arch/x86/mm/pgtable.c

   1 #include <linux/mm.h>
   2 #include <linux/gfp.h>
   3 #include <asm/pgalloc.h>
   4 #include <asm/pgtable.h>
   5 #include <asm/tlb.h>
   6 #include <asm/fixmap.h>
   7 #include <asm/mtrr.h>
   8
   9 #define PGALLOC_GFP (GFP_KERNEL_ACCOUNT | __GFP_NOTRACK | __GFP_ZERO)
  10
  11 #ifdef CONFIG_HIGHPTE
  12 #define PGALLOC_USER_GFP __GFP_HIGHMEM
  13 #else
  14 #define PGALLOC_USER_GFP 0
  15 #endif
  16
  17 gfp_t __userpte_alloc_gfp = PGALLOC_GFP | PGALLOC_USER_GFP;
  18
  19 pte_t *pte_alloc_one_kernel(struct mm_struct *mm, unsigned long address)
  20 {
  21         return (pte_t *)__get_free_page(PGALLOC_GFP & ~__GFP_ACCOUNT);
  22 }
  23
  24 pgtable_t pte_alloc_one(struct mm_struct *mm, unsigned long address)
  25 {
  26         struct page *pte;
  27
  28         pte = alloc_pages(__userpte_alloc_gfp, 0);
  29         if (!pte)
  30                 return NULL;
  31         if (!pgtable_page_ctor(pte)) {
  32                 __free_page(pte);
  33                 return NULL;
  34         }
  35         return pte;
  36 }
  37
  38 static int __init setup_userpte(char *arg)
  39 {
  40         if (!arg)
  41                 return -EINVAL;
  42
  43         /*
  44          * "userpte=nohigh" disables allocation of user pagetables in
  45          * high memory.
  46          */
  47         if (strcmp(arg, "nohigh") == 0)
  48                 __userpte_alloc_gfp &= ~__GFP_HIGHMEM;
  49         else
  50                 return -EINVAL;
  51         return 0;
  52 }
  53 early_param("userpte", setup_userpte);
  54
  55 void ___pte_free_tlb(struct mmu_gather *tlb, struct page *pte)
  56 {
  57         pgtable_page_dtor(pte);
  58         paravirt_release_pte(page_to_pfn(pte));
  59         tlb_remove_page(tlb, pte);
  60 }
  61
  62 #if CONFIG_PGTABLE_LEVELS > 2
  63 void ___pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd)
  64 {
  65         struct page *page = virt_to_page(pmd);
  66         paravirt_release_pmd(__pa(pmd) >> PAGE_SHIFT);
  67         /*
  68          * NOTE! For PAE, any changes to the top page-directory-pointer-table
  69          * entries need a full cr3 reload to flush.
  70          */
  71 #ifdef CONFIG_X86_PAE
  72         tlb->need_flush_all = 1;
  73 #endif
  74         pgtable_pmd_page_dtor(page);
  75         tlb_remove_page(tlb, page);
  76 }
  77
  78 #if CONFIG_PGTABLE_LEVELS > 3
  79 void ___pud_free_tlb(struct mmu_gather *tlb, pud_t *pud)
  80 {
  81         paravirt_release_pud(__pa(pud) >> PAGE_SHIFT);
  82         tlb_remove_page(tlb, virt_to_page(pud));
  83 }
  84 #endif  /* CONFIG_PGTABLE_LEVELS > 3 */
  85 #endif  /* CONFIG_PGTABLE_LEVELS > 2 */
  86
  87 static inline void pgd_list_add(pgd_t *pgd)
  88 {
  89         struct page *page = virt_to_page(pgd);
  90
  91         list_add(&page->lru, &pgd_list);
  92 }
  93
  94 static inline void pgd_list_del(pgd_t *pgd)
  95 {
  96         struct page *page = virt_to_page(pgd);
  97
  98         list_del(&page->lru);
  99 }
 100
 101 #define UNSHARED_PTRS_PER_PGD                           \
 102         (SHARED_KERNEL_PMD ? KERNEL_PGD_BOUNDARY : PTRS_PER_PGD)
 103
 104
 105 static void pgd_set_mm(pgd_t *pgd, struct mm_struct *mm)
