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/sched/sysctl.h>
  24 #include <linux/uaccess.h>
  25 #include <linux/mm-arch-hooks.h>
  26
  27 #include <asm/cacheflush.h>
  28 #include <asm/tlbflush.h>
  29
  30 #include "internal.h"
  31
  32 static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
  33 {
  34         pgd_t *pgd;
  35         pud_t *pud;
  36         pmd_t *pmd;
  37
  38         pgd = pgd_offset(mm, addr);
  39         if (pgd_none_or_clear_bad(pgd))
  40                 return NULL;
  41
  42         pud = pud_offset(pgd, addr);
  43         if (pud_none_or_clear_bad(pud))
  44                 return NULL;
  45
  46         pmd = pmd_offset(pud, addr);
  47         if (pmd_none(*pmd))
  48                 return NULL;
  49
  50         return pmd;
  51 }
  52
  53 static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
  54                             unsigned long addr)
  55 {
  56         pgd_t *pgd;
  57         pud_t *pud;
  58         pmd_t *pmd;
  59
  60         pgd = pgd_offset(mm, addr);
  61         pud = pud_alloc(mm, pgd, addr);
  62         if (!pud)
  63                 return NULL;
  64
  65         pmd = pmd_alloc(mm, pud, addr);
  66         if (!pmd)
  67                 return NULL;
  68
  69         VM_BUG_ON(pmd_trans_huge(*pmd));
  70
  71         return pmd;
  72 }
  73
  74 static pte_t move_soft_dirty_pte(pte_t pte)
  75 {
  76         /*
  77          * Set soft dirty bit so we can notice
  78          * in userspace the ptes were moved.
  79          */
  80 #ifdef CONFIG_MEM_SOFT_DIRTY
  81         if (pte_present(pte))
  82                 pte = pte_mksoft_dirty(pte);
  83         else if (is_swap_pte(pte))
  84                 pte = pte_swp_mksoft_dirty(pte);
  85 #endif
  86         return pte;
  87 }
  88
  89 static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
  90                 unsigned long old_addr, unsigned long old_end,
  91                 struct vm_area_struct *new_vma, pmd_t *new_pmd,
  92                 unsigned long new_addr, bool need_rmap_locks)
  93 {
  94         struct address_space *mapping = NULL;
  95         struct anon_vma *anon_vma = NULL;
  96         struct mm_struct *mm = vma->vm_mm;
  97         pte_t *old_pte, *new_pte, pte;
  98         spinlock_t *old_ptl, *new_ptl;
  99
 100         /*
 101          * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
 102          * locks to ensure that rmap will always observe either the old or the
 103          * new ptes. This is the easiest way to avoid races with
 104          * truncate_pagecache(), page migration, etc...
 105          *
 106          * When need_rmap_locks is false, we use other ways to avoid
 107          * such races:
 108          *
 109          * - During exec() shift_arg_pages(), we use a specially tagged vma
 110          *   which rmap call sites look for using is_vma_temporary_stack().
 111          *
 112          * - During mremap(), new_vma is often known to be placed after vma
 113          *   in rmap traversal order. This ensures rmap will always observe
 114          *   either the old pte, or the new pte, or both (the page table locks
 115          *   serialize access to individual ptes, but only rmap traversal
 116          *   order guarantees that we won't miss both the old and new ptes).
 117          */
 118         if (need_rmap_locks) {
 119                 if (vma->vm_file) {
 120                         mapping = vma->vm_file->f_mapping;
 121                         i_mmap_lock_write(mapping);
 122                 }
 123                 if (vma->anon_vma) {
 124                         anon_vma = vma->anon_vma;
 125                         anon_vma_lock_write(anon_vma);
 126                 }
 127         }
 128
 129         /*
 130          * We don't have to worry about the ordering of src and dst
 131          * pte locks because exclusive mmap_sem prevents deadlock.
