text: /*
   *	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/highmem.h>
  #include <linux/security.h>
  #include <linux/syscalls.h>
  #include <linux/mmu_notifier.h>
  
  #include <asm/uaccess.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;
  	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 pmd;
  }
  
  static pmd_t *alloc_new_pmd(struct mm_struct *mm, unsigned long addr)
  {
  	pgd_t *pgd;
  	pud_t *pud;
  	pmd_t *pmd;
  
  	pgd = pgd_offset(mm, addr);
  	pud = pud_alloc(mm, pgd, addr);
  	if (!pud)
  		return NULL;
  
  	pmd = pmd_alloc(mm, pud, addr);
  	if (!pmd)
  		return NULL;
  
  	if (!pmd_present(*pmd) && __pte_alloc(mm, pmd, addr))
  		return NULL;
  
  	return pmd;
  }
  
  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)
  {
  	struct address_space *mapping = NULL;
  	struct mm_struct *mm = vma->vm_mm;
  	pte_t *old_pte, *new_pte, pte;
  	spinlock_t *old_ptl, *new_ptl;
  	unsigned long old_start;
  
  	old_start = old_addr;
  	mmu_notifier_invalidate_range_start(vma->vm_mm,
  					    old_start, old_end);
  	if (vma->vm_file) {
  		/*
  		 * Subtle point from Rajesh Venkatasubramanian: before
  		 * moving file-based ptes, we must lock truncate_pagecache
  		 * 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;
  	}
  
  	/*
  	 * We don't have to worry about the ordering of src and dst
  	 * pte locks because exclusive mmap_sem prevents deadlock.
  	 */
  	old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
   	new_pte = pte_offset_map_nested(new_pmd, new_addr);
  	new_ptl = pte_lockptr(mm, new_pmd);
  	if (new_ptl != old_ptl)
  		spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
  	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_clear_flush(vma, old_addr, old_pte);
  		pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
  		set_pte_at(mm, new_addr, new_pte, pte);
  	}
  
  	arch_leave_lazy_mmu_mode();
  	if (new_ptl != old_ptl)
  		spin_unlock(new_ptl);
  	pte_unmap_nested(new_pte - 1);
  	pte_unmap_unlock(old_pte - 1, old_ptl);
  	if (mapping)
  		spin_unlock(&mapping->i_mmap_lock);
  	mmu_notifier_invalidate_range_end(vma->vm_mm, old_start, old_end);
  }
  
  #define LATENCY_LIMIT	(64 * PAGE_SIZE)
  
  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 extent, next, old_end;
  	pmd_t *old_pmd, *new_pmd;
  
  	old_end = old_addr + len;
  	flush_cache_range(vma, old_addr, old_end);
  
  	for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
  		cond_resched();
  		next = (old_addr + PMD_SIZE) & PMD_MASK;
  		if (next - 1 > old_end)
  			next = old_end;
  		extent = next - old_addr;
  		old_pmd = get_old_pmd(vma->vm_mm, old_addr);
  		if (!old_pmd)
  			continue;
  		new_pmd = alloc_new_pmd(vma->vm_mm, new_addr);
  		if (!new_pmd)
  			break;
  		next = (new_addr + PMD_SIZE) & PMD_MASK;
  		if (extent > next - new_addr)
  			extent = next - new_addr;
  		if (extent > LATENCY_LIMIT)
  			extent = LATENCY_LIMIT;
  		move_ptes(vma, old_pmd, old_addr, old_addr + extent,
  				new_vma, new_pmd, new_addr);
  	}
  
  	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)
  {
  	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;
  
