mm/mremap.c

   1 /*
   2  *      mm/mremap.c
   3  *
   4  *      (C) Copyright 1996 Linus Torvalds
   5  *
   6  *      Address space accounting code   <alan@lxorguk.ukuu.org.uk>
   7  *      (C) Copyright 2002 Red Hat Inc, All Rights Reserved
   8  */
   9
  10 #include <linux/mm.h>
  11 #include <linux/hugetlb.h>
  12 #include <linux/shm.h>
  13 #include <linux/ksm.h>
  14 #include <linux/mman.h>
  15 #include <linux/swap.h>
  16 #include <linux/capability.h>
  17 #include <linux/fs.h>
  18 #include <linux/swapops.h>
  19 #include <linux/highmem.h>
  20 #include <linux/security.h>
  21 #include <linux/syscalls.h>
  22 #include <linux/mmu_notifier.h>
  23 #include <linux/uaccess.h>
  24 #include <linux/mm-arch-hooks.h>
  25
  26 #include <asm/cacheflush.h>
  27 #include <asm/tlbflush.h>
  28
  29 #include "internal.h"
  30
  31 static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
  32 {
  33         pgd_t *pgd;
  34         pud_t *pud;
  35         pmd_t *pmd;
  36
  37         pgd = pgd_offset(mm, addr);
  38         if (pgd_none_or_clear_bad(pgd))
  39                 return NULL;
  40
  41         pud = pud_offset(pgd, addr);
  42         if (pud_none_or_clear_bad(pud))
  43                 return NULL;
  44
  45         pmd = pmd_offset(pud, addr);
  46         if (pmd_none(*pmd))
  47                 return NULL;
  48
  49         return pmd;
  50 }
  51
  52 static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
  53                             unsigned long addr)
  54 {
  55         pgd_t *pgd;
  56         pud_t *pud;
  57         pmd_t *pmd;
  58
  59         pgd = pgd_offset(mm, addr);
  60         pud = pud_alloc(mm, pgd, addr);
  61         if (!pud)
  62                 return NULL;
  63
  64         pmd = pmd_alloc(mm, pud, addr);
  65         if (!pmd)
  66                 return NULL;
  67
  68         VM_BUG_ON(pmd_trans_huge(*pmd));
  69
  70         return pmd;
  71 }
  72
  73 static void take_rmap_locks(struct vm_area_struct *vma)
  74 {
  75         if (vma->vm_file)
  76                 i_mmap_lock_write(vma->vm_file->f_mapping);
  77         if (vma->anon_vma)
  78                 anon_vma_lock_write(vma->anon_vma);
  79 }
  80
  81 static void drop_rmap_locks(struct vm_area_struct *vma)
  82 {
  83         if (vma->anon_vma)
  84                 anon_vma_unlock_write(vma->anon_vma);
  85         if (vma->vm_file)
  86                 i_mmap_unlock_write(vma->vm_file->f_mapping);
  87 }
  88
  89 static pte_t move_soft_dirty_pte(pte_t pte)
  90 {
  91         /*
  92          * Set soft dirty bit so we can notice
  93          * in userspace the ptes were moved.
  94          */
  95 #ifdef CONFIG_MEM_SOFT_DIRTY
  96         if (pte_present(pte))
  97                 pte = pte_mksoft_dirty(pte);
  98         else if (is_swap_pte(pte))
  99                 pte = pte_swp_mksoft_dirty(pte);
 100 #endif
 101         return pte;
 102 }
 103
 104 static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
 105                 unsigned long old_addr, unsigned long old_end,
 106                 struct vm_area_struct *new_vma, pmd_t *new_pmd,
 107                 unsigned long new_addr, bool need_rmap_locks)
 108 {
 109         struct mm_struct *mm = vma->vm_mm;
 110         pte_t *old_pte, *new_pte, pte;
 111         spinlock_t *old_ptl, *new_ptl;
 112
 113         /*
 114          * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
 115          * locks to ensure that rmap will always observe either the old or the
 116          * new ptes. This is the easiest way to avoid races with
 117          * truncate_pagecache(), page migration, etc...
 118          *
 119          * When need_rmap_locks is false, we use other ways to avoid
 120          * such races:
 121          *
 122          * - During exec() shift_arg_pages(), we use a specially tagged vma
 123          *   which rmap call sites look for using is_vma_temporary_stack().
