~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

TOMOYO Linux Cross Reference
Linux/arch/x86/mm/gup.c

Version: ~ [ linux-5.4-rc7 ] ~ [ linux-5.3.11 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.84 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.154 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.201 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.201 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.19.8 ] ~ [ linux-3.18.140 ] ~ [ linux-3.17.8 ] ~ [ linux-3.16.77 ] ~ [ linux-3.15.10 ] ~ [ linux-3.14.79 ] ~ [ linux-3.13.11 ] ~ [ linux-3.12.74 ] ~ [ linux-3.11.10 ] ~ [ linux-3.10.108 ] ~ [ linux-3.9.11 ] ~ [ linux-3.8.13 ] ~ [ linux-3.7.10 ] ~ [ linux-3.6.11 ] ~ [ linux-3.5.7 ] ~ [ linux-3.4.113 ] ~ [ linux-3.3.8 ] ~ [ linux-3.2.102 ] ~ [ linux-3.1.10 ] ~ [ linux-3.0.101 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
Architecture: ~ [ i386 ] ~ [ alpha ] ~ [ m68k ] ~ [ mips ] ~ [ ppc ] ~ [ sparc ] ~ [ sparc64 ] ~

  1 /*
  2  * Lockless get_user_pages_fast for x86
  3  *
  4  * Copyright (C) 2008 Nick Piggin
  5  * Copyright (C) 2008 Novell Inc.
  6  */
  7 #include <linux/sched.h>
  8 #include <linux/mm.h>
  9 #include <linux/vmstat.h>
 10 #include <linux/highmem.h>
 11 
 12 #include <asm/pgtable.h>
 13 
 14 static inline pte_t gup_get_pte(pte_t *ptep)
 15 {
 16 #ifndef CONFIG_X86_PAE
 17         return ACCESS_ONCE(*ptep);
 18 #else
 19         /*
 20          * With get_user_pages_fast, we walk down the pagetables without taking
 21          * any locks.  For this we would like to load the pointers atoimcally,
 22          * but that is not possible (without expensive cmpxchg8b) on PAE.  What
 23          * we do have is the guarantee that a pte will only either go from not
 24          * present to present, or present to not present or both -- it will not
 25          * switch to a completely different present page without a TLB flush in
 26          * between; something that we are blocking by holding interrupts off.
 27          *
 28          * Setting ptes from not present to present goes:
 29          * ptep->pte_high = h;
 30          * smp_wmb();
 31          * ptep->pte_low = l;
 32          *
 33          * And present to not present goes:
 34          * ptep->pte_low = 0;
 35          * smp_wmb();
 36          * ptep->pte_high = 0;
 37          *
 38          * We must ensure here that the load of pte_low sees l iff pte_high
 39          * sees h. We load pte_high *after* loading pte_low, which ensures we
 40          * don't see an older value of pte_high.  *Then* we recheck pte_low,
 41          * which ensures that we haven't picked up a changed pte high. We might
 42          * have got rubbish values from pte_low and pte_high, but we are
 43          * guaranteed that pte_low will not have the present bit set *unless*
 44          * it is 'l'. And get_user_pages_fast only operates on present ptes, so
 45          * we're safe.
 46          *
 47          * gup_get_pte should not be used or copied outside gup.c without being
 48          * very careful -- it does not atomically load the pte or anything that
 49          * is likely to be useful for you.
 50          */
 51         pte_t pte;
 52 
 53 retry:
 54         pte.pte_low = ptep->pte_low;
 55         smp_rmb();
 56         pte.pte_high = ptep->pte_high;
 57         smp_rmb();
 58         if (unlikely(pte.pte_low != ptep->pte_low))
 59                 goto retry;
 60 
 61         return pte;
 62 #endif
 63 }
 64 
 65 /*
 66  * The performance critical leaf functions are made noinline otherwise gcc
 67  * inlines everything into a single function which results in too much
 68  * register pressure.
 69  */
 70 static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
 71                 unsigned long end, int write, struct page **pages, int *nr)
 72 {
 73         unsigned long mask;
 74         pte_t *ptep;
 75 
 76         mask = _PAGE_PRESENT|_PAGE_USER;
 77         if (write)
 78                 mask |= _PAGE_RW;
 79 
 80         ptep = pte_offset_map(&pmd, addr);
 81         do {
 82                 pte_t pte = gup_get_pte(ptep);
 83                 struct page *page;
 84 
 85                 if ((pte_flags(pte) & (mask | _PAGE_SPECIAL)) != mask) {
 86                         pte_unmap(ptep);
 87                         return 0;
 88                 }
 89                 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
 90                 page = pte_page(pte);
 91                 get_page(page);
 92                 pages[*nr] = page;
 93                 (*nr)++;
 94 
 95         } while (ptep++, addr += PAGE_SIZE, addr != end);
 96         pte_unmap(ptep - 1);
 97 
 98         return 1;
 99 }
100 
101 static inline void get_head_page_multiple(struct page *page, int nr)
102 {
103         VM_BUG_ON(page != compound_head(page));
104         VM_BUG_ON(page_count(page) == 0);
105         atomic_add(nr, &page->_count);
106 }
107 
108 static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr,
109                 unsigned long end, int write, struct page **pages, int *nr)
