mm/sparse-vmemmap.c - third_party/kernel - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Virtual Memory Map support
  *
  * (C) 2007 sgi. Christoph Lameter.
  *
  * Virtual memory maps allow VM primitives pfn_to_page, page_to_pfn,
  * virt_to_page, page_address() to be implemented as a base offset
  * calculation without memory access.
  *
  * However, virtual mappings need a page table and TLBs. Many Linux
  * architectures already map their physical space using 1-1 mappings
  * via TLBs. For those arches the virtual memory map is essentially
  * for free if we use the same page size as the 1-1 mappings. In that
  * case the overhead consists of a few additional pages that are
  * allocated to create a view of memory for vmemmap.
  *
  * The architecture is expected to provide a vmemmap_populate() function
  * to instantiate the mapping.
  */
 #include <linux/mm.h>
 #include <linux/mmzone.h>
 #include <linux/memblock.h>
 #include <linux/memremap.h>
 #include <linux/highmem.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/vmalloc.h>
 #include <linux/sched.h>
 #include <linux/pgtable.h>
 #include <linux/bootmem_info.h>

 #include <asm/dma.h>
 #include <asm/pgalloc.h>
 #include <asm/tlbflush.h>

 /**
  * struct vmemmap_remap_walk - walk vmemmap page table
  *
  * @remap_pte:		called for each lowest-level entry (PTE).
  * @nr_walked:		the number of walked pte.
  * @reuse_page:		the page which is reused for the tail vmemmap pages.
  * @reuse_addr:		the virtual address of the @reuse_page page.
  * @vmemmap_pages:	the list head of the vmemmap pages that can be freed
  *			or is mapped from.
  */
 struct vmemmap_remap_walk {
 	void (*remap_pte)(pte_t *pte, unsigned long addr,
 			  struct vmemmap_remap_walk *walk);
 	unsigned long nr_walked;
 	struct page *reuse_page;
 	unsigned long reuse_addr;
 	struct list_head *vmemmap_pages;
 };

 static int split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start,
 				  struct vmemmap_remap_walk *walk)
 {
 	pmd_t __pmd;
 	int i;
 	unsigned long addr = start;
 	struct page *page = pmd_page(*pmd);
 	pte_t *pgtable = pte_alloc_one_kernel(&init_mm);

 	if (!pgtable)
 		return -ENOMEM;

 	pmd_populate_kernel(&init_mm, &__pmd, pgtable);

 	for (i = 0; i < PMD_SIZE / PAGE_SIZE; i++, addr += PAGE_SIZE) {
 		pte_t entry, *pte;
 		pgprot_t pgprot = PAGE_KERNEL;

 		entry = mk_pte(page + i, pgprot);
 		pte = pte_offset_kernel(&__pmd, addr);
 		set_pte_at(&init_mm, addr, pte, entry);
 	}

 	/* Make pte visible before pmd. See comment in __pte_alloc(). */
 	smp_wmb();
 	pmd_populate_kernel(&init_mm, pmd, pgtable);

 	flush_tlb_kernel_range(start, start + PMD_SIZE);

 	return 0;
 }

 static void vmemmap_pte_range(pmd_t *pmd, unsigned long addr,
 			      unsigned long end,
 			      struct vmemmap_remap_walk *walk)
 {
 	pte_t *pte = pte_offset_kernel(pmd, addr);

 	/*
 	 * The reuse_page is found 'first' in table walk before we start
 	 * remapping (which is calling @walk->remap_pte).
 	 */
 	if (!walk->reuse_page) {
 		walk->reuse_page = pte_page(*pte);
 		/*
 		 * Because the reuse address is part of the range that we are
 		 * walking, skip the reuse address range.
 		 */
 		addr += PAGE_SIZE;
 		pte++;
 		walk->nr_walked++;
 	}

 	for (; addr != end; addr += PAGE_SIZE, pte++) {
 		walk->remap_pte(pte, addr, walk);
 		walk->nr_walked++;
 	}
 }

 static int vmemmap_pmd_range(pud_t *pud, unsigned long addr,
 			     unsigned long end,
 			     struct vmemmap_remap_walk *walk)
 {
 	pmd_t *pmd;
 	unsigned long next;

 	pmd = pmd_offset(pud, addr);
 	do {
 		if (pmd_leaf(*pmd)) {
 			int ret;

 			ret = split_vmemmap_huge_pmd(pmd, addr & PMD_MASK, walk);
 			if (ret)
 				return ret;
 		}
 		next = pmd_addr_end(addr, end);
 		vmemmap_pte_range(pmd, addr, next, walk);
 	} while (pmd++, addr = next, addr != end);

 	return 0;
 }

 static int vmemmap_pud_range(p4d_t *p4d, unsigned long addr,
 			     unsigned long end,
 			     struct vmemmap_remap_walk *walk)
 {
 	pud_t *pud;
 	unsigned long next;

 	pud = pud_offset(p4d, addr);
 	do {
 		int ret;

 		next = pud_addr_end(addr, end);
 		ret = vmemmap_pmd_range(pud, addr, next, walk);
 		if (ret)
 			return ret;
 	} while (pud++, addr = next, addr != end);

