1 /*
2 * Lockless get_user_pages_fast for powerpc
3 *
4 * Copyright (C) 2008 Nick Piggin
5 * Copyright (C) 2008 Novell Inc.
6 */
7 #undef DEBUG
8
9 #include <linux/sched.h>
10 #include <linux/mm.h>
11 #include <linux/hugetlb.h>
12 #include <linux/vmstat.h>
13 #include <linux/pagemap.h>
14 #include <linux/rwsem.h>
15 #include <asm/pgtable.h>
16
17 #ifdef __HAVE_ARCH_PTE_SPECIAL
18
19 /*
20 * The performance critical leaf functions are made noinline otherwise gcc
21 * inlines everything into a single function which results in too much
22 * register pressure.
23 */
gup_pte_range(pmd_t pmd,unsigned long addr,unsigned long end,int write,struct page ** pages,int * nr)24 static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
25 unsigned long end, int write, struct page **pages, int *nr)
26 {
27 unsigned long mask, result;
28 pte_t *ptep;
29
30 result = _PAGE_PRESENT|_PAGE_USER;
31 if (write)
32 result |= _PAGE_RW;
33 mask = result | _PAGE_SPECIAL;
34
35 ptep = pte_offset_kernel(&pmd, addr);
36 do {
37 pte_t pte = *ptep;
38 struct page *page;
39
40 if ((pte_val(pte) & mask) != result)
41 return 0;
42 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
43 page = pte_page(pte);
44 if (!page_cache_get_speculative(page))
45 return 0;
46 if (unlikely(pte_val(pte) != pte_val(*ptep))) {
47 put_page(page);
48 return 0;
49 }
50 pages[*nr] = page;
51 (*nr)++;
52
53 } while (ptep++, addr += PAGE_SIZE, addr != end);
54
55 return 1;
56 }
57
gup_pmd_range(pud_t pud,unsigned long addr,unsigned long end,int write,struct page ** pages,int * nr)58 static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
59 int write, struct page **pages, int *nr)
60 {
61 unsigned long next;
62 pmd_t *pmdp;
63
64 pmdp = pmd_offset(&pud, addr);
65 do {
66 pmd_t pmd = *pmdp;
67
68 next = pmd_addr_end(addr, end);
69 if (pmd_none(pmd))
70 return 0;
71 if (is_hugepd(pmdp)) {
72 if (!gup_hugepd((hugepd_t *)pmdp, PMD_SHIFT,
73 addr, next, write, pages, nr))
74 return 0;
75 } else if (!gup_pte_range(pmd, addr, next, write, pages, nr))
76 return 0;
77 } while (pmdp++, addr = next, addr != end);
78
79 return 1;
80 }
81
gup_pud_range(pgd_t pgd,unsigned long addr,unsigned long end,int write,struct page ** pages,int * nr)82 static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
83 int write, struct page **pages, int *nr)
84 {
85 unsigned long next;
86 pud_t *pudp;
87
88 pudp = pud_offset(&pgd, addr);
89 do {
90 pud_t pud = *pudp;
91
92 next = pud_addr_end(addr, end);
93 if (pud_none(pud))
94 return 0;
95 if (is_hugepd(pudp)) {
96 if (!gup_hugepd((hugepd_t *)pudp, PUD_SHIFT,
97 addr, next, write, pages, nr))
98 return 0;
99 } else if (!gup_pmd_range(pud, addr, next, write, pages, nr))
100 return 0;
101 } while (pudp++, addr = next, addr != end);
102
103 return 1;
104 }
105
get_user_pages_fast(unsigned long start,int nr_pages,int write,struct page ** pages)106 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
107 struct page **pages)
108 {
109 struct mm_struct *mm = current->mm;
110 unsigned long addr, len, end;
111 unsigned long next;
112 pgd_t *pgdp;
113 int nr = 0;
114
115 pr_devel("%s(%lx,%x,%s)\n", __func__, start, nr_pages, write ? "write" : "read");
116
117 start &= PAGE_MASK;
118 addr = start;
119 len = (unsigned long) nr_pages << PAGE_SHIFT;
120 end = start + len;
121
122 if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
123 start, len)))
124 goto slow_irqon;
125
126 pr_devel(" aligned: %lx .. %lx\n", start, end);
127
128 /*
129 * XXX: batch / limit 'nr', to avoid large irq off latency
130 * needs some instrumenting to determine the common sizes used by
131 * important workloads (eg. DB2), and whether limiting the batch size
132 * will decrease performance.
133 *
134 * It seems like we're in the clear for the moment. Direct-IO is
135 * the main guy that batches up lots of get_user_pages, and even
136 * they are limited to 64-at-a-time which is not so many.
137 */
138 /*
139 * This doesn't prevent pagetable teardown, but does prevent
140 * the pagetables from being freed on powerpc.
141 *
142 * So long as we atomically load page table pointers versus teardown,
143 * we can follow the address down to the the page and take a ref on it.
144 */
145 local_irq_disable();
146
147 pgdp = pgd_offset(mm, addr);
148 do {
149 pgd_t pgd = *pgdp;
150
151 pr_devel(" %016lx: normal pgd %p\n", addr,
152 (void *)pgd_val(pgd));
153 next = pgd_addr_end(addr, end);
154 if (pgd_none(pgd))
155 goto slow;
156 if (is_hugepd(pgdp)) {
157 if (!gup_hugepd((hugepd_t *)pgdp, PGDIR_SHIFT,
158 addr, next, write, pages, &nr))
159 goto slow;
160 } else if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
161 goto slow;
162 } while (pgdp++, addr = next, addr != end);
163
164 local_irq_enable();
165
166 VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
167 return nr;
168
169 {
170 int ret;
171
172 slow:
173 local_irq_enable();
174 slow_irqon:
175 pr_devel(" slow path ! nr = %d\n", nr);
176
177 /* Try to get the remaining pages with get_user_pages */
178 start += nr << PAGE_SHIFT;
179 pages += nr;
180
181 down_read(&mm->mmap_sem);
182 ret = get_user_pages(current, mm, start,
183 (end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
184 up_read(&mm->mmap_sem);
185
186 /* Have to be a bit careful with return values */
187 if (nr > 0) {
188 if (ret < 0)
189 ret = nr;
190 else
191 ret += nr;
192 }
193
194 return ret;
195 }
196 }
197
198 #endif /* __HAVE_ARCH_PTE_SPECIAL */
199