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Linux/mm/hmm.c

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  1 // SPDX-License-Identifier: GPL-2.0-or-later
  2 /*
  3  * Copyright 2013 Red Hat Inc.
  4  *
  5  * Authors: Jérôme Glisse <jglisse@redhat.com>
  6  */
  7 /*
  8  * Refer to include/linux/hmm.h for information about heterogeneous memory
  9  * management or HMM for short.
 10  */
 11 #include <linux/pagewalk.h>
 12 #include <linux/hmm.h>
 13 #include <linux/init.h>
 14 #include <linux/rmap.h>
 15 #include <linux/swap.h>
 16 #include <linux/slab.h>
 17 #include <linux/sched.h>
 18 #include <linux/mmzone.h>
 19 #include <linux/pagemap.h>
 20 #include <linux/swapops.h>
 21 #include <linux/hugetlb.h>
 22 #include <linux/memremap.h>
 23 #include <linux/sched/mm.h>
 24 #include <linux/jump_label.h>
 25 #include <linux/dma-mapping.h>
 26 #include <linux/mmu_notifier.h>
 27 #include <linux/memory_hotplug.h>
 28 
 29 #include "internal.h"
 30 
 31 struct hmm_vma_walk {
 32         struct hmm_range        *range;
 33         unsigned long           last;
 34 };
 35 
 36 enum {
 37         HMM_NEED_FAULT = 1 << 0,
 38         HMM_NEED_WRITE_FAULT = 1 << 1,
 39         HMM_NEED_ALL_BITS = HMM_NEED_FAULT | HMM_NEED_WRITE_FAULT,
 40 };
 41 
 42 static int hmm_pfns_fill(unsigned long addr, unsigned long end,
 43                          struct hmm_range *range, unsigned long cpu_flags)
 44 {
 45         unsigned long i = (addr - range->start) >> PAGE_SHIFT;
 46 
 47         for (; addr < end; addr += PAGE_SIZE, i++)
 48                 range->hmm_pfns[i] = cpu_flags;
 49         return 0;
 50 }
 51 
 52 /*
 53  * hmm_vma_fault() - fault in a range lacking valid pmd or pte(s)
 54  * @addr: range virtual start address (inclusive)
 55  * @end: range virtual end address (exclusive)
 56  * @required_fault: HMM_NEED_* flags
 57  * @walk: mm_walk structure
 58  * Return: -EBUSY after page fault, or page fault error
 59  *
 60  * This function will be called whenever pmd_none() or pte_none() returns true,
 61  * or whenever there is no page directory covering the virtual address range.
 62  */
 63 static int hmm_vma_fault(unsigned long addr, unsigned long end,
 64                          unsigned int required_fault, struct mm_walk *walk)
 65 {
 66         struct hmm_vma_walk *hmm_vma_walk = walk->private;
 67         struct vm_area_struct *vma = walk->vma;
 68         unsigned int fault_flags = FAULT_FLAG_REMOTE;
 69 
 70         WARN_ON_ONCE(!required_fault);
 71         hmm_vma_walk->last = addr;
 72 
 73         if (required_fault & HMM_NEED_WRITE_FAULT) {
 74                 if (!(vma->vm_flags & VM_WRITE))
 75                         return -EPERM;
 76                 fault_flags |= FAULT_FLAG_WRITE;
 77         }
 78 
 79         for (; addr < end; addr += PAGE_SIZE)
 80                 if (handle_mm_fault(vma, addr, fault_flags, NULL) &
 81                     VM_FAULT_ERROR)
 82                         return -EFAULT;
 83         return -EBUSY;
 84 }
 85 
 86 static unsigned int hmm_pte_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
 87                                        unsigned long pfn_req_flags,
 88                                        unsigned long cpu_flags)
 89 {
 90         struct hmm_range *range = hmm_vma_walk->range;
 91 
 92         /*
 93          * So we not only consider the individual per page request we also
 94          * consider the default flags requested for the range. The API can
 95          * be used 2 ways. The first one where the HMM user coalesces
 96          * multiple page faults into one request and sets flags per pfn for
 97          * those faults. The second one where the HMM user wants to pre-
 98          * fault a range with specific flags. For the latter one it is a
 99          * waste to have the user pre-fill the pfn arrays with a default
100          * flags value.
