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Martin Schwidefsky80217142010-10-25 16:10:11 +02001/*
2 * Lockless get_user_pages_fast for s390
3 *
4 * Copyright IBM Corp. 2010
5 * Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>
6 */
7#include <linux/sched.h>
8#include <linux/mm.h>
9#include <linux/hugetlb.h>
10#include <linux/vmstat.h>
11#include <linux/pagemap.h>
12#include <linux/rwsem.h>
13#include <asm/pgtable.h>
14
15/*
16 * The performance critical leaf functions are made noinline otherwise gcc
17 * inlines everything into a single function which results in too much
18 * register pressure.
19 */
20static inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
21 unsigned long end, int write, struct page **pages, int *nr)
22{
Martin Schwidefsky25591b02010-11-10 10:05:51 +010023 unsigned long mask;
Martin Schwidefsky80217142010-10-25 16:10:11 +020024 pte_t *ptep, pte;
25 struct page *page;
26
Martin Schwidefskye5098612013-07-23 20:57:57 +020027 mask = (write ? _PAGE_PROTECT : 0) | _PAGE_INVALID | _PAGE_SPECIAL;
Martin Schwidefsky80217142010-10-25 16:10:11 +020028
29 ptep = ((pte_t *) pmd_deref(pmd)) + pte_index(addr);
30 do {
31 pte = *ptep;
32 barrier();
Martin Schwidefsky25591b02010-11-10 10:05:51 +010033 if ((pte_val(pte) & mask) != 0)
Martin Schwidefsky80217142010-10-25 16:10:11 +020034 return 0;
35 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
36 page = pte_page(pte);
37 if (!page_cache_get_speculative(page))
38 return 0;
39 if (unlikely(pte_val(pte) != pte_val(*ptep))) {
40 put_page(page);
41 return 0;
42 }
43 pages[*nr] = page;
44 (*nr)++;
45
46 } while (ptep++, addr += PAGE_SIZE, addr != end);
47
48 return 1;
49}
50
51static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
52 unsigned long end, int write, struct page **pages, int *nr)
53{
54 unsigned long mask, result;
Andrea Arcangeli220a2eb2011-11-02 13:37:25 -070055 struct page *head, *page, *tail;
Martin Schwidefsky80217142010-10-25 16:10:11 +020056 int refs;
57
Martin Schwidefskye5098612013-07-23 20:57:57 +020058 result = write ? 0 : _SEGMENT_ENTRY_PROTECT;
59 mask = result | _SEGMENT_ENTRY_INVALID;
Martin Schwidefsky80217142010-10-25 16:10:11 +020060 if ((pmd_val(pmd) & mask) != result)
61 return 0;
62 VM_BUG_ON(!pfn_valid(pmd_val(pmd) >> PAGE_SHIFT));
63
64 refs = 0;
65 head = pmd_page(pmd);
66 page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
Andrea Arcangeli220a2eb2011-11-02 13:37:25 -070067 tail = page;
Martin Schwidefsky80217142010-10-25 16:10:11 +020068 do {
69 VM_BUG_ON(compound_head(page) != head);
70 pages[*nr] = page;
71 (*nr)++;
72 page++;
73 refs++;
74 } while (addr += PAGE_SIZE, addr != end);
75
76 if (!page_cache_add_speculative(head, refs)) {
77 *nr -= refs;
78 return 0;
79 }
80
81 if (unlikely(pmd_val(pmd) != pmd_val(*pmdp))) {
82 *nr -= refs;
83 while (refs--)
84 put_page(head);
Andrea Arcangeli0693bc92011-11-02 13:37:28 -070085 return 0;
86 }
87
88 /*
89 * Any tail page need their mapcount reference taken before we
90 * return.
91 */
92 while (refs--) {
93 if (PageTail(tail))
94 get_huge_page_tail(tail);
95 tail++;
Martin Schwidefsky80217142010-10-25 16:10:11 +020096 }
97
98 return 1;
99}
100
101
102static inline int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr,
103 unsigned long end, int write, struct page **pages, int *nr)
104{
105 unsigned long next;
106 pmd_t *pmdp, pmd;
107
108 pmdp = (pmd_t *) pudp;
109#ifdef CONFIG_64BIT
110 if ((pud_val(pud) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R3)
111 pmdp = (pmd_t *) pud_deref(pud);
112 pmdp += pmd_index(addr);
113#endif
114 do {
115 pmd = *pmdp;
116 barrier();
117 next = pmd_addr_end(addr, end);
Gerald Schaefer75077af2012-10-08 16:30:15 -0700118 /*
119 * The pmd_trans_splitting() check below explains why
120 * pmdp_splitting_flush() has to serialize with
121 * smp_call_function() against our disabled IRQs, to stop
122 * this gup-fast code from running while we set the
123 * splitting bit in the pmd. Returning zero will take
124 * the slow path that will call wait_split_huge_page()
125 * if the pmd is still in splitting state.
