arch/arm64/mm/mmu.c

   1 /*
   2  * Based on arch/arm/mm/mmu.c
   3  *
   4  * Copyright (C) 1995-2005 Russell King
   5  * Copyright (C) 2012 ARM Ltd.
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18  */
  19
  20 #include <linux/export.h>
  21 #include <linux/kernel.h>
  22 #include <linux/errno.h>
  23 #include <linux/init.h>
  24 #include <linux/libfdt.h>
  25 #include <linux/mman.h>
  26 #include <linux/nodemask.h>
  27 #include <linux/memblock.h>
  28 #include <linux/fs.h>
  29 #include <linux/io.h>
  30 #include <linux/slab.h>
  31 #include <linux/stop_machine.h>
  32
  33 #include <asm/barrier.h>
  34 #include <asm/cputype.h>
  35 #include <asm/fixmap.h>
  36 #include <asm/kernel-pgtable.h>
  37 #include <asm/sections.h>
  38 #include <asm/setup.h>
  39 #include <asm/sizes.h>
  40 #include <asm/tlb.h>
  41 #include <asm/memblock.h>
  42 #include <asm/mmu_context.h>
  43
  44 #include "mm.h"
  45
  46 u64 idmap_t0sz = TCR_T0SZ(VA_BITS);
  47
  48 /*
  49  * Empty_zero_page is a special page that is used for zero-initialized data
  50  * and COW.
  51  */
  52 unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss;
  53 EXPORT_SYMBOL(empty_zero_page);
  54
  55 pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
  56                               unsigned long size, pgprot_t vma_prot)
  57 {
  58         if (!pfn_valid(pfn))
  59                 return pgprot_noncached(vma_prot);
  60         else if (file->f_flags & O_SYNC)
  61                 return pgprot_writecombine(vma_prot);
  62         return vma_prot;
  63 }
  64 EXPORT_SYMBOL(phys_mem_access_prot);
  65
  66 static phys_addr_t __init early_pgtable_alloc(void)
  67 {
  68         phys_addr_t phys;
  69         void *ptr;
  70
  71         phys = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
  72         BUG_ON(!phys);
  73
  74         /*
  75          * The FIX_{PGD,PUD,PMD} slots may be in active use, but the FIX_PTE
  76          * slot will be free, so we can (ab)use the FIX_PTE slot to initialise
  77          * any level of table.
  78          */
  79         ptr = pte_set_fixmap(phys);
  80
  81         memset(ptr, 0, PAGE_SIZE);
  82
  83         /*
  84          * Implicit barriers also ensure the zeroed page is visible to the page
  85          * table walker
  86          */
  87         pte_clear_fixmap();
  88
  89         return phys;
  90 }
  91
  92 /*
  93  * remap a PMD into pages
  94  */
  95 static void split_pmd(pmd_t *pmd, pte_t *pte)
  96 {
  97         unsigned long pfn = pmd_pfn(*pmd);
  98         int i = 0;
  99
 100         do {
 101                 /*
 102                  * Need to have the least restrictive permissions available
 103                  * permissions will be fixed up later
 104                  */
 105                 set_pte(pte, pfn_pte(pfn, PAGE_KERNEL_EXEC));
 106                 pfn++;
 107         } while (pte++, i++, i < PTRS_PER_PTE);
 108 }
 109
 110 static void alloc_init_pte(pmd_t *pmd, unsigned long addr,
 111                                   unsigned long end, unsigned long pfn,
 112                                   pgprot_t prot,
 113                                   phys_addr_t (*pgtable_alloc)(void))
 114 {
 115         pte_t *pte;
 116
 117         if (pmd_none(*pmd) || pmd_sect(*pmd)) {
 118                 phys_addr_t pte_phys = pgtable_alloc();
 119                 pte = pte_set_fixmap(pte_phys);
 120                 if (pmd_sect(*pmd))
 121                         split_pmd(pmd, pte);
 122                 __pmd_populate(pmd, pte_phys, PMD_TYPE_TABLE);
 123                 flush_tlb_all();
 124                 pte_clear_fixmap();
 125         }
 126         BUG_ON(pmd_bad(*pmd));
 127
 128         pte = pte_set_fixmap_offset(pmd, addr);
 129         do {
 130                 set_pte(pte, pfn_pte(pfn, prot));
 131                 pfn++;
 132         } while (pte++, addr += PAGE_SIZE, addr != end);
 133
 134         pte_clear_fixmap();
 135 }
 136
 137 static void split_pud(pud_t *old_pud, pmd_t *pmd)
 138 {
 139         unsigned long addr = pud_pfn(*old_pud) << PAGE_SHIFT;
 140         pgprot_t prot = __pgprot(pud_val(*old_pud) ^ addr);
 141         int i = 0;
 142
 143         do {
 144                 set_pmd(pmd, __pmd(addr | pgprot_val(prot)));
 145                 addr += PMD_SIZE;
 146         } while (pmd++, i++, i < PTRS_PER_PMD);
 147 }
 148
 149 static void alloc_init_pmd(struct mm_struct *mm, pud_t *pud,
 150                                   unsigned long addr, unsigned long end,
 151                                   phys_addr_t phys, pgprot_t prot,
 152                                   phys_addr_t (*pgtable_alloc)(void))
 153 {
 154         pmd_t *pmd;
 155         unsigned long next;
 156
 157         /*
 158          * Check for initial section mappings in the pgd/pud and remove them.
