arch/arm64/mm/mmu.c - kernel/msm-4.19 - Gitiles

 /*
  * Based on arch/arm/mm/mmu.c
  *
  * Copyright (C) 1995-2005 Russell King
  * Copyright (C) 2012 ARM Ltd.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */

 #include <linux/export.h>
 #include <linux/kernel.h>
 #include <linux/errno.h>
 #include <linux/init.h>
 #include <linux/libfdt.h>
 #include <linux/mman.h>
 #include <linux/nodemask.h>
 #include <linux/memblock.h>
 #include <linux/fs.h>
 #include <linux/io.h>
 #include <linux/slab.h>
 #include <linux/stop_machine.h>

 #include <asm/cputype.h>
 #include <asm/fixmap.h>
 #include <asm/kernel-pgtable.h>
 #include <asm/sections.h>
 #include <asm/setup.h>
 #include <asm/sizes.h>
 #include <asm/tlb.h>
 #include <asm/memblock.h>
 #include <asm/mmu_context.h>

 #include "mm.h"

 u64 idmap_t0sz = TCR_T0SZ(VA_BITS);

 /*
  * Empty_zero_page is a special page that is used for zero-initialized data
  * and COW.
  */
 struct page *empty_zero_page;
 EXPORT_SYMBOL(empty_zero_page);

 pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
 			      unsigned long size, pgprot_t vma_prot)
 {
 	if (!pfn_valid(pfn))
 		return pgprot_noncached(vma_prot);
 	else if (file->f_flags & O_SYNC)
 		return pgprot_writecombine(vma_prot);
 	return vma_prot;
 }
 EXPORT_SYMBOL(phys_mem_access_prot);

 static void __init *early_alloc(unsigned long sz)
 {
 	void *ptr = __va(memblock_alloc(sz, sz));
 	BUG_ON(!ptr);
 	memset(ptr, 0, sz);
 	return ptr;
 }

 /*
  * remap a PMD into pages
  */
 static void split_pmd(pmd_t *pmd, pte_t *pte)
 {
 	unsigned long pfn = pmd_pfn(*pmd);
 	int i = 0;

 	do {
 		/*
 		 * Need to have the least restrictive permissions available
 		 * permissions will be fixed up later. Default the new page
 		 * range as contiguous ptes.
 		 */
 		set_pte(pte, pfn_pte(pfn, PAGE_KERNEL_EXEC_CONT));
 		pfn++;
 	} while (pte++, i++, i < PTRS_PER_PTE);
 }

 /*
  * Given a PTE with the CONT bit set, determine where the CONT range
  * starts, and clear the entire range of PTE CONT bits.
  */
 static void clear_cont_pte_range(pte_t *pte, unsigned long addr)
 {
 	int i;

 	pte -= CONT_RANGE_OFFSET(addr);
 	for (i = 0; i < CONT_PTES; i++) {
 		set_pte(pte, pte_mknoncont(*pte));
 		pte++;
 	}
 	flush_tlb_all();
 }

 /*
  * Given a range of PTEs set the pfn and provided page protection flags
  */
 static void __populate_init_pte(pte_t *pte, unsigned long addr,
 				unsigned long end, phys_addr_t phys,
 				pgprot_t prot)
 {
 	unsigned long pfn = __phys_to_pfn(phys);

 	do {
 		/* clear all the bits except the pfn, then apply the prot */
 		set_pte(pte, pfn_pte(pfn, prot));
 		pte++;
 		pfn++;
 		addr += PAGE_SIZE;
 	} while (addr != end);
 }

 static void alloc_init_pte(pmd_t *pmd, unsigned long addr,
 				  unsigned long end, phys_addr_t phys,
 				  pgprot_t prot,
 				  void *(*alloc)(unsigned long size))
 {
 	pte_t *pte;
 	unsigned long next;

 	if (pmd_none(*pmd) || pmd_sect(*pmd)) {
 		pte = alloc(PTRS_PER_PTE * sizeof(pte_t));
 		if (pmd_sect(*pmd))
 			split_pmd(pmd, pte);
 		__pmd_populate(pmd, __pa(pte), PMD_TYPE_TABLE);
 		flush_tlb_all();
 	}
 	BUG_ON(pmd_bad(*pmd));

 	pte = pte_offset_kernel(pmd, addr);
 	do {
 		next = min(end, (addr + CONT_SIZE) & CONT_MASK);
 		if (((addr | next | phys) & ~CONT_MASK) == 0) {
 			/* a block of CONT_PTES  */
 			__populate_init_pte(pte, addr, next, phys,
 					    __pgprot(pgprot_val(prot) | PTE_CONT));
 		} else {
 			/*
 			 * If the range being split is already inside of a
 			 * contiguous range but this PTE isn't going to be
 			 * contiguous, then we want to unmark the adjacent
 			 * ranges, then update the portion of the range we
 			 * are interrested in.
 			 */
 			 clear_cont_pte_range(pte, addr);
 			 __populate_init_pte(pte, addr, next, phys, prot);
 		}

 		pte += (next - addr) >> PAGE_SHIFT;
 		phys += next - addr;
 		addr = next;
 	} while (addr != end);
 }

 static void split_pud(pud_t *old_pud, pmd_t *pmd)
 {
 	unsigned long addr = pud_pfn(*old_pud) << PAGE_SHIFT;
 	pgprot_t prot = __pgprot(pud_val(*old_pud) ^ addr);
 	int i = 0;

 	do {
 		set_pmd(pmd, __pmd(addr | pgprot_val(prot)));
 		addr += PMD_SIZE;
 	} while (pmd++, i++, i < PTRS_PER_PMD);
 }

 static void alloc_init_pmd(struct mm_struct *mm, pud_t *pud,
 				  unsigned long addr, unsigned long end,
 				  phys_addr_t phys, pgprot_t prot,
 				  void *(*alloc)(unsigned long size))
 {
 	pmd_t *pmd;
 	unsigned long next;

