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/export.h>
   9#include <linux/backing-dev.h>
  10#include <linux/mm.h>
  11#include <linux/swap.h>
  12#include <linux/file.h>
  13#include <linux/mman.h>
  14#include <linux/pagemap.h>
  15#include <linux/swapops.h>
  16#include <linux/rmap.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 int mm_counter(struct page *page)
  27{
  28        return PageAnon(page) ? MM_ANONPAGES : MM_FILEPAGES;
  29}
  30
  31static void zap_pte(struct mm_struct *mm, struct vm_area_struct *vma,
  32                        unsigned long addr, pte_t *ptep)
  33{
  34        pte_t pte = *ptep;
  35        struct page *page;
  36        swp_entry_t entry;
  37
  38        if (pte_present(pte)) {
  39                flush_cache_page(vma, addr, pte_pfn(pte));
  40                pte = ptep_clear_flush_notify(vma, addr, ptep);
  41                page = vm_normal_page(vma, addr, pte);
  42                if (page) {
  43                        if (pte_dirty(pte))
  44                                set_page_dirty(page);
  45                        update_hiwater_rss(mm);
  46                        dec_mm_counter(mm, mm_counter(page));
  47                        page_remove_rmap(page);
  48                        page_cache_release(page);
  49                }
  50        } else {        /* zap_pte() is not called when pte_none() */
  51                if (!pte_file(pte)) {
  52                        update_hiwater_rss(mm);
  53                        entry = pte_to_swp_entry(pte);
  54                        if (non_swap_entry(entry)) {
  55                                if (is_migration_entry(entry)) {
  56                                        page = migration_entry_to_page(entry);
  57                                        dec_mm_counter(mm, mm_counter(page));
  58                                }
  59                        } else {
  60                                free_swap_and_cache(entry);
  61                                dec_mm_counter(mm, MM_SWAPENTS);
  62                        }
  63                }
  64                pte_clear_not_present_full(mm, addr, ptep, 0);
  65        }
  66}
  67
  68/*
  69 * Install a file pte to a given virtual memory address, release any
  70 * previously existing mapping.
  71 */
  72static int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
  73                unsigned long addr, unsigned long pgoff, pgprot_t prot)
  74{
  75        int err = -ENOMEM;
  76        pte_t *pte, ptfile;
  77        spinlock_t *ptl;
  78
  79        pte = get_locked_pte(mm, addr, &ptl);
  80        if (!pte)
  81                goto out;
  82
  83        ptfile = pgoff_to_pte(pgoff);
  84
  85        if (!pte_none(*pte))
  86                zap_pte(mm, vma, addr, pte);
  87
  88        set_pte_at(mm, addr, pte, pte_file_mksoft_dirty(ptfile));
  89        /*
  90         * We don't need to run update_mmu_cache() here because the "file pte"
  91         * being installed by install_file_pte() is not a real pte - it's a
  92         * non-present entry (like a swap entry), noting what file offset should
  93         * be mapped there when there's a fault (in a non-linear vma where
  94         * that's not obvious).
  95         */
  96        pte_unmap_unlock(pte, ptl);
  97        err = 0;
  98out:
  99        return err;
 100}
 101
 102int generic_file_remap_pages(struct vm_area_struct *vma, unsigned long addr,
 103                             unsigned long size, pgoff_t pgoff)
 104{
 105        struct mm_struct *mm = vma->vm_mm;
 106        int err;
 107
 108        do {
 109                err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot);
 110                if (err)
 111                        return err;
 112
 113                size -= PAGE_SIZE;
 114                addr += PAGE_SIZE;
 115                pgoff++;
 116        } while (size);
 117
 118        return 0;
 119}
 120EXPORT_SYMBOL(generic_file_remap_pages);
 121
 122/**
 123 * sys_remap_file_pages - remap arbitrary pages of an existing VM_SHARED vma
 124 * @start: start of the remapped virtual memory range
 125 * @size: size of the remapped virtual memory range
 126 * @prot: new protection bits of the range (see NOTE)
 127 * @pgoff: to-be-mapped page of the backing store file
 128 * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
 129 *
 130 * sys_remap_file_pages remaps arbitrary pages of an existing VM_SHARED vma
 131 * (shared backing store file).
 132 *
 133 * This syscall works purely via pagetables, so it's the most efficient
 134 * way to map the same (large) file into a given virtual window. Unlike
 135 * mmap()/mremap() it does not create any new vmas. The new mappings are
 136 * also safe across swapout.
 137 *
 138 * NOTE: the @prot parameter right now is ignored (but must be zero),
 139 * and the vma's default protection is used. Arbitrary protections
 140 * might be implemented in the future.
