Commit | Line | Data |
---|---|---|
8174c430 NP |
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> | |
8ee53820 | 11 | #include <linux/swap.h> |
8174c430 NP |
12 | |
13 | #include <asm/pgtable.h> | |
14 | ||
15 | static inline pte_t gup_get_pte(pte_t *ptep) | |
16 | { | |
17 | #ifndef CONFIG_X86_PAE | |
14cf3d97 | 18 | return READ_ONCE(*ptep); |
8174c430 NP |
19 | #else |
20 | /* | |
21 | * With get_user_pages_fast, we walk down the pagetables without taking | |
ab09809f | 22 | * any locks. For this we would like to load the pointers atomically, |
8174c430 NP |
23 | * but that is not possible (without expensive cmpxchg8b) on PAE. What |
24 | * we do have is the guarantee that a pte will only either go from not | |
25 | * present to present, or present to not present or both -- it will not | |
26 | * switch to a completely different present page without a TLB flush in | |
27 | * between; something that we are blocking by holding interrupts off. | |
28 | * | |
29 | * Setting ptes from not present to present goes: | |
30 | * ptep->pte_high = h; | |
31 | * smp_wmb(); | |
32 | * ptep->pte_low = l; | |
33 | * | |
34 | * And present to not present goes: | |
35 | * ptep->pte_low = 0; | |
36 | * smp_wmb(); | |
37 | * ptep->pte_high = 0; | |
38 | * | |
39 | * We must ensure here that the load of pte_low sees l iff pte_high | |
40 | * sees h. We load pte_high *after* loading pte_low, which ensures we | |
41 | * don't see an older value of pte_high. *Then* we recheck pte_low, | |
42 | * which ensures that we haven't picked up a changed pte high. We might | |
43 | * have got rubbish values from pte_low and pte_high, but we are | |
44 | * guaranteed that pte_low will not have the present bit set *unless* | |
45 | * it is 'l'. And get_user_pages_fast only operates on present ptes, so | |
46 | * we're safe. | |
47 | * | |
48 | * gup_get_pte should not be used or copied outside gup.c without being | |
49 | * very careful -- it does not atomically load the pte or anything that | |
50 | * is likely to be useful for you. | |
51 | */ | |
52 | pte_t pte; | |
53 | ||
54 | retry: | |
55 | pte.pte_low = ptep->pte_low; | |
56 | smp_rmb(); | |
57 | pte.pte_high = ptep->pte_high; | |
58 | smp_rmb(); | |
59 | if (unlikely(pte.pte_low != ptep->pte_low)) | |
60 | goto retry; | |
61 | ||
62 | return pte; | |
63 | #endif | |
64 | } | |
65 | ||
66 | /* | |
67 | * The performance critical leaf functions are made noinline otherwise gcc | |
68 | * inlines everything into a single function which results in too much | |
69 | * register pressure. | |
70 | */ | |
71 | static noinline int gup_pte_range(pmd_t pmd, unsigned long addr, | |
72 | unsigned long end, int write, struct page **pages, int *nr) | |
73 | { | |
74 | unsigned long mask; | |
75 | pte_t *ptep; | |
76 | ||
77 | mask = _PAGE_PRESENT|_PAGE_USER; | |
78 | if (write) | |
79 | mask |= _PAGE_RW; | |
80 | ||
81 | ptep = pte_offset_map(&pmd, addr); | |
82 | do { | |
83 | pte_t pte = gup_get_pte(ptep); | |
84 | struct page *page; | |
85 | ||
2b4847e7 | 86 | /* Similar to the PMD case, NUMA hinting must take slow path */ |
8a0516ed | 87 | if (pte_protnone(pte)) { |
2b4847e7 MG |
88 | pte_unmap(ptep); |
89 | return 0; | |
90 | } | |
91 | ||
606ee44d | 92 | if ((pte_flags(pte) & (mask | _PAGE_SPECIAL)) != mask) { |
8174c430 NP |
93 | pte_unmap(ptep); |
94 | return 0; | |
95 | } | |
96 | VM_BUG_ON(!pfn_valid(pte_pfn(pte))); | |
97 | page = pte_page(pte); | |
98 | get_page(page); | |
8ee53820 | 99 | SetPageReferenced(page); |
8174c430 NP |
100 | pages[*nr] = page; |
101 | (*nr)++; | |
102 | ||
103 | } while (ptep++, addr += PAGE_SIZE, addr != end); | |
