_lazy_mmu_mode();

  	if (force_flush)
  		flush_tlb_range(vma, old_end - len, old_end);

  	if (new_ptl != old_ptl)
  		spin_unlock(new_ptl);

  	pte_unmap(new_pte - 1);

  	pte_unmap_unlock(old_pte - 1, old_ptl);

  	if (need_rmap_locks)
  		drop_rmap_locks(vma);

  }

  #ifdef CONFIG_HAVE_MOVE_PMD
  static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,

  		  unsigned long new_addr, pmd_t *old_pmd, pmd_t *new_pmd)

  {
  	spinlock_t *old_ptl, *new_ptl;
  	struct mm_struct *mm = vma->vm_mm;
  	pmd_t pmd;

  	/*
  	 * The destination pmd shouldn't be established, free_pgtables()

  	 * should have released it.
  	 *
  	 * However, there's a case during execve() where we use mremap
  	 * to move the initial stack, and in that case the target area
  	 * may overlap the source area (always moving down).
  	 *
  	 * If everything is PMD-aligned, that works fine, as moving
  	 * each pmd down will clear the source pmd. But if we first
  	 * have a few 4kB-only pages that get moved down, and then
  	 * hit the "now the rest is PMD-aligned, let's do everything
  	 * one pmd at a time", we will still have the old (now empty
  	 * of any 4kB pages, but still there) PMD in the page table
  	 * tree.
  	 *
  	 * Warn on it once - because we really should try to figure
  	 * out how to do this better - but then say "I won't move
  	 * this pmd".
  	 *
  	 * One alternative might be to just unmap the target pmd at
  	 * this point, and verify that it really is empty. We'll see.

  	 */

  	if (WARN_ON_ONCE(!pmd_none(*new_pmd)))

  		return false;
  
  	/*
  	 * We don't have to worry about the ordering of src and dst

  	 * ptlocks because exclusive mmap_lock prevents deadlock.

  	 */
  	old_ptl = pmd_lock(vma->vm_mm, old_pmd);
  	new_ptl = pmd_lockptr(mm, new_pmd);
  	if (new_ptl != old_ptl)
  		spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
  
  	/* Clear the pmd */
  	pmd = *old_pmd;
  	pmd_clear(old_pmd);
  
  	VM_BUG_ON(!pmd_none(*new_pmd));
  
  	/* Set the new pmd */
  	set_pmd_at(mm, new_addr, new_pmd, pmd);
  	flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
  	if (new_ptl != old_ptl)
  		spin_unlock(new_ptl);
  	spin_unlock(old_ptl);
  
  	return true;
  }
  #endif

  unsigned long move_page_tables(struct vm_area_struct *vma,

  		unsigned long old_addr, struct vm_area_struct *new_vma,

  		unsigned long new_addr, unsigned long len,
  		bool need_rmap_locks)

  {

  	unsigned long extent, next, old_end;

  	struct mmu_notifier_range range;

  	pmd_t *old_pmd, *new_pmd;

  	old_end = old_addr + len;
  	flush_cache_range(vma, old_addr, old_end);

  	mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, vma->vm_mm,
  				old_addr, old_end);

  	mmu_notifier_invalidate_range_start(&range);

  	for (; old_addr < old_end; old_addr += extent, new_addr += extent) {

  		cond_resched();

  		next = (old_addr + PMD_SIZE) & PMD_MASK;

  		/* even if next overflowed, extent below will be ok */

  		extent = next - old_addr;

  		if (extent > old_end - old_addr)
  			extent = old_end - old_addr;

  		next = (new_addr + PMD_SIZE) & PMD_MASK;
  		if (extent > next - new_addr)
  			extent = next - new_addr;

  		old_pmd = get_old_pmd(vma->vm_mm, old_addr);
  		if (!old_pmd)
  			continue;

  		new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);

  		if (!new_pmd)
  			break;

  		if (is_swap_pmd(*old_pmd) || pmd_trans_huge(*old_pmd) || pmd_devmap(*old_pmd)) {

  			if (extent == HPAGE_PMD_SIZE) {

  				bool moved;

  				/* See comment in move_ptes() */
  				if (need_rmap_locks)

  					take_rmap_locks(vma);

  				moved = move_huge_pmd(vma, old_addr, new_addr,

  						      old_pmd, new_pmd);

  				if (need_rmap_locks)

  					drop_rmap_locks(vma);

  				if (moved)

  					continue;

