Linux 6.9-rc1

[linux-2.6-microblaze.git] / mm / memory_hotplug.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/mm/memory_hotplug.c
 *
 *  Copyright (C)
 */

#include <linux/stddef.h>
#include <linux/mm.h>
#include <linux/sched/signal.h>
#include <linux/swap.h>
#include <linux/interrupt.h>
#include <linux/pagemap.h>
#include <linux/compiler.h>
#include <linux/export.h>
#include <linux/pagevec.h>
#include <linux/writeback.h>
#include <linux/slab.h>
#include <linux/sysctl.h>
#include <linux/cpu.h>
#include <linux/memory.h>
#include <linux/memremap.h>
#include <linux/memory_hotplug.h>
#include <linux/vmalloc.h>
#include <linux/ioport.h>
#include <linux/delay.h>
#include <linux/migrate.h>
#include <linux/page-isolation.h>
#include <linux/pfn.h>
#include <linux/suspend.h>
#include <linux/mm_inline.h>
#include <linux/firmware-map.h>
#include <linux/stop_machine.h>
#include <linux/hugetlb.h>
#include <linux/memblock.h>
#include <linux/compaction.h>
#include <linux/rmap.h>
#include <linux/module.h>

#include <asm/tlbflush.h>

#include "internal.h"
#include "shuffle.h"

#ifdef CONFIG_MHP_MEMMAP_ON_MEMORY
/*
 * memory_hotplug.memmap_on_memory parameter
 */
static bool memmap_on_memory __ro_after_init;
module_param(memmap_on_memory, bool, 0444);
MODULE_PARM_DESC(memmap_on_memory, "Enable memmap on memory for memory hotplug");

static inline bool mhp_memmap_on_memory(void)
{
        return memmap_on_memory;
}
#else
static inline bool mhp_memmap_on_memory(void)
{
        return false;
}
#endif

enum {
        ONLINE_POLICY_CONTIG_ZONES = 0,
        ONLINE_POLICY_AUTO_MOVABLE,
};

static const char * const online_policy_to_str[] = {
        [ONLINE_POLICY_CONTIG_ZONES] = "contig-zones",
        [ONLINE_POLICY_AUTO_MOVABLE] = "auto-movable",
};

static int set_online_policy(const char *val, const struct kernel_param *kp)
{
        int ret = sysfs_match_string(online_policy_to_str, val);

        if (ret < 0)
                return ret;
        *((int *)kp->arg) = ret;
        return 0;
}

static int get_online_policy(char *buffer, const struct kernel_param *kp)
{
        return sprintf(buffer, "%s\n", online_policy_to_str[*((int *)kp->arg)]);
}

/*
 * memory_hotplug.online_policy: configure online behavior when onlining without
 * specifying a zone (MMOP_ONLINE)
 *
 * "contig-zones": keep zone contiguous
 * "auto-movable": online memory to ZONE_MOVABLE if the configuration
 *                 (auto_movable_ratio, auto_movable_numa_aware) allows for it
 */
static int online_policy __read_mostly = ONLINE_POLICY_CONTIG_ZONES;
static const struct kernel_param_ops online_policy_ops = {
        .set = set_online_policy,
        .get = get_online_policy,
};
module_param_cb(online_policy, &online_policy_ops, &online_policy, 0644);
MODULE_PARM_DESC(online_policy,
                "Set the online policy (\"contig-zones\", \"auto-movable\") "
                "Default: \"contig-zones\"");

/*
 * memory_hotplug.auto_movable_ratio: specify maximum MOVABLE:KERNEL ratio
 *
 * The ratio represent an upper limit and the kernel might decide to not
 * online some memory to ZONE_MOVABLE -- e.g., because hotplugged KERNEL memory
 * doesn't allow for more MOVABLE memory.
 */
static unsigned int auto_movable_ratio __read_mostly = 301;
module_param(auto_movable_ratio, uint, 0644);
MODULE_PARM_DESC(auto_movable_ratio,
                "Set the maximum ratio of MOVABLE:KERNEL memory in the system "
                "in percent for \"auto-movable\" online policy. Default: 301");

/*
 * memory_hotplug.auto_movable_numa_aware: consider numa node stats
 */
#ifdef CONFIG_NUMA
static bool auto_movable_numa_aware __read_mostly = true;
module_param(auto_movable_numa_aware, bool, 0644);
MODULE_PARM_DESC(auto_movable_numa_aware,
                "Consider numa node stats in addition to global stats in "
                "\"auto-movable\" online policy. Default: true");
#endif /* CONFIG_NUMA */

