Documentation: Add documentation for Processor MMIO Stale Data

[mirror_ubuntu-jammy-kernel.git] / mm / sparse.c

// SPDX-License-Identifier: GPL-2.0
/*
 * sparse memory mappings.
 */
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/mmzone.h>
#include <linux/memblock.h>
#include <linux/compiler.h>
#include <linux/highmem.h>
#include <linux/export.h>
#include <linux/spinlock.h>
#include <linux/vmalloc.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/bootmem_info.h>

#include "internal.h"
#include <asm/dma.h>

/*
 * Permanent SPARSEMEM data:
 *
 * 1) mem_section       - memory sections, mem_map's for valid memory
 */
#ifdef CONFIG_SPARSEMEM_EXTREME
struct mem_section **mem_section;
#else
struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT]
        ____cacheline_internodealigned_in_smp;
#endif
EXPORT_SYMBOL(mem_section);

#ifdef NODE_NOT_IN_PAGE_FLAGS
/*
 * If we did not store the node number in the page then we have to
 * do a lookup in the section_to_node_table in order to find which
 * node the page belongs to.
 */
#if MAX_NUMNODES <= 256
static u8 section_to_node_table[NR_MEM_SECTIONS] __cacheline_aligned;
#else
static u16 section_to_node_table[NR_MEM_SECTIONS] __cacheline_aligned;
#endif

int page_to_nid(const struct page *page)
{
        return section_to_node_table[page_to_section(page)];
}
EXPORT_SYMBOL(page_to_nid);

static void set_section_nid(unsigned long section_nr, int nid)
{
        section_to_node_table[section_nr] = nid;
}
#else /* !NODE_NOT_IN_PAGE_FLAGS */
static inline void set_section_nid(unsigned long section_nr, int nid)
{
}
#endif

#ifdef CONFIG_SPARSEMEM_EXTREME
static noinline struct mem_section __ref *sparse_index_alloc(int nid)
{
        struct mem_section *section = NULL;
        unsigned long array_size = SECTIONS_PER_ROOT *
                                   sizeof(struct mem_section);

        if (slab_is_available()) {
                section = kzalloc_node(array_size, GFP_KERNEL, nid);
        } else {
                section = memblock_alloc_node(array_size, SMP_CACHE_BYTES,
                                              nid);
                if (!section)
                        panic("%s: Failed to allocate %lu bytes nid=%d\n",
                              __func__, array_size, nid);
        }

        return section;
}

static int __meminit sparse_index_init(unsigned long section_nr, int nid)
{
        unsigned long root = SECTION_NR_TO_ROOT(section_nr);
        struct mem_section *section;

        /*
         * An existing section is possible in the sub-section hotplug
         * case. First hot-add instantiates, follow-on hot-add reuses
         * the existing section.
         *
         * The mem_hotplug_lock resolves the apparent race below.
         */
        if (mem_section[root])
                return 0;

        section = sparse_index_alloc(nid);
        if (!section)
                return -ENOMEM;

        mem_section[root] = section;

        return 0;
}
#else /* !SPARSEMEM_EXTREME */
static inline int sparse_index_init(unsigned long section_nr, int nid)
{
        return 0;
}
#endif

/*
 * During early boot, before section_mem_map is used for an actual
 * mem_map, we use section_mem_map to store the section's NUMA
 * node.  This keeps us from having to use another data structure.  The
 * node information is cleared just before we store the real mem_map.
 */
static inline unsigned long sparse_encode_early_nid(int nid)
{
        return ((unsigned long)nid << SECTION_NID_SHIFT);
}

static inline int sparse_early_nid(struct mem_section *section)
{
        return (section->section_mem_map >> SECTION_NID_SHIFT);
}

/* Validate the physical addressing limitations of the model */
void __meminit mminit_validate_memmodel_limits(unsigned long *start_pfn,
                                                unsigned long *end_pfn)
{
        unsigned long max_sparsemem_pfn = 1UL << (MAX_PHYSMEM_BITS-PAGE_SHIFT);