 106 {
 107         BUILD_BUG_ON(sizeof(virt_to_page(pgd)->index) < sizeof(mm));
 108         virt_to_page(pgd)->index = (pgoff_t)mm;
 109 }
 110
 111 struct mm_struct *pgd_page_get_mm(struct page *page)
 112 {
 113         return (struct mm_struct *)page->index;
 114 }
 115
 116 static void pgd_ctor(struct mm_struct *mm, pgd_t *pgd)
 117 {
 118         /* If the pgd points to a shared pagetable level (either the
 119            ptes in non-PAE, or shared PMD in PAE), then just copy the
 120            references from swapper_pg_dir. */
 121         if (CONFIG_PGTABLE_LEVELS == 2 ||
 122             (CONFIG_PGTABLE_LEVELS == 3 && SHARED_KERNEL_PMD) ||
 123             CONFIG_PGTABLE_LEVELS == 4) {
 124                 clone_pgd_range(pgd + KERNEL_PGD_BOUNDARY,
 125                                 swapper_pg_dir + KERNEL_PGD_BOUNDARY,
 126                                 KERNEL_PGD_PTRS);
 127         }
 128
 129         /* list required to sync kernel mapping updates */
 130         if (!SHARED_KERNEL_PMD) {
 131                 pgd_set_mm(pgd, mm);
 132                 pgd_list_add(pgd);
 133         }
 134 }
 135
 136 static void pgd_dtor(pgd_t *pgd)
 137 {
 138         if (SHARED_KERNEL_PMD)
 139                 return;
 140
 141         spin_lock(&pgd_lock);
 142         pgd_list_del(pgd);
 143         spin_unlock(&pgd_lock);
 144 }
 145
 146 /*
 147  * List of all pgd's needed for non-PAE so it can invalidate entries
 148  * in both cached and uncached pgd's; not needed for PAE since the
 149  * kernel pmd is shared. If PAE were not to share the pmd a similar
 150  * tactic would be needed. This is essentially codepath-based locking
 151  * against pageattr.c; it is the unique case in which a valid change
 152  * of kernel pagetables can't be lazily synchronized by vmalloc faults.
 153  * vmalloc faults work because attached pagetables are never freed.
 154  * -- nyc
 155  */
 156
 157 #ifdef CONFIG_X86_PAE
 158 /*
 159  * In PAE mode, we need to do a cr3 reload (=tlb flush) when
 160  * updating the top-level pagetable entries to guarantee the
 161  * processor notices the update.  Since this is expensive, and
 162  * all 4 top-level entries are used almost immediately in a
 163  * new process's life, we just pre-populate them here.
 164  *
 165  * Also, if we're in a paravirt environment where the kernel pmd is
 166  * not shared between pagetables (!SHARED_KERNEL_PMDS), we allocate
 167  * and initialize the kernel pmds here.
 168  */
 169 #define PREALLOCATED_PMDS       UNSHARED_PTRS_PER_PGD
 170
 171 void pud_populate(struct mm_struct *mm, pud_t *pudp, pmd_t *pmd)
 172 {
 173         paravirt_alloc_pmd(mm, __pa(pmd) >> PAGE_SHIFT);
 174
 175         /* Note: almost everything apart from _PAGE_PRESENT is
 176            reserved at the pmd (PDPT) level. */
 177         set_pud(pudp, __pud(__pa(pmd) | _PAGE_PRESENT));
 178
 179         /*
 180          * According to Intel App note "TLBs, Paging-Structure Caches,
 181          * and Their Invalidation", April 2007, document 317080-001,
 182          * section 8.1: in PAE mode we explicitly have to flush the
 183          * TLB via cr3 if the top-level pgd is changed...