  			}

  			split_huge_pmd(vma, old_pmd, old_addr);

  			if (pmd_trans_unstable(old_pmd))

  				continue;

  		} else if (extent == PMD_SIZE) {
  #ifdef CONFIG_HAVE_MOVE_PMD
  			/*
  			 * If the extent is PMD-sized, try to speed the move by
  			 * moving at the PMD level if possible.
  			 */
  			bool moved;
  
  			if (need_rmap_locks)
  				take_rmap_locks(vma);
  			moved = move_normal_pmd(vma, old_addr, new_addr,

  						old_pmd, new_pmd);

  			if (need_rmap_locks)
  				drop_rmap_locks(vma);
  			if (moved)
  				continue;
  #endif

  		}

  		if (pte_alloc(new_vma->vm_mm, new_pmd))

  			break;

  		move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma,

  			  new_pmd, new_addr, need_rmap_locks);

  	}

  	mmu_notifier_invalidate_range_end(&range);

  
  	return len + old_addr - old_end;	/* how much done */

  }
  
  static unsigned long move_vma(struct vm_area_struct *vma,
  		unsigned long old_addr, unsigned long old_len,

  		unsigned long new_len, unsigned long new_addr,

  		bool *locked, unsigned long flags,
  		struct vm_userfaultfd_ctx *uf, struct list_head *uf_unmap)

  {
  	struct mm_struct *mm = vma->vm_mm;
  	struct vm_area_struct *new_vma;
  	unsigned long vm_flags = vma->vm_flags;
  	unsigned long new_pgoff;
  	unsigned long moved_len;
  	unsigned long excess = 0;

  	unsigned long hiwater_vm;

  	int split = 0;

  	int err;

  	bool need_rmap_locks;

  
  	/*
  	 * We'd prefer to avoid failure later on in do_munmap:
  	 * which may split one vma into three before unmapping.
  	 */
  	if (mm->map_count >= sysctl_max_map_count - 3)
  		return -ENOMEM;

  	/*
  	 * Advise KSM to break any KSM pages in the area to be moved:
  	 * it would be confusing if they were to turn up at the new
  	 * location, where they happen to coincide with different KSM
  	 * pages recently unmapped.  But leave vma->vm_flags as it was,
  	 * so KSM can come around to merge on vma and new_vma afterwards.
  	 */

  	err = ksm_madvise(vma, old_addr, old_addr + old_len,
  						MADV_UNMERGEABLE, &vm_flags);
  	if (err)
  		return err;

  	new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);

  	new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
  			   &need_rmap_locks);

  	if (!new_vma)
  		return -ENOMEM;

  	moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
  				     need_rmap_locks);

  	if (moved_len < old_len) {

  		err = -ENOMEM;

  	} else if (vma->vm_ops && vma->vm_ops->mremap) {
  		err = vma->vm_ops->mremap(new_vma);

  	}
  
  	if (unlikely(err)) {

  		/*
  		 * On error, move entries back from new area to old,
  		 * which will succeed since page tables still there,
  		 * and then proceed to unmap new area instead of old.
  		 */

  		move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
  				 true);

  		vma = new_vma;
  		old_len = new_len;
  		old_addr = new_addr;

  		new_addr = err;

  	} else {

  		mremap_userfaultfd_prep(new_vma, uf);

  		arch_remap(mm, old_addr, old_addr + old_len,
  			   new_addr, new_addr + new_len);

  	}

  
  	/* Conceal VM_ACCOUNT so old reservation is not undone */
  	if (vm_flags & VM_ACCOUNT) {
  		vma->vm_flags &= ~VM_ACCOUNT;
  		excess = vma->vm_end - vma->vm_start - old_len;
  		if (old_addr > vma->vm_start &&
  		    old_addr + old_len < vma->vm_end)
  			split = 1;
  	}

  	/*

  	 * If we failed to move page tables we still do total_vm increment
  	 * since do_munmap() will decrement it by old_len == new_len.
  	 *
  	 * Since total_vm is about to be raised artificially high for a
  	 * moment, we need to restore high watermark afterwards: if stats
  	 * are taken meanwhile, total_vm and hiwater_vm appear too high.
  	 * If this were a serious issue, we'd add a flag to do_munmap().