/*
 * online_page_callback contains pointer to current page onlining function.
 * Initially it is generic_online_page(). If it is required it could be
 * changed by calling set_online_page_callback() for callback registration
 * and restore_online_page_callback() for generic callback restore.
 */

static online_page_callback_t online_page_callback = generic_online_page;
static DEFINE_MUTEX(online_page_callback_lock);

DEFINE_STATIC_PERCPU_RWSEM(mem_hotplug_lock);

void get_online_mems(void)
{
        percpu_down_read(&mem_hotplug_lock);
}

void put_online_mems(void)
{
        percpu_up_read(&mem_hotplug_lock);
}

bool movable_node_enabled = false;

#ifndef CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE
int mhp_default_online_type = MMOP_OFFLINE;
#else
int mhp_default_online_type = MMOP_ONLINE;
#endif

static int __init setup_memhp_default_state(char *str)
{
        const int online_type = mhp_online_type_from_str(str);

        if (online_type >= 0)
                mhp_default_online_type = online_type;

        return 1;
}
__setup("memhp_default_state=", setup_memhp_default_state);

void mem_hotplug_begin(void)
{
        cpus_read_lock();
        percpu_down_write(&mem_hotplug_lock);
}

void mem_hotplug_done(void)
{
        percpu_up_write(&mem_hotplug_lock);
        cpus_read_unlock();
}

u64 max_mem_size = U64_MAX;

/* add this memory to iomem resource */
static struct resource *register_memory_resource(u64 start, u64 size,
                                                 const char *resource_name)
{
        struct resource *res;
        unsigned long flags =  IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;

        if (strcmp(resource_name, "System RAM"))
                flags |= IORESOURCE_SYSRAM_DRIVER_MANAGED;

        if (!mhp_range_allowed(start, size, true))
                return ERR_PTR(-E2BIG);

        /*
         * Make sure value parsed from 'mem=' only restricts memory adding
         * while booting, so that memory hotplug won't be impacted. Please
         * refer to document of 'mem=' in kernel-parameters.txt for more
         * details.
         */
        if (start + size > max_mem_size && system_state < SYSTEM_RUNNING)
                return ERR_PTR(-E2BIG);

        /*
         * Request ownership of the new memory range.  This might be
         * a child of an existing resource that was present but
         * not marked as busy.
         */
        res = __request_region(&iomem_resource, start, size,
                               resource_name, flags);

        if (!res) {
                pr_debug("Unable to reserve System RAM region: %016llx->%016llx\n",
                                start, start + size);
                return ERR_PTR(-EEXIST);
        }
        return res;
}

static void release_memory_resource(struct resource *res)
{
        if (!res)
                return;
        release_resource(res);
        kfree(res);
}

static int check_pfn_span(unsigned long pfn, unsigned long nr_pages)
{
        /*
         * Disallow all operations smaller than a sub-section and only
         * allow operations smaller than a section for
         * SPARSEMEM_VMEMMAP. Note that check_hotplug_memory_range()
         * enforces a larger memory_block_size_bytes() granularity for
         * memory that will be marked online, so this check should only
         * fire for direct arch_{add,remove}_memory() users outside of
         * add_memory_resource().
         */
        unsigned long min_align;

        if (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP))
                min_align = PAGES_PER_SUBSECTION;
        else
                min_align = PAGES_PER_SECTION;
        if (!IS_ALIGNED(pfn | nr_pages, min_align))
                return -EINVAL;
        return 0;
}

/*
 * Return page for the valid pfn only if the page is online. All pfn
 * walkers which rely on the fully initialized page->flags and others
 * should use this rather than pfn_valid && pfn_to_page
 */
struct page *pfn_to_online_page(unsigned long pfn)
{
        unsigned long nr = pfn_to_section_nr(pfn);
        struct dev_pagemap *pgmap;
        struct mem_section *ms;

        if (nr >= NR_MEM_SECTIONS)
                return NULL;

        ms = __nr_to_section(nr);
        if (!online_section(ms))
                return NULL;

        /*
         * Save some code text when online_section() +
         * pfn_section_valid() are sufficient.
         */
        if (IS_ENABLED(CONFIG_HAVE_ARCH_PFN_VALID) && !pfn_valid(pfn))
                return NULL;

        if (!pfn_section_valid(ms, pfn))
                return NULL;

        if (!online_device_section(ms))
                return pfn_to_page(pfn);