 184          */
 185         flush_tlb_mm(mm);
 186 }
 187 #else  /* !CONFIG_X86_PAE */
 188
 189 /* No need to prepopulate any pagetable entries in non-PAE modes. */
 190 #define PREALLOCATED_PMDS       0
 191
 192 #endif  /* CONFIG_X86_PAE */
 193
 194 static void free_pmds(struct mm_struct *mm, pmd_t *pmds[])
 195 {
 196         int i;
 197
 198         for(i = 0; i < PREALLOCATED_PMDS; i++)
 199                 if (pmds[i]) {
 200                         pgtable_pmd_page_dtor(virt_to_page(pmds[i]));
 201                         free_page((unsigned long)pmds[i]);
 202                         mm_dec_nr_pmds(mm);
 203                 }
 204 }
 205
 206 static int preallocate_pmds(struct mm_struct *mm, pmd_t *pmds[])
 207 {
 208         int i;
 209         bool failed = false;
 210         gfp_t gfp = PGALLOC_GFP;
 211
 212         if (mm == &init_mm)
 213                 gfp &= ~__GFP_ACCOUNT;
 214
 215         for(i = 0; i < PREALLOCATED_PMDS; i++) {
 216                 pmd_t *pmd = (pmd_t *)__get_free_page(gfp);
 217                 if (!pmd)
 218                         failed = true;
 219                 if (pmd && !pgtable_pmd_page_ctor(virt_to_page(pmd))) {
 220                         free_page((unsigned long)pmd);
 221                         pmd = NULL;
 222                         failed = true;
 223                 }
 224                 if (pmd)
 225                         mm_inc_nr_pmds(mm);
 226                 pmds[i] = pmd;
 227         }
 228
 229         if (failed) {
 230                 free_pmds(mm, pmds);
 231                 return -ENOMEM;
 232         }
 233
 234         return 0;
 235 }
 236
 237 /*
 238  * Mop up any pmd pages which may still be attached to the pgd.
 239  * Normally they will be freed by munmap/exit_mmap, but any pmd we
 240  * preallocate which never got a corresponding vma will need to be
 241  * freed manually.
 242  */
 243 static void pgd_mop_up_pmds(struct mm_struct *mm, pgd_t *pgdp)
 244 {
 245         int i;
 246
 247         for(i = 0; i < PREALLOCATED_PMDS; i++) {
 248                 pgd_t pgd = pgdp[i];
 249
 250                 if (pgd_val(pgd) != 0) {
 251                         pmd_t *pmd = (pmd_t *)pgd_page_vaddr(pgd);
 252
 253                         pgdp[i] = native_make_pgd(0);
 254
 255                         paravirt_release_pmd(pgd_val(pgd) >> PAGE_SHIFT);
 256                         pmd_free(mm, pmd);
 257                         mm_dec_nr_pmds(mm);
 258                 }
 259         }
 260 }
 261
 262 static void pgd_prepopulate_pmd(struct mm_struct *mm, pgd_t *pgd, pmd_t *pmds[])
 263 {
 264         p4d_t *p4d;
 265         pud_t *pud;
 266         int i;
 267
 268         if (PREALLOCATED_PMDS == 0) /* Work around gcc-3.4.x bug */
 269                 return;
 270
 271         p4d = p4d_offset(pgd, 0);
 272         pud = pud_offset(p4d, 0);
 273
 274         for (i = 0; i < PREALLOCATED_PMDS; i++, pud++) {
 275                 pmd_t *pmd = pmds[i];
 276
 277                 if (i >= KERNEL_PGD_BOUNDARY)
 278                         memcpy(pmd, (pmd_t *)pgd_page_vaddr(swapper_pg_dir[i]),
 279                                sizeof(pmd_t) * PTRS_PER_PMD);
 280
 281                 pud_populate(mm, pud, pmd);
 282         }
 283 }
 284
 285 /*
 286  * Xen paravirt assumes pgd table should be in one page. 64 bit kernel also
 287  * assumes that pgd should be in one page.
 288  *
 289  * But kernel with PAE paging that is not running as a Xen domain
 290  * only needs to allocate 32 bytes for pgd instead of one page.
 291  */
 292 #ifdef CONFIG_X86_PAE
 293
 294 #include <linux/slab.h>
 295
 296 #define PGD_SIZE        (PTRS_PER_PGD * sizeof(pgd_t))
 297 #define PGD_ALIGN       32
 298
 299 static struct kmem_cache *pgd_cache;
 300
 301 static int __init pgd_cache_init(void)
 302 {
 303         /*
 304          * When PAE kernel is running as a Xen domain, it does not use
 305          * shared kernel pmd. And this requires a whole page for pgd.
 306          */
 307         if (!SHARED_KERNEL_PMD)
 308                 return 0;
 309
 310         /*
 311          * when PAE kernel is not running as a Xen domain, it uses
 312          * shared kernel pmd. Shared kernel pmd does not require a whole
 313          * page for pgd. We are able to just allocate a 32-byte for pgd.
 314          * During boot time, we create a 32-byte slab for pgd table allocation.