 	/*
 	 * Check for initial section mappings in the pgd/pud and remove them.
 	 */
 	if (pud_none(*pud) || pud_sect(*pud)) {
 		pmd = alloc(PTRS_PER_PMD * sizeof(pmd_t));
 		if (pud_sect(*pud)) {
 			/*
 			 * need to have the 1G of mappings continue to be
 			 * present
 			 */
 			split_pud(pud, pmd);
 		}
 		pud_populate(mm, pud, pmd);
 		flush_tlb_all();
 	}
 	BUG_ON(pud_bad(*pud));

 	pmd = pmd_offset(pud, addr);
 	do {
 		next = pmd_addr_end(addr, end);
 		/* try section mapping first */
 		if (((addr | next | phys) & ~SECTION_MASK) == 0) {
 			pmd_t old_pmd =*pmd;
 			set_pmd(pmd, __pmd(phys |
 					   pgprot_val(mk_sect_prot(prot))));
 			/*
 			 * Check for previous table entries created during
 			 * boot (__create_page_tables) and flush them.
 			 */
 			if (!pmd_none(old_pmd)) {
 				flush_tlb_all();
 				if (pmd_table(old_pmd)) {
 					phys_addr_t table = __pa(pte_offset_map(&old_pmd, 0));
 					if (!WARN_ON_ONCE(slab_is_available()))
 						memblock_free(table, PAGE_SIZE);
 				}
 			}
 		} else {
 			alloc_init_pte(pmd, addr, next, phys, prot, alloc);
 		}
 		phys += next - addr;
 	} while (pmd++, addr = next, addr != end);
 }

 static inline bool use_1G_block(unsigned long addr, unsigned long next,
 			unsigned long phys)
 {
 	if (PAGE_SHIFT != 12)
 		return false;

 	if (((addr | next | phys) & ~PUD_MASK) != 0)
 		return false;

 	return true;
 }

 static void alloc_init_pud(struct mm_struct *mm, pgd_t *pgd,
 				  unsigned long addr, unsigned long end,
 				  phys_addr_t phys, pgprot_t prot,
 				  void *(*alloc)(unsigned long size))
 {
 	pud_t *pud;
 	unsigned long next;

 	if (pgd_none(*pgd)) {
 		pud = alloc(PTRS_PER_PUD * sizeof(pud_t));
 		pgd_populate(mm, pgd, pud);
 	}
 	BUG_ON(pgd_bad(*pgd));

 	pud = pud_offset(pgd, addr);
 	do {
 		next = pud_addr_end(addr, end);

 		/*
 		 * For 4K granule only, attempt to put down a 1GB block
 		 */
 		if (use_1G_block(addr, next, phys)) {
 			pud_t old_pud = *pud;
 			set_pud(pud, __pud(phys |
 					   pgprot_val(mk_sect_prot(prot))));

 			/*
 			 * If we have an old value for a pud, it will
 			 * be pointing to a pmd table that we no longer
 			 * need (from swapper_pg_dir).
 			 *
 			 * Look up the old pmd table and free it.
 			 */
 			if (!pud_none(old_pud)) {
 				flush_tlb_all();
 				if (pud_table(old_pud)) {
 					phys_addr_t table = __pa(pmd_offset(&old_pud, 0));
 					if (!WARN_ON_ONCE(slab_is_available()))
 						memblock_free(table, PAGE_SIZE);
 				}
 			}
 		} else {
 			alloc_init_pmd(mm, pud, addr, next, phys, prot, alloc);
 		}
 		phys += next - addr;
 	} while (pud++, addr = next, addr != end);
 }

 /*
  * Create the page directory entries and any necessary page tables for the
  * mapping specified by 'md'.
  */
 static void  __create_mapping(struct mm_struct *mm, pgd_t *pgd,
 				    phys_addr_t phys, unsigned long virt,
 				    phys_addr_t size, pgprot_t prot,
 				    void *(*alloc)(unsigned long size))
 {
 	unsigned long addr, length, end, next;

 	addr = virt & PAGE_MASK;
 	length = PAGE_ALIGN(size + (virt & ~PAGE_MASK));

 	end = addr + length;
 	do {
 		next = pgd_addr_end(addr, end);
 		alloc_init_pud(mm, pgd, addr, next, phys, prot, alloc);
 		phys += next - addr;
 	} while (pgd++, addr = next, addr != end);
 }

 static void *late_alloc(unsigned long size)
 {
 	void *ptr;

 	BUG_ON(size > PAGE_SIZE);
 	ptr = (void *)__get_free_page(PGALLOC_GFP);
 	BUG_ON(!ptr);
 	return ptr;
 }

 static void __init create_mapping(phys_addr_t phys, unsigned long virt,
 				  phys_addr_t size, pgprot_t prot)
 {
 	if (virt < VMALLOC_START) {
 		pr_warn("BUG: not creating mapping for %pa at 0x%016lx - outside kernel range\n",
 			&phys, virt);
 		return;
 	}
 	__create_mapping(&init_mm, pgd_offset_k(virt & PAGE_MASK), phys, virt,
 			 size, prot, early_alloc);
 }

 void __init create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
 			       unsigned long virt, phys_addr_t size,
 			       pgprot_t prot)
 {
 	__create_mapping(mm, pgd_offset(mm, virt), phys, virt, size, prot,
 				late_alloc);
 }

 static void create_mapping_late(phys_addr_t phys, unsigned long virt,
 				  phys_addr_t size, pgprot_t prot)
 {
 	if (virt < VMALLOC_START) {
 		pr_warn("BUG: not creating mapping for %pa at 0x%016lx - outside kernel range\n",
 			&phys, virt);
 		return;
 	}

 	return __create_mapping(&init_mm, pgd_offset_k(virt & PAGE_MASK),
 				phys, virt, size, prot, late_alloc);
 }

 #ifdef CONFIG_DEBUG_RODATA
 static void __init __map_memblock(phys_addr_t start, phys_addr_t end)
 {
 	/*
 	 * Set up the executable regions using the existing section mappings
 	 * for now. This will get more fine grained later once all memory
 	 * is mapped
 	 */
 	unsigned long kernel_x_start = round_down(__pa(_stext), SWAPPER_BLOCK_SIZE);
 	unsigned long kernel_x_end = round_up(__pa(__init_end), SWAPPER_BLOCK_SIZE);

 	if (end < kernel_x_start) {
 		create_mapping(start, __phys_to_virt(start),
 			end - start, PAGE_KERNEL);
 	} else if (start >= kernel_x_end) {
 		create_mapping(start, __phys_to_virt(start),
 			end - start, PAGE_KERNEL);
 	} else {
 		if (start < kernel_x_start)
 			create_mapping(start, __phys_to_virt(start),
 				kernel_x_start - start,
 				PAGE_KERNEL);
 		create_mapping(kernel_x_start,
 				__phys_to_virt(kernel_x_start),
 				kernel_x_end - kernel_x_start,
 				PAGE_KERNEL_EXEC);
 		if (kernel_x_end < end)
 			create_mapping(kernel_x_end,
 				__phys_to_virt(kernel_x_end),
 				end - kernel_x_end,
 				PAGE_KERNEL);
 	}

