mm/hmm.c

   1 /*
   2  * Copyright 2013 Red Hat Inc.
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * Authors: Jérôme Glisse <jglisse@redhat.com>
  15  */
  16 /*
  17  * Refer to include/linux/hmm.h for information about heterogeneous memory
  18  * management or HMM for short.
  19  */
  20 #include <linux/mm.h>
  21 #include <linux/hmm.h>
  22 #include <linux/init.h>
  23 #include <linux/rmap.h>
  24 #include <linux/swap.h>
  25 #include <linux/slab.h>
  26 #include <linux/sched.h>
  27 #include <linux/mmzone.h>
  28 #include <linux/pagemap.h>
  29 #include <linux/swapops.h>
  30 #include <linux/hugetlb.h>
  31 #include <linux/memremap.h>
  32 #include <linux/jump_label.h>
  33 #include <linux/mmu_notifier.h>
  34 #include <linux/memory_hotplug.h>
  35
  36 #define PA_SECTION_SIZE (1UL << PA_SECTION_SHIFT)
  37
  38 #if IS_ENABLED(CONFIG_HMM_MIRROR)
  39 static const struct mmu_notifier_ops hmm_mmu_notifier_ops;
  40
  41 /*
  42  * struct hmm - HMM per mm struct
  43  *
  44  * @mm: mm struct this HMM struct is bound to
  45  * @lock: lock protecting ranges list
  46  * @ranges: list of range being snapshotted
  47  * @mirrors: list of mirrors for this mm
  48  * @mmu_notifier: mmu notifier to track updates to CPU page table
  49  * @mirrors_sem: read/write semaphore protecting the mirrors list
  50  */
  51 struct hmm {
  52         struct mm_struct        *mm;
  53         spinlock_t              lock;
  54         struct list_head        ranges;
  55         struct list_head        mirrors;
  56         struct mmu_notifier     mmu_notifier;
  57         struct rw_semaphore     mirrors_sem;
  58 };
  59
  60 /*
  61  * hmm_register - register HMM against an mm (HMM internal)
  62  *
  63  * @mm: mm struct to attach to
  64  *
  65  * This is not intended to be used directly by device drivers. It allocates an
  66  * HMM struct if mm does not have one, and initializes it.
  67  */
  68 static struct hmm *hmm_register(struct mm_struct *mm)
  69 {
  70         struct hmm *hmm = READ_ONCE(mm->hmm);
  71         bool cleanup = false;
  72
  73         /*
  74          * The hmm struct can only be freed once the mm_struct goes away,
  75          * hence we should always have pre-allocated an new hmm struct
  76          * above.
  77          */
  78         if (hmm)
  79                 return hmm;
  80
  81         hmm = kmalloc(sizeof(*hmm), GFP_KERNEL);
  82         if (!hmm)
  83                 return NULL;
  84         INIT_LIST_HEAD(&hmm->mirrors);
  85         init_rwsem(&hmm->mirrors_sem);
  86         hmm->mmu_notifier.ops = NULL;
  87         INIT_LIST_HEAD(&hmm->ranges);
  88         spin_lock_init(&hmm->lock);
  89         hmm->mm = mm;
  90
  91         spin_lock(&mm->page_table_lock);
  92         if (!mm->hmm)
  93                 mm->hmm = hmm;
  94         else
  95                 cleanup = true;
  96         spin_unlock(&mm->page_table_lock);
  97
  98         if (cleanup)
  99                 goto error;
 100
 101         /*
 102          * We should only get here if hold the mmap_sem in write mode ie on
 103          * registration of first mirror through hmm_mirror_register()
 104          */
 105         hmm->mmu_notifier.ops = &hmm_mmu_notifier_ops;
 106         if (__mmu_notifier_register(&hmm->mmu_notifier, mm))
 107                 goto error_mm;
 108
 109         return mm->hmm;
 110
 111 error_mm:
 112         spin_lock(&mm->page_table_lock);
 113         if (mm->hmm == hmm)
 114                 mm->hmm = NULL;
 115         spin_unlock(&mm->page_table_lock);
 116 error:
 117         kfree(hmm);
 118         return NULL;
 119 }
 120
 121 void hmm_mm_destroy(struct mm_struct *mm)
 122 {
 123         kfree(mm->hmm);
 124 }
 125
 126 static int hmm_invalidate_range(struct hmm *hmm, bool device,
 127                                 const struct hmm_update *update)
 128 {
 129         struct hmm_mirror *mirror;
 130         struct hmm_range *range;
 131
 132         spin_lock(&hmm->lock);
 133         list_for_each_entry(range, &hmm->ranges, list) {
 134                 unsigned long addr, idx, npages;
 135
 136                 if (update->end < range->start || update->start >= range->end)
 137                         continue;
 138
 139                 range->valid = false;
 140                 addr = max(update->start, range->start);
 141                 idx = (addr - range->start) >> PAGE_SHIFT;
 142                 npages = (min(range->end, update->end) - addr) >> PAGE_SHIFT;
 143                 memset(&range->pfns[idx], 0, sizeof(*range->pfns) * npages);
 144         }
 145         spin_unlock(&hmm->lock);
 146
 147         if (!device)
 148                 return 0;
 149
 150         down_read(&hmm->mirrors_sem);
 151         list_for_each_entry(mirror, &hmm->mirrors, list) {
 152                 int ret;
 153
 154                 ret = mirror->ops->sync_cpu_device_pagetables(mirror, update);
 155                 if (!update->blockable && ret == -EAGAIN) {
 156                         up_read(&hmm->mirrors_sem);
 157                         return -EAGAIN;
 158                 }
 159         }
 160         up_read(&hmm->mirrors_sem);
 161
 162         return 0;
 163 }
 164
 165 static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm)
 166 {
 167         struct hmm_mirror *mirror;
 168         struct hmm *hmm = mm->hmm;
 169
 170         down_write(&hmm->mirrors_sem);
 171         mirror = list_first_entry_or_null(&hmm->mirrors, struct hmm_mirror,
 172                                           list);
 173         while (mirror) {
 174                 list_del_init(&mirror->list);
 175                 if (mirror->ops->release) {
 176                         /*
 177                          * Drop mirrors_sem so callback can wait on any pending
 178                          * work that might itself trigger mmu_notifier callback
 179                          * and thus would deadlock with us.
