mm/mremap.c - linux - Git at Google

 /*
  *	mm/mremap.c
  *
  *	(C) Copyright 1996 Linus Torvalds
  *
  *	Address space accounting code	<alan@redhat.com>
  *	(C) Copyright 2002 Red Hat Inc, All Rights Reserved
  */

 #include <linux/mm.h>
 #include <linux/hugetlb.h>
 #include <linux/slab.h>
 #include <linux/shm.h>
 #include <linux/mman.h>
 #include <linux/swap.h>
 #include <linux/fs.h>
 #include <linux/highmem.h>
 #include <linux/security.h>
 #include <linux/syscalls.h>

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

 static pte_t *get_one_pte_map_nested(struct mm_struct *mm, unsigned long addr)
 {
 	pgd_t *pgd;
 	pud_t *pud;
 	pmd_t *pmd;
 	pte_t *pte = NULL;

 	pgd = pgd_offset(mm, addr);
 	if (pgd_none_or_clear_bad(pgd))
 		goto end;

 	pud = pud_offset(pgd, addr);
 	if (pud_none_or_clear_bad(pud))
 		goto end;

 	pmd = pmd_offset(pud, addr);
 	if (pmd_none_or_clear_bad(pmd))
 		goto end;

 	pte = pte_offset_map_nested(pmd, addr);
 	if (pte_none(*pte)) {
 		pte_unmap_nested(pte);
 		pte = NULL;
 	}
 end:
 	return pte;
 }

 static pte_t *get_one_pte_map(struct mm_struct *mm, unsigned long addr)
 {
 	pgd_t *pgd;
 	pud_t *pud;
 	pmd_t *pmd;

 	pgd = pgd_offset(mm, addr);
 	if (pgd_none_or_clear_bad(pgd))
 		return NULL;

 	pud = pud_offset(pgd, addr);
 	if (pud_none_or_clear_bad(pud))
 		return NULL;

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

 	return pte_offset_map(pmd, addr);
 }

 static inline pte_t *alloc_one_pte_map(struct mm_struct *mm, unsigned long addr)
 {
 	pgd_t *pgd;
 	pud_t *pud;
 	pmd_t *pmd;
 	pte_t *pte = NULL;

 	pgd = pgd_offset(mm, addr);

 	pud = pud_alloc(mm, pgd, addr);
 	if (!pud)
 		return NULL;
 	pmd = pmd_alloc(mm, pud, addr);
 	if (pmd)
 		pte = pte_alloc_map(mm, pmd, addr);
 	return pte;
 }

 static int
 move_one_page(struct vm_area_struct *vma, unsigned long old_addr,
 		struct vm_area_struct *new_vma, unsigned long new_addr)
 {
 	struct address_space *mapping = NULL;
 	struct mm_struct *mm = vma->vm_mm;
 	int error = 0;
 	pte_t *src, *dst;

 	if (vma->vm_file) {
 		/*
 		 * Subtle point from Rajesh Venkatasubramanian: before
 		 * moving file-based ptes, we must lock vmtruncate out,
 		 * since it might clean the dst vma before the src vma,
 		 * and we propagate stale pages into the dst afterward.
 		 */
 		mapping = vma->vm_file->f_mapping;
 		spin_lock(&mapping->i_mmap_lock);
 		if (new_vma->vm_truncate_count &&
 		    new_vma->vm_truncate_count != vma->vm_truncate_count)
 			new_vma->vm_truncate_count = 0;
 	}
 	spin_lock(&mm->page_table_lock);

 	src = get_one_pte_map_nested(mm, old_addr);
 	if (src) {
 		/*
 		 * Look to see whether alloc_one_pte_map needs to perform a
 		 * memory allocation.  If it does then we need to drop the
 		 * atomic kmap
 		 */
 		dst = get_one_pte_map(mm, new_addr);
 		if (unlikely(!dst)) {
 			pte_unmap_nested(src);
 			if (mapping)
 				spin_unlock(&mapping->i_mmap_lock);
 			dst = alloc_one_pte_map(mm, new_addr);
 			if (mapping && !spin_trylock(&mapping->i_mmap_lock)) {
 				spin_unlock(&mm->page_table_lock);
 				spin_lock(&mapping->i_mmap_lock);
 				spin_lock(&mm->page_table_lock);
 			}
 			src = get_one_pte_map_nested(mm, old_addr);
 		}
 		/*
 		 * Since alloc_one_pte_map can drop and re-acquire
 		 * page_table_lock, we should re-check the src entry...
 		 */
 		if (src) {
 			if (dst) {
 				pte_t pte;
 				pte = ptep_clear_flush(vma, old_addr, src);

