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
   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
  19 #include <asm/mmu_context.h>
  20 #include <asm/cacheflush.h>
  21 #include <asm/tlbflush.h>
  22
  23 static int zap_pte(struct mm_struct *mm, struct vm_area_struct *vma,
  24                         unsigned long addr, pte_t *ptep)
  25 {
  26         pte_t pte = *ptep;
  27         struct page *page = NULL;
  28
  29         if (pte_present(pte)) {
  30                 flush_cache_page(vma, addr, pte_pfn(pte));
  31                 pte = ptep_clear_flush(vma, addr, ptep);
  32                 page = vm_normal_page(vma, addr, pte);
  33                 if (page) {
  34                         if (pte_dirty(pte))
  35                                 set_page_dirty(page);
  36                         page_remove_rmap(page, vma);
  37                         page_cache_release(page);
  38                 }
  39         } else {
  40                 if (!pte_file(pte))
  41                         free_swap_and_cache(pte_to_swp_entry(pte));
  42                 pte_clear_not_present_full(mm, addr, ptep, 0);
  43         }
  44         return !!page;
  45 }
  46
  47 /*
  48  * Install a file page to a given virtual memory address, release any
  49  * previously existing mapping.
  50  */
  51 int install_page(struct mm_struct *mm, struct vm_area_struct *vma,
  52                 unsigned long addr, struct page *page, pgprot_t prot)
  53 {
  54         struct inode *inode;
  55         pgoff_t size;
  56         int err = -ENOMEM;
  57         pte_t *pte;
  58         pte_t pte_val;
  59         spinlock_t *ptl;
  60
  61         pte = get_locked_pte(mm, addr, &ptl);
  62         if (!pte)
  63                 goto out;
  64
  65         /*
  66          * This page may have been truncated. Tell the
  67          * caller about it.
  68          */
  69         err = -EINVAL;
  70         inode = vma->vm_file->f_mapping->host;
  71         size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
  72         if (!page->mapping || page->index >= size)
  73                 goto unlock;
  74         err = -ENOMEM;
  75         if (page_mapcount(page) > INT_MAX/2)
  76                 goto unlock;
  77
  78         if (pte_none(*pte) || !zap_pte(mm, vma, addr, pte))
  79                 inc_mm_counter(mm, file_rss);
  80
  81         flush_icache_page(vma, page);
  82         pte_val = mk_pte(page, prot);
  83         set_pte_at(mm, addr, pte, pte_val);
  84         page_add_file_rmap(page);
  85         update_mmu_cache(vma, addr, pte_val);
  86         lazy_mmu_prot_update(pte_val);
  87         err = 0;
  88 unlock:
  89         pte_unmap_unlock(pte, ptl);
  90 out:
  91         return err;
  92 }
  93 EXPORT_SYMBOL(install_page);
  94
  95 /*
  96  * Install a file pte to a given virtual memory address, release any
  97  * previously existing mapping.
  98  */
  99 int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
 100                 unsigned long addr, unsigned long pgoff, pgprot_t prot)
 101 {
 102         int err = -ENOMEM;
 103         pte_t *pte;
 104         spinlock_t *ptl;
 105
 106         pte = get_locked_pte(mm, addr, &ptl);
 107         if (!pte)
 108                 goto out;
 109
 110         if (!pte_none(*pte) && zap_pte(mm, vma, addr, pte)) {
 111                 update_hiwater_rss(mm);
 112                 dec_mm_counter(mm, file_rss);
 113         }
 114
 115         set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));
 116         /*
 117          * We don't need to run update_mmu_cache() here because the "file pte"
 118          * being installed by install_file_pte() is not a real pte - it's a
 119          * non-present entry (like a swap entry), noting what file offset should
 120          * be mapped there when there's a fault (in a non-linear vma where
 121          * that's not obvious).
 122          */
 123         pte_unmap_unlock(pte, ptl);
 124         err = 0;
 125 out:
 126         return err;
 127 }
 128
 129 static int populate_range(struct mm_struct *mm, struct vm_area_struct *vma,
 130                         unsigned long addr, unsigned long size, pgoff_t pgoff)
 131 {
 132         int err;
 133
 134         do {
 135                 err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot);
 136                 if (err)
 137                         return err;
 138
 139                 size -= PAGE_SIZE;
 140                 addr += PAGE_SIZE;
 141                 pgoff++;
 142         } while (size);
 143
 144         return 0;
 145
 146 }
 147
 148 /***
 149  * sys_remap_file_pages - remap arbitrary pages of a shared backing store
 150  *                        file within an existing vma.