 }
 #else
 static void __init __map_memblock(phys_addr_t start, phys_addr_t end)
 {
 	create_mapping(start, __phys_to_virt(start), end - start,
 			PAGE_KERNEL_EXEC);
 }
 #endif

 static void __init map_mem(void)
 {
 	struct memblock_region *reg;
 	phys_addr_t limit;

 	/*
 	 * Temporarily limit the memblock range. We need to do this as
 	 * create_mapping requires puds, pmds and ptes to be allocated from
 	 * memory addressable from the initial direct kernel mapping.
 	 *
 	 * The initial direct kernel mapping, located at swapper_pg_dir, gives
 	 * us PUD_SIZE (with SECTION maps) or PMD_SIZE (without SECTION maps,
 	 * memory starting from PHYS_OFFSET (which must be aligned to 2MB as
 	 * per Documentation/arm64/booting.txt).
 	 */
 	limit = PHYS_OFFSET + SWAPPER_INIT_MAP_SIZE;
 	memblock_set_current_limit(limit);

 	/* map all the memory banks */
 	for_each_memblock(memory, reg) {
 		phys_addr_t start = reg->base;
 		phys_addr_t end = start + reg->size;

 		if (start >= end)
 			break;

 		if (ARM64_SWAPPER_USES_SECTION_MAPS) {
 			/*
 			 * For the first memory bank align the start address and
 			 * current memblock limit to prevent create_mapping() from
 			 * allocating pte page tables from unmapped memory. With
 			 * the section maps, if the first block doesn't end on section
 			 * size boundary, create_mapping() will try to allocate a pte
 			 * page, which may be returned from an unmapped area.
 			 * When section maps are not used, the pte page table for the
 			 * current limit is already present in swapper_pg_dir.
 			 */
 			if (start < limit)
 				start = ALIGN(start, SECTION_SIZE);
 			if (end < limit) {
 				limit = end & SECTION_MASK;
 				memblock_set_current_limit(limit);
 			}
 		}
 		__map_memblock(start, end);
 	}

 	/* Limit no longer required. */
 	memblock_set_current_limit(MEMBLOCK_ALLOC_ANYWHERE);
 }

 static void __init fixup_executable(void)
 {
 #ifdef CONFIG_DEBUG_RODATA
 	/* now that we are actually fully mapped, make the start/end more fine grained */
 	if (!IS_ALIGNED((unsigned long)_stext, SWAPPER_BLOCK_SIZE)) {
 		unsigned long aligned_start = round_down(__pa(_stext),
 							 SWAPPER_BLOCK_SIZE);

 		create_mapping(aligned_start, __phys_to_virt(aligned_start),
 				__pa(_stext) - aligned_start,
 				PAGE_KERNEL);
 	}

 	if (!IS_ALIGNED((unsigned long)__init_end, SWAPPER_BLOCK_SIZE)) {
 		unsigned long aligned_end = round_up(__pa(__init_end),
 							  SWAPPER_BLOCK_SIZE);
 		create_mapping(__pa(__init_end), (unsigned long)__init_end,
 				aligned_end - __pa(__init_end),
 				PAGE_KERNEL);
 	}
 #endif
 }

 #ifdef CONFIG_DEBUG_RODATA
 void mark_rodata_ro(void)
 {
 	create_mapping_late(__pa(_stext), (unsigned long)_stext,
 				(unsigned long)_etext - (unsigned long)_stext,
 				PAGE_KERNEL_ROX);

 }
 #endif

 void fixup_init(void)
 {
 	create_mapping_late(__pa(__init_begin), (unsigned long)__init_begin,
 			(unsigned long)__init_end - (unsigned long)__init_begin,
 			PAGE_KERNEL);
 }

 /*
  * paging_init() sets up the page tables, initialises the zone memory
  * maps and sets up the zero page.
  */
 void __init paging_init(void)
 {
 	void *zero_page;

 	map_mem();
 	fixup_executable();

 	/* allocate the zero page. */
 	zero_page = early_alloc(PAGE_SIZE);

 	bootmem_init();

 	empty_zero_page = virt_to_page(zero_page);

 	/*
 	 * TTBR0 is only used for the identity mapping at this stage. Make it
 	 * point to zero page to avoid speculatively fetching new entries.
 	 */
 	cpu_set_reserved_ttbr0();
 	local_flush_tlb_all();
 	cpu_set_default_tcr_t0sz();
 }

 /*
  * Check whether a kernel address is valid (derived from arch/x86/).
  */
 int kern_addr_valid(unsigned long addr)
 {
 	pgd_t *pgd;
 	pud_t *pud;
 	pmd_t *pmd;
 	pte_t *pte;

 	if ((((long)addr) >> VA_BITS) != -1UL)
 		return 0;

 	pgd = pgd_offset_k(addr);
 	if (pgd_none(*pgd))
 		return 0;

 	pud = pud_offset(pgd, addr);
 	if (pud_none(*pud))
 		return 0;

 	if (pud_sect(*pud))
 		return pfn_valid(pud_pfn(*pud));

 	pmd = pmd_offset(pud, addr);
 	if (pmd_none(*pmd))
 		return 0;

 	if (pmd_sect(*pmd))
 		return pfn_valid(pmd_pfn(*pmd));

 	pte = pte_offset_kernel(pmd, addr);
 	if (pte_none(*pte))
 		return 0;

 	return pfn_valid(pte_pfn(*pte));
 }
 #ifdef CONFIG_SPARSEMEM_VMEMMAP
 #if !ARM64_SWAPPER_USES_SECTION_MAPS
 int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node)
 {
 	return vmemmap_populate_basepages(start, end, node);
 }
 #else	/* !ARM64_SWAPPER_USES_SECTION_MAPS */
 int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node)
 {
 	unsigned long addr = start;
 	unsigned long next;
 	pgd_t *pgd;
 	pud_t *pud;
 	pmd_t *pmd;

