arch/s390/mm/gup.c

   1 /*
   2  *  Lockless get_user_pages_fast for s390
   3  *
   4  *  Copyright IBM Corp. 2010
   5  *  Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>
   6  */
   7 #include <linux/sched.h>
   8 #include <linux/mm.h>
   9 #include <linux/hugetlb.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 inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
  21                 unsigned long end, int write, struct page **pages, int *nr)
  22 {
  23         unsigned long mask;
  24         pte_t *ptep, pte;
  25         struct page *page;
  26
  27         mask = (write ? _PAGE_RO : 0) | _PAGE_INVALID | _PAGE_SPECIAL;
  28
  29         ptep = ((pte_t *) pmd_deref(pmd)) + pte_index(addr);
  30         do {
  31                 pte = *ptep;
  32                 barrier();
  33                 if ((pte_val(pte) & mask) != 0)
  34                         return 0;
  35                 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
  36                 page = pte_page(pte);
  37                 if (!page_cache_get_speculative(page))
  38                         return 0;
  39                 if (unlikely(pte_val(pte) != pte_val(*ptep))) {
  40                         put_page(page);
  41                         return 0;
  42                 }
  43                 pages[*nr] = page;
  44                 (*nr)++;
  45
  46         } while (ptep++, addr += PAGE_SIZE, addr != end);
  47
  48         return 1;
  49 }
  50
  51 static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
  52                 unsigned long end, int write, struct page **pages, int *nr)
  53 {
  54         unsigned long mask, result;
  55         struct page *head, *page;
  56         int refs;
  57
  58         result = write ? 0 : _SEGMENT_ENTRY_RO;
  59         mask = result | _SEGMENT_ENTRY_INV;
  60         if ((pmd_val(pmd) & mask) != result)
  61                 return 0;
  62         VM_BUG_ON(!pfn_valid(pmd_val(pmd) >> PAGE_SHIFT));
  63
  64         refs = 0;
  65         head = pmd_page(pmd);
  66         page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
  67         do {
  68                 VM_BUG_ON(compound_head(page) != head);
  69                 pages[*nr] = page;
  70                 (*nr)++;
  71                 page++;
  72                 refs++;
  73         } while (addr += PAGE_SIZE, addr != end);
  74
  75         if (!page_cache_add_speculative(head, refs)) {
  76                 *nr -= refs;
  77                 return 0;
  78         }
  79
  80         if (unlikely(pmd_val(pmd) != pmd_val(*pmdp))) {
  81                 *nr -= refs;
  82                 while (refs--)
  83                         put_page(head);
  84         }
  85
  86         return 1;
  87 }
  88
  89
  90 static inline int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr,
  91                 unsigned long end, int write, struct page **pages, int *nr)
  92 {
  93         unsigned long next;
  94         pmd_t *pmdp, pmd;
  95
  96         pmdp = (pmd_t *) pudp;
  97 #ifdef CONFIG_64BIT
  98         if ((pud_val(pud) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R3)
  99                 pmdp = (pmd_t *) pud_deref(pud);
 100         pmdp += pmd_index(addr);
 101 #endif
 102         do {
 103                 pmd = *pmdp;
 104                 barrier();
 105                 next = pmd_addr_end(addr, end);
 106                 if (pmd_none(pmd))
 107                         return 0;
 108                 if (unlikely(pmd_huge(pmd))) {
 109                         if (!gup_huge_pmd(pmdp, pmd, addr, next,
 110                                           write, pages, nr))
 111                                 return 0;
 112                 } else if (!gup_pte_range(pmdp, pmd, addr, next,
 113                                           write, pages, nr))
 114                         return 0;
 115         } while (pmdp++, addr = next, addr != end);
 116
 117         return 1;
 118 }
 119
 120 static inline int gup_pud_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr,
 121                 unsigned long end, int write, struct page **pages, int *nr)
 122 {
 123         unsigned long next;
 124         pud_t *pudp, pud;
 125
 126         pudp = (pud_t *) pgdp;
 127 #ifdef CONFIG_64BIT
 128         if ((pgd_val(pgd) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R2)
 129                 pudp = (pud_t *) pgd_deref(pgd);
 130         pudp += pud_index(addr);
 131 #endif
 132         do {
 133                 pud = *pudp;
 134                 barrier();
 135                 next = pud_addr_end(addr, end);
 136                 if (pud_none(pud))
 137                         return 0;
 138                 if (!gup_pmd_range(pudp, pud, addr, next, write, pages, nr))
 139                         return 0;
 140         } while (pudp++, addr = next, addr != end);
 141
 142         return 1;
 143 }
 144
 145 /**
 146  * get_user_pages_fast() - pin user pages in memory
 147  * @start:      starting user address
 148  * @nr_pages:   number of pages from start to pin
 149  * @write:      whether pages will be written to
 150  * @pages:      array that receives pointers to the pages pinned.
 151  *              Should be at least nr_pages long.
 152  *
 153  * Attempt to pin user pages in memory without taking mm->mmap_sem.
 154  * If not successful, it will fall back to taking the lock and
 155  * calling get_user_pages().
 156  *
 157  * Returns number of pages pinned. This may be fewer than the number
 158  * requested. If nr_pages is 0 or negative, returns 0. If no pages
 159  * were pinned, returns -errno.
 160  */
 161 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 162                         struct page **pages)
 163 {
 164         struct mm_struct *mm = current->mm;
 165         unsigned long addr, len, end;
 166         unsigned long next;
 167         pgd_t *pgdp, pgd;
 168         int nr = 0;
 169
 170         start &= PAGE_MASK;
 171         addr = start;
 172         len = (unsigned long) nr_pages << PAGE_SHIFT;
 173         end = start + len;
 174         if (end < start)
 175                 goto slow_irqon;
 176
 177         /*
 178          * local_irq_disable() doesn't prevent pagetable teardown, but does
 179          * prevent the pagetables from being freed on s390.
 180          *
 181          * So long as we atomically load page table pointers versus teardown,
 182          * we can follow the address down to the the page and take a ref on it.
 183          */
 184         local_irq_disable();
 185         pgdp = pgd_offset(mm, addr);
 186         do {
 187                 pgd = *pgdp;
 188                 barrier();
 189                 next = pgd_addr_end(addr, end);
 190                 if (pgd_none(pgd))
 191                         goto slow;
 192                 if (!gup_pud_range(pgdp, pgd, addr, next, write, pages, &nr))
 193                         goto slow;
 194         } while (pgdp++, addr = next, addr != end);
 195         local_irq_enable();
 196
 197         VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
 198         return nr;
 199
 200         {
 201                 int ret;
 202 slow:
 203                 local_irq_enable();
 204 slow_irqon:
 205                 /* Try to get the remaining pages with get_user_pages */
 206                 start += nr << PAGE_SHIFT;
 207                 pages += nr;
 208
 209                 down_read(&mm->mmap_sem);
 210                 ret = get_user_pages(current, mm, start,
 211                         (end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
 212                 up_read(&mm->mmap_sem);
 213
 214                 /* Have to be a bit careful with return values */
 215                 if (nr > 0) {
 216                         if (ret < 0)
 217                                 ret = nr;
 218                         else
 219                                 ret += nr;
 220                 }
 221
 222                 return ret;
 223         }
 224 }