101          */
102         pfn_req_flags &= range->pfn_flags_mask;
103         pfn_req_flags |= range->default_flags;
104 
105         /* We aren't ask to do anything ... */
106         if (!(pfn_req_flags & HMM_PFN_REQ_FAULT))
107                 return 0;
108 
109         /* Need to write fault ? */
110         if ((pfn_req_flags & HMM_PFN_REQ_WRITE) &&
111             !(cpu_flags & HMM_PFN_WRITE))
112                 return HMM_NEED_FAULT | HMM_NEED_WRITE_FAULT;
113 
114         /* If CPU page table is not valid then we need to fault */
115         if (!(cpu_flags & HMM_PFN_VALID))
116                 return HMM_NEED_FAULT;
117         return 0;
118 }
119 
120 static unsigned int
121 hmm_range_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
122                      const unsigned long hmm_pfns[], unsigned long npages,
123                      unsigned long cpu_flags)
124 {
125         struct hmm_range *range = hmm_vma_walk->range;
126         unsigned int required_fault = 0;
127         unsigned long i;
128 
129         /*
130          * If the default flags do not request to fault pages, and the mask does
131          * not allow for individual pages to be faulted, then
132          * hmm_pte_need_fault() will always return 0.
133          */
134         if (!((range->default_flags | range->pfn_flags_mask) &
135               HMM_PFN_REQ_FAULT))
136                 return 0;
137 
138         for (i = 0; i < npages; ++i) {
139                 required_fault |= hmm_pte_need_fault(hmm_vma_walk, hmm_pfns[i],
140                                                      cpu_flags);
141                 if (required_fault == HMM_NEED_ALL_BITS)
142                         return required_fault;
143         }
144         return required_fault;
145 }
146 
147 static int hmm_vma_walk_hole(unsigned long addr, unsigned long end,
148                              __always_unused int depth, struct mm_walk *walk)
149 {
150         struct hmm_vma_walk *hmm_vma_walk = walk->private;
151         struct hmm_range *range = hmm_vma_walk->range;
152         unsigned int required_fault;
153         unsigned long i, npages;
154         unsigned long *hmm_pfns;
155 
156         i = (addr - range->start) >> PAGE_SHIFT;
157         npages = (end - addr) >> PAGE_SHIFT;
158         hmm_pfns = &range->hmm_pfns[i];
159         required_fault =
160                 hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0);
161         if (!walk->vma) {
162                 if (required_fault)
163                         return -EFAULT;
164                 return hmm_pfns_fill(addr, end, range, HMM_PFN_ERROR);
165         }
166         if (required_fault)
167                 return hmm_vma_fault(addr, end, required_fault, walk);
168         return hmm_pfns_fill(addr, end, range, 0);
169 }
170 
171 static inline unsigned long hmm_pfn_flags_order(unsigned long order)
172 {
173         return order << HMM_PFN_ORDER_SHIFT;
174 }
175 
176 static inline unsigned long pmd_to_hmm_pfn_flags(struct hmm_range *range,
177                                                  pmd_t pmd)
178 {
179         if (pmd_protnone(pmd))
180                 return 0;
181         return (pmd_write(pmd) ? (HMM_PFN_VALID | HMM_PFN_WRITE) :
182                                  HMM_PFN_VALID) |
183                hmm_pfn_flags_order(PMD_SHIFT - PAGE_SHIFT);
184 }
185 
186 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
187 static int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr,
188                               unsigned long end, unsigned long hmm_pfns[],
189                               pmd_t pmd)
190 {
191         struct hmm_vma_walk *hmm_vma_walk = walk->private;
192         struct hmm_range *range = hmm_vma_walk->range;
193         unsigned long pfn, npages, i;
194         unsigned int required_fault;
195         unsigned long cpu_flags;
196 
197         npages = (end - addr) >> PAGE_SHIFT;
198         cpu_flags = pmd_to_hmm_pfn_flags(range, pmd);
199         required_fault =
200                 hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, cpu_flags);
