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1 /*
2 * Lockless get_user_pages_fast for SuperH
3 *
4 * Copyright (C) 2009 - 2010 Paul Mundt
5 *
6 * Cloned from the x86 and PowerPC versions, by:
7 *
8 * Copyright (C) 2008 Nick Piggin
9 * Copyright (C) 2008 Novell Inc.
10 */
11 #include <linux/sched.h>
12 #include <linux/mm.h>
13 #include <linux/vmstat.h>
14 #include <linux/highmem.h>
15 #include <asm/pgtable.h>
16
17 static inline pte_t gup_get_pte(pte_t *ptep)
18 {
19 #ifndef CONFIG_X2TLB
20 return READ_ONCE(*ptep);
21 #else
22 /*
23 * With get_user_pages_fast, we walk down the pagetables without
24 * taking any locks. For this we would like to load the pointers
25 * atomically, but that is not possible with 64-bit PTEs. What
26 * we do have is the guarantee that a pte will only either go
27 * from not present to present, or present to not present or both
28 * -- it will not switch to a completely different present page
29 * without a TLB flush in between; something that we are blocking
30 * by holding interrupts off.
31 *
32 * Setting ptes from not present to present goes:
33 * ptep->pte_high = h;
34 * smp_wmb();
35 * ptep->pte_low = l;
36 *
37 * And present to not present goes:
38 * ptep->pte_low = 0;
39 * smp_wmb();
40 * ptep->pte_high = 0;
41 *
42 * We must ensure here that the load of pte_low sees l iff pte_high
43 * sees h. We load pte_high *after* loading pte_low, which ensures we
44 * don't see an older value of pte_high. *Then* we recheck pte_low,
45 * which ensures that we haven't picked up a changed pte high. We might
46 * have got rubbish values from pte_low and pte_high, but we are
47 * guaranteed that pte_low will not have the present bit set *unless*
48 * it is 'l'. And get_user_pages_fast only operates on present ptes, so
49 * we're safe.
50 *
51 * gup_get_pte should not be used or copied outside gup.c without being
52 * very careful -- it does not atomically load the pte or anything that
53 * is likely to be useful for you.
54 */
55 pte_t pte;
56
57 retry:
58 pte.pte_low = ptep->pte_low;
59 smp_rmb();
60 pte.pte_high = ptep->pte_high;
61 smp_rmb();
62 if (unlikely(pte.pte_low != ptep->pte_low))
63 goto retry;
64
65 return pte;
66 #endif
67 }
68
69 /*
70 * The performance critical leaf functions are made noinline otherwise gcc
71 * inlines everything into a single function which results in too much
72 * register pressure.
73 */
74 static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
75 unsigned long end, int write, struct page **pages, int *nr)
76 {
77 u64 mask, result;
78 pte_t *ptep;
79
80 #ifdef CONFIG_X2TLB
81 result = _PAGE_PRESENT | _PAGE_EXT(_PAGE_EXT_KERN_READ | _PAGE_EXT_USER_READ);
82 if (write)
83 result |= _PAGE_EXT(_PAGE_EXT_KERN_WRITE | _PAGE_EXT_USER_WRITE);
84 #elif defined(CONFIG_SUPERH64)
85 result = _PAGE_PRESENT | _PAGE_USER | _PAGE_READ;
86 if (write)
87 result |= _PAGE_WRITE;
88 #else
89 result = _PAGE_PRESENT | _PAGE_USER;
90 if (write)
91 result |= _PAGE_RW;
92 #endif
93
94 mask = result | _PAGE_SPECIAL;
95
96 ptep = pte_offset_map(&pmd, addr);
97 do {
98 pte_t pte = gup_get_pte(ptep);
99 struct page *page;
100
101 if ((pte_val(pte) & mask) != result) {
102 pte_unmap(ptep);
103 return 0;
104 }
105 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
106 page = pte_page(pte);
107 get_page(page);
108 __flush_anon_page(page, addr);
109 flush_dcache_page(page);
110 pages[*nr] = page;
111 (*nr)++;
112
113 } while (ptep++, addr += PAGE_SIZE, addr != end);
114 pte_unmap(ptep - 1);
115
116 return 1;
117 }
118
119 static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
120 int write, struct page **pages, int *nr)
121 {
122 unsigned long next;
123 pmd_t *pmdp;
124
125 pmdp = pmd_offset(&pud, addr);
126 do {
127 pmd_t pmd = *pmdp;
128
129 next = pmd_addr_end(addr, end);
130 if (pmd_none(pmd))
131 return 0;
132 if (!gup_pte_range(pmd, addr, next, write, pages, nr))
133 return 0;
134 } while (pmdp++, addr = next, addr != end);
135
136 return 1;
137 }
138
139 static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
140 int write, struct page **pages, int *nr)
141 {
142 unsigned long next;
143 pud_t *pudp;
144
145 pudp = pud_offset(&pgd, addr);
146 do {
147 pud_t pud = *pudp;
148
149 next = pud_addr_end(addr, end);
150 if (pud_none(pud))
151 return 0;
152 if (!gup_pmd_range(pud, addr, next, write, pages, nr))
153 return 0;
154 } while (pudp++, addr = next, addr != end);
155
156 return 1;
157 }
158
159 /*
160 * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
161 * back to the regular GUP.
