075877b1cbc0e099048d85eed0155e162fe7bc87
[linux-2.6.git] / mm / hugetlb.c
1 /*
2  * Generic hugetlb support.
3  * (C) William Irwin, April 2004
4  */
5 #include <linux/gfp.h>
6 #include <linux/list.h>
7 #include <linux/init.h>
8 #include <linux/module.h>
9 #include <linux/mm.h>
10 #include <linux/sysctl.h>
11 #include <linux/highmem.h>
12 #include <linux/nodemask.h>
13 #include <linux/pagemap.h>
14 #include <linux/mempolicy.h>
15 #include <linux/cpuset.h>
16 #include <linux/mutex.h>
17
18 #include <asm/page.h>
19 #include <asm/pgtable.h>
20
21 #include <linux/hugetlb.h>
22 #include "internal.h"
23
24 const unsigned long hugetlb_zero = 0, hugetlb_infinity = ~0UL;
25 static unsigned long nr_huge_pages, free_huge_pages, reserved_huge_pages;
26 unsigned long max_huge_pages;
27 static struct list_head hugepage_freelists[MAX_NUMNODES];
28 static unsigned int nr_huge_pages_node[MAX_NUMNODES];
29 static unsigned int free_huge_pages_node[MAX_NUMNODES];
30 /*
31  * Protects updates to hugepage_freelists, nr_huge_pages, and free_huge_pages
32  */
33 static DEFINE_SPINLOCK(hugetlb_lock);
34
35 static void clear_huge_page(struct page *page, unsigned long addr)
36 {
37         int i;
38
39         might_sleep();
40         for (i = 0; i < (HPAGE_SIZE/PAGE_SIZE); i++) {
41                 cond_resched();
42                 clear_user_highpage(page + i, addr);
43         }
44 }
45
46 static void copy_huge_page(struct page *dst, struct page *src,
47                            unsigned long addr)
48 {
49         int i;
50
51         might_sleep();
52         for (i = 0; i < HPAGE_SIZE/PAGE_SIZE; i++) {
53                 cond_resched();
54                 copy_user_highpage(dst + i, src + i, addr + i*PAGE_SIZE);
55         }
56 }
57
58 static void enqueue_huge_page(struct page *page)
59 {
60         int nid = page_to_nid(page);
61         list_add(&page->lru, &hugepage_freelists[nid]);
62         free_huge_pages++;
63         free_huge_pages_node[nid]++;
64 }
65
66 static struct page *dequeue_huge_page(struct vm_area_struct *vma,
67                                 unsigned long address)
68 {
69         int nid = numa_node_id();
70         struct page *page = NULL;
71         struct zonelist *zonelist = huge_zonelist(vma, address);
72         struct zone **z;
73
74         for (z = zonelist->zones; *z; z++) {
75                 nid = (*z)->zone_pgdat->node_id;
76                 if (cpuset_zone_allowed(*z, GFP_HIGHUSER) &&
77                     !list_empty(&hugepage_freelists[nid]))
78                         break;
79         }
80
81         if (*z) {
82                 page = list_entry(hugepage_freelists[nid].next,
83                                   struct page, lru);
84                 list_del(&page->lru);
85                 free_huge_pages--;
86                 free_huge_pages_node[nid]--;
87         }
88         return page;
89 }
90
91 static void free_huge_page(struct page *page)
92 {
93         BUG_ON(page_count(page));
94
95         INIT_LIST_HEAD(&page->lru);
96
97         spin_lock(&hugetlb_lock);
98         enqueue_huge_page(page);
99         spin_unlock(&hugetlb_lock);
100 }
101
102 static int alloc_fresh_huge_page(void)
103 {
104         static int nid = 0;
105         struct page *page;
106         page = alloc_pages_node(nid, GFP_HIGHUSER|__GFP_COMP|__GFP_NOWARN,
107                                         HUGETLB_PAGE_ORDER);
108         nid = (nid + 1) % num_online_nodes();
109         if (page) {
110                 page[1].lru.next = (void *)free_huge_page;      /* dtor */
111                 spin_lock(&hugetlb_lock);
112                 nr_huge_pages++;
113                 nr_huge_pages_node[page_to_nid(page)]++;
114                 spin_unlock(&hugetlb_lock);
115                 put_page(page); /* free it into the hugepage allocator */
116                 return 1;
117         }
118         return 0;
119 }
120
