LXR linux/mm/fremap.c

   1/*
   2 *   linux/mm/fremap.c
   3 * 
   4 * Explicit pagetable population and nonlinear (random) mappings support.
   5 *
   6 * started by Ingo Molnar, Copyright (C) 2002, 2003
   7 */
   8#include <linux/backing-dev.h>
   9#include <linux/mm.h>
  10#include <linux/swap.h>
  11#include <linux/file.h>
  12#include <linux/mman.h>
  13#include <linux/pagemap.h>
  14#include <linux/swapops.h>
  15#include <linux/rmap.h>
  16#include <linux/module.h>
  17#include <linux/syscalls.h>
  18#include <linux/mmu_notifier.h>
  19
  20#include <asm/mmu_context.h>
  21#include <asm/cacheflush.h>
  22#include <asm/tlbflush.h>
  23
  24#include "internal.h"
  25
  26static void zap_pte(struct mm_struct *mm, struct vm_area_struct *vma,
  27                        unsigned long addr, pte_t *ptep)
  28{
  29        pte_t pte = *ptep;
  30
  31        if (pte_present(pte)) {
  32                struct page *page;
  33
  34                flush_cache_page(vma, addr, pte_pfn(pte));
  35                pte = ptep_clear_flush(vma, addr, ptep);
  36                page = vm_normal_page(vma, addr, pte);
  37                if (page) {
  38                        if (pte_dirty(pte))
  39                                set_page_dirty(page);
  40                        page_remove_rmap(page);
  41                        page_cache_release(page);
  42                        update_hiwater_rss(mm);
  43                        dec_mm_counter(mm, MM_FILEPAGES);
  44                }
  45        } else {
  46                if (!pte_file(pte))
  47                        free_swap_and_cache(pte_to_swp_entry(pte));
  48                pte_clear_not_present_full(mm, addr, ptep, 0);
  49        }
  50}
  51
  52/*
  53 * Install a file pte to a given virtual memory address, release any
  54 * previously existing mapping.
  55 */
  56static int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
  57                unsigned long addr, unsigned long pgoff, pgprot_t prot)
  58{
  59        int err = -ENOMEM;
  60        pte_t *pte;
  61        spinlock_t *ptl;
  62
  63        pte = get_locked_pte(mm, addr, &ptl);
  64        if (!pte)
  65                goto out;
  66
  67        if (!pte_none(*pte))
  68                zap_pte(mm, vma, addr, pte);
  69
  70        set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));
  71        /*
  72         * We don't need to run update_mmu_cache() here because the "file pte"
  73         * being installed by install_file_pte() is not a real pte - it's a
  74         * non-present entry (like a swap entry), noting what file offset should
  75         * be mapped there when there's a fault (in a non-linear vma where
  76         * that's not obvious).
  77         */
  78        pte_unmap_unlock(pte, ptl);
  79        err = 0;
  80out:
  81        return err;
  82}
  83
  84static int populate_range(struct mm_struct *mm, struct vm_area_struct *vma,
  85                        unsigned long addr, unsigned long size, pgoff_t pgoff)
  86{
  87        int err;
  88
  89        do {
  90                err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot);
  91                if (err)
  92                        return err;
  93
  94                size -= PAGE_SIZE;
  95                addr += PAGE_SIZE;
  96                pgoff++;
  97        } while (size);
  98
  99        return 0;
 100
 101}
 102
 103/**
 104 * sys_remap_file_pages - remap arbitrary pages of an existing VM_SHARED vma
 105 * @start: start of the remapped virtual memory range
 106 * @size: size of the remapped virtual memory range
 107 * @prot: new protection bits of the range (see NOTE)
 108 * @pgoff: to-be-mapped page of the backing store file
 109 * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
 110 *
 111 * sys_remap_file_pages remaps arbitrary pages of an existing VM_SHARED vma
 112 * (shared backing store file).
 113 *
 114 * This syscall works purely via pagetables, so it's the most efficient
 115 * way to map the same (large) file into a given virtual window. Unlike
 116 * mmap()/mremap() it does not create any new vmas. The new mappings are
 117 * also safe across swapout.
 118 *
 119 * NOTE: the @prot parameter right now is ignored (but must be zero),
 120 * and the vma's default protection is used. Arbitrary protections
 121 * might be implemented in the future.
