Commit 667b279baa529a1b5bd120d4ce3df643a5749263
1 parent
a16382ce1c
Exists in
master
and in
7 other branches
sh: lockless get_user_pages_fast()
Implement get_user_pages_fast without locking in the fastpath on sh. Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Showing 2 changed files with 274 additions and 1 deletions Side-by-side Diff
arch/sh/mm/Makefile
... | ... | @@ -15,7 +15,7 @@ |
15 | 15 | obj-y += $(cacheops-y) |
16 | 16 | |
17 | 17 | mmu-y := nommu.o extable_32.o |
18 | -mmu-$(CONFIG_MMU) := extable_$(BITS).o fault_$(BITS).o \ | |
18 | +mmu-$(CONFIG_MMU) := extable_$(BITS).o fault_$(BITS).o gup.o \ | |
19 | 19 | ioremap.o kmap.o pgtable.o tlbflush_$(BITS).o |
20 | 20 | |
21 | 21 | obj-y += $(mmu-y) |
arch/sh/mm/gup.c
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 ACCESS_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 | + pages[*nr] = page; | |
109 | + (*nr)++; | |
110 | + | |
111 | + } while (ptep++, addr += PAGE_SIZE, addr != end); | |
112 | + pte_unmap(ptep - 1); | |
113 | + | |
114 | + return 1; | |
115 | +} | |
116 | + | |
117 | +static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end, | |
118 | + int write, struct page **pages, int *nr) | |
119 | +{ | |
120 | + unsigned long next; | |
121 | + pmd_t *pmdp; | |
122 | + | |
123 | + pmdp = pmd_offset(&pud, addr); | |
124 | + do { | |
125 | + pmd_t pmd = *pmdp; | |
126 | + | |
127 | + next = pmd_addr_end(addr, end); | |
128 | + if (pmd_none(pmd)) | |
129 | + return 0; | |
130 | + if (!gup_pte_range(pmd, addr, next, write, pages, nr)) | |
131 | + return 0; | |
132 | + } while (pmdp++, addr = next, addr != end); | |
133 | + | |
134 | + return 1; | |
135 | +} | |
136 | + | |
137 | +static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end, | |
138 | + int write, struct page **pages, int *nr) | |
139 | +{ | |
140 | + unsigned long next; | |
141 | + pud_t *pudp; | |
142 | + | |
143 | + pudp = pud_offset(&pgd, addr); | |
144 | + do { | |
145 | + pud_t pud = *pudp; | |
146 | + | |
147 | + next = pud_addr_end(addr, end); | |
148 | + if (pud_none(pud)) | |
149 | + return 0; | |
150 | + if (!gup_pmd_range(pud, addr, next, write, pages, nr)) | |
151 | + return 0; | |
152 | + } while (pudp++, addr = next, addr != end); | |
153 | + | |
154 | + return 1; | |
155 | +} | |
156 | + | |
157 | +/* | |
158 | + * Like get_user_pages_fast() except its IRQ-safe in that it won't fall | |
159 | + * back to the regular GUP. | |
160 | + */ | |
161 | +int __get_user_pages_fast(unsigned long start, int nr_pages, int write, | |
162 | + struct page **pages) | |
163 | +{ | |
164 | + struct mm_struct *mm = current->mm; | |
165 | + unsigned long addr, len, end; | |
166 | + unsigned long next; | |
167 | + unsigned long flags; | |
168 | + pgd_t *pgdp; | |
169 | + int nr = 0; | |
170 | + | |
171 | + start &= PAGE_MASK; | |
172 | + addr = start; | |
173 | + len = (unsigned long) nr_pages << PAGE_SHIFT; | |
174 | + end = start + len; | |
175 | + if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ, | |
176 | + (void __user *)start, len))) | |
177 | + return 0; | |
178 | + | |
179 | + /* | |
180 | + * This doesn't prevent pagetable teardown, but does prevent | |
181 | + * the pagetables and pages from being freed. | |
182 | + */ | |
183 | + local_irq_save(flags); | |
184 | + pgdp = pgd_offset(mm, addr); | |
185 | + do { | |
186 | + pgd_t pgd = *pgdp; | |
187 | + | |
188 | + next = pgd_addr_end(addr, end); | |
189 | + if (pgd_none(pgd)) | |
190 | + break; | |
191 | + if (!gup_pud_range(pgd, addr, next, write, pages, &nr)) | |
192 | + break; | |
193 | + } while (pgdp++, addr = next, addr != end); | |
194 | + local_irq_restore(flags); | |
195 | + | |
196 | + return nr; | |
197 | +} | |
198 | + | |
199 | +/** | |
200 | + * get_user_pages_fast() - pin user pages in memory | |
201 | + * @start: starting user address | |
202 | + * @nr_pages: number of pages from start to pin | |
203 | + * @write: whether pages will be written to | |
204 | + * @pages: array that receives pointers to the pages pinned. | |
205 | + * Should be at least nr_pages long. | |
206 | + * | |
207 | + * Attempt to pin user pages in memory without taking mm->mmap_sem. | |
208 | + * If not successful, it will fall back to taking the lock and | |
209 | + * calling get_user_pages(). | |
210 | + * | |
211 | + * Returns number of pages pinned. This may be fewer than the number | |
212 | + * requested. If nr_pages is 0 or negative, returns 0. If no pages | |
213 | + * were pinned, returns -errno. | |
214 | + */ | |
215 | +int get_user_pages_fast(unsigned long start, int nr_pages, int write, | |
216 | + struct page **pages) | |
217 | +{ | |
218 | + struct mm_struct *mm = current->mm; | |
219 | + unsigned long addr, len, end; | |
220 | + unsigned long next; | |
221 | + pgd_t *pgdp; | |
222 | + int nr = 0; | |
223 | + | |
224 | + start &= PAGE_MASK; | |
225 | + addr = start; | |
226 | + len = (unsigned long) nr_pages << PAGE_SHIFT; | |
227 | + | |
228 | + end = start + len; | |
229 | + if (end < start) | |
230 | + goto slow_irqon; | |
231 | + | |
232 | + local_irq_disable(); | |
233 | + pgdp = pgd_offset(mm, addr); | |
234 | + do { | |
235 | + pgd_t pgd = *pgdp; | |
236 | + | |
237 | + next = pgd_addr_end(addr, end); | |
238 | + if (pgd_none(pgd)) | |
239 | + goto slow; | |
240 | + if (!gup_pud_range(pgd, addr, next, write, pages, &nr)) | |
241 | + goto slow; | |
242 | + } while (pgdp++, addr = next, addr != end); | |
243 | + local_irq_enable(); | |
244 | + | |
245 | + VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT); | |
246 | + return nr; | |
247 | + | |
248 | + { | |
249 | + int ret; | |
250 | + | |
251 | +slow: | |
252 | + local_irq_enable(); | |
253 | +slow_irqon: | |
254 | + /* Try to get the remaining pages with get_user_pages */ | |
255 | + start += nr << PAGE_SHIFT; | |
256 | + pages += nr; | |
257 | + | |
258 | + down_read(&mm->mmap_sem); | |
259 | + ret = get_user_pages(current, mm, start, | |
260 | + (end - start) >> PAGE_SHIFT, write, 0, pages, NULL); | |
261 | + up_read(&mm->mmap_sem); | |
262 | + | |
263 | + /* Have to be a bit careful with return values */ | |
264 | + if (nr > 0) { | |
265 | + if (ret < 0) | |
266 | + ret = nr; | |
267 | + else | |
268 | + ret += nr; | |
269 | + } | |
270 | + | |
271 | + return ret; | |
272 | + } | |
273 | +} |