121 static struct page *alloc_huge_page(struct vm_area_struct *vma,
122                                     unsigned long addr)
123 {
124         struct inode *inode = vma->vm_file->f_dentry->d_inode;
125         struct page *page;
126         int use_reserve = 0;
127         unsigned long idx;
128
129         spin_lock(&hugetlb_lock);
130
131         if (vma->vm_flags & VM_MAYSHARE) {
132
133                 /* idx = radix tree index, i.e. offset into file in
134                  * HPAGE_SIZE units */
135                 idx = ((addr - vma->vm_start) >> HPAGE_SHIFT)
136                         + (vma->vm_pgoff >> (HPAGE_SHIFT - PAGE_SHIFT));
137
138                 /* The hugetlbfs specific inode info stores the number
139                  * of "guaranteed available" (huge) pages.  That is,
140                  * the first 'prereserved_hpages' pages of the inode
141                  * are either already instantiated, or have been
142                  * pre-reserved (by hugetlb_reserve_for_inode()). Here
143                  * we're in the process of instantiating the page, so
144                  * we use this to determine whether to draw from the
145                  * pre-reserved pool or the truly free pool. */
146                 if (idx < HUGETLBFS_I(inode)->prereserved_hpages)
147                         use_reserve = 1;
148         }
149
150         if (!use_reserve) {
151                 if (free_huge_pages <= reserved_huge_pages)
152                         goto fail;
153         } else {
154                 BUG_ON(reserved_huge_pages == 0);
155                 reserved_huge_pages--;
156         }
157
158         page = dequeue_huge_page(vma, addr);
159         if (!page)
160                 goto fail;
161
162         spin_unlock(&hugetlb_lock);
163         set_page_refcounted(page);
164         return page;
165
166  fail:
167         WARN_ON(use_reserve); /* reserved allocations shouldn't fail */
168         spin_unlock(&hugetlb_lock);
169         return NULL;
170 }
171
172 /* hugetlb_extend_reservation()
173  *
174  * Ensure that at least 'atleast' hugepages are, and will remain,
175  * available to instantiate the first 'atleast' pages of the given
176  * inode.  If the inode doesn't already have this many pages reserved
177  * or instantiated, set aside some hugepages in the reserved pool to
178  * satisfy later faults (or fail now if there aren't enough, rather
179  * than getting the SIGBUS later).
180  */
181 int hugetlb_extend_reservation(struct hugetlbfs_inode_info *info,
182                                unsigned long atleast)
183 {
184         struct inode *inode = &info->vfs_inode;
185         unsigned long change_in_reserve = 0;
186         int ret = 0;
187
188         spin_lock(&hugetlb_lock);
189         read_lock_irq(&inode->i_mapping->tree_lock);
190
191         if (info->prereserved_hpages >= atleast)
192                 goto out;
193
194         /* Because we always call this on shared mappings, none of the
195          * pages beyond info->prereserved_hpages can have been
196          * instantiated, so we need to reserve all of them now. */
197         change_in_reserve = atleast - info->prereserved_hpages;
198
199         if ((reserved_huge_pages + change_in_reserve) > free_huge_pages) {
200                 ret = -ENOMEM;
201                 goto out;
202         }
203
204         reserved_huge_pages += change_in_reserve;
205         info->prereserved_hpages = atleast;
206
207  out:
208         read_unlock_irq(&inode->i_mapping->tree_lock);
209         spin_unlock(&hugetlb_lock);
210
211         return ret;
212 }
213
214 /* hugetlb_truncate_reservation()
215  *
216  * This returns pages reserved for the given inode to the general free
217  * hugepage pool.  If the inode has any pages prereserved, but not
218  * instantiated, beyond offset (atmost << HPAGE_SIZE), then release
219  * them.