  	 */

  	hiwater_vm = mm->hiwater_vm;

  	vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT);

  	/* Tell pfnmap has moved from this vma */
  	if (unlikely(vma->vm_flags & VM_PFNMAP))
  		untrack_pfn_moved(vma);

  	if (unlikely(!err && (flags & MREMAP_DONTUNMAP))) {
  		if (vm_flags & VM_ACCOUNT) {
  			/* Always put back VM_ACCOUNT since we won't unmap */
  			vma->vm_flags |= VM_ACCOUNT;

  			vm_acct_memory(new_len >> PAGE_SHIFT);

  		}

  		/*
  		 * VMAs can actually be merged back together in copy_vma
  		 * calling merge_vma. This can happen with anonymous vmas
  		 * which have not yet been faulted, so if we were to consider
  		 * this VMA split we'll end up adding VM_ACCOUNT on the
  		 * next VMA, which is completely unrelated if this VMA
  		 * was re-merged.
  		 */
  		if (split && new_vma == vma)
  			split = 0;

  		/* We always clear VM_LOCKED[ONFAULT] on the old vma */
  		vma->vm_flags &= VM_LOCKED_CLEAR_MASK;
  
  		/* Because we won't unmap we don't need to touch locked_vm */
  		goto out;
  	}

  	if (do_munmap(mm, old_addr, old_len, uf_unmap) < 0) {

  		/* OOM: unable to split vma, just get accounts right */
  		vm_unacct_memory(excess >> PAGE_SHIFT);
  		excess = 0;
  	}

  
  	if (vm_flags & VM_LOCKED) {
  		mm->locked_vm += new_len >> PAGE_SHIFT;
  		*locked = true;
  	}
  out:

  	mm->hiwater_vm = hiwater_vm;

  
  	/* Restore VM_ACCOUNT if one or two pieces of vma left */
  	if (excess) {
  		vma->vm_flags |= VM_ACCOUNT;
  		if (split)
  			vma->vm_next->vm_flags |= VM_ACCOUNT;
  	}

  	return new_addr;
  }

  static struct vm_area_struct *vma_to_resize(unsigned long addr,

  	unsigned long old_len, unsigned long new_len, unsigned long flags,
  	unsigned long *p)

  {
  	struct mm_struct *mm = current->mm;
  	struct vm_area_struct *vma = find_vma(mm, addr);

  	unsigned long pgoff;

  
  	if (!vma || vma->vm_start > addr)

  		return ERR_PTR(-EFAULT);

  	/*
  	 * !old_len is a special case where an attempt is made to 'duplicate'
  	 * a mapping.  This makes no sense for private mappings as it will
  	 * instead create a fresh/new mapping unrelated to the original.  This
  	 * is contrary to the basic idea of mremap which creates new mappings
  	 * based on the original.  There are no known use cases for this
  	 * behavior.  As a result, fail such attempts.
  	 */
  	if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) {
  		pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap.  This is not supported.
  ", current->comm, current->pid);
  		return ERR_PTR(-EINVAL);
  	}

  	if (flags & MREMAP_DONTUNMAP && (!vma_is_anonymous(vma) ||
  			vma->vm_flags & VM_SHARED))
  		return ERR_PTR(-EINVAL);

  	if (is_vm_hugetlb_page(vma))

  		return ERR_PTR(-EINVAL);

  
  	/* We can't remap across vm area boundaries */
  	if (old_len > vma->vm_end - addr)

  		return ERR_PTR(-EFAULT);

  	if (new_len == old_len)
  		return vma;

  	/* Need to be careful about a growing mapping */

  	pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
  	pgoff += vma->vm_pgoff;
  	if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
  		return ERR_PTR(-EINVAL);
  
  	if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
  		return ERR_PTR(-EFAULT);

  
  	if (vma->vm_flags & VM_LOCKED) {
  		unsigned long locked, lock_limit;
  		locked = mm->locked_vm << PAGE_SHIFT;

  		lock_limit = rlimit(RLIMIT_MEMLOCK);

  		locked += new_len - old_len;
  		if (locked > lock_limit && !capable(CAP_IPC_LOCK))

  			return ERR_PTR(-EAGAIN);

  	}

  	if (!may_expand_vm(mm, vma->vm_flags,
  				(new_len - old_len) >> PAGE_SHIFT))

  		return ERR_PTR(-ENOMEM);

  
  	if (vma->vm_flags & VM_ACCOUNT) {
  		unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;

  		if (security_vm_enough_memory_mm(mm, charged))

  			return ERR_PTR(-ENOMEM);

  		*p = charged;
  	}
  
  	return vma;