 	do {
 		next = pmd_addr_end(addr, end);

 		pgd = vmemmap_pgd_populate(addr, node);
 		if (!pgd)
 			return -ENOMEM;

 		pud = vmemmap_pud_populate(pgd, addr, node);
 		if (!pud)
 			return -ENOMEM;

 		pmd = pmd_offset(pud, addr);
 		if (pmd_none(*pmd)) {
 			void *p = NULL;

 			p = vmemmap_alloc_block_buf(PMD_SIZE, node);
 			if (!p)
 				return -ENOMEM;

 			set_pmd(pmd, __pmd(__pa(p) | PROT_SECT_NORMAL));
 		} else
 			vmemmap_verify((pte_t *)pmd, node, addr, next);
 	} while (addr = next, addr != end);

 	return 0;
 }
 #endif	/* CONFIG_ARM64_64K_PAGES */
 void vmemmap_free(unsigned long start, unsigned long end)
 {
 }
 #endif	/* CONFIG_SPARSEMEM_VMEMMAP */

 static pte_t bm_pte[PTRS_PER_PTE] __page_aligned_bss;
 #if CONFIG_PGTABLE_LEVELS > 2
 static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss;
 #endif
 #if CONFIG_PGTABLE_LEVELS > 3
 static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss;
 #endif

 static inline pud_t * fixmap_pud(unsigned long addr)
 {
 	pgd_t *pgd = pgd_offset_k(addr);

 	BUG_ON(pgd_none(*pgd) || pgd_bad(*pgd));

 	return pud_offset(pgd, addr);
 }

 static inline pmd_t * fixmap_pmd(unsigned long addr)
 {
 	pud_t *pud = fixmap_pud(addr);

 	BUG_ON(pud_none(*pud) || pud_bad(*pud));

 	return pmd_offset(pud, addr);
 }

 static inline pte_t * fixmap_pte(unsigned long addr)
 {
 	pmd_t *pmd = fixmap_pmd(addr);

 	BUG_ON(pmd_none(*pmd) || pmd_bad(*pmd));

 	return pte_offset_kernel(pmd, addr);
 }

 void __init early_fixmap_init(void)
 {
 	pgd_t *pgd;
 	pud_t *pud;
 	pmd_t *pmd;
 	unsigned long addr = FIXADDR_START;

 	pgd = pgd_offset_k(addr);
 	pgd_populate(&init_mm, pgd, bm_pud);
 	pud = pud_offset(pgd, addr);
 	pud_populate(&init_mm, pud, bm_pmd);
 	pmd = pmd_offset(pud, addr);
 	pmd_populate_kernel(&init_mm, pmd, bm_pte);

 	/*
 	 * The boot-ioremap range spans multiple pmds, for which
 	 * we are not preparted:
 	 */
 	BUILD_BUG_ON((__fix_to_virt(FIX_BTMAP_BEGIN) >> PMD_SHIFT)
 		     != (__fix_to_virt(FIX_BTMAP_END) >> PMD_SHIFT));

 	if ((pmd != fixmap_pmd(fix_to_virt(FIX_BTMAP_BEGIN)))
 	     || pmd != fixmap_pmd(fix_to_virt(FIX_BTMAP_END))) {
 		WARN_ON(1);
 		pr_warn("pmd %p != %p, %p\n",
 			pmd, fixmap_pmd(fix_to_virt(FIX_BTMAP_BEGIN)),
 			fixmap_pmd(fix_to_virt(FIX_BTMAP_END)));
 		pr_warn("fix_to_virt(FIX_BTMAP_BEGIN): %08lx\n",
 			fix_to_virt(FIX_BTMAP_BEGIN));
 		pr_warn("fix_to_virt(FIX_BTMAP_END):   %08lx\n",
 			fix_to_virt(FIX_BTMAP_END));

 		pr_warn("FIX_BTMAP_END:       %d\n", FIX_BTMAP_END);
 		pr_warn("FIX_BTMAP_BEGIN:     %d\n", FIX_BTMAP_BEGIN);
 	}
 }

 void __set_fixmap(enum fixed_addresses idx,
 			       phys_addr_t phys, pgprot_t flags)
 {
 	unsigned long addr = __fix_to_virt(idx);
 	pte_t *pte;

 	BUG_ON(idx <= FIX_HOLE || idx >= __end_of_fixed_addresses);

 	pte = fixmap_pte(addr);

 	if (pgprot_val(flags)) {
 		set_pte(pte, pfn_pte(phys >> PAGE_SHIFT, flags));
 	} else {
 		pte_clear(&init_mm, addr, pte);
 		flush_tlb_kernel_range(addr, addr+PAGE_SIZE);
 	}
 }

 void *__init fixmap_remap_fdt(phys_addr_t dt_phys)
 {
 	const u64 dt_virt_base = __fix_to_virt(FIX_FDT);
 	pgprot_t prot = PAGE_KERNEL_RO;
 	int size, offset;
 	void *dt_virt;

 	/*
 	 * Check whether the physical FDT address is set and meets the minimum
 	 * alignment requirement. Since we are relying on MIN_FDT_ALIGN to be
 	 * at least 8 bytes so that we can always access the size field of the
 	 * FDT header after mapping the first chunk, double check here if that
 	 * is indeed the case.
 	 */
 	BUILD_BUG_ON(MIN_FDT_ALIGN < 8);
 	if (!dt_phys || dt_phys % MIN_FDT_ALIGN)
 		return NULL;

 	/*
 	 * Make sure that the FDT region can be mapped without the need to
 	 * allocate additional translation table pages, so that it is safe
 	 * to call create_mapping() this early.
 	 *
 	 * On 64k pages, the FDT will be mapped using PTEs, so we need to
 	 * be in the same PMD as the rest of the fixmap.
 	 * On 4k pages, we'll use section mappings for the FDT so we only
 	 * have to be in the same PUD.
 	 */
 	BUILD_BUG_ON(dt_virt_base % SZ_2M);

 	BUILD_BUG_ON(__fix_to_virt(FIX_FDT_END) >> SWAPPER_TABLE_SHIFT !=
 		     __fix_to_virt(FIX_BTMAP_BEGIN) >> SWAPPER_TABLE_SHIFT);

 	offset = dt_phys % SWAPPER_BLOCK_SIZE;
 	dt_virt = (void *)dt_virt_base + offset;