 124          *
 125          * - During mremap(), new_vma is often known to be placed after vma
 126          *   in rmap traversal order. This ensures rmap will always observe
 127          *   either the old pte, or the new pte, or both (the page table locks
 128          *   serialize access to individual ptes, but only rmap traversal
 129          *   order guarantees that we won't miss both the old and new ptes).
 130          */
 131         if (need_rmap_locks)
 132                 take_rmap_locks(vma);
 133
 134         /*
 135          * We don't have to worry about the ordering of src and dst
 136          * pte locks because exclusive mmap_sem prevents deadlock.
 137          */
 138         old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
 139         new_pte = pte_offset_map(new_pmd, new_addr);
 140         new_ptl = pte_lockptr(mm, new_pmd);
 141         if (new_ptl != old_ptl)
 142                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
 143         arch_enter_lazy_mmu_mode();
 144
 145         for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
 146                                    new_pte++, new_addr += PAGE_SIZE) {
 147                 if (pte_none(*old_pte))
 148                         continue;
 149                 pte = ptep_get_and_clear(mm, old_addr, old_pte);
 150                 pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
 151                 pte = move_soft_dirty_pte(pte);
 152                 set_pte_at(mm, new_addr, new_pte, pte);
 153         }
 154
 155         arch_leave_lazy_mmu_mode();
 156         if (new_ptl != old_ptl)
 157                 spin_unlock(new_ptl);
 158         pte_unmap(new_pte - 1);
 159         pte_unmap_unlock(old_pte - 1, old_ptl);
 160         if (need_rmap_locks)
 161                 drop_rmap_locks(vma);
 162 }
 163
 164 #define LATENCY_LIMIT   (64 * PAGE_SIZE)
 165
 166 unsigned long move_page_tables(struct vm_area_struct *vma,
 167                 unsigned long old_addr, struct vm_area_struct *new_vma,
 168                 unsigned long new_addr, unsigned long len,
 169                 bool need_rmap_locks)
 170 {
 171         unsigned long extent, next, old_end;
 172         pmd_t *old_pmd, *new_pmd;
 173         bool need_flush = false;
 174         unsigned long mmun_start;       /* For mmu_notifiers */
 175         unsigned long mmun_end;         /* For mmu_notifiers */
 176
 177         old_end = old_addr + len;
 178         flush_cache_range(vma, old_addr, old_end);
 179
 180         mmun_start = old_addr;
 181         mmun_end   = old_end;
 182         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
 183
 184         for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
 185                 cond_resched();
 186                 next = (old_addr + PMD_SIZE) & PMD_MASK;
 187                 /* even if next overflowed, extent below will be ok */
 188                 extent = next - old_addr;
 189                 if (extent > old_end - old_addr)
 190                         extent = old_end - old_addr;
 191                 old_pmd = get_old_pmd(vma->vm_mm, old_addr);
 192                 if (!old_pmd)
 193                         continue;
 194                 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
 195                 if (!new_pmd)
 196                         break;
 197                 if (pmd_trans_huge(*old_pmd)) {
 198                         if (extent == HPAGE_PMD_SIZE) {
 199                                 bool moved;
 200                                 /* See comment in move_ptes() */
 201                                 if (need_rmap_locks)
 202                                         take_rmap_locks(vma);
 203                                 moved = move_huge_pmd(vma, old_addr, new_addr,
 204                                                     old_end, old_pmd, new_pmd);
 205                                 if (need_rmap_locks)
 206                                         drop_rmap_locks(vma);
 207                                 if (moved) {
 208                                         need_flush = true;
 209                                         continue;
 210                                 }
 211                         }
 212                         split_huge_pmd(vma, old_pmd, old_addr);
 213                         if (pmd_trans_unstable(old_pmd))
 214                                 continue;
 215                 }
 216                 if (pte_alloc(new_vma->vm_mm, new_pmd, new_addr))
 217                         break;
 218                 next = (new_addr + PMD_SIZE) & PMD_MASK;
 219                 if (extent > next - new_addr)
 220                         extent = next - new_addr;
 221                 if (extent > LATENCY_LIMIT)
 222                         extent = LATENCY_LIMIT;
 223                 move_ptes(vma, old_pmd, old_addr, old_addr + extent,
 224                           new_vma, new_pmd, new_addr, need_rmap_locks);
 225                 need_flush = true;
 226         }
 227         if (likely(need_flush))
 228                 flush_tlb_range(vma, old_end-len, old_addr);
 229
 230         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
 231
 232         return len + old_addr - old_end;        /* how much done */
 233 }
 234
 235 static unsigned long move_vma(struct vm_area_struct *vma,
 236                 unsigned long old_addr, unsigned long old_len,
 237                 unsigned long new_len, unsigned long new_addr, bool *locked)
 238 {
 239         struct mm_struct *mm = vma->vm_mm;
 240         struct vm_area_struct *new_vma;
 241         unsigned long vm_flags = vma->vm_flags;
 242         unsigned long new_pgoff;
 243         unsigned long moved_len;
 244         unsigned long excess = 0;
 245         unsigned long hiwater_vm;
 246         int split = 0;
 247         int err;
 248         bool need_rmap_locks;
 249
 250         /*
 251          * We'd prefer to avoid failure later on in do_munmap:
 252          * which may split one vma into three before unmapping.
