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(pud_t *pud, unsigned long addr, unsigned long end,
 150                                   phys_addr_t phys, pgprot_t prot,
 151                                   phys_addr_t (*pgtable_alloc)(void))
 152 {
 153         pmd_t *pmd;
 154         unsigned long next;
 155
 156         /*
 157          * Check for initial section mappings in the pgd/pud and remove them.
 158          */
 159         if (pud_none(*pud) || pud_sect(*pud)) {
 160                 phys_addr_t pmd_phys = pgtable_alloc();
 161                 pmd = pmd_set_fixmap(pmd_phys);
 162                 if (pud_sect(*pud)) {
 163                         /*
 164                          * need to have the 1G of mappings continue to be
 165                          * present
 166                          */
 167                         split_pud(pud, pmd);
 168                 }
 169                 __pud_populate(pud, pmd_phys, PUD_TYPE_TABLE);
 170                 flush_tlb_all();
 171                 pmd_clear_fixmap();
 172         }
 173         BUG_ON(pud_bad(*pud));
 174
 175         pmd = pmd_set_fixmap_offset(pud, addr);
 176         do {
 177                 next = pmd_addr_end(addr, end);
 178                 /* try section mapping first */
 179                 if (((addr | next | phys) & ~SECTION_MASK) == 0) {
 180                         pmd_t old_pmd =*pmd;
 181                         set_pmd(pmd, __pmd(phys |
 182                                            pgprot_val(mk_sect_prot(prot))));
 183                         /*
 184                          * Check for previous table entries created during
 185                          * boot (__create_page_tables) and flush them.
 186                          */
 187                         if (!pmd_none(old_pmd)) {
 188                                 flush_tlb_all();
 189                                 if (pmd_table(old_pmd)) {
 190                                         phys_addr_t table = pmd_page_paddr(old_pmd);
 191                                         if (!WARN_ON_ONCE(slab_is_available()))
 192                                                 memblock_free(table, PAGE_SIZE);
 193                                 }
 194                         }
 195                 } else {
 196                         alloc_init_pte(pmd, addr, next, __phys_to_pfn(phys),
 197                                        prot, pgtable_alloc);
 198                 }
 199                 phys += next - addr;
 200         } while (pmd++, addr = next, addr != end);
 201
 202         pmd_clear_fixmap();
 203 }
 204
 205 static inline bool use_1G_block(unsigned long addr, unsigned long next,
 206                         unsigned long phys)
 207 {
 208         if (PAGE_SHIFT != 12)
 209                 return false;
 210
 211         if (((addr | next | phys) & ~PUD_MASK) != 0)
 212                 return false;
 213
 214         return true;
 215 }
 216
 217 static void alloc_init_pud(pgd_t *pgd, unsigned long addr, unsigned long end,
 218                                   phys_addr_t phys, pgprot_t prot,
 219                                   phys_addr_t (*pgtable_alloc)(void))
 220 {
 221         pud_t *pud;
 222         unsigned long next;
 223
 224         if (pgd_none(*pgd)) {
 225                 phys_addr_t pud_phys = pgtable_alloc();
 226                 __pgd_populate(pgd, pud_phys, PUD_TYPE_TABLE);
 227         }
 228         BUG_ON(pgd_bad(*pgd));
 229
 230         pud = pud_set_fixmap_offset(pgd, addr);
 231         do {
 232                 next = pud_addr_end(addr, end);
 233
 234                 /*
 235                  * For 4K granule only, attempt to put down a 1GB block
 236                  */
 237                 if (use_1G_block(addr, next, phys)) {
 238                         pud_t old_pud = *pud;
 239                         set_pud(pud, __pud(phys |
 240                                            pgprot_val(mk_sect_prot(prot))));
 241
 242                         /*
 243                          * If we have an old value for a pud, it will
 244                          * be pointing to a pmd table that we no longer
 245                          * need (from swapper_pg_dir).
 246                          *
 247                          * Look up the old pmd table and free it.