 	return 0;
 }

 static int vmemmap_p4d_range(pgd_t *pgd, unsigned long addr,
 			     unsigned long end,
 			     struct vmemmap_remap_walk *walk)
 {
 	p4d_t *p4d;
 	unsigned long next;

 	p4d = p4d_offset(pgd, addr);
 	do {
 		int ret;

 		next = p4d_addr_end(addr, end);
 		ret = vmemmap_pud_range(p4d, addr, next, walk);
 		if (ret)
 			return ret;
 	} while (p4d++, addr = next, addr != end);

 	return 0;
 }

 static int vmemmap_remap_range(unsigned long start, unsigned long end,
 			       struct vmemmap_remap_walk *walk)
 {
 	unsigned long addr = start;
 	unsigned long next;
 	pgd_t *pgd;

 	VM_BUG_ON(!IS_ALIGNED(start, PAGE_SIZE));
 	VM_BUG_ON(!IS_ALIGNED(end, PAGE_SIZE));

 	pgd = pgd_offset_k(addr);
 	do {
 		int ret;

 		next = pgd_addr_end(addr, end);
 		ret = vmemmap_p4d_range(pgd, addr, next, walk);
 		if (ret)
 			return ret;
 	} while (pgd++, addr = next, addr != end);

 	/*
 	 * We only change the mapping of the vmemmap virtual address range
 	 * [@start + PAGE_SIZE, end), so we only need to flush the TLB which
 	 * belongs to the range.
 	 */
 	flush_tlb_kernel_range(start + PAGE_SIZE, end);

 	return 0;
 }

 /*
  * Free a vmemmap page. A vmemmap page can be allocated from the memblock
  * allocator or buddy allocator. If the PG_reserved flag is set, it means
  * that it allocated from the memblock allocator, just free it via the
  * free_bootmem_page(). Otherwise, use __free_page().
  */
 static inline void free_vmemmap_page(struct page *page)
 {
 	if (PageReserved(page))
 		free_bootmem_page(page);
 	else
 		__free_page(page);
 }

 /* Free a list of the vmemmap pages */
 static void free_vmemmap_page_list(struct list_head *list)
 {
 	struct page *page, *next;

 	list_for_each_entry_safe(page, next, list, lru) {
 		list_del(&page->lru);
 		free_vmemmap_page(page);
 	}
 }

 static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
 			      struct vmemmap_remap_walk *walk)
 {
 	/*
 	 * Remap the tail pages as read-only to catch illegal write operation
 	 * to the tail pages.
 	 */
 	pgprot_t pgprot = PAGE_KERNEL_RO;
 	pte_t entry = mk_pte(walk->reuse_page, pgprot);
 	struct page *page = pte_page(*pte);

 	list_add_tail(&page->lru, walk->vmemmap_pages);
 	set_pte_at(&init_mm, addr, pte, entry);
 }

 static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
 				struct vmemmap_remap_walk *walk)
 {
 	pgprot_t pgprot = PAGE_KERNEL;
 	struct page *page;
 	void *to;

 	BUG_ON(pte_page(*pte) != walk->reuse_page);

 	page = list_first_entry(walk->vmemmap_pages, struct page, lru);
 	list_del(&page->lru);
 	to = page_to_virt(page);
 	copy_page(to, (void *)walk->reuse_addr);

 	set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot));
 }

 /**
  * vmemmap_remap_free - remap the vmemmap virtual address range [@start, @end)
  *			to the page which @reuse is mapped to, then free vmemmap
  *			which the range are mapped to.
  * @start:	start address of the vmemmap virtual address range that we want
  *		to remap.
  * @end:	end address of the vmemmap virtual address range that we want to
  *		remap.
  * @reuse:	reuse address.
  *
  * Return: %0 on success, negative error code otherwise.
  */
 int vmemmap_remap_free(unsigned long start, unsigned long end,
 		       unsigned long reuse)
 {
 	int ret;
 	LIST_HEAD(vmemmap_pages);
 	struct vmemmap_remap_walk walk = {
 		.remap_pte	= vmemmap_remap_pte,
 		.reuse_addr	= reuse,
 		.vmemmap_pages	= &vmemmap_pages,
 	};

 	/*
 	 * In order to make remapping routine most efficient for the huge pages,
 	 * the routine of vmemmap page table walking has the following rules
 	 * (see more details from the vmemmap_pte_range()):
 	 *
 	 * - The range [@start, @end) and the range [@reuse, @reuse + PAGE_SIZE)
 	 *   should be continuous.
 	 * - The @reuse address is part of the range [@reuse, @end) that we are
 	 *   walking which is passed to vmemmap_remap_range().
 	 * - The @reuse address is the first in the complete range.
 	 *
 	 * So we need to make sure that @start and @reuse meet the above rules.
 	 */
 	BUG_ON(start - reuse != PAGE_SIZE);

 	mmap_write_lock(&init_mm);
 	ret = vmemmap_remap_range(reuse, end, &walk);
 	mmap_write_downgrade(&init_mm);