 159          */
 160         if (pud_none(*pud) || pud_sect(*pud)) {
 161                 phys_addr_t pmd_phys = pgtable_alloc();
 162                 pmd = pmd_set_fixmap(pmd_phys);
 163                 if (pud_sect(*pud)) {
 164                         /*
 165                          * need to have the 1G of mappings continue to be
 166                          * present
 167                          */
 168                         split_pud(pud, pmd);
 169                 }
 170                 __pud_populate(pud, pmd_phys, PUD_TYPE_TABLE);
 171                 flush_tlb_all();
 172                 pmd_clear_fixmap();
 173         }
 174         BUG_ON(pud_bad(*pud));
 175
 176         pmd = pmd_set_fixmap_offset(pud, addr);
 177         do {
 178                 next = pmd_addr_end(addr, end);
 179                 /* try section mapping first */
 180                 if (((addr | next | phys) & ~SECTION_MASK) == 0) {
 181                         pmd_t old_pmd =*pmd;
 182                         set_pmd(pmd, __pmd(phys |
 183                                            pgprot_val(mk_sect_prot(prot))));
 184                         /*
 185                          * Check for previous table entries created during
 186                          * boot (__create_page_tables) and flush them.
 187                          */
 188                         if (!pmd_none(old_pmd)) {
 189                                 flush_tlb_all();
 190                                 if (pmd_table(old_pmd)) {
 191                                         phys_addr_t table = pmd_page_paddr(old_pmd);
 192                                         if (!WARN_ON_ONCE(slab_is_available()))
 193                                                 memblock_free(table, PAGE_SIZE);
 194                                 }
 195                         }
 196                 } else {
 197                         alloc_init_pte(pmd, addr, next, __phys_to_pfn(phys),
 198                                        prot, pgtable_alloc);
 199                 }
 200                 phys += next - addr;
 201         } while (pmd++, addr = next, addr != end);
 202
 203         pmd_clear_fixmap();
 204 }
 205
 206 static inline bool use_1G_block(unsigned long addr, unsigned long next,
 207                         unsigned long phys)
 208 {
 209         if (PAGE_SHIFT != 12)
 210                 return false;
 211
 212         if (((addr | next | phys) & ~PUD_MASK) != 0)
 213                 return false;
 214
 215         return true;
 216 }
 217
 218 static void alloc_init_pud(struct mm_struct *mm, pgd_t *pgd,
 219                                   unsigned long addr, unsigned long end,
 220                                   phys_addr_t phys, pgprot_t prot,
 221                                   phys_addr_t (*pgtable_alloc)(void))
 222 {
 223         pud_t *pud;
 224         unsigned long next;
 225
 226         if (pgd_none(*pgd)) {
 227                 phys_addr_t pud_phys = pgtable_alloc();
 228                 __pgd_populate(pgd, pud_phys, PUD_TYPE_TABLE);
 229         }
 230         BUG_ON(pgd_bad(*pgd));
 231
 232         pud = pud_set_fixmap_offset(pgd, addr);
 233         do {
 234                 next = pud_addr_end(addr, end);
 235
 236                 /*
 237                  * For 4K granule only, attempt to put down a 1GB block
 238                  */
 239                 if (use_1G_block(addr, next, phys)) {
 240                         pud_t old_pud = *pud;
 241                         set_pud(pud, __pud(phys |
 242                                            pgprot_val(mk_sect_prot(prot))));
 243
 244                         /*
 245                          * If we have an old value for a pud, it will
 246                          * be pointing to a pmd table that we no longer
 247                          * need (from swapper_pg_dir).
