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 */ 20static 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 /* 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 if (!page_cache_get_speculative(page)) 41 return 0; 42 if (unlikely(pte_val(pte) != pte_val(*ptep))) { 43 put_page(page); 44 return 0; 45 } 46 pages[*nr] = page; 47 (*nr)++; 48 49 } while (ptep++, addr += PAGE_SIZE, addr != end); 50 51 return 1; 52} 53 54static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr, 55 unsigned long end, int write, struct page **pages, int *nr) 56{ 57 unsigned long mask, result; 58 struct page *head, *page, *tail; 59 int refs; 60 61 result = write ? 0 : _SEGMENT_ENTRY_PROTECT; 62 mask = result | _SEGMENT_ENTRY_INVALID; 63 if ((pmd_val(pmd) & mask) != result) 64 return 0; 65 VM_BUG_ON(!pfn_valid(pmd_val(pmd) >> PAGE_SHIFT)); 66 67 refs = 0; 68 head = pmd_page(pmd); 69 page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT); 70 tail = page; 71 do { 72 VM_BUG_ON(compound_head(page) != head); 73 pages[*nr] = page; 74 (*nr)++; 75 page++; 76 refs++; 77 } while (addr += PAGE_SIZE, addr != end); 78 79 if (!page_cache_add_speculative(head, refs)) { 80 *nr -= refs; 81 return 0; 82 } 83 84 if (unlikely(pmd_val(pmd) != pmd_val(*pmdp))) { 85 *nr -= refs; 86 while (refs--) 87 put_page(head); 88 return 0; 89 } 90 91 /* 92 * Any tail page need their mapcount reference taken before we 93 * return. 94 */ 95 while (refs--) { 96 if (PageTail(tail)) 97 get_huge_page_tail(tail); 98 tail++; 99 } 100 101 return 1; 102} 103 104 105static inline int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr, 106 unsigned long end, int write, struct page **pages, int *nr) 107{ 108 unsigned long next; 109 pmd_t *pmdp, pmd; 110 111 pmdp = (pmd_t *) pudp; 112 if ((pud_val(pud) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R3) 113 pmdp = (pmd_t *) pud_deref(pud); 114 pmdp += pmd_index(addr); 115 do { 116 pmd = *pmdp; 117 barrier(); 118 next = pmd_addr_end(addr, end); 119 /* 120 * The pmd_trans_splitting() check below explains why 121 * pmdp_splitting_flush() has to serialize with 122 * smp_call_function() against our disabled IRQs, to stop 123 * this gup-fast code from running while we set the 124 * splitting bit in the pmd. Returning zero will take 125 * the slow path that will call wait_split_huge_page() 126 * if the pmd is still in splitting state. 127 */ 128 if (pmd_none(pmd) || pmd_trans_splitting(pmd)) 129 return 0; 130 if (unlikely(pmd_large(pmd))) { 131 /* 132 * NUMA hinting faults need to be handled in the GUP 133 * slowpath for accounting purposes and so that they 134 * can be serialised against THP migration. 135 */ 136 if (pmd_protnone(pmd)) 137 return 0; 138 if (!gup_huge_pmd(pmdp, pmd, addr, next, 139 write, pages, nr)) 140 return 0; 141 } else if (!gup_pte_range(pmdp, pmd, addr, next, 142 write, pages, nr)) 143 return 0; 144 } while (pmdp++, addr = next, addr != end); 145 146 return 1; 147} 148 149static inline int gup_pud_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr, 150 unsigned long end, int write, struct page **pages, int *nr) 151{ 152 unsigned long next; 153 pud_t *pudp, pud; 154 155 pudp = (pud_t *) pgdp; 156 if ((pgd_val(pgd) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R2) 157 pudp = (pud_t *) pgd_deref(pgd); 158 pudp += pud_index(addr); 159 do { 160 pud = *pudp; 161 barrier(); 162 next = pud_addr_end(addr, end); 163 if (pud_none(pud)) 164 return 0; 165 if (!gup_pmd_range(pudp, pud, addr, next, write, pages, nr)) 166 return 0; 167 } while (pudp++, addr = next, addr != end); 168 169 return 1; 170} 171 172/* 173 * Like get_user_pages_fast() except its IRQ-safe in that it won't fall 174 * back to the regular GUP. 175 */ 176int __get_user_pages_fast(unsigned long start, int nr_pages, int write, 177 struct page **pages) 178{ 179 struct mm_struct *mm = current->mm; 180 unsigned long addr, len, end; 181 unsigned long next, flags; 182 pgd_t *pgdp, pgd; 183 int nr = 0; 184 185 start &= PAGE_MASK; 186 addr = start; 187 len = (unsigned long) nr_pages << PAGE_SHIFT; 188 end = start + len; 189 if ((end <= start) || (end > TASK_SIZE)) 190 return 0; 191 /* 192 * local_irq_save() doesn't prevent pagetable teardown, but does 193 * prevent the pagetables from being freed on s390. 194 * 195 * So long as we atomically load page table pointers versus teardown, 196 * we can follow the address down to the the page and take a ref on it. 197 */ 198 local_irq_save(flags); 199 pgdp = pgd_offset(mm, addr); 200 do { 201 pgd = *pgdp; 202 barrier(); 203 next = pgd_addr_end(addr, end); 204 if (pgd_none(pgd)) 205 break; 206 if (!gup_pud_range(pgdp, pgd, addr, next, write, pages, &nr)) 207 break; 208 } while (pgdp++, addr = next, addr != end); 209 local_irq_restore(flags); 210 211 return nr; 212} 213 214/** 215 * get_user_pages_fast() - pin user pages in memory 216 * @start: starting user address 217 * @nr_pages: number of pages from start to pin 218 * @write: whether pages will be written to 219 * @pages: array that receives pointers to the pages pinned. 220 * Should be at least nr_pages long. 221 * 222 * Attempt to pin user pages in memory without taking mm->mmap_sem. 223 * If not successful, it will fall back to taking the lock and 224 * calling get_user_pages(). 225 * 226 * Returns number of pages pinned. This may be fewer than the number 227 * requested. If nr_pages is 0 or negative, returns 0. If no pages 228 * were pinned, returns -errno. 229 */ 230int get_user_pages_fast(unsigned long start, int nr_pages, int write, 231 struct page **pages) 232{ 233 struct mm_struct *mm = current->mm; 234 int nr, ret; 235 236 start &= PAGE_MASK; 237 nr = __get_user_pages_fast(start, nr_pages, write, pages); 238 if (nr == nr_pages) 239 return nr; 240 241 /* Try to get the remaining pages with get_user_pages */ 242 start += nr << PAGE_SHIFT; 243 pages += nr; 244 ret = get_user_pages_unlocked(current, mm, start, 245 nr_pages - nr, write, 0, pages); 246 /* Have to be a bit careful with return values */ 247 if (nr > 0) 248 ret = (ret < 0) ? nr : ret + nr; 249 return ret; 250} 251