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