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

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