linux/mm/sparse-vmemmap.c

// 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/pgalloc.h>

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

#include "hugetlb_vmemmap.h"

/*
 * Flags for vmemmap_populate_range and friends.
 */
/* Get a ref on the head page struct page, for ZONE_DEVICE compound pages */
#define VMEMMAP_POPULATE_PAGEREF	0x0001

#include "internal.h"

/*
 * 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 memmap_alloc(size, align, goal, node, false);
}

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

	return vmemmap_alloc_block(size, node);
}

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(ptep_get(pte));
	int actual_node = early_pfn_to_nid(pfn);

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

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

		if (ptpfn == (unsigned long)-1) {
			p = vmemmap_alloc_block_buf(PAGE_SIZE, node, altmap);
			if (!p)
				return NULL;
			ptpfn = PHYS_PFN(__pa(p));
		} else {
			/*
			 * When a PTE/PMD entry is freed from the init_mm
			 * there's a free_pages() call to this page allocated
			 * above. Thus this get_page() is paired with the
			 * put_page_testzero() on the freeing path.
			 * This can only called by certain ZONE_DEVICE path,
			 * and through vmemmap_populate_compound_pages() when
			 * slab is available.
			 */
			if (flags & VMEMMAP_POPULATE_PAGEREF)
				get_page(pfn_to_page(ptpfn));
		}
		entry = pfn_pte(ptpfn, 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;
}

static 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;
		kernel_pte_init(p);
		pmd_populate_kernel(&init_mm, pmd, p);
	}
	return pmd;
}

static 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;
		pmd_init(p);
		pud_populate(&init_mm, pud, p);
	}
	return pud;
}

static 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;
		pud_init(p);
		p4d_populate_kernel(addr, p4d, p);
	}
	return p4d;
}

static 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_kernel(addr, pgd, p);
	}
	return pgd;
}

static pte_t * __meminit vmemmap_populate_address(unsigned long addr, int node,
					      struct vmem_altmap *altmap,
					      unsigned long ptpfn,
					      unsigned long flags)
{
	pgd_t *pgd;
	p4d_t *p4d;
	pud_t *pud;
	pmd_t *pmd;
	pte_t *pte;

	pgd = vmemmap_pgd_populate(addr, node);
	if (!pgd)
		return NULL;
	p4d = vmemmap_p4d_populate(pgd, addr, node);
	if (!p4d)
		return NULL;
	pud = vmemmap_pud_populate(p4d, addr, node);
	if (!pud)
		return NULL;
	pmd = vmemmap_pmd_populate(pud, addr, node);
	if (!pmd)
		return NULL;
	pte = vmemmap_pte_populate(pmd, addr, node, altmap, ptpfn, flags);
	if (!pte)
		return NULL;
	vmemmap_verify(pte, node, addr, addr + PAGE_SIZE);

	return pte;
}

static int __meminit vmemmap_populate_range(unsigned long start,
					    unsigned long end, int node,
					    struct vmem_altmap *altmap,
					    unsigned long ptpfn,
					    unsigned long flags)
{
	unsigned long addr = start;
	pte_t *pte;

	for (; addr < end; addr += PAGE_SIZE) {
		pte = vmemmap_populate_address(addr, node, altmap,
					       ptpfn, flags);
		if (!pte)
			return -ENOMEM;
	}

	return 0;
}

int __meminit vmemmap_populate_basepages(unsigned long start, unsigned long end,
					 int node, struct vmem_altmap *altmap)
{
	return vmemmap_populate_range(start, end, node, altmap, -1, 0);
}

/*
 * Write protect the mirrored tail page structs for HVO. This will be
 * called from the hugetlb code when gathering and initializing the
 * memblock allocated gigantic pages. The write protect can't be
 * done earlier, since it can't be guaranteed that the reserved
 * page structures will not be written to during initialization,
 * even if CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled.
 *
 * The PTEs are known to exist, and nothing else should be touching
 * these pages. The caller is responsible for any TLB flushing.
 */
void vmemmap_wrprotect_hvo(unsigned long addr, unsigned long end,
				    int node, unsigned long headsize)
{
	unsigned long maddr;
	pte_t *pte;

	for (maddr = addr + headsize; maddr < end; maddr += PAGE_SIZE) {
		pte = virt_to_kpte(maddr);
		ptep_set_wrprotect(&init_mm, maddr, pte);
	}
}