        /*
         * Slowpath: when ZONE_DEVICE collides with
         * ZONE_{NORMAL,MOVABLE} within the same section some pfns in
         * the section may be 'offline' but 'valid'. Only
         * get_dev_pagemap() can determine sub-section online status.
         */
        pgmap = get_dev_pagemap(pfn, NULL);
        put_dev_pagemap(pgmap);

        /* The presence of a pgmap indicates ZONE_DEVICE offline pfn */
        if (pgmap)
                return NULL;

        return pfn_to_page(pfn);
}
EXPORT_SYMBOL_GPL(pfn_to_online_page);

int __ref __add_pages(int nid, unsigned long pfn, unsigned long nr_pages,
                struct mhp_params *params)
{
        const unsigned long end_pfn = pfn + nr_pages;
        unsigned long cur_nr_pages;
        int err;
        struct vmem_altmap *altmap = params->altmap;

        if (WARN_ON_ONCE(!pgprot_val(params->pgprot)))
                return -EINVAL;

        VM_BUG_ON(!mhp_range_allowed(PFN_PHYS(pfn), nr_pages * PAGE_SIZE, false));

        if (altmap) {
                /*
                 * Validate altmap is within bounds of the total request
                 */
                if (altmap->base_pfn != pfn
                                || vmem_altmap_offset(altmap) > nr_pages) {
                        pr_warn_once("memory add fail, invalid altmap\n");
                        return -EINVAL;
                }
                altmap->alloc = 0;
        }

        if (check_pfn_span(pfn, nr_pages)) {
                WARN(1, "Misaligned %s start: %#lx end: #%lx\n", __func__, pfn, pfn + nr_pages - 1);
                return -EINVAL;
        }

        for (; pfn < end_pfn; pfn += cur_nr_pages) {
                /* Select all remaining pages up to the next section boundary */
                cur_nr_pages = min(end_pfn - pfn,
                                   SECTION_ALIGN_UP(pfn + 1) - pfn);
                err = sparse_add_section(nid, pfn, cur_nr_pages, altmap,
                                         params->pgmap);
                if (err)
                        break;
                cond_resched();
        }
        vmemmap_populate_print_last();
        return err;
}

/* find the smallest valid pfn in the range [start_pfn, end_pfn) */
static unsigned long find_smallest_section_pfn(int nid, struct zone *zone,
                                     unsigned long start_pfn,
                                     unsigned long end_pfn)
{
        for (; start_pfn < end_pfn; start_pfn += PAGES_PER_SUBSECTION) {
                if (unlikely(!pfn_to_online_page(start_pfn)))
                        continue;

                if (unlikely(pfn_to_nid(start_pfn) != nid))
                        continue;

                if (zone != page_zone(pfn_to_page(start_pfn)))
                        continue;

                return start_pfn;
        }

        return 0;
}

/* find the biggest valid pfn in the range [start_pfn, end_pfn). */
static unsigned long find_biggest_section_pfn(int nid, struct zone *zone,
                                    unsigned long start_pfn,
                                    unsigned long end_pfn)
{
        unsigned long pfn;

        /* pfn is the end pfn of a memory section. */
        pfn = end_pfn - 1;
        for (; pfn >= start_pfn; pfn -= PAGES_PER_SUBSECTION) {
                if (unlikely(!pfn_to_online_page(pfn)))
                        continue;

                if (unlikely(pfn_to_nid(pfn) != nid))
                        continue;

                if (zone != page_zone(pfn_to_page(pfn)))
                        continue;

                return pfn;
        }

        return 0;
}

static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
                             unsigned long end_pfn)
{
        unsigned long pfn;
        int nid = zone_to_nid(zone);

