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                         int err = 0;
 196                         if (extent == HPAGE_PMD_SIZE) {
 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                                 err = 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                         }
 208                         if (err > 0) {
 209                                 need_flush = true;
 210                                 continue;
 211                         } else if (!err) {
 212                                 split_huge_page_pmd(vma, old_addr, old_pmd);
 213                         }
 214                         VM_BUG_ON(pmd_trans_huge(*old_pmd));
 215                 }
 216                 if (pmd_none(*new_pmd) && __pte_alloc(new_vma->vm_mm, new_vma,
 217                                                       new_pmd, new_addr))
 218                         break;
 219                 next = (new_addr + PMD_SIZE) & PMD_MASK;
 220                 if (extent > next - new_addr)
 221                         extent = next - new_addr;
 222                 if (extent > LATENCY_LIMIT)
 223                         extent = LATENCY_LIMIT;
 224                 move_ptes(vma, old_pmd, old_addr, old_addr + extent,
 225                           new_vma, new_pmd, new_addr, need_rmap_locks);
 226                 need_flush = true;
 227         }
 228         if (likely(need_flush))
 229                 flush_tlb_range(vma, old_end-len, old_addr);
 230
 231         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
 232
 233         return len + old_addr - old_end;        /* how much done */
 234 }
 235
 236 static unsigned long move_vma(struct vm_area_struct *vma,
 237                 unsigned long old_addr, unsigned long old_len,
 238                 unsigned long new_len, unsigned long new_addr, bool *locked)
 239 {
 240         struct mm_struct *mm = vma->vm_mm;
 241         struct vm_area_struct *new_vma;
 242         unsigned long vm_flags = vma->vm_flags;
 243         unsigned long new_pgoff;
 244         unsigned long moved_len;
 245         unsigned long excess = 0;
 246         unsigned long hiwater_vm;
 247         int split = 0;
 248         int err;
 249         bool need_rmap_locks;
 250
 251         /*
 252          * We'd prefer to avoid failure later on in do_munmap:
 253          * which may split one vma into three before unmapping.
 254          */
 255         if (mm->map_count >= sysctl_max_map_count - 3)
 256                 return -ENOMEM;
 257
 258         /*
 259          * Advise KSM to break any KSM pages in the area to be moved:
 260          * it would be confusing if they were to turn up at the new
 261          * location, where they happen to coincide with different KSM
 262          * pages recently unmapped.  But leave vma->vm_flags as it was,
 263          * so KSM can come around to merge on vma and new_vma afterwards.
 264          */
 265         err = ksm_madvise(vma, old_addr, old_addr + old_len,
 266                                                 MADV_UNMERGEABLE, &vm_flags);
 267         if (err)
 268                 return err;
 269
 270         new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
 271         new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
 272                            &need_rmap_locks);
 273         if (!new_vma)
 274                 return -ENOMEM;
 275
 276         moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
 277                                      need_rmap_locks);
 278         if (moved_len < old_len) {
 279                 err = -ENOMEM;
 280         } else if (vma->vm_ops && vma->vm_ops->mremap) {
 281                 err = vma->vm_ops->mremap(new_vma);
 282         }
 283
 284         if (unlikely(err)) {
 285                 /*
 286                  * On error, move entries back from new area to old,
 287                  * which will succeed since page tables still there,
 288                  * and then proceed to unmap new area instead of old.
 289                  */
 290                 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
 291                                  true);
 292                 vma = new_vma;
 293                 old_len = new_len;
 294                 old_addr = new_addr;
 295                 new_addr = err;
 296         } else {
 297                 arch_remap(mm, old_addr, old_addr + old_len,
 298                            new_addr, new_addr + new_len);
 299         }
 300
 301         /* Conceal VM_ACCOUNT so old reservation is not undone */
 302         if (vm_flags & VM_ACCOUNT) {
 303                 vma->vm_flags &= ~VM_ACCOUNT;
 304                 excess = vma->vm_end - vma->vm_start - old_len;
 305                 if (old_addr > vma->vm_start &&
 306                     old_addr + old_len < vma->vm_end)
 307                         split = 1;
 308         }
 309
 310         /*
 311          * If we failed to move page tables we still do total_vm increment
 312          * since do_munmap() will decrement it by old_len == new_len.
 313          *
 314          * Since total_vm is about to be raised artificially high for a
 315          * moment, we need to restore high watermark afterwards: if stats
 316          * are taken meanwhile, total_vm and hiwater_vm appear too high.
