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* linux/mm/fremap.c
* Explicit pagetable population and nonlinear (random) mappings support.
* started by Ingo Molnar, Copyright (C) 2002, 2003
#include <linux/backing-dev.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/file.h>
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/swapops.h>
#include <linux/rmap.h>
#include <linux/module.h>
#include <linux/syscalls.h>
#include <linux/mmu_notifier.h>
#include <asm/mmu_context.h>
#include <asm/cacheflush.h>
#include <asm/tlbflush.h>
#include "internal.h"
static void zap_pte(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long addr, pte_t *ptep)
pte_t pte = *ptep;
if (pte_present(pte)) {
struct page *page;
flush_cache_page(vma, addr, pte_pfn(pte));
pte = ptep_clear_flush(vma, addr, ptep);
page = vm_normal_page(vma, addr, pte);
if (page) {
if (pte_dirty(pte))
dec_mm_counter(mm, MM_FILEPAGES);
} else {
if (!pte_file(pte))
pte_clear_not_present_full(mm, addr, ptep, 0);
* Install a file pte to a given virtual memory address, release any
* previously existing mapping.
static int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long addr, unsigned long pgoff, pgprot_t prot)
int err = -ENOMEM;
pte_t *pte;
spinlock_t *ptl;
pte = get_locked_pte(mm, addr, &ptl);
if (!pte)
goto out;
if (!pte_none(*pte))
zap_pte(mm, vma, addr, pte);
set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));
* We don't need to run update_mmu_cache() here because the "file pte"
* being installed by install_file_pte() is not a real pte - it's a
* non-present entry (like a swap entry), noting what file offset should
* be mapped there when there's a fault (in a non-linear vma where
* that's not obvious).
pte_unmap_unlock(pte, ptl);
err = 0;
return err;
static int populate_range(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long addr, unsigned long size, pgoff_t pgoff)
int err;
do {
err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot);
if (err)
return err;
size -= PAGE_SIZE;
addr += PAGE_SIZE;
} while (size);
return 0;
* sys_remap_file_pages - remap arbitrary pages of an existing VM_SHARED vma
* @start: start of the remapped virtual memory range
* @size: size of the remapped virtual memory range
* @prot: new protection bits of the range (see NOTE)
* @pgoff: to-be-mapped page of the backing store file
* @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
* sys_remap_file_pages remaps arbitrary pages of an existing VM_SHARED vma
* (shared backing store file).
* This syscall works purely via pagetables, so it's the most efficient
* way to map the same (large) file into a given virtual window. Unlike
* mmap()/mremap() it does not create any new vmas. The new mappings are
* also safe across swapout.
* NOTE: the @prot parameter right now is ignored (but must be zero),
* and the vma's default protection is used. Arbitrary protections
* might be implemented in the future.
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 address_space *mapping;
struct vm_area_struct *vma;
int err = -EINVAL;
int has_write_lock = 0;
if (prot)
return err;
* Sanitize the syscall parameters:
start = start & PAGE_MASK;
size = size & PAGE_MASK;
/* Does the address range wrap, or is the span zero-sized? */
if (start + size <= start)
return err;
/* Does pgoff wrap? */
if (pgoff + (size >> PAGE_SHIFT) < pgoff)
return err;
/* Can we represent this offset inside this architecture's pte's? */
if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
return err;
/* We need down_write() to change vma->vm_flags. */
vma = find_vma(mm, start);
* Make sure the vma is shared, that it supports prefaulting,
* and that the remapped range is valid and fully within
* the single existing vma. vm_private_data is used as a
* swapout cursor in a VM_NONLINEAR vma.
if (!vma || !(vma->vm_flags & VM_SHARED))
goto out;
if (vma->vm_private_data && !(vma->vm_flags & VM_NONLINEAR))
goto out;
if (!(vma->vm_flags & VM_CAN_NONLINEAR))
goto out;
if (start < vma->vm_start || start + size > vma->vm_end)
goto out;
/* Must set VM_NONLINEAR before any pages are populated. */
if (!(vma->vm_flags & VM_NONLINEAR)) {
/* Don't need a nonlinear mapping, exit success */
if (pgoff == linear_page_index(vma, start)) {
err = 0;
goto out;
if (!has_write_lock) {
has_write_lock = 1;
goto retry;
mapping = vma->vm_file->f_mapping;
* page_mkclean doesn't work on nonlinear vmas, so if
* dirty pages need to be accounted, emulate with linear
* vmas.
if (mapping_cap_account_dirty(mapping)) {
unsigned long addr;
struct file *file = vma->vm_file;
flags &= MAP_NONBLOCK;
addr = mmap_region(file, start, size,
flags, vma->vm_flags, pgoff);
if (IS_ERR_VALUE(addr)) {
err = addr;
} else {
BUG_ON(addr != start);
err = 0;
goto out;
vma->vm_flags |= VM_NONLINEAR;
vma_prio_tree_remove(vma, &mapping->i_mmap);
vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
if (vma->vm_flags & VM_LOCKED) {
* drop PG_Mlocked flag for over-mapped range
vm_flags_t saved_flags = vma->vm_flags;
munlock_vma_pages_range(vma, start, start + size);
vma->vm_flags = saved_flags;
mmu_notifier_invalidate_range_start(mm, start, start + size);
err = populate_range(mm, vma, start, size, pgoff);
mmu_notifier_invalidate_range_end(mm, start, start + size);
if (!err && !(flags & MAP_NONBLOCK)) {
if (vma->vm_flags & VM_LOCKED) {
* might be mapping previously unmapped range of file
mlock_vma_pages_range(vma, start, start + size);
} else {
if (unlikely(has_write_lock)) {
has_write_lock = 0;
make_pages_present(start, start+size);
* We can't clear VM_NONLINEAR because we'd have to do
* it after ->populate completes, and that would prevent
* downgrading the lock. (Locks can't be upgraded).
if (likely(!has_write_lock))
return err;
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