 248                          *
 249                          * Look up the old pmd table and free it.
 250                          */
 251                         if (!pud_none(old_pud)) {
 252                                 flush_tlb_all();
 253                                 if (pud_table(old_pud)) {
 254                                         phys_addr_t table = pud_page_paddr(old_pud);
 255                                         if (!WARN_ON_ONCE(slab_is_available()))
 256                                                 memblock_free(table, PAGE_SIZE);
 257                                 }
 258                         }
 259                 } else {
 260                         alloc_init_pmd(mm, pud, addr, next, phys, prot,
 261                                        pgtable_alloc);
 262                 }
 263                 phys += next - addr;
 264         } while (pud++, addr = next, addr != end);
 265
 266         pud_clear_fixmap();
 267 }
 268
 269 /*
 270  * Create the page directory entries and any necessary page tables for the
 271  * mapping specified by 'md'.
 272  */
 273 static void  __create_mapping(struct mm_struct *mm, pgd_t *pgd,
 274                                     phys_addr_t phys, unsigned long virt,
 275                                     phys_addr_t size, pgprot_t prot,
 276                                     phys_addr_t (*pgtable_alloc)(void))
 277 {
 278         unsigned long addr, length, end, next;
 279
 280         /*
 281          * If the virtual and physical address don't have the same offset
 282          * within a page, we cannot map the region as the caller expects.
 283          */
 284         if (WARN_ON((phys ^ virt) & ~PAGE_MASK))
 285                 return;
 286
 287         phys &= PAGE_MASK;
 288         addr = virt & PAGE_MASK;
 289         length = PAGE_ALIGN(size + (virt & ~PAGE_MASK));
 290
 291         end = addr + length;
 292         do {
 293                 next = pgd_addr_end(addr, end);
 294                 alloc_init_pud(mm, pgd, addr, next, phys, prot, pgtable_alloc);
 295                 phys += next - addr;
 296         } while (pgd++, addr = next, addr != end);
 297 }
 298
 299 static phys_addr_t late_pgtable_alloc(void)
 300 {
 301         void *ptr = (void *)__get_free_page(PGALLOC_GFP);
 302         BUG_ON(!ptr);
 303
 304         /* Ensure the zeroed page is visible to the page table walker */
 305         dsb(ishst);
 306         return __pa(ptr);
 307 }
 308
 309 static void __init create_mapping(phys_addr_t phys, unsigned long virt,
 310                                   phys_addr_t size, pgprot_t prot)
 311 {
 312         if (virt < VMALLOC_START) {
 313                 pr_warn("BUG: not creating mapping for %pa at 0x%016lx - outside kernel range\n",
 314                         &phys, virt);
 315                 return;
 316         }
 317         __create_mapping(&init_mm, pgd_offset_k(virt), phys, virt,
 318                          size, prot, early_pgtable_alloc);
 319 }
 320
 321 void __init create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
 322                                unsigned long virt, phys_addr_t size,
 323                                pgprot_t prot)
 324 {
 325         __create_mapping(mm, pgd_offset(mm, virt), phys, virt, size, prot,
 326                                 late_pgtable_alloc);
 327 }
 328
 329 static void create_mapping_late(phys_addr_t phys, unsigned long virt,
 330                                   phys_addr_t size, pgprot_t prot)
 331 {
 332         if (virt < VMALLOC_START) {
 333                 pr_warn("BUG: not creating mapping for %pa at 0x%016lx - outside kernel range\n",
 334                         &phys, virt);
 335                 return;
 336         }
 337
 338         return __create_mapping(&init_mm, pgd_offset_k(virt),
 339                                 phys, virt, size, prot, late_pgtable_alloc);
 340 }
 341
 342 #ifdef CONFIG_DEBUG_RODATA
 343 static void __init __map_memblock(phys_addr_t start, phys_addr_t end)
 344 {
 345         /*
 346          * Set up the executable regions using the existing section mappings