        if (zone->zone_start_pfn == start_pfn) {
                /*
                 * If the section is smallest section in the zone, it need
                 * shrink zone->zone_start_pfn and zone->zone_spanned_pages.
                 * In this case, we find second smallest valid mem_section
                 * for shrinking zone.
                 */
                pfn = find_smallest_section_pfn(nid, zone, end_pfn,
                                                zone_end_pfn(zone));
                if (pfn) {
                        zone->spanned_pages = zone_end_pfn(zone) - pfn;
                        zone->zone_start_pfn = pfn;
                } else {
                        zone->zone_start_pfn = 0;
                        zone->spanned_pages = 0;
                }
        } else if (zone_end_pfn(zone) == end_pfn) {
                /*
                 * If the section is biggest section in the zone, it need
                 * shrink zone->spanned_pages.
                 * In this case, we find second biggest valid mem_section for
                 * shrinking zone.
                 */
                pfn = find_biggest_section_pfn(nid, zone, zone->zone_start_pfn,
                                               start_pfn);
                if (pfn)
                        zone->spanned_pages = pfn - zone->zone_start_pfn + 1;
                else {
                        zone->zone_start_pfn = 0;
                        zone->spanned_pages = 0;
                }
        }
}

static void update_pgdat_span(struct pglist_data *pgdat)
{
        unsigned long node_start_pfn = 0, node_end_pfn = 0;
        struct zone *zone;

        for (zone = pgdat->node_zones;
             zone < pgdat->node_zones + MAX_NR_ZONES; zone++) {
                unsigned long end_pfn = zone_end_pfn(zone);

                /* No need to lock the zones, they can't change. */
                if (!zone->spanned_pages)
                        continue;
                if (!node_end_pfn) {
                        node_start_pfn = zone->zone_start_pfn;
                        node_end_pfn = end_pfn;
                        continue;
                }

                if (end_pfn > node_end_pfn)
                        node_end_pfn = end_pfn;
                if (zone->zone_start_pfn < node_start_pfn)
                        node_start_pfn = zone->zone_start_pfn;
        }

        pgdat->node_start_pfn = node_start_pfn;
        pgdat->node_spanned_pages = node_end_pfn - node_start_pfn;
}

void __ref remove_pfn_range_from_zone(struct zone *zone,
                                      unsigned long start_pfn,
                                      unsigned long nr_pages)
{
        const unsigned long end_pfn = start_pfn + nr_pages;
        struct pglist_data *pgdat = zone->zone_pgdat;
        unsigned long pfn, cur_nr_pages;

        /* Poison struct pages because they are now uninitialized again. */
        for (pfn = start_pfn; pfn < end_pfn; pfn += cur_nr_pages) {
                cond_resched();

                /* Select all remaining pages up to the next section boundary */
                cur_nr_pages =
                        min(end_pfn - pfn, SECTION_ALIGN_UP(pfn + 1) - pfn);
                page_init_poison(pfn_to_page(pfn),
                                 sizeof(struct page) * cur_nr_pages);
        }

        /*
         * Zone shrinking code cannot properly deal with ZONE_DEVICE. So
         * we will not try to shrink the zones - which is okay as
         * set_zone_contiguous() cannot deal with ZONE_DEVICE either way.
         */
        if (zone_is_zone_device(zone))
                return;

        clear_zone_contiguous(zone);

        shrink_zone_span(zone, start_pfn, start_pfn + nr_pages);
        update_pgdat_span(pgdat);

        set_zone_contiguous(zone);
}

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

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

        sparse_remove_section(ms, pfn, nr_pages, map_offset, altmap);
}

/**
 * __remove_pages() - remove sections of pages
 * @pfn: starting pageframe (must be aligned to start of a section)
 * @nr_pages: number of pages to remove (must be multiple of section size)
 * @altmap: alternative device page map or %NULL if default memmap is used
 *
 * Generic helper function to remove section mappings and sysfs entries
 * for the section of the memory we are removing. Caller needs to make
 * sure that pages are marked reserved and zones are adjust properly by
 * calling offline_pages().
 */
void __remove_pages(unsigned long pfn, unsigned long nr_pages,
                    struct vmem_altmap *altmap)
{
        const unsigned long end_pfn = pfn + nr_pages;
        unsigned long cur_nr_pages;
        unsigned long map_offset = 0;

        map_offset = vmem_altmap_offset(altmap);

        if (check_pfn_span(pfn, nr_pages)) {
                WARN(1, "Misaligned %s start: %#lx end: #%lx\n", __func__, pfn, pfn + nr_pages - 1);
                return;
        }

        for (; pfn < end_pfn; pfn += cur_nr_pages) {
                cond_resched();
                /* Select all remaining pages up to the next section boundary */
                cur_nr_pages = min(end_pfn - pfn,
                                   SECTION_ALIGN_UP(pfn + 1) - pfn);
                __remove_section(pfn, cur_nr_pages, map_offset, altmap);
                map_offset = 0;
        }
}