 122 */
 123SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
 124                unsigned long, prot, unsigned long, pgoff, unsigned long, flags)
 125{
 126        struct mm_struct *mm = current->mm;
 127        struct address_space *mapping;
 128        struct vm_area_struct *vma;
 129        int err = -EINVAL;
 130        int has_write_lock = 0;
 131
 132        if (prot)
 133                return err;
 134        /*
 135         * Sanitize the syscall parameters:
 136         */
 137        start = start & PAGE_MASK;
 138        size = size & PAGE_MASK;
 139
 140        /* Does the address range wrap, or is the span zero-sized? */
 141        if (start + size <= start)
 142                return err;
 143
 144        /* Does pgoff wrap? */
 145        if (pgoff + (size >> PAGE_SHIFT) < pgoff)
 146                return err;
 147
 148        /* Can we represent this offset inside this architecture's pte's? */
 149#if PTE_FILE_MAX_BITS < BITS_PER_LONG
 150        if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
 151                return err;
 152#endif
 153
 154        /* We need down_write() to change vma->vm_flags. */
 155        down_read(&mm->mmap_sem);
 156 retry:
 157        vma = find_vma(mm, start);
 158
 159        /*
 160         * Make sure the vma is shared, that it supports prefaulting,
 161         * and that the remapped range is valid and fully within
 162         * the single existing vma.  vm_private_data is used as a
 163         * swapout cursor in a VM_NONLINEAR vma.
 164         */
 165        if (!vma || !(vma->vm_flags & VM_SHARED))
 166                goto out;
 167
 168        if (vma->vm_private_data && !(vma->vm_flags & VM_NONLINEAR))
 169                goto out;
 170
 171        if (!(vma->vm_flags & VM_CAN_NONLINEAR))
 172                goto out;
 173
 174        if (start < vma->vm_start || start + size > vma->vm_end)
 175                goto out;
 176
 177        /* Must set VM_NONLINEAR before any pages are populated. */
 178        if (!(vma->vm_flags & VM_NONLINEAR)) {
 179                /* Don't need a nonlinear mapping, exit success */
 180                if (pgoff == linear_page_index(vma, start)) {
 181                        err = 0;
 182                        goto out;
 183                }
 184
 185                if (!has_write_lock) {
 186                        up_read(&mm->mmap_sem);
 187                        down_write(&mm->mmap_sem);
 188                        has_write_lock = 1;
 189                        goto retry;
 190                }
 191                mapping = vma->vm_file->f_mapping;
 192                /*
 193                 * page_mkclean doesn't work on nonlinear vmas, so if
 194                 * dirty pages need to be accounted, emulate with linear
 195                 * vmas.
 196                 */
 197                if (mapping_cap_account_dirty(mapping)) {
 198                        unsigned long addr;
 199                        struct file *file = vma->vm_file;
 200
 201                        flags &= MAP_NONBLOCK;
 202                        get_file(file);
 203                        addr = mmap_region(file, start, size,
 204                                        flags, vma->vm_flags, pgoff);
 205                        fput(file);
 206                        if (IS_ERR_VALUE(addr)) {
 207                                err = addr;
 208                        } else {
 209                                BUG_ON(addr != start);
 210                                err = 0;
 211                        }
 212                        goto out;
 213                }
 214                spin_lock(&mapping->i_mmap_lock);
 215                flush_dcache_mmap_lock(mapping);
 216                vma->vm_flags |= VM_NONLINEAR;
 217                vma_prio_tree_remove(vma, &mapping->i_mmap);
 218                vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
 219                flush_dcache_mmap_unlock(mapping);
 220                spin_unlock(&mapping->i_mmap_lock);
 221        }
 222
 223        if (vma->vm_flags & VM_LOCKED) {
 224                /*
 225                 * drop PG_Mlocked flag for over-mapped range
 226                 */
 227                unsigned int saved_flags = vma->vm_flags;
 228                munlock_vma_pages_range(vma, start, start + size);
 229                vma->vm_flags = saved_flags;
 230        }
 231
 232        mmu_notifier_invalidate_range_start(mm, start, start + size);
 233        err = populate_range(mm, vma, start, size, pgoff);
 234        mmu_notifier_invalidate_range_end(mm, start, start + size);
 235        if (!err && !(flags & MAP_NONBLOCK)) {
 236                if (vma->vm_flags & VM_LOCKED) {
 237                        /*
 238                         * might be mapping previously unmapped range of file
 239                         */
 240                        mlock_vma_pages_range(vma, start, start + size);
 241                } else {
 242                        if (unlikely(has_write_lock)) {
 243                                downgrade_write(&mm->mmap_sem);
 244                                has_write_lock = 0;
 245                        }
 246                        make_pages_present(start, start+size);
 247                }
 248        }
 249
 250        /*
 251         * We can't clear VM_NONLINEAR because we'd have to do
 252         * it after ->populate completes, and that would prevent
 253         * downgrading the lock.  (Locks can't be upgraded).
 254         */
 255
 256out:
 257        if (likely(!has_write_lock))
 258                up_read(&mm->mmap_sem);
 259        else
 260                up_write(&mm->mmap_sem);
 261
 262        return err;
 263}
 264