 	/* map the first chunk so we can read the size from the header */
 	create_mapping(round_down(dt_phys, SWAPPER_BLOCK_SIZE), dt_virt_base,
 		       SWAPPER_BLOCK_SIZE, prot);

 	if (fdt_check_header(dt_virt) != 0)
 		return NULL;

 	size = fdt_totalsize(dt_virt);
 	if (size > MAX_FDT_SIZE)
 		return NULL;

 	if (offset + size > SWAPPER_BLOCK_SIZE)
 		create_mapping(round_down(dt_phys, SWAPPER_BLOCK_SIZE), dt_virt_base,
 			       round_up(offset + size, SWAPPER_BLOCK_SIZE), prot);

 	memblock_reserve(dt_phys, size);

 	return dt_virt;
 }
	/*
	* Based on arch/arm/mm/mmu.c
	*
	* Copyright (C) 1995-2005 Russell King
	* Copyright (C) 2012 ARM Ltd.
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License version 2 as
	* published by the Free Software Foundation.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program. If not, see <http://www.gnu.org/licenses/>.
	*/

	#include <linux/export.h>
	#include <linux/kernel.h>
	#include <linux/errno.h>
	#include <linux/init.h>
	#include <linux/libfdt.h>
	#include <linux/mman.h>
	#include <linux/nodemask.h>
	#include <linux/memblock.h>
	#include <linux/fs.h>
	#include <linux/io.h>
	#include <linux/slab.h>
	#include <linux/stop_machine.h>

	#include <asm/cputype.h>
	#include <asm/fixmap.h>
	#include <asm/kernel-pgtable.h>
	#include <asm/sections.h>
	#include <asm/setup.h>
	#include <asm/sizes.h>
	#include <asm/tlb.h>
	#include <asm/memblock.h>
	#include <asm/mmu_context.h>

	#include "mm.h"

	u64 idmap_t0sz = TCR_T0SZ(VA_BITS);

	/*
	* Empty_zero_page is a special page that is used for zero-initialized data
	* and COW.
	*/
	struct page *empty_zero_page;
	EXPORT_SYMBOL(empty_zero_page);

	pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
	unsigned long size, pgprot_t vma_prot)
	{
	if (!pfn_valid(pfn))
	return pgprot_noncached(vma_prot);
	else if (file->f_flags & O_SYNC)
	return pgprot_writecombine(vma_prot);
	return vma_prot;
	}
	EXPORT_SYMBOL(phys_mem_access_prot);

	static void __init *early_alloc(unsigned long sz)
	{
	void *ptr = __va(memblock_alloc(sz, sz));
	BUG_ON(!ptr);
	memset(ptr, 0, sz);
	return ptr;
	}

	/*
	* remap a PMD into pages
	*/
	static void split_pmd(pmd_t pmd, pte_t pte)
	{
	unsigned long pfn = pmd_pfn(*pmd);
	int i = 0;

	do {
	/*
	* Need to have the least restrictive permissions available
	* permissions will be fixed up later. Default the new page
	* range as contiguous ptes.
	*/
	set_pte(pte, pfn_pte(pfn, PAGE_KERNEL_EXEC_CONT));
	pfn++;
	} while (pte++, i++, i < PTRS_PER_PTE);
	}

	/*
	* Given a PTE with the CONT bit set, determine where the CONT range
	* starts, and clear the entire range of PTE CONT bits.
	*/
	static void clear_cont_pte_range(pte_t *pte, unsigned long addr)
	{
	int i;

	pte -= CONT_RANGE_OFFSET(addr);
	for (i = 0; i < CONT_PTES; i++) {
	set_pte(pte, pte_mknoncont(*pte));
	pte++;
	}
	flush_tlb_all();
	}

	/*
	* Given a range of PTEs set the pfn and provided page protection flags
	*/
	static void __populate_init_pte(pte_t *pte, unsigned long addr,
	unsigned long end, phys_addr_t phys,
	pgprot_t prot)
	{
	unsigned long pfn = __phys_to_pfn(phys);

	do {
	/* clear all the bits except the pfn, then apply the prot */
	set_pte(pte, pfn_pte(pfn, prot));
	pte++;
	pfn++;
	addr += PAGE_SIZE;
	} while (addr != end);
	}

	static void alloc_init_pte(pmd_t *pmd, unsigned long addr,
	unsigned long end, phys_addr_t phys,
	pgprot_t prot,
	void (alloc)(unsigned long size))
	{
	pte_t *pte;
	unsigned long next;

	if (pmd_none(pmd) \|\| pmd_sect(pmd)) {
	pte = alloc(PTRS_PER_PTE * sizeof(pte_t));
	if (pmd_sect(*pmd))
	split_pmd(pmd, pte);
	__pmd_populate(pmd, __pa(pte), PMD_TYPE_TABLE);
	flush_tlb_all();
	}
	BUG_ON(pmd_bad(*pmd));

	pte = pte_offset_kernel(pmd, addr);
	do {
	next = min(end, (addr + CONT_SIZE) & CONT_MASK);
	if (((addr \| next \| phys) & ~CONT_MASK) == 0) {
	/* a block of CONT_PTES */
	__populate_init_pte(pte, addr, next, phys,
	__pgprot(pgprot_val(prot) \| PTE_CONT));
	} else {
	/*
	* If the range being split is already inside of a
	* contiguous range but this PTE isn't going to be
	* contiguous, then we want to unmark the adjacent
	* ranges, then update the portion of the range we
	* are interrested in.
	*/
	clear_cont_pte_range(pte, addr);
	__populate_init_pte(pte, addr, next, phys, prot);
	}

	pte += (next - addr) >> PAGE_SHIFT;
	phys += next - addr;
	addr = next;
	} while (addr != end);
	}

	static void split_pud(pud_t old_pud, pmd_t pmd)
	{
	unsigned long addr = pud_pfn(*old_pud) << PAGE_SHIFT;
	pgprot_t prot = __pgprot(pud_val(*old_pud) ^ addr);
	int i = 0;

	do {
	set_pmd(pmd, __pmd(addr \| pgprot_val(prot)));
	addr += PMD_SIZE;
	} while (pmd++, i++, i < PTRS_PER_PMD);
	}

	static void alloc_init_pmd(struct mm_struct mm, pud_t pud,
	unsigned long addr, unsigned long end,
	phys_addr_t phys, pgprot_t prot,
	void (alloc)(unsigned long size))
	{
	pmd_t *pmd;
	unsigned long next;