 				/* ZERO_PAGE can be dependant on virtual addr */
 				pte = move_pte(pte, new_vma->vm_page_prot,
 							old_addr, new_addr);
 				set_pte_at(mm, new_addr, dst, pte);
 			} else
 				error = -ENOMEM;
 			pte_unmap_nested(src);
 		}
 		if (dst)
 			pte_unmap(dst);
 	}
 	spin_unlock(&mm->page_table_lock);
 	if (mapping)
 		spin_unlock(&mapping->i_mmap_lock);
 	return error;
 }

 static 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)
 {
 	unsigned long offset;

 	flush_cache_range(vma, old_addr, old_addr + len);

 	/*
 	 * This is not the clever way to do this, but we're taking the
 	 * easy way out on the assumption that most remappings will be
 	 * only a few pages.. This also makes error recovery easier.
 	 */
 	for (offset = 0; offset < len; offset += PAGE_SIZE) {
 		if (move_one_page(vma, old_addr + offset,
 				new_vma, new_addr + offset) < 0)
 			break;
 		cond_resched();
 	}
 	return offset;
 }

 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)
 {
 	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;
 	int split = 0;

 	/*
 	 * 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;

 	new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
 	new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff);
 	if (!new_vma)
 		return -ENOMEM;

 	moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len);
 	if (moved_len < old_len) {
 		/*
 		 * 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);
 		vma = new_vma;
 		old_len = new_len;
 		old_addr = new_addr;
 		new_addr = -ENOMEM;
 	}

 	/* 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
 	 */
 	mm->total_vm += new_len >> PAGE_SHIFT;
 	__vm_stat_account(mm, vma->vm_flags, vma->vm_file, new_len>>PAGE_SHIFT);

 	if (do_munmap(mm, old_addr, old_len) < 0) {
 		/* OOM: unable to split vma, just get accounts right */
 		vm_unacct_memory(excess >> PAGE_SHIFT);
 		excess = 0;
 	}

 	/* 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;
 	}

 	if (vm_flags & VM_LOCKED) {
 		mm->locked_vm += new_len >> PAGE_SHIFT;
 		if (new_len > old_len)
 			make_pages_present(new_addr + old_len,
 					   new_addr + new_len);
 	}

 	return new_addr;
 }

 /*
  * 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.
  */
 unsigned long do_mremap(unsigned long addr,
 	unsigned long old_len, unsigned long new_len,
 	unsigned long flags, unsigned long new_addr)
 {
 	struct vm_area_struct *vma;
 	unsigned long ret = -EINVAL;
 	unsigned long charged = 0;

 	if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
 		goto out;

 	if (addr & ~PAGE_MASK)
 		goto out;

 	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)
 		goto out;

 	/* new_addr is only valid if MREMAP_FIXED is specified */
 	if (flags & MREMAP_FIXED) {
 		if (new_addr & ~PAGE_MASK)
 			goto out;
 		if (!(flags & MREMAP_MAYMOVE))
 			goto out;

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

 		/* Check if the location we're moving into overlaps the
 		 * old location at all, and fail if it does.
 		 */
 		if ((new_addr <= addr) && (new_addr+new_len) > addr)
 			goto out;

 		if ((addr <= new_addr) && (addr+old_len) > new_addr)
 			goto out;

 		ret = do_munmap(current->mm, new_addr, new_len);
 		if (ret)
 			goto out;
 	}

 	/*
 	 * Always allow a shrinking remap: that just unmaps
 	 * the unnecessary pages..
 	 * do_munmap does all the needed commit accounting
 	 */
 	if (old_len >= new_len) {
 		ret = do_munmap(current->mm, addr+new_len, old_len - new_len);
 		if (ret && old_len != new_len)
 			goto out;
 		ret = addr;
 		if (!(flags & MREMAP_FIXED) || (new_addr == addr))
 			goto out;
 		old_len = new_len;
 	}

