arch/powerpc/mm/hugetlbpage.c

   1 /*
   2  * PPC Huge TLB Page Support for Kernel.
   3  *
   4  * Copyright (C) 2003 David Gibson, IBM Corporation.
   5  * Copyright (C) 2011 Becky Bruce, Freescale Semiconductor
   6  *
   7  * Based on the IA-32 version:
   8  * Copyright (C) 2002, Rohit Seth <rohit.seth@intel.com>
   9  */
  10
  11 #include <linux/mm.h>
  12 #include <linux/io.h>
  13 #include <linux/slab.h>
  14 #include <linux/hugetlb.h>
  15 #include <linux/export.h>
  16 #include <linux/of_fdt.h>
  17 #include <linux/memblock.h>
  18 #include <linux/moduleparam.h>
  19 #include <linux/swap.h>
  20 #include <linux/swapops.h>
  21 #include <linux/kmemleak.h>
  22 #include <asm/pgtable.h>
  23 #include <asm/pgalloc.h>
  24 #include <asm/tlb.h>
  25 #include <asm/setup.h>
  26 #include <asm/hugetlb.h>
  27 #include <asm/pte-walk.h>
  28
  29 bool hugetlb_disabled = false;
  30
  31 #define hugepd_none(hpd)        (hpd_val(hpd) == 0)
  32
  33 #define PTE_T_ORDER     (__builtin_ffs(sizeof(pte_t)) - __builtin_ffs(sizeof(void *)))
  34
  35 pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr, unsigned long sz)
  36 {
  37         /*
  38          * Only called for hugetlbfs pages, hence can ignore THP and the
  39          * irq disabled walk.
  40          */
  41         return __find_linux_pte(mm->pgd, addr, NULL, NULL);
  42 }
  43
  44 static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp,
  45                            unsigned long address, unsigned int pdshift,
  46                            unsigned int pshift, spinlock_t *ptl)
  47 {
  48         struct kmem_cache *cachep;
  49         pte_t *new;
  50         int i;
  51         int num_hugepd;
  52
  53         if (pshift >= pdshift) {
  54                 cachep = PGT_CACHE(PTE_T_ORDER);
  55                 num_hugepd = 1 << (pshift - pdshift);
  56         } else if (IS_ENABLED(CONFIG_PPC_8xx)) {
  57                 cachep = PGT_CACHE(PTE_INDEX_SIZE);
  58                 num_hugepd = 1;
  59         } else {
  60                 cachep = PGT_CACHE(pdshift - pshift);
  61                 num_hugepd = 1;
  62         }
  63
  64         new = kmem_cache_alloc(cachep, pgtable_gfp_flags(mm, GFP_KERNEL));
  65
  66         BUG_ON(pshift > HUGEPD_SHIFT_MASK);
  67         BUG_ON((unsigned long)new & HUGEPD_SHIFT_MASK);
  68
  69         if (! new)
  70                 return -ENOMEM;
  71
  72         /*
  73          * Make sure other cpus find the hugepd set only after a
  74          * properly initialized page table is visible to them.
  75          * For more details look for comment in __pte_alloc().
  76          */
  77         smp_wmb();
  78
  79         spin_lock(ptl);
  80         /*
  81          * We have multiple higher-level entries that point to the same
  82          * actual pte location.  Fill in each as we go and backtrack on error.
  83          * We need all of these so the DTLB pgtable walk code can find the
  84          * right higher-level entry without knowing if it's a hugepage or not.
  85          */
  86         for (i = 0; i < num_hugepd; i++, hpdp++) {
  87                 if (unlikely(!hugepd_none(*hpdp)))
  88                         break;
  89                 hugepd_populate(hpdp, new, pshift);
  90         }
  91         /* If we bailed from the for loop early, an error occurred, clean up */
  92         if (i < num_hugepd) {
  93                 for (i = i - 1 ; i >= 0; i--, hpdp--)
  94                         *hpdp = __hugepd(0);
  95                 kmem_cache_free(cachep, new);
  96         } else {
  97                 kmemleak_ignore(new);
  98         }
  99         spin_unlock(ptl);
 100         return 0;
 101 }
 102
 103 /*
 104  * At this point we do the placement change only for BOOK3S 64. This would
 105  * possibly work on other subarchs.