 132          */
 133         old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
 134         new_pte = pte_offset_map(new_pmd, new_addr);
 135         new_ptl = pte_lockptr(mm, new_pmd);
 136         if (new_ptl != old_ptl)
 137                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
 138         arch_enter_lazy_mmu_mode();
 139
 140         for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
 141                                    new_pte++, new_addr += PAGE_SIZE) {
 142                 if (pte_none(*old_pte))
 143                         continue;
 144                 pte = ptep_get_and_clear(mm, old_addr, old_pte);
 145                 pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
 146                 pte = move_soft_dirty_pte(pte);
 147                 set_pte_at(mm, new_addr, new_pte, pte);
 148         }
 149
 150         arch_leave_lazy_mmu_mode();
 151         if (new_ptl != old_ptl)
 152                 spin_unlock(new_ptl);
 153         pte_unmap(new_pte - 1);
 154         pte_unmap_unlock(old_pte - 1, old_ptl);
 155         if (anon_vma)
 156                 anon_vma_unlock_write(anon_vma);
 157         if (mapping)
 158                 i_mmap_unlock_write(mapping);
 159 }
 160
 161 #define LATENCY_LIMIT   (64 * PAGE_SIZE)
 162
 163 unsigned long move_page_tables(struct vm_area_struct *vma,
 164                 unsigned long old_addr, struct vm_area_struct *new_vma,
 165                 unsigned long new_addr, unsigned long len,
 166                 bool need_rmap_locks)
 167 {
 168         unsigned long extent, next, old_end;
 169         pmd_t *old_pmd, *new_pmd;
 170         bool need_flush = false;
 171         unsigned long mmun_start;       /* For mmu_notifiers */
 172         unsigned long mmun_end;         /* For mmu_notifiers */
 173
 174         old_end = old_addr + len;
 175         flush_cache_range(vma, old_addr, old_end);
 176
 177         mmun_start = old_addr;
 178         mmun_end   = old_end;
 179         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
 180
 181         for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
 182                 cond_resched();
 183                 next = (old_addr + PMD_SIZE) & PMD_MASK;
 184                 /* even if next overflowed, extent below will be ok */
 185                 extent = next - old_addr;
 186                 if (extent > old_end - old_addr)
 187                         extent = old_end - old_addr;
 188                 old_pmd = get_old_pmd(vma->vm_mm, old_addr);
 189                 if (!old_pmd)
 190                         continue;
 191                 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
 192                 if (!new_pmd)
 193                         break;
 194                 if (pmd_trans_huge(*old_pmd)) {
 195                         if (extent == HPAGE_PMD_SIZE) {
 196                                 bool moved;
 197                                 VM_BUG_ON_VMA(vma->vm_file || !vma->anon_vma,
 198                                               vma);
 199                                 /* See comment in move_ptes() */
 200                                 if (need_rmap_locks)
 201                                         anon_vma_lock_write(vma->anon_vma);
 202                                 moved = move_huge_pmd(vma, new_vma, old_addr,
 203                                                     new_addr, old_end,
 204                                                     old_pmd, new_pmd);
 205                                 if (need_rmap_locks)
 206                                         anon_vma_unlock_write(vma->anon_vma);
 207                                 if (moved) {
 208                                         need_flush = true;
 209                                         continue;
 210                                 }
 211                         }
 212                         split_huge_pmd(vma, old_pmd, old_addr);
 213                         VM_BUG_ON(pmd_trans_huge(*old_pmd));
 214                 }
 215                 if (pmd_none(*new_pmd) && __pte_alloc(new_vma->vm_mm, new_vma,
 216                                                       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, vma->vm_file, new_len>>PAGE_SHIFT);
 320
 321         if (do_munmap(mm, old_addr, old_len) < 0) {
 322                 /* OOM: unable to split vma, just get accounts right */
 323                 vm_unacct_memory(excess >> PAGE_SHIFT);
 324                 excess = 0;
 325         }
 326         mm->hiwater_vm = hiwater_vm;
 327
 328         /* Restore VM_ACCOUNT if one or two pieces of vma left */
 329         if (excess) {
 330                 vma->vm_flags |= VM_ACCOUNT;
 331                 if (split)
 332                         vma->vm_next->vm_flags |= VM_ACCOUNT;
 333         }
 334
 335         if (vm_flags & VM_LOCKED) {
