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