 	if (ret && walk.nr_walked) {
 		end = reuse + walk.nr_walked * PAGE_SIZE;
 		/*
 		 * vmemmap_pages contains pages from the previous
 		 * vmemmap_remap_range call which failed.  These
 		 * are pages which were removed from the vmemmap.
 		 * They will be restored in the following call.
 		 */
 		walk = (struct vmemmap_remap_walk) {
 			.remap_pte	= vmemmap_restore_pte,
 			.reuse_addr	= reuse,
 			.vmemmap_pages	= &vmemmap_pages,
 		};

 		vmemmap_remap_range(reuse, end, &walk);
 	}
 	mmap_read_unlock(&init_mm);

 	free_vmemmap_page_list(&vmemmap_pages);

 	return ret;
 }

 static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
 				   gfp_t gfp_mask, struct list_head *list)
 {
 	unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
 	int nid = page_to_nid((struct page *)start);
 	struct page *page, *next;

 	while (nr_pages--) {
 		page = alloc_pages_node(nid, gfp_mask, 0);
 		if (!page)
 			goto out;
 		list_add_tail(&page->lru, list);
 	}

 	return 0;
 out:
 	list_for_each_entry_safe(page, next, list, lru)
 		__free_pages(page, 0);
 	return -ENOMEM;
 }

 /**
  * vmemmap_remap_alloc - remap the vmemmap virtual address range [@start, end)
  *			 to the page which is from the @vmemmap_pages
  *			 respectively.
  * @start:	start address of the vmemmap virtual address range that we want
  *		to remap.
  * @end:	end address of the vmemmap virtual address range that we want to
  *		remap.
  * @reuse:	reuse address.
  * @gfp_mask:	GFP flag for allocating vmemmap pages.
  *
  * Return: %0 on success, negative error code otherwise.
  */
 int vmemmap_remap_alloc(unsigned long start, unsigned long end,
 			unsigned long reuse, gfp_t gfp_mask)
 {
 	LIST_HEAD(vmemmap_pages);
 	struct vmemmap_remap_walk walk = {
 		.remap_pte	= vmemmap_restore_pte,
 		.reuse_addr	= reuse,
 		.vmemmap_pages	= &vmemmap_pages,
 	};

 	/* See the comment in the vmemmap_remap_free(). */
 	BUG_ON(start - reuse != PAGE_SIZE);

 	if (alloc_vmemmap_page_list(start, end, gfp_mask, &vmemmap_pages))
 		return -ENOMEM;

 	mmap_read_lock(&init_mm);
 	vmemmap_remap_range(reuse, end, &walk);
 	mmap_read_unlock(&init_mm);

 	return 0;
 }

 /*
  * Allocate a block of memory to be used to back the virtual memory map
  * or to back the page tables that are used to create the mapping.
  * Uses the main allocators if they are available, else bootmem.
  */

 static void * __ref __earlyonly_bootmem_alloc(int node,
 				unsigned long size,
 				unsigned long align,
 				unsigned long goal)
 {
 	return memblock_alloc_try_nid_raw(size, align, goal,
 					       MEMBLOCK_ALLOC_ACCESSIBLE, node);
 }

 void * __meminit vmemmap_alloc_block(unsigned long size, int node)
 {
 	/* If the main allocator is up use that, fallback to bootmem. */
 	if (slab_is_available()) {
 		gfp_t gfp_mask = GFP_KERNEL|__GFP_RETRY_MAYFAIL|__GFP_NOWARN;
 		int order = get_order(size);
 		static bool warned;
 		struct page *page;

 		page = alloc_pages_node(node, gfp_mask, order);
 		if (page)
 			return page_address(page);

 		if (!warned) {
 			warn_alloc(gfp_mask & ~__GFP_NOWARN, NULL,
 				   "vmemmap alloc failure: order:%u", order);
 			warned = true;
 		}
 		return NULL;
 	} else
 		return __earlyonly_bootmem_alloc(node, size, size,
 				__pa(MAX_DMA_ADDRESS));
 }

 static void * __meminit altmap_alloc_block_buf(unsigned long size,
 					       struct vmem_altmap *altmap);

 /* need to make sure size is all the same during early stage */
 void * __meminit vmemmap_alloc_block_buf(unsigned long size, int node,
 					 struct vmem_altmap *altmap)
 {
 	void *ptr;

 	if (altmap)
 		return altmap_alloc_block_buf(size, altmap);

 	ptr = sparse_buffer_alloc(size);
 	if (!ptr)
 		ptr = vmemmap_alloc_block(size, node);
 	return ptr;
 }

 static unsigned long __meminit vmem_altmap_next_pfn(struct vmem_altmap *altmap)
 {
 	return altmap->base_pfn + altmap->reserve + altmap->alloc
 		+ altmap->align;
 }

 static unsigned long __meminit vmem_altmap_nr_free(struct vmem_altmap *altmap)
 {
 	unsigned long allocated = altmap->alloc + altmap->align;

 	if (altmap->free > allocated)
 		return altmap->free - allocated;
 	return 0;
 }

 static void * __meminit altmap_alloc_block_buf(unsigned long size,
 					       struct vmem_altmap *altmap)
 {
 	unsigned long pfn, nr_pfns, nr_align;

