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         struct page *head, *page;
  24         unsigned long mask;
  25         pte_t *ptep, pte;
  26
  27         mask = (write ? _PAGE_PROTECT : 0) | _PAGE_INVALID | _PAGE_SPECIAL;
  28
  29         ptep = ((pte_t *) pmd_deref(pmd)) + pte_index(addr);
  30         do {
  31                 pte = *ptep;
  32                 barrier();
  33                 /* Similar to the PMD case, NUMA hinting must take slow path */
  34                 if (pte_protnone(pte))
  35                         return 0;
  36                 if ((pte_val(pte) & mask) != 0)
  37                         return 0;
  38                 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
  39                 page = pte_page(pte);
  40                 head = compound_head(page);
  41                 if (!page_cache_get_speculative(head))
  42                         return 0;
  43                 if (unlikely(pte_val(pte) != pte_val(*ptep))) {
  44                         put_page(head);
  45                         return 0;
  46                 }
  47                 VM_BUG_ON_PAGE(compound_head(page) != head, page);
  48                 pages[*nr] = page;
  49                 (*nr)++;
  50
  51         } while (ptep++, addr += PAGE_SIZE, addr != end);
  52
  53         return 1;
  54 }
  55
  56 static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
  57                 unsigned long end, int write, struct page **pages, int *nr)
  58 {
  59         unsigned long mask, result;
  60         struct page *head, *page;
  61         int refs;
  62
  63         result = write ? 0 : _SEGMENT_ENTRY_PROTECT;
  64         mask = result | _SEGMENT_ENTRY_INVALID;
  65         if ((pmd_val(pmd) & mask) != result)
  66                 return 0;
  67         VM_BUG_ON(!pfn_valid(pmd_val(pmd) >> PAGE_SHIFT));
  68
  69         refs = 0;
  70         head = pmd_page(pmd);
  71         page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
  72         do {
  73                 VM_BUG_ON(compound_head(page) != head);
  74                 pages[*nr] = page;
  75                 (*nr)++;
  76                 page++;
  77                 refs++;
  78         } while (addr += PAGE_SIZE, addr != end);
  79
  80         if (!page_cache_add_speculative(head, refs)) {
  81                 *nr -= refs;
  82                 return 0;
  83         }
  84
  85         if (unlikely(pmd_val(pmd) != pmd_val(*pmdp))) {
  86                 *nr -= refs;
  87                 while (refs--)
  88                         put_page(head);
  89                 return 0;
  90         }
  91
  92         return 1;
  93 }
  94
  95
  96 static inline int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr,
  97                 unsigned long end, int write, struct page **pages, int *nr)
  98 {
  99         unsigned long next;
 100         pmd_t *pmdp, pmd;
 101
 102         pmdp = (pmd_t *) pudp;
 103         if ((pud_val(pud) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R3)
 104                 pmdp = (pmd_t *) pud_deref(pud);
 105         pmdp += pmd_index(addr);
 106         do {
 107                 pmd = *pmdp;
 108                 barrier();
 109                 next = pmd_addr_end(addr, end);
 110                 if (pmd_none(pmd))
 111                         return 0;
 112                 if (unlikely(pmd_large(pmd))) {
 113                         /*
 114                          * NUMA hinting faults need to be handled in the GUP
 115                          * slowpath for accounting purposes and so that they
 116                          * can be serialised against THP migration.