 317          * If this were a serious issue, we'd add a flag to do_munmap().
 318          */
 319         hiwater_vm = mm->hiwater_vm;
 320         vm_stat_account(mm, vma->vm_flags, vma->vm_file, new_len>>PAGE_SHIFT);
 321
 322         if (do_munmap(mm, old_addr, old_len) < 0) {
 323                 /* OOM: unable to split vma, just get accounts right */
 324                 vm_unacct_memory(excess >> PAGE_SHIFT);
 325                 excess = 0;
 326         }
 327         mm->hiwater_vm = hiwater_vm;
 328
 329         /* Restore VM_ACCOUNT if one or two pieces of vma left */
 330         if (excess) {
 331                 vma->vm_flags |= VM_ACCOUNT;
 332                 if (split)
 333                         vma->vm_next->vm_flags |= VM_ACCOUNT;
 334         }
 335
 336         if (vm_flags & VM_LOCKED) {
 337                 mm->locked_vm += new_len >> PAGE_SHIFT;
 338                 *locked = true;
 339         }
 340
 341         return new_addr;
 342 }
 343
 344 static struct vm_area_struct *vma_to_resize(unsigned long addr,
 345         unsigned long old_len, unsigned long new_len, unsigned long *p)
 346 {
 347         struct mm_struct *mm = current->mm;
 348         struct vm_area_struct *vma = find_vma(mm, addr);
 349         unsigned long pgoff;
 350
 351         if (!vma || vma->vm_start > addr)
 352                 return ERR_PTR(-EFAULT);
 353
 354         if (is_vm_hugetlb_page(vma))
 355                 return ERR_PTR(-EINVAL);
 356
 357         /* We can't remap across vm area boundaries */
 358         if (old_len > vma->vm_end - addr)
 359                 return ERR_PTR(-EFAULT);
 360
 361         if (new_len == old_len)
 362                 return vma;
 363
 364         /* Need to be careful about a growing mapping */
 365         pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
 366         pgoff += vma->vm_pgoff;
 367         if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
 368                 return ERR_PTR(-EINVAL);
 369
 370         if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
 371                 return ERR_PTR(-EFAULT);
 372
 373         if (vma->vm_flags & VM_LOCKED) {
 374                 unsigned long locked, lock_limit;
 375                 locked = mm->locked_vm << PAGE_SHIFT;
 376                 lock_limit = rlimit(RLIMIT_MEMLOCK);
 377                 locked += new_len - old_len;
 378                 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
 379                         return ERR_PTR(-EAGAIN);
 380         }
 381
 382         if (!may_expand_vm(mm, (new_len - old_len) >> PAGE_SHIFT))
 383                 return ERR_PTR(-ENOMEM);
 384
 385         if (vma->vm_flags & VM_ACCOUNT) {
 386                 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
 387                 if (security_vm_enough_memory_mm(mm, charged))
 388                         return ERR_PTR(-ENOMEM);
 389                 *p = charged;
 390         }
 391
 392         return vma;
 393 }
 394
 395 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 396                 unsigned long new_addr, unsigned long new_len, bool *locked)
 397 {
 398         struct mm_struct *mm = current->mm;
 399         struct vm_area_struct *vma;
 400         unsigned long ret = -EINVAL;
 401         unsigned long charged = 0;
 402         unsigned long map_flags;
 403
 404         if (offset_in_page(new_addr))
 405                 goto out;
 406
 407         if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
 408                 goto out;
 409
 410         /* Ensure the old/new locations do not overlap */
 411         if (addr + old_len > new_addr && new_addr + new_len > addr)
 412                 goto out;
 413
 414         ret = do_munmap(mm, new_addr, new_len);
 415         if (ret)
 416                 goto out;
 417
 418         if (old_len >= new_len) {
 419                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
 420                 if (ret && old_len != new_len)
 421                         goto out;
 422                 old_len = new_len;
 423         }
 424
 425         vma = vma_to_resize(addr, old_len, new_len, &charged);
 426         if (IS_ERR(vma)) {
 427                 ret = PTR_ERR(vma);
 428                 goto out;
 429         }
 430
 431         map_flags = MAP_FIXED;
 432         if (vma->vm_flags & VM_MAYSHARE)
 433                 map_flags |= MAP_SHARED;
 434
 435         ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
 436                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
 437                                 map_flags);
 438         if (offset_in_page(ret))
 439                 goto out1;
 440
 441         ret = move_vma(vma, addr, old_len, new_len, new_addr, locked);
 442         if (!(offset_in_page(ret)))
 443                 goto out;
 444 out1:
 445         vm_unacct_memory(charged);
 446
 447 out:
 448         return ret;
 449 }
 450
 451 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
 452 {
 453         unsigned long end = vma->vm_end + delta;
 454         if (end < vma->vm_end) /* overflow */
 455                 return 0;
 456         if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
 457                 return 0;
 458         if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
 459                               0, MAP_FIXED) & ~PAGE_MASK)
 460                 return 0;
 461         return 1;
 462 }
 463
 464 /*
 465  * Expand (or shrink) an existing mapping, potentially moving it at the
 466  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 467  *
 468  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
 469  * This option implies MREMAP_MAYMOVE.
