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: JÃ©rÃ´me 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 defined(CONFIG_DEVICE_PRIVATE) || defined(CONFIG_DEVICE_PUBLIC)
  39 /*
  40  * Device private memory see HMM (Documentation/vm/hmm.txt) or hmm.h
  41  */
  42 DEFINE_STATIC_KEY_FALSE(device_private_key);
  43 EXPORT_SYMBOL(device_private_key);
  44 #endif /* CONFIG_DEVICE_PRIVATE || CONFIG_DEVICE_PUBLIC */
  45
  46
  47 #if IS_ENABLED(CONFIG_HMM_MIRROR)
  48 static const struct mmu_notifier_ops hmm_mmu_notifier_ops;
  49
  50 /*
  51  * struct hmm - HMM per mm struct
  52  *
  53  * @mm: mm struct this HMM struct is bound to
  54  * @lock: lock protecting ranges list
  55  * @sequence: we track updates to the CPU page table with a sequence number
  56  * @ranges: list of range being snapshotted
  57  * @mirrors: list of mirrors for this mm
  58  * @mmu_notifier: mmu notifier to track updates to CPU page table
  59  * @mirrors_sem: read/write semaphore protecting the mirrors list
  60  */
  61 struct hmm {
  62         struct mm_struct        *mm;
  63         spinlock_t              lock;
  64         atomic_t                sequence;
  65         struct list_head        ranges;
  66         struct list_head        mirrors;
  67         struct mmu_notifier     mmu_notifier;
  68         struct rw_semaphore     mirrors_sem;
  69 };
  70
  71 /*
  72  * hmm_register - register HMM against an mm (HMM internal)
  73  *
  74  * @mm: mm struct to attach to
  75  *
  76  * This is not intended to be used directly by device drivers. It allocates an
  77  * HMM struct if mm does not have one, and initializes it.
  78  */
  79 static struct hmm *hmm_register(struct mm_struct *mm)
  80 {
  81         struct hmm *hmm = READ_ONCE(mm->hmm);
  82         bool cleanup = false;
  83
  84         /*
  85          * The hmm struct can only be freed once the mm_struct goes away,
  86          * hence we should always have pre-allocated an new hmm struct
  87          * above.
  88          */
  89         if (hmm)
  90                 return hmm;
  91
  92         hmm = kmalloc(sizeof(*hmm), GFP_KERNEL);
  93         if (!hmm)
  94                 return NULL;
  95         INIT_LIST_HEAD(&hmm->mirrors);
  96         init_rwsem(&hmm->mirrors_sem);
  97         atomic_set(&hmm->sequence, 0);
  98         hmm->mmu_notifier.ops = NULL;
  99         INIT_LIST_HEAD(&hmm->ranges);
 100         spin_lock_init(&hmm->lock);
 101         hmm->mm = mm;
 102
 103         /*
 104          * We should only get here if hold the mmap_sem in write mode ie on
 105          * registration of first mirror through hmm_mirror_register()
 106          */
 107         hmm->mmu_notifier.ops = &hmm_mmu_notifier_ops;
 108         if (__mmu_notifier_register(&hmm->mmu_notifier, mm)) {
 109                 kfree(hmm);
 110                 return NULL;
 111         }
 112
 113         spin_lock(&mm->page_table_lock);
 114         if (!mm->hmm)
 115                 mm->hmm = hmm;
 116         else
 117                 cleanup = true;
 118         spin_unlock(&mm->page_table_lock);
 119
 120         if (cleanup) {
 121                 mmu_notifier_unregister(&hmm->mmu_notifier, mm);
 122                 kfree(hmm);
 123         }
 124
 125         return mm->hmm;
 126 }
 127
 128 void hmm_mm_destroy(struct mm_struct *mm)
 129 {
 130         kfree(mm->hmm);
 131 }
 132
 133 static void hmm_invalidate_range(struct hmm *hmm,
 134                                  enum hmm_update_type action,
 135                                  unsigned long start,
 136                                  unsigned long end)
 137 {
 138         struct hmm_mirror *mirror;
 139         struct hmm_range *range;
 140
 141         spin_lock(&hmm->lock);
 142         list_for_each_entry(range, &hmm->ranges, list) {
 143                 unsigned long addr, idx, npages;
 144
 145                 if (end < range->start || start >= range->end)
 146                         continue;
 147
 148                 range->valid = false;
 149                 addr = max(start, range->start);
 150                 idx = (addr - range->start) >> PAGE_SHIFT;
 151                 npages = (min(range->end, end) - addr) >> PAGE_SHIFT;
 152                 memset(&range->pfns[idx], 0, sizeof(*range->pfns) * npages);
 153         }
 154         spin_unlock(&hmm->lock);
 155
 156         down_read(&hmm->mirrors_sem);
 157         list_for_each_entry(mirror, &hmm->mirrors, list)
 158                 mirror->ops->sync_cpu_device_pagetables(mirror, action,
 159                                                         start, end);
 160         up_read(&hmm->mirrors_sem);
 161 }
 162
 163 static void hmm_invalidate_range_start(struct mmu_notifier *mn,
 164                                        struct mm_struct *mm,
 165                                        unsigned long start,
 166                                        unsigned long end)
 167 {
 168         struct hmm *hmm = mm->hmm;
 169
 170         VM_BUG_ON(!hmm);
 171
 172         atomic_inc(&hmm->sequence);
 173 }
 174
 175 static void hmm_invalidate_range_end(struct mmu_notifier *mn,
 176                                      struct mm_struct *mm,
 177                                      unsigned long start,
 178                                      unsigned long end)
 179 {
 180         struct hmm *hmm = mm->hmm;
 181
 182         VM_BUG_ON(!hmm);
 183
 184         hmm_invalidate_range(mm->hmm, HMM_UPDATE_INVALIDATE, start, end);
 185 }
 186
 187 static const struct mmu_notifier_ops hmm_mmu_notifier_ops = {
 188         .invalidate_range_start = hmm_invalidate_range_start,
 189         .invalidate_range_end   = hmm_invalidate_range_end,
 190 };
 191
 192 /*
 193  * hmm_mirror_register() - register a mirror against an mm
 194  *
 195  * @mirror: new mirror struct to register
 196  * @mm: mm to register against
 197  *
 198  * To start mirroring a process address space, the device driver must register
 199  * an HMM mirror struct.
