mm/gup.c

   1 #include <linux/kernel.h>
   2 #include <linux/errno.h>
   3 #include <linux/err.h>
   4 #include <linux/spinlock.h>
   5
   6 #include <linux/mm.h>
   7 #include <linux/memremap.h>
   8 #include <linux/pagemap.h>
   9 #include <linux/rmap.h>
  10 #include <linux/swap.h>
  11 #include <linux/swapops.h>
  12
  13 #include <linux/sched/signal.h>
  14 #include <linux/rwsem.h>
  15 #include <linux/hugetlb.h>
  16 #include <linux/migrate.h>
  17 #include <linux/mm_inline.h>
  18 #include <linux/sched/mm.h>
  19
  20 #include <asm/mmu_context.h>
  21 #include <asm/pgtable.h>
  22 #include <asm/tlbflush.h>
  23
  24 #include "internal.h"
  25
  26 struct follow_page_context {
  27         struct dev_pagemap *pgmap;
  28         unsigned int page_mask;
  29 };
  30
  31 static struct page *no_page_table(struct vm_area_struct *vma,
  32                 unsigned int flags)
  33 {
  34         /*
  35          * When core dumping an enormous anonymous area that nobody
  36          * has touched so far, we don't want to allocate unnecessary pages or
  37          * page tables.  Return error instead of NULL to skip handle_mm_fault,
  38          * then get_dump_page() will return NULL to leave a hole in the dump.
  39          * But we can only make this optimization where a hole would surely
  40          * be zero-filled if handle_mm_fault() actually did handle it.
  41          */
  42         if ((flags & FOLL_DUMP) && (!vma->vm_ops || !vma->vm_ops->fault))
  43                 return ERR_PTR(-EFAULT);
  44         return NULL;
  45 }
  46
  47 static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
  48                 pte_t *pte, unsigned int flags)
  49 {
  50         /* No page to get reference */
  51         if (flags & FOLL_GET)
  52                 return -EFAULT;
  53
  54         if (flags & FOLL_TOUCH) {
  55                 pte_t entry = *pte;
  56
  57                 if (flags & FOLL_WRITE)
  58                         entry = pte_mkdirty(entry);
  59                 entry = pte_mkyoung(entry);
  60
  61                 if (!pte_same(*pte, entry)) {
  62                         set_pte_at(vma->vm_mm, address, pte, entry);
  63                         update_mmu_cache(vma, address, pte);
  64                 }
  65         }
  66
  67         /* Proper page table entry exists, but no corresponding struct page */
  68         return -EEXIST;
  69 }
  70
  71 /*
  72  * FOLL_FORCE can write to even unwritable pte's, but only
  73  * after we've gone through a COW cycle and they are dirty.
  74  */
  75 static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
  76 {
  77         return pte_write(pte) ||
  78                 ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
  79 }
  80
  81 static struct page *follow_page_pte(struct vm_area_struct *vma,
  82                 unsigned long address, pmd_t *pmd, unsigned int flags,
  83                 struct dev_pagemap **pgmap)
  84 {
  85         struct mm_struct *mm = vma->vm_mm;
  86         struct page *page;
  87         spinlock_t *ptl;
  88         pte_t *ptep, pte;
  89
  90 retry:
  91         if (unlikely(pmd_bad(*pmd)))
  92                 return no_page_table(vma, flags);
  93
  94         ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
  95         pte = *ptep;
  96         if (!pte_present(pte)) {
  97                 swp_entry_t entry;
  98                 /*
  99                  * KSM's break_ksm() relies upon recognizing a ksm page
 100                  * even while it is being migrated, so for that case we
 101                  * need migration_entry_wait().
 102                  */
 103                 if (likely(!(flags & FOLL_MIGRATION)))
 104                         goto no_page;
 105                 if (pte_none(pte))
 106                         goto no_page;
 107                 entry = pte_to_swp_entry(pte);
 108                 if (!is_migration_entry(entry))
 109                         goto no_page;
 110                 pte_unmap_unlock(ptep, ptl);
 111                 migration_entry_wait(mm, pmd, address);
 112                 goto retry;
 113         }
 114         if ((flags & FOLL_NUMA) && pte_protnone(pte))
 115                 goto no_page;
 116         if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags)) {
 117                 pte_unmap_unlock(ptep, ptl);
 118                 return NULL;
 119         }
 120
 121         page = vm_normal_page(vma, address, pte);
 122         if (!page && pte_devmap(pte) && (flags & FOLL_GET)) {
 123                 /*
 124                  * Only return device mapping pages in the FOLL_GET case since
 125                  * they are only valid while holding the pgmap reference.
 126                  */
 127                 *pgmap = get_dev_pagemap(pte_pfn(pte), *pgmap);
 128                 if (*pgmap)
 129                         page = pte_page(pte);
 130                 else
 131                         goto no_page;
 132         } else if (unlikely(!page)) {
 133                 if (flags & FOLL_DUMP) {
 134                         /* Avoid special (like zero) pages in core dumps */
 135                         page = ERR_PTR(-EFAULT);
 136                         goto out;
 137                 }
 138
 139                 if (is_zero_pfn(pte_pfn(pte))) {
 140                         page = pte_page(pte);
 141                 } else {
 142                         int ret;
 143
 144                         ret = follow_pfn_pte(vma, address, ptep, flags);
 145                         page = ERR_PTR(ret);
 146                         goto out;
 147                 }
 148         }
 149
 150         if (flags & FOLL_SPLIT && PageTransCompound(page)) {
 151                 int ret;
 152                 get_page(page);
 153                 pte_unmap_unlock(ptep, ptl);
 154                 lock_page(page);
 155                 ret = split_huge_page(page);
 156                 unlock_page(page);
 157                 put_page(page);
 158                 if (ret)
 159                         return ERR_PTR(ret);
 160                 goto retry;
 161         }
 162
 163         if (flags & FOLL_GET)
 164                 get_page(page);
 165         if (flags & FOLL_TOUCH) {
 166                 if ((flags & FOLL_WRITE) &&
 167                     !pte_dirty(pte) && !PageDirty(page))
 168                         set_page_dirty(page);
 169                 /*
 170                  * pte_mkyoung() would be more correct here, but atomic care
 171                  * is needed to avoid losing the dirty bit: it is easier to use
 172                  * mark_page_accessed().
 173                  */
 174                 mark_page_accessed(page);
 175         }
 176         if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
 177                 /* Do not mlock pte-mapped THP */
 178                 if (PageTransCompound(page))
 179                         goto out;
 180
 181                 /*
 182                  * The preliminary mapping check is mainly to avoid the
 183                  * pointless overhead of lock_page on the ZERO_PAGE
 184                  * which might bounce very badly if there is contention.
 185                  *
 186                  * If the page is already locked, we don't need to
 187                  * handle it now - vmscan will handle it later if and
 188                  * when it attempts to reclaim the page.
 189                  */
 190                 if (page->mapping && trylock_page(page)) {
 191                         lru_add_drain();  /* push cached pages to LRU */
 192                         /*
 193                          * Because we lock page here, and migration is
 194                          * blocked by the pte's page reference, and we
 195                          * know the page is still mapped, we don't even
 196                          * need to check for file-cache page truncation.
 197                          */
 198                         mlock_vma_page(page);
 199                         unlock_page(page);
 200                 }
 201         }
 202 out:
 203         pte_unmap_unlock(ptep, ptl);
 204         return page;
 205 no_page:
 206         pte_unmap_unlock(ptep, ptl);
 207         if (!pte_none(pte))
 208                 return NULL;
 209         return no_page_table(vma, flags);
 210 }
 211
 212 static struct page *follow_pmd_mask(struct vm_area_struct *vma,
 213                                     unsigned long address, pud_t *pudp,
 214                                     unsigned int flags,
 215                                     struct follow_page_context *ctx)
 216 {
 217         pmd_t *pmd, pmdval;
 218         spinlock_t *ptl;
 219         struct page *page;
 220         struct mm_struct *mm = vma->vm_mm;
 221
 222         pmd = pmd_offset(pudp, address);
 223         /*
 224          * The READ_ONCE() will stabilize the pmdval in a register or
 225          * on the stack so that it will stop changing under the code.
