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