        /*
         * Sanity checks - do not allow an architecture to pass
         * in larger pfns than the maximum scope of sparsemem:
         */
        if (*start_pfn > max_sparsemem_pfn) {
                mminit_dprintk(MMINIT_WARNING, "pfnvalidation",
                        "Start of range %lu -> %lu exceeds SPARSEMEM max %lu\n",
                        *start_pfn, *end_pfn, max_sparsemem_pfn);
                WARN_ON_ONCE(1);
                *start_pfn = max_sparsemem_pfn;
                *end_pfn = max_sparsemem_pfn;
        } else if (*end_pfn > max_sparsemem_pfn) {
                mminit_dprintk(MMINIT_WARNING, "pfnvalidation",
                        "End of range %lu -> %lu exceeds SPARSEMEM max %lu\n",
                        *start_pfn, *end_pfn, max_sparsemem_pfn);
                WARN_ON_ONCE(1);
                *end_pfn = max_sparsemem_pfn;
        }
}

/*
 * There are a number of times that we loop over NR_MEM_SECTIONS,
 * looking for section_present() on each.  But, when we have very
 * large physical address spaces, NR_MEM_SECTIONS can also be
 * very large which makes the loops quite long.
 *
 * Keeping track of this gives us an easy way to break out of
 * those loops early.
 */
unsigned long __highest_present_section_nr;
static void __section_mark_present(struct mem_section *ms,
                unsigned long section_nr)
{
        if (section_nr > __highest_present_section_nr)
                __highest_present_section_nr = section_nr;

        ms->section_mem_map |= SECTION_MARKED_PRESENT;
}

#define for_each_present_section_nr(start, section_nr)          \
        for (section_nr = next_present_section_nr(start-1);     \
             ((section_nr != -1) &&                             \
              (section_nr <= __highest_present_section_nr));    \
             section_nr = next_present_section_nr(section_nr))

static inline unsigned long first_present_section_nr(void)
{
        return next_present_section_nr(-1);
}

#ifdef CONFIG_SPARSEMEM_VMEMMAP
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 subsection_map_init(unsigned long pfn, unsigned long nr_pages)
{
        int end_sec = pfn_to_section_nr(pfn + nr_pages - 1);
        unsigned long nr, start_sec = pfn_to_section_nr(pfn);

        if (!nr_pages)
                return;

        for (nr = start_sec; nr <= end_sec; 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;
        }
}
#else
void __init subsection_map_init(unsigned long pfn, unsigned long nr_pages)
{
}
#endif

/* Record a memory area against a node. */
static void __init memory_present(int nid, unsigned long start, unsigned long end)
{
        unsigned long pfn;

#ifdef CONFIG_SPARSEMEM_EXTREME
        if (unlikely(!mem_section)) {
                unsigned long size, align;

                size = sizeof(struct mem_section *) * NR_SECTION_ROOTS;
                align = 1 << (INTERNODE_CACHE_SHIFT);
                mem_section = memblock_alloc(size, align);
                if (!mem_section)
                        panic("%s: Failed to allocate %lu bytes align=0x%lx\n",
                              __func__, size, align);
        }
#endif

        start &= PAGE_SECTION_MASK;
        mminit_validate_memmodel_limits(&start, &end);
        for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION) {
                unsigned long section = pfn_to_section_nr(pfn);
                struct mem_section *ms;

                sparse_index_init(section, nid);
                set_section_nid(section, nid);

                ms = __nr_to_section(section);
                if (!ms->section_mem_map) {
                        ms->section_mem_map = sparse_encode_early_nid(nid) |
                                                        SECTION_IS_ONLINE;
                        __section_mark_present(ms, section);
                }
        }
}

/*
 * Mark all memblocks as present using memory_present().
 * This is a convenience function that is useful to mark all of the systems
 * memory as present during initialization.
 */
static void __init memblocks_present(void)
{
        unsigned long start, end;
        int i, nid;

        for_each_mem_pfn_range(i, MAX_NUMNODES, &start, &end, &nid)
                memory_present(nid, start, end);
}