 315          */
 316         pgd_cache = kmem_cache_create("pgd_cache", PGD_SIZE, PGD_ALIGN,
 317                                       SLAB_PANIC, NULL);
 318         if (!pgd_cache)
 319                 return -ENOMEM;
 320
 321         return 0;
 322 }
 323 core_initcall(pgd_cache_init);
 324
 325 static inline pgd_t *_pgd_alloc(void)
 326 {
 327         /*
 328          * If no SHARED_KERNEL_PMD, PAE kernel is running as a Xen domain.
 329          * We allocate one page for pgd.
 330          */
 331         if (!SHARED_KERNEL_PMD)
 332                 return (pgd_t *)__get_free_page(PGALLOC_GFP);
 333
 334         /*
 335          * Now PAE kernel is not running as a Xen domain. We can allocate
 336          * a 32-byte slab for pgd to save memory space.
 337          */
 338         return kmem_cache_alloc(pgd_cache, PGALLOC_GFP);
 339 }
 340
 341 static inline void _pgd_free(pgd_t *pgd)
 342 {
 343         if (!SHARED_KERNEL_PMD)
 344                 free_page((unsigned long)pgd);
 345         else
 346                 kmem_cache_free(pgd_cache, pgd);
 347 }
 348 #else
 349 static inline pgd_t *_pgd_alloc(void)
 350 {
 351         return (pgd_t *)__get_free_page(PGALLOC_GFP);
 352 }
 353
 354 static inline void _pgd_free(pgd_t *pgd)
 355 {
 356         free_page((unsigned long)pgd);
 357 }
 358 #endif /* CONFIG_X86_PAE */
 359
 360 pgd_t *pgd_alloc(struct mm_struct *mm)
 361 {
 362         pgd_t *pgd;
 363         pmd_t *pmds[PREALLOCATED_PMDS];
 364
 365         pgd = _pgd_alloc();
 366
 367         if (pgd == NULL)
 368                 goto out;
 369
 370         mm->pgd = pgd;
 371
 372         if (preallocate_pmds(mm, pmds) != 0)
 373                 goto out_free_pgd;
 374
 375         if (paravirt_pgd_alloc(mm) != 0)
 376                 goto out_free_pmds;
 377
 378         /*
 379          * Make sure that pre-populating the pmds is atomic with
 380          * respect to anything walking the pgd_list, so that they
 381          * never see a partially populated pgd.
 382          */
 383         spin_lock(&pgd_lock);
 384
 385         pgd_ctor(mm, pgd);
 386         pgd_prepopulate_pmd(mm, pgd, pmds);
 387
 388         spin_unlock(&pgd_lock);
 389
 390         return pgd;
 391
 392 out_free_pmds:
 393         free_pmds(mm, pmds);
 394 out_free_pgd:
 395         _pgd_free(pgd);
 396 out:
 397         return NULL;
 398 }
 399
 400 void pgd_free(struct mm_struct *mm, pgd_t *pgd)
 401 {
 402         pgd_mop_up_pmds(mm, pgd);
 403         pgd_dtor(pgd);
 404         paravirt_pgd_free(mm, pgd);
 405         _pgd_free(pgd);
 406 }
 407
 408 /*
 409  * Used to set accessed or dirty bits in the page table entries
 410  * on other architectures. On x86, the accessed and dirty bits
 411  * are tracked by hardware. However, do_wp_page calls this function
 412  * to also make the pte writeable at the same time the dirty bit is
 413  * set. In that case we do actually need to write the PTE.
 414  */
 415 int ptep_set_access_flags(struct vm_area_struct *vma,
 416                           unsigned long address, pte_t *ptep,
 417                           pte_t entry, int dirty)
 418 {
 419         int changed = !pte_same(*ptep, entry);
 420
 421         if (changed && dirty) {
 422                 *ptep = entry;
 423                 pte_update(vma->vm_mm, address, ptep);
 424         }
 425
 426         return changed;
 427 }
 428
 429 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 430 int pmdp_set_access_flags(struct vm_area_struct *vma,
 431                           unsigned long address, pmd_t *pmdp,
 432                           pmd_t entry, int dirty)
 433 {
 434         int changed = !pmd_same(*pmdp, entry);
 435
 436         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 437
 438         if (changed && dirty) {
 439                 *pmdp = entry;
 440                 /*
 441                  * We had a write-protection fault here and changed the pmd
 442                  * to to more permissive. No need to flush the TLB for that,
 443                  * #PF is architecturally guaranteed to do that and in the
 444                  * worst-case we'll generate a spurious fault.