 180                          */
 181                         up_write(&hmm->mirrors_sem);
 182                         mirror->ops->release(mirror);
 183                         down_write(&hmm->mirrors_sem);
 184                 }
 185                 mirror = list_first_entry_or_null(&hmm->mirrors,
 186                                                   struct hmm_mirror, list);
 187         }
 188         up_write(&hmm->mirrors_sem);
 189 }
 190
 191 static int hmm_invalidate_range_start(struct mmu_notifier *mn,
 192                         const struct mmu_notifier_range *range)
 193 {
 194         struct hmm_update update;
 195         struct hmm *hmm = range->mm->hmm;
 196
 197         VM_BUG_ON(!hmm);
 198
 199         update.start = range->start;
 200         update.end = range->end;
 201         update.event = HMM_UPDATE_INVALIDATE;
 202         update.blockable = range->blockable;
 203         return hmm_invalidate_range(hmm, true, &update);
 204 }
 205
 206 static void hmm_invalidate_range_end(struct mmu_notifier *mn,
 207                         const struct mmu_notifier_range *range)
 208 {
 209         struct hmm_update update;
 210         struct hmm *hmm = range->mm->hmm;
 211
 212         VM_BUG_ON(!hmm);
 213
 214         update.start = range->start;
 215         update.end = range->end;
 216         update.event = HMM_UPDATE_INVALIDATE;
 217         update.blockable = true;
 218         hmm_invalidate_range(hmm, false, &update);
 219 }
 220
 221 static const struct mmu_notifier_ops hmm_mmu_notifier_ops = {
 222         .release                = hmm_release,
 223         .invalidate_range_start = hmm_invalidate_range_start,
 224         .invalidate_range_end   = hmm_invalidate_range_end,
 225 };
 226
 227 /*
 228  * hmm_mirror_register() - register a mirror against an mm
 229  *
 230  * @mirror: new mirror struct to register
 231  * @mm: mm to register against
 232  *
 233  * To start mirroring a process address space, the device driver must register
 234  * an HMM mirror struct.
 235  *
 236  * THE mm->mmap_sem MUST BE HELD IN WRITE MODE !
 237  */
 238 int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm)
 239 {
 240         /* Sanity check */
 241         if (!mm || !mirror || !mirror->ops)
 242                 return -EINVAL;
 243
 244 again:
 245         mirror->hmm = hmm_register(mm);
 246         if (!mirror->hmm)
 247                 return -ENOMEM;
 248
 249         down_write(&mirror->hmm->mirrors_sem);
 250         if (mirror->hmm->mm == NULL) {
 251                 /*
 252                  * A racing hmm_mirror_unregister() is about to destroy the hmm
 253                  * struct. Try again to allocate a new one.
 254                  */
 255                 up_write(&mirror->hmm->mirrors_sem);
 256                 mirror->hmm = NULL;
 257                 goto again;
 258         } else {
 259                 list_add(&mirror->list, &mirror->hmm->mirrors);
 260                 up_write(&mirror->hmm->mirrors_sem);
 261         }
 262
 263         return 0;
 264 }
 265 EXPORT_SYMBOL(hmm_mirror_register);
 266
 267 /*
 268  * hmm_mirror_unregister() - unregister a mirror
 269  *
 270  * @mirror: new mirror struct to register
 271  *
 272  * Stop mirroring a process address space, and cleanup.
 273  */
 274 void hmm_mirror_unregister(struct hmm_mirror *mirror)
 275 {
 276         bool should_unregister = false;
 277         struct mm_struct *mm;
 278         struct hmm *hmm;
 279
 280         if (mirror->hmm == NULL)
 281                 return;
 282
 283         hmm = mirror->hmm;
 284         down_write(&hmm->mirrors_sem);
 285         list_del_init(&mirror->list);
 286         should_unregister = list_empty(&hmm->mirrors);
 287         mirror->hmm = NULL;
 288         mm = hmm->mm;
 289         hmm->mm = NULL;
 290         up_write(&hmm->mirrors_sem);
 291
 292         if (!should_unregister || mm == NULL)
 293                 return;
 294
 295         mmu_notifier_unregister_no_release(&hmm->mmu_notifier, mm);
 296
 297         spin_lock(&mm->page_table_lock);
 298         if (mm->hmm == hmm)
 299                 mm->hmm = NULL;
 300         spin_unlock(&mm->page_table_lock);
 301
 302         kfree(hmm);
 303 }
 304 EXPORT_SYMBOL(hmm_mirror_unregister);
 305
 306 struct hmm_vma_walk {
 307         struct hmm_range        *range;
 308         unsigned long           last;
 309         bool                    fault;
 310         bool                    block;
 311 };
 312
 313 static int hmm_vma_do_fault(struct mm_walk *walk, unsigned long addr,
 314                             bool write_fault, uint64_t *pfn)
 315 {
 316         unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_REMOTE;
 317         struct hmm_vma_walk *hmm_vma_walk = walk->private;
 318         struct hmm_range *range = hmm_vma_walk->range;
 319         struct vm_area_struct *vma = walk->vma;
 320         vm_fault_t ret;
 321
 322         flags |= hmm_vma_walk->block ? 0 : FAULT_FLAG_ALLOW_RETRY;
 323         flags |= write_fault ? FAULT_FLAG_WRITE : 0;
 324         ret = handle_mm_fault(vma, addr, flags);
 325         if (ret & VM_FAULT_RETRY)
 326                 return -EBUSY;
 327         if (ret & VM_FAULT_ERROR) {
 328                 *pfn = range->values[HMM_PFN_ERROR];
 329                 return -EFAULT;
 330         }
 331
 332         return -EAGAIN;
 333 }
 334
 335 static int hmm_pfns_bad(unsigned long addr,
 336                         unsigned long end,
 337                         struct mm_walk *walk)
 338 {
 339         struct hmm_vma_walk *hmm_vma_walk = walk->private;
 340         struct hmm_range *range = hmm_vma_walk->range;
 341         uint64_t *pfns = range->pfns;
 342         unsigned long i;
 343
 344         i = (addr - range->start) >> PAGE_SHIFT;
 345         for (; addr < end; addr += PAGE_SIZE, i++)
 346                 pfns[i] = range->values[HMM_PFN_ERROR];
 347
 348         return 0;
 349 }
 350
 351 /*
 352  * hmm_vma_walk_hole() - handle a range lacking valid pmd or pte(s)
 353  * @start: range virtual start address (inclusive)
 354  * @end: range virtual end address (exclusive)
 355  * @fault: should we fault or not ?
