mm/hmm.c

   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          * Since each architecture defines a struct page for the zero page, just
 299          * fall through and treat it like a normal page.
 300          */
 301         if (pte_special(pte) && !is_zero_pfn(pte_pfn(pte))) {
 302                 if (hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0)) {
 303                         pte_unmap(ptep);
 304                         return -EFAULT;
 305                 }
 306                 *hmm_pfn = HMM_PFN_ERROR;
 307                 return 0;
 308         }
 309
 310         *hmm_pfn = pte_pfn(pte) | cpu_flags;
 311         return 0;
 312
 313 fault:
 314         pte_unmap(ptep);
 315         /* Fault any virtual address we were asked to fault */
 316         return hmm_vma_fault(addr, end, required_fault, walk);
 317 }
 318
 319 static int hmm_vma_walk_pmd(pmd_t *pmdp,
 320                             unsigned long start,
 321                             unsigned long end,
 322                             struct mm_walk *walk)
 323 {
 324         struct hmm_vma_walk *hmm_vma_walk = walk->private;
 325         struct hmm_range *range = hmm_vma_walk->range;
 326         unsigned long *hmm_pfns =
 327                 &range->hmm_pfns[(start - range->start) >> PAGE_SHIFT];
 328         unsigned long npages = (end - start) >> PAGE_SHIFT;
 329         unsigned long addr = start;
 330         pte_t *ptep;
 331         pmd_t pmd;
 332
 333 again:
 334         pmd = READ_ONCE(*pmdp);
 335         if (pmd_none(pmd))
 336                 return hmm_vma_walk_hole(start, end, -1, walk);
 337
 338         if (thp_migration_supported() && is_pmd_migration_entry(pmd)) {
 339                 if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0)) {
 340                         hmm_vma_walk->last = addr;
 341                         pmd_migration_entry_wait(walk->mm, pmdp);
 342                         return -EBUSY;
 343                 }
 344                 return hmm_pfns_fill(start, end, range, 0);
 345         }
 346
 347         if (!pmd_present(pmd)) {
 348                 if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0))
 349                         return -EFAULT;
 350                 return hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);
 351         }
 352
 353         if (pmd_devmap(pmd) || pmd_trans_huge(pmd)) {
 354                 /*
 355                  * No need to take pmd_lock here, even if some other thread
 356                  * is splitting the huge pmd we will get that event through
 357                  * mmu_notifier callback.
 358                  *
 359                  * So just read pmd value and check again it's a transparent
 360                  * huge or device mapping one and compute corresponding pfn
 361                  * values.
 362                  */
 363                 pmd = pmd_read_atomic(pmdp);
 364                 barrier();
 365                 if (!pmd_devmap(pmd) && !pmd_trans_huge(pmd))
 366                         goto again;
 367
 368                 return hmm_vma_handle_pmd(walk, addr, end, hmm_pfns, pmd);
 369         }
 370
 371         /*
 372          * We have handled all the valid cases above ie either none, migration,
 373          * huge or transparent huge. At this point either it is a valid pmd
 374          * entry pointing to pte directory or it is a bad pmd that will not
 375          * recover.