126 */
127 if (pmd_none(pmd) || pmd_trans_splitting(pmd))
Martin Schwidefsky80217142010-10-25 16:10:11 +0200128 return 0;
Gerald Schaefer156152f2012-10-25 17:24:12 +0200129 if (unlikely(pmd_large(pmd))) {
Martin Schwidefsky80217142010-10-25 16:10:11 +0200130 if (!gup_huge_pmd(pmdp, pmd, addr, next,
131 write, pages, nr))
132 return 0;
133 } else if (!gup_pte_range(pmdp, pmd, addr, next,
134 write, pages, nr))
135 return 0;
136 } while (pmdp++, addr = next, addr != end);
137
138 return 1;
139}
140
141static inline int gup_pud_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr,
142 unsigned long end, int write, struct page **pages, int *nr)
143{
144 unsigned long next;
145 pud_t *pudp, pud;
146
147 pudp = (pud_t *) pgdp;
148#ifdef CONFIG_64BIT
149 if ((pgd_val(pgd) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R2)
150 pudp = (pud_t *) pgd_deref(pgd);
151 pudp += pud_index(addr);
152#endif
153 do {
154 pud = *pudp;
155 barrier();
156 next = pud_addr_end(addr, end);
157 if (pud_none(pud))
158 return 0;
159 if (!gup_pmd_range(pudp, pud, addr, next, write, pages, nr))
160 return 0;
161 } while (pudp++, addr = next, addr != end);
162
163 return 1;
164}
165
Gerald Schaefer34cda992012-09-04 15:37:55 +0200166/*
167 * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
168 * back to the regular GUP.
169 */
170int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
171 struct page **pages)
172{
173 struct mm_struct *mm = current->mm;
174 unsigned long addr, len, end;
175 unsigned long next, flags;
176 pgd_t *pgdp, pgd;
177 int nr = 0;
178
179 start &= PAGE_MASK;
180 addr = start;
181 len = (unsigned long) nr_pages << PAGE_SHIFT;
182 end = start + len;
Heiko Carstenseb0bf922013-10-08 09:29:09 +0200183 if ((end <= start) || (end > TASK_SIZE))
Gerald Schaefer34cda992012-09-04 15:37:55 +0200184 return 0;
Heiko Carstens01997bb2013-10-07 16:14:50 +0200185 /*
186 * local_irq_save() doesn't prevent pagetable teardown, but does
187 * prevent the pagetables from being freed on s390.
188 *
189 * So long as we atomically load page table pointers versus teardown,
190 * we can follow the address down to the the page and take a ref on it.
191 */
Gerald Schaefer34cda992012-09-04 15:37:55 +0200192 local_irq_save(flags);
193 pgdp = pgd_offset(mm, addr);
194 do {
195 pgd = *pgdp;
196 barrier();
197 next = pgd_addr_end(addr, end);
198 if (pgd_none(pgd))
199 break;
200 if (!gup_pud_range(pgdp, pgd, addr, next, write, pages, &nr))
201 break;
202 } while (pgdp++, addr = next, addr != end);
203 local_irq_restore(flags);
204
205 return nr;
206}
207
Martin Schwidefsky80217142010-10-25 16:10:11 +0200208/**
209 * get_user_pages_fast() - pin user pages in memory
210 * @start: starting user address
211 * @nr_pages: number of pages from start to pin
212 * @write: whether pages will be written to
213 * @pages: array that receives pointers to the pages pinned.
214 * Should be at least nr_pages long.
215 *
216 * Attempt to pin user pages in memory without taking mm->mmap_sem.
217 * If not successful, it will fall back to taking the lock and
218 * calling get_user_pages().
219 *
220 * Returns number of pages pinned. This may be fewer than the number
221 * requested. If nr_pages is 0 or negative, returns 0. If no pages
222 * were pinned, returns -errno.
223 */
224int get_user_pages_fast(unsigned long start, int nr_pages, int write,
225 struct page **pages)
226{
227 struct mm_struct *mm = current->mm;
Heiko Carstens01997bb2013-10-07 16:14:50 +0200228 int nr, ret;
Martin Schwidefsky80217142010-10-25 16:10:11 +0200229
230 start &= PAGE_MASK;
Heiko Carstens01997bb2013-10-07 16:14:50 +0200231 nr = __get_user_pages_fast(start, nr_pages, write, pages);
232 if (nr == nr_pages)
233 return nr;
Martin Schwidefsky80217142010-10-25 16:10:11 +0200234
Heiko Carstens01997bb2013-10-07 16:14:50 +0200235 /* Try to get the remaining pages with get_user_pages */
236 start += nr << PAGE_SHIFT;
237 pages += nr;
238 down_read(&mm->mmap_sem);
239 ret = get_user_pages(current, mm, start,
240 nr_pages - nr, write, 0, pages, NULL);
241 up_read(&mm->mmap_sem);
242 /* Have to be a bit careful with return values */
243 if (nr > 0)
244 ret = (ret < 0) ? nr : ret + nr;
245 return ret;
Martin Schwidefsky80217142010-10-25 16:10:11 +0200246}