  }

  static unsigned long mremap_to(unsigned long addr, unsigned long old_len,

  		unsigned long new_addr, unsigned long new_len, bool *locked,

  		unsigned long flags, struct vm_userfaultfd_ctx *uf,

  		struct list_head *uf_unmap_early,

  		struct list_head *uf_unmap)

  {
  	struct mm_struct *mm = current->mm;
  	struct vm_area_struct *vma;
  	unsigned long ret = -EINVAL;
  	unsigned long charged = 0;

  	unsigned long map_flags = 0;

  	if (offset_in_page(new_addr))

  		goto out;
  
  	if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
  		goto out;

  	/* Ensure the old/new locations do not overlap */
  	if (addr + old_len > new_addr && new_addr + new_len > addr)

  		goto out;

  	/*
  	 * move_vma() need us to stay 4 maps below the threshold, otherwise
  	 * it will bail out at the very beginning.
  	 * That is a problem if we have already unmaped the regions here
  	 * (new_addr, and old_addr), because userspace will not know the
  	 * state of the vma's after it gets -ENOMEM.
  	 * So, to avoid such scenario we can pre-compute if the whole
  	 * operation has high chances to success map-wise.
  	 * Worst-scenario case is when both vma's (new_addr and old_addr) get
  	 * split in 3 before unmaping it.
  	 * That means 2 more maps (1 for each) to the ones we already hold.
  	 * Check whether current map count plus 2 still leads us to 4 maps below
  	 * the threshold, otherwise return -ENOMEM here to be more safe.
  	 */
  	if ((mm->map_count + 2) >= sysctl_max_map_count - 3)
  		return -ENOMEM;

  	if (flags & MREMAP_FIXED) {
  		ret = do_munmap(mm, new_addr, new_len, uf_unmap_early);
  		if (ret)
  			goto out;
  	}

  
  	if (old_len >= new_len) {

  		ret = do_munmap(mm, addr+new_len, old_len - new_len, uf_unmap);

  		if (ret && old_len != new_len)
  			goto out;
  		old_len = new_len;
  	}

  	vma = vma_to_resize(addr, old_len, new_len, flags, &charged);

  	if (IS_ERR(vma)) {
  		ret = PTR_ERR(vma);
  		goto out;
  	}

  	/* MREMAP_DONTUNMAP expands by old_len since old_len == new_len */
  	if (flags & MREMAP_DONTUNMAP &&
  		!may_expand_vm(mm, vma->vm_flags, old_len >> PAGE_SHIFT)) {
  		ret = -ENOMEM;
  		goto out;
  	}
  
  	if (flags & MREMAP_FIXED)
  		map_flags |= MAP_FIXED;

  	if (vma->vm_flags & VM_MAYSHARE)
  		map_flags |= MAP_SHARED;

  	ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
  				((addr - vma->vm_start) >> PAGE_SHIFT),
  				map_flags);

  	if (IS_ERR_VALUE(ret))

  		goto out1;

  	/* We got a new mapping */
  	if (!(flags & MREMAP_FIXED))
  		new_addr = ret;
  
  	ret = move_vma(vma, addr, old_len, new_len, new_addr, locked, flags, uf,

  		       uf_unmap);

  	if (!(offset_in_page(ret)))

  		goto out;

  out1:
  	vm_unacct_memory(charged);

  
  out:
  	return ret;
  }

  static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
  {

  	unsigned long end = vma->vm_end + delta;

  	if (end < vma->vm_end) /* overflow */

  		return 0;

  	if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */

  		return 0;
  	if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
  			      0, MAP_FIXED) & ~PAGE_MASK)

  		return 0;

  	return 1;
  }

  /*
   * Expand (or shrink) an existing mapping, potentially moving it at the
   * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
   *
   * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
   * This option implies MREMAP_MAYMOVE.
   */

  SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
  		unsigned long, new_len, unsigned long, flags,
  		unsigned long, new_addr)

  {

  	struct mm_struct *mm = current->mm;

  	struct vm_area_struct *vma;
  	unsigned long ret = -EINVAL;
  	unsigned long charged = 0;

  	bool locked = false;

  	bool downgraded = false;

  	struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX;

  	LIST_HEAD(uf_unmap_early);

  	LIST_HEAD(uf_unmap);

  	/*
  	 * There is a deliberate asymmetry here: we strip the pointer tag
  	 * from the old address but leave the new address alone. This is
  	 * for consistency with mmap(), where we prevent the creation of
  	 * aliasing mappings in userspace by leaving the tag bits of the
  	 * mapping address intact. A non-zero tag will cause the subsequent
  	 * range checks to reject the address as invalid.
  	 *
  	 * See Documentation/arm64/tagged-address-abi.rst for more information.
  	 */

  	addr = untagged_addr(addr);

  	if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP))

  		return ret;
  
  	if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
  		return ret;