104 | pte_unmap(ptep - 1); | |
105 | ||
106 | return 1; | |
107 | } | |
108 | ||
109 | static inline void get_head_page_multiple(struct page *page, int nr) | |
110 | { | |
309381fe SL |
111 | VM_BUG_ON_PAGE(page != compound_head(page), page); |
112 | VM_BUG_ON_PAGE(page_count(page) == 0, page); | |
8174c430 | 113 | atomic_add(nr, &page->_count); |
8ee53820 | 114 | SetPageReferenced(page); |
8174c430 NP |
115 | } |
116 | ||
117 | static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr, | |
118 | unsigned long end, int write, struct page **pages, int *nr) | |
119 | { | |
120 | unsigned long mask; | |
8174c430 NP |
121 | struct page *head, *page; |
122 | int refs; | |
123 | ||
124 | mask = _PAGE_PRESENT|_PAGE_USER; | |
125 | if (write) | |
126 | mask |= _PAGE_RW; | |
daf3e35c | 127 | if ((pmd_flags(pmd) & mask) != mask) |
8174c430 NP |
128 | return 0; |
129 | /* hugepages are never "special" */ | |
daf3e35c TK |
130 | VM_BUG_ON(pmd_flags(pmd) & _PAGE_SPECIAL); |
131 | VM_BUG_ON(!pfn_valid(pmd_pfn(pmd))); | |
8174c430 NP |
132 | |
133 | refs = 0; | |
daf3e35c | 134 | head = pmd_page(pmd); |
652ea695 | 135 | page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT); |
8174c430 | 136 | do { |
309381fe | 137 | VM_BUG_ON_PAGE(compound_head(page) != head, page); |
8174c430 | 138 | pages[*nr] = page; |
91807063 AA |
139 | if (PageTail(page)) |
140 | get_huge_page_tail(page); | |
8174c430 NP |
141 | (*nr)++; |
142 | page++; | |
143 | refs++; | |
144 | } while (addr += PAGE_SIZE, addr != end); | |
145 | get_head_page_multiple(head, refs); | |
146 | ||
147 | return 1; | |
148 | } | |
149 | ||
150 | static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end, | |
151 | int write, struct page **pages, int *nr) | |
152 | { | |
153 | unsigned long next; | |
154 | pmd_t *pmdp; | |
155 | ||
156 | pmdp = pmd_offset(&pud, addr); | |
157 | do { | |
158 | pmd_t pmd = *pmdp; | |
159 | ||
160 | next = pmd_addr_end(addr, end); | |
64cc6ae0 AA |
161 | /* |
162 | * The pmd_trans_splitting() check below explains why | |
163 | * pmdp_splitting_flush has to flush the tlb, to stop | |
164 | * this gup-fast code from running while we set the | |
165 | * splitting bit in the pmd. Returning zero will take | |
166 | * the slow path that will call wait_split_huge_page() | |
167 | * if the pmd is still in splitting state. gup-fast | |
168 | * can't because it has irq disabled and | |
169 | * wait_split_huge_page() would never return as the | |
170 | * tlb flush IPI wouldn't run. | |
171 | */ | |
172 | if (pmd_none(pmd) || pmd_trans_splitting(pmd)) | |
8174c430 | 173 | return 0; |
cbef8478 | 174 | if (unlikely(pmd_large(pmd) || !pmd_present(pmd))) { |
2b4847e7 MG |
175 | /* |
176 | * NUMA hinting faults need to be handled in the GUP | |
177 | * slowpath for accounting purposes and so that they | |
178 | * can be serialised against THP migration. | |
179 | */ | |
8a0516ed | 180 | if (pmd_protnone(pmd)) |
2b4847e7 | 181 | return 0; |
8174c430 NP |
182 | if (!gup_huge_pmd(pmd, addr, next, write, pages, nr)) |
183 | return 0; | |
184 | } else { | |
185 | if (!gup_pte_range(pmd, addr, next, write, pages, nr)) | |
186 | return 0; | |
187 | } | |
188 | } while (pmdp++, addr = next, addr != end); | |
189 | ||
190 | return 1; | |
191 | } | |
192 | ||
652ea695 NP |
193 | static noinline int gup_huge_pud(pud_t pud, unsigned long addr, |
194 | unsigned long end, int write, struct page **pages, int *nr) | |
195 | { | |
196 | unsigned long mask; | |
652ea695 NP |
197 | struct page *head, *page; |
198 | int refs; | |
199 | ||
200 | mask = _PAGE_PRESENT|_PAGE_USER; | |
201 | if (write) | |
