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