 356  * @write_fault: write fault ?
 357  * @walk: mm_walk structure
 358  * Returns: 0 on success, -EAGAIN after page fault, or page fault error
 359  *
 360  * This function will be called whenever pmd_none() or pte_none() returns true,
 361  * or whenever there is no page directory covering the virtual address range.
 362  */
 363 static int hmm_vma_walk_hole_(unsigned long addr, unsigned long end,
 364                               bool fault, bool write_fault,
 365                               struct mm_walk *walk)
 366 {
 367         struct hmm_vma_walk *hmm_vma_walk = walk->private;
 368         struct hmm_range *range = hmm_vma_walk->range;
 369         uint64_t *pfns = range->pfns;
 370         unsigned long i;
 371
 372         hmm_vma_walk->last = addr;
 373         i = (addr - range->start) >> PAGE_SHIFT;
 374         for (; addr < end; addr += PAGE_SIZE, i++) {
 375                 pfns[i] = range->values[HMM_PFN_NONE];
 376                 if (fault || write_fault) {
 377                         int ret;
 378
 379                         ret = hmm_vma_do_fault(walk, addr, write_fault,
 380                                                &pfns[i]);
 381                         if (ret != -EAGAIN)
 382                                 return ret;
 383                 }
 384         }
 385
 386         return (fault || write_fault) ? -EAGAIN : 0;
 387 }
 388
 389 static inline void hmm_pte_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
 390                                       uint64_t pfns, uint64_t cpu_flags,
 391                                       bool *fault, bool *write_fault)
 392 {
 393         struct hmm_range *range = hmm_vma_walk->range;
 394
 395         *fault = *write_fault = false;
 396         if (!hmm_vma_walk->fault)
 397                 return;
 398
 399         /* We aren't ask to do anything ... */
 400         if (!(pfns & range->flags[HMM_PFN_VALID]))
 401                 return;
 402         /* If this is device memory than only fault if explicitly requested */
 403         if ((cpu_flags & range->flags[HMM_PFN_DEVICE_PRIVATE])) {
 404                 /* Do we fault on device memory ? */
 405                 if (pfns & range->flags[HMM_PFN_DEVICE_PRIVATE]) {
 406                         *write_fault = pfns & range->flags[HMM_PFN_WRITE];
 407                         *fault = true;
 408                 }
 409                 return;
 410         }
 411
 412         /* If CPU page table is not valid then we need to fault */
 413         *fault = !(cpu_flags & range->flags[HMM_PFN_VALID]);
 414         /* Need to write fault ? */
 415         if ((pfns & range->flags[HMM_PFN_WRITE]) &&
 416             !(cpu_flags & range->flags[HMM_PFN_WRITE])) {
 417                 *write_fault = true;
 418                 *fault = true;
 419         }
 420 }
 421
 422 static void hmm_range_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
 423                                  const uint64_t *pfns, unsigned long npages,
 424                                  uint64_t cpu_flags, bool *fault,
 425                                  bool *write_fault)
 426 {
 427         unsigned long i;
 428
 429         if (!hmm_vma_walk->fault) {
 430                 *fault = *write_fault = false;
 431                 return;
 432         }
 433
 434         for (i = 0; i < npages; ++i) {
 435                 hmm_pte_need_fault(hmm_vma_walk, pfns[i], cpu_flags,
 436                                    fault, write_fault);
 437                 if ((*fault) || (*write_fault))
 438                         return;
 439         }
 440 }
 441
 442 static int hmm_vma_walk_hole(unsigned long addr, unsigned long end,
 443                              struct mm_walk *walk)
 444 {
 445         struct hmm_vma_walk *hmm_vma_walk = walk->private;
 446         struct hmm_range *range = hmm_vma_walk->range;
 447         bool fault, write_fault;
 448         unsigned long i, npages;
 449         uint64_t *pfns;
 450
 451         i = (addr - range->start) >> PAGE_SHIFT;
 452         npages = (end - addr) >> PAGE_SHIFT;
 453         pfns = &range->pfns[i];
 454         hmm_range_need_fault(hmm_vma_walk, pfns, npages,
 455                              0, &fault, &write_fault);
 456         return hmm_vma_walk_hole_(addr, end, fault, write_fault, walk);
 457 }
 458
 459 static inline uint64_t pmd_to_hmm_pfn_flags(struct hmm_range *range, pmd_t pmd)
 460 {
 461         if (pmd_protnone(pmd))
 462                 return 0;
 463         return pmd_write(pmd) ? range->flags[HMM_PFN_VALID] |
 464                                 range->flags[HMM_PFN_WRITE] :
 465                                 range->flags[HMM_PFN_VALID];
 466 }
 467
 468 static int hmm_vma_handle_pmd(struct mm_walk *walk,
 469                               unsigned long addr,
 470                               unsigned long end,
 471                               uint64_t *pfns,
 472                               pmd_t pmd)
 473 {
 474         struct hmm_vma_walk *hmm_vma_walk = walk->private;
 475         struct hmm_range *range = hmm_vma_walk->range;
 476         unsigned long pfn, npages, i;
 477         bool fault, write_fault;
 478         uint64_t cpu_flags;
 479
 480         npages = (end - addr) >> PAGE_SHIFT;
 481         cpu_flags = pmd_to_hmm_pfn_flags(range, pmd);
 482         hmm_range_need_fault(hmm_vma_walk, pfns, npages, cpu_flags,
 483                              &fault, &write_fault);
 484
 485         if (pmd_protnone(pmd) || fault || write_fault)
 486                 return hmm_vma_walk_hole_(addr, end, fault, write_fault, walk);
 487
 488         pfn = pmd_pfn(pmd) + pte_index(addr);
 489         for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++)
 490                 pfns[i] = hmm_pfn_from_pfn(range, pfn) | cpu_flags;
 491         hmm_vma_walk->last = end;
 492         return 0;
 493 }
 494
 495 static inline uint64_t pte_to_hmm_pfn_flags(struct hmm_range *range, pte_t pte)
 496 {
 497         if (pte_none(pte) || !pte_present(pte))
 498                 return 0;
 499         return pte_write(pte) ? range->flags[HMM_PFN_VALID] |
 500                                 range->flags[HMM_PFN_WRITE] :
 501                                 range->flags[HMM_PFN_VALID];
