linux/mm/fremap.c
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   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 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
  84int generic_file_remap_pages(struct vm_area_struct *vma, unsigned long addr,
  85                             unsigned long size, pgoff_t pgoff)
  86{
  87        struct mm_struct *mm = vma->vm_mm;
  88        int err;
  89
  90        do {
  91                err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot);
  92                if (err)
  93                        return err;
  94
  95                size -= PAGE_SIZE;
  96                addr += PAGE_SIZE;
  97                pgoff++;
  98        } while (size);
  99
 100        return 0;
 101}
 102EXPORT_SYMBOL(generic_file_remap_pages);
 103
 104/**
 105 * sys_remap_file_pages - remap arbitrary pages of an existing VM_SHARED vma
 106 * @start: start of the remapped virtual memory range
 107 * @size: size of the remapped virtual memory range
 108 * @prot: new protection bits of the range (see NOTE)
 109 * @pgoff: to-be-mapped page of the backing store file
 110 * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
 111 *
 112 * sys_remap_file_pages remaps arbitrary pages of an existing VM_SHARED vma
 113 * (shared backing store file).
 114 *
 115 * This syscall works purely via pagetables, so it's the most efficient
 116 * way to map the same (large) file into a given virtual window. Unlike
 117 * mmap()/mremap() it does not create any new vmas. The new mappings are
 118 * also safe across swapout.
 119 *
 120 * NOTE: the @prot parameter right now is ignored (but must be zero),
 121 * and the vma's default protection is used. Arbitrary protections
 122 * might be implemented in the future.
 123 */
 124SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
 125                unsigned long, prot, unsigned long, pgoff, unsigned long, flags)
 126{
 127        struct mm_struct *mm = current->mm;
 128        struct address_space *mapping;
 129        struct vm_area_struct *vma;
 130        int err = -EINVAL;
 131        int has_write_lock = 0;
 132
 133        if (prot)
 134                return err;
 135        /*
 136         * Sanitize the syscall parameters:
 137         */
 138        start = start & PAGE_MASK;
 139        size = size & PAGE_MASK;
 140
 141        /* Does the address range wrap, or is the span zero-sized? */
 142        if (start + size <= start)
 143                return err;
 144
 145        /* Does pgoff wrap? */
 146        if (pgoff + (size >> PAGE_SHIFT) < pgoff)
 147                return err;
 148
 149        /* Can we represent this offset inside this architecture's pte's? */
 150#if PTE_FILE_MAX_BITS < BITS_PER_LONG
 151        if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
 152                return err;
 153#endif
 154
 155        /* We need down_write() to change vma->vm_flags. */
 156        down_read(&mm->mmap_sem);
 157 retry:
 158        vma = find_vma(mm, start);
 159
 160        /*
 161         * Make sure the vma is shared, that it supports prefaulting,
 162         * and that the remapped range is valid and fully within
 163         * the single existing vma.  vm_private_data is used as a
 164         * swapout cursor in a VM_NONLINEAR vma.
 165         */
 166        if (!vma || !(vma->vm_flags & VM_SHARED))
 167                goto out;
 168
 169        if (vma->vm_private_data && !(vma->vm_flags & VM_NONLINEAR))
 170                goto out;
 171
 172        if (!vma->vm_ops || !vma->vm_ops->remap_pages)
 173                goto out;
 174
 175        if (start < vma->vm_start || start + size > vma->vm_end)
 176                goto out;
 177
 178        /* Must set VM_NONLINEAR before any pages are populated. */
 179        if (!(vma->vm_flags & VM_NONLINEAR)) {
 180                /* Don't need a nonlinear mapping, exit success */
 181                if (pgoff == linear_page_index(vma, start)) {
 182                        err = 0;
 183                        goto out;
 184                }
 185
 186                if (!has_write_lock) {
 187                        up_read(&mm->mmap_sem);
 188                        down_write(&mm->mmap_sem);
 189                        has_write_lock = 1;
 190                        goto retry;
 191                }
 192                mapping = vma->vm_file->f_mapping;
 193                /*
 194                 * page_mkclean doesn't work on nonlinear vmas, so if
 195                 * dirty pages need to be accounted, emulate with linear
 196                 * vmas.
 197                 */
 198                if (mapping_cap_account_dirty(mapping)) {
 199                        unsigned long addr;
 200                        struct file *file = get_file(vma->vm_file);
 201
 202                        flags &= MAP_NONBLOCK;
 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                mutex_lock(&mapping->i_mmap_mutex);
 215                flush_dcache_mmap_lock(mapping);
 216                vma->vm_flags |= VM_NONLINEAR;
 217                vma_interval_tree_remove(vma, &mapping->i_mmap);
 218                vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
 219                flush_dcache_mmap_unlock(mapping);
 220                mutex_unlock(&mapping->i_mmap_mutex);
 221        }
 222
 223        if (vma->vm_flags & VM_LOCKED) {
 224                /*
 225                 * drop PG_Mlocked flag for over-mapped range
 226                 */
 227                vm_flags_t 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 = vma->vm_ops->remap_pages(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
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