/*
 * Subtle, we encode the real pfn into the mem_map such that
 * the identity pfn - section_mem_map will return the actual
 * physical page frame number.
 */
static unsigned long sparse_encode_mem_map(struct page *mem_map, unsigned long pnum)
{
        unsigned long coded_mem_map =
                (unsigned long)(mem_map - (section_nr_to_pfn(pnum)));
        BUILD_BUG_ON(SECTION_MAP_LAST_BIT > (1UL<<PFN_SECTION_SHIFT));
        BUG_ON(coded_mem_map & ~SECTION_MAP_MASK);
        return coded_mem_map;
}

#ifdef CONFIG_MEMORY_HOTPLUG
/*
 * Decode mem_map from the coded memmap
 */
struct page *sparse_decode_mem_map(unsigned long coded_mem_map, unsigned long pnum)
{
        /* mask off the extra low bits of information */
        coded_mem_map &= SECTION_MAP_MASK;
        return ((struct page *)coded_mem_map) + section_nr_to_pfn(pnum);
}
#endif /* CONFIG_MEMORY_HOTPLUG */

static void __meminit sparse_init_one_section(struct mem_section *ms,
                unsigned long pnum, struct page *mem_map,
                struct mem_section_usage *usage, unsigned long flags)
{
        ms->section_mem_map &= ~SECTION_MAP_MASK;
        ms->section_mem_map |= sparse_encode_mem_map(mem_map, pnum)
                | SECTION_HAS_MEM_MAP | flags;
        ms->usage = usage;
}

static unsigned long usemap_size(void)
{
        return BITS_TO_LONGS(SECTION_BLOCKFLAGS_BITS) * sizeof(unsigned long);
}

size_t mem_section_usage_size(void)
{
        return sizeof(struct mem_section_usage) + usemap_size();
}

static inline phys_addr_t pgdat_to_phys(struct pglist_data *pgdat)
{
#ifndef CONFIG_NUMA
        VM_BUG_ON(pgdat != &contig_page_data);
        return __pa_symbol(&contig_page_data);
#else
        return __pa(pgdat);
#endif
}

#ifdef CONFIG_MEMORY_HOTREMOVE
static struct mem_section_usage * __init
sparse_early_usemaps_alloc_pgdat_section(struct pglist_data *pgdat,
                                         unsigned long size)
{
        struct mem_section_usage *usage;
        unsigned long goal, limit;
        int nid;
        /*
         * A page may contain usemaps for other sections preventing the
         * page being freed and making a section unremovable while
         * other sections referencing the usemap remain active. Similarly,
         * a pgdat can prevent a section being removed. If section A
         * contains a pgdat and section B contains the usemap, both
         * sections become inter-dependent. This allocates usemaps
         * from the same section as the pgdat where possible to avoid
         * this problem.
         */
        goal = pgdat_to_phys(pgdat) & (PAGE_SECTION_MASK << PAGE_SHIFT);
        limit = goal + (1UL << PA_SECTION_SHIFT);
        nid = early_pfn_to_nid(goal >> PAGE_SHIFT);
again:
        usage = memblock_alloc_try_nid(size, SMP_CACHE_BYTES, goal, limit, nid);
        if (!usage && limit) {
                limit = 0;
                goto again;
        }
        return usage;
}

static void __init check_usemap_section_nr(int nid,
                struct mem_section_usage *usage)
{
        unsigned long usemap_snr, pgdat_snr;
        static unsigned long old_usemap_snr;
        static unsigned long old_pgdat_snr;
        struct pglist_data *pgdat = NODE_DATA(nid);
        int usemap_nid;