	/*
	* Check for initial section mappings in the pgd/pud and remove them.
	*/
	if (pud_none(pud) \|\| pud_sect(pud)) {
	pmd = alloc(PTRS_PER_PMD * sizeof(pmd_t));
	if (pud_sect(*pud)) {
	/*
	* need to have the 1G of mappings continue to be
	* present
	*/
	split_pud(pud, pmd);
	}
	pud_populate(mm, pud, pmd);
	flush_tlb_all();
	}
	BUG_ON(pud_bad(*pud));

	pmd = pmd_offset(pud, addr);
	do {
	next = pmd_addr_end(addr, end);
	/* try section mapping first */
	if (((addr \| next \| phys) & ~SECTION_MASK) == 0) {
	pmd_t old_pmd =*pmd;
	set_pmd(pmd, __pmd(phys \|
	pgprot_val(mk_sect_prot(prot))));
	/*
	* Check for previous table entries created during
	* boot (__create_page_tables) and flush them.
	*/
	if (!pmd_none(old_pmd)) {
	flush_tlb_all();
	if (pmd_table(old_pmd)) {
	phys_addr_t table = __pa(pte_offset_map(&old_pmd, 0));
	if (!WARN_ON_ONCE(slab_is_available()))
	memblock_free(table, PAGE_SIZE);
	}
	}
	} else {
	alloc_init_pte(pmd, addr, next, phys, prot, alloc);
	}
	phys += next - addr;
	} while (pmd++, addr = next, addr != end);
	}

	static inline bool use_1G_block(unsigned long addr, unsigned long next,
	unsigned long phys)
	{
	if (PAGE_SHIFT != 12)
	return false;

	if (((addr \| next \| phys) & ~PUD_MASK) != 0)
	return false;

	return true;
	}

	static void alloc_init_pud(struct mm_struct mm, pgd_t pgd,
	unsigned long addr, unsigned long end,
	phys_addr_t phys, pgprot_t prot,
	void (alloc)(unsigned long size))
	{
	pud_t *pud;
	unsigned long next;

	if (pgd_none(*pgd)) {
	pud = alloc(PTRS_PER_PUD * sizeof(pud_t));
	pgd_populate(mm, pgd, pud);
	}
	BUG_ON(pgd_bad(*pgd));

	pud = pud_offset(pgd, addr);
	do {
	next = pud_addr_end(addr, end);

	/*
	* For 4K granule only, attempt to put down a 1GB block
	*/
	if (use_1G_block(addr, next, phys)) {
	pud_t old_pud = *pud;
	set_pud(pud, __pud(phys \|
	pgprot_val(mk_sect_prot(prot))));

	/*
	* If we have an old value for a pud, it will
	* be pointing to a pmd table that we no longer
	* need (from swapper_pg_dir).
	*
	* Look up the old pmd table and free it.
	*/
	if (!pud_none(old_pud)) {
	flush_tlb_all();
	if (pud_table(old_pud)) {
	phys_addr_t table = __pa(pmd_offset(&old_pud, 0));
	if (!WARN_ON_ONCE(slab_is_available()))
	memblock_free(table, PAGE_SIZE);
	}
	}
	} else {
	alloc_init_pmd(mm, pud, addr, next, phys, prot, alloc);
	}
	phys += next - addr;
	} while (pud++, addr = next, addr != end);
	}

	/*
	* Create the page directory entries and any necessary page tables for the
	* mapping specified by 'md'.
	*/
	static void __create_mapping(struct mm_struct mm, pgd_t pgd,
	phys_addr_t phys, unsigned long virt,
	phys_addr_t size, pgprot_t prot,
	void (alloc)(unsigned long size))
	{
	unsigned long addr, length, end, next;

	addr = virt & PAGE_MASK;
	length = PAGE_ALIGN(size + (virt & ~PAGE_MASK));

	end = addr + length;
	do {
	next = pgd_addr_end(addr, end);
	alloc_init_pud(mm, pgd, addr, next, phys, prot, alloc);
	phys += next - addr;
	} while (pgd++, addr = next, addr != end);
	}

	static void *late_alloc(unsigned long size)
	{
	void *ptr;

	BUG_ON(size > PAGE_SIZE);
	ptr = (void *)__get_free_page(PGALLOC_GFP);
	BUG_ON(!ptr);
	return ptr;
	}

	static void __init create_mapping(phys_addr_t phys, unsigned long virt,
	phys_addr_t size, pgprot_t prot)
	{
	if (virt < VMALLOC_START) {
	pr_warn("BUG: not creating mapping for %pa at 0x%016lx - outside kernel range\n",
	&phys, virt);
	return;
	}
	__create_mapping(&init_mm, pgd_offset_k(virt & PAGE_MASK), phys, virt,
	size, prot, early_alloc);
	}

	void __init create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
	unsigned long virt, phys_addr_t size,
	pgprot_t prot)
	{
	__create_mapping(mm, pgd_offset(mm, virt), phys, virt, size, prot,
	late_alloc);
	}

	static void create_mapping_late(phys_addr_t phys, unsigned long virt,
	phys_addr_t size, pgprot_t prot)
	{
	if (virt < VMALLOC_START) {
	pr_warn("BUG: not creating mapping for %pa at 0x%016lx - outside kernel range\n",
	&phys, virt);
	return;
	}

	return __create_mapping(&init_mm, pgd_offset_k(virt & PAGE_MASK),
	phys, virt, size, prot, late_alloc);
	}

	#ifdef CONFIG_DEBUG_RODATA
	static void __init __map_memblock(phys_addr_t start, phys_addr_t end)
	{
	/*
	* Set up the executable regions using the existing section mappings
	* for now. This will get more fine grained later once all memory
	* is mapped
	*/
	unsigned long kernel_x_start = round_down(__pa(_stext), SWAPPER_BLOCK_SIZE);
	unsigned long kernel_x_end = round_up(__pa(__init_end), SWAPPER_BLOCK_SIZE);

	if (end < kernel_x_start) {
	create_mapping(start, __phys_to_virt(start),
	end - start, PAGE_KERNEL);
	} else if (start >= kernel_x_end) {
	create_mapping(start, __phys_to_virt(start),
	end - start, PAGE_KERNEL);
	} else {
	if (start < kernel_x_start)
	create_mapping(start, __phys_to_virt(start),
	kernel_x_start - start,
	PAGE_KERNEL);
	create_mapping(kernel_x_start,
	__phys_to_virt(kernel_x_start),
	kernel_x_end - kernel_x_start,
	PAGE_KERNEL_EXEC);
	if (kernel_x_end < end)
	create_mapping(kernel_x_end,
	__phys_to_virt(kernel_x_end),
	end - kernel_x_end,
	PAGE_KERNEL);
	}