int set_online_page_callback(online_page_callback_t callback)
{
        int rc = -EINVAL;

        get_online_mems();
        mutex_lock(&online_page_callback_lock);

        if (online_page_callback == generic_online_page) {
                online_page_callback = callback;
                rc = 0;
        }

        mutex_unlock(&online_page_callback_lock);
        put_online_mems();

        return rc;
}
EXPORT_SYMBOL_GPL(set_online_page_callback);

int restore_online_page_callback(online_page_callback_t callback)
{
        int rc = -EINVAL;

        get_online_mems();
        mutex_lock(&online_page_callback_lock);

        if (online_page_callback == callback) {
                online_page_callback = generic_online_page;
                rc = 0;
        }

        mutex_unlock(&online_page_callback_lock);
        put_online_mems();

        return rc;
}
EXPORT_SYMBOL_GPL(restore_online_page_callback);

void generic_online_page(struct page *page, unsigned int order)
{
        /*
         * Freeing the page with debug_pagealloc enabled will try to unmap it,
         * so we should map it first. This is better than introducing a special
         * case in page freeing fast path.
         */
        debug_pagealloc_map_pages(page, 1 << order);
        __free_pages_core(page, order);
        totalram_pages_add(1UL << order);
}
EXPORT_SYMBOL_GPL(generic_online_page);

static void online_pages_range(unsigned long start_pfn, unsigned long nr_pages)
{
        const unsigned long end_pfn = start_pfn + nr_pages;
        unsigned long pfn;

        /*
         * Online the pages in MAX_ORDER - 1 aligned chunks. The callback might
         * decide to not expose all pages to the buddy (e.g., expose them
         * later). We account all pages as being online and belonging to this
         * zone ("present").
         * When using memmap_on_memory, the range might not be aligned to
         * MAX_ORDER_NR_PAGES - 1, but pageblock aligned. __ffs() will detect
         * this and the first chunk to online will be pageblock_nr_pages.
         */
        for (pfn = start_pfn; pfn < end_pfn;) {
                int order = min(MAX_ORDER - 1UL, __ffs(pfn));

                (*online_page_callback)(pfn_to_page(pfn), order);
                pfn += (1UL << order);
        }

        /* mark all involved sections as online */
        online_mem_sections(start_pfn, end_pfn);
}

/* check which state of node_states will be changed when online memory */
static void node_states_check_changes_online(unsigned long nr_pages,
        struct zone *zone, struct memory_notify *arg)
{
        int nid = zone_to_nid(zone);

        arg->status_change_nid = NUMA_NO_NODE;
        arg->status_change_nid_normal = NUMA_NO_NODE;

        if (!node_state(nid, N_MEMORY))
                arg->status_change_nid = nid;
        if (zone_idx(zone) <= ZONE_NORMAL && !node_state(nid, N_NORMAL_MEMORY))
                arg->status_change_nid_normal = nid;
}

static void node_states_set_node(int node, struct memory_notify *arg)
{
        if (arg->status_change_nid_normal >= 0)
                node_set_state(node, N_NORMAL_MEMORY);

        if (arg->status_change_nid >= 0)
                node_set_state(node, N_MEMORY);
}

static void __meminit resize_zone_range(struct zone *zone, unsigned long start_pfn,
                unsigned long nr_pages)
{
        unsigned long old_end_pfn = zone_end_pfn(zone);

        if (zone_is_empty(zone) || start_pfn < zone->zone_start_pfn)
                zone->zone_start_pfn = start_pfn;

        zone->spanned_pages = max(start_pfn + nr_pages, old_end_pfn) - zone->zone_start_pfn;
}

static void __meminit resize_pgdat_range(struct pglist_data *pgdat, unsigned long start_pfn,
                                     unsigned long nr_pages)
{
        unsigned long old_end_pfn = pgdat_end_pfn(pgdat);

        if (!pgdat->node_spanned_pages || start_pfn < pgdat->node_start_pfn)
                pgdat->node_start_pfn = start_pfn;

        pgdat->node_spanned_pages = max(start_pfn + nr_pages, old_end_pfn) - pgdat->node_start_pfn;

}

#ifdef CONFIG_ZONE_DEVICE
static void section_taint_zone_device(unsigned long pfn)
{
        struct mem_section *ms = __pfn_to_section(pfn);

        ms->section_mem_map |= SECTION_TAINT_ZONE_DEVICE;
}
#else
static inline void section_taint_zone_device(unsigned long pfn)
{
}
#endif

