1/* 2 * Lockless get_user_pages_fast for SuperH 3 * 4 * Copyright (C) 2009 - 2010 Paul Mundt 5 * 6 * Cloned from the x86 and PowerPC versions, by: 7 * 8 * Copyright (C) 2008 Nick Piggin 9 * Copyright (C) 2008 Novell Inc. 10 */ 11#include <linux/sched.h> 12#include <linux/mm.h> 13#include <linux/vmstat.h> 14#include <linux/highmem.h> 15#include <asm/pgtable.h> 16 17static inline pte_t gup_get_pte(pte_t *ptep) 18{ 19#ifndef CONFIG_X2TLB 20 return READ_ONCE(*ptep); 21#else 22 /* 23 * With get_user_pages_fast, we walk down the pagetables without 24 * taking any locks. For this we would like to load the pointers 25 * atomically, but that is not possible with 64-bit PTEs. What 26 * we do have is the guarantee that a pte will only either go 27 * from not present to present, or present to not present or both 28 * -- it will not switch to a completely different present page 29 * without a TLB flush in between; something that we are blocking 30 * by holding interrupts off. 31 * 32 * Setting ptes from not present to present goes: 33 * ptep->pte_high = h; 34 * smp_wmb(); 35 * ptep->pte_low = l; 36 * 37 * And present to not present goes: 38 * ptep->pte_low = 0; 39 * smp_wmb(); 40 * ptep->pte_high = 0; 41 * 42 * We must ensure here that the load of pte_low sees l iff pte_high 43 * sees h. We load pte_high *after* loading pte_low, which ensures we 44 * don't see an older value of pte_high. *Then* we recheck pte_low, 45 * which ensures that we haven't picked up a changed pte high. We might 46 * have got rubbish values from pte_low and pte_high, but we are 47 * guaranteed that pte_low will not have the present bit set *unless* 48 * it is 'l'. And get_user_pages_fast only operates on present ptes, so 49 * we're safe. 50 * 51 * gup_get_pte should not be used or copied outside gup.c without being 52 * very careful -- it does not atomically load the pte or anything that 53 * is likely to be useful for you. 54 */ 55 pte_t pte; 56 57retry: 58 pte.pte_low = ptep->pte_low; 59 smp_rmb(); 60 pte.pte_high = ptep->pte_high; 61 smp_rmb(); 62 if (unlikely(pte.pte_low != ptep->pte_low)) 63 goto retry; 64 65 return pte; 66#endif 67} 68 69/* 70 * The performance critical leaf functions are made noinline otherwise gcc 71 * inlines everything into a single function which results in too much 72 * register pressure. 73 */ 74static noinline int gup_pte_range(pmd_t pmd, unsigned long addr, 75 unsigned long end, int write, struct page **pages, int *nr) 76{ 77 u64 mask, result; 78 pte_t *ptep; 79 80#ifdef CONFIG_X2TLB 81 result = _PAGE_PRESENT | _PAGE_EXT(_PAGE_EXT_KERN_READ | _PAGE_EXT_USER_READ); 82 if (write) 83 result |= _PAGE_EXT(_PAGE_EXT_KERN_WRITE | _PAGE_EXT_USER_WRITE); 84#elif defined(CONFIG_SUPERH64) 85 result = _PAGE_PRESENT | _PAGE_USER | _PAGE_READ; 86 if (write) 87 result |= _PAGE_WRITE; 88#else 89 result = _PAGE_PRESENT | _PAGE_USER; 90 if (write) 91 result |= _PAGE_RW; 92#endif 93 94 mask = result | _PAGE_SPECIAL; 95 96 ptep = pte_offset_map(&pmd, addr); 97 do { 98 pte_t pte = gup_get_pte(ptep); 99 struct page *page; 100 101 if ((pte_val(pte) & mask) != result) { 102 pte_unmap(ptep); 103 return 0; 104 } 105 VM_BUG_ON(!pfn_valid(pte_pfn(pte))); 106 page = pte_page(pte); 107 get_page(page); 108 __flush_anon_page(page, addr); 109 flush_dcache_page(page); 110 pages[*nr] = page; 111 (*nr)++; 112 113 } while (ptep++, addr += PAGE_SIZE, addr != end); 114 pte_unmap(ptep - 1); 115 116 return 1; 117} 118 119static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end, 120 int write, struct page **pages, int *nr) 121{ 122 unsigned long next; 123 pmd_t *pmdp; 124 125 pmdp = pmd_offset(&pud, addr); 126 do { 127 pmd_t pmd = *pmdp; 128 129 next = pmd_addr_end(addr, end); 130 if (pmd_none(pmd)) 131 return 0; 132 if (!gup_pte_range(pmd, addr, next, write, pages, nr)) 133 return 0; 134 } while (pmdp++, addr = next, addr != end); 135 136 return 1; 137} 138 139static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end, 140 int write, struct page **pages, int *nr) 141{ 142 unsigned long next; 143 pud_t *pudp; 144 145 pudp = pud_offset(&pgd, addr); 146 do { 147 pud_t pud = *pudp; 148 149 next = pud_addr_end(addr, end); 150 if (pud_none(pud)) 151 return 0; 152 if (!gup_pmd_range(pud, addr, next, write, pages, nr)) 153 return 0; 154 } while (pudp++, addr = next, addr != end); 155 156 return 1; 157} 158 159/* 160 * Like get_user_pages_fast() except its IRQ-safe in that it won't fall 161 * back to the regular GUP. 162 */ 163int __get_user_pages_fast(unsigned long start, int nr_pages, int write, 164 struct page **pages) 165{ 166 struct mm_struct *mm = current->mm; 167 unsigned long addr, len, end; 168 unsigned long next; 169 unsigned long flags; 170 pgd_t *pgdp; 171 int nr = 0; 172 173 start &= PAGE_MASK; 174 addr = start; 175 len = (unsigned long) nr_pages << PAGE_SHIFT; 176 end = start + len; 177 if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ, 178 (void __user *)start, len))) 179 return 0; 180 181 /* 182 * This doesn't prevent pagetable teardown, but does prevent 183 * the pagetables and pages from being freed. 184 */ 185 local_irq_save(flags); 186 pgdp = pgd_offset(mm, addr); 187 do { 188 pgd_t pgd = *pgdp; 189 190 next = pgd_addr_end(addr, end); 191 if (pgd_none(pgd)) 192 break; 193 if (!gup_pud_range(pgd, addr, next, write, pages, &nr)) 194 break; 195 } while (pgdp++, addr = next, addr != end); 196 local_irq_restore(flags); 197 198 return nr; 199} 200 201/** 202 * get_user_pages_fast() - pin user pages in memory 203 * @start: starting user address 204 * @nr_pages: number of pages from start to pin 205 * @write: whether pages will be written to 206 * @pages: array that receives pointers to the pages pinned. 207 * Should be at least nr_pages long. 208 * 209 * Attempt to pin user pages in memory without taking mm->mmap_sem. 210 * If not successful, it will fall back to taking the lock and 211 * calling get_user_pages(). 212 * 213 * Returns number of pages pinned. This may be fewer than the number 214 * requested. If nr_pages is 0 or negative, returns 0. If no pages 215 * were pinned, returns -errno. 216 */ 217int get_user_pages_fast(unsigned long start, int nr_pages, int write, 218 struct page **pages) 219{ 220 struct mm_struct *mm = current->mm; 221 unsigned long addr, len, end; 222 unsigned long next; 223 pgd_t *pgdp; 224 int nr = 0; 225 226 start &= PAGE_MASK; 227 addr = start; 228 len = (unsigned long) nr_pages << PAGE_SHIFT; 229 230 end = start + len; 231 if (end < start) 232 goto slow_irqon; 233 234 local_irq_disable(); 235 pgdp = pgd_offset(mm, addr); 236 do { 237 pgd_t pgd = *pgdp; 238 239 next = pgd_addr_end(addr, end); 240 if (pgd_none(pgd)) 241 goto slow; 242 if (!gup_pud_range(pgd, addr, next, write, pages, &nr)) 243 goto slow; 244 } while (pgdp++, addr = next, addr != end); 245 local_irq_enable(); 246 247 VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT); 248 return nr; 249 250 { 251 int ret; 252 253slow: 254 local_irq_enable(); 255slow_irqon: 256 /* Try to get the remaining pages with get_user_pages */ 257 start += nr << PAGE_SHIFT; 258 pages += nr; 259 260 ret = get_user_pages_unlocked(current, mm, start, 261 (end - start) >> PAGE_SHIFT, write, 0, pages); 262 263 /* Have to be a bit careful with return values */ 264 if (nr > 0) { 265 if (ret < 0) 266 ret = nr; 267 else 268 ret += nr; 269 } 270 271 return ret; 272 } 273} 274