201         if (required_fault)
202                 return hmm_vma_fault(addr, end, required_fault, walk);
203 
204         pfn = pmd_pfn(pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
205         for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++)
206                 hmm_pfns[i] = pfn | cpu_flags;
207         return 0;
208 }
209 #else /* CONFIG_TRANSPARENT_HUGEPAGE */
210 /* stub to allow the code below to compile */
211 int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr,
212                 unsigned long end, unsigned long hmm_pfns[], pmd_t pmd);
213 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
214 
215 static inline bool hmm_is_device_private_entry(struct hmm_range *range,
216                 swp_entry_t entry)
217 {
218         return is_device_private_entry(entry) &&
219                 pfn_swap_entry_to_page(entry)->pgmap->owner ==
220                 range->dev_private_owner;
221 }
222 
223 static inline unsigned long pte_to_hmm_pfn_flags(struct hmm_range *range,
224                                                  pte_t pte)
225 {
226         if (pte_none(pte) || !pte_present(pte) || pte_protnone(pte))
227                 return 0;
228         return pte_write(pte) ? (HMM_PFN_VALID | HMM_PFN_WRITE) : HMM_PFN_VALID;
229 }
230 
231 static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
232                               unsigned long end, pmd_t *pmdp, pte_t *ptep,
233                               unsigned long *hmm_pfn)
234 {
235         struct hmm_vma_walk *hmm_vma_walk = walk->private;
236         struct hmm_range *range = hmm_vma_walk->range;
237         unsigned int required_fault;
238         unsigned long cpu_flags;
239         pte_t pte = *ptep;
240         uint64_t pfn_req_flags = *hmm_pfn;
241 
242         if (pte_none(pte)) {
243                 required_fault =
244                         hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0);
245                 if (required_fault)
246                         goto fault;
247                 *hmm_pfn = 0;
248                 return 0;
249         }
250 
251         if (!pte_present(pte)) {
252                 swp_entry_t entry = pte_to_swp_entry(pte);
253 
254                 /*
255                  * Never fault in device private pages, but just report
256                  * the PFN even if not present.
257                  */
258                 if (hmm_is_device_private_entry(range, entry)) {
259                         cpu_flags = HMM_PFN_VALID;
260                         if (is_writable_device_private_entry(entry))
261                                 cpu_flags |= HMM_PFN_WRITE;
262                         *hmm_pfn = swp_offset(entry) | cpu_flags;
263                         return 0;
264                 }
265 
266                 required_fault =
267                         hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0);
268                 if (!required_fault) {
269                         *hmm_pfn = 0;
270                         return 0;
271                 }
272 
273                 if (!non_swap_entry(entry))
274                         goto fault;
275 
276                 if (is_device_exclusive_entry(entry))
277                         goto fault;
278 
279                 if (is_migration_entry(entry)) {
280                         pte_unmap(ptep);
281                         hmm_vma_walk->last = addr;
282                         migration_entry_wait(walk->mm, pmdp, addr);
283                         return -EBUSY;
284                 }
285 
286                 /* Report error for everything else */
287                 pte_unmap(ptep);
288                 return -EFAULT;
289         }
290 
291         cpu_flags = pte_to_hmm_pfn_flags(range, pte);
292         required_fault =
293                 hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, cpu_flags);
294         if (required_fault)
295                 goto fault;
296 
297         /*
298          * Bypass devmap pte such as DAX page when all pfn requested
299          * flags(pfn_req_flags) are fulfilled.