#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
static __meminit struct page *vmemmap_get_tail(unsigned int order, struct zone *zone)
{
	struct page *p, *tail;
	unsigned int idx;
	int node = zone_to_nid(zone);

	if (WARN_ON_ONCE(order < VMEMMAP_TAIL_MIN_ORDER))
		return NULL;
	if (WARN_ON_ONCE(order > MAX_FOLIO_ORDER))
		return NULL;

	idx = order - VMEMMAP_TAIL_MIN_ORDER;
	tail = zone->vmemmap_tails[idx];
	if (tail)
		return tail;

	/*
	 * Only allocate the page, but do not initialize it.
	 *
	 * Any initialization done here will be overwritten by memmap_init().
	 *
	 * hugetlb_vmemmap_init() will take care of initialization after
	 * memmap_init().
	 */

	p = vmemmap_alloc_block_zero(PAGE_SIZE, node);
	if (!p)
		return NULL;

	tail = virt_to_page(p);
	zone->vmemmap_tails[idx] = tail;

	return tail;
}

int __meminit vmemmap_populate_hvo(unsigned long addr, unsigned long end,
				       unsigned int order, struct zone *zone,
				       unsigned long headsize)
{
	unsigned long maddr;
	struct page *tail;
	pte_t *pte;
	int node = zone_to_nid(zone);

	tail = vmemmap_get_tail(order, zone);
	if (!tail)
		return -ENOMEM;

	for (maddr = addr; maddr < addr + headsize; maddr += PAGE_SIZE) {
		pte = vmemmap_populate_address(maddr, node, NULL, -1, 0);
		if (!pte)
			return -ENOMEM;
	}

	/*
	 * Reuse the last page struct page mapped above for the rest.
	 */
	return vmemmap_populate_range(maddr, end, node, NULL,
				      page_to_pfn(tail), 0);
}
#endif

void __weak __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
				      unsigned long addr, unsigned long next)
{
}

int __weak __meminit vmemmap_check_pmd(pmd_t *pmd, int node,
				       unsigned long addr, unsigned long next)
{
	return 0;
}

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

	for (addr = start; addr < end; addr = next) {
		next = pmd_addr_end(addr, end);

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

			p = vmemmap_alloc_block_buf(PMD_SIZE, node, altmap);
			if (p) {
				vmemmap_set_pmd(pmd, p, node, addr, next);
				continue;
			} else if (altmap) {
				/*
				 * No fallback: In any case we care about, the
				 * altmap should be reasonably sized and aligned
				 * such that vmemmap_alloc_block_buf() will always
				 * succeed. For consistency with the PTE case,
				 * return an error here as failure could indicate
				 * a configuration issue with the size of the altmap.
				 */
				return -ENOMEM;
			}
		} else if (vmemmap_check_pmd(pmd, node, addr, next))
			continue;
		if (vmemmap_populate_basepages(addr, next, node, altmap))
			return -ENOMEM;
	}
	return 0;
}

#ifndef vmemmap_populate_compound_pages
/*
 * For compound pages bigger than section size (e.g. x86 1G compound
 * pages with 2M subsection size) fill the rest of sections as tail
 * pages.
 *
 * Note that memremap_pages() resets @nr_range value and will increment
 * it after each range successful onlining. Thus the value or @nr_range
 * at section memmap populate corresponds to the in-progress range
 * being onlined here.
 */
static bool __meminit reuse_compound_section(unsigned long start_pfn,
					     struct dev_pagemap *pgmap)
{
	unsigned long nr_pages = pgmap_vmemmap_nr(pgmap);
	unsigned long offset = start_pfn -
		PHYS_PFN(pgmap->ranges[pgmap->nr_range].start);

	return !IS_ALIGNED(offset, nr_pages) && nr_pages > PAGES_PER_SUBSECTION;
}

static pte_t * __meminit compound_section_tail_page(unsigned long addr)
{
	pte_t *pte;

	addr -= PAGE_SIZE;

	/*
	 * Assuming sections are populated sequentially, the previous section's
	 * page data can be reused.
	 */
	pte = pte_offset_kernel(pmd_off_k(addr), addr);
	if (!pte)
		return NULL;

	return pte;
}

static int __meminit vmemmap_populate_compound_pages(unsigned long start_pfn,
						     unsigned long start,
						     unsigned long end, int node,
						     struct dev_pagemap *pgmap)
{
	unsigned long size, addr;
	pte_t *pte;
	int rc;

	if (reuse_compound_section(start_pfn, pgmap)) {
		pte = compound_section_tail_page(start);
		if (!pte)
			return -ENOMEM;