 226          */
 227         pmdval = READ_ONCE(*pmd);
 228         if (pmd_none(pmdval))
 229                 return no_page_table(vma, flags);
 230         if (pmd_huge(pmdval) && vma->vm_flags & VM_HUGETLB) {
 231                 page = follow_huge_pmd(mm, address, pmd, flags);
 232                 if (page)
 233                         return page;
 234                 return no_page_table(vma, flags);
 235         }
 236         if (is_hugepd(__hugepd(pmd_val(pmdval)))) {
 237                 page = follow_huge_pd(vma, address,
 238                                       __hugepd(pmd_val(pmdval)), flags,
 239                                       PMD_SHIFT);
 240                 if (page)
 241                         return page;
 242                 return no_page_table(vma, flags);
 243         }
 244 retry:
 245         if (!pmd_present(pmdval)) {
 246                 if (likely(!(flags & FOLL_MIGRATION)))
 247                         return no_page_table(vma, flags);
 248                 VM_BUG_ON(thp_migration_supported() &&
 249                                   !is_pmd_migration_entry(pmdval));
 250                 if (is_pmd_migration_entry(pmdval))
 251                         pmd_migration_entry_wait(mm, pmd);
 252                 pmdval = READ_ONCE(*pmd);
 253                 /*
 254                  * MADV_DONTNEED may convert the pmd to null because
 255                  * mmap_sem is held in read mode
 256                  */
 257                 if (pmd_none(pmdval))
 258                         return no_page_table(vma, flags);
 259                 goto retry;
 260         }
 261         if (pmd_devmap(pmdval)) {
 262                 ptl = pmd_lock(mm, pmd);
 263                 page = follow_devmap_pmd(vma, address, pmd, flags, &ctx->pgmap);
 264                 spin_unlock(ptl);
 265                 if (page)
 266                         return page;
 267         }
 268         if (likely(!pmd_trans_huge(pmdval)))
 269                 return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
 270
 271         if ((flags & FOLL_NUMA) && pmd_protnone(pmdval))
 272                 return no_page_table(vma, flags);
 273
 274 retry_locked:
 275         ptl = pmd_lock(mm, pmd);
 276         if (unlikely(pmd_none(*pmd))) {
 277                 spin_unlock(ptl);
 278                 return no_page_table(vma, flags);
 279         }
 280         if (unlikely(!pmd_present(*pmd))) {
 281                 spin_unlock(ptl);
 282                 if (likely(!(flags & FOLL_MIGRATION)))
 283                         return no_page_table(vma, flags);
 284                 pmd_migration_entry_wait(mm, pmd);
 285                 goto retry_locked;
 286         }
 287         if (unlikely(!pmd_trans_huge(*pmd))) {
 288                 spin_unlock(ptl);
 289                 return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
 290         }
 291         if (flags & FOLL_SPLIT) {
 292                 int ret;
 293                 page = pmd_page(*pmd);
 294                 if (is_huge_zero_page(page)) {
 295                         spin_unlock(ptl);
 296                         ret = 0;
 297                         split_huge_pmd(vma, pmd, address);
 298                         if (pmd_trans_unstable(pmd))
 299                                 ret = -EBUSY;
 300                 } else {
 301                         get_page(page);
 302                         spin_unlock(ptl);
 303                         lock_page(page);
 304                         ret = split_huge_page(page);
 305                         unlock_page(page);
 306                         put_page(page);
 307                         if (pmd_none(*pmd))
 308                                 return no_page_table(vma, flags);
 309                 }
 310
 311                 return ret ? ERR_PTR(ret) :
 312                         follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
 313         }
 314         page = follow_trans_huge_pmd(vma, address, pmd, flags);
 315         spin_unlock(ptl);
 316         ctx->page_mask = HPAGE_PMD_NR - 1;
 317         return page;
 318 }
 319
 320 static struct page *follow_pud_mask(struct vm_area_struct *vma,
 321                                     unsigned long address, p4d_t *p4dp,
 322                                     unsigned int flags,
 323                                     struct follow_page_context *ctx)
 324 {
 325         pud_t *pud;
 326         spinlock_t *ptl;
 327         struct page *page;
 328         struct mm_struct *mm = vma->vm_mm;
 329
 330         pud = pud_offset(p4dp, address);
 331         if (pud_none(*pud))
 332                 return no_page_table(vma, flags);
 333         if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
 334                 page = follow_huge_pud(mm, address, pud, flags);
 335                 if (page)
 336                         return page;
 337                 return no_page_table(vma, flags);
 338         }
 339         if (is_hugepd(__hugepd(pud_val(*pud)))) {
 340                 page = follow_huge_pd(vma, address,
 341                                       __hugepd(pud_val(*pud)), flags,
 342                                       PUD_SHIFT);
 343                 if (page)
 344                         return page;
 345                 return no_page_table(vma, flags);
 346         }
 347         if (pud_devmap(*pud)) {
 348                 ptl = pud_lock(mm, pud);
 349                 page = follow_devmap_pud(vma, address, pud, flags, &ctx->pgmap);
 350                 spin_unlock(ptl);
 351                 if (page)
 352                         return page;
 353         }
 354         if (unlikely(pud_bad(*pud)))
 355                 return no_page_table(vma, flags);
 356
 357         return follow_pmd_mask(vma, address, pud, flags, ctx);
 358 }
 359
 360 static struct page *follow_p4d_mask(struct vm_area_struct *vma,
 361                                     unsigned long address, pgd_t *pgdp,
 362                                     unsigned int flags,
 363                                     struct follow_page_context *ctx)
 364 {
 365         p4d_t *p4d;
 366         struct page *page;
 367
 368         p4d = p4d_offset(pgdp, address);
 369         if (p4d_none(*p4d))
 370                 return no_page_table(vma, flags);
 371         BUILD_BUG_ON(p4d_huge(*p4d));
 372         if (unlikely(p4d_bad(*p4d)))
 373                 return no_page_table(vma, flags);
 374
 375         if (is_hugepd(__hugepd(p4d_val(*p4d)))) {
 376                 page = follow_huge_pd(vma, address,
 377                                       __hugepd(p4d_val(*p4d)), flags,
 378                                       P4D_SHIFT);
 379                 if (page)
 380                         return page;
 381                 return no_page_table(vma, flags);
 382         }
 383         return follow_pud_mask(vma, address, p4d, flags, ctx);
 384 }
 385
 386 /**
 387  * follow_page_mask - look up a page descriptor from a user-virtual address
 388  * @vma: vm_area_struct mapping @address
 389  * @address: virtual address to look up
 390  * @flags: flags modifying lookup behaviour
 391  * @ctx: contains dev_pagemap for %ZONE_DEVICE memory pinning and a
 392  *       pointer to output page_mask
 393  *
 394  * @flags can have FOLL_ flags set, defined in <linux/mm.h>
 395  *
 396  * When getting pages from ZONE_DEVICE memory, the @ctx->pgmap caches
 397  * the device's dev_pagemap metadata to avoid repeating expensive lookups.
 398  *
 399  * On output, the @ctx->page_mask is set according to the size of the page.
 400  *
 401  * Return: the mapped (struct page *), %NULL if no mapping exists, or
 402  * an error pointer if there is a mapping to something not represented
 403  * by a page descriptor (see also vm_normal_page()).
 404  */
 405 struct page *follow_page_mask(struct vm_area_struct *vma,
 406                               unsigned long address, unsigned int flags,
 407                               struct follow_page_context *ctx)
 408 {
 409         pgd_t *pgd;
 410         struct page *page;
 411         struct mm_struct *mm = vma->vm_mm;
 412
 413         ctx->page_mask = 0;
 414
 415         /* make this handle hugepd */
 416         page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
 417         if (!IS_ERR(page)) {
 418                 BUG_ON(flags & FOLL_GET);
 419                 return page;
 420         }
 421
 422         pgd = pgd_offset(mm, address);
 423
 424         if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
 425                 return no_page_table(vma, flags);
 426
 427         if (pgd_huge(*pgd)) {
 428                 page = follow_huge_pgd(mm, address, pgd, flags);
 429                 if (page)
 430                         return page;
 431                 return no_page_table(vma, flags);
 432         }
 433         if (is_hugepd(__hugepd(pgd_val(*pgd)))) {
 434                 page = follow_huge_pd(vma, address,
 435                                       __hugepd(pgd_val(*pgd)), flags,
 436                                       PGDIR_SHIFT);
 437                 if (page)
 438                         return page;
 439                 return no_page_table(vma, flags);
 440         }
 441
 442         return follow_p4d_mask(vma, address, pgd, flags, ctx);
 443 }
 444
 445 struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
 446                          unsigned int foll_flags)
 447 {
 448         struct follow_page_context ctx = { NULL };
 449         struct page *page;
 450
 451         page = follow_page_mask(vma, address, foll_flags, &ctx);
 452         if (ctx.pgmap)
 453                 put_dev_pagemap(ctx.pgmap);
 454         return page;
 455 }
 456
 457 static int get_gate_page(struct mm_struct *mm, unsigned long address,
 458                 unsigned int gup_flags, struct vm_area_struct **vma,
 459                 struct page **page)
 460 {
 461         pgd_t *pgd;
 462         p4d_t *p4d;
 463         pud_t *pud;
 464         pmd_t *pmd;
 465         pte_t *pte;
 466         int ret = -EFAULT;
 467
 468         /* user gate pages are read-only */
 469         if (gup_flags & FOLL_WRITE)
 470                 return -EFAULT;
 471         if (address > TASK_SIZE)
 472                 pgd = pgd_offset_k(address);
 473         else
 474                 pgd = pgd_offset_gate(mm, address);
 475         BUG_ON(pgd_none(*pgd));
 476         p4d = p4d_offset(pgd, address);
 477         BUG_ON(p4d_none(*p4d));
 478         pud = pud_offset(p4d, address);
 479         BUG_ON(pud_none(*pud));
 480         pmd = pmd_offset(pud, address);
 481         if (!pmd_present(*pmd))
 482                 return -EFAULT;
 483         VM_BUG_ON(pmd_trans_huge(*pmd));
 484         pte = pte_offset_map(pmd, address);
 485         if (pte_none(*pte))
 486                 goto unmap;
 487         *vma = get_gate_vma(mm);
 488         if (!page)
 489                 goto out;
 490         *page = vm_normal_page(*vma, address, *pte);
 491         if (!*page) {
 492                 if ((gup_flags & FOLL_DUMP) || !is_zero_pfn(pte_pfn(*pte)))
 493                         goto unmap;
 494                 *page = pte_page(*pte);
 495
 496                 /*
 497                  * This should never happen (a device public page in the gate
 498                  * area).
 499                  */
 500                 if (is_device_public_page(*page))
 501                         goto unmap;
 502         }
 503         get_page(*page);
 504 out:
 505         ret = 0;
 506 unmap:
 507         pte_unmap(pte);
 508         return ret;
 509 }
 510
 511 /*
 512  * mmap_sem must be held on entry.  If @nonblocking != NULL and
 513  * *@flags does not include FOLL_NOWAIT, the mmap_sem may be released.
