1 /*
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 */
gup_pte_range(pmd_t * pmdp,pmd_t pmd,unsigned long addr,unsigned long end,int write,struct page ** pages,int * nr)20 static 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 {
23 unsigned long mask;
24 pte_t *ptep, pte;
25 struct page *page;
26
27 mask = (write ? _PAGE_PROTECT : 0) | _PAGE_INVALID | _PAGE_SPECIAL;
28
29 ptep = ((pte_t *) pmd_deref(pmd)) + pte_index(addr);
30 do {
31 pte = *ptep;
32 barrier();
33 if ((pte_val(pte) & mask) != 0)
34 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
gup_huge_pmd(pmd_t * pmdp,pmd_t pmd,unsigned long addr,unsigned long end,int write,struct page ** pages,int * nr)51 static 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;
55 struct page *head, *page, *tail;
56 int refs;
57
58 result = write ? 0 : _SEGMENT_ENTRY_PROTECT;
59 mask = result | _SEGMENT_ENTRY_INVALID;
60 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);
67 tail = page;
68 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);
85 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++;
96 }
97
98 return 1;
99 }
100
101
gup_pmd_range(pud_t * pudp,pud_t pud,unsigned long addr,unsigned long end,int write,struct page ** pages,int * nr)102 static 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);
118 /*
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))
128 return 0;
129 if (unlikely(pmd_large(pmd))) {
130 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
gup_pud_range(pgd_t * pgdp,pgd_t pgd,unsigned long addr,unsigned long end,int write,struct page ** pages,int * nr)141 static 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
166 /*
167 * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
168 * back to the regular GUP.
169 */
__get_user_pages_fast(unsigned long start,int nr_pages,int write,struct page ** pages)170 int __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;
183 if ((end <= start) || (end > TASK_SIZE))
184 return 0;
185 /*
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 */
192 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
208 /**
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 */
get_user_pages_fast(unsigned long start,int nr_pages,int write,struct page ** pages)224 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
225 struct page **pages)
226 {
227 struct mm_struct *mm = current->mm;
228 int nr, ret;
229
230 start &= PAGE_MASK;
231 nr = __get_user_pages_fast(start, nr_pages, write, pages);
232 if (nr == nr_pages)
233 return nr;
234
235 /* 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;
246 }
247