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Linux/arch/s390/mm/gup.c

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  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_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                 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, *tail;
 56         int refs;
 57 
 58         result = write ? 0 : _SEGMENT_ENTRY_PROTECT;
 59         mask = result | _SEGMENT_ENTRY_INVALID;
 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         tail = page;
 68         do {
 69                 VM_BUG_ON(compound_head(page) != head);
 70                 pages[*nr] = page;
 71                 (*nr)++;
 72                 page++;
 73                 refs++;
 74         } while (addr += PAGE_SIZE, addr != end);
 75 
 76         if (!page_cache_add_speculative(head, refs)) {
 77                 *nr -= refs;
 78                 return 0;
 79         }
 80 
 81         if (unlikely(pmd_val(pmd) != pmd_val(*pmdp))) {
 82                 *nr -= refs;
 83                 while (refs--)
 84                         put_page(head);
 85                 return 0;
 86         }
 87 
 88         /*
 89          * Any tail page need their mapcount reference taken before we
 90          * return.
 91          */
 92         while (refs--) {
 93                 if (PageTail(tail))
 94                         get_huge_page_tail(tail);
 95                 tail++;
 96         }
 97 
 98         return 1;
 99 }
100 
101 
102 static inline int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr,
103                 unsigned long end, int write, struct page **pages, int *nr)
104 {
105         unsigned long next;
106         pmd_t *pmdp, pmd;
107 
108         pmdp = (pmd_t *) pudp;
109 #ifdef CONFIG_64BIT
110         if ((pud_val(pud) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R3)
111                 pmdp = (pmd_t *) pud_deref(pud);
112         pmdp += pmd_index(addr);
113 #endif
114         do {
115                 pmd = *pmdp;
116                 barrier();
117                 next = pmd_addr_end(addr, end);
118                 /*
119                  * The pmd_trans_splitting() check below explains why
120                  * pmdp_splitting_flush() has to serialize with
121                  * smp_call_function() against our disabled IRQs, to stop
122                  * this gup-fast code from running while we set the
123                  * splitting bit in the pmd. Returning zero will take
124                  * the slow path that will call wait_split_huge_page()
125                  * if the pmd is still in splitting state.
126                  */
127                 if (pmd_none(pmd) || pmd_trans_splitting(pmd))
128                         return 0;
129                 if (unlikely(pmd_large(pmd))) {
130                         if (!gup_huge_pmd(pmdp, pmd, addr, next,
131                                           write, pages, nr))
132                                 return 0;
133                 } else if (!gup_pte_range(pmdp, pmd, addr, next,
134                                           write, pages, nr))
135                         return 0;
136         } while (pmdp++, addr = next, addr != end);
137 
138         return 1;
139 }
140 
141 static inline int gup_pud_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr,
142                 unsigned long end, int write, struct page **pages, int *nr)
143 {
144         unsigned long next;
145         pud_t *pudp, pud;
146 
147         pudp = (pud_t *) pgdp;
148 #ifdef CONFIG_64BIT
149         if ((pgd_val(pgd) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R2)
150                 pudp = (pud_t *) pgd_deref(pgd);
151         pudp += pud_index(addr);
152 #endif
153         do {
154                 pud = *pudp;
155                 barrier();
156                 next = pud_addr_end(addr, end);
157                 if (pud_none(pud))
158                         return 0;
159                 if (!gup_pmd_range(pudp, pud, addr, next, write, pages, nr))
160                         return 0;
161         } while (pudp++, addr = next, addr != end);
162 
163         return 1;
164 }
165 
166 /*
167  * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
168  * back to the regular GUP.
169  */
170 int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
171                           struct page **pages)
172 {
173         struct mm_struct *mm = current->mm;
174         unsigned long addr, len, end;
175         unsigned long next, flags;
176         pgd_t *pgdp, pgd;
177         int nr = 0;
178 
179         start &= PAGE_MASK;
180         addr = start;
181         len = (unsigned long) nr_pages << PAGE_SHIFT;
182         end = start + len;
183         if ((end <= start) || (end > TASK_SIZE))
184                 return 0;
185         /*
186          * local_irq_save() doesn't prevent pagetable teardown, but does
187          * prevent the pagetables from being freed on s390.
188          *
189          * So long as we atomically load page table pointers versus teardown,
190          * we can follow the address down to the the page and take a ref on it.
191          */
192         local_irq_save(flags);
193         pgdp = pgd_offset(mm, addr);
194         do {
195                 pgd = *pgdp;
196                 barrier();
197                 next = pgd_addr_end(addr, end);
198                 if (pgd_none(pgd))
199                         break;
200                 if (!gup_pud_range(pgdp, pgd, addr, next, write, pages, &nr))
201                         break;
202         } while (pgdp++, addr = next, addr != end);
203         local_irq_restore(flags);
204 
205         return nr;
206 }
207 
208 /**
209  * get_user_pages_fast() - pin user pages in memory
210  * @start:      starting user address
211  * @nr_pages:   number of pages from start to pin
212  * @write:      whether pages will be written to
213  * @pages:      array that receives pointers to the pages pinned.
214  *              Should be at least nr_pages long.
215  *
216  * Attempt to pin user pages in memory without taking mm->mmap_sem.
217  * If not successful, it will fall back to taking the lock and
218  * calling get_user_pages().
219  *
220  * Returns number of pages pinned. This may be fewer than the number
221  * requested. If nr_pages is 0 or negative, returns 0. If no pages
222  * were pinned, returns -errno.
223  */
224 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
225                         struct page **pages)
226 {
227         struct mm_struct *mm = current->mm;
228         int nr, ret;
229 
230         start &= PAGE_MASK;
231         nr = __get_user_pages_fast(start, nr_pages, write, pages);
232         if (nr == nr_pages)
233                 return nr;
234 
235         /* Try to get the remaining pages with get_user_pages */
236         start += nr << PAGE_SHIFT;
237         pages += nr;
238         down_read(&mm->mmap_sem);
239         ret = get_user_pages(current, mm, start,
240                              nr_pages - nr, write, 0, pages, NULL);
241         up_read(&mm->mmap_sem);
242         /* Have to be a bit careful with return values */
243         if (nr > 0)
244                 ret = (ret < 0) ? nr : ret + nr;
245         return ret;
246 }
247 

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