 514  * If it is, *@nonblocking will be set to 0 and -EBUSY returned.
 515  */
 516 static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
 517                 unsigned long address, unsigned int *flags, int *nonblocking)
 518 {
 519         unsigned int fault_flags = 0;
 520         vm_fault_t ret;
 521
 522         /* mlock all present pages, but do not fault in new pages */
 523         if ((*flags & (FOLL_POPULATE | FOLL_MLOCK)) == FOLL_MLOCK)
 524                 return -ENOENT;
 525         if (*flags & FOLL_WRITE)
 526                 fault_flags |= FAULT_FLAG_WRITE;
 527         if (*flags & FOLL_REMOTE)
 528                 fault_flags |= FAULT_FLAG_REMOTE;
 529         if (nonblocking)
 530                 fault_flags |= FAULT_FLAG_ALLOW_RETRY;
 531         if (*flags & FOLL_NOWAIT)
 532                 fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
 533         if (*flags & FOLL_TRIED) {
 534                 VM_WARN_ON_ONCE(fault_flags & FAULT_FLAG_ALLOW_RETRY);
 535                 fault_flags |= FAULT_FLAG_TRIED;
 536         }
 537
 538         ret = handle_mm_fault(vma, address, fault_flags);
 539         if (ret & VM_FAULT_ERROR) {
 540                 int err = vm_fault_to_errno(ret, *flags);
 541
 542                 if (err)
 543                         return err;
 544                 BUG();
 545         }
 546
 547         if (tsk) {
 548                 if (ret & VM_FAULT_MAJOR)
 549                         tsk->maj_flt++;
 550                 else
 551                         tsk->min_flt++;
 552         }
 553
 554         if (ret & VM_FAULT_RETRY) {
 555                 if (nonblocking && !(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
 556                         *nonblocking = 0;
 557                 return -EBUSY;
 558         }
 559
 560         /*
 561          * The VM_FAULT_WRITE bit tells us that do_wp_page has broken COW when
 562          * necessary, even if maybe_mkwrite decided not to set pte_write. We
 563          * can thus safely do subsequent page lookups as if they were reads.
 564          * But only do so when looping for pte_write is futile: in some cases
 565          * userspace may also be wanting to write to the gotten user page,
 566          * which a read fault here might prevent (a readonly page might get
 567          * reCOWed by userspace write).
 568          */
 569         if ((ret & VM_FAULT_WRITE) && !(vma->vm_flags & VM_WRITE))
 570                 *flags |= FOLL_COW;
 571         return 0;
 572 }
 573
 574 static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
 575 {
 576         vm_flags_t vm_flags = vma->vm_flags;
 577         int write = (gup_flags & FOLL_WRITE);
 578         int foreign = (gup_flags & FOLL_REMOTE);
 579
 580         if (vm_flags & (VM_IO | VM_PFNMAP))
 581                 return -EFAULT;
 582
 583         if (gup_flags & FOLL_ANON && !vma_is_anonymous(vma))
 584                 return -EFAULT;
 585
 586         if (write) {
 587                 if (!(vm_flags & VM_WRITE)) {
 588                         if (!(gup_flags & FOLL_FORCE))
 589                                 return -EFAULT;
 590                         /*
 591                          * We used to let the write,force case do COW in a
 592                          * VM_MAYWRITE VM_SHARED !VM_WRITE vma, so ptrace could
 593                          * set a breakpoint in a read-only mapping of an
 594                          * executable, without corrupting the file (yet only
 595                          * when that file had been opened for writing!).
 596                          * Anon pages in shared mappings are surprising: now
 597                          * just reject it.
 598                          */
 599                         if (!is_cow_mapping(vm_flags))
 600                                 return -EFAULT;
 601                 }
 602         } else if (!(vm_flags & VM_READ)) {
 603                 if (!(gup_flags & FOLL_FORCE))
 604                         return -EFAULT;
 605                 /*
 606                  * Is there actually any vma we can reach here which does not
 607                  * have VM_MAYREAD set?
 608                  */
 609                 if (!(vm_flags & VM_MAYREAD))
 610                         return -EFAULT;
 611         }
 612         /*
 613          * gups are always data accesses, not instruction
 614          * fetches, so execute=false here
 615          */
 616         if (!arch_vma_access_permitted(vma, write, false, foreign))
 617                 return -EFAULT;
 618         return 0;
 619 }
 620
 621 /**
 622  * __get_user_pages() - pin user pages in memory
 623  * @tsk:        task_struct of target task
 624  * @mm:         mm_struct of target mm
 625  * @start:      starting user address
 626  * @nr_pages:   number of pages from start to pin
 627  * @gup_flags:  flags modifying pin behaviour
 628  * @pages:      array that receives pointers to the pages pinned.
 629  *              Should be at least nr_pages long. Or NULL, if caller
 630  *              only intends to ensure the pages are faulted in.
 631  * @vmas:       array of pointers to vmas corresponding to each page.
 632  *              Or NULL if the caller does not require them.
 633  * @nonblocking: whether waiting for disk IO or mmap_sem contention
 634  *
 635  * Returns number of pages pinned. This may be fewer than the number
 636  * requested. If nr_pages is 0 or negative, returns 0. If no pages
 637  * were pinned, returns -errno. Each page returned must be released
 638  * with a put_page() call when it is finished with. vmas will only
 639  * remain valid while mmap_sem is held.
 640  *
 641  * Must be called with mmap_sem held.  It may be released.  See below.
 642  *
 643  * __get_user_pages walks a process's page tables and takes a reference to
 644  * each struct page that each user address corresponds to at a given
 645  * instant. That is, it takes the page that would be accessed if a user
 646  * thread accesses the given user virtual address at that instant.
 647  *
 648  * This does not guarantee that the page exists in the user mappings when
 649  * __get_user_pages returns, and there may even be a completely different
 650  * page there in some cases (eg. if mmapped pagecache has been invalidated
 651  * and subsequently re faulted). However it does guarantee that the page
 652  * won't be freed completely. And mostly callers simply care that the page
 653  * contains data that was valid *at some point in time*. Typically, an IO
 654  * or similar operation cannot guarantee anything stronger anyway because
 655  * locks can't be held over the syscall boundary.
 656  *
 657  * If @gup_flags & FOLL_WRITE == 0, the page must not be written to. If
 658  * the page is written to, set_page_dirty (or set_page_dirty_lock, as
 659  * appropriate) must be called after the page is finished with, and
 660  * before put_page is called.
 661  *
 662  * If @nonblocking != NULL, __get_user_pages will not wait for disk IO
 663  * or mmap_sem contention, and if waiting is needed to pin all pages,
 664  * *@nonblocking will be set to 0.  Further, if @gup_flags does not
 665  * include FOLL_NOWAIT, the mmap_sem will be released via up_read() in
 666  * this case.
 667  *
 668  * A caller using such a combination of @nonblocking and @gup_flags
 669  * must therefore hold the mmap_sem for reading only, and recognize
 670  * when it's been released.  Otherwise, it must be held for either
 671  * reading or writing and will not be released.
 672  *
 673  * In most cases, get_user_pages or get_user_pages_fast should be used
 674  * instead of __get_user_pages. __get_user_pages should be used only if
 675  * you need some special @gup_flags.
 676  */
 677 static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 678                 unsigned long start, unsigned long nr_pages,
 679                 unsigned int gup_flags, struct page **pages,
 680                 struct vm_area_struct **vmas, int *nonblocking)
 681 {
 682         long ret = 0, i = 0;
 683         struct vm_area_struct *vma = NULL;
 684         struct follow_page_context ctx = { NULL };
 685
 686         if (!nr_pages)
 687                 return 0;
 688
 689         VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));
 690
 691         /*
 692          * If FOLL_FORCE is set then do not force a full fault as the hinting
 693          * fault information is unrelated to the reference behaviour of a task
 694          * using the address space
 695          */
 696         if (!(gup_flags & FOLL_FORCE))
 697                 gup_flags |= FOLL_NUMA;
 698
 699         do {
 700                 struct page *page;
 701                 unsigned int foll_flags = gup_flags;
 702                 unsigned int page_increm;
 703
 704                 /* first iteration or cross vma bound */
 705                 if (!vma || start >= vma->vm_end) {
 706                         vma = find_extend_vma(mm, start);
 707                         if (!vma && in_gate_area(mm, start)) {
 708                                 ret = get_gate_page(mm, start & PAGE_MASK,
 709                                                 gup_flags, &vma,
 710                                                 pages ? &pages[i] : NULL);
 711                                 if (ret)
 712                                         goto out;
 713                                 ctx.page_mask = 0;
 714                                 goto next_page;
 715                         }
 716
 717                         if (!vma || check_vma_flags(vma, gup_flags)) {
 718                                 ret = -EFAULT;
 719                                 goto out;
 720                         }
 721                         if (is_vm_hugetlb_page(vma)) {
 722                                 i = follow_hugetlb_page(mm, vma, pages, vmas,
 723                                                 &start, &nr_pages, i,
 724                                                 gup_flags, nonblocking);
 725                                 continue;
 726                         }
 727                 }
 728 retry:
 729                 /*
 730                  * If we have a pending SIGKILL, don't keep faulting pages and
 731                  * potentially allocating memory.