300          * Since each architecture defines a struct page for the zero page, just
301          * fall through and treat it like a normal page.
302          */
303         if (pte_special(pte) && !pte_devmap(pte) &&
304             !is_zero_pfn(pte_pfn(pte))) {
305                 if (hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0)) {
306                         pte_unmap(ptep);
307                         return -EFAULT;
308                 }
309                 *hmm_pfn = HMM_PFN_ERROR;
310                 return 0;
311         }
312 
313         *hmm_pfn = pte_pfn(pte) | cpu_flags;
314         return 0;
315 
316 fault:
317         pte_unmap(ptep);
318         /* Fault any virtual address we were asked to fault */
319         return hmm_vma_fault(addr, end, required_fault, walk);
320 }
321 
322 static int hmm_vma_walk_pmd(pmd_t *pmdp,
323                             unsigned long start,
324                             unsigned long end,
325                             struct mm_walk *walk)
326 {
327         struct hmm_vma_walk *hmm_vma_walk = walk->private;
328         struct hmm_range *range = hmm_vma_walk->range;
329         unsigned long *hmm_pfns =
330                 &range->hmm_pfns[(start - range->start) >> PAGE_SHIFT];
331         unsigned long npages = (end - start) >> PAGE_SHIFT;
332         unsigned long addr = start;
333         pte_t *ptep;
334         pmd_t pmd;
335 
336 again:
337         pmd = READ_ONCE(*pmdp);
338         if (pmd_none(pmd))
339                 return hmm_vma_walk_hole(start, end, -1, walk);
340 
341         if (thp_migration_supported() && is_pmd_migration_entry(pmd)) {
342                 if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0)) {
343                         hmm_vma_walk->last = addr;
344                         pmd_migration_entry_wait(walk->mm, pmdp);
345                         return -EBUSY;
346                 }
347                 return hmm_pfns_fill(start, end, range, 0);
348         }
349 
350         if (!pmd_present(pmd)) {
351                 if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0))
352                         return -EFAULT;
353                 return hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);
354         }
355 
356         if (pmd_devmap(pmd) || pmd_trans_huge(pmd)) {
357                 /*
358                  * No need to take pmd_lock here, even if some other thread
359                  * is splitting the huge pmd we will get that event through
360                  * mmu_notifier callback.
361                  *
362                  * So just read pmd value and check again it's a transparent
363                  * huge or device mapping one and compute corresponding pfn
364                  * values.
365                  */
366                 pmd = pmd_read_atomic(pmdp);
367                 barrier();
368                 if (!pmd_devmap(pmd) && !pmd_trans_huge(pmd))
369                         goto again;
370 
371                 return hmm_vma_handle_pmd(walk, addr, end, hmm_pfns, pmd);
372         }
373 
374         /*
375          * We have handled all the valid cases above ie either none, migration,
376          * huge or transparent huge. At this point either it is a valid pmd
377          * entry pointing to pte directory or it is a bad pmd that will not
378          * recover.