        /* First call */
        if (!old_usemap_snr) {
                old_usemap_snr = NR_MEM_SECTIONS;
                old_pgdat_snr = NR_MEM_SECTIONS;
        }

        usemap_snr = pfn_to_section_nr(__pa(usage) >> PAGE_SHIFT);
        pgdat_snr = pfn_to_section_nr(pgdat_to_phys(pgdat) >> PAGE_SHIFT);
        if (usemap_snr == pgdat_snr)
                return;

        if (old_usemap_snr == usemap_snr && old_pgdat_snr == pgdat_snr)
                /* skip redundant message */
                return;

        old_usemap_snr = usemap_snr;
        old_pgdat_snr = pgdat_snr;

        usemap_nid = sparse_early_nid(__nr_to_section(usemap_snr));
        if (usemap_nid != nid) {
                pr_info("node %d must be removed before remove section %ld\n",
                        nid, usemap_snr);
                return;
        }
        /*
         * There is a circular dependency.
         * Some platforms allow un-removable section because they will just
         * gather other removable sections for dynamic partitioning.
         * Just notify un-removable section's number here.
         */
        pr_info("Section %ld and %ld (node %d) have a circular dependency on usemap and pgdat allocations\n",
                usemap_snr, pgdat_snr, nid);
}
#else
static struct mem_section_usage * __init
sparse_early_usemaps_alloc_pgdat_section(struct pglist_data *pgdat,
                                         unsigned long size)
{
        return memblock_alloc_node(size, SMP_CACHE_BYTES, pgdat->node_id);
}

static void __init check_usemap_section_nr(int nid,
                struct mem_section_usage *usage)
{
}
#endif /* CONFIG_MEMORY_HOTREMOVE */

#ifdef CONFIG_SPARSEMEM_VMEMMAP
static unsigned long __init section_map_size(void)
{
        return ALIGN(sizeof(struct page) * PAGES_PER_SECTION, PMD_SIZE);
}

#else
static unsigned long __init section_map_size(void)
{
        return PAGE_ALIGN(sizeof(struct page) * PAGES_PER_SECTION);
}

struct page __init *__populate_section_memmap(unsigned long pfn,
                unsigned long nr_pages, int nid, struct vmem_altmap *altmap)
{
        unsigned long size = section_map_size();
        struct page *map = sparse_buffer_alloc(size);
        phys_addr_t addr = __pa(MAX_DMA_ADDRESS);

        if (map)
                return map;

        map = memmap_alloc(size, size, addr, nid, false);
        if (!map)
                panic("%s: Failed to allocate %lu bytes align=0x%lx nid=%d from=%pa\n",
                      __func__, size, PAGE_SIZE, nid, &addr);

        return map;
}
#endif /* !CONFIG_SPARSEMEM_VMEMMAP */

static void *sparsemap_buf __meminitdata;
static void *sparsemap_buf_end __meminitdata;

static inline void __meminit sparse_buffer_free(unsigned long size)
{
        WARN_ON(!sparsemap_buf || size == 0);
        memblock_free_early(__pa(sparsemap_buf), size);
}

static void __init sparse_buffer_init(unsigned long size, int nid)
{
        phys_addr_t addr = __pa(MAX_DMA_ADDRESS);
        WARN_ON(sparsemap_buf); /* forgot to call sparse_buffer_fini()? */
        /*
         * Pre-allocated buffer is mainly used by __populate_section_memmap
         * and we want it to be properly aligned to the section size - this is
         * especially the case for VMEMMAP which maps memmap to PMDs
         */
        sparsemap_buf = memmap_alloc(size, section_map_size(), addr, nid, true);
        sparsemap_buf_end = sparsemap_buf + size;
}

static void __init sparse_buffer_fini(void)
{
        unsigned long size = sparsemap_buf_end - sparsemap_buf;

        if (sparsemap_buf && size > 0)
                sparse_buffer_free(size);
        sparsemap_buf = NULL;
}

void * __meminit sparse_buffer_alloc(unsigned long size)
{
        void *ptr = NULL;

        if (sparsemap_buf) {
                ptr = (void *) roundup((unsigned long)sparsemap_buf, size);
                if (ptr + size > sparsemap_buf_end)
                        ptr = NULL;
                else {
                        /* Free redundant aligned space */
                        if ((unsigned long)(ptr - sparsemap_buf) > 0)
                                sparse_buffer_free((unsigned long)(ptr - sparsemap_buf));
                        sparsemap_buf = ptr + size;
                }
        }
        return ptr;
}