162 */
163 int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
164 struct page **pages)
165 {
166 struct mm_struct *mm = current->mm;
167 unsigned long addr, len, end;
168 unsigned long next;
169 unsigned long flags;
170 pgd_t *pgdp;
171 int nr = 0;
172
173 start &= PAGE_MASK;
174 addr = start;
175 len = (unsigned long) nr_pages << PAGE_SHIFT;
176 end = start + len;
177 if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
178 (void __user *)start, len)))
179 return 0;
180
181 /*
182 * This doesn't prevent pagetable teardown, but does prevent
183 * the pagetables and pages from being freed.
184 */
185 local_irq_save(flags);
186 pgdp = pgd_offset(mm, addr);
187 do {
188 pgd_t pgd = *pgdp;
189
190 next = pgd_addr_end(addr, end);
191 if (pgd_none(pgd))
192 break;
193 if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
194 break;
195 } while (pgdp++, addr = next, addr != end);
196 local_irq_restore(flags);
197
198 return nr;
199 }
200
201 /**
202 * get_user_pages_fast() - pin user pages in memory
203 * @start: starting user address
204 * @nr_pages: number of pages from start to pin
205 * @write: whether pages will be written to
206 * @pages: array that receives pointers to the pages pinned.
207 * Should be at least nr_pages long.
208 *
209 * Attempt to pin user pages in memory without taking mm->mmap_sem.
210 * If not successful, it will fall back to taking the lock and
211 * calling get_user_pages().
212 *
213 * Returns number of pages pinned. This may be fewer than the number
214 * requested. If nr_pages is 0 or negative, returns 0. If no pages
215 * were pinned, returns -errno.
216 */
217 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
218 struct page **pages)
219 {
220 struct mm_struct *mm = current->mm;
221 unsigned long addr, len, end;
222 unsigned long next;
223 pgd_t *pgdp;
224 int nr = 0;
225
226 start &= PAGE_MASK;
227 addr = start;
228 len = (unsigned long) nr_pages << PAGE_SHIFT;
229
230 end = start + len;
231 if (end < start)
232 goto slow_irqon;
233
234 local_irq_disable();
235 pgdp = pgd_offset(mm, addr);
236 do {
237 pgd_t pgd = *pgdp;
238
239 next = pgd_addr_end(addr, end);
240 if (pgd_none(pgd))
241 goto slow;
242 if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
243 goto slow;
244 } while (pgdp++, addr = next, addr != end);
245 local_irq_enable();
246
247 VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
248 return nr;
249
250 {
251 int ret;
252
253 slow:
254 local_irq_enable();
255 slow_irqon:
256 /* Try to get the remaining pages with get_user_pages */
257 start += nr << PAGE_SHIFT;
258 pages += nr;
259
260 ret = get_user_pages_unlocked(start,
261 (end - start) >> PAGE_SHIFT, pages,
262 write ? FOLL_WRITE : 0);
263
264 /* Have to be a bit careful with return values */
265 if (nr > 0) {
266 if (ret < 0)
267 ret = nr;
268 else
269 ret += nr;
270 }
271
272 return ret;
273 }
274 }