 732                  */
 733                 if (fatal_signal_pending(current)) {
 734                         ret = -ERESTARTSYS;
 735                         goto out;
 736                 }
 737                 cond_resched();
 738
 739                 page = follow_page_mask(vma, start, foll_flags, &ctx);
 740                 if (!page) {
 741                         ret = faultin_page(tsk, vma, start, &foll_flags,
 742                                         nonblocking);
 743                         switch (ret) {
 744                         case 0:
 745                                 goto retry;
 746                         case -EBUSY:
 747                                 ret = 0;
 748                                 /* FALLTHRU */
 749                         case -EFAULT:
 750                         case -ENOMEM:
 751                         case -EHWPOISON:
 752                                 goto out;
 753                         case -ENOENT:
 754                                 goto next_page;
 755                         }
 756                         BUG();
 757                 } else if (PTR_ERR(page) == -EEXIST) {
 758                         /*
 759                          * Proper page table entry exists, but no corresponding
 760                          * struct page.
 761                          */
 762                         goto next_page;
 763                 } else if (IS_ERR(page)) {
 764                         ret = PTR_ERR(page);
 765                         goto out;
 766                 }
 767                 if (pages) {
 768                         pages[i] = page;
 769                         flush_anon_page(vma, page, start);
 770                         flush_dcache_page(page);
 771                         ctx.page_mask = 0;
 772                 }
 773 next_page:
 774                 if (vmas) {
 775                         vmas[i] = vma;
 776                         ctx.page_mask = 0;
 777                 }
 778                 page_increm = 1 + (~(start >> PAGE_SHIFT) & ctx.page_mask);
 779                 if (page_increm > nr_pages)
 780                         page_increm = nr_pages;
 781                 i += page_increm;
 782                 start += page_increm * PAGE_SIZE;
 783                 nr_pages -= page_increm;
 784         } while (nr_pages);
 785 out:
 786         if (ctx.pgmap)
 787                 put_dev_pagemap(ctx.pgmap);
 788         return i ? i : ret;
 789 }
 790
 791 static bool vma_permits_fault(struct vm_area_struct *vma,
 792                               unsigned int fault_flags)
 793 {
 794         bool write   = !!(fault_flags & FAULT_FLAG_WRITE);
 795         bool foreign = !!(fault_flags & FAULT_FLAG_REMOTE);
 796         vm_flags_t vm_flags = write ? VM_WRITE : VM_READ;
 797
 798         if (!(vm_flags & vma->vm_flags))
 799                 return false;
 800
 801         /*
 802          * The architecture might have a hardware protection
 803          * mechanism other than read/write that can deny access.
 804          *
 805          * gup always represents data access, not instruction
 806          * fetches, so execute=false here:
 807          */
 808         if (!arch_vma_access_permitted(vma, write, false, foreign))
 809                 return false;
 810
 811         return true;
 812 }
 813
 814 /*
 815  * fixup_user_fault() - manually resolve a user page fault
 816  * @tsk:        the task_struct to use for page fault accounting, or
 817  *              NULL if faults are not to be recorded.
 818  * @mm:         mm_struct of target mm
 819  * @address:    user address
 820  * @fault_flags:flags to pass down to handle_mm_fault()
 821  * @unlocked:   did we unlock the mmap_sem while retrying, maybe NULL if caller
 822  *              does not allow retry
 823  *
 824  * This is meant to be called in the specific scenario where for locking reasons
 825  * we try to access user memory in atomic context (within a pagefault_disable()
 826  * section), this returns -EFAULT, and we want to resolve the user fault before
 827  * trying again.
 828  *
 829  * Typically this is meant to be used by the futex code.
 830  *
 831  * The main difference with get_user_pages() is that this function will
 832  * unconditionally call handle_mm_fault() which will in turn perform all the
 833  * necessary SW fixup of the dirty and young bits in the PTE, while
 834  * get_user_pages() only guarantees to update these in the struct page.
 835  *
 836  * This is important for some architectures where those bits also gate the
 837  * access permission to the page because they are maintained in software.  On
 838  * such architectures, gup() will not be enough to make a subsequent access
 839  * succeed.
 840  *
 841  * This function will not return with an unlocked mmap_sem. So it has not the
 842  * same semantics wrt the @mm->mmap_sem as does filemap_fault().
 843  */
 844 int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
 845                      unsigned long address, unsigned int fault_flags,
 846                      bool *unlocked)
 847 {
 848         struct vm_area_struct *vma;
 849         vm_fault_t ret, major = 0;
 850
 851         if (unlocked)
 852                 fault_flags |= FAULT_FLAG_ALLOW_RETRY;
 853
 854 retry:
 855         vma = find_extend_vma(mm, address);
 856         if (!vma || address < vma->vm_start)
 857                 return -EFAULT;
 858
 859         if (!vma_permits_fault(vma, fault_flags))
 860                 return -EFAULT;
 861
 862         ret = handle_mm_fault(vma, address, fault_flags);
 863         major |= ret & VM_FAULT_MAJOR;
 864         if (ret & VM_FAULT_ERROR) {
 865                 int err = vm_fault_to_errno(ret, 0);
 866
 867                 if (err)
 868                         return err;
 869                 BUG();
 870         }
 871
 872         if (ret & VM_FAULT_RETRY) {
 873                 down_read(&mm->mmap_sem);
 874                 if (!(fault_flags & FAULT_FLAG_TRIED)) {
 875                         *unlocked = true;
 876                         fault_flags &= ~FAULT_FLAG_ALLOW_RETRY;
 877                         fault_flags |= FAULT_FLAG_TRIED;
 878                         goto retry;
 879                 }
 880         }
 881
 882         if (tsk) {
 883                 if (major)
 884                         tsk->maj_flt++;
 885                 else
 886                         tsk->min_flt++;
 887         }
 888         return 0;
 889 }
 890 EXPORT_SYMBOL_GPL(fixup_user_fault);
 891
 892 static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
 893                                                 struct mm_struct *mm,
 894                                                 unsigned long start,
 895                                                 unsigned long nr_pages,
 896                                                 struct page **pages,
 897                                                 struct vm_area_struct **vmas,
 898                                                 int *locked,
 899                                                 unsigned int flags)
 900 {
 901         long ret, pages_done;
 902         bool lock_dropped;
 903
 904         if (locked) {
 905                 /* if VM_FAULT_RETRY can be returned, vmas become invalid */
 906                 BUG_ON(vmas);
 907                 /* check caller initialized locked */
 908                 BUG_ON(*locked != 1);
 909         }
 910
 911         if (pages)
 912                 flags |= FOLL_GET;
 913
 914         pages_done = 0;
 915         lock_dropped = false;
 916         for (;;) {
 917                 ret = __get_user_pages(tsk, mm, start, nr_pages, flags, pages,
 918                                        vmas, locked);
 919                 if (!locked)
 920                         /* VM_FAULT_RETRY couldn't trigger, bypass */
 921                         return ret;
 922
 923                 /* VM_FAULT_RETRY cannot return errors */
 924                 if (!*locked) {
 925                         BUG_ON(ret < 0);
 926                         BUG_ON(ret >= nr_pages);
 927                 }
 928
 929                 if (!pages)
 930                         /* If it's a prefault don't insist harder */
 931                         return ret;
 932
 933                 if (ret > 0) {
 934                         nr_pages -= ret;
 935                         pages_done += ret;
 936                         if (!nr_pages)
 937                                 break;
 938                 }
 939                 if (*locked) {
 940                         /*
 941                          * VM_FAULT_RETRY didn't trigger or it was a
 942                          * FOLL_NOWAIT.
 943                          */
 944                         if (!pages_done)
 945                                 pages_done = ret;
 946                         break;
 947                 }
 948                 /* VM_FAULT_RETRY triggered, so seek to the faulting offset */
 949                 pages += ret;
 950                 start += ret << PAGE_SHIFT;
 951
 952                 /*
 953                  * Repeat on the address that fired VM_FAULT_RETRY
 954                  * without FAULT_FLAG_ALLOW_RETRY but with
 955                  * FAULT_FLAG_TRIED.
 956                  */
 957                 *locked = 1;
 958                 lock_dropped = true;
 959                 down_read(&mm->mmap_sem);
 960                 ret = __get_user_pages(tsk, mm, start, 1, flags | FOLL_TRIED,
 961                                        pages, NULL, NULL);
 962                 if (ret != 1) {
 963                         BUG_ON(ret > 1);
 964                         if (!pages_done)
 965                                 pages_done = ret;
 966                         break;
 967                 }
 968                 nr_pages--;
 969                 pages_done++;
 970                 if (!nr_pages)
 971                         break;
 972                 pages++;
 973                 start += PAGE_SIZE;
 974         }
 975         if (lock_dropped && *locked) {
 976                 /*
 977                  * We must let the caller know we temporarily dropped the lock
 978                  * and so the critical section protected by it was lost.
 979                  */
 980                 up_read(&mm->mmap_sem);
 981                 *locked = 0;
 982         }
 983         return pages_done;
 984 }
 985
 986 /*
 987  * We can leverage the VM_FAULT_RETRY functionality in the page fault
 988  * paths better by using either get_user_pages_locked() or
 989  * get_user_pages_unlocked().