 151  * @start: start of the remapped virtual memory range
 152  * @size: size of the remapped virtual memory range
 153  * @prot: new protection bits of the range
 154  * @pgoff: to be mapped page of the backing store file
 155  * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
 156  *
 157  * this syscall works purely via pagetables, so it's the most efficient
 158  * way to map the same (large) file into a given virtual window. Unlike
 159  * mmap()/mremap() it does not create any new vmas. The new mappings are
 160  * also safe across swapout.
 161  *
 162  * NOTE: the 'prot' parameter right now is ignored, and the vma's default
 163  * protection is used. Arbitrary protections might be implemented in the
 164  * future.
 165  */
 166 asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size,
 167         unsigned long __prot, unsigned long pgoff, unsigned long flags)
 168 {
 169         struct mm_struct *mm = current->mm;
 170         struct address_space *mapping;
 171         unsigned long end = start + size;
 172         struct vm_area_struct *vma;
 173         int err = -EINVAL;
 174         int has_write_lock = 0;
 175
 176         if (__prot)
 177                 return err;
 178         /*
 179          * Sanitize the syscall parameters:
 180          */
 181         start = start & PAGE_MASK;
 182         size = size & PAGE_MASK;
 183
 184         /* Does the address range wrap, or is the span zero-sized? */
 185         if (start + size <= start)
 186                 return err;
 187
 188         /* Can we represent this offset inside this architecture's pte's? */
 189 #if PTE_FILE_MAX_BITS < BITS_PER_LONG
 190         if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
 191                 return err;
 192 #endif
 193
 194         /* We need down_write() to change vma->vm_flags. */
 195         down_read(&mm->mmap_sem);
 196  retry:
 197         vma = find_vma(mm, start);
 198
 199         /*
 200          * Make sure the vma is shared, that it supports prefaulting,
 201          * and that the remapped range is valid and fully within
 202          * the single existing vma.  vm_private_data is used as a
 203          * swapout cursor in a VM_NONLINEAR vma.
 204          */
 205         if (!vma || !(vma->vm_flags & VM_SHARED))
 206                 goto out;
 207
 208         if (vma->vm_private_data && !(vma->vm_flags & VM_NONLINEAR))
 209                 goto out;
 210
 211         if ((!vma->vm_ops || !vma->vm_ops->populate) &&
 212                                         !(vma->vm_flags & VM_CAN_NONLINEAR))
 213                 goto out;
 214
 215         if (end <= start || start < vma->vm_start || end > vma->vm_end)
 216                 goto out;
 217
 218         /* Must set VM_NONLINEAR before any pages are populated. */
 219         if (!(vma->vm_flags & VM_NONLINEAR)) {
 220                 /* Don't need a nonlinear mapping, exit success */
 221                 if (pgoff == linear_page_index(vma, start)) {
 222                         err = 0;
 223                         goto out;
 224                 }
 225
 226                 if (!has_write_lock) {
 227                         up_read(&mm->mmap_sem);
 228                         down_write(&mm->mmap_sem);
 229                         has_write_lock = 1;
 230                         goto retry;
 231                 }
 232                 mapping = vma->vm_file->f_mapping;
 233                 spin_lock(&mapping->i_mmap_lock);
 234                 flush_dcache_mmap_lock(mapping);
 235                 vma->vm_flags |= VM_NONLINEAR;
 236                 vma_prio_tree_remove(vma, &mapping->i_mmap);
 237                 vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
 238                 flush_dcache_mmap_unlock(mapping);
 239                 spin_unlock(&mapping->i_mmap_lock);
 240         }
 241
 242         if (vma->vm_flags & VM_CAN_NONLINEAR) {
 243                 err = populate_range(mm, vma, start, size, pgoff);
 244                 if (!err && !(flags & MAP_NONBLOCK)) {
 245                         if (unlikely(has_write_lock)) {
 246                                 downgrade_write(&mm->mmap_sem);
 247                                 has_write_lock = 0;
 248                         }
 249                         make_pages_present(start, start+size);
 250                 }
 251         } else
 252                 err = vma->vm_ops->populate(vma, start, size, vma->vm_page_prot,
 253                                                 pgoff, flags & MAP_NONBLOCK);
 254
 255         /*
 256          * We can't clear VM_NONLINEAR because we'd have to do
 257          * it after ->populate completes, and that would prevent
 258          * downgrading the lock.  (Locks can't be upgraded).
 259          */
 260
 261 out:
 262         if (likely(!has_write_lock))
 263                 up_read(&mm->mmap_sem);
 264         else
 265                 up_write(&mm->mmap_sem);
 266
 267         return err;
 268 }
 269