110 {
111         unsigned long mask;
112         pte_t pte = *(pte_t *)&pmd;
113         struct page *head, *page;
114         int refs;
115 
116         mask = _PAGE_PRESENT|_PAGE_USER;
117         if (write)
118                 mask |= _PAGE_RW;
119         if ((pte_flags(pte) & mask) != mask)
120                 return 0;
121         /* hugepages are never "special" */
122         VM_BUG_ON(pte_flags(pte) & _PAGE_SPECIAL);
123         VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
124 
125         refs = 0;
126         head = pte_page(pte);
127         page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
128         do {
129                 VM_BUG_ON(compound_head(page) != head);
130                 pages[*nr] = page;
131                 (*nr)++;
132                 page++;
133                 refs++;
134         } while (addr += PAGE_SIZE, addr != end);
135         get_head_page_multiple(head, refs);
136 
137         return 1;
138 }
139 
140 static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
141                 int write, struct page **pages, int *nr)
142 {
143         unsigned long next;
144         pmd_t *pmdp;
145 
146         pmdp = pmd_offset(&pud, addr);
147         do {
148                 pmd_t pmd = *pmdp;
149 
150                 next = pmd_addr_end(addr, end);
151                 if (pmd_none(pmd))
152                         return 0;
153                 if (unlikely(pmd_large(pmd))) {
154                         if (!gup_huge_pmd(pmd, addr, next, write, pages, nr))
155                                 return 0;
156                 } else {
157                         if (!gup_pte_range(pmd, addr, next, write, pages, nr))
158                                 return 0;
159                 }
160         } while (pmdp++, addr = next, addr != end);
161 
162         return 1;
163 }
164 
165 static noinline int gup_huge_pud(pud_t pud, unsigned long addr,
166                 unsigned long end, int write, struct page **pages, int *nr)
167 {
168         unsigned long mask;
169         pte_t pte = *(pte_t *)&pud;
170         struct page *head, *page;
171         int refs;
172 
173         mask = _PAGE_PRESENT|_PAGE_USER;
174         if (write)
175                 mask |= _PAGE_RW;
176         if ((pte_flags(pte) & mask) != mask)
177                 return 0;
178         /* hugepages are never "special" */
179         VM_BUG_ON(pte_flags(pte) & _PAGE_SPECIAL);
180         VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
181 
182         refs = 0;
183         head = pte_page(pte);
184         page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
185         do {
186                 VM_BUG_ON(compound_head(page) != head);
187                 pages[*nr] = page;
188                 (*nr)++;
189                 page++;
190                 refs++;
191         } while (addr += PAGE_SIZE, addr != end);
192         get_head_page_multiple(head, refs);
193 
194         return 1;
195 }
196 
197 static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
198                         int write, struct page **pages, int *nr)
199 {
200         unsigned long next;
201         pud_t *pudp;
202 
203         pudp = pud_offset(&pgd, addr);
204         do {
205                 pud_t pud = *pudp;
206 
207                 next = pud_addr_end(addr, end);
208                 if (pud_none(pud))
209                         return 0;
210                 if (unlikely(pud_large(pud))) {
211                         if (!gup_huge_pud(pud, addr, next, write, pages, nr))
212                                 return 0;
213                 } else {
214                         if (!gup_pmd_range(pud, addr, next, write, pages, nr))
215                                 return 0;
216                 }
217         } while (pudp++, addr = next, addr != end);
218 
219         return 1;
220 }
221 
222 /*
223  * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
224  * back to the regular GUP.
225  */
226 int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
227                           struct page **pages)
228 {
229         struct mm_struct *mm = current->mm;
230         unsigned long addr, len, end;
231         unsigned long next;
232         unsigned long flags;
233         pgd_t *pgdp;
234         int nr = 0;
235 
236         start &= PAGE_MASK;
237         addr = start;
238         len = (unsigned long) nr_pages << PAGE_SHIFT;
239         end = start + len;
240         if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
241                                         (void __user *)start, len)))
242                 return 0;
243 
244         /*
245          * XXX: batch / limit 'nr', to avoid large irq off latency
246          * needs some instrumenting to determine the common sizes used by
247          * important workloads (eg. DB2), and whether limiting the batch size
248          * will decrease performance.
249          *
250          * It seems like we're in the clear for the moment. Direct-IO is