 200  *
 201  * THE mm->mmap_sem MUST BE HELD IN WRITE MODE !
 202  */
 203 int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm)
 204 {
 205         /* Sanity check */
 206         if (!mm || !mirror || !mirror->ops)
 207                 return -EINVAL;
 208
 209         mirror->hmm = hmm_register(mm);
 210         if (!mirror->hmm)
 211                 return -ENOMEM;
 212
 213         down_write(&mirror->hmm->mirrors_sem);
 214         list_add(&mirror->list, &mirror->hmm->mirrors);
 215         up_write(&mirror->hmm->mirrors_sem);
 216
 217         return 0;
 218 }
 219 EXPORT_SYMBOL(hmm_mirror_register);
 220
 221 /*
 222  * hmm_mirror_unregister() - unregister a mirror
 223  *
 224  * @mirror: new mirror struct to register
 225  *
 226  * Stop mirroring a process address space, and cleanup.
 227  */
 228 void hmm_mirror_unregister(struct hmm_mirror *mirror)
 229 {
 230         struct hmm *hmm = mirror->hmm;
 231
 232         down_write(&hmm->mirrors_sem);
 233         list_del(&mirror->list);
 234         up_write(&hmm->mirrors_sem);
 235 }
 236 EXPORT_SYMBOL(hmm_mirror_unregister);
 237
 238 struct hmm_vma_walk {
 239         struct hmm_range        *range;
 240         unsigned long           last;
 241         bool                    fault;
 242         bool                    block;
 243         bool                    write;
 244 };
 245
 246 static int hmm_vma_do_fault(struct mm_walk *walk,
 247                             unsigned long addr,
 248                             hmm_pfn_t *pfn)
 249 {
 250         unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_REMOTE;
 251         struct hmm_vma_walk *hmm_vma_walk = walk->private;
 252         struct vm_area_struct *vma = walk->vma;
 253         int r;
 254
 255         flags |= hmm_vma_walk->block ? 0 : FAULT_FLAG_ALLOW_RETRY;
 256         flags |= hmm_vma_walk->write ? FAULT_FLAG_WRITE : 0;
 257         r = handle_mm_fault(vma, addr, flags);
 258         if (r & VM_FAULT_RETRY)
 259                 return -EBUSY;
 260         if (r & VM_FAULT_ERROR) {
 261                 *pfn = HMM_PFN_ERROR;
 262                 return -EFAULT;
 263         }
 264
 265         return -EAGAIN;
 266 }
 267
 268 static void hmm_pfns_special(hmm_pfn_t *pfns,
 269                              unsigned long addr,
 270                              unsigned long end)
 271 {
 272         for (; addr < end; addr += PAGE_SIZE, pfns++)
 273                 *pfns = HMM_PFN_SPECIAL;
 274 }
 275
 276 static int hmm_pfns_bad(unsigned long addr,
 277                         unsigned long end,
 278                         struct mm_walk *walk)
 279 {
 280         struct hmm_range *range = walk->private;
 281         hmm_pfn_t *pfns = range->pfns;
 282         unsigned long i;
 283
 284         i = (addr - range->start) >> PAGE_SHIFT;
 285         for (; addr < end; addr += PAGE_SIZE, i++)
 286                 pfns[i] = HMM_PFN_ERROR;
 287
 288         return 0;
 289 }
 290
 291 static void hmm_pfns_clear(hmm_pfn_t *pfns,
 292                            unsigned long addr,
 293                            unsigned long end)
 294 {
 295         for (; addr < end; addr += PAGE_SIZE, pfns++)
 296                 *pfns = 0;
 297 }
 298
 299 static int hmm_vma_walk_hole(unsigned long addr,
 300                              unsigned long end,
 301                              struct mm_walk *walk)
 302 {
 303         struct hmm_vma_walk *hmm_vma_walk = walk->private;
 304         struct hmm_range *range = hmm_vma_walk->range;
 305         hmm_pfn_t *pfns = range->pfns;
 306         unsigned long i;
 307
 308         hmm_vma_walk->last = addr;
 309         i = (addr - range->start) >> PAGE_SHIFT;
 310         for (; addr < end; addr += PAGE_SIZE, i++) {
 311                 pfns[i] = HMM_PFN_EMPTY;
 312                 if (hmm_vma_walk->fault) {
 313                         int ret;
 314
 315                         ret = hmm_vma_do_fault(walk, addr, &pfns[i]);
 316                         if (ret != -EAGAIN)
 317                                 return ret;
 318                 }
 319         }
 320
 321         return hmm_vma_walk->fault ? -EAGAIN : 0;
 322 }
 323
 324 static int hmm_vma_walk_clear(unsigned long addr,
 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         hmm_pfn_t *pfns = range->pfns;
 331         unsigned long i;
 332
 333         hmm_vma_walk->last = addr;
 334         i = (addr - range->start) >> PAGE_SHIFT;
 335         for (; addr < end; addr += PAGE_SIZE, i++) {
 336                 pfns[i] = 0;
 337                 if (hmm_vma_walk->fault) {
 338                         int ret;
 339
 340                         ret = hmm_vma_do_fault(walk, addr, &pfns[i]);
 341                         if (ret != -EAGAIN)
 342                                 return ret;
 343                 }
 344         }
 345
 346         return hmm_vma_walk->fault ? -EAGAIN : 0;
 347 }
 348
 349 static int hmm_vma_walk_pmd(pmd_t *pmdp,
 350                             unsigned long start,
 351                             unsigned long end,
 352                             struct mm_walk *walk)
 353 {
 354         struct hmm_vma_walk *hmm_vma_walk = walk->private;
 355         struct hmm_range *range = hmm_vma_walk->range;
 356         struct vm_area_struct *vma = walk->vma;
 357         hmm_pfn_t *pfns = range->pfns;
 358         unsigned long addr = start, i;
 359         bool write_fault;
 360         hmm_pfn_t flag;
 361         pte_t *ptep;
 362
 363         i = (addr - range->start) >> PAGE_SHIFT;
 364         flag = vma->vm_flags & VM_READ ? HMM_PFN_READ : 0;
 365         write_fault = hmm_vma_walk->fault & hmm_vma_walk->write;
 366
 367 again:
 368         if (pmd_none(*pmdp))
 369                 return hmm_vma_walk_hole(start, end, walk);
 370
 371         if (pmd_huge(*pmdp) && vma->vm_flags & VM_HUGETLB)
 372                 return hmm_pfns_bad(start, end, walk);
 373
 374         if (pmd_devmap(*pmdp) || pmd_trans_huge(*pmdp)) {
 375                 unsigned long pfn;
 376                 pmd_t pmd;
 377
 378                 /*
 379                  * No need to take pmd_lock here, even if some other threads
 380                  * is splitting the huge pmd we will get that event through
 381                  * mmu_notifier callback.