 106  */
 107 pte_t *huge_pte_alloc(struct mm_struct *mm, unsigned long addr, unsigned long sz)
 108 {
 109         pgd_t *pg;
 110         pud_t *pu;
 111         pmd_t *pm;
 112         hugepd_t *hpdp = NULL;
 113         unsigned pshift = __ffs(sz);
 114         unsigned pdshift = PGDIR_SHIFT;
 115         spinlock_t *ptl;
 116
 117         addr &= ~(sz-1);
 118         pg = pgd_offset(mm, addr);
 119
 120 #ifdef CONFIG_PPC_BOOK3S_64
 121         if (pshift == PGDIR_SHIFT)
 122                 /* 16GB huge page */
 123                 return (pte_t *) pg;
 124         else if (pshift > PUD_SHIFT) {
 125                 /*
 126                  * We need to use hugepd table
 127                  */
 128                 ptl = &mm->page_table_lock;
 129                 hpdp = (hugepd_t *)pg;
 130         } else {
 131                 pdshift = PUD_SHIFT;
 132                 pu = pud_alloc(mm, pg, addr);
 133                 if (pshift == PUD_SHIFT)
 134                         return (pte_t *)pu;
 135                 else if (pshift > PMD_SHIFT) {
 136                         ptl = pud_lockptr(mm, pu);
 137                         hpdp = (hugepd_t *)pu;
 138                 } else {
 139                         pdshift = PMD_SHIFT;
 140                         pm = pmd_alloc(mm, pu, addr);
 141                         if (pshift == PMD_SHIFT)
 142                                 /* 16MB hugepage */
 143                                 return (pte_t *)pm;
 144                         else {
 145                                 ptl = pmd_lockptr(mm, pm);
 146                                 hpdp = (hugepd_t *)pm;
 147                         }
 148                 }
 149         }
 150 #else
 151         if (pshift >= PGDIR_SHIFT) {
 152                 ptl = &mm->page_table_lock;
 153                 hpdp = (hugepd_t *)pg;
 154         } else {
 155                 pdshift = PUD_SHIFT;
 156                 pu = pud_alloc(mm, pg, addr);
 157                 if (pshift >= PUD_SHIFT) {
 158                         ptl = pud_lockptr(mm, pu);
 159                         hpdp = (hugepd_t *)pu;
 160                 } else {
 161                         pdshift = PMD_SHIFT;
 162                         pm = pmd_alloc(mm, pu, addr);
 163                         ptl = pmd_lockptr(mm, pm);
 164                         hpdp = (hugepd_t *)pm;
 165                 }
 166         }
 167 #endif
 168         if (!hpdp)
 169                 return NULL;
 170
 171         BUG_ON(!hugepd_none(*hpdp) && !hugepd_ok(*hpdp));
 172
 173         if (hugepd_none(*hpdp) && __hugepte_alloc(mm, hpdp, addr,
 174                                                   pdshift, pshift, ptl))
 175                 return NULL;
 176
 177         return hugepte_offset(*hpdp, addr, pdshift);
 178 }
 179
 180 #ifdef CONFIG_PPC_BOOK3S_64
 181 /*
 182  * Tracks gpages after the device tree is scanned and before the
 183  * huge_boot_pages list is ready on pseries.
 184  */
 185 #define MAX_NUMBER_GPAGES       1024
 186 __initdata static u64 gpage_freearray[MAX_NUMBER_GPAGES];
 187 __initdata static unsigned nr_gpages;
 188
 189 /*
 190  * Build list of addresses of gigantic pages.  This function is used in early
 191  * boot before the buddy allocator is setup.