		/*
		 * Reuse the page that was populated in the prior iteration
		 * with just tail struct pages.
		 */
		return vmemmap_populate_range(start, end, node, NULL,
					      pte_pfn(ptep_get(pte)),
					      VMEMMAP_POPULATE_PAGEREF);
	}

	size = min(end - start, pgmap_vmemmap_nr(pgmap) * sizeof(struct page));
	for (addr = start; addr < end; addr += size) {
		unsigned long next, last = addr + size;

		/* Populate the head page vmemmap page */
		pte = vmemmap_populate_address(addr, node, NULL, -1, 0);
		if (!pte)
			return -ENOMEM;

		/* Populate the tail pages vmemmap page */
		next = addr + PAGE_SIZE;
		pte = vmemmap_populate_address(next, node, NULL, -1, 0);
		if (!pte)
			return -ENOMEM;

		/*
		 * Reuse the previous page for the rest of tail pages
		 * See layout diagram in Documentation/mm/vmemmap_dedup.rst
		 */
		next += PAGE_SIZE;
		rc = vmemmap_populate_range(next, last, node, NULL,
					    pte_pfn(ptep_get(pte)),
					    VMEMMAP_POPULATE_PAGEREF);
		if (rc)
			return -ENOMEM;
	}

	return 0;
}

#endif

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

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

	if (vmemmap_can_optimize(altmap, pgmap))
		r = vmemmap_populate_compound_pages(pfn, start, end, nid, pgmap);
	else
		r = vmemmap_populate(start, end, nid, altmap);

	if (r < 0)
		return NULL;

	return pfn_to_page(pfn);
}

#ifdef CONFIG_SPARSEMEM_VMEMMAP_PREINIT
/*
 * This is called just before initializing sections for a NUMA node.
 * Any special initialization that needs to be done before the
 * generic initialization can be done from here. Sections that
 * are initialized in hooks called from here will be skipped by
 * the generic initialization.
 */
void __init sparse_vmemmap_init_nid_early(int nid)
{
	hugetlb_vmemmap_init_early(nid);
}

/*
 * This is called just before the initialization of page structures
 * through memmap_init. Zones are now initialized, so any work that
 * needs to be done that needs zone information can be done from
 * here.
 */
void __init sparse_vmemmap_init_nid_late(int nid)
{
	hugetlb_vmemmap_init_late(nid);
}
#endif

static void subsection_mask_set(unsigned long *map, unsigned long pfn,
		unsigned long nr_pages)
{
	int idx = subsection_map_index(pfn);
	int end = subsection_map_index(pfn + nr_pages - 1);

	bitmap_set(map, idx, end - idx + 1);
}

void __init sparse_init_subsection_map(unsigned long pfn, unsigned long nr_pages)
{
	int end_sec_nr = pfn_to_section_nr(pfn + nr_pages - 1);
	unsigned long nr, start_sec_nr = pfn_to_section_nr(pfn);

	for (nr = start_sec_nr; nr <= end_sec_nr; nr++) {
		struct mem_section *ms;
		unsigned long pfns;

		pfns = min(nr_pages, PAGES_PER_SECTION
				- (pfn & ~PAGE_SECTION_MASK));
		ms = __nr_to_section(nr);
		subsection_mask_set(ms->usage->subsection_map, pfn, pfns);

		pr_debug("%s: sec: %lu pfns: %lu set(%d, %d)\n", __func__, nr,
				pfns, subsection_map_index(pfn),
				subsection_map_index(pfn + pfns - 1));

		pfn += pfns;
		nr_pages -= pfns;
	}
}

#ifdef CONFIG_MEMORY_HOTPLUG

/* Mark all memory sections within the pfn range as online */
void online_mem_sections(unsigned long start_pfn, unsigned long end_pfn)
{
	unsigned long pfn;

	for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
		unsigned long section_nr = pfn_to_section_nr(pfn);
		struct mem_section *ms = __nr_to_section(section_nr);

		ms->section_mem_map |= SECTION_IS_ONLINE;
	}
}

/* Mark all memory sections within the pfn range as offline */
void offline_mem_sections(unsigned long start_pfn, unsigned long end_pfn)
{
	unsigned long pfn;