 117                          */
 118                         if (pmd_protnone(pmd))
 119                                 return 0;
 120                         if (!gup_huge_pmd(pmdp, pmd, addr, next,
 121                                           write, pages, nr))
 122                                 return 0;
 123                 } else if (!gup_pte_range(pmdp, pmd, addr, next,
 124                                           write, pages, nr))
 125                         return 0;
 126         } while (pmdp++, addr = next, addr != end);
 127
 128         return 1;
 129 }
 130
 131 static int gup_huge_pud(pud_t *pudp, pud_t pud, unsigned long addr,
 132                 unsigned long end, int write, struct page **pages, int *nr)
 133 {
 134         struct page *head, *page;
 135         unsigned long mask;
 136         int refs;
 137
 138         mask = (write ? _REGION_ENTRY_PROTECT : 0) | _REGION_ENTRY_INVALID;
 139         if ((pud_val(pud) & mask) != 0)
 140                 return 0;
 141         VM_BUG_ON(!pfn_valid(pud_pfn(pud)));
 142
 143         refs = 0;
 144         head = pud_page(pud);
 145         page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
 146         do {
 147                 VM_BUG_ON_PAGE(compound_head(page) != head, page);
 148                 pages[*nr] = page;
 149                 (*nr)++;
 150                 page++;
 151                 refs++;
 152         } while (addr += PAGE_SIZE, addr != end);
 153
 154         if (!page_cache_add_speculative(head, refs)) {
 155                 *nr -= refs;
 156                 return 0;
 157         }
 158
 159         if (unlikely(pud_val(pud) != pud_val(*pudp))) {
 160                 *nr -= refs;
 161                 while (refs--)
 162                         put_page(head);
 163                 return 0;
 164         }
 165
 166         return 1;
 167 }
 168
 169 static inline int gup_pud_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr,
 170                 unsigned long end, int write, struct page **pages, int *nr)
 171 {
 172         unsigned long next;
 173         pud_t *pudp, pud;
 174
 175         pudp = (pud_t *) pgdp;
 176         if ((pgd_val(pgd) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R2)
 177                 pudp = (pud_t *) pgd_deref(pgd);
 178         pudp += pud_index(addr);
 179         do {
 180                 pud = *pudp;
 181                 barrier();
 182                 next = pud_addr_end(addr, end);
 183                 if (pud_none(pud))
 184                         return 0;
 185                 if (unlikely(pud_large(pud))) {
 186                         if (!gup_huge_pud(pudp, pud, addr, next, write, pages,
 187                                           nr))
 188                                 return 0;
 189                 } else if (!gup_pmd_range(pudp, pud, addr, next, write, pages,
 190                                           nr))
 191                         return 0;
 192         } while (pudp++, addr = next, addr != end);
 193
 194         return 1;
 195 }
 196
 197 /*
 198  * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
 199  * back to the regular GUP.
 200  */
 201 int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 202                           struct page **pages)
 203 {
 204         struct mm_struct *mm = current->mm;
 205         unsigned long addr, len, end;
 206         unsigned long next, flags;
 207         pgd_t *pgdp, pgd;
 208         int nr = 0;
 209
 210         start &= PAGE_MASK;
 211         addr = start;
 212         len = (unsigned long) nr_pages << PAGE_SHIFT;
 213         end = start + len;
 214         if ((end <= start) || (end > TASK_SIZE))
 215                 return 0;
 216         /*
 217          * local_irq_save() doesn't prevent pagetable teardown, but does
 218          * prevent the pagetables from being freed on s390.
 219          *
 220          * So long as we atomically load page table pointers versus teardown,
 221          * we can follow the address down to the the page and take a ref on it.
 222          */
 223         local_irq_save(flags);
 224         pgdp = pgd_offset(mm, addr);
 225         do {
 226                 pgd = *pgdp;
 227                 barrier();
 228                 next = pgd_addr_end(addr, end);
 229                 if (pgd_none(pgd))
 230                         break;
 231                 if (!gup_pud_range(pgdp, pgd, addr, next, write, pages, &nr))
 232                         break;
 233         } while (pgdp++, addr = next, addr != end);
 234         local_irq_restore(flags);
 235
 236         return nr;
 237 }
 238
 239 /**
 240  * get_user_pages_fast() - pin user pages in memory
 241  * @start:      starting user address
 242  * @nr_pages:   number of pages from start to pin
 243  * @write:      whether pages will be written to
 244  * @pages:      array that receives pointers to the pages pinned.
 245  *              Should be at least nr_pages long.
 246  *
 247  * Attempt to pin user pages in memory without taking mm->mmap_sem.
 248  * If not successful, it will fall back to taking the lock and
 249  * calling get_user_pages().
 250  *
 251  * Returns number of pages pinned. This may be fewer than the number
 252  * requested. If nr_pages is 0 or negative, returns 0. If no pages
 253  * were pinned, returns -errno.
 254  */
 255 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 256                         struct page **pages)
 257 {
 258         int nr, ret;
 259
 260         might_sleep();
 261         start &= PAGE_MASK;
 262         nr = __get_user_pages_fast(start, nr_pages, write, pages);
 263         if (nr == nr_pages)
 264                 return nr;
 265
 266         /* Try to get the remaining pages with get_user_pages */
 267         start += nr << PAGE_SHIFT;
 268         pages += nr;
 269         ret = get_user_pages_unlocked(start, nr_pages - nr, write, 0, pages);
 270         /* Have to be a bit careful with return values */
 271         if (nr > 0)
 272                 ret = (ret < 0) ? nr : ret + nr;
 273         return ret;
 274 }