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linux/mm/mremap.c
Nick Piggin 9a61c349b2 [PATCH] mm: remap ZERO_PAGE mappings 
filemap_xip's nopage routine maps the ZERO_PAGE into readonly mappings, if it
has no data page to map there: then if the hole in the file is later filled,
__xip_unmap uses an rmap technique to replace the ZERO_PAGEs mapped for that
offset by the newly allocated file page, so that established mappings will see
the newly written data.

However, on MIPS (alone) there's not one but as many as eight ZERO_PAGEs,
chosen for coloring by user virtual address; and if mremap has meanwhile been
used to move a mapping containing a ZERO_PAGE, it will generally not match the
ZERO_PAGE(address) __xip_unmap is looking for.

To maintain XIP's established mappings correctly on MIPS, we need Nick's fix
to mremap's move_one_page (originally presented as an optimization), to
replace the ZERO_PAGE appropriate to the old address by the ZERO_PAGE
appropriate to the new address.

(But when I first saw this, I was thinking the ZERO_PAGEs themselves would get
corrupted, very bad.  Now I think it's the other way round, that the
established mappings will fail to see the newly written data: incorrect, but
not corrupting everything else.  Whether filemap_xip's technique is generally
safe, I'd hesitate to say in a hurry: it's interesting, but we've never tried
to do that in tmpfs.)

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-09-05 00:05:44 -07:00

436 lines
11 KiB
C
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/*
* 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 */
if (pfn_valid(pte_pfn(pte)) &&
pte_page(pte) == ZERO_PAGE(old_addr))
pte = pte_wrprotect(mk_pte(ZERO_PAGE(new_addr), new_vma->vm_page_prot));
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;
}
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