 502 }
 503
 504 static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
 505                               unsigned long end, pmd_t *pmdp, pte_t *ptep,
 506                               uint64_t *pfn)
 507 {
 508         struct hmm_vma_walk *hmm_vma_walk = walk->private;
 509         struct hmm_range *range = hmm_vma_walk->range;
 510         struct vm_area_struct *vma = walk->vma;
 511         bool fault, write_fault;
 512         uint64_t cpu_flags;
 513         pte_t pte = *ptep;
 514         uint64_t orig_pfn = *pfn;
 515
 516         *pfn = range->values[HMM_PFN_NONE];
 517         cpu_flags = pte_to_hmm_pfn_flags(range, pte);
 518         hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags,
 519                            &fault, &write_fault);
 520
 521         if (pte_none(pte)) {
 522                 if (fault || write_fault)
 523                         goto fault;
 524                 return 0;
 525         }
 526
 527         if (!pte_present(pte)) {
 528                 swp_entry_t entry = pte_to_swp_entry(pte);
 529
 530                 if (!non_swap_entry(entry)) {
 531                         if (fault || write_fault)
 532                                 goto fault;
 533                         return 0;
 534                 }
 535
 536                 /*
 537                  * This is a special swap entry, ignore migration, use
 538                  * device and report anything else as error.
 539                  */
 540                 if (is_device_private_entry(entry)) {
 541                         cpu_flags = range->flags[HMM_PFN_VALID] |
 542                                 range->flags[HMM_PFN_DEVICE_PRIVATE];
 543                         cpu_flags |= is_write_device_private_entry(entry) ?
 544                                 range->flags[HMM_PFN_WRITE] : 0;
 545                         hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags,
 546                                            &fault, &write_fault);
 547                         if (fault || write_fault)
 548                                 goto fault;
 549                         *pfn = hmm_pfn_from_pfn(range, swp_offset(entry));
 550                         *pfn |= cpu_flags;
 551                         return 0;
 552                 }
 553
 554                 if (is_migration_entry(entry)) {
 555                         if (fault || write_fault) {
 556                                 pte_unmap(ptep);
 557                                 hmm_vma_walk->last = addr;
 558                                 migration_entry_wait(vma->vm_mm,
 559                                                      pmdp, addr);
 560                                 return -EAGAIN;
 561                         }
 562                         return 0;
 563                 }
 564
 565                 /* Report error for everything else */
 566                 *pfn = range->values[HMM_PFN_ERROR];
 567                 return -EFAULT;
 568         }
 569
 570         if (fault || write_fault)
 571                 goto fault;
 572
 573         *pfn = hmm_pfn_from_pfn(range, pte_pfn(pte)) | cpu_flags;
 574         return 0;
 575
 576 fault:
 577         pte_unmap(ptep);
 578         /* Fault any virtual address we were asked to fault */
 579         return hmm_vma_walk_hole_(addr, end, fault, write_fault, walk);
 580 }
 581
 582 static int hmm_vma_walk_pmd(pmd_t *pmdp,
 583                             unsigned long start,
 584                             unsigned long end,
 585                             struct mm_walk *walk)
 586 {
 587         struct hmm_vma_walk *hmm_vma_walk = walk->private;
 588         struct hmm_range *range = hmm_vma_walk->range;
 589         struct vm_area_struct *vma = walk->vma;
 590         uint64_t *pfns = range->pfns;
 591         unsigned long addr = start, i;
 592         pte_t *ptep;
 593         pmd_t pmd;
 594
 595
 596 again:
 597         pmd = READ_ONCE(*pmdp);
 598         if (pmd_none(pmd))
 599                 return hmm_vma_walk_hole(start, end, walk);
 600
 601         if (pmd_huge(pmd) && (range->vma->vm_flags & VM_HUGETLB))
 602                 return hmm_pfns_bad(start, end, walk);
 603
 604         if (thp_migration_supported() && is_pmd_migration_entry(pmd)) {
 605                 bool fault, write_fault;
 606                 unsigned long npages;
 607                 uint64_t *pfns;
 608
 609                 i = (addr - range->start) >> PAGE_SHIFT;
 610                 npages = (end - addr) >> PAGE_SHIFT;
 611                 pfns = &range->pfns[i];
 612
 613                 hmm_range_need_fault(hmm_vma_walk, pfns, npages,
 614                                      0, &fault, &write_fault);
 615                 if (fault || write_fault) {
 616                         hmm_vma_walk->last = addr;
 617                         pmd_migration_entry_wait(vma->vm_mm, pmdp);
 618                         return -EAGAIN;
 619                 }
 620                 return 0;
 621         } else if (!pmd_present(pmd))
 622                 return hmm_pfns_bad(start, end, walk);
 623
 624         if (pmd_devmap(pmd) || pmd_trans_huge(pmd)) {
 625                 /*
 626                  * No need to take pmd_lock here, even if some other threads
 627                  * is splitting the huge pmd we will get that event through
 628                  * mmu_notifier callback.
 629                  *
 630                  * So just read pmd value and check again its a transparent
 631                  * huge or device mapping one and compute corresponding pfn
 632                  * values.
 633                  */
 634                 pmd = pmd_read_atomic(pmdp);
 635                 barrier();
 636                 if (!pmd_devmap(pmd) && !pmd_trans_huge(pmd))
 637                         goto again;
 638
 639                 i = (addr - range->start) >> PAGE_SHIFT;
 640                 return hmm_vma_handle_pmd(walk, addr, end, &pfns[i], pmd);
 641         }
 642
 643         /*
 644          * We have handled all the valid case above ie either none, migration,
 645          * huge or transparent huge. At this point either it is a valid pmd
 646          * entry pointing to pte directory or it is a bad pmd that will not
 647          * recover.