 990  *
 991  * get_user_pages_locked() is suitable to replace the form:
 992  *
 993  *      down_read(&mm->mmap_sem);
 994  *      do_something()
 995  *      get_user_pages(tsk, mm, ..., pages, NULL);
 996  *      up_read(&mm->mmap_sem);
 997  *
 998  *  to:
 999  *
1000  *      int locked = 1;
1001  *      down_read(&mm->mmap_sem);
1002  *      do_something()
1003  *      get_user_pages_locked(tsk, mm, ..., pages, &locked);
1004  *      if (locked)
1005  *          up_read(&mm->mmap_sem);
1006  */
1007 long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
1008                            unsigned int gup_flags, struct page **pages,
1009                            int *locked)
1010 {
1011         return __get_user_pages_locked(current, current->mm, start, nr_pages,
1012                                        pages, NULL, locked,
1013                                        gup_flags | FOLL_TOUCH);
1014 }
1015 EXPORT_SYMBOL(get_user_pages_locked);
1016
1017 /*
1018  * get_user_pages_unlocked() is suitable to replace the form:
1019  *
1020  *      down_read(&mm->mmap_sem);
1021  *      get_user_pages(tsk, mm, ..., pages, NULL);
1022  *      up_read(&mm->mmap_sem);
1023  *
1024  *  with:
1025  *
1026  *      get_user_pages_unlocked(tsk, mm, ..., pages);
1027  *
1028  * It is functionally equivalent to get_user_pages_fast so
1029  * get_user_pages_fast should be used instead if specific gup_flags
1030  * (e.g. FOLL_FORCE) are not required.
1031  */
1032 long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
1033                              struct page **pages, unsigned int gup_flags)
1034 {
1035         struct mm_struct *mm = current->mm;
1036         int locked = 1;
1037         long ret;
1038
1039         down_read(&mm->mmap_sem);
1040         ret = __get_user_pages_locked(current, mm, start, nr_pages, pages, NULL,
1041                                       &locked, gup_flags | FOLL_TOUCH);
1042         if (locked)
1043                 up_read(&mm->mmap_sem);
1044         return ret;
1045 }
1046 EXPORT_SYMBOL(get_user_pages_unlocked);
1047
1048 /*
1049  * get_user_pages_remote() - pin user pages in memory
1050  * @tsk:        the task_struct to use for page fault accounting, or
1051  *              NULL if faults are not to be recorded.
1052  * @mm:         mm_struct of target mm
1053  * @start:      starting user address
1054  * @nr_pages:   number of pages from start to pin
1055  * @gup_flags:  flags modifying lookup behaviour
1056  * @pages:      array that receives pointers to the pages pinned.
1057  *              Should be at least nr_pages long. Or NULL, if caller
1058  *              only intends to ensure the pages are faulted in.
1059  * @vmas:       array of pointers to vmas corresponding to each page.
1060  *              Or NULL if the caller does not require them.
1061  * @locked:     pointer to lock flag indicating whether lock is held and
1062  *              subsequently whether VM_FAULT_RETRY functionality can be
1063  *              utilised. Lock must initially be held.
1064  *
1065  * Returns number of pages pinned. This may be fewer than the number
1066  * requested. If nr_pages is 0 or negative, returns 0. If no pages
1067  * were pinned, returns -errno. Each page returned must be released
1068  * with a put_page() call when it is finished with. vmas will only
1069  * remain valid while mmap_sem is held.
1070  *
1071  * Must be called with mmap_sem held for read or write.
1072  *
1073  * get_user_pages walks a process's page tables and takes a reference to
1074  * each struct page that each user address corresponds to at a given
1075  * instant. That is, it takes the page that would be accessed if a user
1076  * thread accesses the given user virtual address at that instant.
1077  *
1078  * This does not guarantee that the page exists in the user mappings when
1079  * get_user_pages returns, and there may even be a completely different
1080  * page there in some cases (eg. if mmapped pagecache has been invalidated
1081  * and subsequently re faulted). However it does guarantee that the page
1082  * won't be freed completely. And mostly callers simply care that the page
1083  * contains data that was valid *at some point in time*. Typically, an IO
1084  * or similar operation cannot guarantee anything stronger anyway because
1085  * locks can't be held over the syscall boundary.
1086  *
1087  * If gup_flags & FOLL_WRITE == 0, the page must not be written to. If the page
1088  * is written to, set_page_dirty (or set_page_dirty_lock, as appropriate) must
1089  * be called after the page is finished with, and before put_page is called.
1090  *
1091  * get_user_pages is typically used for fewer-copy IO operations, to get a
1092  * handle on the memory by some means other than accesses via the user virtual
1093  * addresses. The pages may be submitted for DMA to devices or accessed via
1094  * their kernel linear mapping (via the kmap APIs). Care should be taken to
1095  * use the correct cache flushing APIs.
1096  *
1097  * See also get_user_pages_fast, for performance critical applications.
1098  *
1099  * get_user_pages should be phased out in favor of
1100  * get_user_pages_locked|unlocked or get_user_pages_fast. Nothing
1101  * should use get_user_pages because it cannot pass
1102  * FAULT_FLAG_ALLOW_RETRY to handle_mm_fault.
1103  */
1104 long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
1105                 unsigned long start, unsigned long nr_pages,
1106                 unsigned int gup_flags, struct page **pages,
1107                 struct vm_area_struct **vmas, int *locked)
1108 {
1109         return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
1110                                        locked,
1111                                        gup_flags | FOLL_TOUCH | FOLL_REMOTE);
1112 }
1113 EXPORT_SYMBOL(get_user_pages_remote);
1114
1115 /*
1116  * This is the same as get_user_pages_remote(), just with a
1117  * less-flexible calling convention where we assume that the task
1118  * and mm being operated on are the current task's and don't allow
1119  * passing of a locked parameter.  We also obviously don't pass
1120  * FOLL_REMOTE in here.
1121  */
1122 long get_user_pages(unsigned long start, unsigned long nr_pages,
1123                 unsigned int gup_flags, struct page **pages,
1124                 struct vm_area_struct **vmas)
1125 {
1126         return __get_user_pages_locked(current, current->mm, start, nr_pages,
1127                                        pages, vmas, NULL,
1128                                        gup_flags | FOLL_TOUCH);
1129 }
1130 EXPORT_SYMBOL(get_user_pages);
1131
1132 #if defined(CONFIG_FS_DAX) || defined (CONFIG_CMA)
1133
1134 #ifdef CONFIG_FS_DAX
1135 static bool check_dax_vmas(struct vm_area_struct **vmas, long nr_pages)
1136 {
1137         long i;
1138         struct vm_area_struct *vma_prev = NULL;
1139
1140         for (i = 0; i < nr_pages; i++) {
1141                 struct vm_area_struct *vma = vmas[i];
1142
1143                 if (vma == vma_prev)
1144                         continue;
1145
1146                 vma_prev = vma;
1147
1148                 if (vma_is_fsdax(vma))
1149                         return true;
1150         }
1151         return false;
1152 }
1153 #else
1154 static inline bool check_dax_vmas(struct vm_area_struct **vmas, long nr_pages)
1155 {
1156         return false;
1157 }
1158 #endif
1159
1160 #ifdef CONFIG_CMA
1161 static struct page *new_non_cma_page(struct page *page, unsigned long private)
1162 {
1163         /*
1164          * We want to make sure we allocate the new page from the same node
1165          * as the source page.
1166          */
1167         int nid = page_to_nid(page);
1168         /*
1169          * Trying to allocate a page for migration. Ignore allocation
1170          * failure warnings. We don't force __GFP_THISNODE here because
1171          * this node here is the node where we have CMA reservation and
1172          * in some case these nodes will have really less non movable
1173          * allocation memory.
1174          */
1175         gfp_t gfp_mask = GFP_USER | __GFP_NOWARN;
1176
1177         if (PageHighMem(page))
1178                 gfp_mask |= __GFP_HIGHMEM;
1179
1180 #ifdef CONFIG_HUGETLB_PAGE
1181         if (PageHuge(page)) {
1182                 struct hstate *h = page_hstate(page);
1183                 /*
1184                  * We don't want to dequeue from the pool because pool pages will
1185                  * mostly be from the CMA region.
1186                  */
1187                 return alloc_migrate_huge_page(h, gfp_mask, nid, NULL);
1188         }
1189 #endif
1190         if (PageTransHuge(page)) {
1191                 struct page *thp;
1192                 /*
1193                  * ignore allocation failure warnings
1194                  */
1195                 gfp_t thp_gfpmask = GFP_TRANSHUGE | __GFP_NOWARN;
1196
1197                 /*
1198                  * Remove the movable mask so that we don't allocate from
1199                  * CMA area again.
1200                  */
1201                 thp_gfpmask &= ~__GFP_MOVABLE;
1202                 thp = __alloc_pages_node(nid, thp_gfpmask, HPAGE_PMD_ORDER);
1203                 if (!thp)
1204                         return NULL;
1205                 prep_transhuge_page(thp);
1206                 return thp;
1207         }
1208
1209         return __alloc_pages_node(nid, gfp_mask, 0);
1210 }
1211
1212 static long check_and_migrate_cma_pages(unsigned long start, long nr_pages,
1213                                         unsigned int gup_flags,
1214                                         struct page **pages,
1215                                         struct vm_area_struct **vmas)
1216 {
1217         long i;
1218         bool drain_allow = true;
1219         bool migrate_allow = true;
1220         LIST_HEAD(cma_page_list);
1221
1222 check_again:
1223         for (i = 0; i < nr_pages; i++) {
1224                 /*
1225                  * If we get a page from the CMA zone, since we are going to
1226                  * be pinning these entries, we might as well move them out
1227                  * of the CMA zone if possible.
