fremap.c revision ba470de43188cdbff795b5da43a1474523c6c2fb
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#include <linux/backing-dev.h> 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#include <linux/mmu_notifier.h> 19 20#include <asm/mmu_context.h> 21#include <asm/cacheflush.h> 22#include <asm/tlbflush.h> 23 24#include "internal.h" 25 26static void zap_pte(struct mm_struct *mm, struct vm_area_struct *vma, 27 unsigned long addr, pte_t *ptep) 28{ 29 pte_t pte = *ptep; 30 31 if (pte_present(pte)) { 32 struct page *page; 33 34 flush_cache_page(vma, addr, pte_pfn(pte)); 35 pte = ptep_clear_flush(vma, addr, ptep); 36 page = vm_normal_page(vma, addr, pte); 37 if (page) { 38 if (pte_dirty(pte)) 39 set_page_dirty(page); 40 page_remove_rmap(page, vma); 41 page_cache_release(page); 42 update_hiwater_rss(mm); 43 dec_mm_counter(mm, file_rss); 44 } 45 } else { 46 if (!pte_file(pte)) 47 free_swap_and_cache(pte_to_swp_entry(pte)); 48 pte_clear_not_present_full(mm, addr, ptep, 0); 49 } 50} 51 52/* 53 * Install a file pte to a given virtual memory address, release any 54 * previously existing mapping. 55 */ 56static int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma, 57 unsigned long addr, unsigned long pgoff, pgprot_t prot) 58{ 59 int err = -ENOMEM; 60 pte_t *pte; 61 spinlock_t *ptl; 62 63 pte = get_locked_pte(mm, addr, &ptl); 64 if (!pte) 65 goto out; 66 67 if (!pte_none(*pte)) 68 zap_pte(mm, vma, addr, pte); 69 70 set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff)); 71 /* 72 * We don't need to run update_mmu_cache() here because the "file pte" 73 * being installed by install_file_pte() is not a real pte - it's a 74 * non-present entry (like a swap entry), noting what file offset should 75 * be mapped there when there's a fault (in a non-linear vma where 76 * that's not obvious). 77 */ 78 pte_unmap_unlock(pte, ptl); 79 err = 0; 80out: 81 return err; 82} 83 84static int populate_range(struct mm_struct *mm, struct vm_area_struct *vma, 85 unsigned long addr, unsigned long size, pgoff_t pgoff) 86{ 87 int err; 88 89 do { 90 err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot); 91 if (err) 92 return err; 93 94 size -= PAGE_SIZE; 95 addr += PAGE_SIZE; 96 pgoff++; 97 } while (size); 98 99 return 0; 100 101} 102 103/** 104 * sys_remap_file_pages - remap arbitrary pages of an existing VM_SHARED vma 105 * @start: start of the remapped virtual memory range 106 * @size: size of the remapped virtual memory range 107 * @prot: new protection bits of the range (see NOTE) 108 * @pgoff: to-be-mapped page of the backing store file 109 * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO. 110 * 111 * sys_remap_file_pages remaps arbitrary pages of an existing VM_SHARED vma 112 * (shared backing store file). 113 * 114 * This syscall works purely via pagetables, so it's the most efficient 115 * way to map the same (large) file into a given virtual window. Unlike 116 * mmap()/mremap() it does not create any new vmas. The new mappings are 117 * also safe across swapout. 118 * 119 * NOTE: the @prot parameter right now is ignored (but must be zero), 120 * and the vma's default protection is used. Arbitrary protections 121 * might be implemented in the future. 