 648          */
 649         if (pmd_bad(pmd))
 650                 return hmm_pfns_bad(start, end, walk);
 651
 652         ptep = pte_offset_map(pmdp, addr);
 653         i = (addr - range->start) >> PAGE_SHIFT;
 654         for (; addr < end; addr += PAGE_SIZE, ptep++, i++) {
 655                 int r;
 656
 657                 r = hmm_vma_handle_pte(walk, addr, end, pmdp, ptep, &pfns[i]);
 658                 if (r) {
 659                         /* hmm_vma_handle_pte() did unmap pte directory */
 660                         hmm_vma_walk->last = addr;
 661                         return r;
 662                 }
 663         }
 664         pte_unmap(ptep - 1);
 665
 666         hmm_vma_walk->last = addr;
 667         return 0;
 668 }
 669
 670 static void hmm_pfns_clear(struct hmm_range *range,
 671                            uint64_t *pfns,
 672                            unsigned long addr,
 673                            unsigned long end)
 674 {
 675         for (; addr < end; addr += PAGE_SIZE, pfns++)
 676                 *pfns = range->values[HMM_PFN_NONE];
 677 }
 678
 679 static void hmm_pfns_special(struct hmm_range *range)
 680 {
 681         unsigned long addr = range->start, i = 0;
 682
 683         for (; addr < range->end; addr += PAGE_SIZE, i++)
 684                 range->pfns[i] = range->values[HMM_PFN_SPECIAL];
 685 }
 686
 687 /*
 688  * hmm_vma_get_pfns() - snapshot CPU page table for a range of virtual addresses
 689  * @range: range being snapshotted
 690  * Returns: -EINVAL if invalid argument, -ENOMEM out of memory, -EPERM invalid
 691  *          vma permission, 0 success
 692  *
 693  * This snapshots the CPU page table for a range of virtual addresses. Snapshot
 694  * validity is tracked by range struct. See hmm_vma_range_done() for further
 695  * information.
 696  *
 697  * The range struct is initialized here. It tracks the CPU page table, but only
 698  * if the function returns success (0), in which case the caller must then call
 699  * hmm_vma_range_done() to stop CPU page table update tracking on this range.
 700  *
 701  * NOT CALLING hmm_vma_range_done() IF FUNCTION RETURNS 0 WILL LEAD TO SERIOUS
 702  * MEMORY CORRUPTION ! YOU HAVE BEEN WARNED !
 703  */
 704 int hmm_vma_get_pfns(struct hmm_range *range)
 705 {
 706         struct vm_area_struct *vma = range->vma;
 707         struct hmm_vma_walk hmm_vma_walk;
 708         struct mm_walk mm_walk;
 709         struct hmm *hmm;
 710
 711         /* Sanity check, this really should not happen ! */
 712         if (range->start < vma->vm_start || range->start >= vma->vm_end)
 713                 return -EINVAL;
 714         if (range->end < vma->vm_start || range->end > vma->vm_end)
 715                 return -EINVAL;
 716
 717         hmm = hmm_register(vma->vm_mm);
 718         if (!hmm)
 719                 return -ENOMEM;
 720         /* Caller must have registered a mirror, via hmm_mirror_register() ! */
 721         if (!hmm->mmu_notifier.ops)
 722                 return -EINVAL;
 723
 724         /* FIXME support hugetlb fs */
 725         if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL) ||
 726                         vma_is_dax(vma)) {
 727                 hmm_pfns_special(range);
 728                 return -EINVAL;
 729         }
 730
 731         if (!(vma->vm_flags & VM_READ)) {
 732                 /*
 733                  * If vma do not allow read access, then assume that it does
 734                  * not allow write access, either. Architecture that allow
 735                  * write without read access are not supported by HMM, because
 736                  * operations such has atomic access would not work.
 737                  */
 738                 hmm_pfns_clear(range, range->pfns, range->start, range->end);
 739                 return -EPERM;
 740         }
 741
 742         /* Initialize range to track CPU page table update */
 743         spin_lock(&hmm->lock);
 744         range->valid = true;
 745         list_add_rcu(&range->list, &hmm->ranges);
 746         spin_unlock(&hmm->lock);
 747
 748         hmm_vma_walk.fault = false;
 749         hmm_vma_walk.range = range;
 750         mm_walk.private = &hmm_vma_walk;
 751
 752         mm_walk.vma = vma;
 753         mm_walk.mm = vma->vm_mm;
 754         mm_walk.pte_entry = NULL;
 755         mm_walk.test_walk = NULL;
 756         mm_walk.hugetlb_entry = NULL;
 757         mm_walk.pmd_entry = hmm_vma_walk_pmd;
 758         mm_walk.pte_hole = hmm_vma_walk_hole;
 759
 760         walk_page_range(range->start, range->end, &mm_walk);
 761         return 0;
 762 }
 763 EXPORT_SYMBOL(hmm_vma_get_pfns);
 764
 765 /*
 766  * hmm_vma_range_done() - stop tracking change to CPU page table over a range
 767  * @range: range being tracked
 768  * Returns: false if range data has been invalidated, true otherwise
 769  *
 770  * Range struct is used to track updates to the CPU page table after a call to
 771  * either hmm_vma_get_pfns() or hmm_vma_fault(). Once the device driver is done
 772  * using the data,  or wants to lock updates to the data it got from those
 773  * functions, it must call the hmm_vma_range_done() function, which will then
 774  * stop tracking CPU page table updates.
 775  *
 776  * Note that device driver must still implement general CPU page table update
 777  * tracking either by using hmm_mirror (see hmm_mirror_register()) or by using
 778  * the mmu_notifier API directly.
 779  *
 780  * CPU page table update tracking done through hmm_range is only temporary and
 781  * to be used while trying to duplicate CPU page table contents for a range of
 782  * virtual addresses.