1228                  */
1229                 if (is_migrate_cma_page(pages[i])) {
1230
1231                         struct page *head = compound_head(pages[i]);
1232
1233                         if (PageHuge(head)) {
1234                                 isolate_huge_page(head, &cma_page_list);
1235                         } else {
1236                                 if (!PageLRU(head) && drain_allow) {
1237                                         lru_add_drain_all();
1238                                         drain_allow = false;
1239                                 }
1240
1241                                 if (!isolate_lru_page(head)) {
1242                                         list_add_tail(&head->lru, &cma_page_list);
1243                                         mod_node_page_state(page_pgdat(head),
1244                                                             NR_ISOLATED_ANON +
1245                                                             page_is_file_cache(head),
1246                                                             hpage_nr_pages(head));
1247                                 }
1248                         }
1249                 }
1250         }
1251
1252         if (!list_empty(&cma_page_list)) {
1253                 /*
1254                  * drop the above get_user_pages reference.
1255                  */
1256                 for (i = 0; i < nr_pages; i++)
1257                         put_page(pages[i]);
1258
1259                 if (migrate_pages(&cma_page_list, new_non_cma_page,
1260                                   NULL, 0, MIGRATE_SYNC, MR_CONTIG_RANGE)) {
1261                         /*
1262                          * some of the pages failed migration. Do get_user_pages
1263                          * without migration.
1264                          */
1265                         migrate_allow = false;
1266
1267                         if (!list_empty(&cma_page_list))
1268                                 putback_movable_pages(&cma_page_list);
1269                 }
1270                 /*
1271                  * We did migrate all the pages, Try to get the page references again
1272                  * migrating any new CMA pages which we failed to isolate earlier.
1273                  */
1274                 nr_pages = get_user_pages(start, nr_pages, gup_flags, pages, vmas);
1275                 if ((nr_pages > 0) && migrate_allow) {
1276                         drain_allow = true;
1277                         goto check_again;
1278                 }
1279         }
1280
1281         return nr_pages;
1282 }
1283 #else
1284 static inline long check_and_migrate_cma_pages(unsigned long start, long nr_pages,
1285                                                unsigned int gup_flags,
1286                                                struct page **pages,
1287                                                struct vm_area_struct **vmas)
1288 {
1289         return nr_pages;
1290 }
1291 #endif
1292
1293 /*
1294  * This is the same as get_user_pages() in that it assumes we are
1295  * operating on the current task's mm, but it goes further to validate
1296  * that the vmas associated with the address range are suitable for
1297  * longterm elevated page reference counts. For example, filesystem-dax
1298  * mappings are subject to the lifetime enforced by the filesystem and
1299  * we need guarantees that longterm users like RDMA and V4L2 only
1300  * establish mappings that have a kernel enforced revocation mechanism.
1301  *
1302  * "longterm" == userspace controlled elevated page count lifetime.
1303  * Contrast this to iov_iter_get_pages() usages which are transient.
1304  */
1305 long get_user_pages_longterm(unsigned long start, unsigned long nr_pages,
1306                              unsigned int gup_flags, struct page **pages,
1307                              struct vm_area_struct **vmas_arg)
1308 {
1309         struct vm_area_struct **vmas = vmas_arg;
1310         unsigned long flags;
1311         long rc, i;
1312
1313         if (!pages)
1314                 return -EINVAL;
1315
1316         if (!vmas) {
1317                 vmas = kcalloc(nr_pages, sizeof(struct vm_area_struct *),
1318                                GFP_KERNEL);
1319                 if (!vmas)
1320                         return -ENOMEM;
1321         }
1322
1323         flags = memalloc_nocma_save();
1324         rc = get_user_pages(start, nr_pages, gup_flags, pages, vmas);
1325         memalloc_nocma_restore(flags);
1326         if (rc < 0)
1327                 goto out;
1328
1329         if (check_dax_vmas(vmas, rc)) {
1330                 for (i = 0; i < rc; i++)
1331                         put_page(pages[i]);
1332                 rc = -EOPNOTSUPP;
1333                 goto out;
1334         }
1335
1336         rc = check_and_migrate_cma_pages(start, rc, gup_flags, pages, vmas);
1337 out:
1338         if (vmas != vmas_arg)
1339                 kfree(vmas);
1340         return rc;
1341 }
1342 EXPORT_SYMBOL(get_user_pages_longterm);
1343 #endif /* CONFIG_FS_DAX */
1344
1345 /**
1346  * populate_vma_page_range() -  populate a range of pages in the vma.
1347  * @vma:   target vma
1348  * @start: start address
1349  * @end:   end address
1350  * @nonblocking:
1351  *
1352  * This takes care of mlocking the pages too if VM_LOCKED is set.
1353  *
1354  * return 0 on success, negative error code on error.
1355  *
1356  * vma->vm_mm->mmap_sem must be held.
1357  *
1358  * If @nonblocking is NULL, it may be held for read or write and will
1359  * be unperturbed.
1360  *
1361  * If @nonblocking is non-NULL, it must held for read only and may be
1362  * released.  If it's released, *@nonblocking will be set to 0.
1363  */
1364 long populate_vma_page_range(struct vm_area_struct *vma,
1365                 unsigned long start, unsigned long end, int *nonblocking)
1366 {
1367         struct mm_struct *mm = vma->vm_mm;
1368         unsigned long nr_pages = (end - start) / PAGE_SIZE;
1369         int gup_flags;
1370
1371         VM_BUG_ON(start & ~PAGE_MASK);
1372         VM_BUG_ON(end   & ~PAGE_MASK);
1373         VM_BUG_ON_VMA(start < vma->vm_start, vma);
1374         VM_BUG_ON_VMA(end   > vma->vm_end, vma);
1375         VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm);
1376
1377         gup_flags = FOLL_TOUCH | FOLL_POPULATE | FOLL_MLOCK;
1378         if (vma->vm_flags & VM_LOCKONFAULT)
1379                 gup_flags &= ~FOLL_POPULATE;
1380         /*
1381          * We want to touch writable mappings with a write fault in order
1382          * to break COW, except for shared mappings because these don't COW
1383          * and we would not want to dirty them for nothing.
1384          */
1385         if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
1386                 gup_flags |= FOLL_WRITE;
1387
1388         /*
1389          * We want mlock to succeed for regions that have any permissions
1390          * other than PROT_NONE.
1391          */
1392         if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
1393                 gup_flags |= FOLL_FORCE;
1394
1395         /*
1396          * We made sure addr is within a VMA, so the following will
1397          * not result in a stack expansion that recurses back here.
1398          */
1399         return __get_user_pages(current, mm, start, nr_pages, gup_flags,
1400                                 NULL, NULL, nonblocking);
1401 }
1402
1403 /*
1404  * __mm_populate - populate and/or mlock pages within a range of address space.
1405  *
1406  * This is used to implement mlock() and the MAP_POPULATE / MAP_LOCKED mmap
1407  * flags. VMAs must be already marked with the desired vm_flags, and
1408  * mmap_sem must not be held.
1409  */
1410 int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
1411 {
1412         struct mm_struct *mm = current->mm;
1413         unsigned long end, nstart, nend;
1414         struct vm_area_struct *vma = NULL;
1415         int locked = 0;
1416         long ret = 0;
1417
1418         end = start + len;
1419
1420         for (nstart = start; nstart < end; nstart = nend) {
1421                 /*
1422                  * We want to fault in pages for [nstart; end) address range.
1423                  * Find first corresponding VMA.
1424                  */
1425                 if (!locked) {
1426                         locked = 1;
1427                         down_read(&mm->mmap_sem);
1428                         vma = find_vma(mm, nstart);
1429                 } else if (nstart >= vma->vm_end)
1430                         vma = vma->vm_next;
1431                 if (!vma || vma->vm_start >= end)
1432                         break;
1433                 /*
1434                  * Set [nstart; nend) to intersection of desired address
1435                  * range with the first VMA. Also, skip undesirable VMA types.
1436                  */
1437                 nend = min(end, vma->vm_end);
1438                 if (vma->vm_flags & (VM_IO | VM_PFNMAP))
1439                         continue;
1440                 if (nstart < vma->vm_start)
1441                         nstart = vma->vm_start;
1442                 /*
1443                  * Now fault in a range of pages. populate_vma_page_range()
1444                  * double checks the vma flags, so that it won't mlock pages
1445                  * if the vma was already munlocked.
1446                  */
1447                 ret = populate_vma_page_range(vma, nstart, nend, &locked);
1448                 if (ret < 0) {
1449                         if (ignore_errors) {
1450                                 ret = 0;
1451                                 continue;       /* continue at next VMA */
1452                         }
1453                         break;
1454                 }
1455                 nend = nstart + ret * PAGE_SIZE;
1456                 ret = 0;
1457         }
1458         if (locked)
1459                 up_read(&mm->mmap_sem);
1460         return ret;     /* 0 or negative error code */
1461 }
1462
1463 /**
1464  * get_dump_page() - pin user page in memory while writing it to core dump
1465  * @addr: user address
1466  *
1467  * Returns struct page pointer of user page pinned for dump,
1468  * to be freed afterwards by put_page().
1469  *
1470  * Returns NULL on any kind of failure - a hole must then be inserted into
1471  * the corefile, to preserve alignment with its headers; and also returns
1472  * NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
1473  * allowing a hole to be left in the corefile to save diskspace.
1474  *
1475  * Called without mmap_sem, but after all other threads have been killed.
1476  */
1477 #ifdef CONFIG_ELF_CORE
1478 struct page *get_dump_page(unsigned long addr)
1479 {
1480         struct vm_area_struct *vma;
1481         struct page *page;
1482
1483         if (__get_user_pages(current, current->mm, addr, 1,
1484                              FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma,
1485                              NULL) < 1)
1486                 return NULL;
1487         flush_cache_page(vma, addr, page_to_pfn(page));
1488         return page;
1489 }
1490 #endif /* CONFIG_ELF_CORE */
1491
1492 /*
1493  * Generic Fast GUP
1494  *
1495  * get_user_pages_fast attempts to pin user pages by walking the page
1496  * tables directly and avoids taking locks. Thus the walker needs to be
1497  * protected from page table pages being freed from under it, and should
1498  * block any THP splits.