 	if (size & ~PAGE_MASK) {
 		pr_warn_once("%s: allocations must be multiple of PAGE_SIZE (%ld)\n",
 				__func__, size);
 		return NULL;
 	}

 	pfn = vmem_altmap_next_pfn(altmap);
 	nr_pfns = size >> PAGE_SHIFT;
 	nr_align = 1UL << find_first_bit(&nr_pfns, BITS_PER_LONG);
 	nr_align = ALIGN(pfn, nr_align) - pfn;
 	if (nr_pfns + nr_align > vmem_altmap_nr_free(altmap))
 		return NULL;

 	altmap->alloc += nr_pfns;
 	altmap->align += nr_align;
 	pfn += nr_align;

 	pr_debug("%s: pfn: %#lx alloc: %ld align: %ld nr: %#lx\n",
 			__func__, pfn, altmap->alloc, altmap->align, nr_pfns);
 	return __va(__pfn_to_phys(pfn));
 }

 void __meminit vmemmap_verify(pte_t *pte, int node,
 				unsigned long start, unsigned long end)
 {
 	unsigned long pfn = pte_pfn(*pte);
 	int actual_node = early_pfn_to_nid(pfn);

 	if (node_distance(actual_node, node) > LOCAL_DISTANCE)
 		pr_warn("[%lx-%lx] potential offnode page_structs\n",
 			start, end - 1);
 }

 pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, int node,
 				       struct vmem_altmap *altmap)
 {
 	pte_t *pte = pte_offset_kernel(pmd, addr);
 	if (pte_none(*pte)) {
 		pte_t entry;
 		void *p;

 		p = vmemmap_alloc_block_buf(PAGE_SIZE, node, altmap);
 		if (!p)
 			return NULL;
 		entry = pfn_pte(__pa(p) >> PAGE_SHIFT, PAGE_KERNEL);
 		set_pte_at(&init_mm, addr, pte, entry);
 	}
 	return pte;
 }

 static void * __meminit vmemmap_alloc_block_zero(unsigned long size, int node)
 {
 	void *p = vmemmap_alloc_block(size, node);

 	if (!p)
 		return NULL;
 	memset(p, 0, size);

 	return p;
 }

 pmd_t * __meminit vmemmap_pmd_populate(pud_t *pud, unsigned long addr, int node)
 {
 	pmd_t *pmd = pmd_offset(pud, addr);
 	if (pmd_none(*pmd)) {
 		void *p = vmemmap_alloc_block_zero(PAGE_SIZE, node);
 		if (!p)
 			return NULL;
 		pmd_populate_kernel(&init_mm, pmd, p);
 	}
 	return pmd;
 }

 pud_t * __meminit vmemmap_pud_populate(p4d_t *p4d, unsigned long addr, int node)
 {
 	pud_t *pud = pud_offset(p4d, addr);
 	if (pud_none(*pud)) {
 		void *p = vmemmap_alloc_block_zero(PAGE_SIZE, node);
 		if (!p)
 			return NULL;
 		pud_populate(&init_mm, pud, p);
 	}
 	return pud;
 }

 p4d_t * __meminit vmemmap_p4d_populate(pgd_t *pgd, unsigned long addr, int node)
 {
 	p4d_t *p4d = p4d_offset(pgd, addr);
 	if (p4d_none(*p4d)) {
 		void *p = vmemmap_alloc_block_zero(PAGE_SIZE, node);
 		if (!p)
 			return NULL;
 		p4d_populate(&init_mm, p4d, p);
 	}
 	return p4d;
 }

 pgd_t * __meminit vmemmap_pgd_populate(unsigned long addr, int node)
 {
 	pgd_t *pgd = pgd_offset_k(addr);
 	if (pgd_none(*pgd)) {
 		void *p = vmemmap_alloc_block_zero(PAGE_SIZE, node);
 		if (!p)
 			return NULL;
 		pgd_populate(&init_mm, pgd, p);
 	}
 	return pgd;
 }

 int __meminit vmemmap_populate_basepages(unsigned long start, unsigned long end,
 					 int node, struct vmem_altmap *altmap)
 {
 	unsigned long addr = start;
 	pgd_t *pgd;
 	p4d_t *p4d;
 	pud_t *pud;
 	pmd_t *pmd;
 	pte_t *pte;

 	for (; addr < end; addr += PAGE_SIZE) {
 		pgd = vmemmap_pgd_populate(addr, node);
 		if (!pgd)
 			return -ENOMEM;
 		p4d = vmemmap_p4d_populate(pgd, addr, node);
 		if (!p4d)
 			return -ENOMEM;
 		pud = vmemmap_pud_populate(p4d, addr, node);
 		if (!pud)
 			return -ENOMEM;
 		pmd = vmemmap_pmd_populate(pud, addr, node);
 		if (!pmd)
 			return -ENOMEM;
 		pte = vmemmap_pte_populate(pmd, addr, node, altmap);
 		if (!pte)
 			return -ENOMEM;
 		vmemmap_verify(pte, node, addr, addr + PAGE_SIZE);
 	}