  	/*
  	 * MREMAP_DONTUNMAP is always a move and it does not allow resizing
  	 * in the process.
  	 */
  	if (flags & MREMAP_DONTUNMAP &&
  			(!(flags & MREMAP_MAYMOVE) || old_len != new_len))
  		return ret;

  	if (offset_in_page(addr))

  		return ret;

  
  	old_len = PAGE_ALIGN(old_len);
  	new_len = PAGE_ALIGN(new_len);
  
  	/*
  	 * We allow a zero old-len as a special case
  	 * for DOS-emu "duplicate shm area" thing. But
  	 * a zero new-len is nonsensical.
  	 */
  	if (!new_len)

  		return ret;

  	if (mmap_write_lock_killable(current->mm))

  		return -EINTR;

  	if (flags & (MREMAP_FIXED | MREMAP_DONTUNMAP)) {

  		ret = mremap_to(addr, old_len, new_addr, new_len,

  				&locked, flags, &uf, &uf_unmap_early,
  				&uf_unmap);

  		goto out;

  	}
  
  	/*
  	 * Always allow a shrinking remap: that just unmaps
  	 * the unnecessary pages..

  	 * __do_munmap does all the needed commit accounting, and

  	 * downgrades mmap_lock to read if so directed.

  	 */
  	if (old_len >= new_len) {

  		int retval;
  
  		retval = __do_munmap(mm, addr+new_len, old_len - new_len,
  				  &uf_unmap, true);
  		if (retval < 0 && old_len != new_len) {
  			ret = retval;

  			goto out;

  		/* Returning 1 indicates mmap_lock is downgraded to read. */

  		} else if (retval == 1)
  			downgraded = true;

  		ret = addr;

  		goto out;

  	}
  
  	/*

  	 * Ok, we need to grow..

  	 */

  	vma = vma_to_resize(addr, old_len, new_len, flags, &charged);

  	if (IS_ERR(vma)) {
  		ret = PTR_ERR(vma);

  		goto out;

  	}

  	/* old_len exactly to the end of the area..

  	 */

  	if (old_len == vma->vm_end - addr) {

  		/* can we just expand the current mapping? */

  		if (vma_expandable(vma, new_len - old_len)) {

  			int pages = (new_len - old_len) >> PAGE_SHIFT;

  			if (vma_adjust(vma, vma->vm_start, addr + new_len,
  				       vma->vm_pgoff, NULL)) {
  				ret = -ENOMEM;
  				goto out;
  			}

  			vm_stat_account(mm, vma->vm_flags, pages);

  			if (vma->vm_flags & VM_LOCKED) {

  				mm->locked_vm += pages;

  				locked = true;
  				new_addr = addr;

  			}
  			ret = addr;
  			goto out;
  		}
  	}
  
  	/*
  	 * We weren't able to just expand or shrink the area,
  	 * we need to create a new one and move it..
  	 */
  	ret = -ENOMEM;
  	if (flags & MREMAP_MAYMOVE) {

  		unsigned long map_flags = 0;
  		if (vma->vm_flags & VM_MAYSHARE)
  			map_flags |= MAP_SHARED;
  
  		new_addr = get_unmapped_area(vma->vm_file, 0, new_len,

  					vma->vm_pgoff +
  					((addr - vma->vm_start) >> PAGE_SHIFT),
  					map_flags);

  		if (IS_ERR_VALUE(new_addr)) {

  			ret = new_addr;
  			goto out;

  		}

  		ret = move_vma(vma, addr, old_len, new_len, new_addr,

  			       &locked, flags, &uf, &uf_unmap);

  	}
  out:

  	if (offset_in_page(ret)) {

  		vm_unacct_memory(charged);

  		locked = false;

  	}

  	if (downgraded)

  		mmap_read_unlock(current->mm);

  	else

  		mmap_write_unlock(current->mm);

  	if (locked && new_len > old_len)
  		mm_populate(new_addr + old_len, new_len - old_len);

  	userfaultfd_unmap_complete(mm, &uf_unmap_early);

  	mremap_userfaultfd_complete(&uf, addr, ret, old_len);

  	userfaultfd_unmap_complete(mm, &uf_unmap);

  	return ret;
  }