/*
 * Associate the pfn range with the given zone, initializing the memmaps
 * and resizing the pgdat/zone data to span the added pages. After this
 * call, all affected pages are PG_reserved.
 *
 * All aligned pageblocks are initialized to the specified migratetype
 * (usually MIGRATE_MOVABLE). Besides setting the migratetype, no related
 * zone stats (e.g., nr_isolate_pageblock) are touched.
 */
void __ref move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
                                  unsigned long nr_pages,
                                  struct vmem_altmap *altmap, int migratetype)
{
        struct pglist_data *pgdat = zone->zone_pgdat;
        int nid = pgdat->node_id;

        clear_zone_contiguous(zone);

        if (zone_is_empty(zone))
                init_currently_empty_zone(zone, start_pfn, nr_pages);
        resize_zone_range(zone, start_pfn, nr_pages);
        resize_pgdat_range(pgdat, start_pfn, nr_pages);

        /*
         * Subsection population requires care in pfn_to_online_page().
         * Set the taint to enable the slow path detection of
         * ZONE_DEVICE pages in an otherwise  ZONE_{NORMAL,MOVABLE}
         * section.
         */
        if (zone_is_zone_device(zone)) {
                if (!IS_ALIGNED(start_pfn, PAGES_PER_SECTION))
                        section_taint_zone_device(start_pfn);
                if (!IS_ALIGNED(start_pfn + nr_pages, PAGES_PER_SECTION))
                        section_taint_zone_device(start_pfn + nr_pages);
        }

        /*
         * TODO now we have a visible range of pages which are not associated
         * with their zone properly. Not nice but set_pfnblock_flags_mask
         * expects the zone spans the pfn range. All the pages in the range
         * are reserved so nobody should be touching them so we should be safe
         */
        memmap_init_range(nr_pages, nid, zone_idx(zone), start_pfn, 0,
                         MEMINIT_HOTPLUG, altmap, migratetype);

        set_zone_contiguous(zone);
}

struct auto_movable_stats {
        unsigned long kernel_early_pages;
        unsigned long movable_pages;
};

static void auto_movable_stats_account_zone(struct auto_movable_stats *stats,
                                            struct zone *zone)
{
        if (zone_idx(zone) == ZONE_MOVABLE) {
                stats->movable_pages += zone->present_pages;
        } else {
                stats->kernel_early_pages += zone->present_early_pages;
#ifdef CONFIG_CMA
                /*
                 * CMA pages (never on hotplugged memory) behave like
                 * ZONE_MOVABLE.
                 */
                stats->movable_pages += zone->cma_pages;
                stats->kernel_early_pages -= zone->cma_pages;
#endif /* CONFIG_CMA */
        }
}
struct auto_movable_group_stats {
        unsigned long movable_pages;
        unsigned long req_kernel_early_pages;
};

static int auto_movable_stats_account_group(struct memory_group *group,
                                           void *arg)
{
        const int ratio = READ_ONCE(auto_movable_ratio);
        struct auto_movable_group_stats *stats = arg;
        long pages;

        /*
         * We don't support modifying the config while the auto-movable online
         * policy is already enabled. Just avoid the division by zero below.
         */
        if (!ratio)
                return 0;

        /*
         * Calculate how many early kernel pages this group requires to
         * satisfy the configured zone ratio.
         */
        pages = group->present_movable_pages * 100 / ratio;
        pages -= group->present_kernel_pages;

        if (pages > 0)
                stats->req_kernel_early_pages += pages;
        stats->movable_pages += group->present_movable_pages;
        return 0;
}

static bool auto_movable_can_online_movable(int nid, struct memory_group *group,
                                            unsigned long nr_pages)
{
        unsigned long kernel_early_pages, movable_pages;
        struct auto_movable_group_stats group_stats = {};
        struct auto_movable_stats stats = {};
        pg_data_t *pgdat = NODE_DATA(nid);
        struct zone *zone;
        int i;

        /* Walk all relevant zones and collect MOVABLE vs. KERNEL stats. */
        if (nid == NUMA_NO_NODE) {
                /* TODO: cache values */
                for_each_populated_zone(zone)
                        auto_movable_stats_account_zone(&stats, zone);
        } else {
                for (i = 0; i < MAX_NR_ZONES; i++) {
                        zone = pgdat->node_zones + i;
                        if (populated_zone(zone))
                                auto_movable_stats_account_zone(&stats, zone);
                }
        }

        kernel_early_pages = stats.kernel_early_pages;
        movable_pages = stats.movable_pages;