	}
	#else
	static void __init __map_memblock(phys_addr_t start, phys_addr_t end)
	{
	create_mapping(start, __phys_to_virt(start), end - start,
	PAGE_KERNEL_EXEC);
	}
	#endif

	static void __init map_mem(void)
	{
	struct memblock_region *reg;
	phys_addr_t limit;

	/*
	* Temporarily limit the memblock range. We need to do this as
	* create_mapping requires puds, pmds and ptes to be allocated from
	* memory addressable from the initial direct kernel mapping.
	*
	* The initial direct kernel mapping, located at swapper_pg_dir, gives
	* us PUD_SIZE (with SECTION maps) or PMD_SIZE (without SECTION maps,
	* memory starting from PHYS_OFFSET (which must be aligned to 2MB as
	* per Documentation/arm64/booting.txt).
	*/
	limit = PHYS_OFFSET + SWAPPER_INIT_MAP_SIZE;
	memblock_set_current_limit(limit);

	/* map all the memory banks */
	for_each_memblock(memory, reg) {
	phys_addr_t start = reg->base;
	phys_addr_t end = start + reg->size;

	if (start >= end)
	break;

	if (ARM64_SWAPPER_USES_SECTION_MAPS) {
	/*
	* For the first memory bank align the start address and
	* current memblock limit to prevent create_mapping() from
	* allocating pte page tables from unmapped memory. With
	* the section maps, if the first block doesn't end on section
	* size boundary, create_mapping() will try to allocate a pte
	* page, which may be returned from an unmapped area.
	* When section maps are not used, the pte page table for the
	* current limit is already present in swapper_pg_dir.
	*/
	if (start < limit)
	start = ALIGN(start, SECTION_SIZE);
	if (end < limit) {
	limit = end & SECTION_MASK;
	memblock_set_current_limit(limit);
	}
	}
	__map_memblock(start, end);
	}

	/* Limit no longer required. */
	memblock_set_current_limit(MEMBLOCK_ALLOC_ANYWHERE);
	}

	static void __init fixup_executable(void)
	{
	#ifdef CONFIG_DEBUG_RODATA
	/* now that we are actually fully mapped, make the start/end more fine grained */
	if (!IS_ALIGNED((unsigned long)_stext, SWAPPER_BLOCK_SIZE)) {
	unsigned long aligned_start = round_down(__pa(_stext),
	SWAPPER_BLOCK_SIZE);

	create_mapping(aligned_start, __phys_to_virt(aligned_start),
	__pa(_stext) - aligned_start,
	PAGE_KERNEL);
	}

	if (!IS_ALIGNED((unsigned long)__init_end, SWAPPER_BLOCK_SIZE)) {
	unsigned long aligned_end = round_up(__pa(__init_end),
	SWAPPER_BLOCK_SIZE);
	create_mapping(__pa(__init_end), (unsigned long)__init_end,
	aligned_end - __pa(__init_end),
	PAGE_KERNEL);
	}
	#endif
	}

	#ifdef CONFIG_DEBUG_RODATA
	void mark_rodata_ro(void)
	{
	create_mapping_late(__pa(_stext), (unsigned long)_stext,
	(unsigned long)_etext - (unsigned long)_stext,
	PAGE_KERNEL_ROX);

	}
	#endif

	void fixup_init(void)
	{
	create_mapping_late(__pa(__init_begin), (unsigned long)__init_begin,
	(unsigned long)__init_end - (unsigned long)__init_begin,
	PAGE_KERNEL);
	}

	/*
	* paging_init() sets up the page tables, initialises the zone memory
	* maps and sets up the zero page.
	*/
	void __init paging_init(void)
	{
	void *zero_page;

	map_mem();
	fixup_executable();

	/* allocate the zero page. */
	zero_page = early_alloc(PAGE_SIZE);

	bootmem_init();

	empty_zero_page = virt_to_page(zero_page);

	/*
	* TTBR0 is only used for the identity mapping at this stage. Make it
	* point to zero page to avoid speculatively fetching new entries.
	*/
	cpu_set_reserved_ttbr0();
	local_flush_tlb_all();
	cpu_set_default_tcr_t0sz();
	}

	/*
	* Check whether a kernel address is valid (derived from arch/x86/).
	*/
	int kern_addr_valid(unsigned long addr)
	{
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd;
	pte_t *pte;

	if ((((long)addr) >> VA_BITS) != -1UL)
	return 0;

	pgd = pgd_offset_k(addr);
	if (pgd_none(*pgd))
	return 0;

	pud = pud_offset(pgd, addr);
	if (pud_none(*pud))
	return 0;

	if (pud_sect(*pud))
	return pfn_valid(pud_pfn(*pud));

	pmd = pmd_offset(pud, addr);
	if (pmd_none(*pmd))
	return 0;

	if (pmd_sect(*pmd))
	return pfn_valid(pmd_pfn(*pmd));

	pte = pte_offset_kernel(pmd, addr);
	if (pte_none(*pte))
	return 0;

	return pfn_valid(pte_pfn(*pte));
	}
	#ifdef CONFIG_SPARSEMEM_VMEMMAP
	#if !ARM64_SWAPPER_USES_SECTION_MAPS
	int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node)
	{
	return vmemmap_populate_basepages(start, end, node);
	}
	#else /* !ARM64_SWAPPER_USES_SECTION_MAPS */
	int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node)
	{
	unsigned long addr = start;
	unsigned long next;
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd;

	do {
	next = pmd_addr_end(addr, end);

	pgd = vmemmap_pgd_populate(addr, node);
	if (!pgd)
	return -ENOMEM;

	pud = vmemmap_pud_populate(pgd, addr, node);
	if (!pud)
	return -ENOMEM;

	pmd = pmd_offset(pud, addr);
	if (pmd_none(*pmd)) {
	void *p = NULL;