 336                 mm->locked_vm += new_len >> PAGE_SHIFT;
 337                 *locked = true;
 338         }
 339
 340         return new_addr;
 341 }
 342
 343 static struct vm_area_struct *vma_to_resize(unsigned long addr,
 344         unsigned long old_len, unsigned long new_len, unsigned long *p)
 345 {
 346         struct mm_struct *mm = current->mm;
 347         struct vm_area_struct *vma = find_vma(mm, addr);
 348         unsigned long pgoff;
 349
 350         if (!vma || vma->vm_start > addr)
 351                 return ERR_PTR(-EFAULT);
 352
 353         if (is_vm_hugetlb_page(vma))
 354                 return ERR_PTR(-EINVAL);
 355
 356         /* We can't remap across vm area boundaries */
 357         if (old_len > vma->vm_end - addr)
 358                 return ERR_PTR(-EFAULT);
 359
 360         if (new_len == old_len)
 361                 return vma;
 362
 363         /* Need to be careful about a growing mapping */
 364         pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
 365         pgoff += vma->vm_pgoff;
 366         if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
 367                 return ERR_PTR(-EINVAL);
 368
 369         if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
 370                 return ERR_PTR(-EFAULT);
 371
 372         if (vma->vm_flags & VM_LOCKED) {
 373                 unsigned long locked, lock_limit;
 374                 locked = mm->locked_vm << PAGE_SHIFT;
 375                 lock_limit = rlimit(RLIMIT_MEMLOCK);
 376                 locked += new_len - old_len;
 377                 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
 378                         return ERR_PTR(-EAGAIN);
 379         }
 380
 381         if (!may_expand_vm(mm, (new_len - old_len) >> PAGE_SHIFT))
 382                 return ERR_PTR(-ENOMEM);
 383
 384         if (vma->vm_flags & VM_ACCOUNT) {
 385                 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
 386                 if (security_vm_enough_memory_mm(mm, charged))
 387                         return ERR_PTR(-ENOMEM);
 388                 *p = charged;
 389         }
 390
 391         return vma;
 392 }
 393
 394 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 395                 unsigned long new_addr, unsigned long new_len, bool *locked)
 396 {
 397         struct mm_struct *mm = current->mm;
 398         struct vm_area_struct *vma;
 399         unsigned long ret = -EINVAL;
 400         unsigned long charged = 0;
 401         unsigned long map_flags;
 402
 403         if (offset_in_page(new_addr))
 404                 goto out;
 405
 406         if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
 407                 goto out;
 408
 409         /* Ensure the old/new locations do not overlap */
 410         if (addr + old_len > new_addr && new_addr + new_len > addr)
 411                 goto out;
 412
 413         ret = do_munmap(mm, new_addr, new_len);
 414         if (ret)
 415                 goto out;
 416
 417         if (old_len >= new_len) {
 418                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
 419                 if (ret && old_len != new_len)
 420                         goto out;
 421                 old_len = new_len;
 422         }
 423
 424         vma = vma_to_resize(addr, old_len, new_len, &charged);
 425         if (IS_ERR(vma)) {
 426                 ret = PTR_ERR(vma);
 427                 goto out;
 428         }
 429
 430         map_flags = MAP_FIXED;
 431         if (vma->vm_flags & VM_MAYSHARE)
 432                 map_flags |= MAP_SHARED;
 433
 434         ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
 435                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
 436                                 map_flags);
 437         if (offset_in_page(ret))
 438                 goto out1;
 439
 440         ret = move_vma(vma, addr, old_len, new_len, new_addr, locked);
 441         if (!(offset_in_page(ret)))
 442                 goto out;
 443 out1:
 444         vm_unacct_memory(charged);
 445
 446 out:
 447         return ret;
 448 }
 449
 450 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
 451 {
 452         unsigned long end = vma->vm_end + delta;
 453         if (end < vma->vm_end) /* overflow */
 454                 return 0;
 455         if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
 456                 return 0;
 457         if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
 458                               0, MAP_FIXED) & ~PAGE_MASK)
 459                 return 0;
 460         return 1;
 461 }
 462
 463 /*
 464  * Expand (or shrink) an existing mapping, potentially moving it at the
 465  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 466  *
 467  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
 468  * This option implies MREMAP_MAYMOVE.