 470  */
 471 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 472                 unsigned long, new_len, unsigned long, flags,
 473                 unsigned long, new_addr)
 474 {
 475         struct mm_struct *mm = current->mm;
 476         struct vm_area_struct *vma;
 477         unsigned long ret = -EINVAL;
 478         unsigned long charged = 0;
 479         bool locked = false;
 480
 481         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
 482                 return ret;
 483
 484         if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
 485                 return ret;
 486
 487         if (offset_in_page(addr))
 488                 return ret;
 489
 490         old_len = PAGE_ALIGN(old_len);
 491         new_len = PAGE_ALIGN(new_len);
 492
 493         /*
 494          * We allow a zero old-len as a special case
 495          * for DOS-emu "duplicate shm area" thing. But
 496          * a zero new-len is nonsensical.
 497          */
 498         if (!new_len)
 499                 return ret;
 500
 501         down_write(&current->mm->mmap_sem);
 502
 503         if (flags & MREMAP_FIXED) {
 504                 ret = mremap_to(addr, old_len, new_addr, new_len,
 505                                 &locked);
 506                 goto out;
 507         }
 508
 509         /*
 510          * Always allow a shrinking remap: that just unmaps
 511          * the unnecessary pages..
 512          * do_munmap does all the needed commit accounting
 513          */
 514         if (old_len >= new_len) {
 515                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
 516                 if (ret && old_len != new_len)
 517                         goto out;
 518                 ret = addr;
 519                 goto out;
 520         }
 521
 522         /*
 523          * Ok, we need to grow..
 524          */
 525         vma = vma_to_resize(addr, old_len, new_len, &charged);
 526         if (IS_ERR(vma)) {
 527                 ret = PTR_ERR(vma);
 528                 goto out;
 529         }
 530
 531         /* old_len exactly to the end of the area..
 532          */
 533         if (old_len == vma->vm_end - addr) {
 534                 /* can we just expand the current mapping? */
 535                 if (vma_expandable(vma, new_len - old_len)) {
 536                         int pages = (new_len - old_len) >> PAGE_SHIFT;
 537
 538                         if (vma_adjust(vma, vma->vm_start, addr + new_len,
 539                                        vma->vm_pgoff, NULL)) {
 540                                 ret = -ENOMEM;
 541                                 goto out;
 542                         }
 543
 544                         vm_stat_account(mm, vma->vm_flags, vma->vm_file, pages);
 545                         if (vma->vm_flags & VM_LOCKED) {
 546                                 mm->locked_vm += pages;
 547                                 locked = true;
 548                                 new_addr = addr;
 549                         }
 550                         ret = addr;
 551                         goto out;
 552                 }
 553         }
 554
 555         /*
 556          * We weren't able to just expand or shrink the area,
 557          * we need to create a new one and move it..
 558          */
 559         ret = -ENOMEM;
 560         if (flags & MREMAP_MAYMOVE) {
 561                 unsigned long map_flags = 0;
 562                 if (vma->vm_flags & VM_MAYSHARE)
 563                         map_flags |= MAP_SHARED;
 564
 565                 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
 566                                         vma->vm_pgoff +
 567                                         ((addr - vma->vm_start) >> PAGE_SHIFT),
 568                                         map_flags);
 569                 if (offset_in_page(new_addr)) {
 570                         ret = new_addr;
 571                         goto out;
 572                 }
 573
 574                 ret = move_vma(vma, addr, old_len, new_len, new_addr, &locked);
 575         }
 576 out:
 577         if (offset_in_page(ret)) {
 578                 vm_unacct_memory(charged);
 579                 locked = 0;
 580         }
 581         up_write(&current->mm->mmap_sem);
 582         if (locked && new_len > old_len)
 583                 mm_populate(new_addr + old_len, new_len - old_len);
 584         return ret;
 585 }