 783  *
 784  * There are two ways to use this :
 785  * again:
 786  *   hmm_vma_get_pfns(range); or hmm_vma_fault(...);
 787  *   trans = device_build_page_table_update_transaction(pfns);
 788  *   device_page_table_lock();
 789  *   if (!hmm_vma_range_done(range)) {
 790  *     device_page_table_unlock();
 791  *     goto again;
 792  *   }
 793  *   device_commit_transaction(trans);
 794  *   device_page_table_unlock();
 795  *
 796  * Or:
 797  *   hmm_vma_get_pfns(range); or hmm_vma_fault(...);
 798  *   device_page_table_lock();
 799  *   hmm_vma_range_done(range);
 800  *   device_update_page_table(range->pfns);
 801  *   device_page_table_unlock();
 802  */
 803 bool hmm_vma_range_done(struct hmm_range *range)
 804 {
 805         unsigned long npages = (range->end - range->start) >> PAGE_SHIFT;
 806         struct hmm *hmm;
 807
 808         if (range->end <= range->start) {
 809                 BUG();
 810                 return false;
 811         }
 812
 813         hmm = hmm_register(range->vma->vm_mm);
 814         if (!hmm) {
 815                 memset(range->pfns, 0, sizeof(*range->pfns) * npages);
 816                 return false;
 817         }
 818
 819         spin_lock(&hmm->lock);
 820         list_del_rcu(&range->list);
 821         spin_unlock(&hmm->lock);
 822
 823         return range->valid;
 824 }
 825 EXPORT_SYMBOL(hmm_vma_range_done);
 826
 827 /*
 828  * hmm_vma_fault() - try to fault some address in a virtual address range
 829  * @range: range being faulted
 830  * @block: allow blocking on fault (if true it sleeps and do not drop mmap_sem)
 831  * Returns: 0 success, error otherwise (-EAGAIN means mmap_sem have been drop)
 832  *
 833  * This is similar to a regular CPU page fault except that it will not trigger
 834  * any memory migration if the memory being faulted is not accessible by CPUs.
 835  *
 836  * On error, for one virtual address in the range, the function will mark the
 837  * corresponding HMM pfn entry with an error flag.
 838  *
 839  * Expected use pattern:
 840  * retry:
 841  *   down_read(&mm->mmap_sem);
 842  *   // Find vma and address device wants to fault, initialize hmm_pfn_t
 843  *   // array accordingly
 844  *   ret = hmm_vma_fault(range, write, block);
 845  *   switch (ret) {
 846  *   case -EAGAIN:
 847  *     hmm_vma_range_done(range);
 848  *     // You might want to rate limit or yield to play nicely, you may
 849  *     // also commit any valid pfn in the array assuming that you are
 850  *     // getting true from hmm_vma_range_monitor_end()
 851  *     goto retry;
 852  *   case 0:
 853  *     break;
 854  *   case -ENOMEM:
 855  *   case -EINVAL:
 856  *   case -EPERM:
 857  *   default:
 858  *     // Handle error !
 859  *     up_read(&mm->mmap_sem)
 860  *     return;
 861  *   }
 862  *   // Take device driver lock that serialize device page table update
 863  *   driver_lock_device_page_table_update();
 864  *   hmm_vma_range_done(range);
 865  *   // Commit pfns we got from hmm_vma_fault()
 866  *   driver_unlock_device_page_table_update();
 867  *   up_read(&mm->mmap_sem)
 868  *
 869  * YOU MUST CALL hmm_vma_range_done() AFTER THIS FUNCTION RETURN SUCCESS (0)
 870  * BEFORE FREEING THE range struct OR YOU WILL HAVE SERIOUS MEMORY CORRUPTION !
 871  *
 872  * YOU HAVE BEEN WARNED !
 873  */
 874 int hmm_vma_fault(struct hmm_range *range, bool block)
 875 {
 876         struct vm_area_struct *vma = range->vma;
 877         unsigned long start = range->start;
 878         struct hmm_vma_walk hmm_vma_walk;
 879         struct mm_walk mm_walk;
 880         struct hmm *hmm;
 881         int ret;
 882
 883         /* Sanity check, this really should not happen ! */
 884         if (range->start < vma->vm_start || range->start >= vma->vm_end)
 885                 return -EINVAL;
 886         if (range->end < vma->vm_start || range->end > vma->vm_end)
 887                 return -EINVAL;
 888
 889         hmm = hmm_register(vma->vm_mm);
 890         if (!hmm) {
 891                 hmm_pfns_clear(range, range->pfns, range->start, range->end);
 892                 return -ENOMEM;
 893         }
 894         /* Caller must have registered a mirror using hmm_mirror_register() */
 895         if (!hmm->mmu_notifier.ops)
 896                 return -EINVAL;
 897
 898         /* FIXME support hugetlb fs */
 899         if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL) ||
 900                         vma_is_dax(vma)) {
 901                 hmm_pfns_special(range);
 902                 return -EINVAL;
 903         }
 904
 905         if (!(vma->vm_flags & VM_READ)) {
 906                 /*
 907                  * If vma do not allow read access, then assume that it does
 908                  * not allow write access, either. Architecture that allow
 909                  * write without read access are not supported by HMM, because
 910                  * operations such has atomic access would not work.