 192  */
 193 void __init pseries_add_gpage(u64 addr, u64 page_size, unsigned long number_of_pages)
 194 {
 195         if (!addr)
 196                 return;
 197         while (number_of_pages > 0) {
 198                 gpage_freearray[nr_gpages] = addr;
 199                 nr_gpages++;
 200                 number_of_pages--;
 201                 addr += page_size;
 202         }
 203 }
 204
 205 int __init pseries_alloc_bootmem_huge_page(struct hstate *hstate)
 206 {
 207         struct huge_bootmem_page *m;
 208         if (nr_gpages == 0)
 209                 return 0;
 210         m = phys_to_virt(gpage_freearray[--nr_gpages]);
 211         gpage_freearray[nr_gpages] = 0;
 212         list_add(&m->list, &huge_boot_pages);
 213         m->hstate = hstate;
 214         return 1;
 215 }
 216 #endif
 217
 218
 219 int __init alloc_bootmem_huge_page(struct hstate *h)
 220 {
 221
 222 #ifdef CONFIG_PPC_BOOK3S_64
 223         if (firmware_has_feature(FW_FEATURE_LPAR) && !radix_enabled())
 224                 return pseries_alloc_bootmem_huge_page(h);
 225 #endif
 226         return __alloc_bootmem_huge_page(h);
 227 }
 228
 229 #ifndef CONFIG_PPC_BOOK3S_64
 230 #define HUGEPD_FREELIST_SIZE \
 231         ((PAGE_SIZE - sizeof(struct hugepd_freelist)) / sizeof(pte_t))
 232
 233 struct hugepd_freelist {
 234         struct rcu_head rcu;
 235         unsigned int index;
 236         void *ptes[0];
 237 };
 238
 239 static DEFINE_PER_CPU(struct hugepd_freelist *, hugepd_freelist_cur);
 240
 241 static void hugepd_free_rcu_callback(struct rcu_head *head)
 242 {
 243         struct hugepd_freelist *batch =
 244                 container_of(head, struct hugepd_freelist, rcu);
 245         unsigned int i;
 246
 247         for (i = 0; i < batch->index; i++)
 248                 kmem_cache_free(PGT_CACHE(PTE_T_ORDER), batch->ptes[i]);
 249
 250         free_page((unsigned long)batch);
 251 }
 252
 253 static void hugepd_free(struct mmu_gather *tlb, void *hugepte)
 254 {
 255         struct hugepd_freelist **batchp;
 256
 257         batchp = &get_cpu_var(hugepd_freelist_cur);
 258
 259         if (atomic_read(&tlb->mm->mm_users) < 2 ||
 260             mm_is_thread_local(tlb->mm)) {
 261                 kmem_cache_free(PGT_CACHE(PTE_T_ORDER), hugepte);
 262                 put_cpu_var(hugepd_freelist_cur);
 263                 return;
 264         }
 265
 266         if (*batchp == NULL) {
 267                 *batchp = (struct hugepd_freelist *)__get_free_page(GFP_ATOMIC);
 268                 (*batchp)->index = 0;
 269         }
 270
 271         (*batchp)->ptes[(*batchp)->index++] = hugepte;
 272         if ((*batchp)->index == HUGEPD_FREELIST_SIZE) {
 273                 call_rcu(&(*batchp)->rcu, hugepd_free_rcu_callback);
 274                 *batchp = NULL;
 275         }
 276         put_cpu_var(hugepd_freelist_cur);
 277 }
 278 #else
 279 static inline void hugepd_free(struct mmu_gather *tlb, void *hugepte) {}
 280 #endif
 281
 282 static void free_hugepd_range(struct mmu_gather *tlb, hugepd_t *hpdp, int pdshift,
 283                               unsigned long start, unsigned long end,
 284                               unsigned long floor, unsigned long ceiling)
 285 {
 286         pte_t *hugepte = hugepd_page(*hpdp);
 287         int i;
 288
 289         unsigned long pdmask = ~((1UL << pdshift) - 1);
 290         unsigned int num_hugepd = 1;
 291         unsigned int shift = hugepd_shift(*hpdp);
 292
 293         /* Note: On fsl the hpdp may be the first of several */
 294         if (shift > pdshift)
 295                 num_hugepd = 1 << (shift - pdshift);
 296
 297         start &= pdmask;
 298         if (start < floor)
 299                 return;
 300         if (ceiling) {
 301                 ceiling &= pdmask;
 302                 if (! ceiling)
 303                         return;
 304         }
 305         if (end - 1 > ceiling - 1)
 306                 return;
 307
 308         for (i = 0; i < num_hugepd; i++, hpdp++)
 309                 *hpdp = __hugepd(0);
 310
 311         if (shift >= pdshift)
 312                 hugepd_free(tlb, hugepte);
 313         else if (IS_ENABLED(CONFIG_PPC_8xx))
 314                 pgtable_free_tlb(tlb, hugepte,
 315                                  get_hugepd_cache_index(PTE_INDEX_SIZE));
 316         else
 317                 pgtable_free_tlb(tlb, hugepte,
 318                                  get_hugepd_cache_index(pdshift - shift));
 319 }
 320
 321 static void hugetlb_free_pmd_range(struct mmu_gather *tlb, pud_t *pud,
 322                                    unsigned long addr, unsigned long end,
 323                                    unsigned long floor, unsigned long ceiling)
 324 {
 325         pmd_t *pmd;
 326         unsigned long next;
 327         unsigned long start;
 328
 329         start = addr;
 330         do {
 331                 unsigned long more;
 332
 333                 pmd = pmd_offset(pud, addr);
 334                 next = pmd_addr_end(addr, end);
 335                 if (!is_hugepd(__hugepd(pmd_val(*pmd)))) {
 336                         /*
 337                          * if it is not hugepd pointer, we should already find
 338                          * it cleared.