void __weak __meminit vmemmap_populate_print_last(void)
{
}

/*
 * Initialize sparse on a specific node. The node spans [pnum_begin, pnum_end)
 * And number of present sections in this node is map_count.
 */
static void __init sparse_init_nid(int nid, unsigned long pnum_begin,
                                   unsigned long pnum_end,
                                   unsigned long map_count)
{
        struct mem_section_usage *usage;
        unsigned long pnum;
        struct page *map;

        usage = sparse_early_usemaps_alloc_pgdat_section(NODE_DATA(nid),
                        mem_section_usage_size() * map_count);
        if (!usage) {
                pr_err("%s: node[%d] usemap allocation failed", __func__, nid);
                goto failed;
        }
        sparse_buffer_init(map_count * section_map_size(), nid);
        for_each_present_section_nr(pnum_begin, pnum) {
                unsigned long pfn = section_nr_to_pfn(pnum);

                if (pnum >= pnum_end)
                        break;

                map = __populate_section_memmap(pfn, PAGES_PER_SECTION,
                                nid, NULL);
                if (!map) {
                        pr_err("%s: node[%d] memory map backing failed. Some memory will not be available.",
                               __func__, nid);
                        pnum_begin = pnum;
                        sparse_buffer_fini();
                        goto failed;
                }
                check_usemap_section_nr(nid, usage);
                sparse_init_one_section(__nr_to_section(pnum), pnum, map, usage,
                                SECTION_IS_EARLY);
                usage = (void *) usage + mem_section_usage_size();
        }
        sparse_buffer_fini();
        return;
failed:
        /* We failed to allocate, mark all the following pnums as not present */
        for_each_present_section_nr(pnum_begin, pnum) {
                struct mem_section *ms;

                if (pnum >= pnum_end)
                        break;
                ms = __nr_to_section(pnum);
                ms->section_mem_map = 0;
        }
}

/*
 * Allocate the accumulated non-linear sections, allocate a mem_map
 * for each and record the physical to section mapping.
 */
void __init sparse_init(void)
{
        unsigned long pnum_end, pnum_begin, map_count = 1;
        int nid_begin;

        memblocks_present();

        pnum_begin = first_present_section_nr();
        nid_begin = sparse_early_nid(__nr_to_section(pnum_begin));

        /* Setup pageblock_order for HUGETLB_PAGE_SIZE_VARIABLE */
        set_pageblock_order();

        for_each_present_section_nr(pnum_begin + 1, pnum_end) {
                int nid = sparse_early_nid(__nr_to_section(pnum_end));

                if (nid == nid_begin) {
                        map_count++;
                        continue;
                }
                /* Init node with sections in range [pnum_begin, pnum_end) */
                sparse_init_nid(nid_begin, pnum_begin, pnum_end, map_count);
                nid_begin = nid;
                pnum_begin = pnum_end;
                map_count = 1;
        }
        /* cover the last node */
        sparse_init_nid(nid_begin, pnum_begin, pnum_end, map_count);
        vmemmap_populate_print_last();
}

#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;

                /* onlining code should never touch invalid ranges */
                if (WARN_ON(!valid_section_nr(section_nr)))
                        continue;

                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;

                /*
                 * TODO this needs some double checking. Offlining code makes
                 * sure to check pfn_valid but those checks might be just bogus
                 */
                if (WARN_ON(!valid_section_nr(section_nr)))
                        continue;

                ms = __nr_to_section(section_nr);
                ms->section_mem_map &= ~SECTION_IS_ONLINE;
        }
}