 	/*
 	 * Ok, we need to grow..  or relocate.
 	 */
 	ret = -EFAULT;
 	vma = find_vma(current->mm, addr);
 	if (!vma || vma->vm_start > addr)
 		goto out;
 	if (is_vm_hugetlb_page(vma)) {
 		ret = -EINVAL;
 		goto out;
 	}
 	/* We can't remap across vm area boundaries */
 	if (old_len > vma->vm_end - addr)
 		goto out;
 	if (vma->vm_flags & VM_DONTEXPAND) {
 		if (new_len > old_len)
 			goto out;
 	}
 	if (vma->vm_flags & VM_LOCKED) {
 		unsigned long locked, lock_limit;
 		locked = current->mm->locked_vm << PAGE_SHIFT;
 		lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
 		locked += new_len - old_len;
 		ret = -EAGAIN;
 		if (locked > lock_limit && !capable(CAP_IPC_LOCK))
 			goto out;
 	}
 	if (!may_expand_vm(current->mm, (new_len - old_len) >> PAGE_SHIFT)) {
 		ret = -ENOMEM;
 		goto out;
 	}

 	if (vma->vm_flags & VM_ACCOUNT) {
 		charged = (new_len - old_len) >> PAGE_SHIFT;
 		if (security_vm_enough_memory(charged))
 			goto out_nc;
 	}

 	/* old_len exactly to the end of the area..
 	 * And we're not relocating the area.
 	 */
 	if (old_len == vma->vm_end - addr &&
 	    !((flags & MREMAP_FIXED) && (addr != new_addr)) &&
 	    (old_len != new_len || !(flags & MREMAP_MAYMOVE))) {
 		unsigned long max_addr = TASK_SIZE;
 		if (vma->vm_next)
 			max_addr = vma->vm_next->vm_start;
 		/* can we just expand the current mapping? */
 		if (max_addr - addr >= new_len) {
 			int pages = (new_len - old_len) >> PAGE_SHIFT;

 			vma_adjust(vma, vma->vm_start,
 				addr + new_len, vma->vm_pgoff, NULL);

 			current->mm->total_vm += pages;
 			__vm_stat_account(vma->vm_mm, vma->vm_flags,
 							vma->vm_file, pages);
 			if (vma->vm_flags & VM_LOCKED) {
 				current->mm->locked_vm += pages;
 				make_pages_present(addr + old_len,
 						   addr + new_len);
 			}
 			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) {
 		if (!(flags & MREMAP_FIXED)) {
 			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, map_flags);
 			ret = new_addr;
 			if (new_addr & ~PAGE_MASK)
 				goto out;
 		}
 		ret = move_vma(vma, addr, old_len, new_len, new_addr);
 	}
 out:
 	if (ret & ~PAGE_MASK)
 		vm_unacct_memory(charged);
 out_nc:
 	return ret;
 }

 asmlinkage unsigned long sys_mremap(unsigned long addr,
 	unsigned long old_len, unsigned long new_len,
 	unsigned long flags, unsigned long new_addr)
 {
 	unsigned long ret;

 	down_write(&current->mm->mmap_sem);
 	ret = do_mremap(addr, old_len, new_len, flags, new_addr);
 	up_write(&current->mm->mmap_sem);
 	return ret;
 }
	/*
	* mm/mremap.c
	*
	* (C) Copyright 1996 Linus Torvalds
	*
	* Address space accounting code <alan@redhat.com>
	* (C) Copyright 2002 Red Hat Inc, All Rights Reserved
	*/

	#include <linux/mm.h>
	#include <linux/hugetlb.h>
	#include <linux/slab.h>
	#include <linux/shm.h>
	#include <linux/mman.h>
	#include <linux/swap.h>
	#include <linux/fs.h>
	#include <linux/highmem.h>
	#include <linux/security.h>
	#include <linux/syscalls.h>

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

	static pte_t get_one_pte_map_nested(struct mm_struct mm, unsigned long addr)
	{
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd;
	pte_t *pte = NULL;

	pgd = pgd_offset(mm, addr);
	if (pgd_none_or_clear_bad(pgd))
	goto end;

	pud = pud_offset(pgd, addr);
	if (pud_none_or_clear_bad(pud))
	goto end;

	pmd = pmd_offset(pud, addr);
	if (pmd_none_or_clear_bad(pmd))
	goto end;

	pte = pte_offset_map_nested(pmd, addr);
	if (pte_none(*pte)) {
	pte_unmap_nested(pte);
	pte = NULL;
	}
	end:
	return pte;
	}

	static pte_t get_one_pte_map(struct mm_struct mm, unsigned long addr)
	{
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd;

	pgd = pgd_offset(mm, addr);
	if (pgd_none_or_clear_bad(pgd))
	return NULL;

	pud = pud_offset(pgd, addr);
	if (pud_none_or_clear_bad(pud))
	return NULL;