 376          */
 377         if (pmd_bad(pmd)) {
 378                 if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0))
 379                         return -EFAULT;
 380                 return hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);
 381         }
 382
 383         ptep = pte_offset_map(pmdp, addr);
 384         for (; addr < end; addr += PAGE_SIZE, ptep++, hmm_pfns++) {
 385                 int r;
 386
 387                 r = hmm_vma_handle_pte(walk, addr, end, pmdp, ptep, hmm_pfns);
 388                 if (r) {
 389                         /* hmm_vma_handle_pte() did pte_unmap() */
 390                         return r;
 391                 }
 392         }
 393         pte_unmap(ptep - 1);
 394         return 0;
 395 }
 396
 397 #if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && \
 398     defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
 399 static inline unsigned long pud_to_hmm_pfn_flags(struct hmm_range *range,
 400                                                  pud_t pud)
 401 {
 402         if (!pud_present(pud))
 403                 return 0;
 404         return (pud_write(pud) ? (HMM_PFN_VALID | HMM_PFN_WRITE) :
 405                                  HMM_PFN_VALID) |
 406                hmm_pfn_flags_order(PUD_SHIFT - PAGE_SHIFT);
 407 }
 408
 409 static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
 410                 struct mm_walk *walk)
 411 {
 412         struct hmm_vma_walk *hmm_vma_walk = walk->private;
 413         struct hmm_range *range = hmm_vma_walk->range;
 414         unsigned long addr = start;
 415         pud_t pud;
 416         int ret = 0;
 417         spinlock_t *ptl = pud_trans_huge_lock(pudp, walk->vma);
 418
 419         if (!ptl)
 420                 return 0;
 421
 422         /* Normally we don't want to split the huge page */
 423         walk->action = ACTION_CONTINUE;
 424
 425         pud = READ_ONCE(*pudp);
 426         if (pud_none(pud)) {
 427                 spin_unlock(ptl);
 428                 return hmm_vma_walk_hole(start, end, -1, walk);
 429         }
 430
 431         if (pud_huge(pud) && pud_devmap(pud)) {
 432                 unsigned long i, npages, pfn;
 433                 unsigned int required_fault;
 434                 unsigned long *hmm_pfns;
 435                 unsigned long cpu_flags;
 436
 437                 if (!pud_present(pud)) {
 438                         spin_unlock(ptl);
 439                         return hmm_vma_walk_hole(start, end, -1, walk);
 440                 }
 441
 442                 i = (addr - range->start) >> PAGE_SHIFT;
 443                 npages = (end - addr) >> PAGE_SHIFT;
 444                 hmm_pfns = &range->hmm_pfns[i];
 445
 446                 cpu_flags = pud_to_hmm_pfn_flags(range, pud);
 447                 required_fault = hmm_range_need_fault(hmm_vma_walk, hmm_pfns,
 448                                                       npages, cpu_flags);
 449                 if (required_fault) {
 450                         spin_unlock(ptl);
 451                         return hmm_vma_fault(addr, end, required_fault, walk);
 452                 }
 453
 454                 pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
 455                 for (i = 0; i < npages; ++i, ++pfn)
 456                         hmm_pfns[i] = pfn | cpu_flags;
 457                 goto out_unlock;
 458         }
 459
 460         /* Ask for the PUD to be split */
 461         walk->action = ACTION_SUBTREE;
 462
 463 out_unlock:
 464         spin_unlock(ptl);
 465         return ret;
 466 }
 467 #else
 468 #define hmm_vma_walk_pud        NULL
 469 #endif
 470
 471 #ifdef CONFIG_HUGETLB_PAGE
 472 static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
 473                                       unsigned long start, unsigned long end,
 474                                       struct mm_walk *walk)
 475 {
 476         unsigned long addr = start, i, pfn;
 477         struct hmm_vma_walk *hmm_vma_walk = walk->private;
 478         struct hmm_range *range = hmm_vma_walk->range;
 479         struct vm_area_struct *vma = walk->vma;
 480         unsigned int required_fault;
 481         unsigned long pfn_req_flags;
 482         unsigned long cpu_flags;
 483         spinlock_t *ptl;
 484         pte_t entry;
 485
 486         ptl = huge_pte_lock(hstate_vma(vma), walk->mm, pte);
 487         entry = huge_ptep_get(pte);
 488
 489         i = (start - range->start) >> PAGE_SHIFT;
 490         pfn_req_flags = range->hmm_pfns[i];
 491         cpu_flags = pte_to_hmm_pfn_flags(range, entry) |
 492                     hmm_pfn_flags_order(huge_page_order(hstate_vma(vma)));
 493         required_fault =
 494                 hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, cpu_flags);
 495         if (required_fault) {
 496                 spin_unlock(ptl);
 497                 return hmm_vma_fault(addr, end, required_fault, walk);
 498         }
 499
 500         pfn = pte_pfn(entry) + ((start & ~hmask) >> PAGE_SHIFT);
 501         for (; addr < end; addr += PAGE_SIZE, i++, pfn++)
 502                 range->hmm_pfns[i] = pfn | cpu_flags;
 503
 504         spin_unlock(ptl);
 505         return 0;
 506 }
 507 #else
 508 #define hmm_vma_walk_hugetlb_entry NULL
 509 #endif /* CONFIG_HUGETLB_PAGE */
 510
 511 static int hmm_vma_walk_test(unsigned long start, unsigned long end,
 512                              struct mm_walk *walk)
 513 {
 514         struct hmm_vma_walk *hmm_vma_walk = walk->private;
 515         struct hmm_range *range = hmm_vma_walk->range;
 516         struct vm_area_struct *vma = walk->vma;
 517
 518         if (!(vma->vm_flags & (VM_IO | VM_PFNMAP | VM_MIXEDMAP)) &&
 519             vma->vm_flags & VM_READ)
 520                 return 0;
 521
 522         /*
 523          * vma ranges that don't have struct page backing them or map I/O
 524          * devices directly cannot be handled by hmm_range_fault().