  	/*
  	 * 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);
  	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.
  	 *
  	 * 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;
  	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;
  	}
  	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;
  	}
  
  	if (vm_flags & VM_LOCKED) {
  		mm->locked_vm += new_len >> PAGE_SHIFT;
  		if (new_len > old_len)
  			mlock_vma_pages_range(new_vma, new_addr + old_len,
  						       new_addr + new_len);
  	}
  
  	return new_addr;
  }
  
  static struct vm_area_struct *vma_to_resize(unsigned long addr,
  	unsigned long old_len, unsigned long new_len, unsigned long *p)
  {
  	struct mm_struct *mm = current->mm;
  	struct vm_area_struct *vma = find_vma(mm, addr);
  
  	if (!vma || vma->vm_start > addr)
  		goto Efault;
  
  	if (is_vm_hugetlb_page(vma))
  		goto Einval;
  
  	/* We can't remap across vm area boundaries */
  	if (old_len > vma->vm_end - addr)
  		goto Efault;
  
  	if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)) {
  		if (new_len > old_len)
  			goto 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))
  			goto Eagain;
  	}
  
  	if (!may_expand_vm(mm, (new_len - old_len) >> PAGE_SHIFT))
  		goto Enomem;
  
  	if (vma->vm_flags & VM_ACCOUNT) {
  		unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
  		if (security_vm_enough_memory(charged))
  			goto Efault;
  		*p = charged;
  	}
  
  	return vma;
  
  Efault:	/* very odd choice for most of the cases, but... */
  	return ERR_PTR(-EFAULT);
  Einval:
  	return ERR_PTR(-EINVAL);
  Enomem:
  	return ERR_PTR(-ENOMEM);
  Eagain:
  	return ERR_PTR(-EAGAIN);
  }
  
  static unsigned long mremap_to(unsigned long addr,
  	unsigned long old_len, unsigned long new_addr,
  	unsigned long new_len)
  {
  	struct mm_struct *mm = current->mm;
  	struct vm_area_struct *vma;
  	unsigned long ret = -EINVAL;
  	unsigned long charged = 0;
  	unsigned long map_flags;
  
  	if (new_addr & ~PAGE_MASK)
  		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 = security_file_mmap(NULL, 0, 0, 0, new_addr, 1);
  	if (ret)
  		goto out;
  
  	ret = do_munmap(mm, new_addr, new_len);
  	if (ret)
  		goto out;
  
  	if (old_len >= new_len) {
  		ret = do_munmap(mm, addr+new_len, old_len - new_len);
  		if (ret && old_len != new_len)
  			goto out;
  		old_len = new_len;
  	}
  
  	vma = vma_to_resize(addr, old_len, new_len, &charged);
  	if (IS_ERR(vma)) {
  		ret = PTR_ERR(vma);
  		goto out;
  	}
  
  	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 (ret & ~PAGE_MASK)
  		goto out1;
  
  	ret = move_vma(vma, addr, old_len, new_len, new_addr);
  	if (!(ret & ~PAGE_MASK))
  		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.
   */
  unsigned long do_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;
  
  	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;
  
  	if (flags & MREMAP_FIXED) {
  		if (flags & MREMAP_MAYMOVE)
  			ret = mremap_to(addr, old_len, new_addr, new_len);
  		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(mm, addr+new_len, old_len - new_len);
  		if (ret && old_len != new_len)
  			goto out;
  		ret = addr;
  		goto out;
  	}
  
  	/*
  	 * Ok, we need to grow..
  	 */
  	vma = vma_to_resize(addr, old_len, new_len, &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;
  			}
  
  			mm->total_vm += pages;
  			vm_stat_account(mm, vma->vm_flags, vma->vm_file, pages);
  			if (vma->vm_flags & VM_LOCKED) {
  				mm->locked_vm += pages;
  				mlock_vma_pages_range(vma, 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) {
  		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 (new_addr & ~PAGE_MASK) {
  			ret = new_addr;
  			goto out;
  		}
  
  		ret = security_file_mmap(NULL, 0, 0, 0, new_addr, 1);
  		if (ret)
  			goto out;
  		ret = move_vma(vma, addr, old_len, new_len, new_addr);
  	}
  out:
  	if (ret & ~PAGE_MASK)
  		vm_unacct_memory(charged);
  	return ret;
  }
  
  SYSCALL_DEFINE5(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;
  }
  