 248                          */
 249                         if (!pud_none(old_pud)) {
 250                                 flush_tlb_all();
 251                                 if (pud_table(old_pud)) {
 252                                         phys_addr_t table = pud_page_paddr(old_pud);
 253                                         if (!WARN_ON_ONCE(slab_is_available()))
 254                                                 memblock_free(table, PAGE_SIZE);
 255                                 }
 256                         }
 257                 } else {
 258                         alloc_init_pmd(pud, addr, next, phys, prot,
 259                                        pgtable_alloc);
 260                 }
 261                 phys += next - addr;
 262         } while (pud++, addr = next, addr != end);
 263
 264         pud_clear_fixmap();
 265 }
 266
 267 /*
 268  * Create the page directory entries and any necessary page tables for the
 269  * mapping specified by 'md'.
 270  */
 271 static void init_pgd(pgd_t *pgd, phys_addr_t phys, unsigned long virt,
 272                                     phys_addr_t size, pgprot_t prot,
 273                                     phys_addr_t (*pgtable_alloc)(void))
 274 {
 275         unsigned long addr, length, end, next;
 276
 277         addr = virt & PAGE_MASK;
 278         length = PAGE_ALIGN(size + (virt & ~PAGE_MASK));
 279
 280         end = addr + length;
 281         do {
 282                 next = pgd_addr_end(addr, end);
 283                 alloc_init_pud(pgd, addr, next, phys, prot, pgtable_alloc);
 284                 phys += next - addr;
 285         } while (pgd++, addr = next, addr != end);
 286 }
 287
 288 static phys_addr_t late_pgtable_alloc(void)
 289 {
 290         void *ptr = (void *)__get_free_page(PGALLOC_GFP);
 291         BUG_ON(!ptr);
 292
 293         /* Ensure the zeroed page is visible to the page table walker */
 294         dsb(ishst);
 295         return __pa(ptr);
 296 }
 297
 298 static void __create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys,
 299                                  unsigned long virt, phys_addr_t size,
 300                                  pgprot_t prot,
 301                                  phys_addr_t (*alloc)(void))
 302 {
 303         init_pgd(pgd_offset_raw(pgdir, virt), phys, virt, size, prot, alloc);
 304 }
 305
 306 static void __init create_mapping(phys_addr_t phys, unsigned long virt,
 307                                   phys_addr_t size, pgprot_t prot)
 308 {
 309         if (virt < VMALLOC_START) {
 310                 pr_warn("BUG: not creating mapping for %pa at 0x%016lx - outside kernel range\n",
 311                         &phys, virt);
 312                 return;
 313         }
 314         __create_pgd_mapping(init_mm.pgd, phys, virt, size, prot,
 315                              early_pgtable_alloc);
 316 }
 317
 318 void __init create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
 319                                unsigned long virt, phys_addr_t size,
 320                                pgprot_t prot)
 321 {
 322         __create_pgd_mapping(mm->pgd, phys, virt, size, prot,
 323                              late_pgtable_alloc);
 324 }
 325
 326 static void create_mapping_late(phys_addr_t phys, unsigned long virt,
 327                                   phys_addr_t size, pgprot_t prot)
 328 {
 329         if (virt < VMALLOC_START) {
 330                 pr_warn("BUG: not creating mapping for %pa at 0x%016lx - outside kernel range\n",
 331                         &phys, virt);
 332                 return;
 333         }
 334
 335         __create_pgd_mapping(init_mm.pgd, phys, virt, size, prot,
 336                              late_pgtable_alloc);
 337 }
 338
 339 #ifdef CONFIG_DEBUG_RODATA
 340 static void __init __map_memblock(phys_addr_t start, phys_addr_t end)
 341 {
 342         /*
 343          * Set up the executable regions using the existing section mappings
 344          * for now. This will get more fine grained later once all memory
 345          * is mapped