	p = vmemmap_alloc_block_buf(PMD_SIZE, node);
	if (!p)
	return -ENOMEM;

	set_pmd(pmd, __pmd(__pa(p) \| PROT_SECT_NORMAL));
	} else
	vmemmap_verify((pte_t *)pmd, node, addr, next);
	} while (addr = next, addr != end);

	return 0;
	}
	#endif /* CONFIG_ARM64_64K_PAGES */
	void vmemmap_free(unsigned long start, unsigned long end)
	{
	}
	#endif /* CONFIG_SPARSEMEM_VMEMMAP */

	static pte_t bm_pte[PTRS_PER_PTE] __page_aligned_bss;
	#if CONFIG_PGTABLE_LEVELS > 2
	static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss;
	#endif
	#if CONFIG_PGTABLE_LEVELS > 3
	static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss;
	#endif

	static inline pud_t * fixmap_pud(unsigned long addr)
	{
	pgd_t *pgd = pgd_offset_k(addr);

	BUG_ON(pgd_none(pgd) \|\| pgd_bad(pgd));

	return pud_offset(pgd, addr);
	}

	static inline pmd_t * fixmap_pmd(unsigned long addr)
	{
	pud_t *pud = fixmap_pud(addr);

	BUG_ON(pud_none(pud) \|\| pud_bad(pud));

	return pmd_offset(pud, addr);
	}

	static inline pte_t * fixmap_pte(unsigned long addr)
	{
	pmd_t *pmd = fixmap_pmd(addr);

	BUG_ON(pmd_none(pmd) \|\| pmd_bad(pmd));

	return pte_offset_kernel(pmd, addr);
	}

	void __init early_fixmap_init(void)
	{
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd;
	unsigned long addr = FIXADDR_START;

	pgd = pgd_offset_k(addr);
	pgd_populate(&init_mm, pgd, bm_pud);
	pud = pud_offset(pgd, addr);
	pud_populate(&init_mm, pud, bm_pmd);
	pmd = pmd_offset(pud, addr);
	pmd_populate_kernel(&init_mm, pmd, bm_pte);

	/*
	* The boot-ioremap range spans multiple pmds, for which
	* we are not preparted:
	*/
	BUILD_BUG_ON((__fix_to_virt(FIX_BTMAP_BEGIN) >> PMD_SHIFT)
	!= (__fix_to_virt(FIX_BTMAP_END) >> PMD_SHIFT));

	if ((pmd != fixmap_pmd(fix_to_virt(FIX_BTMAP_BEGIN)))
	\|\| pmd != fixmap_pmd(fix_to_virt(FIX_BTMAP_END))) {
	WARN_ON(1);
	pr_warn("pmd %p != %p, %p\n",
	pmd, fixmap_pmd(fix_to_virt(FIX_BTMAP_BEGIN)),
	fixmap_pmd(fix_to_virt(FIX_BTMAP_END)));
	pr_warn("fix_to_virt(FIX_BTMAP_BEGIN): %08lx\n",
	fix_to_virt(FIX_BTMAP_BEGIN));
	pr_warn("fix_to_virt(FIX_BTMAP_END): %08lx\n",
	fix_to_virt(FIX_BTMAP_END));

	pr_warn("FIX_BTMAP_END: %d\n", FIX_BTMAP_END);
	pr_warn("FIX_BTMAP_BEGIN: %d\n", FIX_BTMAP_BEGIN);
	}
	}

	void __set_fixmap(enum fixed_addresses idx,
	phys_addr_t phys, pgprot_t flags)
	{
	unsigned long addr = __fix_to_virt(idx);
	pte_t *pte;

	BUG_ON(idx <= FIX_HOLE \|\| idx >= __end_of_fixed_addresses);

	pte = fixmap_pte(addr);

	if (pgprot_val(flags)) {
	set_pte(pte, pfn_pte(phys >> PAGE_SHIFT, flags));
	} else {
	pte_clear(&init_mm, addr, pte);
	flush_tlb_kernel_range(addr, addr+PAGE_SIZE);
	}
	}

	void *__init fixmap_remap_fdt(phys_addr_t dt_phys)
	{
	const u64 dt_virt_base = __fix_to_virt(FIX_FDT);
	pgprot_t prot = PAGE_KERNEL_RO;
	int size, offset;
	void *dt_virt;

	/*
	* Check whether the physical FDT address is set and meets the minimum
	* alignment requirement. Since we are relying on MIN_FDT_ALIGN to be
	* at least 8 bytes so that we can always access the size field of the
	* FDT header after mapping the first chunk, double check here if that
	* is indeed the case.
	*/
	BUILD_BUG_ON(MIN_FDT_ALIGN < 8);
	if (!dt_phys \|\| dt_phys % MIN_FDT_ALIGN)
	return NULL;

	/*
	* Make sure that the FDT region can be mapped without the need to
	* allocate additional translation table pages, so that it is safe
	* to call create_mapping() this early.
	*
	* On 64k pages, the FDT will be mapped using PTEs, so we need to
	* be in the same PMD as the rest of the fixmap.
	* On 4k pages, we'll use section mappings for the FDT so we only
	* have to be in the same PUD.
	*/
	BUILD_BUG_ON(dt_virt_base % SZ_2M);

	BUILD_BUG_ON(__fix_to_virt(FIX_FDT_END) >> SWAPPER_TABLE_SHIFT !=
	__fix_to_virt(FIX_BTMAP_BEGIN) >> SWAPPER_TABLE_SHIFT);

	offset = dt_phys % SWAPPER_BLOCK_SIZE;
	dt_virt = (void *)dt_virt_base + offset;

	/* map the first chunk so we can read the size from the header */
	create_mapping(round_down(dt_phys, SWAPPER_BLOCK_SIZE), dt_virt_base,
	SWAPPER_BLOCK_SIZE, prot);

	if (fdt_check_header(dt_virt) != 0)
	return NULL;

	size = fdt_totalsize(dt_virt);
	if (size > MAX_FDT_SIZE)
	return NULL;

	if (offset + size > SWAPPER_BLOCK_SIZE)
	create_mapping(round_down(dt_phys, SWAPPER_BLOCK_SIZE), dt_virt_base,
	round_up(offset + size, SWAPPER_BLOCK_SIZE), prot);

	memblock_reserve(dt_phys, size);

	return dt_virt;
	}