 525          *
 526          * If the vma does not allow read access, then assume that it does not
 527          * allow write access either. HMM does not support architectures that
 528          * allow write without read.
 529          *
 530          * If a fault is requested for an unsupported range then it is a hard
 531          * failure.
 532          */
 533         if (hmm_range_need_fault(hmm_vma_walk,
 534                                  range->hmm_pfns +
 535                                          ((start - range->start) >> PAGE_SHIFT),
 536                                  (end - start) >> PAGE_SHIFT, 0))
 537                 return -EFAULT;
 538
 539         hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);
 540
 541         /* Skip this vma and continue processing the next vma. */
 542         return 1;
 543 }
 544
 545 static const struct mm_walk_ops hmm_walk_ops = {
 546         .pud_entry      = hmm_vma_walk_pud,
 547         .pmd_entry      = hmm_vma_walk_pmd,
 548         .pte_hole       = hmm_vma_walk_hole,
 549         .hugetlb_entry  = hmm_vma_walk_hugetlb_entry,
 550         .test_walk      = hmm_vma_walk_test,
 551 };
 552
 553 /**
 554  * hmm_range_fault - try to fault some address in a virtual address range
 555  * @range:      argument structure
 556  *
 557  * Returns 0 on success or one of the following error codes:
 558  *
 559  * -EINVAL:     Invalid arguments or mm or virtual address is in an invalid vma
 560  *              (e.g., device file vma).
 561  * -ENOMEM:     Out of memory.
 562  * -EPERM:      Invalid permission (e.g., asking for write and range is read
 563  *              only).
 564  * -EBUSY:      The range has been invalidated and the caller needs to wait for
 565  *              the invalidation to finish.
 566  * -EFAULT:     A page was requested to be valid and could not be made valid
 567  *              ie it has no backing VMA or it is illegal to access
 568  *
 569  * This is similar to get_user_pages(), except that it can read the page tables
 570  * without mutating them (ie causing faults).
 571  */
 572 int hmm_range_fault(struct hmm_range *range)
 573 {
 574         struct hmm_vma_walk hmm_vma_walk = {
 575                 .range = range,
 576                 .last = range->start,
 577         };
 578         struct mm_struct *mm = range->notifier->mm;
 579         int ret;
 580
 581         mmap_assert_locked(mm);
 582
 583         do {
 584                 /* If range is no longer valid force retry. */
 585                 if (mmu_interval_check_retry(range->notifier,
 586                                              range->notifier_seq))
 587                         return -EBUSY;
 588                 ret = walk_page_range(mm, hmm_vma_walk.last, range->end,
 589                                       &hmm_walk_ops, &hmm_vma_walk);
 590                 /*
 591                  * When -EBUSY is returned the loop restarts with
 592                  * hmm_vma_walk.last set to an address that has not been stored
 593                  * in pfns. All entries < last in the pfn array are set to their
 594                  * output, and all >= are still at their input values.
 595                  */
 596         } while (ret == -EBUSY);
 597         return ret;
 598 }
 599 EXPORT_SYMBOL(hmm_range_fault);