 	return 0;
 }

 struct page * __meminit __populate_section_memmap(unsigned long pfn,
 		unsigned long nr_pages, int nid, struct vmem_altmap *altmap)
 {
 	unsigned long start = (unsigned long) pfn_to_page(pfn);
 	unsigned long end = start + nr_pages * sizeof(struct page);

 	if (WARN_ON_ONCE(!IS_ALIGNED(pfn, PAGES_PER_SUBSECTION) ||
 		!IS_ALIGNED(nr_pages, PAGES_PER_SUBSECTION)))
 		return NULL;

 	if (vmemmap_populate(start, end, nid, altmap))
 		return NULL;

 	return pfn_to_page(pfn);
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* Virtual Memory Map support
	*
	* (C) 2007 sgi. Christoph Lameter.
	*
	* Virtual memory maps allow VM primitives pfn_to_page, page_to_pfn,
	* virt_to_page, page_address() to be implemented as a base offset
	* calculation without memory access.
	*
	* However, virtual mappings need a page table and TLBs. Many Linux
	* architectures already map their physical space using 1-1 mappings
	* via TLBs. For those arches the virtual memory map is essentially
	* for free if we use the same page size as the 1-1 mappings. In that
	* case the overhead consists of a few additional pages that are
	* allocated to create a view of memory for vmemmap.
	*
	* The architecture is expected to provide a vmemmap_populate() function
	* to instantiate the mapping.
	*/
	#include <linux/mm.h>
	#include <linux/mmzone.h>
	#include <linux/memblock.h>
	#include <linux/memremap.h>
	#include <linux/highmem.h>
	#include <linux/slab.h>
	#include <linux/spinlock.h>
	#include <linux/vmalloc.h>
	#include <linux/sched.h>
	#include <linux/pgtable.h>
	#include <linux/bootmem_info.h>

	#include <asm/dma.h>
	#include <asm/pgalloc.h>
	#include <asm/tlbflush.h>

	/**
	* struct vmemmap_remap_walk - walk vmemmap page table
	*
	* @remap_pte: called for each lowest-level entry (PTE).
	* @nr_walked: the number of walked pte.
	* @reuse_page: the page which is reused for the tail vmemmap pages.
	* @reuse_addr: the virtual address of the @reuse_page page.
	* @vmemmap_pages: the list head of the vmemmap pages that can be freed
	* or is mapped from.
	*/
	struct vmemmap_remap_walk {
	void (remap_pte)(pte_t pte, unsigned long addr,
	struct vmemmap_remap_walk *walk);
	unsigned long nr_walked;
	struct page *reuse_page;
	unsigned long reuse_addr;
	struct list_head *vmemmap_pages;
	};

	static int split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start,
	struct vmemmap_remap_walk *walk)
	{
	pmd_t __pmd;
	int i;
	unsigned long addr = start;
	struct page page = pmd_page(pmd);
	pte_t *pgtable = pte_alloc_one_kernel(&init_mm);

	if (!pgtable)
	return -ENOMEM;

	pmd_populate_kernel(&init_mm, &__pmd, pgtable);

	for (i = 0; i < PMD_SIZE / PAGE_SIZE; i++, addr += PAGE_SIZE) {
	pte_t entry, *pte;
	pgprot_t pgprot = PAGE_KERNEL;

	entry = mk_pte(page + i, pgprot);
	pte = pte_offset_kernel(&__pmd, addr);
	set_pte_at(&init_mm, addr, pte, entry);
	}

	/* Make pte visible before pmd. See comment in __pte_alloc(). */
	smp_wmb();
	pmd_populate_kernel(&init_mm, pmd, pgtable);

	flush_tlb_kernel_range(start, start + PMD_SIZE);

	return 0;
	}

	static void vmemmap_pte_range(pmd_t *pmd, unsigned long addr,
	unsigned long end,
	struct vmemmap_remap_walk *walk)
	{
	pte_t *pte = pte_offset_kernel(pmd, addr);

	/*
	* The reuse_page is found 'first' in table walk before we start
	* remapping (which is calling @walk->remap_pte).
	*/
	if (!walk->reuse_page) {
	walk->reuse_page = pte_page(*pte);
	/*
	* Because the reuse address is part of the range that we are
	* walking, skip the reuse address range.
	*/
	addr += PAGE_SIZE;
	pte++;
	walk->nr_walked++;
	}

	for (; addr != end; addr += PAGE_SIZE, pte++) {
	walk->remap_pte(pte, addr, walk);
	walk->nr_walked++;
	}
	}

	static int vmemmap_pmd_range(pud_t *pud, unsigned long addr,
	unsigned long end,
	struct vmemmap_remap_walk *walk)
	{
	pmd_t *pmd;
	unsigned long next;

	pmd = pmd_offset(pud, addr);
	do {
	if (pmd_leaf(*pmd)) {
	int ret;

	ret = split_vmemmap_huge_pmd(pmd, addr & PMD_MASK, walk);
	if (ret)
	return ret;
	}
	next = pmd_addr_end(addr, end);
	vmemmap_pte_range(pmd, addr, next, walk);
	} while (pmd++, addr = next, addr != end);

	return 0;
	}

	static int vmemmap_pud_range(p4d_t *p4d, unsigned long addr,
	unsigned long end,
	struct vmemmap_remap_walk *walk)
	{
	pud_t *pud;
	unsigned long next;