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

	return pte_offset_map(pmd, addr);
	}

	static inline pte_t alloc_one_pte_map(struct mm_struct mm, unsigned long addr)
	{
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd;
	pte_t *pte = NULL;

	pgd = pgd_offset(mm, addr);

	pud = pud_alloc(mm, pgd, addr);
	if (!pud)
	return NULL;
	pmd = pmd_alloc(mm, pud, addr);
	if (pmd)
	pte = pte_alloc_map(mm, pmd, addr);
	return pte;
	}

	static int
	move_one_page(struct vm_area_struct *vma, unsigned long old_addr,
	struct vm_area_struct *new_vma, unsigned long new_addr)
	{
	struct address_space *mapping = NULL;
	struct mm_struct *mm = vma->vm_mm;
	int error = 0;
	pte_t src, dst;

	if (vma->vm_file) {
	/*
	* Subtle point from Rajesh Venkatasubramanian: before
	* moving file-based ptes, we must lock vmtruncate out,
	* since it might clean the dst vma before the src vma,
	* and we propagate stale pages into the dst afterward.
	*/
	mapping = vma->vm_file->f_mapping;
	spin_lock(&mapping->i_mmap_lock);
	if (new_vma->vm_truncate_count &&
	new_vma->vm_truncate_count != vma->vm_truncate_count)
	new_vma->vm_truncate_count = 0;
	}
	spin_lock(&mm->page_table_lock);

	src = get_one_pte_map_nested(mm, old_addr);
	if (src) {
	/*
	* Look to see whether alloc_one_pte_map needs to perform a
	* memory allocation. If it does then we need to drop the
	* atomic kmap
	*/
	dst = get_one_pte_map(mm, new_addr);
	if (unlikely(!dst)) {
	pte_unmap_nested(src);
	if (mapping)
	spin_unlock(&mapping->i_mmap_lock);
	dst = alloc_one_pte_map(mm, new_addr);
	if (mapping && !spin_trylock(&mapping->i_mmap_lock)) {
	spin_unlock(&mm->page_table_lock);
	spin_lock(&mapping->i_mmap_lock);
	spin_lock(&mm->page_table_lock);
	}
	src = get_one_pte_map_nested(mm, old_addr);
	}
	/*
	* Since alloc_one_pte_map can drop and re-acquire
	* page_table_lock, we should re-check the src entry...
	*/
	if (src) {
	if (dst) {
	pte_t pte;
	pte = ptep_clear_flush(vma, old_addr, src);

	/* ZERO_PAGE can be dependant on virtual addr */
	pte = move_pte(pte, new_vma->vm_page_prot,
	old_addr, new_addr);
	set_pte_at(mm, new_addr, dst, pte);
	} else
	error = -ENOMEM;
	pte_unmap_nested(src);
	}
	if (dst)
	pte_unmap(dst);
	}
	spin_unlock(&mm->page_table_lock);
	if (mapping)
	spin_unlock(&mapping->i_mmap_lock);
	return error;
	}

	static 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)
	{
	unsigned long offset;

	flush_cache_range(vma, old_addr, old_addr + len);

	/*
	* This is not the clever way to do this, but we're taking the
	* easy way out on the assumption that most remappings will be
	* only a few pages.. This also makes error recovery easier.
	*/
	for (offset = 0; offset < len; offset += PAGE_SIZE) {
	if (move_one_page(vma, old_addr + offset,
	new_vma, new_addr + offset) < 0)
	break;
	cond_resched();
	}
	return offset;
	}

	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)
	{
	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;
	int split = 0;

	/*
	* 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;

	new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
	new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff);
	if (!new_vma)
	return -ENOMEM;

	moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len);
	if (moved_len < old_len) {
	/*
	* 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);
	vma = new_vma;
	old_len = new_len;
	old_addr = new_addr;
	new_addr = -ENOMEM;
	}

	/* 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
	*/
	mm->total_vm += new_len >> PAGE_SHIFT;
	__vm_stat_account(mm, vma->vm_flags, vma->vm_file, new_len>>PAGE_SHIFT);

	if (do_munmap(mm, old_addr, old_len) < 0) {
	/* OOM: unable to split vma, just get accounts right */
	vm_unacct_memory(excess >> PAGE_SHIFT);
	excess = 0;
	}

	/* 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;
	}

	if (vm_flags & VM_LOCKED) {
	mm->locked_vm += new_len >> PAGE_SHIFT;
	if (new_len > old_len)
	make_pages_present(new_addr + old_len,
	new_addr + new_len);
	}

	return new_addr;
	}

	/*
	* 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.
	*/
	unsigned long do_mremap(unsigned long addr,
	unsigned long old_len, unsigned long new_len,
	unsigned long flags, unsigned long new_addr)
	{
	struct vm_area_struct *vma;
	unsigned long ret = -EINVAL;
	unsigned long charged = 0;

	if (flags & ~(MREMAP_FIXED \| MREMAP_MAYMOVE))
	goto out;

	if (addr & ~PAGE_MASK)
	goto out;