 382                  *
 383                  * So just read pmd value and check again its a transparent
 384                  * huge or device mapping one and compute corresponding pfn
 385                  * values.
 386                  */
 387                 pmd = pmd_read_atomic(pmdp);
 388                 barrier();
 389                 if (!pmd_devmap(pmd) && !pmd_trans_huge(pmd))
 390                         goto again;
 391                 if (pmd_protnone(pmd))
 392                         return hmm_vma_walk_clear(start, end, walk);
 393
 394                 if (write_fault && !pmd_write(pmd))
 395                         return hmm_vma_walk_clear(start, end, walk);
 396
 397                 pfn = pmd_pfn(pmd) + pte_index(addr);
 398                 flag |= pmd_write(pmd) ? HMM_PFN_WRITE : 0;
 399                 for (; addr < end; addr += PAGE_SIZE, i++, pfn++)
 400                         pfns[i] = hmm_pfn_t_from_pfn(pfn) | flag;
 401                 return 0;
 402         }
 403
 404         if (pmd_bad(*pmdp))
 405                 return hmm_pfns_bad(start, end, walk);
 406
 407         ptep = pte_offset_map(pmdp, addr);
 408         for (; addr < end; addr += PAGE_SIZE, ptep++, i++) {
 409                 pte_t pte = *ptep;
 410
 411                 pfns[i] = 0;
 412
 413                 if (pte_none(pte)) {
 414                         pfns[i] = HMM_PFN_EMPTY;
 415                         if (hmm_vma_walk->fault)
 416                                 goto fault;
 417                         continue;
 418                 }
 419
 420                 if (!pte_present(pte)) {
 421                         swp_entry_t entry;
 422
 423                         if (!non_swap_entry(entry)) {
 424                                 if (hmm_vma_walk->fault)
 425                                         goto fault;
 426                                 continue;
 427                         }
 428
 429                         entry = pte_to_swp_entry(pte);
 430
 431                         /*
 432                          * This is a special swap entry, ignore migration, use
 433                          * device and report anything else as error.
 434                          */
 435                         if (is_device_private_entry(entry)) {
 436                                 pfns[i] = hmm_pfn_t_from_pfn(swp_offset(entry));
 437                                 if (is_write_device_private_entry(entry)) {
 438                                         pfns[i] |= HMM_PFN_WRITE;
 439                                 } else if (write_fault)
 440                                         goto fault;
 441                                 pfns[i] |= HMM_PFN_DEVICE_UNADDRESSABLE;
 442                                 pfns[i] |= flag;
 443                         } else if (is_migration_entry(entry)) {
 444                                 if (hmm_vma_walk->fault) {
 445                                         pte_unmap(ptep);
 446                                         hmm_vma_walk->last = addr;
 447                                         migration_entry_wait(vma->vm_mm,
 448                                                              pmdp, addr);
 449                                         return -EAGAIN;
 450                                 }
 451                                 continue;
 452                         } else {
 453                                 /* Report error for everything else */
 454                                 pfns[i] = HMM_PFN_ERROR;
 455                         }
 456                         continue;
 457                 }
 458
 459                 if (write_fault && !pte_write(pte))
 460                         goto fault;
 461
 462                 pfns[i] = hmm_pfn_t_from_pfn(pte_pfn(pte)) | flag;
 463                 pfns[i] |= pte_write(pte) ? HMM_PFN_WRITE : 0;
 464                 continue;
 465
 466 fault:
 467                 pte_unmap(ptep);
 468                 /* Fault all pages in range */
 469                 return hmm_vma_walk_clear(start, end, walk);
 470         }
 471         pte_unmap(ptep - 1);
 472
 473         return 0;
 474 }
 475
 476 /*
 477  * hmm_vma_get_pfns() - snapshot CPU page table for a range of virtual addresses
 478  * @vma: virtual memory area containing the virtual address range
 479  * @range: used to track snapshot validity
 480  * @start: range virtual start address (inclusive)
 481  * @end: range virtual end address (exclusive)
 482  * @entries: array of hmm_pfn_t: provided by the caller, filled in by function
 483  * Returns: -EINVAL if invalid argument, -ENOMEM out of memory, 0 success
 484  *
 485  * This snapshots the CPU page table for a range of virtual addresses. Snapshot
 486  * validity is tracked by range struct. See hmm_vma_range_done() for further
 487  * information.
 488  *
 489  * The range struct is initialized here. It tracks the CPU page table, but only
 490  * if the function returns success (0), in which case the caller must then call
 491  * hmm_vma_range_done() to stop CPU page table update tracking on this range.
 492  *
 493  * NOT CALLING hmm_vma_range_done() IF FUNCTION RETURNS 0 WILL LEAD TO SERIOUS
 494  * MEMORY CORRUPTION ! YOU HAVE BEEN WARNED !