202 | mask |= _PAGE_RW; | |
daf3e35c | 203 | if ((pud_flags(pud) & mask) != mask) |
652ea695 NP |
204 | return 0; |
205 | /* hugepages are never "special" */ | |
daf3e35c TK |
206 | VM_BUG_ON(pud_flags(pud) & _PAGE_SPECIAL); |
207 | VM_BUG_ON(!pfn_valid(pud_pfn(pud))); | |
652ea695 NP |
208 | |
209 | refs = 0; | |
daf3e35c | 210 | head = pud_page(pud); |
652ea695 NP |
211 | page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT); |
212 | do { | |
309381fe | 213 | VM_BUG_ON_PAGE(compound_head(page) != head, page); |
652ea695 | 214 | pages[*nr] = page; |
b6999b19 YS |
215 | if (PageTail(page)) |
216 | get_huge_page_tail(page); | |
652ea695 NP |
217 | (*nr)++; |
218 | page++; | |
219 | refs++; | |
220 | } while (addr += PAGE_SIZE, addr != end); | |
221 | get_head_page_multiple(head, refs); | |
222 | ||
223 | return 1; | |
224 | } | |
225 | ||
8174c430 NP |
226 | static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end, |
227 | int write, struct page **pages, int *nr) | |
228 | { | |
229 | unsigned long next; | |
230 | pud_t *pudp; | |
231 | ||
232 | pudp = pud_offset(&pgd, addr); | |
233 | do { | |
234 | pud_t pud = *pudp; | |
235 | ||
236 | next = pud_addr_end(addr, end); | |
237 | if (pud_none(pud)) | |
238 | return 0; | |
652ea695 NP |
239 | if (unlikely(pud_large(pud))) { |
240 | if (!gup_huge_pud(pud, addr, next, write, pages, nr)) | |
241 | return 0; | |
242 | } else { | |
243 | if (!gup_pmd_range(pud, addr, next, write, pages, nr)) | |
244 | return 0; | |
245 | } | |
8174c430 NP |
246 | } while (pudp++, addr = next, addr != end); |
247 | ||
248 | return 1; | |
249 | } | |
250 | ||
465a454f PZ |
251 | /* |
252 | * Like get_user_pages_fast() except its IRQ-safe in that it won't fall | |
253 | * back to the regular GUP. | |
254 | */ | |
255 | int __get_user_pages_fast(unsigned long start, int nr_pages, int write, | |
256 | struct page **pages) | |
257 | { | |
258 | struct mm_struct *mm = current->mm; | |
259 | unsigned long addr, len, end; | |
260 | unsigned long next; | |
261 | unsigned long flags; | |
262 | pgd_t *pgdp; | |
263 | int nr = 0; | |
264 | ||
265 | start &= PAGE_MASK; | |
266 | addr = start; | |
267 | len = (unsigned long) nr_pages << PAGE_SHIFT; | |
268 | end = start + len; | |
269 | if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ, | |
270 | (void __user *)start, len))) | |
271 | return 0; | |
272 | ||
273 | /* | |
274 | * XXX: batch / limit 'nr', to avoid large irq off latency | |
275 | * needs some instrumenting to determine the common sizes used by | |
276 | * important workloads (eg. DB2), and whether limiting the batch size | |
277 | * will decrease performance. | |
278 | * | |
279 | * It seems like we're in the clear for the moment. Direct-IO is | |
280 | * the main guy that batches up lots of get_user_pages, and even | |
281 | * they are limited to 64-at-a-time which is not so many. | |
282 | */ | |
283 | /* | |
284 | * This doesn't prevent pagetable teardown, but does prevent | |
285 | * the pagetables and pages from being freed on x86. | |
286 | * | |
287 | * So long as we atomically load page table pointers versus teardown | |
288 | * (which we do on x86, with the above PAE exception), we can follow the | |
289 | * address down to the the page and take a ref on it. | |
290 | */ | |
291 | local_irq_save(flags); | |
292 | pgdp = pgd_offset(mm, addr); | |
293 | do { | |
294 | pgd_t pgd = *pgdp; | |
295 | ||
296 | next = pgd_addr_end(addr, end); | |
297 | if (pgd_none(pgd)) | |
298 | break; | |
299 | if (!gup_pud_range(pgd, addr, next, write, pages, &nr)) | |
300 | break; | |
301 | } while (pgdp++, addr = next, addr != end); | |