220  */
221 void hugetlb_truncate_reservation(struct hugetlbfs_inode_info *info,
222                                   unsigned long atmost)
223 {
224         struct inode *inode = &info->vfs_inode;
225         struct address_space *mapping = inode->i_mapping;
226         unsigned long idx;
227         unsigned long change_in_reserve = 0;
228         struct page *page;
229
230         spin_lock(&hugetlb_lock);
231         read_lock_irq(&inode->i_mapping->tree_lock);
232
233         if (info->prereserved_hpages <= atmost)
234                 goto out;
235
236         /* Count pages which were reserved, but not instantiated, and
237          * which we can now release. */
238         for (idx = atmost; idx < info->prereserved_hpages; idx++) {
239                 page = radix_tree_lookup(&mapping->page_tree, idx);
240                 if (!page)
241                         /* Pages which are already instantiated can't
242                          * be unreserved (and in fact have already
243                          * been removed from the reserved pool) */
244                         change_in_reserve++;
245         }
246
247         BUG_ON(reserved_huge_pages < change_in_reserve);
248         reserved_huge_pages -= change_in_reserve;
249         info->prereserved_hpages = atmost;
250
251  out:
252         read_unlock_irq(&inode->i_mapping->tree_lock);
253         spin_unlock(&hugetlb_lock);
254 }
255
256 static int __init hugetlb_init(void)
257 {
258         unsigned long i;
259
260         if (HPAGE_SHIFT == 0)
261                 return 0;
262
263         for (i = 0; i < MAX_NUMNODES; ++i)
264                 INIT_LIST_HEAD(&hugepage_freelists[i]);
265
266         for (i = 0; i < max_huge_pages; ++i) {
267                 if (!alloc_fresh_huge_page())
268                         break;
269         }
270         max_huge_pages = free_huge_pages = nr_huge_pages = i;
271         printk("Total HugeTLB memory allocated, %ld\n", free_huge_pages);
272         return 0;
273 }
274 module_init(hugetlb_init);
275
276 static int __init hugetlb_setup(char *s)
277 {
278         if (sscanf(s, "%lu", &max_huge_pages) <= 0)
279                 max_huge_pages = 0;
280         return 1;
281 }
282 __setup("hugepages=", hugetlb_setup);
283
284 #ifdef CONFIG_SYSCTL
285 static void update_and_free_page(struct page *page)
286 {
287         int i;
288         nr_huge_pages--;
289         nr_huge_pages_node[page_zone(page)->zone_pgdat->node_id]--;
290         for (i = 0; i < (HPAGE_SIZE / PAGE_SIZE); i++) {
291                 page[i].flags &= ~(1 << PG_locked | 1 << PG_error | 1 << PG_referenced |
292                                 1 << PG_dirty | 1 << PG_active | 1 << PG_reserved |
293                                 1 << PG_private | 1<< PG_writeback);
294         }
295         page[1].lru.next = NULL;
296         set_page_refcounted(page);
297         __free_pages(page, HUGETLB_PAGE_ORDER);
298 }
299
300 #ifdef CONFIG_HIGHMEM
301 static void try_to_free_low(unsigned long count)
302 {
303         int i, nid;
304         for (i = 0; i < MAX_NUMNODES; ++i) {
305                 struct page *page, *next;
306                 list_for_each_entry_safe(page, next, &hugepage_freelists[i], lru) {
307                         if (PageHighMem(page))
308                                 continue;
309                         list_del(&page->lru);
310                         update_and_free_page(page);
311                         nid = page_zone(page)->zone_pgdat->node_id;
312                         free_huge_pages--;
313                         free_huge_pages_node[nid]--;
314                         if (count >= nr_huge_pages)
315                                 return;
316                 }
317         }
318 }
319 #else
320 static inline void try_to_free_low(unsigned long count)
321 {
322 }
323 #endif
324
325 static unsigned long set_max_huge_pages(unsigned long count)
326 {
327         while (count > nr_huge_pages) {
328                 if (!alloc_fresh_huge_page())
329                         return nr_huge_pages;
330         }
331         if (count >= nr_huge_pages)
332                 return nr_huge_pages;
333
334         spin_lock(&hugetlb_lock);
335         try_to_free_low(count);
336         while (count < nr_huge_pages) {
337                 struct page *page = dequeue_huge_page(NULL, 0);
338                 if (!page)
339                         break;
340                 update_and_free_page(page);
341         }
342         spin_unlock(&hugetlb_lock);
343         return nr_huge_pages;
344 }
345
346 int hugetlb_sysctl_handler(struct ctl_table *table, int write,
347                            struct file *file, void __user *buffer,
348                            size_t *length, loff_t *ppos)
349 {
350         proc_doulongvec_minmax(table, write, file, buffer, length, ppos);
351         max_huge_pages = set_max_huge_pages(max_huge_pages);
352         return 0;
353 }
354 #endif /* CONFIG_SYSCTL */
355
356 int hugetlb_report_meminfo(char *buf)
357 {
358         return sprintf(buf,
359                         "HugePages_Total: %5lu\n"
360                         "HugePages_Free:  %5lu\n"
361                         "HugePages_Rsvd:  %5lu\n"
362                         "Hugepagesize:    %5lu kB\n",
363                         nr_huge_pages,
364                         free_huge_pages,
365                         reserved_huge_pages,
366                         HPAGE_SIZE/1024);
367 }
368
369 int hugetlb_report_node_meminfo(int nid, char *buf)
370 {
371         return sprintf(buf,
372                 "Node %d HugePages_Total: %5u\n"
373                 "Node %d HugePages_Free:  %5u\n",
374                 nid, nr_huge_pages_node[nid],
375                 nid, free_huge_pages_node[nid]);
376 }
377
378 /* Return the number pages of memory we physically have, in PAGE_SIZE units. */
379 unsigned long hugetlb_total_pages(void)
380 {
381         return nr_huge_pages * (HPAGE_SIZE / PAGE_SIZE);
382 }
383
384 /*
385  * We cannot handle pagefaults against hugetlb pages at all.  They cause
386  * handle_mm_fault() to try to instantiate regular-sized pages in the
387  * hugegpage VMA.  do_page_fault() is supposed to trap this, so BUG is we get
388  * this far.
