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