 253          */
 254         if (mm->map_count >= sysctl_max_map_count - 3)
 255                 return -ENOMEM;
 256
 257         /*
 258          * Advise KSM to break any KSM pages in the area to be moved:
 259          * it would be confusing if they were to turn up at the new
 260          * location, where they happen to coincide with different KSM
 261          * pages recently unmapped.  But leave vma->vm_flags as it was,
 262          * so KSM can come around to merge on vma and new_vma afterwards.
 263          */
 264         err = ksm_madvise(vma, old_addr, old_addr + old_len,
 265                                                 MADV_UNMERGEABLE, &vm_flags);
 266         if (err)
 267                 return err;
 268
 269         new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
 270         new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
 271                            &need_rmap_locks);
 272         if (!new_vma)
 273                 return -ENOMEM;
 274
 275         moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
 276                                      need_rmap_locks);
 277         if (moved_len < old_len) {
 278                 err = -ENOMEM;
 279         } else if (vma->vm_ops && vma->vm_ops->mremap) {
 280                 err = vma->vm_ops->mremap(new_vma);
 281         }
 282
 283         if (unlikely(err)) {
 284                 /*
 285                  * On error, move entries back from new area to old,
 286                  * which will succeed since page tables still there,
 287                  * and then proceed to unmap new area instead of old.
 288                  */
 289                 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
 290                                  true);
 291                 vma = new_vma;
 292                 old_len = new_len;
 293                 old_addr = new_addr;
 294                 new_addr = err;
 295         } else {
 296                 arch_remap(mm, old_addr, old_addr + old_len,
 297                            new_addr, new_addr + new_len);
 298         }
 299
 300         /* Conceal VM_ACCOUNT so old reservation is not undone */
 301         if (vm_flags & VM_ACCOUNT) {
 302                 vma->vm_flags &= ~VM_ACCOUNT;
 303                 excess = vma->vm_end - vma->vm_start - old_len;
 304                 if (old_addr > vma->vm_start &&
 305                     old_addr + old_len < vma->vm_end)
 306                         split = 1;
 307         }
 308
 309         /*
 310          * If we failed to move page tables we still do total_vm increment
 311          * since do_munmap() will decrement it by old_len == new_len.
 312          *
 313          * Since total_vm is about to be raised artificially high for a
 314          * moment, we need to restore high watermark afterwards: if stats
 315          * are taken meanwhile, total_vm and hiwater_vm appear too high.
 316          * If this were a serious issue, we'd add a flag to do_munmap().
