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 inline void 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
  28         if (pte_none(pte))
  29                 return;
  30         if (pte_present(pte)) {
  31                 unsigned long pfn = pte_pfn(pte);
  32
  33                 flush_cache_page(vma, addr, pfn);
  34                 pte = ptep_clear_flush(vma, addr, ptep);
  35                 if (pfn_valid(pfn)) {
  36                         struct page *page = pfn_to_page(pfn);
  37                         if (!PageReserved(page)) {
  38                                 if (pte_dirty(pte))
  39                                         set_page_dirty(page);
  40                                 page_remove_rmap(page);
  41                                 page_cache_release(page);
  42                                 dec_mm_counter(mm, rss);
  43                         }
  44                 }
  45         } else {
  46                 if (!pte_file(pte))
  47                         free_swap_and_cache(pte_to_swp_entry(pte));
  48                 pte_clear(mm, addr, ptep);
  49         }
  50 }
  51
  52 /*
  53  * Install a file page to a given virtual memory address, release any
  54  * previously existing mapping.
  55  */
  56 int install_page(struct mm_struct *mm, struct vm_area_struct *vma,
  57                 unsigned long addr, struct page *page, pgprot_t prot)
  58 {
  59         struct inode *inode;
  60         pgoff_t size;
  61         int err = -ENOMEM;
  62         pte_t *pte;
  63         pmd_t *pmd;
  64         pud_t *pud;
  65         pgd_t *pgd;
  66         pte_t pte_val;
  67
  68         pgd = pgd_offset(mm, addr);
  69         spin_lock(&mm->page_table_lock);
  70
  71         pud = pud_alloc(mm, pgd, addr);
  72         if (!pud)
  73                 goto err_unlock;
  74
  75         pmd = pmd_alloc(mm, pud, addr);
  76         if (!pmd)
  77                 goto err_unlock;
  78
  79         pte = pte_alloc_map(mm, pmd, addr);
  80         if (!pte)
  81                 goto err_unlock;
  82
  83         /*
  84          * This page may have been truncated. Tell the
  85          * caller about it.
  86          */
  87         err = -EINVAL;
  88         inode = vma->vm_file->f_mapping->host;
  89         size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
  90         if (!page->mapping || page->index >= size)
  91                 goto err_unlock;
  92         err = -ENOMEM;
  93         if (page_mapcount(page) > INT_MAX/2)
  94                 goto err_unlock;
  95
  96         zap_pte(mm, vma, addr, pte);
  97
  98         inc_mm_counter(mm,rss);
  99         flush_icache_page(vma, page);
 100         set_pte_at(mm, addr, pte, mk_pte(page, prot));
 101         page_add_file_rmap(page);
 102         pte_val = *pte;
 103         pte_unmap(pte);
 104         update_mmu_cache(vma, addr, pte_val);
 105
 106         err = 0;
 107 err_unlock:
 108         spin_unlock(&mm->page_table_lock);
 109         return err;
 110 }
 111 EXPORT_SYMBOL(install_page);
 112
 113
 114 /*
 115  * Install a file pte to a given virtual memory address, release any
 116  * previously existing mapping.
 117  */
 118 int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
 119                 unsigned long addr, unsigned long pgoff, pgprot_t prot)
 120 {
 121         int err = -ENOMEM;
 122         pte_t *pte;
 123         pmd_t *pmd;
 124         pud_t *pud;
 125         pgd_t *pgd;
 126         pte_t pte_val;
 127
 128         pgd = pgd_offset(mm, addr);
 129         spin_lock(&mm->page_table_lock);
 130
 131         pud = pud_alloc(mm, pgd, addr);
 132         if (!pud)
 133                 goto err_unlock;
 134
 135         pmd = pmd_alloc(mm, pud, addr);
 136         if (!pmd)
 137                 goto err_unlock;
 138
 139         pte = pte_alloc_map(mm, pmd, addr);
 140         if (!pte)
 141                 goto err_unlock;
 142
 143         zap_pte(mm, vma, addr, pte);
 144
 145         set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));
 146         pte_val = *pte;
 147         pte_unmap(pte);
 148         update_mmu_cache(vma, addr, pte_val);
 149         spin_unlock(&mm->page_table_lock);
 150         return 0;
 151
 152 err_unlock:
 153         spin_unlock(&mm->page_table_lock);
 154         return err;
 155 }
 156
 157
 158 /***
 159  * sys_remap_file_pages - remap arbitrary pages of a shared backing store
 160  *                        file within an existing vma.
