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                         if (pmd_none(*old_pmd))
 214                                 continue;
 215                         VM_BUG_ON(pmd_trans_huge(*old_pmd));
 216                 }
 217                 if (pmd_none(*new_pmd) && __pte_alloc(new_vma->vm_mm, new_vma,
 218                                                       new_pmd, new_addr))
 219                         break;
 220                 next = (new_addr + PMD_SIZE) & PMD_MASK;
 221                 if (extent > next - new_addr)
 222                         extent = next - new_addr;
 223                 if (extent > LATENCY_LIMIT)
 224                         extent = LATENCY_LIMIT;
 225                 move_ptes(vma, old_pmd, old_addr, old_addr + extent,
 226                           new_vma, new_pmd, new_addr, need_rmap_locks);
 227                 need_flush = true;
 228         }
 229         if (likely(need_flush))
 230                 flush_tlb_range(vma, old_end-len, old_addr);
 231
 232         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
 233
 234         return len + old_addr - old_end;        /* how much done */
 235 }
 236
 237 static unsigned long move_vma(struct vm_area_struct *vma,
 238                 unsigned long old_addr, unsigned long old_len,
 239                 unsigned long new_len, unsigned long new_addr, bool *locked)
 240 {
 241         struct mm_struct *mm = vma->vm_mm;
 242         struct vm_area_struct *new_vma;
 243         unsigned long vm_flags = vma->vm_flags;
 244         unsigned long new_pgoff;
 245         unsigned long moved_len;
 246         unsigned long excess = 0;
 247         unsigned long hiwater_vm;
 248         int split = 0;
 249         int err;
 250         bool need_rmap_locks;
 251
 252         /*
 253          * We'd prefer to avoid failure later on in do_munmap:
 254          * which may split one vma into three before unmapping.
 255          */
 256         if (mm->map_count >= sysctl_max_map_count - 3)
 257                 return -ENOMEM;
 258
 259         /*
 260          * Advise KSM to break any KSM pages in the area to be moved:
 261          * it would be confusing if they were to turn up at the new
 262          * location, where they happen to coincide with different KSM
 263          * pages recently unmapped.  But leave vma->vm_flags as it was,
 264          * so KSM can come around to merge on vma and new_vma afterwards.
 265          */
 266         err = ksm_madvise(vma, old_addr, old_addr + old_len,
 267                                                 MADV_UNMERGEABLE, &vm_flags);
 268         if (err)
 269                 return err;
 270
 271         new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
 272         new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
 273                            &need_rmap_locks);
 274         if (!new_vma)
 275                 return -ENOMEM;
 276
 277         moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
 278                                      need_rmap_locks);
 279         if (moved_len < old_len) {
 280                 err = -ENOMEM;
 281         } else if (vma->vm_ops && vma->vm_ops->mremap) {
 282                 err = vma->vm_ops->mremap(new_vma);
 283         }
 284
 285         if (unlikely(err)) {
 286                 /*
 287                  * On error, move entries back from new area to old,
 288                  * which will succeed since page tables still there,
 289                  * and then proceed to unmap new area instead of old.
 290                  */
 291                 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
 292                                  true);
 293                 vma = new_vma;
 294                 old_len = new_len;
 295                 old_addr = new_addr;
 296                 new_addr = err;
 297         } else {
 298                 arch_remap(mm, old_addr, old_addr + old_len,
 299                            new_addr, new_addr + new_len);
 300         }
 301
 302         /* Conceal VM_ACCOUNT so old reservation is not undone */
 303         if (vm_flags & VM_ACCOUNT) {
 304                 vma->vm_flags &= ~VM_ACCOUNT;
 305                 excess = vma->vm_end - vma->vm_start - old_len;
 306                 if (old_addr > vma->vm_start &&
 307                     old_addr + old_len < vma->vm_end)
 308                         split = 1;
 309         }
 310
 311         /*
 312          * If we failed to move page tables we still do total_vm increment
 313          * since do_munmap() will decrement it by old_len == new_len.
 314          *
 315          * Since total_vm is about to be raised artificially high for a
 316          * moment, we need to restore high watermark afterwards: if stats
 317          * are taken meanwhile, total_vm and hiwater_vm appear too high.
 318          * If this were a serious issue, we'd add a flag to do_munmap().