 317          */
 318         hiwater_vm = mm->hiwater_vm;
 319         vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT);
 320
 321         /* Tell pfnmap has moved from this vma */
 322         if (unlikely(vma->vm_flags & VM_PFNMAP))
 323                 untrack_pfn_moved(vma);
 324
 325         if (do_munmap(mm, old_addr, old_len) < 0) {
 326                 /* OOM: unable to split vma, just get accounts right */
 327                 vm_unacct_memory(excess >> PAGE_SHIFT);
 328                 excess = 0;
 329         }
 330         mm->hiwater_vm = hiwater_vm;
 331
 332         /* Restore VM_ACCOUNT if one or two pieces of vma left */
 333         if (excess) {
 334                 vma->vm_flags |= VM_ACCOUNT;
 335                 if (split)
 336                         vma->vm_next->vm_flags |= VM_ACCOUNT;
 337         }
 338
 339         if (vm_flags & VM_LOCKED) {
 340                 mm->locked_vm += new_len >> PAGE_SHIFT;
 341                 *locked = true;
 342         }
 343
 344         return new_addr;
 345 }
 346
 347 static struct vm_area_struct *vma_to_resize(unsigned long addr,
 348         unsigned long old_len, unsigned long new_len, unsigned long *p)
 349 {
 350         struct mm_struct *mm = current->mm;
 351         struct vm_area_struct *vma = find_vma(mm, addr);
 352         unsigned long pgoff;
 353
 354         if (!vma || vma->vm_start > addr)
 355                 return ERR_PTR(-EFAULT);
 356
 357         if (is_vm_hugetlb_page(vma))
 358                 return ERR_PTR(-EINVAL);
 359
 360         /* We can't remap across vm area boundaries */
 361         if (old_len > vma->vm_end - addr)
 362                 return ERR_PTR(-EFAULT);
 363
 364         if (new_len == old_len)
 365                 return vma;
 366
 367         /* Need to be careful about a growing mapping */
 368         pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
 369         pgoff += vma->vm_pgoff;
 370         if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
 371                 return ERR_PTR(-EINVAL);
 372
 373         if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
 374                 return ERR_PTR(-EFAULT);
 375
 376         if (vma->vm_flags & VM_LOCKED) {
 377                 unsigned long locked, lock_limit;
 378                 locked = mm->locked_vm << PAGE_SHIFT;
 379                 lock_limit = rlimit(RLIMIT_MEMLOCK);
 380                 locked += new_len - old_len;
 381                 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
 382                         return ERR_PTR(-EAGAIN);
 383         }
 384
 385         if (!may_expand_vm(mm, vma->vm_flags,
 386                                 (new_len - old_len) >> PAGE_SHIFT))
 387                 return ERR_PTR(-ENOMEM);
 388
 389         if (vma->vm_flags & VM_ACCOUNT) {
 390                 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
 391                 if (security_vm_enough_memory_mm(mm, charged))
 392                         return ERR_PTR(-ENOMEM);
 393                 *p = charged;
 394         }
 395
 396         return vma;
 397 }
 398
 399 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 400                 unsigned long new_addr, unsigned long new_len, bool *locked)
 401 {
 402         struct mm_struct *mm = current->mm;
 403         struct vm_area_struct *vma;
 404         unsigned long ret = -EINVAL;
 405         unsigned long charged = 0;
 406         unsigned long map_flags;
 407
 408         if (offset_in_page(new_addr))
 409                 goto out;
 410
 411         if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
 412                 goto out;
 413
 414         /* Ensure the old/new locations do not overlap */
 415         if (addr + old_len > new_addr && new_addr + new_len > addr)
 416                 goto out;
 417
 418         ret = do_munmap(mm, new_addr, new_len);
 419         if (ret)
 420                 goto out;
 421
 422         if (old_len >= new_len) {
 423                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
 424                 if (ret && old_len != new_len)
 425                         goto out;
 426                 old_len = new_len;
 427         }
 428
 429         vma = vma_to_resize(addr, old_len, new_len, &charged);
 430         if (IS_ERR(vma)) {
 431                 ret = PTR_ERR(vma);
 432                 goto out;
 433         }
 434
 435         map_flags = MAP_FIXED;
 436         if (vma->vm_flags & VM_MAYSHARE)
 437                 map_flags |= MAP_SHARED;
 438
 439         ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
 440                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
 441                                 map_flags);
 442         if (offset_in_page(ret))
 443                 goto out1;
 444
 445         ret = move_vma(vma, addr, old_len, new_len, new_addr, locked);
 446         if (!(offset_in_page(ret)))
 447                 goto out;
 448 out1:
 449         vm_unacct_memory(charged);
 450
 451 out:
 452         return ret;
 453 }
 454
 455 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
 456 {
 457         unsigned long end = vma->vm_end + delta;
 458         if (end < vma->vm_end) /* overflow */
 459                 return 0;
 460         if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
 461                 return 0;
 462         if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
 463                               0, MAP_FIXED) & ~PAGE_MASK)
 464                 return 0;
 465         return 1;
 466 }
 467
 468 /*
 469  * Expand (or shrink) an existing mapping, potentially moving it at the
 470  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 471  *
 472  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
 473  * This option implies MREMAP_MAYMOVE.
