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_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
  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
 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 }