302 | local_irq_restore(flags); | |
303 | ||
304 | return nr; | |
305 | } | |
306 | ||
a0d22f48 AG |
307 | /** |
308 | * get_user_pages_fast() - pin user pages in memory | |
309 | * @start: starting user address | |
310 | * @nr_pages: number of pages from start to pin | |
311 | * @write: whether pages will be written to | |
312 | * @pages: array that receives pointers to the pages pinned. | |
313 | * Should be at least nr_pages long. | |
314 | * | |
315 | * Attempt to pin user pages in memory without taking mm->mmap_sem. | |
316 | * If not successful, it will fall back to taking the lock and | |
317 | * calling get_user_pages(). | |
318 | * | |
319 | * Returns number of pages pinned. This may be fewer than the number | |
320 | * requested. If nr_pages is 0 or negative, returns 0. If no pages | |
321 | * were pinned, returns -errno. | |
322 | */ | |
8174c430 NP |
323 | int get_user_pages_fast(unsigned long start, int nr_pages, int write, |
324 | struct page **pages) | |
325 | { | |
326 | struct mm_struct *mm = current->mm; | |
9b79022c | 327 | unsigned long addr, len, end; |
8174c430 NP |
328 | unsigned long next; |
329 | pgd_t *pgdp; | |
330 | int nr = 0; | |
331 | ||
9b79022c LT |
332 | start &= PAGE_MASK; |
333 | addr = start; | |
334 | len = (unsigned long) nr_pages << PAGE_SHIFT; | |
7f818906 | 335 | |
9b79022c | 336 | end = start + len; |
7f818906 LT |
337 | if (end < start) |
338 | goto slow_irqon; | |
339 | ||
340 | #ifdef CONFIG_X86_64 | |
341 | if (end >> __VIRTUAL_MASK_SHIFT) | |
8174c430 | 342 | goto slow_irqon; |
7f818906 | 343 | #endif |
8174c430 NP |
344 | |
345 | /* | |
346 | * XXX: batch / limit 'nr', to avoid large irq off latency | |
347 | * needs some instrumenting to determine the common sizes used by | |
348 | * important workloads (eg. DB2), and whether limiting the batch size | |
349 | * will decrease performance. | |
350 | * | |
351 | * It seems like we're in the clear for the moment. Direct-IO is | |
352 | * the main guy that batches up lots of get_user_pages, and even | |
353 | * they are limited to 64-at-a-time which is not so many. | |
354 | */ | |
355 | /* | |
356 | * This doesn't prevent pagetable teardown, but does prevent | |
357 | * the pagetables and pages from being freed on x86. | |
358 | * | |
359 | * So long as we atomically load page table pointers versus teardown | |
360 | * (which we do on x86, with the above PAE exception), we can follow the | |
361 | * address down to the the page and take a ref on it. | |
362 | */ | |
363 | local_irq_disable(); | |
364 | pgdp = pgd_offset(mm, addr); | |
365 | do { | |
366 | pgd_t pgd = *pgdp; | |
367 | ||
368 | next = pgd_addr_end(addr, end); | |
369 | if (pgd_none(pgd)) | |
370 | goto slow; | |
371 | if (!gup_pud_range(pgd, addr, next, write, pages, &nr)) | |
372 | goto slow; | |
373 | } while (pgdp++, addr = next, addr != end); | |
374 | local_irq_enable(); | |
375 | ||
376 | VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT); | |
377 | return nr; | |
378 | ||
379 | { | |
380 | int ret; | |
381 | ||
382 | slow: | |
383 | local_irq_enable(); | |
384 | slow_irqon: | |
385 | /* Try to get the remaining pages with get_user_pages */ | |
386 | start += nr << PAGE_SHIFT; | |
387 | pages += nr; | |
388 | ||
a7b78075 AA |
389 | ret = get_user_pages_unlocked(current, mm, start, |
390 | (end - start) >> PAGE_SHIFT, | |
391 | write, 0, pages); | |
8174c430 NP |
392 | |
393 | /* Have to be a bit careful with return values */ | |
394 | if (nr > 0) { | |
395 | if (ret < 0) | |
396 | ret = nr; | |
397 | else | |
398 | ret += nr; | |
399 | } | |
400 | ||
401 | return ret; | |
402 | } | |
403 | } |