122 */ 123asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size, 124 unsigned long prot, unsigned long pgoff, unsigned long flags) 125{ 126 struct mm_struct *mm = current->mm; 127 struct address_space *mapping; 128 unsigned long end = start + size; 129 struct vm_area_struct *vma; 130 int err = -EINVAL; 131 int has_write_lock = 0; 132 133 if (prot) 134 return err; 135 /* 136 * Sanitize the syscall parameters: 137 */ 138 start = start & PAGE_MASK; 139 size = size & PAGE_MASK; 140 141 /* Does the address range wrap, or is the span zero-sized? */ 142 if (start + size <= start) 143 return err; 144 145 /* Can we represent this offset inside this architecture's pte's? */ 146#if PTE_FILE_MAX_BITS < BITS_PER_LONG 147 if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS)) 148 return err; 149#endif 150 151 /* We need down_write() to change vma->vm_flags. */ 152 down_read(&mm->mmap_sem); 153 retry: 154 vma = find_vma(mm, start); 155 156 /* 157 * Make sure the vma is shared, that it supports prefaulting, 158 * and that the remapped range is valid and fully within 159 * the single existing vma. vm_private_data is used as a 160 * swapout cursor in a VM_NONLINEAR vma. 161 */ 162 if (!vma || !(vma->vm_flags & VM_SHARED)) 163 goto out; 164 165 if (vma->vm_private_data && !(vma->vm_flags & VM_NONLINEAR)) 166 goto out; 167 168 if (!(vma->vm_flags & VM_CAN_NONLINEAR)) 169 goto out; 170 171 if (end <= start || start < vma->vm_start || end > vma->vm_end) 172 goto out; 173 174 /* Must set VM_NONLINEAR before any pages are populated. */ 175 if (!(vma->vm_flags & VM_NONLINEAR)) { 176 /* Don't need a nonlinear mapping, exit success */ 177 if (pgoff == linear_page_index(vma, start)) { 178 err = 0; 179 goto out; 180 } 181 182 if (!has_write_lock) { 183 up_read(&mm->mmap_sem); 184 down_write(&mm->mmap_sem); 185 has_write_lock = 1; 186 goto retry; 187 } 188 mapping = vma->vm_file->f_mapping; 189 /* 190 * page_mkclean doesn't work on nonlinear vmas, so if 191 * dirty pages need to be accounted, emulate with linear 192 * vmas. 193 */ 194 if (mapping_cap_account_dirty(mapping)) { 195 unsigned long addr; 196 struct file *file = vma->vm_file; 197 198 flags &= MAP_NONBLOCK; 199 get_file(file); 200 addr = mmap_region(file, start, size, 201 flags, vma->vm_flags, pgoff, 1); 202 fput(file); 203 if (IS_ERR_VALUE(addr)) { 204 err = addr; 205 } else { 206 BUG_ON(addr != start); 207 err = 0; 208 } 209 goto out; 210 } 211 spin_lock(&mapping->i_mmap_lock); 212 flush_dcache_mmap_lock(mapping); 213 vma->vm_flags |= VM_NONLINEAR; 214 vma_prio_tree_remove(vma, &mapping->i_mmap); 215 vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear); 216 flush_dcache_mmap_unlock(mapping); 217 spin_unlock(&mapping->i_mmap_lock); 218 } 219 220 if (vma->vm_flags & VM_LOCKED) { 221 /* 222 * drop PG_Mlocked flag for over-mapped range 223 */ 224 unsigned int saved_flags = vma->vm_flags; 225 munlock_vma_pages_range(vma, start, start + size); 226 vma->vm_flags = saved_flags; 227 } 228 229 mmu_notifier_invalidate_range_start(mm, start, start + size); 230 err = populate_range(mm, vma, start, size, pgoff); 231 mmu_notifier_invalidate_range_end(mm, start, start + size); 232 if (!err && !(flags & MAP_NONBLOCK)) { 233 if (vma->vm_flags & VM_LOCKED) { 234 /* 235 * might be mapping previously unmapped range of file 236 */ 237 mlock_vma_pages_range(vma, start, start + size); 238 } else { 239 if (unlikely(has_write_lock)) { 240 downgrade_write(&mm->mmap_sem); 241 has_write_lock = 0; 242 } 243 make_pages_present(start, start+size); 244 } 245 } 246 247 /* 248 * We can't clear VM_NONLINEAR because we'd have to do 249 * it after ->populate completes, and that would prevent 250 * downgrading the lock. (Locks can't be upgraded). 251 */ 252 253out: 254 if (likely(!has_write_lock)) 255 up_read(&mm->mmap_sem); 256 else 257 up_write(&mm->mmap_sem); 258 259 return err; 260} 261