 495  */
 496 int hmm_vma_get_pfns(struct vm_area_struct *vma,
 497                      struct hmm_range *range,
 498                      unsigned long start,
 499                      unsigned long end,
 500                      hmm_pfn_t *pfns)
 501 {
 502         struct hmm_vma_walk hmm_vma_walk;
 503         struct mm_walk mm_walk;
 504         struct hmm *hmm;
 505
 506         /* FIXME support hugetlb fs */
 507         if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL)) {
 508                 hmm_pfns_special(pfns, start, end);
 509                 return -EINVAL;
 510         }
 511
 512         /* Sanity check, this really should not happen ! */
 513         if (start < vma->vm_start || start >= vma->vm_end)
 514                 return -EINVAL;
 515         if (end < vma->vm_start || end > vma->vm_end)
 516                 return -EINVAL;
 517
 518         hmm = hmm_register(vma->vm_mm);
 519         if (!hmm)
 520                 return -ENOMEM;
 521         /* Caller must have registered a mirror, via hmm_mirror_register() ! */
 522         if (!hmm->mmu_notifier.ops)
 523                 return -EINVAL;
 524
 525         /* Initialize range to track CPU page table update */
 526         range->start = start;
 527         range->pfns = pfns;
 528         range->end = end;
 529         spin_lock(&hmm->lock);
 530         range->valid = true;
 531         list_add_rcu(&range->list, &hmm->ranges);
 532         spin_unlock(&hmm->lock);
 533
 534         hmm_vma_walk.fault = false;
 535         hmm_vma_walk.range = range;
 536         mm_walk.private = &hmm_vma_walk;
 537
 538         mm_walk.vma = vma;
 539         mm_walk.mm = vma->vm_mm;
 540         mm_walk.pte_entry = NULL;
 541         mm_walk.test_walk = NULL;
 542         mm_walk.hugetlb_entry = NULL;
 543         mm_walk.pmd_entry = hmm_vma_walk_pmd;
 544         mm_walk.pte_hole = hmm_vma_walk_hole;
 545
 546         walk_page_range(start, end, &mm_walk);
 547         return 0;
 548 }
 549 EXPORT_SYMBOL(hmm_vma_get_pfns);
 550
 551 /*
 552  * hmm_vma_range_done() - stop tracking change to CPU page table over a range
 553  * @vma: virtual memory area containing the virtual address range
 554  * @range: range being tracked
 555  * Returns: false if range data has been invalidated, true otherwise
 556  *
 557  * Range struct is used to track updates to the CPU page table after a call to
 558  * either hmm_vma_get_pfns() or hmm_vma_fault(). Once the device driver is done
 559  * using the data,  or wants to lock updates to the data it got from those
 560  * functions, it must call the hmm_vma_range_done() function, which will then
 561  * stop tracking CPU page table updates.
 562  *
 563  * Note that device driver must still implement general CPU page table update
 564  * tracking either by using hmm_mirror (see hmm_mirror_register()) or by using
 565  * the mmu_notifier API directly.
 566  *
 567  * CPU page table update tracking done through hmm_range is only temporary and
 568  * to be used while trying to duplicate CPU page table contents for a range of
 569  * virtual addresses.
 570  *
 571  * There are two ways to use this :
 572  * again:
 573  *   hmm_vma_get_pfns(vma, range, start, end, pfns); or hmm_vma_fault(...);
 574  *   trans = device_build_page_table_update_transaction(pfns);
 575  *   device_page_table_lock();
 576  *   if (!hmm_vma_range_done(vma, range)) {
 577  *     device_page_table_unlock();
 578  *     goto again;
 579  *   }
 580  *   device_commit_transaction(trans);
 581  *   device_page_table_unlock();
 582  *
 583  * Or:
 584  *   hmm_vma_get_pfns(vma, range, start, end, pfns); or hmm_vma_fault(...);
 585  *   device_page_table_lock();
 586  *   hmm_vma_range_done(vma, range);
 587  *   device_update_page_table(pfns);
 588  *   device_page_table_unlock();
 589  */
 590 bool hmm_vma_range_done(struct vm_area_struct *vma, struct hmm_range *range)
 591 {
 592         unsigned long npages = (range->end - range->start) >> PAGE_SHIFT;
 593         struct hmm *hmm;
 594
 595         if (range->end <= range->start) {
 596                 BUG();
 597                 return false;
 598         }
 599
 600         hmm = hmm_register(vma->vm_mm);
 601         if (!hmm) {
 602                 memset(range->pfns, 0, sizeof(*range->pfns) * npages);
 603                 return false;
 604         }
 605
 606         spin_lock(&hmm->lock);
 607         list_del_rcu(&range->list);
 608         spin_unlock(&hmm->lock);
 609
 610         return range->valid;
 611 }
 612 EXPORT_SYMBOL(hmm_vma_range_done);
 613
 614 /*
 615  * hmm_vma_fault() - try to fault some address in a virtual address range
 616  * @vma: virtual memory area containing the virtual address range
 617  * @range: use to track pfns array content validity
 618  * @start: fault range virtual start address (inclusive)
 619  * @end: fault range virtual end address (exclusive)
 620  * @pfns: array of hmm_pfn_t, only entry with fault flag set will be faulted
 621  * @write: is it a write fault
 622  * @block: allow blocking on fault (if true it sleeps and do not drop mmap_sem)
 623  * Returns: 0 success, error otherwise (-EAGAIN means mmap_sem have been drop)
 624  *
 625  * This is similar to a regular CPU page fault except that it will not trigger
 626  * any memory migration if the memory being faulted is not accessible by CPUs.
 627  *
 628  * On error, for one virtual address in the range, the function will set the
 629  * hmm_pfn_t error flag for the corresponding pfn entry.
 630  *
 631  * Expected use pattern:
 632  * retry:
 633  *   down_read(&mm->mmap_sem);
 634  *   // Find vma and address device wants to fault, initialize hmm_pfn_t
 635  *   // array accordingly
 636  *   ret = hmm_vma_fault(vma, start, end, pfns, allow_retry);
 637  *   switch (ret) {
 638  *   case -EAGAIN:
 639  *     hmm_vma_range_done(vma, range);
 640  *     // You might want to rate limit or yield to play nicely, you may
 641  *     // also commit any valid pfn in the array assuming that you are
 642  *     // getting true from hmm_vma_range_monitor_end()
 643  *     goto retry;
 644  *   case 0:
 645  *     break;
 646  *   default:
 647  *     // Handle error !
