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);
  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 /***
 130  * sys_remap_file_pages - remap arbitrary pages of a shared backing store
 131  *                        file within an existing vma.
 132  * @start: start of the remapped virtual memory range
 133  * @size: size of the remapped virtual memory range
 134  * @prot: new protection bits of the range
 135  * @pgoff: to be mapped page of the backing store file
 136  * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
 137  *
 138  * this syscall works purely via pagetables, so it's the most efficient
 139  * way to map the same (large) file into a given virtual window. Unlike
 140  * mmap()/mremap() it does not create any new vmas. The new mappings are
 141  * also safe across swapout.
 142  *
 143  * NOTE: the 'prot' parameter right now is ignored, and the vma's default
 144  * protection is used. Arbitrary protections might be implemented in the
 145  * future.
 146  */
 147 asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size,
 148         unsigned long __prot, unsigned long pgoff, unsigned long flags)
 149 {
 150         struct mm_struct *mm = current->mm;
 151         struct address_space *mapping;
 152         unsigned long end = start + size;
 153         struct vm_area_struct *vma;
 154         int err = -EINVAL;
 155         int has_write_lock = 0;
 156
 157         if (__prot)
 158                 return err;
 159         /*
 160          * Sanitize the syscall parameters:
 161          */
 162         start = start & PAGE_MASK;
 163         size = size & PAGE_MASK;
 164
 165         /* Does the address range wrap, or is the span zero-sized? */
 166         if (start + size <= start)
 167                 return err;
 168
 169         /* Can we represent this offset inside this architecture's pte's? */
 170 #if PTE_FILE_MAX_BITS < BITS_PER_LONG
 171         if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
 172                 return err;
 173 #endif
 174
 175         /* We need down_write() to change vma->vm_flags. */
 176         down_read(&mm->mmap_sem);
 177  retry:
 178         vma = find_vma(mm, start);
 179
 180         /*
 181          * Make sure the vma is shared, that it supports prefaulting,
 182          * and that the remapped range is valid and fully within
 183          * the single existing vma.  vm_private_data is used as a
 184          * swapout cursor in a VM_NONLINEAR vma.
 185          */
 186         if (vma && (vma->vm_flags & VM_SHARED) &&
 187                 (!vma->vm_private_data || (vma->vm_flags & VM_NONLINEAR)) &&
 188                 vma->vm_ops && vma->vm_ops->populate &&
 189                         end > start && start >= vma->vm_start &&
 190                                 end <= vma->vm_end) {
 191
 192                 /* Must set VM_NONLINEAR before any pages are populated. */
 193                 if (pgoff != linear_page_index(vma, start) &&
 194                     !(vma->vm_flags & VM_NONLINEAR)) {
 195                         if (!has_write_lock) {
 196                                 up_read(&mm->mmap_sem);
 197                                 down_write(&mm->mmap_sem);
 198                                 has_write_lock = 1;
 199                                 goto retry;
 200                         }
 201                         mapping = vma->vm_file->f_mapping;
 202                         spin_lock(&mapping->i_mmap_lock);
 203                         flush_dcache_mmap_lock(mapping);
 204                         vma->vm_flags |= VM_NONLINEAR;
 205                         vma_prio_tree_remove(vma, &mapping->i_mmap);
 206                         vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
 207                         flush_dcache_mmap_unlock(mapping);
 208                         spin_unlock(&mapping->i_mmap_lock);
 209                 }
 210
 211                 err = vma->vm_ops->populate(vma, start, size,
 212                                             vma->vm_page_prot,
 213                                             pgoff, flags & MAP_NONBLOCK);
 214
 215                 /*
 216                  * We can't clear VM_NONLINEAR because we'd have to do
 217                  * it after ->populate completes, and that would prevent
 218                  * downgrading the lock.  (Locks can't be upgraded).
 219                  */
 220         }
 221         if (likely(!has_write_lock))
 222                 up_read(&mm->mmap_sem);
 223         else
 224                 up_write(&mm->mmap_sem);
 225
 226         return err;
 227 }
 228