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 */ 20static 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 69static int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr, 70 unsigned long end, int write, struct page **pages, 71 int *nr) 72{ 73 struct page *head, *page, *tail; 74 int refs; 75 76 if (!(pmd_val(pmd) & _PAGE_VALID)) 77 return 0; 78 79 if (write && !pmd_write(pmd)) 80 return 0; 81 82 refs = 0; 83 head = pmd_page(pmd); 84 page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT); 85 tail = page; 86 do { 87 VM_BUG_ON(compound_head(page) != head); 88 pages[*nr] = page; 89 (*nr)++; 90 page++; 91 refs++; 92 } while (addr += PAGE_SIZE, addr != end); 93 94 if (!page_cache_add_speculative(head, refs)) { 95 *nr -= refs; 96 return 0; 97 } 98 99 if (unlikely(pmd_val(pmd) != pmd_val(*pmdp))) { 100 *nr -= refs; 101 while (refs--) 102 put_page(head); 103 return 0; 104 } 105 106 /* Any tail page need their mapcount reference taken before we 107 * return. 108 */ 109 while (refs--) { 110 if (PageTail(tail)) 111 get_huge_page_tail(tail); 112 tail++; 113 } 114 115 return 1; 116} 117 118static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end, 119 int write, struct page **pages, int *nr) 120{ 121 unsigned long next; 122 pmd_t *pmdp; 123 124 pmdp = pmd_offset(&pud, addr); 125 do { 126 pmd_t pmd = *pmdp; 127 128 next = pmd_addr_end(addr, end); 129 if (pmd_none(pmd) || pmd_trans_splitting(pmd)) 130 return 0; 131 if (unlikely(pmd_large(pmd))) { 132 if (!gup_huge_pmd(pmdp, pmd, addr, next, 133 write, pages, nr)) 134 return 0; 135 } else if (!gup_pte_range(pmd, addr, next, write, 136 pages, nr)) 137 return 0; 138 } while (pmdp++, addr = next, addr != end); 139 140 return 1; 141} 142 143static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end, 144 int write, struct page **pages, int *nr) 145{ 146 unsigned long next; 147 pud_t *pudp; 148 149 pudp = pud_offset(&pgd, addr); 150 do { 151 pud_t pud = *pudp; 152 153 next = pud_addr_end(addr, end); 154 if (pud_none(pud)) 155 return 0; 156 if (!gup_pmd_range(pud, addr, next, write, pages, nr)) 157 return 0; 158 } while (pudp++, addr = next, addr != end); 159 160 return 1; 161} 162 163int __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, flags; 169 pgd_t *pgdp; 170 int nr = 0; 171 172 start &= PAGE_MASK; 173 addr = start; 174 len = (unsigned long) nr_pages << PAGE_SHIFT; 175 end = start + len; 176 177 local_irq_save(flags); 178 pgdp = pgd_offset(mm, addr); 179 do { 180 pgd_t pgd = *pgdp; 181 182 next = pgd_addr_end(addr, end); 183 if (pgd_none(pgd)) 184 break; 185 if (!gup_pud_range(pgd, addr, next, write, pages, &nr)) 186 break; 187 } while (pgdp++, addr = next, addr != end); 188 local_irq_restore(flags); 189 190 return nr; 191} 192 193int get_user_pages_fast(unsigned long start, int nr_pages, int write, 194 struct page **pages) 195{ 196 struct mm_struct *mm = current->mm; 197 unsigned long addr, len, end; 198 unsigned long next; 199 pgd_t *pgdp; 200 int nr = 0; 201 202 start &= PAGE_MASK; 203 addr = start; 204 len = (unsigned long) nr_pages << PAGE_SHIFT; 205 end = start + len; 206 207 /* 208 * XXX: batch / limit 'nr', to avoid large irq off latency 209 * needs some instrumenting to determine the common sizes used by 210 * important workloads (eg. DB2), and whether limiting the batch size 211 * will decrease performance. 212 * 213 * It seems like we're in the clear for the moment. Direct-IO is 214 * the main guy that batches up lots of get_user_pages, and even 215 * they are limited to 64-at-a-time which is not so many. 216 */ 217 /* 218 * This doesn't prevent pagetable teardown, but does prevent 219 * the pagetables from being freed on sparc. 220 * 221 * So long as we atomically load page table pointers versus teardown, 222 * we can follow the address down to the the page and take a ref on it. 223 */ 224 local_irq_disable(); 225 226 pgdp = pgd_offset(mm, addr); 227 do { 228 pgd_t pgd = *pgdp; 229 230 next = pgd_addr_end(addr, end); 231 if (pgd_none(pgd)) 232 goto slow; 233 if (!gup_pud_range(pgd, addr, next, write, pages, &nr)) 234 goto slow; 235 } while (pgdp++, addr = next, addr != end); 236 237 local_irq_enable(); 238 239 VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT); 240 return nr; 241 242 { 243 int ret; 244 245slow: 246 local_irq_enable(); 247 248 /* Try to get the remaining pages with get_user_pages */ 249 start += nr << PAGE_SHIFT; 250 pages += nr; 251 252 ret = get_user_pages_unlocked(current, mm, start, 253 (end - start) >> PAGE_SHIFT, write, 0, pages); 254 255 /* Have to be a bit careful with return values */ 256 if (nr > 0) { 257 if (ret < 0) 258 ret = nr; 259 else 260 ret += nr; 261 } 262 263 return ret; 264 } 265} 266