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
  93         zap_pte(mm, vma, addr, pte);
  94
  95         inc_mm_counter(mm,rss);
  96         flush_icache_page(vma, page);
  97         set_pte_at(mm, addr, pte, mk_pte(page, prot));
  98         page_add_file_rmap(page);
  99         pte_val = *pte;
 100         pte_unmap(pte);
 101         update_mmu_cache(vma, addr, pte_val);
 102
 103         err = 0;
 104 err_unlock:
 105         spin_unlock(&mm->page_table_lock);
 106         return err;
 107 }
 108 EXPORT_SYMBOL(install_page);
 109
 110
 111 /*
 112  * Install a file pte to a given virtual memory address, release any
 113  * previously existing mapping.
 114  */
 115 int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
 116                 unsigned long addr, unsigned long pgoff, pgprot_t prot)
 117 {
 118         int err = -ENOMEM;
 119         pte_t *pte;
 120         pmd_t *pmd;
 121         pud_t *pud;
 122         pgd_t *pgd;
 123         pte_t pte_val;
 124
 125         pgd = pgd_offset(mm, addr);
 126         spin_lock(&mm->page_table_lock);
 127
 128         pud = pud_alloc(mm, pgd, addr);
 129         if (!pud)
 130                 goto err_unlock;
 131
 132         pmd = pmd_alloc(mm, pud, addr);
 133         if (!pmd)
 134                 goto err_unlock;
 135
 136         pte = pte_alloc_map(mm, pmd, addr);
 137         if (!pte)
 138                 goto err_unlock;
 139
 140         zap_pte(mm, vma, addr, pte);
 141
 142         set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));
 143         pte_val = *pte;
 144         pte_unmap(pte);
 145         update_mmu_cache(vma, addr, pte_val);
 146         spin_unlock(&mm->page_table_lock);
 147         return 0;
 148
 149 err_unlock:
 150         spin_unlock(&mm->page_table_lock);
 151         return err;
 152 }
 153
 154
 155 /***
 156  * sys_remap_file_pages - remap arbitrary pages of a shared backing store
 157  *                        file within an existing vma.
 158  * @start: start of the remapped virtual memory range
 159  * @size: size of the remapped virtual memory range
 160  * @prot: new protection bits of the range
 161  * @pgoff: to be mapped page of the backing store file
 162  * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
 163  *
 164  * this syscall works purely via pagetables, so it's the most efficient
 165  * way to map the same (large) file into a given virtual window. Unlike
 166  * mmap()/mremap() it does not create any new vmas. The new mappings are
 167  * also safe across swapout.
 168  *
 169  * NOTE: the 'prot' parameter right now is ignored, and the vma's default
 170  * protection is used. Arbitrary protections might be implemented in the
 171  * future.
 172  */
 173 asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size,
 174         unsigned long __prot, unsigned long pgoff, unsigned long flags)
 175 {
 176         struct mm_struct *mm = current->mm;
 177         struct address_space *mapping;
 178         unsigned long end = start + size;
 179         struct vm_area_struct *vma;
 180         int err = -EINVAL;
 181         int has_write_lock = 0;
 182
 183         if (__prot)
 184                 return err;
 185         /*
 186          * Sanitize the syscall parameters:
 187          */
 188         start = start & PAGE_MASK;
 189         size = size & PAGE_MASK;
 190
 191         /* Does the address range wrap, or is the span zero-sized? */
 192         if (start + size <= start)
 193                 return err;
 194
 195         /* Can we represent this offset inside this architecture's pte's? */
 196 #if PTE_FILE_MAX_BITS < BITS_PER_LONG
 197         if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
 198                 return err;
 199 #endif
 200
 201         /* We need down_write() to change vma->vm_flags. */
 202         down_read(&mm->mmap_sem);
 203  retry:
 204         vma = find_vma(mm, start);
 205
 206         /*
 207          * Make sure the vma is shared, that it supports prefaulting,
 208          * and that the remapped range is valid and fully within
 209          * the single existing vma.  vm_private_data is used as a
 210          * swapout cursor in a VM_NONLINEAR vma (unless VM_RESERVED
 211          * or VM_LOCKED, but VM_LOCKED could be revoked later on).
 212          */
 213         if (vma && (vma->vm_flags & VM_SHARED) &&
 214                 (!vma->vm_private_data ||
 215                         (vma->vm_flags & (VM_NONLINEAR|VM_RESERVED))) &&
 216                 vma->vm_ops && vma->vm_ops->populate &&
 217                         end > start && start >= vma->vm_start &&
 218                                 end <= vma->vm_end) {
 219
 220                 /* Must set VM_NONLINEAR before any pages are populated. */
 221                 if (pgoff != linear_page_index(vma, start) &&
 222                     !(vma->vm_flags & VM_NONLINEAR)) {
 223                         if (!has_write_lock) {
 224                                 up_read(&mm->mmap_sem);
 225                                 down_write(&mm->mmap_sem);
 226                                 has_write_lock = 1;
 227                                 goto retry;
 228                         }
 229                         mapping = vma->vm_file->f_mapping;
 230                         spin_lock(&mapping->i_mmap_lock);
 231                         flush_dcache_mmap_lock(mapping);
 232                         vma->vm_flags |= VM_NONLINEAR;
 233                         vma_prio_tree_remove(vma, &mapping->i_mmap);
 234                         vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
 235                         flush_dcache_mmap_unlock(mapping);
 236                         spin_unlock(&mapping->i_mmap_lock);
 237                 }
 238
 239                 err = vma->vm_ops->populate(vma, start, size,
 240                                             vma->vm_page_prot,
 241                                             pgoff, flags & MAP_NONBLOCK);
 242
 243                 /*
 244                  * We can't clear VM_NONLINEAR because we'd have to do
 245                  * it after ->populate completes, and that would prevent
 246                  * downgrading the lock.  (Locks can't be upgraded).
 247                  */
 248         }
 249         if (likely(!has_write_lock))
 250                 up_read(&mm->mmap_sem);
 251         else
 252                 up_write(&mm->mmap_sem);
 253
 254         return err;
 255 }
 256