389  */
390 static struct page *hugetlb_nopage(struct vm_area_struct *vma,
391                                 unsigned long address, int *unused)
392 {
393         BUG();
394         return NULL;
395 }
396
397 struct vm_operations_struct hugetlb_vm_ops = {
398         .nopage = hugetlb_nopage,
399 };
400
401 static pte_t make_huge_pte(struct vm_area_struct *vma, struct page *page,
402                                 int writable)
403 {
404         pte_t entry;
405
406         if (writable) {
407                 entry =
408                     pte_mkwrite(pte_mkdirty(mk_pte(page, vma->vm_page_prot)));
409         } else {
410                 entry = pte_wrprotect(mk_pte(page, vma->vm_page_prot));
411         }
412         entry = pte_mkyoung(entry);
413         entry = pte_mkhuge(entry);
414
415         return entry;
416 }
417
418 static void set_huge_ptep_writable(struct vm_area_struct *vma,
419                                    unsigned long address, pte_t *ptep)
420 {
421         pte_t entry;
422
423         entry = pte_mkwrite(pte_mkdirty(*ptep));
424         ptep_set_access_flags(vma, address, ptep, entry, 1);
425         update_mmu_cache(vma, address, entry);
426         lazy_mmu_prot_update(entry);
427 }
428
429
430 int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
431                             struct vm_area_struct *vma)
432 {
433         pte_t *src_pte, *dst_pte, entry;
434         struct page *ptepage;
435         unsigned long addr;
436         int cow;
437
438         cow = (vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
439
440         for (addr = vma->vm_start; addr < vma->vm_end; addr += HPAGE_SIZE) {
441                 src_pte = huge_pte_offset(src, addr);
442                 if (!src_pte)
443                         continue;
444                 dst_pte = huge_pte_alloc(dst, addr);
445                 if (!dst_pte)
446                         goto nomem;
447                 spin_lock(&dst->page_table_lock);
448                 spin_lock(&src->page_table_lock);
449                 if (!pte_none(*src_pte)) {
450                         if (cow)
451                                 ptep_set_wrprotect(src, addr, src_pte);
452                         entry = *src_pte;
453                         ptepage = pte_page(entry);
454                         get_page(ptepage);
455                         add_mm_counter(dst, file_rss, HPAGE_SIZE / PAGE_SIZE);
456                         set_huge_pte_at(dst, addr, dst_pte, entry);
457                 }
458                 spin_unlock(&src->page_table_lock);
459                 spin_unlock(&dst->page_table_lock);
460         }
461         return 0;
462
463 nomem:
464         return -ENOMEM;
465 }
466
467 void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
468                           unsigned long end)
469 {
470         struct mm_struct *mm = vma->vm_mm;
471         unsigned long address;
472         pte_t *ptep;
473         pte_t pte;
474         struct page *page;
475
476         WARN_ON(!is_vm_hugetlb_page(vma));
477         BUG_ON(start & ~HPAGE_MASK);
478         BUG_ON(end & ~HPAGE_MASK);
479
480         spin_lock(&mm->page_table_lock);
481
482         /* Update high watermark before we lower rss */
483         update_hiwater_rss(mm);
484
485         for (address = start; address < end; address += HPAGE_SIZE) {
486                 ptep = huge_pte_offset(mm, address);
487                 if (!ptep)
488                         continue;
489
490                 pte = huge_ptep_get_and_clear(mm, address, ptep);
491                 if (pte_none(pte))
492                         continue;
493
494                 page = pte_page(pte);
495                 put_page(page);
496                 add_mm_counter(mm, file_rss, (int) -(HPAGE_SIZE / PAGE_SIZE));
497         }
498
499         spin_unlock(&mm->page_table_lock);
500         flush_tlb_range(vma, start, end);
501 }
502
503 static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
504                         unsigned long address, pte_t *ptep, pte_t pte)
505 {
506         struct page *old_page, *new_page;
507         int avoidcopy;
508
509         old_page = pte_page(pte);
510
511         /* If no-one else is actually using this page, avoid the copy
512          * and just make the page writable */
513         avoidcopy = (page_count(old_page) == 1);
514         if (avoidcopy) {
515                 set_huge_ptep_writable(vma, address, ptep);