 346          */
 347         unsigned long kernel_x_start = round_down(__pa(_stext), SWAPPER_BLOCK_SIZE);
 348         unsigned long kernel_x_end = round_up(__pa(__init_end), SWAPPER_BLOCK_SIZE);
 349
 350         if (end < kernel_x_start) {
 351                 create_mapping(start, __phys_to_virt(start),
 352                         end - start, PAGE_KERNEL);
 353         } else if (start >= kernel_x_end) {
 354                 create_mapping(start, __phys_to_virt(start),
 355                         end - start, PAGE_KERNEL);
 356         } else {
 357                 if (start < kernel_x_start)
 358                         create_mapping(start, __phys_to_virt(start),
 359                                 kernel_x_start - start,
 360                                 PAGE_KERNEL);
 361                 create_mapping(kernel_x_start,
 362                                 __phys_to_virt(kernel_x_start),
 363                                 kernel_x_end - kernel_x_start,
 364                                 PAGE_KERNEL_EXEC);
 365                 if (kernel_x_end < end)
 366                         create_mapping(kernel_x_end,
 367                                 __phys_to_virt(kernel_x_end),
 368                                 end - kernel_x_end,
 369                                 PAGE_KERNEL);
 370         }
 371
 372 }
 373 #else
 374 static void __init __map_memblock(phys_addr_t start, phys_addr_t end)
 375 {
 376         create_mapping(start, __phys_to_virt(start), end - start,
 377                         PAGE_KERNEL_EXEC);
 378 }
 379 #endif
 380
 381 static void __init map_mem(void)
 382 {
 383         struct memblock_region *reg;
 384
 385         /* map all the memory banks */
 386         for_each_memblock(memory, reg) {
 387                 phys_addr_t start = reg->base;
 388                 phys_addr_t end = start + reg->size;
 389
 390                 if (start >= end)
 391                         break;
 392
 393                 __map_memblock(start, end);
 394         }
 395 }
 396
 397 static void __init fixup_executable(void)
 398 {
 399 #ifdef CONFIG_DEBUG_RODATA
 400         /* now that we are actually fully mapped, make the start/end more fine grained */
 401         if (!IS_ALIGNED((unsigned long)_stext, SWAPPER_BLOCK_SIZE)) {
 402                 unsigned long aligned_start = round_down(__pa(_stext),
 403                                                          SWAPPER_BLOCK_SIZE);
 404
 405                 create_mapping(aligned_start, __phys_to_virt(aligned_start),
 406                                 __pa(_stext) - aligned_start,
 407                                 PAGE_KERNEL);
 408         }
 409
 410         if (!IS_ALIGNED((unsigned long)__init_end, SWAPPER_BLOCK_SIZE)) {
 411                 unsigned long aligned_end = round_up(__pa(__init_end),
 412                                                           SWAPPER_BLOCK_SIZE);
 413                 create_mapping(__pa(__init_end), (unsigned long)__init_end,
 414                                 aligned_end - __pa(__init_end),
 415                                 PAGE_KERNEL);
 416         }
 417 #endif
 418 }
 419
 420 #ifdef CONFIG_DEBUG_RODATA
 421 void mark_rodata_ro(void)
 422 {
 423         create_mapping_late(__pa(_stext), (unsigned long)_stext,
 424                                 (unsigned long)_etext - (unsigned long)_stext,
 425                                 PAGE_KERNEL_ROX);
 426
 427 }
 428 #endif
 429
 430 void fixup_init(void)
 431 {
 432         create_mapping_late(__pa(__init_begin), (unsigned long)__init_begin,
 433                         (unsigned long)__init_end - (unsigned long)__init_begin,
 434                         PAGE_KERNEL);
 435 }
 436
 437 /*
 438  * paging_init() sets up the page tables, initialises the zone memory
 439  * maps and sets up the zero page.
 440  */
 441 void __init paging_init(void)
 442 {
 443         map_mem();
 444         fixup_executable();
 445
 446         bootmem_init();
 447 }
 448
 449 /*
 450  * Check whether a kernel address is valid (derived from arch/x86/).
