1 /*
2 * Lockless get_user_pages_fast for sparc, cribbed from powerpc
3 *
4 * Copyright (C) 2008 Nick Piggin
5 * Copyright (C) 2008 Novell Inc.
6 */
7
8 #include <linux/sched.h>
9 #include <linux/mm.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 pmd,unsigned long addr,unsigned long end,int write,struct page ** pages,int * nr)20 static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
21 unsigned long end, int write, struct page **pages, int *nr)
22 {
23 unsigned long mask, result;
24 pte_t *ptep;
25
26 if (tlb_type == hypervisor) {
27 result = _PAGE_PRESENT_4V|_PAGE_P_4V;
28 if (write)
29 result |= _PAGE_WRITE_4V;
30 } else {
31 result = _PAGE_PRESENT_4U|_PAGE_P_4U;
32 if (write)
33 result |= _PAGE_WRITE_4U;
34 }
35 mask = result | _PAGE_SPECIAL;
36
37 ptep = pte_offset_kernel(&pmd, addr);
38 do {
39 struct page *page, *head;
40 pte_t pte = *ptep;
41
42 if ((pte_val(pte) & mask) != result)
43 return 0;
44 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
45
46 /* The hugepage case is simplified on sparc64 because
47 * we encode the sub-page pfn offsets into the
48 * hugepage PTEs. We could optimize this in the future
49 * use page_cache_add_speculative() for the hugepage case.
50 */
51 page = pte_page(pte);
52 head = compound_head(page);
53 if (!page_cache_get_speculative(head))
54 return 0;
55 if (unlikely(pte_val(pte) != pte_val(*ptep))) {
56 put_page(head);
57 return 0;
58 }
59 if (head != page)
60 get_huge_page_tail(page);
61
62 pages[*nr] = page;
63 (*nr)++;
64 } while (ptep++, addr += PAGE_SIZE, addr != end);
65
66 return 1;
67 }
68
gup_pmd_range(pud_t pud,unsigned long addr,unsigned long end,int write,struct page ** pages,int * nr)69 static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
70 int write, struct page **pages, int *nr)
71 {
72 unsigned long next;
73 pmd_t *pmdp;
74
75 pmdp = pmd_offset(&pud, addr);
76 do {
77 pmd_t pmd = *pmdp;
78
79 next = pmd_addr_end(addr, end);
80 if (pmd_none(pmd))
81 return 0;
82 if (!gup_pte_range(pmd, addr, next, write, pages, nr))
83 return 0;
84 } while (pmdp++, addr = next, addr != end);
85
86 return 1;
87 }
88
gup_pud_range(pgd_t pgd,unsigned long addr,unsigned long end,int write,struct page ** pages,int * nr)89 static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
90 int write, struct page **pages, int *nr)
91 {
92 unsigned long next;
93 pud_t *pudp;
94
95 pudp = pud_offset(&pgd, addr);
96 do {
97 pud_t pud = *pudp;
98
99 next = pud_addr_end(addr, end);
100 if (pud_none(pud))
101 return 0;
102 if (!gup_pmd_range(pud, addr, next, write, pages, nr))
103 return 0;
104 } while (pudp++, addr = next, addr != end);
105
106 return 1;
107 }
108
get_user_pages_fast(unsigned long start,int nr_pages,int write,struct page ** pages)109 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
110 struct page **pages)
111 {
112 struct mm_struct *mm = current->mm;
113 unsigned long addr, len, end;
114 unsigned long next;
115 pgd_t *pgdp;
116 int nr = 0;
117
118 start &= PAGE_MASK;
119 addr = start;
120 len = (unsigned long) nr_pages << PAGE_SHIFT;
121 end = start + len;
122
123 /*
124 * XXX: batch / limit 'nr', to avoid large irq off latency
125 * needs some instrumenting to determine the common sizes used by
126 * important workloads (eg. DB2), and whether limiting the batch size
127 * will decrease performance.
128 *
129 * It seems like we're in the clear for the moment. Direct-IO is
130 * the main guy that batches up lots of get_user_pages, and even
131 * they are limited to 64-at-a-time which is not so many.
132 */
133 /*
134 * This doesn't prevent pagetable teardown, but does prevent
135 * the pagetables from being freed on sparc.
136 *
137 * So long as we atomically load page table pointers versus teardown,
138 * we can follow the address down to the the page and take a ref on it.
139 */
140 local_irq_disable();
141
142 pgdp = pgd_offset(mm, addr);
143 do {
144 pgd_t pgd = *pgdp;
145
146 next = pgd_addr_end(addr, end);
147 if (pgd_none(pgd))
148 goto slow;
149 if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
150 goto slow;
151 } while (pgdp++, addr = next, addr != end);
152
153 local_irq_enable();
154
155 VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
156 return nr;
157
158 {
159 int ret;
160
161 slow:
162 local_irq_enable();
163
164 /* Try to get the remaining pages with get_user_pages */
165 start += nr << PAGE_SHIFT;
166 pages += nr;
167
168 down_read(&mm->mmap_sem);
169 ret = get_user_pages(current, mm, start,
170 (end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
171 up_read(&mm->mmap_sem);
172
173 /* Have to be a bit careful with return values */
174 if (nr > 0) {
175 if (ret < 0)
176 ret = nr;
177 else
178 ret += nr;
179 }
180
181 return ret;
182 }
183 }
184