 648  *     up_read(&mm->mmap_sem)
 649  *     return;
 650  *   }
 651  *   // Take device driver lock that serialize device page table update
 652  *   driver_lock_device_page_table_update();
 653  *   hmm_vma_range_done(vma, range);
 654  *   // Commit pfns we got from hmm_vma_fault()
 655  *   driver_unlock_device_page_table_update();
 656  *   up_read(&mm->mmap_sem)
 657  *
 658  * YOU MUST CALL hmm_vma_range_done() AFTER THIS FUNCTION RETURN SUCCESS (0)
 659  * BEFORE FREEING THE range struct OR YOU WILL HAVE SERIOUS MEMORY CORRUPTION !
 660  *
 661  * YOU HAVE BEEN WARNED !
 662  */
 663 int hmm_vma_fault(struct vm_area_struct *vma,
 664                   struct hmm_range *range,
 665                   unsigned long start,
 666                   unsigned long end,
 667                   hmm_pfn_t *pfns,
 668                   bool write,
 669                   bool block)
 670 {
 671         struct hmm_vma_walk hmm_vma_walk;
 672         struct mm_walk mm_walk;
 673         struct hmm *hmm;
 674         int ret;
 675
 676         /* Sanity check, this really should not happen ! */
 677         if (start < vma->vm_start || start >= vma->vm_end)
 678                 return -EINVAL;
 679         if (end < vma->vm_start || end > vma->vm_end)
 680                 return -EINVAL;
 681
 682         hmm = hmm_register(vma->vm_mm);
 683         if (!hmm) {
 684                 hmm_pfns_clear(pfns, start, end);
 685                 return -ENOMEM;
 686         }
 687         /* Caller must have registered a mirror using hmm_mirror_register() */
 688         if (!hmm->mmu_notifier.ops)
 689                 return -EINVAL;
 690
 691         /* Initialize range to track CPU page table update */
 692         range->start = start;
 693         range->pfns = pfns;
 694         range->end = end;
 695         spin_lock(&hmm->lock);
 696         range->valid = true;
 697         list_add_rcu(&range->list, &hmm->ranges);
 698         spin_unlock(&hmm->lock);
 699
 700         /* FIXME support hugetlb fs */
 701         if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL)) {
 702                 hmm_pfns_special(pfns, start, end);
 703                 return 0;
 704         }
 705
 706         hmm_vma_walk.fault = true;
 707         hmm_vma_walk.write = write;
 708         hmm_vma_walk.block = block;
 709         hmm_vma_walk.range = range;
 710         mm_walk.private = &hmm_vma_walk;
 711         hmm_vma_walk.last = range->start;
 712
 713         mm_walk.vma = vma;
 714         mm_walk.mm = vma->vm_mm;
 715         mm_walk.pte_entry = NULL;
 716         mm_walk.test_walk = NULL;
 717         mm_walk.hugetlb_entry = NULL;
 718         mm_walk.pmd_entry = hmm_vma_walk_pmd;
 719         mm_walk.pte_hole = hmm_vma_walk_hole;
 720
 721         do {
 722                 ret = walk_page_range(start, end, &mm_walk);
 723                 start = hmm_vma_walk.last;
 724         } while (ret == -EAGAIN);
 725
 726         if (ret) {
 727                 unsigned long i;
 728
 729                 i = (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;
 730                 hmm_pfns_clear(&pfns[i], hmm_vma_walk.last, end);
 731                 hmm_vma_range_done(vma, range);
 732         }
 733         return ret;
 734 }
 735 EXPORT_SYMBOL(hmm_vma_fault);
 736 #endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */
 737
 738
 739 #if IS_ENABLED(CONFIG_DEVICE_PRIVATE) ||  IS_ENABLED(CONFIG_DEVICE_PUBLIC)
 740 struct page *hmm_vma_alloc_locked_page(struct vm_area_struct *vma,
 741                                        unsigned long addr)
 742 {
 743         struct page *page;
 744
 745         page = alloc_page_vma(GFP_HIGHUSER, vma, addr);
 746         if (!page)
 747                 return NULL;
 748         lock_page(page);
 749         return page;
 750 }
 751 EXPORT_SYMBOL(hmm_vma_alloc_locked_page);
 752
 753
 754 static void hmm_devmem_ref_release(struct percpu_ref *ref)
 755 {
 756         struct hmm_devmem *devmem;
 757
 758         devmem = container_of(ref, struct hmm_devmem, ref);
 759         complete(&devmem->completion);
 760 }
 761
 762 static void hmm_devmem_ref_exit(void *data)
 763 {
 764         struct percpu_ref *ref = data;
 765         struct hmm_devmem *devmem;
 766
 767         devmem = container_of(ref, struct hmm_devmem, ref);
 768         percpu_ref_exit(ref);
 769         devm_remove_action(devmem->device, &hmm_devmem_ref_exit, data);
 770 }
 771
 772 static void hmm_devmem_ref_kill(void *data)
 773 {
 774         struct percpu_ref *ref = data;
 775         struct hmm_devmem *devmem;
 776
 777         devmem = container_of(ref, struct hmm_devmem, ref);
 778         percpu_ref_kill(ref);
 779         wait_for_completion(&devmem->completion);
 780         devm_remove_action(devmem->device, &hmm_devmem_ref_kill, data);
 781 }
 782
 783 static int hmm_devmem_fault(struct vm_area_struct *vma,
 784                             unsigned long addr,
 785                             const struct page *page,
 786                             unsigned int flags,
 787                             pmd_t *pmdp)
 788 {
 789         struct hmm_devmem *devmem = page->pgmap->data;
 790
 791         return devmem->ops->fault(devmem, vma, addr, page, flags, pmdp);
 792 }
 793
 794 static void hmm_devmem_free(struct page *page, void *data)
 795 {
 796         struct hmm_devmem *devmem = data;
 797
 798         devmem->ops->free(devmem, page);
 799 }
 800
 801 static DEFINE_MUTEX(hmm_devmem_lock);
 802 static RADIX_TREE(hmm_devmem_radix, GFP_KERNEL);