	pud = pud_offset(p4d, addr);
	do {
	int ret;

	next = pud_addr_end(addr, end);
	ret = vmemmap_pmd_range(pud, addr, next, walk);
	if (ret)
	return ret;
	} while (pud++, addr = next, addr != end);

	return 0;
	}

	static int vmemmap_p4d_range(pgd_t *pgd, unsigned long addr,
	unsigned long end,
	struct vmemmap_remap_walk *walk)
	{
	p4d_t *p4d;
	unsigned long next;

	p4d = p4d_offset(pgd, addr);
	do {
	int ret;

	next = p4d_addr_end(addr, end);
	ret = vmemmap_pud_range(p4d, addr, next, walk);
	if (ret)
	return ret;
	} while (p4d++, addr = next, addr != end);

	return 0;
	}

	static int vmemmap_remap_range(unsigned long start, unsigned long end,
	struct vmemmap_remap_walk *walk)
	{
	unsigned long addr = start;
	unsigned long next;
	pgd_t *pgd;

	VM_BUG_ON(!IS_ALIGNED(start, PAGE_SIZE));
	VM_BUG_ON(!IS_ALIGNED(end, PAGE_SIZE));

	pgd = pgd_offset_k(addr);
	do {
	int ret;

	next = pgd_addr_end(addr, end);
	ret = vmemmap_p4d_range(pgd, addr, next, walk);
	if (ret)
	return ret;
	} while (pgd++, addr = next, addr != end);

	/*
	* We only change the mapping of the vmemmap virtual address range
	* [@start + PAGE_SIZE, end), so we only need to flush the TLB which
	* belongs to the range.
	*/
	flush_tlb_kernel_range(start + PAGE_SIZE, end);

	return 0;
	}

	/*
	* Free a vmemmap page. A vmemmap page can be allocated from the memblock
	* allocator or buddy allocator. If the PG_reserved flag is set, it means
	* that it allocated from the memblock allocator, just free it via the
	* free_bootmem_page(). Otherwise, use __free_page().
	*/
	static inline void free_vmemmap_page(struct page *page)
	{
	if (PageReserved(page))
	free_bootmem_page(page);
	else
	__free_page(page);
	}

	/* Free a list of the vmemmap pages */
	static void free_vmemmap_page_list(struct list_head *list)
	{
	struct page page, next;

	list_for_each_entry_safe(page, next, list, lru) {
	list_del(&page->lru);
	free_vmemmap_page(page);
	}
	}

	static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
	struct vmemmap_remap_walk *walk)
	{
	/*
	* Remap the tail pages as read-only to catch illegal write operation
	* to the tail pages.
	*/
	pgprot_t pgprot = PAGE_KERNEL_RO;
	pte_t entry = mk_pte(walk->reuse_page, pgprot);
	struct page page = pte_page(pte);

	list_add_tail(&page->lru, walk->vmemmap_pages);
	set_pte_at(&init_mm, addr, pte, entry);
	}

	static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
	struct vmemmap_remap_walk *walk)
	{
	pgprot_t pgprot = PAGE_KERNEL;
	struct page *page;
	void *to;

	BUG_ON(pte_page(*pte) != walk->reuse_page);

	page = list_first_entry(walk->vmemmap_pages, struct page, lru);
	list_del(&page->lru);
	to = page_to_virt(page);
	copy_page(to, (void *)walk->reuse_addr);

	set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot));
	}

	/**
	* vmemmap_remap_free - remap the vmemmap virtual address range [@start, @end)
	* to the page which @reuse is mapped to, then free vmemmap
	* which the range are mapped to.
	* @start: start address of the vmemmap virtual address range that we want
	* to remap.
	* @end: end address of the vmemmap virtual address range that we want to
	* remap.
	* @reuse: reuse address.
	*
	* Return: %0 on success, negative error code otherwise.
	*/
	int vmemmap_remap_free(unsigned long start, unsigned long end,
	unsigned long reuse)
	{
	int ret;
	LIST_HEAD(vmemmap_pages);
	struct vmemmap_remap_walk walk = {
	.remap_pte = vmemmap_remap_pte,
	.reuse_addr = reuse,
	.vmemmap_pages = &vmemmap_pages,
	};

	/*
	* In order to make remapping routine most efficient for the huge pages,
	* the routine of vmemmap page table walking has the following rules
	* (see more details from the vmemmap_pte_range()):
	*
	* - The range [@start, @end) and the range [@reuse, @reuse + PAGE_SIZE)
	* should be continuous.
	* - The @reuse address is part of the range [@reuse, @end) that we are
	* walking which is passed to vmemmap_remap_range().
	* - The @reuse address is the first in the complete range.
	*
	* So we need to make sure that @start and @reuse meet the above rules.
	*/
	BUG_ON(start - reuse != PAGE_SIZE);

	mmap_write_lock(&init_mm);
	ret = vmemmap_remap_range(reuse, end, &walk);
	mmap_write_downgrade(&init_mm);