        /*
         * Kernel memory inside dynamic memory group allows for more MOVABLE
         * memory within the same group. Remove the effect of all but the
         * current group from the stats.
         */
        walk_dynamic_memory_groups(nid, auto_movable_stats_account_group,
                                   group, &group_stats);
        if (kernel_early_pages <= group_stats.req_kernel_early_pages)
                return false;
        kernel_early_pages -= group_stats.req_kernel_early_pages;
        movable_pages -= group_stats.movable_pages;

        if (group && group->is_dynamic)
                kernel_early_pages += group->present_kernel_pages;

        /*
         * Test if we could online the given number of pages to ZONE_MOVABLE
         * and still stay in the configured ratio.
         */
        movable_pages += nr_pages;
        return movable_pages <= (auto_movable_ratio * kernel_early_pages) / 100;
}

/*
 * Returns a default kernel memory zone for the given pfn range.
 * If no kernel zone covers this pfn range it will automatically go
 * to the ZONE_NORMAL.
 */
static struct zone *default_kernel_zone_for_pfn(int nid, unsigned long start_pfn,
                unsigned long nr_pages)
{
        struct pglist_data *pgdat = NODE_DATA(nid);
        int zid;

        for (zid = 0; zid < ZONE_NORMAL; zid++) {
                struct zone *zone = &pgdat->node_zones[zid];

                if (zone_intersects(zone, start_pfn, nr_pages))
                        return zone;
        }

        return &pgdat->node_zones[ZONE_NORMAL];
}

/*
 * Determine to which zone to online memory dynamically based on user
 * configuration and system stats. We care about the following ratio:
 *
 *   MOVABLE : KERNEL
 *
 * Whereby MOVABLE is memory in ZONE_MOVABLE and KERNEL is memory in
 * one of the kernel zones. CMA pages inside one of the kernel zones really
 * behaves like ZONE_MOVABLE, so we treat them accordingly.
 *
 * We don't allow for hotplugged memory in a KERNEL zone to increase the
 * amount of MOVABLE memory we can have, so we end up with:
 *
 *   MOVABLE : KERNEL_EARLY
 *
 * Whereby KERNEL_EARLY is memory in one of the kernel zones, available sinze
 * boot. We base our calculation on KERNEL_EARLY internally, because:
 *
 * a) Hotplugged memory in one of the kernel zones can sometimes still get
 *    hotunplugged, especially when hot(un)plugging individual memory blocks.
 *    There is no coordination across memory devices, therefore "automatic"
 *    hotunplugging, as implemented in hypervisors, could result in zone
 *    imbalances.
 * b) Early/boot memory in one of the kernel zones can usually not get
 *    hotunplugged again (e.g., no firmware interface to unplug, fragmented
 *    with unmovable allocations). While there are corner cases where it might
 *    still work, it is barely relevant in practice.
 *
 * Exceptions are dynamic memory groups, which allow for more MOVABLE
 * memory within the same memory group -- because in that case, there is
 * coordination within the single memory device managed by a single driver.
 *
 * We rely on "present pages" instead of "managed pages", as the latter is
 * highly unreliable and dynamic in virtualized environments, and does not
 * consider boot time allocations. For example, memory ballooning adjusts the
 * managed pages when inflating/deflating the balloon, and balloon compaction
 * can even migrate inflated pages between zones.
 *
 * Using "present pages" is better but some things to keep in mind are:
 *
 * a) Some memblock allocations, such as for the crashkernel area, are
 *    effectively unused by the kernel, yet they account to "present pages".
 *    Fortunately, these allocations are comparatively small in relevant setups
 *    (e.g., fraction of system memory).
 * b) Some hotplugged memory blocks in virtualized environments, esecially
 *    hotplugged by virtio-mem, look like they are completely present, however,
 *    only parts of the memory block are actually currently usable.
 *    "present pages" is an upper limit that can get reached at runtime. As
 *    we base our calculations on KERNEL_EARLY, this is not an issue.
 */
static struct zone *auto_movable_zone_for_pfn(int nid,
                                              struct memory_group *group,
                                              unsigned long pfn,
                                              unsigned long nr_pages)
{
        unsigned long online_pages = 0, max_pages, end_pfn;
        struct page *page;

        if (!auto_movable_ratio)
                goto kernel_zone;

        if (group && !group->is_dynamic) {
                max_pages = group->s.max_pages;
                online_pages = group->present_movable_pages;