	for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
		unsigned long section_nr = pfn_to_section_nr(pfn);
		struct mem_section *ms = __nr_to_section(section_nr);

		ms->section_mem_map &= ~SECTION_IS_ONLINE;
	}
}

static struct page * __meminit populate_section_memmap(unsigned long pfn,
		unsigned long nr_pages, int nid, struct vmem_altmap *altmap,
		struct dev_pagemap *pgmap)
{
	return __populate_section_memmap(pfn, nr_pages, nid, altmap, pgmap);
}

static void depopulate_section_memmap(unsigned long pfn, unsigned long nr_pages,
		struct vmem_altmap *altmap)
{
	unsigned long start = (unsigned long) pfn_to_page(pfn);
	unsigned long end = start + nr_pages * sizeof(struct page);

	vmemmap_free(start, end, altmap);
}
static void free_map_bootmem(struct page *memmap)
{
	unsigned long start = (unsigned long)memmap;
	unsigned long end = (unsigned long)(memmap + PAGES_PER_SECTION);

	vmemmap_free(start, end, NULL);
}

static int clear_subsection_map(unsigned long pfn, unsigned long nr_pages)
{
	DECLARE_BITMAP(map, SUBSECTIONS_PER_SECTION) = { 0 };
	DECLARE_BITMAP(tmp, SUBSECTIONS_PER_SECTION) = { 0 };
	struct mem_section *ms = __pfn_to_section(pfn);
	unsigned long *subsection_map = ms->usage
		? &ms->usage->subsection_map[0] : NULL;

	subsection_mask_set(map, pfn, nr_pages);
	if (subsection_map)
		bitmap_and(tmp, map, subsection_map, SUBSECTIONS_PER_SECTION);

	if (WARN(!subsection_map || !bitmap_equal(tmp, map, SUBSECTIONS_PER_SECTION),
				"section already deactivated (%#lx + %ld)\n",
				pfn, nr_pages))
		return -EINVAL;

	bitmap_xor(subsection_map, map, subsection_map, SUBSECTIONS_PER_SECTION);
	return 0;
}

static bool is_subsection_map_empty(struct mem_section *ms)
{
	return bitmap_empty(&ms->usage->subsection_map[0],
			    SUBSECTIONS_PER_SECTION);
}

static int fill_subsection_map(unsigned long pfn, unsigned long nr_pages)
{
	struct mem_section *ms = __pfn_to_section(pfn);
	DECLARE_BITMAP(map, SUBSECTIONS_PER_SECTION) = { 0 };
	unsigned long *subsection_map;
	int rc = 0;

	subsection_mask_set(map, pfn, nr_pages);

	subsection_map = &ms->usage->subsection_map[0];

	if (bitmap_empty(map, SUBSECTIONS_PER_SECTION))
		rc = -EINVAL;
	else if (bitmap_intersects(map, subsection_map, SUBSECTIONS_PER_SECTION))
		rc = -EEXIST;
	else
		bitmap_or(subsection_map, map, subsection_map,
				SUBSECTIONS_PER_SECTION);

	return rc;
}

/*
 * To deactivate a memory region, there are 3 cases to handle:
 *
 * 1. deactivation of a partial hot-added section:
 *      a) section was present at memory init.
 *      b) section was hot-added post memory init.
 * 2. deactivation of a complete hot-added section.
 * 3. deactivation of a complete section from memory init.
 *
 * For 1, when subsection_map does not empty we will not be freeing the
 * usage map, but still need to free the vmemmap range.
 */
static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
		struct vmem_altmap *altmap)
{
	struct mem_section *ms = __pfn_to_section(pfn);
	bool section_is_early = early_section(ms);
	struct page *memmap = NULL;
	bool empty;

	if (clear_subsection_map(pfn, nr_pages))
		return;

	empty = is_subsection_map_empty(ms);
	if (empty) {
		/*
		 * Mark the section invalid so that valid_section()
		 * return false. This prevents code from dereferencing
		 * ms->usage array.
		 */
		ms->section_mem_map &= ~SECTION_HAS_MEM_MAP;

		/*
		 * When removing an early section, the usage map is kept (as the
		 * usage maps of other sections fall into the same page). It
		 * will be re-used when re-adding the section - which is then no
		 * longer an early section. If the usage map is PageReserved, it
		 * was allocated during boot.
		 */
		if (!PageReserved(virt_to_page(ms->usage))) {
			kfree_rcu(ms->usage, rcu);
			WRITE_ONCE(ms->usage, NULL);
		}
		memmap = pfn_to_page(SECTION_ALIGN_DOWN(pfn));
	}