 339                          */
 340                         WARN_ON(!pmd_none_or_clear_bad(pmd));
 341                         continue;
 342                 }
 343                 /*
 344                  * Increment next by the size of the huge mapping since
 345                  * there may be more than one entry at this level for a
 346                  * single hugepage, but all of them point to
 347                  * the same kmem cache that holds the hugepte.
 348                  */
 349                 more = addr + (1 << hugepd_shift(*(hugepd_t *)pmd));
 350                 if (more > next)
 351                         next = more;
 352
 353                 free_hugepd_range(tlb, (hugepd_t *)pmd, PMD_SHIFT,
 354                                   addr, next, floor, ceiling);
 355         } while (addr = next, addr != end);
 356
 357         start &= PUD_MASK;
 358         if (start < floor)
 359                 return;
 360         if (ceiling) {
 361                 ceiling &= PUD_MASK;
 362                 if (!ceiling)
 363                         return;
 364         }
 365         if (end - 1 > ceiling - 1)
 366                 return;
 367
 368         pmd = pmd_offset(pud, start);
 369         pud_clear(pud);
 370         pmd_free_tlb(tlb, pmd, start);
 371         mm_dec_nr_pmds(tlb->mm);
 372 }
 373
 374 static void hugetlb_free_pud_range(struct mmu_gather *tlb, pgd_t *pgd,
 375                                    unsigned long addr, unsigned long end,
 376                                    unsigned long floor, unsigned long ceiling)
 377 {
 378         pud_t *pud;
 379         unsigned long next;
 380         unsigned long start;
 381
 382         start = addr;
 383         do {
 384                 pud = pud_offset(pgd, addr);
 385                 next = pud_addr_end(addr, end);
 386                 if (!is_hugepd(__hugepd(pud_val(*pud)))) {
 387                         if (pud_none_or_clear_bad(pud))
 388                                 continue;
 389                         hugetlb_free_pmd_range(tlb, pud, addr, next, floor,
 390                                                ceiling);
 391                 } else {
 392                         unsigned long more;
 393                         /*
 394                          * Increment next by the size of the huge mapping since
 395                          * there may be more than one entry at this level for a
 396                          * single hugepage, but all of them point to
 397                          * the same kmem cache that holds the hugepte.
 398                          */
 399                         more = addr + (1 << hugepd_shift(*(hugepd_t *)pud));
 400                         if (more > next)
 401                                 next = more;
 402
 403                         free_hugepd_range(tlb, (hugepd_t *)pud, PUD_SHIFT,
 404                                           addr, next, floor, ceiling);
 405                 }
 406         } while (addr = next, addr != end);
 407
 408         start &= PGDIR_MASK;
 409         if (start < floor)
 410                 return;
 411         if (ceiling) {
 412                 ceiling &= PGDIR_MASK;
 413                 if (!ceiling)
 414                         return;
 415         }
 416         if (end - 1 > ceiling - 1)
 417                 return;
 418
 419         pud = pud_offset(pgd, start);
 420         pgd_clear(pgd);
 421         pud_free_tlb(tlb, pud, start);
 422         mm_dec_nr_puds(tlb->mm);
 423 }
 424
 425 /*
 426  * This function frees user-level page tables of a process.