 451  */
 452 int kern_addr_valid(unsigned long addr)
 453 {
 454         pgd_t *pgd;
 455         pud_t *pud;
 456         pmd_t *pmd;
 457         pte_t *pte;
 458
 459         if ((((long)addr) >> VA_BITS) != -1UL)
 460                 return 0;
 461
 462         pgd = pgd_offset_k(addr);
 463         if (pgd_none(*pgd))
 464                 return 0;
 465
 466         pud = pud_offset(pgd, addr);
 467         if (pud_none(*pud))
 468                 return 0;
 469
 470         if (pud_sect(*pud))
 471                 return pfn_valid(pud_pfn(*pud));
 472
 473         pmd = pmd_offset(pud, addr);
 474         if (pmd_none(*pmd))
 475                 return 0;
 476
 477         if (pmd_sect(*pmd))
 478                 return pfn_valid(pmd_pfn(*pmd));
 479
 480         pte = pte_offset_kernel(pmd, addr);
 481         if (pte_none(*pte))
 482                 return 0;
 483
 484         return pfn_valid(pte_pfn(*pte));
 485 }
 486 #ifdef CONFIG_SPARSEMEM_VMEMMAP
 487 #if !ARM64_SWAPPER_USES_SECTION_MAPS
 488 int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node)
 489 {
 490         return vmemmap_populate_basepages(start, end, node);
 491 }
 492 #else   /* !ARM64_SWAPPER_USES_SECTION_MAPS */
 493 int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node)
 494 {
 495         unsigned long addr = start;
 496         unsigned long next;
 497         pgd_t *pgd;
 498         pud_t *pud;
 499         pmd_t *pmd;
 500
 501         do {
 502                 next = pmd_addr_end(addr, end);
 503
 504                 pgd = vmemmap_pgd_populate(addr, node);
 505                 if (!pgd)
 506                         return -ENOMEM;
 507
 508                 pud = vmemmap_pud_populate(pgd, addr, node);
 509                 if (!pud)
 510                         return -ENOMEM;
 511
 512                 pmd = pmd_offset(pud, addr);
 513                 if (pmd_none(*pmd)) {
 514                         void *p = NULL;
 515
 516                         p = vmemmap_alloc_block_buf(PMD_SIZE, node);
 517                         if (!p)
 518                                 return -ENOMEM;
 519
 520                         set_pmd(pmd, __pmd(__pa(p) | PROT_SECT_NORMAL));
 521                 } else
 522                         vmemmap_verify((pte_t *)pmd, node, addr, next);
 523         } while (addr = next, addr != end);
 524
 525         return 0;
 526 }
 527 #endif  /* CONFIG_ARM64_64K_PAGES */
 528 void vmemmap_free(unsigned long start, unsigned long end)
 529 {
 530 }
 531 #endif  /* CONFIG_SPARSEMEM_VMEMMAP */
 532
 533 static pte_t bm_pte[PTRS_PER_PTE] __page_aligned_bss;
 534 #if CONFIG_PGTABLE_LEVELS > 2
 535 static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss;
 536 #endif
 537 #if CONFIG_PGTABLE_LEVELS > 3
 538 static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss;
 539 #endif
 540
 541 static inline pud_t * fixmap_pud(unsigned long addr)
 542 {
 543         pgd_t *pgd = pgd_offset_k(addr);
 544
 545         BUG_ON(pgd_none(*pgd) || pgd_bad(*pgd));
 546
 547         return pud_offset(pgd, addr);
 548 }
 549
 550 static inline pmd_t * fixmap_pmd(unsigned long addr)
 551 {
 552         pud_t *pud = fixmap_pud(addr);
 553
 554         BUG_ON(pud_none(*pud) || pud_bad(*pud));
 555
 556         return pmd_offset(pud, addr);
 557 }
 558
 559 static inline pte_t * fixmap_pte(unsigned long addr)
 560 {
 561         pmd_t *pmd = fixmap_pmd(addr);
 562
 563         BUG_ON(pmd_none(*pmd) || pmd_bad(*pmd));
 564
 565         return pte_offset_kernel(pmd, addr);
 566 }
 567
 568 void __init early_fixmap_init(void)
 569 {
 570         pgd_t *pgd;
 571         pud_t *pud;
 572         pmd_t *pmd;
 573         unsigned long addr = FIXADDR_START;
 574
 575         pgd = pgd_offset_k(addr);
 576         pgd_populate(&init_mm, pgd, bm_pud);
 577         pud = pud_offset(pgd, addr);
 578         pud_populate(&init_mm, pud, bm_pmd);
 579         pmd = pmd_offset(pud, addr);
 580         pmd_populate_kernel(&init_mm, pmd, bm_pte);
 581
 582         /*
