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          * 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 (!vm_normal_page(walk->vma, addr, pte) &&
 304             !pte_devmap(pte) &&
 305             !is_zero_pfn(pte_pfn(pte))) {
 306                 if (hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0)) {
 307                         pte_unmap(ptep);
 308                         return -EFAULT;
 309                 }
 310                 *hmm_pfn = HMM_PFN_ERROR;
 311                 return 0;
 312         }
 313
 314         *hmm_pfn = pte_pfn(pte) | cpu_flags;
 315         return 0;
 316
 317 fault:
 318         pte_unmap(ptep);
 319         /* Fault any virtual address we were asked to fault */
 320         return hmm_vma_fault(addr, end, required_fault, walk);
 321 }
 322
 323 static int hmm_vma_walk_pmd(pmd_t *pmdp,
 324                             unsigned long start,
 325                             unsigned long end,
 326                             struct mm_walk *walk)
 327 {
 328         struct hmm_vma_walk *hmm_vma_walk = walk->private;
 329         struct hmm_range *range = hmm_vma_walk->range;
 330         unsigned long *hmm_pfns =
 331                 &range->hmm_pfns[(start - range->start) >> PAGE_SHIFT];
 332         unsigned long npages = (end - start) >> PAGE_SHIFT;
 333         unsigned long addr = start;
 334         pte_t *ptep;
 335         pmd_t pmd;
 336
 337 again:
 338         pmd = READ_ONCE(*pmdp);
 339         if (pmd_none(pmd))
 340                 return hmm_vma_walk_hole(start, end, -1, walk);
 341
 342         if (thp_migration_supported() && is_pmd_migration_entry(pmd)) {
 343                 if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0)) {
 344                         hmm_vma_walk->last = addr;
 345                         pmd_migration_entry_wait(walk->mm, pmdp);
 346                         return -EBUSY;
 347                 }
 348                 return hmm_pfns_fill(start, end, range, 0);
 349         }
 350
 351         if (!pmd_present(pmd)) {
 352                 if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0))
 353                         return -EFAULT;
 354                 return hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);
 355         }
 356
 357         if (pmd_devmap(pmd) || pmd_trans_huge(pmd)) {
 358                 /*
 359                  * No need to take pmd_lock here, even if some other thread
 360                  * is splitting the huge pmd we will get that event through
 361                  * mmu_notifier callback.
 362                  *
 363                  * So just read pmd value and check again it's a transparent
 364                  * huge or device mapping one and compute corresponding pfn
 365                  * values.
 366                  */
 367                 pmd = pmd_read_atomic(pmdp);
 368                 barrier();
 369                 if (!pmd_devmap(pmd) && !pmd_trans_huge(pmd))
 370                         goto again;
 371
 372                 return hmm_vma_handle_pmd(walk, addr, end, hmm_pfns, pmd);
 373         }
 374
 375         /*
 376          * We have handled all the valid cases above ie either none, migration,
 377          * huge or transparent huge. At this point either it is a valid pmd
 378          * entry pointing to pte directory or it is a bad pmd that will not
 379          * recover.
 380          */
 381         if (pmd_bad(pmd)) {
 382                 if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0))
 383                         return -EFAULT;
 384                 return hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);
 385         }
 386
 387         ptep = pte_offset_map(pmdp, addr);
 388         for (; addr < end; addr += PAGE_SIZE, ptep++, hmm_pfns++) {
 389                 int r;
 390
 391                 r = hmm_vma_handle_pte(walk, addr, end, pmdp, ptep, hmm_pfns);
 392                 if (r) {
 393                         /* hmm_vma_handle_pte() did pte_unmap() */
 394                         return r;
 395                 }
 396         }
 397         pte_unmap(ptep - 1);
 398         return 0;
 399 }
 400
 401 #if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && \
 402     defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
 403 static inline unsigned long pud_to_hmm_pfn_flags(struct hmm_range *range,
 404                                                  pud_t pud)
 405 {
 406         if (!pud_present(pud))
 407                 return 0;
 408         return (pud_write(pud) ? (HMM_PFN_VALID | HMM_PFN_WRITE) :
 409                                  HMM_PFN_VALID) |
 410                hmm_pfn_flags_order(PUD_SHIFT - PAGE_SHIFT);
 411 }
 412
 413 static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
 414                 struct mm_walk *walk)
 415 {
 416         struct hmm_vma_walk *hmm_vma_walk = walk->private;
 417         struct hmm_range *range = hmm_vma_walk->range;
 418         unsigned long addr = start;
 419         pud_t pud;
 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 0;
 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)) &&
 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);