	if (ret && walk.nr_walked) {
	end = reuse + walk.nr_walked * PAGE_SIZE;
	/*
	* vmemmap_pages contains pages from the previous
	* vmemmap_remap_range call which failed. These
	* are pages which were removed from the vmemmap.
	* They will be restored in the following call.
	*/
	walk = (struct vmemmap_remap_walk) {
	.remap_pte = vmemmap_restore_pte,
	.reuse_addr = reuse,
	.vmemmap_pages = &vmemmap_pages,
	};

	vmemmap_remap_range(reuse, end, &walk);
	}
	mmap_read_unlock(&init_mm);

	free_vmemmap_page_list(&vmemmap_pages);

	return ret;
	}

	static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
	gfp_t gfp_mask, struct list_head *list)
	{
	unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
	int nid = page_to_nid((struct page *)start);
	struct page page, next;

	while (nr_pages--) {
	page = alloc_pages_node(nid, gfp_mask, 0);
	if (!page)
	goto out;
	list_add_tail(&page->lru, list);
	}

	return 0;
	out:
	list_for_each_entry_safe(page, next, list, lru)
	__free_pages(page, 0);
	return -ENOMEM;
	}

	/**
	* vmemmap_remap_alloc - remap the vmemmap virtual address range [@start, end)
	* to the page which is from the @vmemmap_pages
	* respectively.
	* @start: start address of the vmemmap virtual address range that we want
	* to remap.
	* @end: end address of the vmemmap virtual address range that we want to
	* remap.
	* @reuse: reuse address.
	* @gfp_mask: GFP flag for allocating vmemmap pages.
	*
	* Return: %0 on success, negative error code otherwise.
	*/
	int vmemmap_remap_alloc(unsigned long start, unsigned long end,
	unsigned long reuse, gfp_t gfp_mask)
	{
	LIST_HEAD(vmemmap_pages);
	struct vmemmap_remap_walk walk = {
	.remap_pte = vmemmap_restore_pte,
	.reuse_addr = reuse,
	.vmemmap_pages = &vmemmap_pages,
	};

	/* See the comment in the vmemmap_remap_free(). */
	BUG_ON(start - reuse != PAGE_SIZE);

	if (alloc_vmemmap_page_list(start, end, gfp_mask, &vmemmap_pages))
	return -ENOMEM;

	mmap_read_lock(&init_mm);
	vmemmap_remap_range(reuse, end, &walk);
	mmap_read_unlock(&init_mm);

	return 0;
	}

	/*
	* Allocate a block of memory to be used to back the virtual memory map
	* or to back the page tables that are used to create the mapping.
	* Uses the main allocators if they are available, else bootmem.
	*/

	static void * __ref __earlyonly_bootmem_alloc(int node,
	unsigned long size,
	unsigned long align,
	unsigned long goal)
	{
	return memblock_alloc_try_nid_raw(size, align, goal,
	MEMBLOCK_ALLOC_ACCESSIBLE, node);
	}

	void * __meminit vmemmap_alloc_block(unsigned long size, int node)
	{
	/* If the main allocator is up use that, fallback to bootmem. */
	if (slab_is_available()) {
	gfp_t gfp_mask = GFP_KERNEL\|__GFP_RETRY_MAYFAIL\|__GFP_NOWARN;
	int order = get_order(size);
	static bool warned;
	struct page *page;

	page = alloc_pages_node(node, gfp_mask, order);
	if (page)
	return page_address(page);

	if (!warned) {
	warn_alloc(gfp_mask & ~__GFP_NOWARN, NULL,
	"vmemmap alloc failure: order:%u", order);
	warned = true;
	}
	return NULL;
	} else
	return __earlyonly_bootmem_alloc(node, size, size,
	__pa(MAX_DMA_ADDRESS));
	}

	static void * __meminit altmap_alloc_block_buf(unsigned long size,
	struct vmem_altmap *altmap);

	/* need to make sure size is all the same during early stage */
	void * __meminit vmemmap_alloc_block_buf(unsigned long size, int node,
	struct vmem_altmap *altmap)
	{
	void *ptr;

	if (altmap)
	return altmap_alloc_block_buf(size, altmap);

	ptr = sparse_buffer_alloc(size);
	if (!ptr)
	ptr = vmemmap_alloc_block(size, node);
	return ptr;
	}

	static unsigned long __meminit vmem_altmap_next_pfn(struct vmem_altmap *altmap)
	{
	return altmap->base_pfn + altmap->reserve + altmap->alloc
	+ altmap->align;
	}

	static unsigned long __meminit vmem_altmap_nr_free(struct vmem_altmap *altmap)
	{
	unsigned long allocated = altmap->alloc + altmap->align;

	if (altmap->free > allocated)
	return altmap->free - allocated;
	return 0;
	}

	static void * __meminit altmap_alloc_block_buf(unsigned long size,
	struct vmem_altmap *altmap)
	{
	unsigned long pfn, nr_pfns, nr_align;

	if (size & ~PAGE_MASK) {
	pr_warn_once("%s: allocations must be multiple of PAGE_SIZE (%ld)\n",
	__func__, size);
	return NULL;
	}