 347          * for now. This will get more fine grained later once all memory
 348          * is mapped
 349          */
 350         unsigned long kernel_x_start = round_down(__pa(_stext), SWAPPER_BLOCK_SIZE);
 351         unsigned long kernel_x_end = round_up(__pa(__init_end), SWAPPER_BLOCK_SIZE);
 352
 353         if (end < kernel_x_start) {
 354                 create_mapping(start, __phys_to_virt(start),
 355                         end - start, PAGE_KERNEL);
 356         } else if (start >= kernel_x_end) {
 357                 create_mapping(start, __phys_to_virt(start),
 358                         end - start, PAGE_KERNEL);
 359         } else {
 360                 if (start < kernel_x_start)
 361                         create_mapping(start, __phys_to_virt(start),
 362                                 kernel_x_start - start,
 363                                 PAGE_KERNEL);
 364                 create_mapping(kernel_x_start,
 365                                 __phys_to_virt(kernel_x_start),
 366                                 kernel_x_end - kernel_x_start,
 367                                 PAGE_KERNEL_EXEC);
 368                 if (kernel_x_end < end)
 369                         create_mapping(kernel_x_end,
 370                                 __phys_to_virt(kernel_x_end),
 371                                 end - kernel_x_end,
 372                                 PAGE_KERNEL);
 373         }
 374
 375 }
 376 #else
 377 static void __init __map_memblock(phys_addr_t start, phys_addr_t end)
 378 {
 379         create_mapping(start, __phys_to_virt(start), end - start,
 380                         PAGE_KERNEL_EXEC);
 381 }
 382 #endif
 383
 384 static void __init map_mem(void)
 385 {
 386         struct memblock_region *reg;
 387
 388         /* map all the memory banks */
 389         for_each_memblock(memory, reg) {
 390                 phys_addr_t start = reg->base;
 391                 phys_addr_t end = start + reg->size;
 392
 393                 if (start >= end)
 394                         break;
 395
 396                 __map_memblock(start, end);
 397         }
 398 }
 399
 400 static void __init fixup_executable(void)
 401 {
 402 #ifdef CONFIG_DEBUG_RODATA
 403         /* now that we are actually fully mapped, make the start/end more fine grained */
 404         if (!IS_ALIGNED((unsigned long)_stext, SWAPPER_BLOCK_SIZE)) {
 405                 unsigned long aligned_start = round_down(__pa(_stext),
 406                                                          SWAPPER_BLOCK_SIZE);
 407
 408                 create_mapping(aligned_start, __phys_to_virt(aligned_start),
 409                                 __pa(_stext) - aligned_start,
 410                                 PAGE_KERNEL);
 411         }
 412
 413         if (!IS_ALIGNED((unsigned long)__init_end, SWAPPER_BLOCK_SIZE)) {
 414                 unsigned long aligned_end = round_up(__pa(__init_end),
 415                                                           SWAPPER_BLOCK_SIZE);
 416                 create_mapping(__pa(__init_end), (unsigned long)__init_end,
 417                                 aligned_end - __pa(__init_end),
 418                                 PAGE_KERNEL);
 419         }
 420 #endif
 421 }
 422
 423 #ifdef CONFIG_DEBUG_RODATA
 424 void mark_rodata_ro(void)
 425 {
 426         create_mapping_late(__pa(_stext), (unsigned long)_stext,
 427                                 (unsigned long)_etext - (unsigned long)_stext,
 428                                 PAGE_KERNEL_ROX);
 429
 430 }
 431 #endif
 432
 433 void fixup_init(void)
 434 {
 435         create_mapping_late(__pa(__init_begin), (unsigned long)__init_begin,
 436                         (unsigned long)__init_end - (unsigned long)__init_begin,
 437                         PAGE_KERNEL);
 438 }
 439
 440 /*
 441  * paging_init() sets up the page tables, initialises the zone memory
 442  * maps and sets up the zero page.
 443  */
 444 void __init paging_init(void)
 445 {
 446         map_mem();
 447         fixup_executable();
 448
 449         bootmem_init();
 450 }
 451
 452 /*
 453  * Check whether a kernel address is valid (derived from arch/x86/).