 319          */
 320         hiwater_vm = mm->hiwater_vm;
 321         vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT);
 322
 323         /* Tell pfnmap has moved from this vma */
 324         if (unlikely(vma->vm_flags & VM_PFNMAP))
 325                 untrack_pfn_moved(vma);
 326
 327         if (do_munmap(mm, old_addr, old_len) < 0) {
 328                 /* OOM: unable to split vma, just get accounts right */
 329                 vm_unacct_memory(excess >> PAGE_SHIFT);
 330                 excess = 0;
 331         }
 332         mm->hiwater_vm = hiwater_vm;
 333
 334         /* Restore VM_ACCOUNT if one or two pieces of vma left */
 335         if (excess) {
 336                 vma->vm_flags |= VM_ACCOUNT;
 337                 if (split)
 338                         vma->vm_next->vm_flags |= VM_ACCOUNT;
 339         }
 340
 341         if (vm_flags & VM_LOCKED) {
 342                 mm->locked_vm += new_len >> PAGE_SHIFT;
 343                 *locked = true;
 344         }
 345
 346         return new_addr;
 347 }
 348
 349 static struct vm_area_struct *vma_to_resize(unsigned long addr,
 350         unsigned long old_len, unsigned long new_len, unsigned long *p)
 351 {
 352         struct mm_struct *mm = current->mm;
 353         struct vm_area_struct *vma = find_vma(mm, addr);
 354         unsigned long pgoff;
 355
 356         if (!vma || vma->vm_start > addr)
 357                 return ERR_PTR(-EFAULT);
 358
 359         if (is_vm_hugetlb_page(vma))
 360                 return ERR_PTR(-EINVAL);
 361
 362         /* We can't remap across vm area boundaries */
 363         if (old_len > vma->vm_end - addr)
 364                 return ERR_PTR(-EFAULT);
 365
 366         if (new_len == old_len)
 367                 return vma;
 368
 369         /* Need to be careful about a growing mapping */
 370         pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
 371         pgoff += vma->vm_pgoff;
 372         if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
 373                 return ERR_PTR(-EINVAL);
 374
 375         if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
 376                 return ERR_PTR(-EFAULT);
 377
 378         if (vma->vm_flags & VM_LOCKED) {
 379                 unsigned long locked, lock_limit;
 380                 locked = mm->locked_vm << PAGE_SHIFT;
 381                 lock_limit = rlimit(RLIMIT_MEMLOCK);
 382                 locked += new_len - old_len;
 383                 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
 384                         return ERR_PTR(-EAGAIN);
 385         }
 386
 387         if (!may_expand_vm(mm, vma->vm_flags,
 388                                 (new_len - old_len) >> PAGE_SHIFT))
 389                 return ERR_PTR(-ENOMEM);
 390
 391         if (vma->vm_flags & VM_ACCOUNT) {
 392                 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
 393                 if (security_vm_enough_memory_mm(mm, charged))
 394                         return ERR_PTR(-ENOMEM);
 395                 *p = charged;
 396         }
 397
 398         return vma;
 399 }
 400
 401 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 402                 unsigned long new_addr, unsigned long new_len, bool *locked)
 403 {
 404         struct mm_struct *mm = current->mm;
 405         struct vm_area_struct *vma;
 406         unsigned long ret = -EINVAL;
 407         unsigned long charged = 0;
 408         unsigned long map_flags;
 409
 410         if (offset_in_page(new_addr))
 411                 goto out;
 412
 413         if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
 414                 goto out;
 415
 416         /* Ensure the old/new locations do not overlap */
 417         if (addr + old_len > new_addr && new_addr + new_len > addr)
 418                 goto out;
 419
 420         ret = do_munmap(mm, new_addr, new_len);
 421         if (ret)
 422                 goto out;
 423
 424         if (old_len >= new_len) {
 425                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
 426                 if (ret && old_len != new_len)
 427                         goto out;
 428                 old_len = new_len;
 429         }
 430
 431         vma = vma_to_resize(addr, old_len, new_len, &charged);
 432         if (IS_ERR(vma)) {
 433                 ret = PTR_ERR(vma);
 434                 goto out;
 435         }
 436
 437         map_flags = MAP_FIXED;
 438         if (vma->vm_flags & VM_MAYSHARE)
 439                 map_flags |= MAP_SHARED;
 440
 441         ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
 442                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
 443                                 map_flags);
 444         if (offset_in_page(ret))
 445                 goto out1;
 446
 447         ret = move_vma(vma, addr, old_len, new_len, new_addr, locked);
 448         if (!(offset_in_page(ret)))
 449                 goto out;
 450 out1:
 451         vm_unacct_memory(charged);
 452
 453 out:
 454         return ret;
 455 }
 456
 457 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
 458 {
 459         unsigned long end = vma->vm_end + delta;
 460         if (end < vma->vm_end) /* overflow */
 461                 return 0;
 462         if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
 463                 return 0;
 464         if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
 465                               0, MAP_FIXED) & ~PAGE_MASK)
 466                 return 0;
 467         return 1;
 468 }
 469
 470 /*
 471  * Expand (or shrink) an existing mapping, potentially moving it at the
 472  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 473  *
 474  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
 475  * This option implies MREMAP_MAYMOVE.