 141 */
 142SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
 143                unsigned long, prot, unsigned long, pgoff, unsigned long, flags)
 144{
 145        struct mm_struct *mm = current->mm;
 146        struct address_space *mapping;
 147        struct vm_area_struct *vma;
 148        int err = -EINVAL;
 149        int has_write_lock = 0;
 150        vm_flags_t vm_flags = 0;
 151
 152        pr_warn_once("%s (%d) uses deprecated remap_file_pages() syscall. "
 153                        "See Documentation/vm/remap_file_pages.txt.\n",
 154                        current->comm, current->pid);
 155
 156        if (prot)
 157                return err;
 158        /*
 159         * Sanitize the syscall parameters:
 160         */
 161        start = start & PAGE_MASK;
 162        size = size & PAGE_MASK;
 163
 164        /* Does the address range wrap, or is the span zero-sized? */
 165        if (start + size <= start)
 166                return err;
 167
 168        /* Does pgoff wrap? */
 169        if (pgoff + (size >> PAGE_SHIFT) < pgoff)
 170                return err;
 171
 172        /* Can we represent this offset inside this architecture's pte's? */
 173#if PTE_FILE_MAX_BITS < BITS_PER_LONG
 174        if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
 175                return err;
 176#endif
 177
 178        /* We need down_write() to change vma->vm_flags. */
 179        down_read(&mm->mmap_sem);
 180 retry:
 181        vma = find_vma(mm, start);
 182
 183        /*
 184         * Make sure the vma is shared, that it supports prefaulting,
 185         * and that the remapped range is valid and fully within
 186         * the single existing vma.
 187         */
 188        if (!vma || !(vma->vm_flags & VM_SHARED))
 189                goto out;
 190
 191        if (!vma->vm_ops || !vma->vm_ops->remap_pages)
 192                goto out;
 193
 194        if (start < vma->vm_start || start + size > vma->vm_end)
 195                goto out;
 196
 197        /* Must set VM_NONLINEAR before any pages are populated. */
 198        if (!(vma->vm_flags & VM_NONLINEAR)) {
 199                /*
 200                 * vm_private_data is used as a swapout cursor
 201                 * in a VM_NONLINEAR vma.
 202                 */
 203                if (vma->vm_private_data)
 204                        goto out;
 205
 206                /* Don't need a nonlinear mapping, exit success */
 207                if (pgoff == linear_page_index(vma, start)) {
 208                        err = 0;
 209                        goto out;
 210                }
 211
 212                if (!has_write_lock) {
 213get_write_lock:
 214                        up_read(&mm->mmap_sem);
 215                        down_write(&mm->mmap_sem);
 216                        has_write_lock = 1;
 217                        goto retry;
 218                }
 219                mapping = vma->vm_file->f_mapping;
 220                /*
 221                 * page_mkclean doesn't work on nonlinear vmas, so if
 222                 * dirty pages need to be accounted, emulate with linear
 223                 * vmas.
 224                 */
 225                if (mapping_cap_account_dirty(mapping)) {
 226                        unsigned long addr;
 227                        struct file *file = get_file(vma->vm_file);
 228                        /* mmap_region may free vma; grab the info now */
 229                        vm_flags = vma->vm_flags;
 230
 231                        addr = mmap_region(file, start, size, vm_flags, pgoff);
 232                        fput(file);
 233                        if (IS_ERR_VALUE(addr)) {
 234                                err = addr;
 235                        } else {
 236                                BUG_ON(addr != start);
 237                                err = 0;
 238                        }
 239                        goto out_freed;
 240                }
 241                i_mmap_lock_write(mapping);
 242                flush_dcache_mmap_lock(mapping);
 243                vma->vm_flags |= VM_NONLINEAR;
 244                vma_interval_tree_remove(vma, &mapping->i_mmap);
 245                vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
 246                flush_dcache_mmap_unlock(mapping);
 247                i_mmap_unlock_write(mapping);
 248        }
 249
 250        if (vma->vm_flags & VM_LOCKED) {
 251                /*
 252                 * drop PG_Mlocked flag for over-mapped range
 253                 */
 254                if (!has_write_lock)
 255                        goto get_write_lock;
 256                vm_flags = vma->vm_flags;
 257                munlock_vma_pages_range(vma, start, start + size);
 258                vma->vm_flags = vm_flags;
 259        }
 260
 261        mmu_notifier_invalidate_range_start(mm, start, start + size);
 262        err = vma->vm_ops->remap_pages(vma, start, size, pgoff);
 263        mmu_notifier_invalidate_range_end(mm, start, start + size);
 264
 265        /*
 266         * We can't clear VM_NONLINEAR because we'd have to do
 267         * it after ->populate completes, and that would prevent
 268         * downgrading the lock.  (Locks can't be upgraded).
 269         */
 270
 271out:
 272        if (vma)
 273                vm_flags = vma->vm_flags;
 274out_freed:
 275        if (likely(!has_write_lock))
 276                up_read(&mm->mmap_sem);
 277        else
 278                up_write(&mm->mmap_sem);
 279        if (!err && ((vm_flags & VM_LOCKED) || !(flags & MAP_NONBLOCK)))
 280                mm_populate(start, size);
 281
 282        return err;
 283}
 284