1499  *
1500  * One way to achieve this is to have the walker disable interrupts, and
1501  * rely on IPIs from the TLB flushing code blocking before the page table
1502  * pages are freed. This is unsuitable for architectures that do not need
1503  * to broadcast an IPI when invalidating TLBs.
1504  *
1505  * Another way to achieve this is to batch up page table containing pages
1506  * belonging to more than one mm_user, then rcu_sched a callback to free those
1507  * pages. Disabling interrupts will allow the fast_gup walker to both block
1508  * the rcu_sched callback, and an IPI that we broadcast for splitting THPs
1509  * (which is a relatively rare event). The code below adopts this strategy.
1510  *
1511  * Before activating this code, please be aware that the following assumptions
1512  * are currently made:
1513  *
1514  *  *) Either HAVE_RCU_TABLE_FREE is enabled, and tlb_remove_table() is used to
1515  *  free pages containing page tables or TLB flushing requires IPI broadcast.
1516  *
1517  *  *) ptes can be read atomically by the architecture.
1518  *
1519  *  *) access_ok is sufficient to validate userspace address ranges.
1520  *
1521  * The last two assumptions can be relaxed by the addition of helper functions.
1522  *
1523  * This code is based heavily on the PowerPC implementation by Nick Piggin.
1524  */
1525 #ifdef CONFIG_HAVE_GENERIC_GUP
1526
1527 #ifndef gup_get_pte
1528 /*
1529  * We assume that the PTE can be read atomically. If this is not the case for
1530  * your architecture, please provide the helper.
1531  */
1532 static inline pte_t gup_get_pte(pte_t *ptep)
1533 {
1534         return READ_ONCE(*ptep);
1535 }
1536 #endif
1537
1538 static void undo_dev_pagemap(int *nr, int nr_start, struct page **pages)
1539 {
1540         while ((*nr) - nr_start) {
1541                 struct page *page = pages[--(*nr)];
1542
1543                 ClearPageReferenced(page);
1544                 put_page(page);
1545         }
1546 }
1547
1548 #ifdef CONFIG_ARCH_HAS_PTE_SPECIAL
1549 static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
1550                          int write, struct page **pages, int *nr)
1551 {
1552         struct dev_pagemap *pgmap = NULL;
1553         int nr_start = *nr, ret = 0;
1554         pte_t *ptep, *ptem;
1555
1556         ptem = ptep = pte_offset_map(&pmd, addr);
1557         do {
1558                 pte_t pte = gup_get_pte(ptep);
1559                 struct page *head, *page;
1560
1561                 /*
1562                  * Similar to the PMD case below, NUMA hinting must take slow
1563                  * path using the pte_protnone check.
1564                  */
1565                 if (pte_protnone(pte))
1566                         goto pte_unmap;
1567
1568                 if (!pte_access_permitted(pte, write))
1569                         goto pte_unmap;
1570
1571                 if (pte_devmap(pte)) {
1572                         pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
1573                         if (unlikely(!pgmap)) {
1574                                 undo_dev_pagemap(nr, nr_start, pages);
1575                                 goto pte_unmap;
1576                         }
1577                 } else if (pte_special(pte))
1578                         goto pte_unmap;
1579
1580                 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
1581                 page = pte_page(pte);
1582                 head = compound_head(page);
1583
1584                 if (!page_cache_get_speculative(head))
1585                         goto pte_unmap;
1586
1587                 if (unlikely(pte_val(pte) != pte_val(*ptep))) {
1588                         put_page(head);
1589                         goto pte_unmap;
1590                 }
1591
1592                 VM_BUG_ON_PAGE(compound_head(page) != head, page);
1593
1594                 SetPageReferenced(page);
1595                 pages[*nr] = page;
1596                 (*nr)++;
1597
1598         } while (ptep++, addr += PAGE_SIZE, addr != end);
1599
1600         ret = 1;
1601
1602 pte_unmap:
1603         if (pgmap)
1604                 put_dev_pagemap(pgmap);
1605         pte_unmap(ptem);
1606         return ret;
1607 }
1608 #else
1609
1610 /*
1611  * If we can't determine whether or not a pte is special, then fail immediately
1612  * for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not
1613  * to be special.
1614  *
1615  * For a futex to be placed on a THP tail page, get_futex_key requires a
1616  * __get_user_pages_fast implementation that can pin pages. Thus it's still
1617  * useful to have gup_huge_pmd even if we can't operate on ptes.
1618  */
1619 static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
1620                          int write, struct page **pages, int *nr)
1621 {
1622         return 0;
1623 }
1624 #endif /* CONFIG_ARCH_HAS_PTE_SPECIAL */
1625
1626 #if defined(__HAVE_ARCH_PTE_DEVMAP) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
1627 static int __gup_device_huge(unsigned long pfn, unsigned long addr,
1628                 unsigned long end, struct page **pages, int *nr)
1629 {
1630         int nr_start = *nr;
1631         struct dev_pagemap *pgmap = NULL;
1632
1633         do {
1634                 struct page *page = pfn_to_page(pfn);
1635
1636                 pgmap = get_dev_pagemap(pfn, pgmap);
1637                 if (unlikely(!pgmap)) {
1638                         undo_dev_pagemap(nr, nr_start, pages);
1639                         return 0;
1640                 }
1641                 SetPageReferenced(page);
1642                 pages[*nr] = page;
1643                 get_page(page);
1644                 (*nr)++;
1645                 pfn++;
1646         } while (addr += PAGE_SIZE, addr != end);
1647
1648         if (pgmap)
1649                 put_dev_pagemap(pgmap);
1650         return 1;
1651 }
1652
1653 static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
1654                 unsigned long end, struct page **pages, int *nr)
1655 {
1656         unsigned long fault_pfn;
1657         int nr_start = *nr;
1658
1659         fault_pfn = pmd_pfn(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
1660         if (!__gup_device_huge(fault_pfn, addr, end, pages, nr))
1661                 return 0;
1662
1663         if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
1664                 undo_dev_pagemap(nr, nr_start, pages);
1665                 return 0;
1666         }
1667         return 1;
1668 }
1669
1670 static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
1671                 unsigned long end, struct page **pages, int *nr)
1672 {
1673         unsigned long fault_pfn;
1674         int nr_start = *nr;
1675
1676         fault_pfn = pud_pfn(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
1677         if (!__gup_device_huge(fault_pfn, addr, end, pages, nr))
1678                 return 0;
1679
1680         if (unlikely(pud_val(orig) != pud_val(*pudp))) {
1681                 undo_dev_pagemap(nr, nr_start, pages);
1682                 return 0;
1683         }
1684         return 1;
1685 }
1686 #else
1687 static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
1688                 unsigned long end, struct page **pages, int *nr)
1689 {
1690         BUILD_BUG();
1691         return 0;
1692 }
1693
1694 static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr,
1695                 unsigned long end, struct page **pages, int *nr)
1696 {
1697         BUILD_BUG();
1698         return 0;
1699 }
1700 #endif
1701
1702 static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
1703                 unsigned long end, int write, struct page **pages, int *nr)
1704 {
1705         struct page *head, *page;
1706         int refs;
1707
1708         if (!pmd_access_permitted(orig, write))
1709                 return 0;
1710
1711         if (pmd_devmap(orig))
1712                 return __gup_device_huge_pmd(orig, pmdp, addr, end, pages, nr);
1713
1714         refs = 0;
1715         page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
1716         do {
1717                 pages[*nr] = page;
1718                 (*nr)++;
1719                 page++;
1720                 refs++;
1721         } while (addr += PAGE_SIZE, addr != end);
1722
1723         head = compound_head(pmd_page(orig));
1724         if (!page_cache_add_speculative(head, refs)) {
1725                 *nr -= refs;
1726                 return 0;
1727         }
1728
1729         if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
1730                 *nr -= refs;
1731                 while (refs--)
1732                         put_page(head);
1733                 return 0;
1734         }
1735
1736         SetPageReferenced(head);
1737         return 1;
1738 }
1739
1740 static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
1741                 unsigned long end, int write, struct page **pages, int *nr)
1742 {
1743         struct page *head, *page;
1744         int refs;
1745
1746         if (!pud_access_permitted(orig, write))
1747                 return 0;
1748
1749         if (pud_devmap(orig))
1750                 return __gup_device_huge_pud(orig, pudp, addr, end, pages, nr);
1751
1752         refs = 0;
1753         page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
1754         do {
1755                 pages[*nr] = page;
1756                 (*nr)++;
1757                 page++;
1758                 refs++;
1759         } while (addr += PAGE_SIZE, addr != end);
1760
1761         head = compound_head(pud_page(orig));
1762         if (!page_cache_add_speculative(head, refs)) {
1763                 *nr -= refs;
1764                 return 0;
1765         }
1766
1767         if (unlikely(pud_val(orig) != pud_val(*pudp))) {
1768                 *nr -= refs;
1769                 while (refs--)
1770                         put_page(head);
1771                 return 0;
1772         }
1773
1774         SetPageReferenced(head);
1775         return 1;
1776 }
1777
1778 static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
1779                         unsigned long end, int write,
1780                         struct page **pages, int *nr)
1781 {
1782         int refs;
1783         struct page *head, *page;
1784
1785         if (!pgd_access_permitted(orig, write))
1786                 return 0;
1787
1788         BUILD_BUG_ON(pgd_devmap(orig));
1789         refs = 0;
1790         page = pgd_page(orig) + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
1791         do {
1792                 pages[*nr] = page;
1793                 (*nr)++;
1794                 page++;
1795                 refs++;
1796         } while (addr += PAGE_SIZE, addr != end);
1797
1798         head = compound_head(pgd_page(orig));
1799         if (!page_cache_add_speculative(head, refs)) {
1800                 *nr -= refs;
1801                 return 0;
1802         }
1803
1804         if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) {
1805                 *nr -= refs;
1806                 while (refs--)
1807                         put_page(head);
1808                 return 0;
1809         }
1810
1811         SetPageReferenced(head);
1812         return 1;
1813 }
1814
1815 static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
1816                 int write, struct page **pages, int *nr)
1817 {
1818         unsigned long next;
1819         pmd_t *pmdp;
1820
1821         pmdp = pmd_offset(&pud, addr);
1822         do {
1823                 pmd_t pmd = READ_ONCE(*pmdp);
1824
1825                 next = pmd_addr_end(addr, end);
1826                 if (!pmd_present(pmd))
1827                         return 0;
1828
1829                 if (unlikely(pmd_trans_huge(pmd) || pmd_huge(pmd) ||
1830                              pmd_devmap(pmd))) {
1831                         /*
1832                          * NUMA hinting faults need to be handled in the GUP
1833                          * slowpath for accounting purposes and so that they
1834                          * can be serialised against THP migration.