 427  */
 428 void hugetlb_free_pgd_range(struct mmu_gather *tlb,
 429                             unsigned long addr, unsigned long end,
 430                             unsigned long floor, unsigned long ceiling)
 431 {
 432         pgd_t *pgd;
 433         unsigned long next;
 434
 435         /*
 436          * Because there are a number of different possible pagetable
 437          * layouts for hugepage ranges, we limit knowledge of how
 438          * things should be laid out to the allocation path
 439          * (huge_pte_alloc(), above).  Everything else works out the
 440          * structure as it goes from information in the hugepd
 441          * pointers.  That means that we can't here use the
 442          * optimization used in the normal page free_pgd_range(), of
 443          * checking whether we're actually covering a large enough
 444          * range to have to do anything at the top level of the walk
 445          * instead of at the bottom.
 446          *
 447          * To make sense of this, you should probably go read the big
 448          * block comment at the top of the normal free_pgd_range(),
 449          * too.
 450          */
 451
 452         do {
 453                 next = pgd_addr_end(addr, end);
 454                 pgd = pgd_offset(tlb->mm, addr);
 455                 if (!is_hugepd(__hugepd(pgd_val(*pgd)))) {
 456                         if (pgd_none_or_clear_bad(pgd))
 457                                 continue;
 458                         hugetlb_free_pud_range(tlb, pgd, addr, next, floor, ceiling);
 459                 } else {
 460                         unsigned long more;
 461                         /*
 462                          * Increment next by the size of the huge mapping since
 463                          * there may be more than one entry at the pgd level
 464                          * for a single hugepage, but all of them point to the
 465                          * same kmem cache that holds the hugepte.
 466                          */
 467                         more = addr + (1 << hugepd_shift(*(hugepd_t *)pgd));
 468                         if (more > next)
 469                                 next = more;
 470
 471                         free_hugepd_range(tlb, (hugepd_t *)pgd, PGDIR_SHIFT,
 472                                           addr, next, floor, ceiling);
 473                 }
 474         } while (addr = next, addr != end);
 475 }
 476
 477 struct page *follow_huge_pd(struct vm_area_struct *vma,
 478                             unsigned long address, hugepd_t hpd,
 479                             int flags, int pdshift)
 480 {
 481         pte_t *ptep;
 482         spinlock_t *ptl;
 483         struct page *page = NULL;
 484         unsigned long mask;
 485         int shift = hugepd_shift(hpd);
 486         struct mm_struct *mm = vma->vm_mm;
 487
 488 retry:
 489         /*
 490          * hugepage directory entries are protected by mm->page_table_lock
 491          * Use this instead of huge_pte_lockptr
 492          */
 493         ptl = &mm->page_table_lock;
 494         spin_lock(ptl);
 495
 496         ptep = hugepte_offset(hpd, address, pdshift);
 497         if (pte_present(*ptep)) {
 498                 mask = (1UL << shift) - 1;
 499                 page = pte_page(*ptep);
 500                 page += ((address & mask) >> PAGE_SHIFT);
 501                 if (flags & FOLL_GET)
 502                         get_page(page);
 503         } else {
 504                 if (is_hugetlb_entry_migration(*ptep)) {
 505                         spin_unlock(ptl);
 506                         __migration_entry_wait(mm, ptep, ptl);
 507                         goto retry;
 508                 }
 509         }
 510         spin_unlock(ptl);
 511         return page;
 512 }
 513
 514 #ifdef CONFIG_PPC_MM_SLICES
 515 unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
 516                                         unsigned long len, unsigned long pgoff,
 517                                         unsigned long flags)
 518 {
 519         struct hstate *hstate = hstate_file(file);
 520         int mmu_psize = shift_to_mmu_psize(huge_page_shift(hstate));
 521
 522 #ifdef CONFIG_PPC_RADIX_MMU
 523         if (radix_enabled())
 524                 return radix__hugetlb_get_unmapped_area(file, addr, len,
 525                                                        pgoff, flags);
 526 #endif
 527         return slice_get_unmapped_area(addr, len, flags, mmu_psize, 1);
 528 }
 529 #endif
 530