379          */
380         if (pmd_bad(pmd)) {
381                 if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0))
382                         return -EFAULT;
383                 return hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);
384         }
385 
386         ptep = pte_offset_map(pmdp, addr);
387         for (; addr < end; addr += PAGE_SIZE, ptep++, hmm_pfns++) {
388                 int r;
389 
390                 r = hmm_vma_handle_pte(walk, addr, end, pmdp, ptep, hmm_pfns);
391                 if (r) {
392                         /* hmm_vma_handle_pte() did pte_unmap() */
393                         return r;
394                 }
395         }
396         pte_unmap(ptep - 1);
397         return 0;
398 }
399 
400 #if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && \
401     defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
402 static inline unsigned long pud_to_hmm_pfn_flags(struct hmm_range *range,
403                                                  pud_t pud)
404 {
405         if (!pud_present(pud))
406                 return 0;
407         return (pud_write(pud) ? (HMM_PFN_VALID | HMM_PFN_WRITE) :
408                                  HMM_PFN_VALID) |
409                hmm_pfn_flags_order(PUD_SHIFT - PAGE_SHIFT);
410 }
411 
412 static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
413                 struct mm_walk *walk)
414 {
415         struct hmm_vma_walk *hmm_vma_walk = walk->private;
416         struct hmm_range *range = hmm_vma_walk->range;
417         unsigned long addr = start;
418         pud_t pud;
419         int ret = 0;
420         spinlock_t *ptl = pud_trans_huge_lock(pudp, walk->vma);
421 
422         if (!ptl)
423                 return 0;
424 
425         /* Normally we don't want to split the huge page */
426         walk->action = ACTION_CONTINUE;
427 
428         pud = READ_ONCE(*pudp);
429         if (pud_none(pud)) {
430                 spin_unlock(ptl);
431                 return hmm_vma_walk_hole(start, end, -1, walk);
432         }
433 
434         if (pud_huge(pud) && pud_devmap(pud)) {
435                 unsigned long i, npages, pfn;
436                 unsigned int required_fault;
437                 unsigned long *hmm_pfns;
438                 unsigned long cpu_flags;
439 
440                 if (!pud_present(pud)) {
441                         spin_unlock(ptl);
442                         return hmm_vma_walk_hole(start, end, -1, walk);
443                 }
444 
445                 i = (addr - range->start) >> PAGE_SHIFT;
446                 npages = (end - addr) >> PAGE_SHIFT;
447                 hmm_pfns = &range->hmm_pfns[i];
448 
449                 cpu_flags = pud_to_hmm_pfn_flags(range, pud);
450                 required_fault = hmm_range_need_fault(hmm_vma_walk, hmm_pfns,
451                                                       npages, cpu_flags);
452                 if (required_fault) {
453                         spin_unlock(ptl);
454                         return hmm_vma_fault(addr, end, required_fault, walk);
455                 }
456 
457                 pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
458                 for (i = 0; i < npages; ++i, ++pfn)
459                         hmm_pfns[i] = pfn | cpu_flags;
460                 goto out_unlock;
461         }
462 
463         /* Ask for the PUD to be split */
464         walk->action = ACTION_SUBTREE;
465 
466 out_unlock:
467         spin_unlock(ptl);
468         return ret;
469 }
470 #else
471 #define hmm_vma_walk_pud        NULL
472 #endif
473 
474 #ifdef CONFIG_HUGETLB_PAGE
475 static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
476                                       unsigned long start, unsigned long end,
477                                       struct mm_walk *walk)
478 {
479         unsigned long addr = start, i, pfn;
480         struct hmm_vma_walk *hmm_vma_walk = walk->private;
481         struct hmm_range *range = hmm_vma_walk->range;
482         struct vm_area_struct *vma = walk->vma;
483         unsigned int required_fault;
484         unsigned long pfn_req_flags;
485         unsigned long cpu_flags;
486         spinlock_t *ptl;
487         pte_t entry;
488 
489         ptl = huge_pte_lock(hstate_vma(vma), walk->mm, pte);
490         entry = huge_ptep_get(pte);
491 
492         i = (start - range->start) >> PAGE_SHIFT;
493         pfn_req_flags = range->hmm_pfns[i];
494         cpu_flags = pte_to_hmm_pfn_flags(range, entry) |
495                     hmm_pfn_flags_order(huge_page_order(hstate_vma(vma)));
496         required_fault =
497                 hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, cpu_flags);
498         if (required_fault) {
499                 spin_unlock(ptl);
500                 return hmm_vma_fault(addr, end, required_fault, walk);
501         }
502 
503         pfn = pte_pfn(entry) + ((start & ~hmask) >> PAGE_SHIFT);
504         for (; addr < end; addr += PAGE_SIZE, i++, pfn++)
505                 range->hmm_pfns[i] = pfn | cpu_flags;
506 
507         spin_unlock(ptl);
508         return 0;
509 }
510 #else
511 #define hmm_vma_walk_hugetlb_entry NULL
512 #endif /* CONFIG_HUGETLB_PAGE */
513 
514 static int hmm_vma_walk_test(unsigned long start, unsigned long end,
515                              struct mm_walk *walk)
516 {
517         struct hmm_vma_walk *hmm_vma_walk = walk->private;
518         struct hmm_range *range = hmm_vma_walk->range;
519         struct vm_area_struct *vma = walk->vma;
520 
521         if (!(vma->vm_flags & (VM_IO | VM_PFNMAP | VM_MIXEDMAP)) &&
522             vma->vm_flags & VM_READ)
523                 return 0;
524 
525         /*
526          * vma ranges that don't have struct page backing them or map I/O
527          * devices directly cannot be handled by hmm_range_fault().