1835                          */
1836                         if (pmd_protnone(pmd))
1837                                 return 0;
1838
1839                         if (!gup_huge_pmd(pmd, pmdp, addr, next, write,
1840                                 pages, nr))
1841                                 return 0;
1842
1843                 } else if (unlikely(is_hugepd(__hugepd(pmd_val(pmd))))) {
1844                         /*
1845                          * architecture have different format for hugetlbfs
1846                          * pmd format and THP pmd format
1847                          */
1848                         if (!gup_huge_pd(__hugepd(pmd_val(pmd)), addr,
1849                                          PMD_SHIFT, next, write, pages, nr))
1850                                 return 0;
1851                 } else if (!gup_pte_range(pmd, addr, next, write, pages, nr))
1852                         return 0;
1853         } while (pmdp++, addr = next, addr != end);
1854
1855         return 1;
1856 }
1857
1858 static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end,
1859                          int write, struct page **pages, int *nr)
1860 {
1861         unsigned long next;
1862         pud_t *pudp;
1863
1864         pudp = pud_offset(&p4d, addr);
1865         do {
1866                 pud_t pud = READ_ONCE(*pudp);
1867
1868                 next = pud_addr_end(addr, end);
1869                 if (pud_none(pud))
1870                         return 0;
1871                 if (unlikely(pud_huge(pud))) {
1872                         if (!gup_huge_pud(pud, pudp, addr, next, write,
1873                                           pages, nr))
1874                                 return 0;
1875                 } else if (unlikely(is_hugepd(__hugepd(pud_val(pud))))) {
1876                         if (!gup_huge_pd(__hugepd(pud_val(pud)), addr,
1877                                          PUD_SHIFT, next, write, pages, nr))
1878                                 return 0;
1879                 } else if (!gup_pmd_range(pud, addr, next, write, pages, nr))
1880                         return 0;
1881         } while (pudp++, addr = next, addr != end);
1882
1883         return 1;
1884 }
1885
1886 static int gup_p4d_range(pgd_t pgd, unsigned long addr, unsigned long end,
1887                          int write, struct page **pages, int *nr)
1888 {
1889         unsigned long next;
1890         p4d_t *p4dp;
1891
1892         p4dp = p4d_offset(&pgd, addr);
1893         do {
1894                 p4d_t p4d = READ_ONCE(*p4dp);
1895
1896                 next = p4d_addr_end(addr, end);
1897                 if (p4d_none(p4d))
1898                         return 0;
1899                 BUILD_BUG_ON(p4d_huge(p4d));
1900                 if (unlikely(is_hugepd(__hugepd(p4d_val(p4d))))) {
1901                         if (!gup_huge_pd(__hugepd(p4d_val(p4d)), addr,
1902                                          P4D_SHIFT, next, write, pages, nr))
1903                                 return 0;
1904                 } else if (!gup_pud_range(p4d, addr, next, write, pages, nr))
1905                         return 0;
1906         } while (p4dp++, addr = next, addr != end);
1907
1908         return 1;
1909 }
1910
1911 static void gup_pgd_range(unsigned long addr, unsigned long end,
1912                 int write, struct page **pages, int *nr)
1913 {
1914         unsigned long next;
1915         pgd_t *pgdp;
1916
1917         pgdp = pgd_offset(current->mm, addr);
1918         do {
1919                 pgd_t pgd = READ_ONCE(*pgdp);
1920
1921                 next = pgd_addr_end(addr, end);
1922                 if (pgd_none(pgd))
1923                         return;
1924                 if (unlikely(pgd_huge(pgd))) {
1925                         if (!gup_huge_pgd(pgd, pgdp, addr, next, write,
1926                                           pages, nr))
1927                                 return;
1928                 } else if (unlikely(is_hugepd(__hugepd(pgd_val(pgd))))) {
1929                         if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr,
1930                                          PGDIR_SHIFT, next, write, pages, nr))
1931                                 return;
1932                 } else if (!gup_p4d_range(pgd, addr, next, write, pages, nr))
1933                         return;
1934         } while (pgdp++, addr = next, addr != end);
1935 }
1936
1937 #ifndef gup_fast_permitted
1938 /*
1939  * Check if it's allowed to use __get_user_pages_fast() for the range, or
1940  * we need to fall back to the slow version:
1941  */
1942 bool gup_fast_permitted(unsigned long start, int nr_pages)
1943 {
1944         unsigned long len, end;
1945
1946         len = (unsigned long) nr_pages << PAGE_SHIFT;
1947         end = start + len;
1948         return end >= start;
1949 }
1950 #endif
1951
1952 /*
1953  * Like get_user_pages_fast() except it's IRQ-safe in that it won't fall back to
1954  * the regular GUP.
1955  * Note a difference with get_user_pages_fast: this always returns the
1956  * number of pages pinned, 0 if no pages were pinned.
1957  */
1958 int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
1959                           struct page **pages)
1960 {
1961         unsigned long len, end;
1962         unsigned long flags;
1963         int nr = 0;
1964
1965         start &= PAGE_MASK;
1966         len = (unsigned long) nr_pages << PAGE_SHIFT;
1967         end = start + len;
1968
1969         if (unlikely(!access_ok((void __user *)start, len)))
1970                 return 0;
1971
1972         /*
1973          * Disable interrupts.  We use the nested form as we can already have
1974          * interrupts disabled by get_futex_key.
1975          *
1976          * With interrupts disabled, we block page table pages from being
1977          * freed from under us. See struct mmu_table_batch comments in
1978          * include/asm-generic/tlb.h for more details.
1979          *
1980          * We do not adopt an rcu_read_lock(.) here as we also want to
1981          * block IPIs that come from THPs splitting.
1982          */
1983
1984         if (gup_fast_permitted(start, nr_pages)) {
1985                 local_irq_save(flags);
1986                 gup_pgd_range(start, end, write, pages, &nr);
1987                 local_irq_restore(flags);
1988         }
1989
1990         return nr;
1991 }
1992
1993 /**
1994  * get_user_pages_fast() - pin user pages in memory
1995  * @start:      starting user address
1996  * @nr_pages:   number of pages from start to pin
1997  * @write:      whether pages will be written to
1998  * @pages:      array that receives pointers to the pages pinned.
1999  *              Should be at least nr_pages long.
2000  *
2001  * Attempt to pin user pages in memory without taking mm->mmap_sem.
2002  * If not successful, it will fall back to taking the lock and
2003  * calling get_user_pages().
2004  *
2005  * Returns number of pages pinned. This may be fewer than the number
2006  * requested. If nr_pages is 0 or negative, returns 0. If no pages
2007  * were pinned, returns -errno.
2008  */
2009 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
2010                         struct page **pages)
2011 {
2012         unsigned long addr, len, end;
2013         int nr = 0, ret = 0;
2014
2015         start &= PAGE_MASK;
2016         addr = start;
2017         len = (unsigned long) nr_pages << PAGE_SHIFT;
2018         end = start + len;
2019
2020         if (nr_pages <= 0)
2021                 return 0;
2022
2023         if (unlikely(!access_ok((void __user *)start, len)))
2024                 return -EFAULT;
2025
2026         if (gup_fast_permitted(start, nr_pages)) {
2027                 local_irq_disable();
2028                 gup_pgd_range(addr, end, write, pages, &nr);
2029                 local_irq_enable();
2030                 ret = nr;
2031         }
2032
2033         if (nr < nr_pages) {
2034                 /* Try to get the remaining pages with get_user_pages */
2035                 start += nr << PAGE_SHIFT;
2036                 pages += nr;
2037
2038                 ret = get_user_pages_unlocked(start, nr_pages - nr, pages,
2039                                 write ? FOLL_WRITE : 0);
2040
2041                 /* Have to be a bit careful with return values */
2042                 if (nr > 0) {
2043                         if (ret < 0)
2044                                 ret = nr;
2045                         else
2046                                 ret += nr;
2047                 }
2048         }
2049
2050         return ret;
2051 }
2052
2053 #endif /* CONFIG_HAVE_GENERIC_GUP */