 911                  */
 912                 hmm_pfns_clear(range, range->pfns, range->start, range->end);
 913                 return -EPERM;
 914         }
 915
 916         /* Initialize range to track CPU page table update */
 917         spin_lock(&hmm->lock);
 918         range->valid = true;
 919         list_add_rcu(&range->list, &hmm->ranges);
 920         spin_unlock(&hmm->lock);
 921
 922         hmm_vma_walk.fault = true;
 923         hmm_vma_walk.block = block;
 924         hmm_vma_walk.range = range;
 925         mm_walk.private = &hmm_vma_walk;
 926         hmm_vma_walk.last = range->start;
 927
 928         mm_walk.vma = vma;
 929         mm_walk.mm = vma->vm_mm;
 930         mm_walk.pte_entry = NULL;
 931         mm_walk.test_walk = NULL;
 932         mm_walk.hugetlb_entry = NULL;
 933         mm_walk.pmd_entry = hmm_vma_walk_pmd;
 934         mm_walk.pte_hole = hmm_vma_walk_hole;
 935
 936         do {
 937                 ret = walk_page_range(start, range->end, &mm_walk);
 938                 start = hmm_vma_walk.last;
 939         } while (ret == -EAGAIN);
 940
 941         if (ret) {
 942                 unsigned long i;
 943
 944                 i = (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;
 945                 hmm_pfns_clear(range, &range->pfns[i], hmm_vma_walk.last,
 946                                range->end);
 947                 hmm_vma_range_done(range);
 948         }
 949         return ret;
 950 }
 951 EXPORT_SYMBOL(hmm_vma_fault);
 952 #endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */
 953
 954
 955 #if IS_ENABLED(CONFIG_DEVICE_PRIVATE) ||  IS_ENABLED(CONFIG_DEVICE_PUBLIC)
 956 struct page *hmm_vma_alloc_locked_page(struct vm_area_struct *vma,
 957                                        unsigned long addr)
 958 {
 959         struct page *page;
 960
 961         page = alloc_page_vma(GFP_HIGHUSER, vma, addr);
 962         if (!page)
 963                 return NULL;
 964         lock_page(page);
 965         return page;
 966 }
 967 EXPORT_SYMBOL(hmm_vma_alloc_locked_page);
 968
 969
 970 static void hmm_devmem_ref_release(struct percpu_ref *ref)
 971 {
 972         struct hmm_devmem *devmem;
 973
 974         devmem = container_of(ref, struct hmm_devmem, ref);
 975         complete(&devmem->completion);
 976 }
 977
 978 static void hmm_devmem_ref_exit(void *data)
 979 {
 980         struct percpu_ref *ref = data;
 981         struct hmm_devmem *devmem;
 982
 983         devmem = container_of(ref, struct hmm_devmem, ref);
 984         wait_for_completion(&devmem->completion);
 985         percpu_ref_exit(ref);
 986 }
 987
 988 static void hmm_devmem_ref_kill(struct percpu_ref *ref)
 989 {
 990         percpu_ref_kill(ref);
 991 }
 992
 993 static vm_fault_t hmm_devmem_fault(struct vm_area_struct *vma,
 994                             unsigned long addr,
 995                             const struct page *page,
 996                             unsigned int flags,
 997                             pmd_t *pmdp)
 998 {
 999         struct hmm_devmem *devmem = page->pgmap->data;
1000
1001         return devmem->ops->fault(devmem, vma, addr, page, flags, pmdp);
1002 }
1003
1004 static void hmm_devmem_free(struct page *page, void *data)
1005 {
1006         struct hmm_devmem *devmem = data;
1007
1008         page->mapping = NULL;
1009
1010         devmem->ops->free(devmem, page);
1011 }
1012
1013 /*
1014  * hmm_devmem_add() - hotplug ZONE_DEVICE memory for device memory
1015  *
1016  * @ops: memory event device driver callback (see struct hmm_devmem_ops)
1017  * @device: device struct to bind the resource too
1018  * @size: size in bytes of the device memory to add
1019  * Returns: pointer to new hmm_devmem struct ERR_PTR otherwise
1020  *
1021  * This function first finds an empty range of physical address big enough to
1022  * contain the new resource, and then hotplugs it as ZONE_DEVICE memory, which
1023  * in turn allocates struct pages. It does not do anything beyond that; all
1024  * events affecting the memory will go through the various callbacks provided
1025  * by hmm_devmem_ops struct.
1026  *
1027  * Device driver should call this function during device initialization and
1028  * is then responsible of memory management. HMM only provides helpers.
1029  */
1030 struct hmm_devmem *hmm_devmem_add(const struct hmm_devmem_ops *ops,
1031                                   struct device *device,
1032                                   unsigned long size)
1033 {
1034         struct hmm_devmem *devmem;
1035         resource_size_t addr;
1036         void *result;
1037         int ret;
1038
1039         dev_pagemap_get_ops();
1040
1041         devmem = devm_kzalloc(device, sizeof(*devmem), GFP_KERNEL);
1042         if (!devmem)
1043                 return ERR_PTR(-ENOMEM);
1044
1045         init_completion(&devmem->completion);
1046         devmem->pfn_first = -1UL;
1047         devmem->pfn_last = -1UL;
1048         devmem->resource = NULL;
1049         devmem->device = device;
1050         devmem->ops = ops;
1051
1052         ret = percpu_ref_init(&devmem->ref, &hmm_devmem_ref_release,
1053                               0, GFP_KERNEL);
1054         if (ret)
1055                 return ERR_PTR(ret);
1056
1057         ret = devm_add_action_or_reset(device, hmm_devmem_ref_exit, &devmem->ref);
1058         if (ret)
1059                 return ERR_PTR(ret);
1060
1061         size = ALIGN(size, PA_SECTION_SIZE);
1062         addr = min((unsigned long)iomem_resource.end,
1063                    (1UL << MAX_PHYSMEM_BITS) - 1);
1064         addr = addr - size + 1UL;
1065
1066         /*
1067          * FIXME add a new helper to quickly walk resource tree and find free
1068          * range
1069          *
1070          * FIXME what about ioport_resource resource ?