 476  */
 477 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 478                 unsigned long, new_len, unsigned long, flags,
 479                 unsigned long, new_addr)
 480 {
 481         struct mm_struct *mm = current->mm;
 482         struct vm_area_struct *vma;
 483         unsigned long ret = -EINVAL;
 484         unsigned long charged = 0;
 485         bool locked = false;
 486
 487         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
 488                 return ret;
 489
 490         if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
 491                 return ret;
 492
 493         if (offset_in_page(addr))
 494                 return ret;
 495
 496         old_len = PAGE_ALIGN(old_len);
 497         new_len = PAGE_ALIGN(new_len);
 498
 499         /*
 500          * We allow a zero old-len as a special case
 501          * for DOS-emu "duplicate shm area" thing. But
 502          * a zero new-len is nonsensical.
 503          */
 504         if (!new_len)
 505                 return ret;
 506
 507         down_write(&current->mm->mmap_sem);
 508
 509         if (flags & MREMAP_FIXED) {
 510                 ret = mremap_to(addr, old_len, new_addr, new_len,
 511                                 &locked);
 512                 goto out;
 513         }
 514
 515         /*
 516          * Always allow a shrinking remap: that just unmaps
 517          * the unnecessary pages..
 518          * do_munmap does all the needed commit accounting
 519          */
 520         if (old_len >= new_len) {
 521                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
 522                 if (ret && old_len != new_len)
 523                         goto out;
 524                 ret = addr;
 525                 goto out;
 526         }
 527
 528         /*
 529          * Ok, we need to grow..
 530          */
 531         vma = vma_to_resize(addr, old_len, new_len, &charged);
 532         if (IS_ERR(vma)) {
 533                 ret = PTR_ERR(vma);
 534                 goto out;
 535         }
 536
 537         /* old_len exactly to the end of the area..
 538          */
 539         if (old_len == vma->vm_end - addr) {
 540                 /* can we just expand the current mapping? */
 541                 if (vma_expandable(vma, new_len - old_len)) {
 542                         int pages = (new_len - old_len) >> PAGE_SHIFT;
 543
 544                         if (vma_adjust(vma, vma->vm_start, addr + new_len,
 545                                        vma->vm_pgoff, NULL)) {
 546                                 ret = -ENOMEM;
 547                                 goto out;
 548                         }
 549
 550                         vm_stat_account(mm, vma->vm_flags, pages);
 551                         if (vma->vm_flags & VM_LOCKED) {
 552                                 mm->locked_vm += pages;
 553                                 locked = true;
 554                                 new_addr = addr;
 555                         }
 556                         ret = addr;
 557                         goto out;
 558                 }
 559         }
 560
 561         /*
 562          * We weren't able to just expand or shrink the area,
 563          * we need to create a new one and move it..
 564          */
 565         ret = -ENOMEM;
 566         if (flags & MREMAP_MAYMOVE) {
 567                 unsigned long map_flags = 0;
 568                 if (vma->vm_flags & VM_MAYSHARE)
 569                         map_flags |= MAP_SHARED;
 570
 571                 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
 572                                         vma->vm_pgoff +
 573                                         ((addr - vma->vm_start) >> PAGE_SHIFT),
 574                                         map_flags);
 575                 if (offset_in_page(new_addr)) {
 576                         ret = new_addr;
 577                         goto out;
 578                 }
 579
 580                 ret = move_vma(vma, addr, old_len, new_len, new_addr, &locked);
 581         }
 582 out:
 583         if (offset_in_page(ret)) {
 584                 vm_unacct_memory(charged);
 585                 locked = 0;
 586         }
 587         up_write(&current->mm->mmap_sem);
 588         if (locked && new_len > old_len)
 589                 mm_populate(new_addr + old_len, new_len - old_len);
 590         return ret;
 591 }