 474  */
 475 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 476                 unsigned long, new_len, unsigned long, flags,
 477                 unsigned long, new_addr)
 478 {
 479         struct mm_struct *mm = current->mm;
 480         struct vm_area_struct *vma;
 481         unsigned long ret = -EINVAL;
 482         unsigned long charged = 0;
 483         bool locked = false;
 484
 485         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
 486                 return ret;
 487
 488         if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
 489                 return ret;
 490
 491         if (offset_in_page(addr))
 492                 return ret;
 493
 494         old_len = PAGE_ALIGN(old_len);
 495         new_len = PAGE_ALIGN(new_len);
 496
 497         /*
 498          * We allow a zero old-len as a special case
 499          * for DOS-emu "duplicate shm area" thing. But
 500          * a zero new-len is nonsensical.
 501          */
 502         if (!new_len)
 503                 return ret;
 504
 505         if (down_write_killable(&current->mm->mmap_sem))
 506                 return -EINTR;
 507
 508         if (flags & MREMAP_FIXED) {
 509                 ret = mremap_to(addr, old_len, new_addr, new_len,
 510                                 &locked);
 511                 goto out;
 512         }
 513
 514         /*
 515          * Always allow a shrinking remap: that just unmaps
 516          * the unnecessary pages..
 517          * do_munmap does all the needed commit accounting
 518          */
 519         if (old_len >= new_len) {
 520                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
 521                 if (ret && old_len != new_len)
 522                         goto out;
 523                 ret = addr;
 524                 goto out;
 525         }
 526
 527         /*
 528          * Ok, we need to grow..
 529          */
 530         vma = vma_to_resize(addr, old_len, new_len, &charged);
 531         if (IS_ERR(vma)) {
 532                 ret = PTR_ERR(vma);
 533                 goto out;
 534         }
 535
 536         /* old_len exactly to the end of the area..
 537          */
 538         if (old_len == vma->vm_end - addr) {
 539                 /* can we just expand the current mapping? */
 540                 if (vma_expandable(vma, new_len - old_len)) {
 541                         int pages = (new_len - old_len) >> PAGE_SHIFT;
 542
 543                         if (vma_adjust(vma, vma->vm_start, addr + new_len,
 544                                        vma->vm_pgoff, NULL)) {
 545                                 ret = -ENOMEM;
 546                                 goto out;
 547                         }
 548
 549                         vm_stat_account(mm, vma->vm_flags, pages);
 550                         if (vma->vm_flags & VM_LOCKED) {
 551                                 mm->locked_vm += pages;
 552                                 locked = true;
 553                                 new_addr = addr;
 554                         }
 555                         ret = addr;
 556                         goto out;
 557                 }
 558         }
 559
 560         /*
 561          * We weren't able to just expand or shrink the area,
 562          * we need to create a new one and move it..
 563          */
 564         ret = -ENOMEM;
 565         if (flags & MREMAP_MAYMOVE) {
 566                 unsigned long map_flags = 0;
 567                 if (vma->vm_flags & VM_MAYSHARE)
 568                         map_flags |= MAP_SHARED;
 569
 570                 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
 571                                         vma->vm_pgoff +
 572                                         ((addr - vma->vm_start) >> PAGE_SHIFT),
 573                                         map_flags);
 574                 if (offset_in_page(new_addr)) {
 575                         ret = new_addr;
 576                         goto out;
 577                 }
 578
 579                 ret = move_vma(vma, addr, old_len, new_len, new_addr, &locked);
 580         }
 581 out:
 582         if (offset_in_page(ret)) {
 583                 vm_unacct_memory(charged);
 584                 locked = 0;
 585         }
 586         up_write(&current->mm->mmap_sem);
 587         if (locked && new_len > old_len)
 588                 mm_populate(new_addr + old_len, new_len - old_len);
 589         return ret;
 590 }