 161  * @start: start of the remapped virtual memory range
 162  * @size: size of the remapped virtual memory range
 163  * @prot: new protection bits of the range
 164  * @pgoff: to be mapped page of the backing store file
 165  * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
 166  *
 167  * this syscall works purely via pagetables, so it's the most efficient
 168  * way to map the same (large) file into a given virtual window. Unlike
 169  * mmap()/mremap() it does not create any new vmas. The new mappings are
 170  * also safe across swapout.
 171  *
 172  * NOTE: the 'prot' parameter right now is ignored, and the vma's default
 173  * protection is used. Arbitrary protections might be implemented in the
 174  * future.
 175  */
 176 asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size,
 177         unsigned long __prot, unsigned long pgoff, unsigned long flags)
 178 {
 179         struct mm_struct *mm = current->mm;
 180         struct address_space *mapping;
 181         unsigned long end = start + size;
 182         struct vm_area_struct *vma;
 183         int err = -EINVAL;
 184         int has_write_lock = 0;
 185
 186         if (__prot)
 187                 return err;
 188         /*
 189          * Sanitize the syscall parameters:
 190          */
 191         start = start & PAGE_MASK;
 192         size = size & PAGE_MASK;
 193
 194         /* Does the address range wrap, or is the span zero-sized? */
 195         if (start + size <= start)
 196                 return err;
 197
 198         /* Can we represent this offset inside this architecture's pte's? */
 199 #if PTE_FILE_MAX_BITS < BITS_PER_LONG
 200         if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
 201                 return err;
 202 #endif
 203
 204         /* We need down_write() to change vma->vm_flags. */
 205         down_read(&mm->mmap_sem);
 206  retry:
 207         vma = find_vma(mm, start);
 208
 209         /*
 210          * Make sure the vma is shared, that it supports prefaulting,
 211          * and that the remapped range is valid and fully within
 212          * the single existing vma.  vm_private_data is used as a
 213          * swapout cursor in a VM_NONLINEAR vma (unless VM_RESERVED
 214          * or VM_LOCKED, but VM_LOCKED could be revoked later on).
 215          */
 216         if (vma && (vma->vm_flags & VM_SHARED) &&
 217                 (!vma->vm_private_data ||
 218                         (vma->vm_flags & (VM_NONLINEAR|VM_RESERVED))) &&
 219                 vma->vm_ops && vma->vm_ops->populate &&
 220                         end > start && start >= vma->vm_start &&
 221                                 end <= vma->vm_end) {
 222
 223                 /* Must set VM_NONLINEAR before any pages are populated. */
 224                 if (pgoff != linear_page_index(vma, start) &&
 225                     !(vma->vm_flags & VM_NONLINEAR)) {
 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                 err = vma->vm_ops->populate(vma, start, size,
 243                                             vma->vm_page_prot,
 244                                             pgoff, flags & MAP_NONBLOCK);
 245
 246                 /*
 247                  * We can't clear VM_NONLINEAR because we'd have to do
 248                  * it after ->populate completes, and that would prevent
 249                  * downgrading the lock.  (Locks can't be upgraded).
 250                  */
 251         }
 252         if (likely(!has_write_lock))
 253                 up_read(&mm->mmap_sem);
 254         else
 255                 up_write(&mm->mmap_sem);
 256
 257         return err;
 258 }
 259