 445                  */
 446         }
 447
 448         return changed;
 449 }
 450
 451 int pudp_set_access_flags(struct vm_area_struct *vma, unsigned long address,
 452                           pud_t *pudp, pud_t entry, int dirty)
 453 {
 454         int changed = !pud_same(*pudp, entry);
 455
 456         VM_BUG_ON(address & ~HPAGE_PUD_MASK);
 457
 458         if (changed && dirty) {
 459                 *pudp = entry;
 460                 /*
 461                  * We had a write-protection fault here and changed the pud
 462                  * to to more permissive. No need to flush the TLB for that,
 463                  * #PF is architecturally guaranteed to do that and in the
 464                  * worst-case we'll generate a spurious fault.
 465                  */
 466         }
 467
 468         return changed;
 469 }
 470 #endif
 471
 472 int ptep_test_and_clear_young(struct vm_area_struct *vma,
 473                               unsigned long addr, pte_t *ptep)
 474 {
 475         int ret = 0;
 476
 477         if (pte_young(*ptep))
 478                 ret = test_and_clear_bit(_PAGE_BIT_ACCESSED,
 479                                          (unsigned long *) &ptep->pte);
 480
 481         if (ret)
 482                 pte_update(vma->vm_mm, addr, ptep);
 483
 484         return ret;
 485 }
 486
 487 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 488 int pmdp_test_and_clear_young(struct vm_area_struct *vma,
 489                               unsigned long addr, pmd_t *pmdp)
 490 {
 491         int ret = 0;
 492
 493         if (pmd_young(*pmdp))
 494                 ret = test_and_clear_bit(_PAGE_BIT_ACCESSED,
 495                                          (unsigned long *)pmdp);
 496
 497         return ret;
 498 }
 499 int pudp_test_and_clear_young(struct vm_area_struct *vma,
 500                               unsigned long addr, pud_t *pudp)
 501 {
 502         int ret = 0;
 503
 504         if (pud_young(*pudp))
 505                 ret = test_and_clear_bit(_PAGE_BIT_ACCESSED,
 506                                          (unsigned long *)pudp);
 507
 508         return ret;
 509 }
 510 #endif
 511
 512 int ptep_clear_flush_young(struct vm_area_struct *vma,
 513                            unsigned long address, pte_t *ptep)
 514 {
 515         /*
 516          * On x86 CPUs, clearing the accessed bit without a TLB flush
 517          * doesn't cause data corruption. [ It could cause incorrect
 518          * page aging and the (mistaken) reclaim of hot pages, but the
 519          * chance of that should be relatively low. ]
 520          *
 521          * So as a performance optimization don't flush the TLB when
 522          * clearing the accessed bit, it will eventually be flushed by
 523          * a context switch or a VM operation anyway. [ In the rare
 524          * event of it not getting flushed for a long time the delay
 525          * shouldn't really matter because there's no real memory
 526          * pressure for swapout to react to. ]
 527          */
 528         return ptep_test_and_clear_young(vma, address, ptep);
 529 }
 530
 531 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 532 int pmdp_clear_flush_young(struct vm_area_struct *vma,
 533                            unsigned long address, pmd_t *pmdp)
 534 {
 535         int young;
 536
 537         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 538
 539         young = pmdp_test_and_clear_young(vma, address, pmdp);
 540         if (young)
 541                 flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
 542
 543         return young;
 544 }
 545 #endif
 546
 547 /**
 548  * reserve_top_address - reserves a hole in the top of kernel address space
 549  * @reserve - size of hole to reserve
 550  *
 551  * Can be used to relocate the fixmap area and poke a hole in the top
 552  * of kernel address space to make room for a hypervisor.