 803
 804 static void hmm_devmem_radix_release(struct resource *resource)
 805 {
 806         resource_size_t key, align_start, align_size;
 807
 808         align_start = resource->start & ~(PA_SECTION_SIZE - 1);
 809         align_size = ALIGN(resource_size(resource), PA_SECTION_SIZE);
 810
 811         mutex_lock(&hmm_devmem_lock);
 812         for (key = resource->start;
 813              key <= resource->end;
 814              key += PA_SECTION_SIZE)
 815                 radix_tree_delete(&hmm_devmem_radix, key >> PA_SECTION_SHIFT);
 816         mutex_unlock(&hmm_devmem_lock);
 817 }
 818
 819 static void hmm_devmem_release(struct device *dev, void *data)
 820 {
 821         struct hmm_devmem *devmem = data;
 822         struct resource *resource = devmem->resource;
 823         unsigned long start_pfn, npages;
 824         struct zone *zone;
 825         struct page *page;
 826
 827         if (percpu_ref_tryget_live(&devmem->ref)) {
 828                 dev_WARN(dev, "%s: page mapping is still live!\n", __func__);
 829                 percpu_ref_put(&devmem->ref);
 830         }
 831
 832         /* pages are dead and unused, undo the arch mapping */
 833         start_pfn = (resource->start & ~(PA_SECTION_SIZE - 1)) >> PAGE_SHIFT;
 834         npages = ALIGN(resource_size(resource), PA_SECTION_SIZE) >> PAGE_SHIFT;
 835
 836         page = pfn_to_page(start_pfn);
 837         zone = page_zone(page);
 838
 839         mem_hotplug_begin();
 840         if (resource->desc == IORES_DESC_DEVICE_PRIVATE_MEMORY)
 841                 __remove_pages(zone, start_pfn, npages);
 842         else
 843                 arch_remove_memory(start_pfn << PAGE_SHIFT,
 844                                    npages << PAGE_SHIFT);
 845         mem_hotplug_done();
 846
 847         hmm_devmem_radix_release(resource);
 848 }
 849
 850 static struct hmm_devmem *hmm_devmem_find(resource_size_t phys)
 851 {
 852         WARN_ON_ONCE(!rcu_read_lock_held());
 853
 854         return radix_tree_lookup(&hmm_devmem_radix, phys >> PA_SECTION_SHIFT);
 855 }
 856
 857 static int hmm_devmem_pages_create(struct hmm_devmem *devmem)
 858 {
 859         resource_size_t key, align_start, align_size, align_end;
 860         struct device *device = devmem->device;
 861         int ret, nid, is_ram;
 862         unsigned long pfn;
 863
 864         align_start = devmem->resource->start & ~(PA_SECTION_SIZE - 1);
 865         align_size = ALIGN(devmem->resource->start +
 866                            resource_size(devmem->resource),
 867                            PA_SECTION_SIZE) - align_start;
 868
 869         is_ram = region_intersects(align_start, align_size,
 870                                    IORESOURCE_SYSTEM_RAM,
 871                                    IORES_DESC_NONE);
 872         if (is_ram == REGION_MIXED) {
 873                 WARN_ONCE(1, "%s attempted on mixed region %pr\n",
 874                                 __func__, devmem->resource);
 875                 return -ENXIO;
 876         }
 877         if (is_ram == REGION_INTERSECTS)
 878                 return -ENXIO;
 879
 880         if (devmem->resource->desc == IORES_DESC_DEVICE_PUBLIC_MEMORY)
 881                 devmem->pagemap.type = MEMORY_DEVICE_PUBLIC;
 882         else
 883                 devmem->pagemap.type = MEMORY_DEVICE_PRIVATE;
 884
 885         devmem->pagemap.res = devmem->resource;
 886         devmem->pagemap.page_fault = hmm_devmem_fault;
 887         devmem->pagemap.page_free = hmm_devmem_free;
 888         devmem->pagemap.dev = devmem->device;
 889         devmem->pagemap.ref = &devmem->ref;
 890         devmem->pagemap.data = devmem;
 891
 892         mutex_lock(&hmm_devmem_lock);
 893         align_end = align_start + align_size - 1;
 894         for (key = align_start; key <= align_end; key += PA_SECTION_SIZE) {
 895                 struct hmm_devmem *dup;
 896
 897                 rcu_read_lock();
 898                 dup = hmm_devmem_find(key);
 899                 rcu_read_unlock();
 900                 if (dup) {
 901                         dev_err(device, "%s: collides with mapping for %s\n",
 902                                 __func__, dev_name(dup->device));
 903                         mutex_unlock(&hmm_devmem_lock);
 904                         ret = -EBUSY;
 905                         goto error;
 906                 }
 907                 ret = radix_tree_insert(&hmm_devmem_radix,
 908                                         key >> PA_SECTION_SHIFT,
 909                                         devmem);
 910                 if (ret) {
 911                         dev_err(device, "%s: failed: %d\n", __func__, ret);
 912                         mutex_unlock(&hmm_devmem_lock);
 913                         goto error_radix;
 914                 }
 915         }
 916         mutex_unlock(&hmm_devmem_lock);
 917
 918         nid = dev_to_node(device);
 919         if (nid < 0)
 920                 nid = numa_mem_id();
 921
 922         mem_hotplug_begin();
 923         /*
 924          * For device private memory we call add_pages() as we only need to
 925          * allocate and initialize struct page for the device memory. More-
 926          * over the device memory is un-accessible thus we do not want to
 927          * create a linear mapping for the memory like arch_add_memory()
 928          * would do.
 929          *
 930          * For device public memory, which is accesible by the CPU, we do
 931          * want the linear mapping and thus use arch_add_memory().
