arch/sparc/mm/gup.c

   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  */
  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
  60                 pages[*nr] = page;
  61                 (*nr)++;
  62         } while (ptep++, addr += PAGE_SIZE, addr != end);
  63
  64         return 1;
  65 }
  66
  67 static int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
  68                         unsigned long end, int write, struct page **pages,
  69                         int *nr)
  70 {
  71         struct page *head, *page;
  72         int refs;
  73
  74         if (!(pmd_val(pmd) & _PAGE_VALID))
  75                 return 0;
  76
  77         if (write && !pmd_write(pmd))
  78                 return 0;
  79
  80         refs = 0;
  81         head = pmd_page(pmd);
  82         page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
  83         do {
  84                 VM_BUG_ON(compound_head(page) != head);
  85                 pages[*nr] = page;
  86                 (*nr)++;
  87                 page++;
  88                 refs++;
  89         } while (addr += PAGE_SIZE, addr != end);
  90
  91         if (!page_cache_add_speculative(head, refs)) {
  92                 *nr -= refs;
  93                 return 0;
  94         }
  95
  96         if (unlikely(pmd_val(pmd) != pmd_val(*pmdp))) {
  97                 *nr -= refs;
  98                 while (refs--)
  99                         put_page(head);
 100                 return 0;
 101         }
 102
 103         return 1;
 104 }
 105
 106 static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
 107                 int write, struct page **pages, int *nr)
 108 {
 109         unsigned long next;
 110         pmd_t *pmdp;
 111
 112         pmdp = pmd_offset(&pud, addr);
 113         do {
 114                 pmd_t pmd = *pmdp;
 115
 116                 next = pmd_addr_end(addr, end);
 117                 if (pmd_none(pmd) || pmd_trans_splitting(pmd))
 118                         return 0;
 119                 if (unlikely(pmd_large(pmd))) {
 120                         if (!gup_huge_pmd(pmdp, pmd, addr, next,
 121                                           write, pages, nr))
 122                                 return 0;
 123                 } else if (!gup_pte_range(pmd, addr, next, write,
 124                                           pages, nr))
 125                         return 0;
 126         } while (pmdp++, addr = next, addr != end);
 127
 128         return 1;
 129 }
 130
 131 static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
 132                 int write, struct page **pages, int *nr)
 133 {
 134         unsigned long next;
 135         pud_t *pudp;
 136
 137         pudp = pud_offset(&pgd, addr);
 138         do {
 139                 pud_t pud = *pudp;
 140
 141                 next = pud_addr_end(addr, end);
 142                 if (pud_none(pud))
 143                         return 0;
 144                 if (!gup_pmd_range(pud, addr, next, write, pages, nr))
 145                         return 0;
 146         } while (pudp++, addr = next, addr != end);
 147
 148         return 1;
 149 }
 150
 151 int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 152                           struct page **pages)
 153 {
 154         struct mm_struct *mm = current->mm;
 155         unsigned long addr, len, end;
 156         unsigned long next, flags;
 157         pgd_t *pgdp;
 158         int nr = 0;
 159
 160         start &= PAGE_MASK;
 161         addr = start;
 162         len = (unsigned long) nr_pages << PAGE_SHIFT;
 163         end = start + len;
 164
 165         local_irq_save(flags);
 166         pgdp = pgd_offset(mm, addr);
 167         do {
 168                 pgd_t pgd = *pgdp;
 169
 170                 next = pgd_addr_end(addr, end);
 171                 if (pgd_none(pgd))
 172                         break;
 173                 if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
 174                         break;
 175         } while (pgdp++, addr = next, addr != end);
 176         local_irq_restore(flags);
 177
 178         return nr;
 179 }
 180
 181 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 182                         struct page **pages)
 183 {
 184         struct mm_struct *mm = current->mm;
 185         unsigned long addr, len, end;
 186         unsigned long next;
 187         pgd_t *pgdp;
 188         int nr = 0;
 189
 190         start &= PAGE_MASK;
 191         addr = start;
 192         len = (unsigned long) nr_pages << PAGE_SHIFT;
 193         end = start + len;
 194
 195         /*
 196          * XXX: batch / limit 'nr', to avoid large irq off latency
 197          * needs some instrumenting to determine the common sizes used by
 198          * important workloads (eg. DB2), and whether limiting the batch size
 199          * will decrease performance.
 200          *
 201          * It seems like we're in the clear for the moment. Direct-IO is
 202          * the main guy that batches up lots of get_user_pages, and even
 203          * they are limited to 64-at-a-time which is not so many.
 204          */
 205         /*
 206          * This doesn't prevent pagetable teardown, but does prevent
 207          * the pagetables from being freed on sparc.
 208          *
 209          * So long as we atomically load page table pointers versus teardown,
 210          * we can follow the address down to the the page and take a ref on it.
 211          */
 212         local_irq_disable();
 213
 214         pgdp = pgd_offset(mm, addr);
 215         do {
 216                 pgd_t pgd = *pgdp;
 217
 218                 next = pgd_addr_end(addr, end);
 219                 if (pgd_none(pgd))
 220                         goto slow;
 221                 if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
 222                         goto slow;
 223         } while (pgdp++, addr = next, addr != end);
 224
 225         local_irq_enable();
 226
 227         VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
 228         return nr;
 229
 230         {
 231                 int ret;
 232
 233 slow:
 234                 local_irq_enable();
 235
 236                 /* Try to get the remaining pages with get_user_pages */
 237                 start += nr << PAGE_SHIFT;
 238                 pages += nr;
 239
 240                 ret = get_user_pages_unlocked(current, mm, start,
 241                         (end - start) >> PAGE_SHIFT, write, 0, pages);
 242
 243                 /* Have to be a bit careful with return values */
 244                 if (nr > 0) {
 245                         if (ret < 0)
 246                                 ret = nr;
 247                         else
 248                                 ret += nr;
 249                 }
 250
 251                 return ret;
 252         }
 253 }