 583          * The boot-ioremap range spans multiple pmds, for which
 584          * we are not preparted:
 585          */
 586         BUILD_BUG_ON((__fix_to_virt(FIX_BTMAP_BEGIN) >> PMD_SHIFT)
 587                      != (__fix_to_virt(FIX_BTMAP_END) >> PMD_SHIFT));
 588
 589         if ((pmd != fixmap_pmd(fix_to_virt(FIX_BTMAP_BEGIN)))
 590              || pmd != fixmap_pmd(fix_to_virt(FIX_BTMAP_END))) {
 591                 WARN_ON(1);
 592                 pr_warn("pmd %p != %p, %p\n",
 593                         pmd, fixmap_pmd(fix_to_virt(FIX_BTMAP_BEGIN)),
 594                         fixmap_pmd(fix_to_virt(FIX_BTMAP_END)));
 595                 pr_warn("fix_to_virt(FIX_BTMAP_BEGIN): %08lx\n",
 596                         fix_to_virt(FIX_BTMAP_BEGIN));
 597                 pr_warn("fix_to_virt(FIX_BTMAP_END):   %08lx\n",
 598                         fix_to_virt(FIX_BTMAP_END));
 599
 600                 pr_warn("FIX_BTMAP_END:       %d\n", FIX_BTMAP_END);
 601                 pr_warn("FIX_BTMAP_BEGIN:     %d\n", FIX_BTMAP_BEGIN);
 602         }
 603 }
 604
 605 void __set_fixmap(enum fixed_addresses idx,
 606                                phys_addr_t phys, pgprot_t flags)
 607 {
 608         unsigned long addr = __fix_to_virt(idx);
 609         pte_t *pte;
 610
 611         BUG_ON(idx <= FIX_HOLE || idx >= __end_of_fixed_addresses);
 612
 613         pte = fixmap_pte(addr);
 614
 615         if (pgprot_val(flags)) {
 616                 set_pte(pte, pfn_pte(phys >> PAGE_SHIFT, flags));
 617         } else {
 618                 pte_clear(&init_mm, addr, pte);
 619                 flush_tlb_kernel_range(addr, addr+PAGE_SIZE);
 620         }
 621 }
 622
 623 void *__init fixmap_remap_fdt(phys_addr_t dt_phys)
 624 {
 625         const u64 dt_virt_base = __fix_to_virt(FIX_FDT);
 626         pgprot_t prot = PAGE_KERNEL_RO;
 627         int size, offset;
 628         void *dt_virt;
 629
 630         /*
 631          * Check whether the physical FDT address is set and meets the minimum
 632          * alignment requirement. Since we are relying on MIN_FDT_ALIGN to be
 633          * at least 8 bytes so that we can always access the magic and size
 634          * fields of the FDT header after mapping the first chunk, double check
 635          * here if that is indeed the case.
 636          */
 637         BUILD_BUG_ON(MIN_FDT_ALIGN < 8);
 638         if (!dt_phys || dt_phys % MIN_FDT_ALIGN)
 639                 return NULL;
 640
 641         /*
 642          * Make sure that the FDT region can be mapped without the need to
 643          * allocate additional translation table pages, so that it is safe
 644          * to call create_mapping() this early.
 645          *
 646          * On 64k pages, the FDT will be mapped using PTEs, so we need to
 647          * be in the same PMD as the rest of the fixmap.
 648          * On 4k pages, we'll use section mappings for the FDT so we only
 649          * have to be in the same PUD.
 650          */
 651         BUILD_BUG_ON(dt_virt_base % SZ_2M);
 652
 653         BUILD_BUG_ON(__fix_to_virt(FIX_FDT_END) >> SWAPPER_TABLE_SHIFT !=
 654                      __fix_to_virt(FIX_BTMAP_BEGIN) >> SWAPPER_TABLE_SHIFT);
 655
 656         offset = dt_phys % SWAPPER_BLOCK_SIZE;
 657         dt_virt = (void *)dt_virt_base + offset;
 658
 659         /* map the first chunk so we can read the size from the header */
 660         create_mapping(round_down(dt_phys, SWAPPER_BLOCK_SIZE), dt_virt_base,
 661                        SWAPPER_BLOCK_SIZE, prot);
 662
 663         if (fdt_magic(dt_virt) != FDT_MAGIC)
 664                 return NULL;
 665
 666         size = fdt_totalsize(dt_virt);
 667         if (size > MAX_FDT_SIZE)
 668                 return NULL;
 669
 670         if (offset + size > SWAPPER_BLOCK_SIZE)
 671                 create_mapping(round_down(dt_phys, SWAPPER_BLOCK_SIZE), dt_virt_base,
 672                                round_up(offset + size, SWAPPER_BLOCK_SIZE), prot);
 673
 674         memblock_reserve(dt_phys, size);
 675
 676         return dt_virt;
 677 }