	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)
	goto out;

	/* new_addr is only valid if MREMAP_FIXED is specified */
	if (flags & MREMAP_FIXED) {
	if (new_addr & ~PAGE_MASK)
	goto out;
	if (!(flags & MREMAP_MAYMOVE))
	goto out;

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

	/* Check if the location we're moving into overlaps the
	* old location at all, and fail if it does.
	*/
	if ((new_addr <= addr) && (new_addr+new_len) > addr)
	goto out;

	if ((addr <= new_addr) && (addr+old_len) > new_addr)
	goto out;

	ret = do_munmap(current->mm, new_addr, new_len);
	if (ret)
	goto out;
	}

	/*
	* Always allow a shrinking remap: that just unmaps
	* the unnecessary pages..
	* do_munmap does all the needed commit accounting
	*/
	if (old_len >= new_len) {
	ret = do_munmap(current->mm, addr+new_len, old_len - new_len);
	if (ret && old_len != new_len)
	goto out;
	ret = addr;
	if (!(flags & MREMAP_FIXED) \|\| (new_addr == addr))
	goto out;
	old_len = new_len;
	}

	/*
	* Ok, we need to grow.. or relocate.
	*/
	ret = -EFAULT;
	vma = find_vma(current->mm, addr);
	if (!vma \|\| vma->vm_start > addr)
	goto out;
	if (is_vm_hugetlb_page(vma)) {
	ret = -EINVAL;
	goto out;
	}
	/* We can't remap across vm area boundaries */
	if (old_len > vma->vm_end - addr)
	goto out;
	if (vma->vm_flags & VM_DONTEXPAND) {
	if (new_len > old_len)
	goto out;
	}
	if (vma->vm_flags & VM_LOCKED) {
	unsigned long locked, lock_limit;
	locked = current->mm->locked_vm << PAGE_SHIFT;
	lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
	locked += new_len - old_len;
	ret = -EAGAIN;
	if (locked > lock_limit && !capable(CAP_IPC_LOCK))
	goto out;
	}
	if (!may_expand_vm(current->mm, (new_len - old_len) >> PAGE_SHIFT)) {
	ret = -ENOMEM;
	goto out;
	}

	if (vma->vm_flags & VM_ACCOUNT) {
	charged = (new_len - old_len) >> PAGE_SHIFT;
	if (security_vm_enough_memory(charged))
	goto out_nc;
	}

	/* old_len exactly to the end of the area..
	* And we're not relocating the area.
	*/
	if (old_len == vma->vm_end - addr &&
	!((flags & MREMAP_FIXED) && (addr != new_addr)) &&
	(old_len != new_len \|\| !(flags & MREMAP_MAYMOVE))) {
	unsigned long max_addr = TASK_SIZE;
	if (vma->vm_next)
	max_addr = vma->vm_next->vm_start;
	/* can we just expand the current mapping? */
	if (max_addr - addr >= new_len) {
	int pages = (new_len - old_len) >> PAGE_SHIFT;

	vma_adjust(vma, vma->vm_start,
	addr + new_len, vma->vm_pgoff, NULL);

	current->mm->total_vm += pages;
	__vm_stat_account(vma->vm_mm, vma->vm_flags,
	vma->vm_file, pages);
	if (vma->vm_flags & VM_LOCKED) {
	current->mm->locked_vm += pages;
	make_pages_present(addr + old_len,
	addr + new_len);
	}
	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) {
	if (!(flags & MREMAP_FIXED)) {
	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, map_flags);
	ret = new_addr;
	if (new_addr & ~PAGE_MASK)
	goto out;
	}
	ret = move_vma(vma, addr, old_len, new_len, new_addr);
	}
	out:
	if (ret & ~PAGE_MASK)
	vm_unacct_memory(charged);
	out_nc:
	return ret;
	}

	asmlinkage unsigned long sys_mremap(unsigned long addr,
	unsigned long old_len, unsigned long new_len,
	unsigned long flags, unsigned long new_addr)
	{
	unsigned long ret;

	down_write(&current->mm->mmap_sem);
	ret = do_mremap(addr, old_len, new_len, flags, new_addr);
	up_write(&current->mm->mmap_sem);
	return ret;
	}