1071          */
1072         for (; addr > size && addr >= iomem_resource.start; addr -= size) {
1073                 ret = region_intersects(addr, size, 0, IORES_DESC_NONE);
1074                 if (ret != REGION_DISJOINT)
1075                         continue;
1076
1077                 devmem->resource = devm_request_mem_region(device, addr, size,
1078                                                            dev_name(device));
1079                 if (!devmem->resource)
1080                         return ERR_PTR(-ENOMEM);
1081                 break;
1082         }
1083         if (!devmem->resource)
1084                 return ERR_PTR(-ERANGE);
1085
1086         devmem->resource->desc = IORES_DESC_DEVICE_PRIVATE_MEMORY;
1087         devmem->pfn_first = devmem->resource->start >> PAGE_SHIFT;
1088         devmem->pfn_last = devmem->pfn_first +
1089                            (resource_size(devmem->resource) >> PAGE_SHIFT);
1090         devmem->page_fault = hmm_devmem_fault;
1091
1092         devmem->pagemap.type = MEMORY_DEVICE_PRIVATE;
1093         devmem->pagemap.res = *devmem->resource;
1094         devmem->pagemap.page_free = hmm_devmem_free;
1095         devmem->pagemap.altmap_valid = false;
1096         devmem->pagemap.ref = &devmem->ref;
1097         devmem->pagemap.data = devmem;
1098         devmem->pagemap.kill = hmm_devmem_ref_kill;
1099
1100         result = devm_memremap_pages(devmem->device, &devmem->pagemap);
1101         if (IS_ERR(result))
1102                 return result;
1103         return devmem;
1104 }
1105 EXPORT_SYMBOL_GPL(hmm_devmem_add);
1106
1107 struct hmm_devmem *hmm_devmem_add_resource(const struct hmm_devmem_ops *ops,
1108                                            struct device *device,
1109                                            struct resource *res)
1110 {
1111         struct hmm_devmem *devmem;
1112         void *result;
1113         int ret;
1114
1115         if (res->desc != IORES_DESC_DEVICE_PUBLIC_MEMORY)
1116                 return ERR_PTR(-EINVAL);
1117
1118         dev_pagemap_get_ops();
1119
1120         devmem = devm_kzalloc(device, sizeof(*devmem), GFP_KERNEL);
1121         if (!devmem)
1122                 return ERR_PTR(-ENOMEM);
1123
1124         init_completion(&devmem->completion);
1125         devmem->pfn_first = -1UL;
1126         devmem->pfn_last = -1UL;
1127         devmem->resource = res;
1128         devmem->device = device;
1129         devmem->ops = ops;
1130
1131         ret = percpu_ref_init(&devmem->ref, &hmm_devmem_ref_release,
1132                               0, GFP_KERNEL);
1133         if (ret)
1134                 return ERR_PTR(ret);
1135
1136         ret = devm_add_action_or_reset(device, hmm_devmem_ref_exit,
1137                         &devmem->ref);
1138         if (ret)
1139                 return ERR_PTR(ret);
1140
1141         devmem->pfn_first = devmem->resource->start >> PAGE_SHIFT;
1142         devmem->pfn_last = devmem->pfn_first +
1143                            (resource_size(devmem->resource) >> PAGE_SHIFT);
1144         devmem->page_fault = hmm_devmem_fault;
1145
1146         devmem->pagemap.type = MEMORY_DEVICE_PUBLIC;
1147         devmem->pagemap.res = *devmem->resource;
1148         devmem->pagemap.page_free = hmm_devmem_free;
1149         devmem->pagemap.altmap_valid = false;
1150         devmem->pagemap.ref = &devmem->ref;
1151         devmem->pagemap.data = devmem;
1152         devmem->pagemap.kill = hmm_devmem_ref_kill;
1153
1154         result = devm_memremap_pages(devmem->device, &devmem->pagemap);
1155         if (IS_ERR(result))
1156                 return result;
1157         return devmem;
1158 }
1159 EXPORT_SYMBOL_GPL(hmm_devmem_add_resource);
1160
1161 /*
1162  * A device driver that wants to handle multiple devices memory through a
1163  * single fake device can use hmm_device to do so. This is purely a helper
1164  * and it is not needed to make use of any HMM functionality.
1165  */
1166 #define HMM_DEVICE_MAX 256
1167
1168 static DECLARE_BITMAP(hmm_device_mask, HMM_DEVICE_MAX);
1169 static DEFINE_SPINLOCK(hmm_device_lock);
1170 static struct class *hmm_device_class;
1171 static dev_t hmm_device_devt;
1172
1173 static void hmm_device_release(struct device *device)
1174 {
1175         struct hmm_device *hmm_device;
1176
1177         hmm_device = container_of(device, struct hmm_device, device);
1178         spin_lock(&hmm_device_lock);
1179         clear_bit(hmm_device->minor, hmm_device_mask);
1180         spin_unlock(&hmm_device_lock);
1181
1182         kfree(hmm_device);
1183 }
1184
1185 struct hmm_device *hmm_device_new(void *drvdata)
1186 {
1187         struct hmm_device *hmm_device;
1188
1189         hmm_device = kzalloc(sizeof(*hmm_device), GFP_KERNEL);
1190         if (!hmm_device)
1191                 return ERR_PTR(-ENOMEM);
1192
1193         spin_lock(&hmm_device_lock);
1194         hmm_device->minor = find_first_zero_bit(hmm_device_mask, HMM_DEVICE_MAX);
1195         if (hmm_device->minor >= HMM_DEVICE_MAX) {
1196                 spin_unlock(&hmm_device_lock);
1197                 kfree(hmm_device);
1198                 return ERR_PTR(-EBUSY);
1199         }
1200         set_bit(hmm_device->minor, hmm_device_mask);
1201         spin_unlock(&hmm_device_lock);
1202
1203         dev_set_name(&hmm_device->device, "hmm_device%d", hmm_device->minor);
1204         hmm_device->device.devt = MKDEV(MAJOR(hmm_device_devt),
1205                                         hmm_device->minor);
1206         hmm_device->device.release = hmm_device_release;
1207         dev_set_drvdata(&hmm_device->device, drvdata);
1208         hmm_device->device.class = hmm_device_class;
1209         device_initialize(&hmm_device->device);
1210
1211         return hmm_device;
1212 }
1213 EXPORT_SYMBOL(hmm_device_new);
1214
1215 void hmm_device_put(struct hmm_device *hmm_device)
1216 {
1217         put_device(&hmm_device->device);
1218 }
1219 EXPORT_SYMBOL(hmm_device_put);
1220
1221 static int __init hmm_init(void)
1222 {
1223         int ret;
1224
1225         ret = alloc_chrdev_region(&hmm_device_devt, 0,
1226                                   HMM_DEVICE_MAX,
1227                                   "hmm_device");
1228         if (ret)
1229                 return ret;
1230
1231         hmm_device_class = class_create(THIS_MODULE, "hmm_device");
1232         if (IS_ERR(hmm_device_class)) {
1233                 unregister_chrdev_region(hmm_device_devt, HMM_DEVICE_MAX);
1234                 return PTR_ERR(hmm_device_class);
1235         }
1236         return 0;
1237 }
1238
1239 device_initcall(hmm_init);
1240 #endif /* CONFIG_DEVICE_PRIVATE || CONFIG_DEVICE_PUBLIC */