	pfn = vmem_altmap_next_pfn(altmap);
	nr_pfns = size >> PAGE_SHIFT;
	nr_align = 1UL << find_first_bit(&nr_pfns, BITS_PER_LONG);
	nr_align = ALIGN(pfn, nr_align) - pfn;
	if (nr_pfns + nr_align > vmem_altmap_nr_free(altmap))
	return NULL;

	altmap->alloc += nr_pfns;
	altmap->align += nr_align;
	pfn += nr_align;

	pr_debug("%s: pfn: %#lx alloc: %ld align: %ld nr: %#lx\n",
	__func__, pfn, altmap->alloc, altmap->align, nr_pfns);
	return __va(__pfn_to_phys(pfn));
	}

	void __meminit vmemmap_verify(pte_t *pte, int node,
	unsigned long start, unsigned long end)
	{
	unsigned long pfn = pte_pfn(*pte);
	int actual_node = early_pfn_to_nid(pfn);

	if (node_distance(actual_node, node) > LOCAL_DISTANCE)
	pr_warn("[%lx-%lx] potential offnode page_structs\n",
	start, end - 1);
	}

	pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, int node,
	struct vmem_altmap *altmap)
	{
	pte_t *pte = pte_offset_kernel(pmd, addr);
	if (pte_none(*pte)) {
	pte_t entry;
	void *p;

	p = vmemmap_alloc_block_buf(PAGE_SIZE, node, altmap);
	if (!p)
	return NULL;
	entry = pfn_pte(__pa(p) >> PAGE_SHIFT, PAGE_KERNEL);
	set_pte_at(&init_mm, addr, pte, entry);
	}
	return pte;
	}

	static void * __meminit vmemmap_alloc_block_zero(unsigned long size, int node)
	{
	void *p = vmemmap_alloc_block(size, node);

	if (!p)
	return NULL;
	memset(p, 0, size);

	return p;
	}

	pmd_t * __meminit vmemmap_pmd_populate(pud_t *pud, unsigned long addr, int node)
	{
	pmd_t *pmd = pmd_offset(pud, addr);
	if (pmd_none(*pmd)) {
	void *p = vmemmap_alloc_block_zero(PAGE_SIZE, node);
	if (!p)
	return NULL;
	pmd_populate_kernel(&init_mm, pmd, p);
	}
	return pmd;
	}

	pud_t * __meminit vmemmap_pud_populate(p4d_t *p4d, unsigned long addr, int node)
	{
	pud_t *pud = pud_offset(p4d, addr);
	if (pud_none(*pud)) {
	void *p = vmemmap_alloc_block_zero(PAGE_SIZE, node);
	if (!p)
	return NULL;
	pud_populate(&init_mm, pud, p);
	}
	return pud;
	}

	p4d_t * __meminit vmemmap_p4d_populate(pgd_t *pgd, unsigned long addr, int node)
	{
	p4d_t *p4d = p4d_offset(pgd, addr);
	if (p4d_none(*p4d)) {
	void *p = vmemmap_alloc_block_zero(PAGE_SIZE, node);
	if (!p)
	return NULL;
	p4d_populate(&init_mm, p4d, p);
	}
	return p4d;
	}

	pgd_t * __meminit vmemmap_pgd_populate(unsigned long addr, int node)
	{
	pgd_t *pgd = pgd_offset_k(addr);
	if (pgd_none(*pgd)) {
	void *p = vmemmap_alloc_block_zero(PAGE_SIZE, node);
	if (!p)
	return NULL;
	pgd_populate(&init_mm, pgd, p);
	}
	return pgd;
	}

	int __meminit vmemmap_populate_basepages(unsigned long start, unsigned long end,
	int node, struct vmem_altmap *altmap)
	{
	unsigned long addr = start;
	pgd_t *pgd;
	p4d_t *p4d;
	pud_t *pud;
	pmd_t *pmd;
	pte_t *pte;

	for (; addr < end; addr += PAGE_SIZE) {
	pgd = vmemmap_pgd_populate(addr, node);
	if (!pgd)
	return -ENOMEM;
	p4d = vmemmap_p4d_populate(pgd, addr, node);
	if (!p4d)
	return -ENOMEM;
	pud = vmemmap_pud_populate(p4d, addr, node);
	if (!pud)
	return -ENOMEM;
	pmd = vmemmap_pmd_populate(pud, addr, node);
	if (!pmd)
	return -ENOMEM;
	pte = vmemmap_pte_populate(pmd, addr, node, altmap);
	if (!pte)
	return -ENOMEM;
	vmemmap_verify(pte, node, addr, addr + PAGE_SIZE);
	}

	return 0;
	}

	struct page * __meminit __populate_section_memmap(unsigned long pfn,
	unsigned long nr_pages, int nid, struct vmem_altmap *altmap)
	{
	unsigned long start = (unsigned long) pfn_to_page(pfn);
	unsigned long end = start + nr_pages * sizeof(struct page);

	if (WARN_ON_ONCE(!IS_ALIGNED(pfn, PAGES_PER_SUBSECTION) \|\|
	!IS_ALIGNED(nr_pages, PAGES_PER_SUBSECTION)))
	return NULL;

	if (vmemmap_populate(start, end, nid, altmap))
	return NULL;

	return pfn_to_page(pfn);
	}