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    if (pmd_none_or_clear_bad(pmd))
45        return NULL;
46
47    return pmd;
48}
49
50static pmd_t *alloc_new_pmd(struct mm_struct *mm, unsigned long addr)
51{
52    pgd_t *pgd;
53    pud_t *pud;
54    pmd_t *pmd;
55
56    pgd = pgd_offset(mm, addr);
57    pud = pud_alloc(mm, pgd, addr);
58    if (!pud)
59        return NULL;
60
61    pmd = pmd_alloc(mm, pud, addr);
62    if (!pmd)
63        return NULL;
64
65    if (!pmd_present(*pmd) && __pte_alloc(mm, pmd, addr))
66        return NULL;
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    unsigned long old_start;
81
82    old_start = old_addr;
83    mmu_notifier_invalidate_range_start(vma->vm_mm,
84                        old_start, old_end);
85    if (vma->vm_file) {
86        /*
87         * Subtle point from Rajesh Venkatasubramanian: before
88         * moving file-based ptes, we must lock truncate_pagecache
89         * out, since it might clean the dst vma before the src vma,
90         * and we propagate stale pages into the dst afterward.
91         */
92        mapping = vma->vm_file->f_mapping;
93        spin_lock(&mapping->i_mmap_lock);
94        if (new_vma->vm_truncate_count &&
95            new_vma->vm_truncate_count != vma->vm_truncate_count)
96            new_vma->vm_truncate_count = 0;
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_nested(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_nested(new_pte - 1);
123    pte_unmap_unlock(old_pte - 1, old_ptl);
124    if (mapping)
125        spin_unlock(&mapping->i_mmap_lock);
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, 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    if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)) {
280        if (new_len > old_len)
281            goto Efault;
282    }
283
284    if (vma->vm_flags & VM_LOCKED) {
285        unsigned long locked, lock_limit;
286        locked = mm->locked_vm << PAGE_SHIFT;
287        lock_limit = rlimit(RLIMIT_MEMLOCK);
288        locked += new_len - old_len;
289        if (locked > lock_limit && !capable(CAP_IPC_LOCK))
290            goto Eagain;
291    }
292
293    if (!may_expand_vm(mm, (new_len - old_len) >> PAGE_SHIFT))
294        goto Enomem;
295
296    if (vma->vm_flags & VM_ACCOUNT) {
297        unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
298        if (security_vm_enough_memory(charged))
299            goto Efault;
300        *p = charged;
301    }
302
303    return vma;
304
305Efault: /* very odd choice for most of the cases, but... */
306    return ERR_PTR(-EFAULT);
307Einval:
308    return ERR_PTR(-EINVAL);
309Enomem:
310    return ERR_PTR(-ENOMEM);
311Eagain:
312    return ERR_PTR(-EAGAIN);
313}
314
315static unsigned long mremap_to(unsigned long addr,
316    unsigned long old_len, unsigned long new_addr,
317    unsigned long new_len)
318{
319    struct mm_struct *mm = current->mm;
320    struct vm_area_struct *vma;
321    unsigned long ret = -EINVAL;
322    unsigned long charged = 0;
323    unsigned long map_flags;
324
325    if (new_addr & ~PAGE_MASK)
326        goto out;
327
328    if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
329        goto out;
330
331    /* Check if the location we're moving into overlaps the
332     * old location at all, and fail if it does.
333     */
334    if ((new_addr <= addr) && (new_addr+new_len) > addr)
335        goto out;
336
337    if ((addr <= new_addr) && (addr+old_len) > new_addr)
338        goto out;
339
340    ret = security_file_mmap(NULL, 0, 0, 0, new_addr, 1);
341    if (ret)
342        goto out;
343
344    ret = do_munmap(mm, new_addr, new_len);
345    if (ret)
346        goto out;
347
348    if (old_len >= new_len) {
349        ret = do_munmap(mm, addr+new_len, old_len - new_len);
350        if (ret && old_len != new_len)
351            goto out;
352        old_len = new_len;
353    }
354
355    vma = vma_to_resize(addr, old_len, new_len, &charged);
356    if (IS_ERR(vma)) {
357        ret = PTR_ERR(vma);
358        goto out;
359    }
360
361    map_flags = MAP_FIXED;
362    if (vma->vm_flags & VM_MAYSHARE)
363        map_flags |= MAP_SHARED;
364
365    ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
366                ((addr - vma->vm_start) >> PAGE_SHIFT),
367                map_flags);
368    if (ret & ~PAGE_MASK)
369        goto out1;
370
371    ret = move_vma(vma, addr, old_len, new_len, new_addr);
372    if (!(ret & ~PAGE_MASK))
373        goto out;
374out1:
375    vm_unacct_memory(charged);
376
377out:
378    return ret;
379}
380
381static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
382{
383    unsigned long end = vma->vm_end + delta;
384    if (end < vma->vm_end) /* overflow */
385        return 0;
386    if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
387        return 0;
388    if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
389                  0, MAP_FIXED) & ~PAGE_MASK)
390        return 0;
391    return 1;
392}
393
394/*
395 * Expand (or shrink) an existing mapping, potentially moving it at the
396 * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
397 *
398 * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
399 * This option implies MREMAP_MAYMOVE.