 454  */
 455 int kern_addr_valid(unsigned long addr)
 456 {
 457         pgd_t *pgd;
 458         pud_t *pud;
 459         pmd_t *pmd;
 460         pte_t *pte;
 461
 462         if ((((long)addr) >> VA_BITS) != -1UL)
 463                 return 0;
 464
 465         pgd = pgd_offset_k(addr);
 466         if (pgd_none(*pgd))
 467                 return 0;
 468
 469         pud = pud_offset(pgd, addr);
 470         if (pud_none(*pud))
 471                 return 0;
 472
 473         if (pud_sect(*pud))
 474                 return pfn_valid(pud_pfn(*pud));
 475
 476         pmd = pmd_offset(pud, addr);
 477         if (pmd_none(*pmd))
 478                 return 0;
 479
 480         if (pmd_sect(*pmd))
 481                 return pfn_valid(pmd_pfn(*pmd));
 482
 483         pte = pte_offset_kernel(pmd, addr);
 484         if (pte_none(*pte))
 485                 return 0;
 486
 487         return pfn_valid(pte_pfn(*pte));
 488 }
 489 #ifdef CONFIG_SPARSEMEM_VMEMMAP
 490 #if !ARM64_SWAPPER_USES_SECTION_MAPS
 491 int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node)
 492 {
 493         return vmemmap_populate_basepages(start, end, node);
 494 }
 495 #else   /* !ARM64_SWAPPER_USES_SECTION_MAPS */
 496 int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node)
 497 {
 498         unsigned long addr = start;
 499         unsigned long next;
 500         pgd_t *pgd;
 501         pud_t *pud;
 502         pmd_t *pmd;
 503
 504         do {
 505                 next = pmd_addr_end(addr, end);
 506
 507                 pgd = vmemmap_pgd_populate(addr, node);
 508                 if (!pgd)
 509                         return -ENOMEM;
 510
 511                 pud = vmemmap_pud_populate(pgd, addr, node);
 512                 if (!pud)
 513                         return -ENOMEM;
 514
 515                 pmd = pmd_offset(pud, addr);
 516                 if (pmd_none(*pmd)) {
 517                         void *p = NULL;
 518
 519                         p = vmemmap_alloc_block_buf(PMD_SIZE, node);
 520                         if (!p)
 521                                 return -ENOMEM;
 522
 523                         set_pmd(pmd, __pmd(__pa(p) | PROT_SECT_NORMAL));
 524                 } else
 525                         vmemmap_verify((pte_t *)pmd, node, addr, next);
 526         } while (addr = next, addr != end);
 527
 528         return 0;
 529 }
 530 #endif  /* CONFIG_ARM64_64K_PAGES */
 531 void vmemmap_free(unsigned long start, unsigned long end)
 532 {
 533 }
 534 #endif  /* CONFIG_SPARSEMEM_VMEMMAP */
 535
 536 static pte_t bm_pte[PTRS_PER_PTE] __page_aligned_bss;
 537 #if CONFIG_PGTABLE_LEVELS > 2
 538 static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss;
 539 #endif
 540 #if CONFIG_PGTABLE_LEVELS > 3
 541 static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss;
 542 #endif
 543
 544 static inline pud_t * fixmap_pud(unsigned long addr)
 545 {
 546         pgd_t *pgd = pgd_offset_k(addr);
 547
 548         BUG_ON(pgd_none(*pgd) || pgd_bad(*pgd));
 549
 550         return pud_offset(pgd, addr);
 551 }
 552
 553 static inline pmd_t * fixmap_pmd(unsigned long addr)
 554 {
 555         pud_t *pud = fixmap_pud(addr);
 556
 557         BUG_ON(pud_none(*pud) || pud_bad(*pud));
 558
 559         return pmd_offset(pud, addr);
 560 }
 561
 562 static inline pte_t * fixmap_pte(unsigned long addr)
 563 {
 564         pmd_t *pmd = fixmap_pmd(addr);
 565
 566         BUG_ON(pmd_none(*pmd) || pmd_bad(*pmd));
 567
 568         return pte_offset_kernel(pmd, addr);
 569 }
 570
 571 void __init early_fixmap_init(void)
 572 {
 573         pgd_t *pgd;
 574         pud_t *pud;
 575         pmd_t *pmd;
 576         unsigned long addr = FIXADDR_START;
 577
 578         pgd = pgd_offset_k(addr);
 579         pgd_populate(&init_mm, pgd, bm_pud);
 580         pud = pud_offset(pgd, addr);
 581         pud_populate(&init_mm, pud, bm_pmd);
 582         pmd = pmd_offset(pud, addr);
 583         pmd_populate_kernel(&init_mm, pmd, bm_pte);
 584
 585         /*
