powerpc: remove superfluous PageTail checks on the pte gup_fast
[linux-2.6.git] / arch / powerpc / mm / gup.c
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  */
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
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
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
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 */