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

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;
}
#else
struct page * __meminit populate_section_memmap(unsigned long pfn,
                unsigned long nr_pages, int nid, struct vmem_altmap *altmap)
{
        return kvmalloc_node(array_size(sizeof(struct page),
                                        PAGES_PER_SECTION), GFP_KERNEL, nid);
}

static void depopulate_section_memmap(unsigned long pfn, unsigned long nr_pages,
                struct vmem_altmap *altmap)
{
        kvfree(pfn_to_page(pfn));
}

static void free_map_bootmem(struct page *memmap)
{
        unsigned long maps_section_nr, removing_section_nr, i;
        unsigned long magic, nr_pages;
        struct page *page = virt_to_page(memmap);

        nr_pages = PAGE_ALIGN(PAGES_PER_SECTION * sizeof(struct page))
                >> PAGE_SHIFT;

        for (i = 0; i < nr_pages; i++, page++) {
                magic = (unsigned long) page->freelist;

                BUG_ON(magic == NODE_INFO);

                maps_section_nr = pfn_to_section_nr(page_to_pfn(page));
                removing_section_nr = page_private(page);

                /*
                 * When this function is called, the removing section is
                 * logical offlined state. This means all pages are isolated
                 * from page allocator. If removing section's memmap is placed
                 * on the same section, it must not be freed.
                 * If it is freed, page allocator may allocate it which will
                 * be removed physically soon.
                 */
                if (maps_section_nr != removing_section_nr)
                        put_page_bootmem(page);
        }
}

static int clear_subsection_map(unsigned long pfn, unsigned long nr_pages)
{
        return 0;
}

static bool is_subsection_map_empty(struct mem_section *ms)
{
        return true;
}

static int fill_subsection_map(unsigned long pfn, unsigned long nr_pages)
{
        return 0;
}
#endif /* CONFIG_SPARSEMEM_VMEMMAP */

/*
 * To deactivate a memory region, there are 3 cases to handle across
 * two configurations (SPARSEMEM_VMEMMAP={y,n}):
 *
 * 1. deactivation of a partial hot-added section (only possible in
 *    the SPARSEMEM_VMEMMAP=y case).
 *      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.
 *
 * For 2 and 3, the SPARSEMEM_VMEMMAP={y,n} cases are unified
 */
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) {
                unsigned long section_nr = pfn_to_section_nr(pfn);

                /*
                 * 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(ms->usage);
                        ms->usage = NULL;
                }
                memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);
                /*
                 * 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;
        }

        /*
         * The memmap of early sections is always fully populated. See
         * section_activate() and pfn_valid() .
         */
        if (!section_is_early)
                depopulate_section_memmap(pfn, nr_pages, altmap);
        else if (memmap)
                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 mem_section *ms = __pfn_to_section(pfn);
        struct mem_section_usage *usage = NULL;
        struct page *memmap;
        int rc = 0;

        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);
        if (!memmap) {
                section_deactivate(pfn, nr_pages, altmap);
                return ERR_PTR(-ENOMEM);
        }

        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: device page map
 *
 * 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)
{
        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);
        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);
        set_section_nid(section_nr, nid);
        __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;
}

#ifdef CONFIG_MEMORY_FAILURE
static void clear_hwpoisoned_pages(struct page *memmap, int nr_pages)
{
        int i;

        /*
         * A further optimization is to have per section refcounted
         * num_poisoned_pages.  But that would need more space per memmap, so
         * for now just do a quick global check to speed up this routine in the
         * absence of bad pages.
         */
        if (atomic_long_read(&num_poisoned_pages) == 0)
                return;

        for (i = 0; i < nr_pages; i++) {
                if (PageHWPoison(&memmap[i])) {
                        num_poisoned_pages_dec();
                        ClearPageHWPoison(&memmap[i]);
                }
        }
}
#else
static inline void clear_hwpoisoned_pages(struct page *memmap, int nr_pages)
{
}
#endif

void sparse_remove_section(struct mem_section *ms, unsigned long pfn,
                unsigned long nr_pages, unsigned long map_offset,
                struct vmem_altmap *altmap)
{
        clear_hwpoisoned_pages(pfn_to_page(pfn) + map_offset,
                        nr_pages - map_offset);
        section_deactivate(pfn, nr_pages, altmap);
}
#endif /* CONFIG_MEMORY_HOTPLUG */