 531 unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
 532 {
 533         /* With radix we don't use slice, so derive it from vma*/
 534         if (IS_ENABLED(CONFIG_PPC_MM_SLICES) && !radix_enabled()) {
 535                 unsigned int psize = get_slice_psize(vma->vm_mm, vma->vm_start);
 536
 537                 return 1UL << mmu_psize_to_shift(psize);
 538         }
 539         return vma_kernel_pagesize(vma);
 540 }
 541
 542 static int __init add_huge_page_size(unsigned long long size)
 543 {
 544         int shift = __ffs(size);
 545         int mmu_psize;
 546
 547         /* Check that it is a page size supported by the hardware and
 548          * that it fits within pagetable and slice limits. */
 549         if (size <= PAGE_SIZE || !is_power_of_2(size))
 550                 return -EINVAL;
 551
 552         mmu_psize = check_and_get_huge_psize(shift);
 553         if (mmu_psize < 0)
 554                 return -EINVAL;
 555
 556         BUG_ON(mmu_psize_defs[mmu_psize].shift != shift);
 557
 558         /* Return if huge page size has already been setup */
 559         if (size_to_hstate(size))
 560                 return 0;
 561
 562         hugetlb_add_hstate(shift - PAGE_SHIFT);
 563
 564         return 0;
 565 }
 566
 567 static int __init hugepage_setup_sz(char *str)
 568 {
 569         unsigned long long size;
 570
 571         size = memparse(str, &str);
 572
 573         if (add_huge_page_size(size) != 0) {
 574                 hugetlb_bad_size();
 575                 pr_err("Invalid huge page size specified(%llu)\n", size);
 576         }
 577
 578         return 1;
 579 }
 580 __setup("hugepagesz=", hugepage_setup_sz);
 581
 582 static int __init hugetlbpage_init(void)
 583 {
 584         int psize;
 585
 586         if (hugetlb_disabled) {
 587                 pr_info("HugeTLB support is disabled!\n");
 588                 return 0;
 589         }
 590
 591         if (IS_ENABLED(CONFIG_PPC_BOOK3S_64) && !radix_enabled() &&
 592             !mmu_has_feature(MMU_FTR_16M_PAGE))
 593                 return -ENODEV;
 594
 595         for (psize = 0; psize < MMU_PAGE_COUNT; ++psize) {
 596                 unsigned shift;
 597                 unsigned pdshift;
 598
 599                 if (!mmu_psize_defs[psize].shift)
 600                         continue;
 601
 602                 shift = mmu_psize_to_shift(psize);
 603
 604 #ifdef CONFIG_PPC_BOOK3S_64
 605                 if (shift > PGDIR_SHIFT)
 606                         continue;
 607                 else if (shift > PUD_SHIFT)
 608                         pdshift = PGDIR_SHIFT;
 609                 else if (shift > PMD_SHIFT)
 610                         pdshift = PUD_SHIFT;
 611                 else
 612                         pdshift = PMD_SHIFT;
 613 #else
 614                 if (shift < PUD_SHIFT)
 615                         pdshift = PMD_SHIFT;
 616                 else if (shift < PGDIR_SHIFT)
 617                         pdshift = PUD_SHIFT;
 618                 else
 619                         pdshift = PGDIR_SHIFT;
 620 #endif
 621
 622                 if (add_huge_page_size(1ULL << shift) < 0)
 623                         continue;
 624                 /*
 625                  * if we have pdshift and shift value same, we don't
 626                  * use pgt cache for hugepd.
 627                  */
 628                 if (pdshift > shift && IS_ENABLED(CONFIG_PPC_8xx))
 629                         pgtable_cache_add(PTE_INDEX_SIZE);
 630                 else if (pdshift > shift)
 631                         pgtable_cache_add(pdshift - shift);
 632                 else if (IS_ENABLED(CONFIG_PPC_FSL_BOOK3E) || IS_ENABLED(CONFIG_PPC_8xx))
 633                         pgtable_cache_add(PTE_T_ORDER);
 634         }
 635
 636         if (IS_ENABLED(CONFIG_HUGETLB_PAGE_SIZE_VARIABLE))
 637                 hugetlbpage_init_default();
 638
 639         return 0;
 640 }
 641
 642 arch_initcall(hugetlbpage_init);
 643
 644 void flush_dcache_icache_hugepage(struct page *page)
 645 {
 646         int i;
 647         void *start;
 648
 649         BUG_ON(!PageCompound(page));
 650
 651         for (i = 0; i < (1UL << compound_order(page)); i++) {
 652                 if (!PageHighMem(page)) {
 653                         __flush_dcache_icache(page_address(page+i));
 654                 } else {
 655                         start = kmap_atomic(page+i);
 656                         __flush_dcache_icache(start);
 657                         kunmap_atomic(start);
 658                 }
 659         }
 660 }