528          *
529          * If the vma does not allow read access, then assume that it does not
530          * allow write access either. HMM does not support architectures that
531          * allow write without read.
532          *
533          * If a fault is requested for an unsupported range then it is a hard
534          * failure.
535          */
536         if (hmm_range_need_fault(hmm_vma_walk,
537                                  range->hmm_pfns +
538                                          ((start - range->start) >> PAGE_SHIFT),
539                                  (end - start) >> PAGE_SHIFT, 0))
540                 return -EFAULT;
541 
542         hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);
543 
544         /* Skip this vma and continue processing the next vma. */
545         return 1;
546 }
547 
548 static const struct mm_walk_ops hmm_walk_ops = {
549         .pud_entry      = hmm_vma_walk_pud,
550         .pmd_entry      = hmm_vma_walk_pmd,
551         .pte_hole       = hmm_vma_walk_hole,
552         .hugetlb_entry  = hmm_vma_walk_hugetlb_entry,
553         .test_walk      = hmm_vma_walk_test,
554 };
555 
556 /**
557  * hmm_range_fault - try to fault some address in a virtual address range
558  * @range:      argument structure
559  *
560  * Returns 0 on success or one of the following error codes:
561  *
562  * -EINVAL:     Invalid arguments or mm or virtual address is in an invalid vma
563  *              (e.g., device file vma).
564  * -ENOMEM:     Out of memory.
565  * -EPERM:      Invalid permission (e.g., asking for write and range is read
566  *              only).
567  * -EBUSY:      The range has been invalidated and the caller needs to wait for
568  *              the invalidation to finish.
569  * -EFAULT:     A page was requested to be valid and could not be made valid
570  *              ie it has no backing VMA or it is illegal to access
571  *
572  * This is similar to get_user_pages(), except that it can read the page tables
573  * without mutating them (ie causing faults).
574  */
575 int hmm_range_fault(struct hmm_range *range)
576 {
577         struct hmm_vma_walk hmm_vma_walk = {
578                 .range = range,
579                 .last = range->start,
580         };
581         struct mm_struct *mm = range->notifier->mm;
582         int ret;
583 
584         mmap_assert_locked(mm);
585 
586         do {
587                 /* If range is no longer valid force retry. */
588                 if (mmu_interval_check_retry(range->notifier,
589                                              range->notifier_seq))
590                         return -EBUSY;
591                 ret = walk_page_range(mm, hmm_vma_walk.last, range->end,
592                                       &hmm_walk_ops, &hmm_vma_walk);
593                 /*
594                  * When -EBUSY is returned the loop restarts with
595                  * hmm_vma_walk.last set to an address that has not been stored
596                  * in pfns. All entries < last in the pfn array are set to their
597                  * output, and all >= are still at their input values.
598                  */
599         } while (ret == -EBUSY);
600         return ret;
601 }
602 EXPORT_SYMBOL(hmm_range_fault);
603 

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