 469  */
 470 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 471                 unsigned long, new_len, unsigned long, flags,
 472                 unsigned long, new_addr)
 473 {
 474         struct mm_struct *mm = current->mm;
 475         struct vm_area_struct *vma;
 476         unsigned long ret = -EINVAL;
 477         unsigned long charged = 0;
 478         bool locked = false;
 479
 480         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
 481                 return ret;
 482
 483         if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
 484                 return ret;
 485
 486         if (offset_in_page(addr))
 487                 return ret;
 488
 489         old_len = PAGE_ALIGN(old_len);
 490         new_len = PAGE_ALIGN(new_len);
 491
 492         /*
 493          * We allow a zero old-len as a special case
 494          * for DOS-emu "duplicate shm area" thing. But
 495          * a zero new-len is nonsensical.
 496          */
 497         if (!new_len)
 498                 return ret;
 499
 500         down_write(&current->mm->mmap_sem);
 501
 502         if (flags & MREMAP_FIXED) {
 503                 ret = mremap_to(addr, old_len, new_addr, new_len,
 504                                 &locked);
 505                 goto out;
 506         }
 507
 508         /*
 509          * Always allow a shrinking remap: that just unmaps
 510          * the unnecessary pages..
 511          * do_munmap does all the needed commit accounting
 512          */
 513         if (old_len >= new_len) {
 514                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
 515                 if (ret && old_len != new_len)
 516                         goto out;
 517                 ret = addr;
 518                 goto out;
 519         }
 520
 521         /*
 522          * Ok, we need to grow..
 523          */
 524         vma = vma_to_resize(addr, old_len, new_len, &charged);
 525         if (IS_ERR(vma)) {
 526                 ret = PTR_ERR(vma);
 527                 goto out;
 528         }
 529
 530         /* old_len exactly to the end of the area..
 531          */
 532         if (old_len == vma->vm_end - addr) {
 533                 /* can we just expand the current mapping? */
 534                 if (vma_expandable(vma, new_len - old_len)) {
 535                         int pages = (new_len - old_len) >> PAGE_SHIFT;
 536
 537                         if (vma_adjust(vma, vma->vm_start, addr + new_len,
 538                                        vma->vm_pgoff, NULL)) {
 539                                 ret = -ENOMEM;
 540                                 goto out;
 541                         }
 542
 543                         vm_stat_account(mm, vma->vm_flags, vma->vm_file, pages);
 544                         if (vma->vm_flags & VM_LOCKED) {
 545                                 mm->locked_vm += pages;
 546                                 locked = true;
 547                                 new_addr = addr;
 548                         }
 549                         ret = addr;
 550                         goto out;
 551                 }
 552         }
 553
 554         /*
 555          * We weren't able to just expand or shrink the area,
 556          * we need to create a new one and move it..
 557          */
 558         ret = -ENOMEM;
 559         if (flags & MREMAP_MAYMOVE) {
 560                 unsigned long map_flags = 0;
 561                 if (vma->vm_flags & VM_MAYSHARE)
 562                         map_flags |= MAP_SHARED;
 563
 564                 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
 565                                         vma->vm_pgoff +
 566                                         ((addr - vma->vm_start) >> PAGE_SHIFT),
 567                                         map_flags);
 568                 if (offset_in_page(new_addr)) {
 569                         ret = new_addr;
 570                         goto out;
 571                 }
 572
 573                 ret = move_vma(vma, addr, old_len, new_len, new_addr, &locked);
 574         }
 575 out:
 576         if (offset_in_page(ret)) {
 577                 vm_unacct_memory(charged);
 578                 locked = 0;
 579         }
 580         up_write(&current->mm->mmap_sem);
 581         if (locked && new_len > old_len)
 582                 mm_populate(new_addr + old_len, new_len - old_len);
 583         return ret;
 584 }