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                 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
  69 static 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
 118 static 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
 143 static 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
 163 int 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;
 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         /*
 178          * XXX: batch / limit 'nr', to avoid large irq off latency
 179          * needs some instrumenting to determine the common sizes used by
 180          * important workloads (eg. DB2), and whether limiting the batch size
 181          * will decrease performance.
 182          *
 183          * It seems like we're in the clear for the moment. Direct-IO is
 184          * the main guy that batches up lots of get_user_pages, and even
 185          * they are limited to 64-at-a-time which is not so many.
 186          */
 187         /*
 188          * This doesn't prevent pagetable teardown, but does prevent
 189          * the pagetables from being freed on sparc.
 190          *
 191          * So long as we atomically load page table pointers versus teardown,
 192          * we can follow the address down to the the page and take a ref on it.
 193          */
 194         local_irq_disable();
 195
 196         pgdp = pgd_offset(mm, addr);
 197         do {
 198                 pgd_t pgd = *pgdp;
 199
 200                 next = pgd_addr_end(addr, end);
 201                 if (pgd_none(pgd))
 202                         goto slow;
 203                 if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
 204                         goto slow;
 205         } while (pgdp++, addr = next, addr != end);
 206
 207         local_irq_enable();
 208
 209         VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
 210         return nr;
 211
 212         {
 213                 int ret;
 214
 215 slow:
 216                 local_irq_enable();
 217
 218                 /* Try to get the remaining pages with get_user_pages */
 219                 start += nr << PAGE_SHIFT;
 220                 pages += nr;
 221
 222                 down_read(&mm->mmap_sem);
 223                 ret = get_user_pages(current, mm, start,
 224                         (end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
 225                 up_read(&mm->mmap_sem);
 226
 227                 /* Have to be a bit careful with return values */
 228                 if (nr > 0) {
 229                         if (ret < 0)
 230                                 ret = nr;
 231                         else
 232                                 ret += nr;
 233                 }
 234
 235                 return ret;
 236         }
 237 }