251          * the main guy that batches up lots of get_user_pages, and even
252          * they are limited to 64-at-a-time which is not so many.
253          */
254         /*
255          * This doesn't prevent pagetable teardown, but does prevent
256          * the pagetables and pages from being freed on x86.
257          *
258          * So long as we atomically load page table pointers versus teardown
259          * (which we do on x86, with the above PAE exception), we can follow the
260          * address down to the the page and take a ref on it.
261          */
262         local_irq_save(flags);
263         pgdp = pgd_offset(mm, addr);
264         do {
265                 pgd_t pgd = *pgdp;
266 
267                 next = pgd_addr_end(addr, end);
268                 if (pgd_none(pgd))
269                         break;
270                 if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
271                         break;
272         } while (pgdp++, addr = next, addr != end);
273         local_irq_restore(flags);
274 
275         return nr;
276 }
277 
278 /**
279  * get_user_pages_fast() - pin user pages in memory
280  * @start:      starting user address
281  * @nr_pages:   number of pages from start to pin
282  * @write:      whether pages will be written to
283  * @pages:      array that receives pointers to the pages pinned.
284  *              Should be at least nr_pages long.
285  *
286  * Attempt to pin user pages in memory without taking mm->mmap_sem.
287  * If not successful, it will fall back to taking the lock and
288  * calling get_user_pages().
289  *
290  * Returns number of pages pinned. This may be fewer than the number
291  * requested. If nr_pages is 0 or negative, returns 0. If no pages
292  * were pinned, returns -errno.
293  */
294 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
295                         struct page **pages)
296 {
297         struct mm_struct *mm = current->mm;
298         unsigned long addr, len, end;
299         unsigned long next;
300         pgd_t *pgdp;
301         int nr = 0;
302 
303         start &= PAGE_MASK;
304         addr = start;
305         len = (unsigned long) nr_pages << PAGE_SHIFT;
306 
307         end = start + len;
308         if (end < start)
309                 goto slow_irqon;
310 
311 #ifdef CONFIG_X86_64
312         if (end >> __VIRTUAL_MASK_SHIFT)
313                 goto slow_irqon;
314 #endif
315 
316         /*
317          * XXX: batch / limit 'nr', to avoid large irq off latency
318          * needs some instrumenting to determine the common sizes used by
319          * important workloads (eg. DB2), and whether limiting the batch size
320          * will decrease performance.
321          *
322          * It seems like we're in the clear for the moment. Direct-IO is
323          * the main guy that batches up lots of get_user_pages, and even
324          * they are limited to 64-at-a-time which is not so many.
325          */
326         /*
327          * This doesn't prevent pagetable teardown, but does prevent
328          * the pagetables and pages from being freed on x86.
329          *
330          * So long as we atomically load page table pointers versus teardown
331          * (which we do on x86, with the above PAE exception), we can follow the
332          * address down to the the page and take a ref on it.
333          */
334         local_irq_disable();
335         pgdp = pgd_offset(mm, addr);
336         do {
337                 pgd_t pgd = *pgdp;
338 
339                 next = pgd_addr_end(addr, end);
340                 if (pgd_none(pgd))
341                         goto slow;
342                 if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
343                         goto slow;
344         } while (pgdp++, addr = next, addr != end);
345         local_irq_enable();
346 
347         VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
348         return nr;
349 
350         {
351                 int ret;
352 
353 slow:
354                 local_irq_enable();
355 slow_irqon:
356                 /* Try to get the remaining pages with get_user_pages */
357                 start += nr << PAGE_SHIFT;
358                 pages += nr;
359 
360                 down_read(&mm->mmap_sem);
361                 ret = get_user_pages(current, mm, start,
362                         (end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
363                 up_read(&mm->mmap_sem);
364 
365                 /* Have to be a bit careful with return values */
366                 if (nr > 0) {
367                         if (ret < 0)
368                                 ret = nr;
369                         else
370                                 ret += nr;
371                 }
372 
373                 return ret;
374         }
375 }
376 

~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

kernel.org | git.kernel.org | LWN.net | Project Home | Wiki (Japanese) | Wiki (English) | SVN repository | Mail admin

Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.

osdn.jp