400 */
401unsigned long do_mremap(unsigned long addr,
402    unsigned long old_len, unsigned long new_len,
403    unsigned long flags, unsigned long new_addr)
404{
405    struct mm_struct *mm = current->mm;
406    struct vm_area_struct *vma;
407    unsigned long ret = -EINVAL;
408    unsigned long charged = 0;
409
410    if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
411        goto out;
412
413    if (addr & ~PAGE_MASK)
414        goto out;
415
416    old_len = PAGE_ALIGN(old_len);
417    new_len = PAGE_ALIGN(new_len);
418
419    /*
420     * We allow a zero old-len as a special case
421     * for DOS-emu "duplicate shm area" thing. But
422     * a zero new-len is nonsensical.
423     */
424    if (!new_len)
425        goto out;
426
427    if (flags & MREMAP_FIXED) {
428        if (flags & MREMAP_MAYMOVE)
429            ret = mremap_to(addr, old_len, new_addr, new_len);
430        goto out;
431    }
432
433    /*
434     * Always allow a shrinking remap: that just unmaps
435     * the unnecessary pages..
436     * do_munmap does all the needed commit accounting
437     */
438    if (old_len >= new_len) {
439        ret = do_munmap(mm, addr+new_len, old_len - new_len);
440        if (ret && old_len != new_len)
441            goto out;
442        ret = addr;
443        goto out;
444    }
445
446    /*
447     * Ok, we need to grow..
448     */
449    vma = vma_to_resize(addr, old_len, new_len, &charged);
450    if (IS_ERR(vma)) {
451        ret = PTR_ERR(vma);
452        goto out;
453    }
454
455    /* old_len exactly to the end of the area..
456     */
457    if (old_len == vma->vm_end - addr) {
458        /* can we just expand the current mapping? */
459        if (vma_expandable(vma, new_len - old_len)) {
460            int pages = (new_len - old_len) >> PAGE_SHIFT;
461
462            if (vma_adjust(vma, vma->vm_start, addr + new_len,
463                       vma->vm_pgoff, NULL)) {
464                ret = -ENOMEM;
465                goto out;
466            }
467
468            mm->total_vm += pages;
469            vm_stat_account(mm, vma->vm_flags, vma->vm_file, pages);
470            if (vma->vm_flags & VM_LOCKED) {
471                mm->locked_vm += pages;
472                mlock_vma_pages_range(vma, addr + old_len,
473                           addr + new_len);
474            }
475            ret = addr;
476            goto out;
477        }
478    }
479
480    /*
481     * We weren't able to just expand or shrink the area,
482     * we need to create a new one and move it..
483     */
484    ret = -ENOMEM;
485    if (flags & MREMAP_MAYMOVE) {
486        unsigned long map_flags = 0;
487        if (vma->vm_flags & VM_MAYSHARE)
488            map_flags |= MAP_SHARED;
489
490        new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
491                    vma->vm_pgoff +
492                    ((addr - vma->vm_start) >> PAGE_SHIFT),
493                    map_flags);
494        if (new_addr & ~PAGE_MASK) {
495            ret = new_addr;
496            goto out;
497        }
498
499        ret = security_file_mmap(NULL, 0, 0, 0, new_addr, 1);
500        if (ret)
501            goto out;
502        ret = move_vma(vma, addr, old_len, new_len, new_addr);
503    }
504out:
505    if (ret & ~PAGE_MASK)
506        vm_unacct_memory(charged);
507    return ret;
508}
509
510SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
511        unsigned long, new_len, unsigned long, flags,
512        unsigned long, new_addr)
513{
514    unsigned long ret;
515
516    down_write(&current->mm->mmap_sem);
517    ret = do_mremap(addr, old_len, new_len, flags, new_addr);
518    up_write(&current->mm->mmap_sem);
519    return ret;
520}
521

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