	/*
	 * The memmap of early sections is always fully populated. See
	 * section_activate() and pfn_valid() .
	 */
	if (!section_is_early) {
		memmap_pages_add(-1L * (DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE)));
		depopulate_section_memmap(pfn, nr_pages, altmap);
	} else if (memmap) {
		memmap_boot_pages_add(-1L * (DIV_ROUND_UP(nr_pages * sizeof(struct page),
							  PAGE_SIZE)));
		free_map_bootmem(memmap);
	}

	if (empty)
		ms->section_mem_map = (unsigned long)NULL;
}

static struct page * __meminit section_activate(int nid, unsigned long pfn,
		unsigned long nr_pages, struct vmem_altmap *altmap,
		struct dev_pagemap *pgmap)
{
	struct mem_section *ms = __pfn_to_section(pfn);
	struct mem_section_usage *usage = NULL;
	struct page *memmap;
	int rc;

	if (!ms->usage) {
		usage = kzalloc(mem_section_usage_size(), GFP_KERNEL);
		if (!usage)
			return ERR_PTR(-ENOMEM);
		ms->usage = usage;
	}

	rc = fill_subsection_map(pfn, nr_pages);
	if (rc) {
		if (usage)
			ms->usage = NULL;
		kfree(usage);
		return ERR_PTR(rc);
	}

	/*
	 * The early init code does not consider partially populated
	 * initial sections, it simply assumes that memory will never be
	 * referenced.  If we hot-add memory into such a section then we
	 * do not need to populate the memmap and can simply reuse what
	 * is already there.
	 */
	if (nr_pages < PAGES_PER_SECTION && early_section(ms))
		return pfn_to_page(pfn);

	memmap = populate_section_memmap(pfn, nr_pages, nid, altmap, pgmap);
	if (!memmap) {
		section_deactivate(pfn, nr_pages, altmap);
		return ERR_PTR(-ENOMEM);
	}
	memmap_pages_add(DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE));

	return memmap;
}

/**
 * sparse_add_section - add a memory section, or populate an existing one
 * @nid: The node to add section on
 * @start_pfn: start pfn of the memory range
 * @nr_pages: number of pfns to add in the section
 * @altmap: alternate pfns to allocate the memmap backing store
 * @pgmap: alternate compound page geometry for devmap mappings
 *
 * This is only intended for hotplug.
 *
 * Note that only VMEMMAP supports sub-section aligned hotplug,
 * the proper alignment and size are gated by check_pfn_span().
 *
 *
 * Return:
 * * 0		- On success.
 * * -EEXIST	- Section has been present.
 * * -ENOMEM	- Out of memory.
 */
int __meminit sparse_add_section(int nid, unsigned long start_pfn,
		unsigned long nr_pages, struct vmem_altmap *altmap,
		struct dev_pagemap *pgmap)
{
	unsigned long section_nr = pfn_to_section_nr(start_pfn);
	struct mem_section *ms;
	struct page *memmap;
	int ret;

	ret = sparse_index_init(section_nr, nid);
	if (ret < 0)
		return ret;

	memmap = section_activate(nid, start_pfn, nr_pages, altmap, pgmap);
	if (IS_ERR(memmap))
		return PTR_ERR(memmap);

	/*
	 * Poison uninitialized struct pages in order to catch invalid flags
	 * combinations.
	 */
	page_init_poison(memmap, sizeof(struct page) * nr_pages);

	ms = __nr_to_section(section_nr);
	__section_mark_present(ms, section_nr);

	/* Align memmap to section boundary in the subsection case */
	if (section_nr_to_pfn(section_nr) != start_pfn)
		memmap = pfn_to_page(section_nr_to_pfn(section_nr));
	sparse_init_one_section(ms, section_nr, memmap, ms->usage, 0);

	return 0;
}

void sparse_remove_section(unsigned long pfn, unsigned long nr_pages,
			   struct vmem_altmap *altmap)
{
	struct mem_section *ms = __pfn_to_section(pfn);

	if (WARN_ON_ONCE(!valid_section(ms)))
		return;

	section_deactivate(pfn, nr_pages, altmap);
}
#endif /* CONFIG_MEMORY_HOTPLUG */