 932          */
 933         if (devmem->pagemap.type == MEMORY_DEVICE_PUBLIC)
 934                 ret = arch_add_memory(nid, align_start, align_size, false);
 935         else
 936                 ret = add_pages(nid, align_start >> PAGE_SHIFT,
 937                                 align_size >> PAGE_SHIFT, false);
 938         if (ret) {
 939                 mem_hotplug_done();
 940                 goto error_add_memory;
 941         }
 942         move_pfn_range_to_zone(&NODE_DATA(nid)->node_zones[ZONE_DEVICE],
 943                                 align_start >> PAGE_SHIFT,
 944                                 align_size >> PAGE_SHIFT);
 945         mem_hotplug_done();
 946
 947         for (pfn = devmem->pfn_first; pfn < devmem->pfn_last; pfn++) {
 948                 struct page *page = pfn_to_page(pfn);
 949
 950                 page->pgmap = &devmem->pagemap;
 951         }
 952         return 0;
 953
 954 error_add_memory:
 955         untrack_pfn(NULL, PHYS_PFN(align_start), align_size);
 956 error_radix:
 957         hmm_devmem_radix_release(devmem->resource);
 958 error:
 959         return ret;
 960 }
 961
 962 static int hmm_devmem_match(struct device *dev, void *data, void *match_data)
 963 {
 964         struct hmm_devmem *devmem = data;
 965
 966         return devmem->resource == match_data;
 967 }
 968
 969 static void hmm_devmem_pages_remove(struct hmm_devmem *devmem)
 970 {
 971         devres_release(devmem->device, &hmm_devmem_release,
 972                        &hmm_devmem_match, devmem->resource);
 973 }
 974
 975 /*
 976  * hmm_devmem_add() - hotplug ZONE_DEVICE memory for device memory
 977  *
 978  * @ops: memory event device driver callback (see struct hmm_devmem_ops)
 979  * @device: device struct to bind the resource too
 980  * @size: size in bytes of the device memory to add
 981  * Returns: pointer to new hmm_devmem struct ERR_PTR otherwise
 982  *
 983  * This function first finds an empty range of physical address big enough to
 984  * contain the new resource, and then hotplugs it as ZONE_DEVICE memory, which
 985  * in turn allocates struct pages. It does not do anything beyond that; all
 986  * events affecting the memory will go through the various callbacks provided
 987  * by hmm_devmem_ops struct.
 988  *
 989  * Device driver should call this function during device initialization and
 990  * is then responsible of memory management. HMM only provides helpers.
 991  */
 992 struct hmm_devmem *hmm_devmem_add(const struct hmm_devmem_ops *ops,
 993                                   struct device *device,
 994                                   unsigned long size)
 995 {
 996         struct hmm_devmem *devmem;
 997         resource_size_t addr;
 998         int ret;
 999
1000         static_branch_enable(&device_private_key);
1001
1002         devmem = devres_alloc_node(&hmm_devmem_release, sizeof(*devmem),
1003                                    GFP_KERNEL, dev_to_node(device));
1004         if (!devmem)
1005                 return ERR_PTR(-ENOMEM);
1006
1007         init_completion(&devmem->completion);
1008         devmem->pfn_first = -1UL;
1009         devmem->pfn_last = -1UL;
1010         devmem->resource = NULL;
1011         devmem->device = device;
1012         devmem->ops = ops;
1013
1014         ret = percpu_ref_init(&devmem->ref, &hmm_devmem_ref_release,
1015                               0, GFP_KERNEL);
1016         if (ret)
1017                 goto error_percpu_ref;
1018
1019         ret = devm_add_action(device, hmm_devmem_ref_exit, &devmem->ref);
1020         if (ret)
1021                 goto error_devm_add_action;
1022
1023         size = ALIGN(size, PA_SECTION_SIZE);
1024         addr = min((unsigned long)iomem_resource.end,
1025                    (1UL << MAX_PHYSMEM_BITS) - 1);
1026         addr = addr - size + 1UL;
1027
1028         /*
1029          * FIXME add a new helper to quickly walk resource tree and find free
1030          * range
1031          *
1032          * FIXME what about ioport_resource resource ?
1033          */
1034         for (; addr > size && addr >= iomem_resource.start; addr -= size) {
1035                 ret = region_intersects(addr, size, 0, IORES_DESC_NONE);
1036                 if (ret != REGION_DISJOINT)
1037                         continue;
1038
1039                 devmem->resource = devm_request_mem_region(device, addr, size,
1040                                                            dev_name(device));
1041                 if (!devmem->resource) {
1042                         ret = -ENOMEM;
1043                         goto error_no_resource;
1044                 }
1045                 break;
1046         }
1047         if (!devmem->resource) {
1048                 ret = -ERANGE;
1049                 goto error_no_resource;
1050         }
1051
1052         devmem->resource->desc = IORES_DESC_DEVICE_PRIVATE_MEMORY;
1053         devmem->pfn_first = devmem->resource->start >> PAGE_SHIFT;
1054         devmem->pfn_last = devmem->pfn_first +
1055                            (resource_size(devmem->resource) >> PAGE_SHIFT);
1056
1057         ret = hmm_devmem_pages_create(devmem);
1058         if (ret)
1059                 goto error_pages;
1060
1061         devres_add(device, devmem);
1062
1063         ret = devm_add_action(device, hmm_devmem_ref_kill, &devmem->ref);
1064         if (ret) {
1065                 hmm_devmem_remove(devmem);
1066                 return ERR_PTR(ret);
1067         }
1068
1069         return devmem;
1070
1071 error_pages:
1072         devm_release_mem_region(device, devmem->resource->start,
1073                                 resource_size(devmem->resource));
1074 error_no_resource:
1075 error_devm_add_action:
1076         hmm_devmem_ref_kill(&devmem->ref);
1077         hmm_devmem_ref_exit(&devmem->ref);
1078 error_percpu_ref:
1079         devres_free(devmem);
1080         return ERR_PTR(ret);
1081 }
1082 EXPORT_SYMBOL(hmm_devmem_add);
1083
1084 struct hmm_devmem *hmm_devmem_add_resource(const struct hmm_devmem_ops *ops,
1085                                            struct device *device,