516                 return VM_FAULT_MINOR;
517         }
518
519         page_cache_get(old_page);
520         new_page = alloc_huge_page(vma, address);
521
522         if (!new_page) {
523                 page_cache_release(old_page);
524                 return VM_FAULT_OOM;
525         }
526
527         spin_unlock(&mm->page_table_lock);
528         copy_huge_page(new_page, old_page, address);
529         spin_lock(&mm->page_table_lock);
530
531         ptep = huge_pte_offset(mm, address & HPAGE_MASK);
532         if (likely(pte_same(*ptep, pte))) {
533                 /* Break COW */
534                 set_huge_pte_at(mm, address, ptep,
535                                 make_huge_pte(vma, new_page, 1));
536                 /* Make the old page be freed below */
537                 new_page = old_page;
538         }
539         page_cache_release(new_page);
540         page_cache_release(old_page);
541         return VM_FAULT_MINOR;
542 }
543
544 int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
545                         unsigned long address, pte_t *ptep, int write_access)
546 {
547         int ret = VM_FAULT_SIGBUS;
548         unsigned long idx;
549         unsigned long size;
550         struct page *page;
551         struct address_space *mapping;
552         pte_t new_pte;
553
554         mapping = vma->vm_file->f_mapping;
555         idx = ((address - vma->vm_start) >> HPAGE_SHIFT)
556                 + (vma->vm_pgoff >> (HPAGE_SHIFT - PAGE_SHIFT));
557
558         /*
559          * Use page lock to guard against racing truncation
560          * before we get page_table_lock.
561          */
562 retry:
563         page = find_lock_page(mapping, idx);
564         if (!page) {
565                 if (hugetlb_get_quota(mapping))
566                         goto out;
567                 page = alloc_huge_page(vma, address);
568                 if (!page) {
569                         hugetlb_put_quota(mapping);
570                         ret = VM_FAULT_OOM;
571                         goto out;
572                 }
573                 clear_huge_page(page, address);
574
575                 if (vma->vm_flags & VM_SHARED) {
576                         int err;
577
578                         err = add_to_page_cache(page, mapping, idx, GFP_KERNEL);
579                         if (err) {
580                                 put_page(page);
581                                 hugetlb_put_quota(mapping);
582                                 if (err == -EEXIST)
583                                         goto retry;
584                                 goto out;
585                         }
586                 } else
587                         lock_page(page);
588         }
589
590         spin_lock(&mm->page_table_lock);
591         size = i_size_read(mapping->host) >> HPAGE_SHIFT;
592         if (idx >= size)
593                 goto backout;
594
595         ret = VM_FAULT_MINOR;
596         if (!pte_none(*ptep))
597                 goto backout;
598
599         add_mm_counter(mm, file_rss, HPAGE_SIZE / PAGE_SIZE);
600         new_pte = make_huge_pte(vma, page, ((vma->vm_flags & VM_WRITE)
601                                 && (vma->vm_flags & VM_SHARED)));
602         set_huge_pte_at(mm, address, ptep, new_pte);
603
604         if (write_access && !(vma->vm_flags & VM_SHARED)) {
605                 /* Optimization, do the COW without a second fault */
606                 ret = hugetlb_cow(mm, vma, address, ptep, new_pte);
607         }
608
609         spin_unlock(&mm->page_table_lock);
610         unlock_page(page);
611 out:
612         return ret;
613
614 backout:
615         spin_unlock(&mm->page_table_lock);
616         hugetlb_put_quota(mapping);
617         unlock_page(page);
618         put_page(page);
619         goto out;
620 }
621
622 int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
623                         unsigned long address, int write_access)
624 {
625         pte_t *ptep;
626         pte_t entry;
627         int ret;
628         static DEFINE_MUTEX(hugetlb_instantiation_mutex);
629
630         ptep = huge_pte_alloc(mm, address);
631         if (!ptep)
632                 return VM_FAULT_OOM;
633
634         /*
635          * Serialize hugepage allocation and instantiation, so that we don't
636          * get spurious allocation failures if two CPUs race to instantiate
637          * the same page in the page cache.