 553  */
 554 void __init reserve_top_address(unsigned long reserve)
 555 {
 556 #ifdef CONFIG_X86_32
 557         BUG_ON(fixmaps_set > 0);
 558         __FIXADDR_TOP = round_down(-reserve, 1 << PMD_SHIFT) - PAGE_SIZE;
 559         printk(KERN_INFO "Reserving virtual address space above 0x%08lx (rounded to 0x%08lx)\n",
 560                -reserve, __FIXADDR_TOP + PAGE_SIZE);
 561 #endif
 562 }
 563
 564 int fixmaps_set;
 565
 566 void __native_set_fixmap(enum fixed_addresses idx, pte_t pte)
 567 {
 568         unsigned long address = __fix_to_virt(idx);
 569
 570         if (idx >= __end_of_fixed_addresses) {
 571                 BUG();
 572                 return;
 573         }
 574         set_pte_vaddr(address, pte);
 575         fixmaps_set++;
 576 }
 577
 578 void native_set_fixmap(enum fixed_addresses idx, phys_addr_t phys,
 579                        pgprot_t flags)
 580 {
 581         __native_set_fixmap(idx, pfn_pte(phys >> PAGE_SHIFT, flags));
 582 }
 583
 584 #ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
 585 /**
 586  * pud_set_huge - setup kernel PUD mapping
 587  *
 588  * MTRRs can override PAT memory types with 4KiB granularity. Therefore, this
 589  * function sets up a huge page only if any of the following conditions are met:
 590  *
 591  * - MTRRs are disabled, or
 592  *
 593  * - MTRRs are enabled and the range is completely covered by a single MTRR, or
 594  *
 595  * - MTRRs are enabled and the corresponding MTRR memory type is WB, which
 596  *   has no effect on the requested PAT memory type.
 597  *
 598  * Callers should try to decrease page size (1GB -> 2MB -> 4K) if the bigger
 599  * page mapping attempt fails.
 600  *
 601  * Returns 1 on success and 0 on failure.
 602  */
 603 int pud_set_huge(pud_t *pud, phys_addr_t addr, pgprot_t prot)
 604 {
 605         u8 mtrr, uniform;
 606
 607         mtrr = mtrr_type_lookup(addr, addr + PUD_SIZE, &uniform);
 608         if ((mtrr != MTRR_TYPE_INVALID) && (!uniform) &&
 609             (mtrr != MTRR_TYPE_WRBACK))
 610                 return 0;
 611
 612         prot = pgprot_4k_2_large(prot);
 613
 614         set_pte((pte_t *)pud, pfn_pte(
 615                 (u64)addr >> PAGE_SHIFT,
 616                 __pgprot(pgprot_val(prot) | _PAGE_PSE)));
 617
 618         return 1;
 619 }
 620
 621 /**
 622  * pmd_set_huge - setup kernel PMD mapping
 623  *
 624  * See text over pud_set_huge() above.
 625  *
 626  * Returns 1 on success and 0 on failure.
 627  */
 628 int pmd_set_huge(pmd_t *pmd, phys_addr_t addr, pgprot_t prot)
 629 {
 630         u8 mtrr, uniform;
 631
 632         mtrr = mtrr_type_lookup(addr, addr + PMD_SIZE, &uniform);
 633         if ((mtrr != MTRR_TYPE_INVALID) && (!uniform) &&
 634             (mtrr != MTRR_TYPE_WRBACK)) {
 635                 pr_warn_once("%s: Cannot satisfy [mem %#010llx-%#010llx] with a huge-page mapping due to MTRR override.\n",
 636                              __func__, addr, addr + PMD_SIZE);
 637                 return 0;
 638         }
 639
 640         prot = pgprot_4k_2_large(prot);
 641
 642         set_pte((pte_t *)pmd, pfn_pte(
 643                 (u64)addr >> PAGE_SHIFT,
 644                 __pgprot(pgprot_val(prot) | _PAGE_PSE)));
 645
 646         return 1;
 647 }
 648
 649 /**
 650  * pud_clear_huge - clear kernel PUD mapping when it is set
 651  *
 652  * Returns 1 on success and 0 on failure (no PUD map is found).
 653  */
 654 int pud_clear_huge(pud_t *pud)
 655 {
 656         if (pud_large(*pud)) {
 657                 pud_clear(pud);
 658                 return 1;
 659         }
 660
 661         return 0;
 662 }
 663
 664 /**
 665  * pmd_clear_huge - clear kernel PMD mapping when it is set
 666  *
 667  * Returns 1 on success and 0 on failure (no PMD map is found).
 668  */
 669 int pmd_clear_huge(pmd_t *pmd)
 670 {
 671         if (pmd_large(*pmd)) {
 672                 pmd_clear(pmd);
 673                 return 1;
 674         }
 675
 676         return 0;
 677 }
 678 #endif  /* CONFIG_HAVE_ARCH_HUGE_VMAP */