arch/powerpc/mm/gup.c

   1 /*
   2  * Lockless get_user_pages_fast for powerpc
   3  *
   4  * Copyright (C) 2008 Nick Piggin
   5  * Copyright (C) 2008 Novell Inc.
   6  */
   7 #undef DEBUG
   8
   9 #include <linux/sched.h>
  10 #include <linux/mm.h>
  11 #include <linux/hugetlb.h>
  12 #include <linux/vmstat.h>
  13 #include <linux/pagemap.h>
  14 #include <linux/rwsem.h>
  15 #include <asm/pgtable.h>
  16
  17 #ifdef __HAVE_ARCH_PTE_SPECIAL
  18
  19 static inline void get_huge_page_tail(struct page *page)
  20 {
  21         /*
  22          * __split_huge_page_refcount() cannot run
  23          * from under us.
  24          */
  25         VM_BUG_ON(page_mapcount(page) < 0);
  26         VM_BUG_ON(atomic_read(&page->_count) != 0);
  27         atomic_inc(&page->_mapcount);
  28 }
  29
  30 /*
  31  * The performance critical leaf functions are made noinline otherwise gcc
  32  * inlines everything into a single function which results in too much
  33  * register pressure.
  34  */
  35 static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
  36                 unsigned long end, int write, struct page **pages, int *nr)
  37 {
  38         unsigned long mask, result;
  39         pte_t *ptep;
  40
  41         result = _PAGE_PRESENT|_PAGE_USER;
  42         if (write)
  43                 result |= _PAGE_RW;
  44         mask = result | _PAGE_SPECIAL;
  45
  46         ptep = pte_offset_kernel(&pmd, addr);
  47         do {
  48                 pte_t pte = *ptep;
  49                 struct page *page;
  50
  51                 if ((pte_val(pte) & mask) != result)
  52                         return 0;
  53                 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
  54                 page = pte_page(pte);
  55                 if (!page_cache_get_speculative(page))
  56                         return 0;
  57                 if (unlikely(pte_val(pte) != pte_val(*ptep))) {
  58                         put_page(page);
  59                         return 0;
  60                 }
  61                 if (PageTail(page))
  62                         get_huge_page_tail(page);
  63                 pages[*nr] = page;
  64                 (*nr)++;
  65
  66         } while (ptep++, addr += PAGE_SIZE, addr != end);
  67
  68         return 1;
  69 }
  70
  71 static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
  72                 int write, struct page **pages, int *nr)
  73 {
  74         unsigned long next;
  75         pmd_t *pmdp;
  76
  77         pmdp = pmd_offset(&pud, addr);
  78         do {
  79                 pmd_t pmd = *pmdp;
  80
  81                 next = pmd_addr_end(addr, end);
  82                 if (pmd_none(pmd))
  83                         return 0;
  84                 if (is_hugepd(pmdp)) {
  85                         if (!gup_hugepd((hugepd_t *)pmdp, PMD_SHIFT,
  86                                         addr, next, write, pages, nr))
  87                                 return 0;
  88                 } else if (!gup_pte_range(pmd, addr, next, write, pages, nr))
  89                         return 0;
  90         } while (pmdp++, addr = next, addr != end);
  91
  92         return 1;
  93 }
  94
  95 static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
  96                 int write, struct page **pages, int *nr)
  97 {
  98         unsigned long next;
  99         pud_t *pudp;
 100
 101         pudp = pud_offset(&pgd, addr);
 102         do {
 103                 pud_t pud = *pudp;
 104
 105                 next = pud_addr_end(addr, end);
 106                 if (pud_none(pud))
 107                         return 0;
 108                 if (is_hugepd(pudp)) {
 109                         if (!gup_hugepd((hugepd_t *)pudp, PUD_SHIFT,
 110                                         addr, next, write, pages, nr))
 111                                 return 0;
 112                 } else if (!gup_pmd_range(pud, addr, next, write, pages, nr))
 113                         return 0;
 114         } while (pudp++, addr = next, addr != end);
 115
 116         return 1;
 117 }
 118
 119 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 120                         struct page **pages)
 121 {
 122         struct mm_struct *mm = current->mm;
 123         unsigned long addr, len, end;
 124         unsigned long next;
 125         pgd_t *pgdp;
 126         int nr = 0;
 127
 128         pr_devel("%s(%lx,%x,%s)\n", __func__, start, nr_pages, write ? "write" : "read");
 129
 130         start &= PAGE_MASK;
 131         addr = start;
 132         len = (unsigned long) nr_pages << PAGE_SHIFT;
 133         end = start + len;
 134
 135         if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
 136                                         start, len)))
 137                 goto slow_irqon;
 138
 139         pr_devel("  aligned: %lx .. %lx\n", start, end);
 140
 141         /*
 142          * XXX: batch / limit 'nr', to avoid large irq off latency
 143          * needs some instrumenting to determine the common sizes used by
 144          * important workloads (eg. DB2), and whether limiting the batch size
 145          * will decrease performance.
 146          *
 147          * It seems like we're in the clear for the moment. Direct-IO is
 148          * the main guy that batches up lots of get_user_pages, and even
 149          * they are limited to 64-at-a-time which is not so many.
 150          */
 151         /*
 152          * This doesn't prevent pagetable teardown, but does prevent
 153          * the pagetables from being freed on powerpc.
 154          *
 155          * So long as we atomically load page table pointers versus teardown,
 156          * we can follow the address down to the the page and take a ref on it.
 157          */
 158         local_irq_disable();
 159
 160         pgdp = pgd_offset(mm, addr);
 161         do {
 162                 pgd_t pgd = *pgdp;
 163
 164                 pr_devel("  %016lx: normal pgd %p\n", addr,
 165                          (void *)pgd_val(pgd));
 166                 next = pgd_addr_end(addr, end);
 167                 if (pgd_none(pgd))
 168                         goto slow;
 169                 if (is_hugepd(pgdp)) {
 170                         if (!gup_hugepd((hugepd_t *)pgdp, PGDIR_SHIFT,
 171                                         addr, next, write, pages, &nr))
 172                                 goto slow;
 173                 } else if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
 174                         goto slow;
 175         } while (pgdp++, addr = next, addr != end);
 176
 177         local_irq_enable();
 178
 179         VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
 180         return nr;
 181
 182         {
 183                 int ret;
 184
 185 slow:
 186                 local_irq_enable();
 187 slow_irqon:
 188                 pr_devel("  slow path ! nr = %d\n", nr);
 189
 190                 /* Try to get the remaining pages with get_user_pages */
 191                 start += nr << PAGE_SHIFT;
 192                 pages += nr;
 193
 194                 down_read(&mm->mmap_sem);
 195                 ret = get_user_pages(current, mm, start,
 196                         (end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
 197                 up_read(&mm->mmap_sem);
 198
 199                 /* Have to be a bit careful with return values */
 200                 if (nr > 0) {
 201                         if (ret < 0)
 202                                 ret = nr;
 203                         else
 204                                 ret += nr;
 205                 }
 206
 207                 return ret;
 208         }
 209 }
 210
 211 #endif /* __HAVE_ARCH_PTE_SPECIAL */