 586          * The boot-ioremap range spans multiple pmds, for which
 587          * we are not preparted:
 588          */
 589         BUILD_BUG_ON((__fix_to_virt(FIX_BTMAP_BEGIN) >> PMD_SHIFT)
 590                      != (__fix_to_virt(FIX_BTMAP_END) >> PMD_SHIFT));
 591
 592         if ((pmd != fixmap_pmd(fix_to_virt(FIX_BTMAP_BEGIN)))
 593              || pmd != fixmap_pmd(fix_to_virt(FIX_BTMAP_END))) {
 594                 WARN_ON(1);
 595                 pr_warn("pmd %p != %p, %p\n",
 596                         pmd, fixmap_pmd(fix_to_virt(FIX_BTMAP_BEGIN)),
 597                         fixmap_pmd(fix_to_virt(FIX_BTMAP_END)));
 598                 pr_warn("fix_to_virt(FIX_BTMAP_BEGIN): %08lx\n",
 599                         fix_to_virt(FIX_BTMAP_BEGIN));
 600                 pr_warn("fix_to_virt(FIX_BTMAP_END):   %08lx\n",
 601                         fix_to_virt(FIX_BTMAP_END));
 602
 603                 pr_warn("FIX_BTMAP_END:       %d\n", FIX_BTMAP_END);
 604                 pr_warn("FIX_BTMAP_BEGIN:     %d\n", FIX_BTMAP_BEGIN);
 605         }
 606 }
 607
 608 void __set_fixmap(enum fixed_addresses idx,
 609                                phys_addr_t phys, pgprot_t flags)
 610 {
 611         unsigned long addr = __fix_to_virt(idx);
 612         pte_t *pte;
 613
 614         BUG_ON(idx <= FIX_HOLE || idx >= __end_of_fixed_addresses);
 615
 616         pte = fixmap_pte(addr);
 617
 618         if (pgprot_val(flags)) {
 619                 set_pte(pte, pfn_pte(phys >> PAGE_SHIFT, flags));
 620         } else {
 621                 pte_clear(&init_mm, addr, pte);
 622                 flush_tlb_kernel_range(addr, addr+PAGE_SIZE);
 623         }
 624 }
 625
 626 void *__init fixmap_remap_fdt(phys_addr_t dt_phys)
 627 {
 628         const u64 dt_virt_base = __fix_to_virt(FIX_FDT);
 629         pgprot_t prot = PAGE_KERNEL_RO;
 630         int size, offset;
 631         void *dt_virt;
 632
 633         /*
 634          * Check whether the physical FDT address is set and meets the minimum
 635          * alignment requirement. Since we are relying on MIN_FDT_ALIGN to be
 636          * at least 8 bytes so that we can always access the size field of the
 637          * FDT header after mapping the first chunk, double check here if that
 638          * is indeed the case.
 639          */
 640         BUILD_BUG_ON(MIN_FDT_ALIGN < 8);
 641         if (!dt_phys || dt_phys % MIN_FDT_ALIGN)
 642                 return NULL;
 643
 644         /*
 645          * Make sure that the FDT region can be mapped without the need to
 646          * allocate additional translation table pages, so that it is safe
 647          * to call create_mapping() this early.
 648          *
 649          * On 64k pages, the FDT will be mapped using PTEs, so we need to
 650          * be in the same PMD as the rest of the fixmap.
 651          * On 4k pages, we'll use section mappings for the FDT so we only
 652          * have to be in the same PUD.
 653          */
 654         BUILD_BUG_ON(dt_virt_base % SZ_2M);
 655
 656         BUILD_BUG_ON(__fix_to_virt(FIX_FDT_END) >> SWAPPER_TABLE_SHIFT !=
 657                      __fix_to_virt(FIX_BTMAP_BEGIN) >> SWAPPER_TABLE_SHIFT);
 658
 659         offset = dt_phys % SWAPPER_BLOCK_SIZE;
 660         dt_virt = (void *)dt_virt_base + offset;
 661
 662         /* map the first chunk so we can read the size from the header */
 663         create_mapping(round_down(dt_phys, SWAPPER_BLOCK_SIZE), dt_virt_base,
 664                        SWAPPER_BLOCK_SIZE, prot);
 665
 666         if (fdt_check_header(dt_virt) != 0)
 667                 return NULL;
 668
 669         size = fdt_totalsize(dt_virt);
 670         if (size > MAX_FDT_SIZE)
 671                 return NULL;
 672
 673         if (offset + size > SWAPPER_BLOCK_SIZE)
 674                 create_mapping(round_down(dt_phys, SWAPPER_BLOCK_SIZE), dt_virt_base,
 675                                round_up(offset + size, SWAPPER_BLOCK_SIZE), prot);
 676
 677         memblock_reserve(dt_phys, size);
 678
 679         return dt_virt;
 680 }