1086                                            struct resource *res)
1087 {
1088         struct hmm_devmem *devmem;
1089         int ret;
1090
1091         if (res->desc != IORES_DESC_DEVICE_PUBLIC_MEMORY)
1092                 return ERR_PTR(-EINVAL);
1093
1094         static_branch_enable(&device_private_key);
1095
1096         devmem = devres_alloc_node(&hmm_devmem_release, sizeof(*devmem),
1097                                    GFP_KERNEL, dev_to_node(device));
1098         if (!devmem)
1099                 return ERR_PTR(-ENOMEM);
1100
1101         init_completion(&devmem->completion);
1102         devmem->pfn_first = -1UL;
1103         devmem->pfn_last = -1UL;
1104         devmem->resource = res;
1105         devmem->device = device;
1106         devmem->ops = ops;
1107
1108         ret = percpu_ref_init(&devmem->ref, &hmm_devmem_ref_release,
1109                               0, GFP_KERNEL);
1110         if (ret)
1111                 goto error_percpu_ref;
1112
1113         ret = devm_add_action(device, hmm_devmem_ref_exit, &devmem->ref);
1114         if (ret)
1115                 goto error_devm_add_action;
1116
1117
1118         devmem->pfn_first = devmem->resource->start >> PAGE_SHIFT;
1119         devmem->pfn_last = devmem->pfn_first +
1120                            (resource_size(devmem->resource) >> PAGE_SHIFT);
1121
1122         ret = hmm_devmem_pages_create(devmem);
1123         if (ret)
1124                 goto error_devm_add_action;
1125
1126         devres_add(device, devmem);
1127
1128         ret = devm_add_action(device, hmm_devmem_ref_kill, &devmem->ref);
1129         if (ret) {
1130                 hmm_devmem_remove(devmem);
1131                 return ERR_PTR(ret);
1132         }
1133
1134         return devmem;
1135
1136 error_devm_add_action:
1137         hmm_devmem_ref_kill(&devmem->ref);
1138         hmm_devmem_ref_exit(&devmem->ref);
1139 error_percpu_ref:
1140         devres_free(devmem);
1141         return ERR_PTR(ret);
1142 }
1143 EXPORT_SYMBOL(hmm_devmem_add_resource);
1144
1145 /*
1146  * hmm_devmem_remove() - remove device memory (kill and free ZONE_DEVICE)
1147  *
1148  * @devmem: hmm_devmem struct use to track and manage the ZONE_DEVICE memory
1149  *
1150  * This will hot-unplug memory that was hotplugged by hmm_devmem_add on behalf
1151  * of the device driver. It will free struct page and remove the resource that
1152  * reserved the physical address range for this device memory.
1153  */
1154 void hmm_devmem_remove(struct hmm_devmem *devmem)
1155 {
1156         resource_size_t start, size;
1157         struct device *device;
1158         bool cdm = false;
1159
1160         if (!devmem)
1161                 return;
1162
1163         device = devmem->device;
1164         start = devmem->resource->start;
1165         size = resource_size(devmem->resource);
1166
1167         cdm = devmem->resource->desc == IORES_DESC_DEVICE_PUBLIC_MEMORY;
1168         hmm_devmem_ref_kill(&devmem->ref);
1169         hmm_devmem_ref_exit(&devmem->ref);
1170         hmm_devmem_pages_remove(devmem);
1171
1172         if (!cdm)
1173                 devm_release_mem_region(device, start, size);
1174 }
1175 EXPORT_SYMBOL(hmm_devmem_remove);
1176
1177 /*
1178  * A device driver that wants to handle multiple devices memory through a
1179  * single fake device can use hmm_device to do so. This is purely a helper
1180  * and it is not needed to make use of any HMM functionality.
1181  */
1182 #define HMM_DEVICE_MAX 256
1183
1184 static DECLARE_BITMAP(hmm_device_mask, HMM_DEVICE_MAX);
1185 static DEFINE_SPINLOCK(hmm_device_lock);
1186 static struct class *hmm_device_class;
1187 static dev_t hmm_device_devt;
1188
1189 static void hmm_device_release(struct device *device)
1190 {
1191         struct hmm_device *hmm_device;
1192
1193         hmm_device = container_of(device, struct hmm_device, device);
1194         spin_lock(&hmm_device_lock);
1195         clear_bit(hmm_device->minor, hmm_device_mask);
1196         spin_unlock(&hmm_device_lock);
1197
1198         kfree(hmm_device);
1199 }
1200
1201 struct hmm_device *hmm_device_new(void *drvdata)
1202 {
1203         struct hmm_device *hmm_device;
1204
1205         hmm_device = kzalloc(sizeof(*hmm_device), GFP_KERNEL);
1206         if (!hmm_device)
1207                 return ERR_PTR(-ENOMEM);
1208
1209         spin_lock(&hmm_device_lock);
1210         hmm_device->minor = find_first_zero_bit(hmm_device_mask, HMM_DEVICE_MAX);
1211         if (hmm_device->minor >= HMM_DEVICE_MAX) {
1212                 spin_unlock(&hmm_device_lock);
1213                 kfree(hmm_device);
1214                 return ERR_PTR(-EBUSY);
1215         }
1216         set_bit(hmm_device->minor, hmm_device_mask);
1217         spin_unlock(&hmm_device_lock);
1218
1219         dev_set_name(&hmm_device->device, "hmm_device%d", hmm_device->minor);
1220         hmm_device->device.devt = MKDEV(MAJOR(hmm_device_devt),
1221                                         hmm_device->minor);
1222         hmm_device->device.release = hmm_device_release;
1223         dev_set_drvdata(&hmm_device->device, drvdata);
1224         hmm_device->device.class = hmm_device_class;
1225         device_initialize(&hmm_device->device);
1226
1227         return hmm_device;
1228 }
1229 EXPORT_SYMBOL(hmm_device_new);
1230
1231 void hmm_device_put(struct hmm_device *hmm_device)
1232 {
1233         put_device(&hmm_device->device);
1234 }
1235 EXPORT_SYMBOL(hmm_device_put);
1236
1237 static int __init hmm_init(void)
1238 {
1239         int ret;
1240
1241         ret = alloc_chrdev_region(&hmm_device_devt, 0,
1242                                   HMM_DEVICE_MAX,
1243                                   "hmm_device");
1244         if (ret)
1245                 return ret;
1246
1247         hmm_device_class = class_create(THIS_MODULE, "hmm_device");
1248         if (IS_ERR(hmm_device_class)) {
1249                 unregister_chrdev_region(hmm_device_devt, HMM_DEVICE_MAX);
1250                 return PTR_ERR(hmm_device_class);
1251         }
1252         return 0;
1253 }
1254
1255 device_initcall(hmm_init);
1256 #endif /* CONFIG_DEVICE_PRIVATE || CONFIG_DEVICE_PUBLIC */