638          */
639         mutex_lock(&hugetlb_instantiation_mutex);
640         entry = *ptep;
641         if (pte_none(entry)) {
642                 ret = hugetlb_no_page(mm, vma, address, ptep, write_access);
643                 mutex_unlock(&hugetlb_instantiation_mutex);
644                 return ret;
645         }
646
647         ret = VM_FAULT_MINOR;
648
649         spin_lock(&mm->page_table_lock);
650         /* Check for a racing update before calling hugetlb_cow */
651         if (likely(pte_same(entry, *ptep)))
652                 if (write_access && !pte_write(entry))
653                         ret = hugetlb_cow(mm, vma, address, ptep, entry);
654         spin_unlock(&mm->page_table_lock);
655         mutex_unlock(&hugetlb_instantiation_mutex);
656
657         return ret;
658 }
659
660 int follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
661                         struct page **pages, struct vm_area_struct **vmas,
662                         unsigned long *position, int *length, int i)
663 {
664         unsigned long vpfn, vaddr = *position;
665         int remainder = *length;
666
667         vpfn = vaddr/PAGE_SIZE;
668         spin_lock(&mm->page_table_lock);
669         while (vaddr < vma->vm_end && remainder) {
670                 pte_t *pte;
671                 struct page *page;
672
673                 /*
674                  * Some archs (sparc64, sh*) have multiple pte_ts to
675                  * each hugepage.  We have to make * sure we get the
676                  * first, for the page indexing below to work.
677                  */
678                 pte = huge_pte_offset(mm, vaddr & HPAGE_MASK);
679
680                 if (!pte || pte_none(*pte)) {
681                         int ret;
682
683                         spin_unlock(&mm->page_table_lock);
684                         ret = hugetlb_fault(mm, vma, vaddr, 0);
685                         spin_lock(&mm->page_table_lock);
686                         if (ret == VM_FAULT_MINOR)
687                                 continue;
688
689                         remainder = 0;
690                         if (!i)
691                                 i = -EFAULT;
692                         break;
693                 }
694
695                 if (pages) {
696                         page = &pte_page(*pte)[vpfn % (HPAGE_SIZE/PAGE_SIZE)];
697                         get_page(page);
698                         pages[i] = page;
699                 }
700
701                 if (vmas)
702                         vmas[i] = vma;
703
704                 vaddr += PAGE_SIZE;
705                 ++vpfn;
706                 --remainder;
707                 ++i;
708         }
709         spin_unlock(&mm->page_table_lock);
710         *length = remainder;
711         *position = vaddr;
712
713         return i;
714 }
715
716 void hugetlb_change_protection(struct vm_area_struct *vma,
717                 unsigned long address, unsigned long end, pgprot_t newprot)
718 {
719         struct mm_struct *mm = vma->vm_mm;
720         unsigned long start = address;
721         pte_t *ptep;
722         pte_t pte;
723
724         BUG_ON(address >= end);
725         flush_cache_range(vma, address, end);
726
727         spin_lock(&mm->page_table_lock);
728         for (; address < end; address += HPAGE_SIZE) {
729                 ptep = huge_pte_offset(mm, address);
730                 if (!ptep)
731                         continue;
732                 if (!pte_none(*ptep)) {
733                         pte = huge_ptep_get_and_clear(mm, address, ptep);
734                         pte = pte_mkhuge(pte_modify(pte, newprot));
735                         set_huge_pte_at(mm, address, ptep, pte);
736                         lazy_mmu_prot_update(pte);
737                 }
738         }
739         spin_unlock(&mm->page_table_lock);
740
741         flush_tlb_range(vma, start, end);
742 }
743