                /* If anything is !MOVABLE online the rest !MOVABLE. */
                if (group->present_kernel_pages)
                        goto kernel_zone;
        } else if (!group || group->d.unit_pages == nr_pages) {
                max_pages = nr_pages;
        } else {
                max_pages = group->d.unit_pages;
                /*
                 * Take a look at all online sections in the current unit.
                 * We can safely assume that all pages within a section belong
                 * to the same zone, because dynamic memory groups only deal
                 * with hotplugged memory.
                 */
                pfn = ALIGN_DOWN(pfn, group->d.unit_pages);
                end_pfn = pfn + group->d.unit_pages;
                for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
                        page = pfn_to_online_page(pfn);
                        if (!page)
                                continue;
                        /* If anything is !MOVABLE online the rest !MOVABLE. */
                        if (!is_zone_movable_page(page))
                                goto kernel_zone;
                        online_pages += PAGES_PER_SECTION;
                }
        }

        /*
         * Online MOVABLE if we could *currently* online all remaining parts
         * MOVABLE. We expect to (add+) online them immediately next, so if
         * nobody interferes, all will be MOVABLE if possible.
         */
        nr_pages = max_pages - online_pages;
        if (!auto_movable_can_online_movable(NUMA_NO_NODE, group, nr_pages))
                goto kernel_zone;

#ifdef CONFIG_NUMA
        if (auto_movable_numa_aware &&
            !auto_movable_can_online_movable(nid, group, nr_pages))
                goto kernel_zone;
#endif /* CONFIG_NUMA */

        return &NODE_DATA(nid)->node_zones[ZONE_MOVABLE];
kernel_zone:
        return default_kernel_zone_for_pfn(nid, pfn, nr_pages);
}

static inline struct zone *default_zone_for_pfn(int nid, unsigned long start_pfn,
                unsigned long nr_pages)
{
        struct zone *kernel_zone = default_kernel_zone_for_pfn(nid, start_pfn,
                        nr_pages);
        struct zone *movable_zone = &NODE_DATA(nid)->node_zones[ZONE_MOVABLE];
        bool in_kernel = zone_intersects(kernel_zone, start_pfn, nr_pages);
        bool in_movable = zone_intersects(movable_zone, start_pfn, nr_pages);

        /*
         * We inherit the existing zone in a simple case where zones do not
         * overlap in the given range
         */
        if (in_kernel ^ in_movable)
                return (in_kernel) ? kernel_zone : movable_zone;

        /*
         * If the range doesn't belong to any zone or two zones overlap in the
         * given range then we use movable zone only if movable_node is
         * enabled because we always online to a kernel zone by default.
         */
        return movable_node_enabled ? movable_zone : kernel_zone;
}

struct zone *zone_for_pfn_range(int online_type, int nid,
                struct memory_group *group, unsigned long start_pfn,
                unsigned long nr_pages)
{
        if (online_type == MMOP_ONLINE_KERNEL)
                return default_kernel_zone_for_pfn(nid, start_pfn, nr_pages);

        if (online_type == MMOP_ONLINE_MOVABLE)
                return &NODE_DATA(nid)->node_zones[ZONE_MOVABLE];

        if (online_policy == ONLINE_POLICY_AUTO_MOVABLE)
                return auto_movable_zone_for_pfn(nid, group, start_pfn, nr_pages);

        return default_zone_for_pfn(nid, start_pfn, nr_pages);
}

/*
 * This function should only be called by memory_block_{online,offline},
 * and {online,offline}_pages.
 */
void adjust_present_page_count(struct page *page, struct memory_group *group,
                               long nr_pages)
{
        struct zone *zone = page_zone(page);
        const bool movable = zone_idx(zone) == ZONE_MOVABLE;

        /*
         * We only support onlining/offlining/adding/removing of complete
         * memory blocks; therefore, either all is either early or hotplugged.
         */
        if (early_section(__pfn_to_section(page_to_pfn(page))))
                zone->present_early_pages += nr_pages;
        zone->present_pages += nr_pages;
        zone->zone_pgdat->node_present_pages += nr_pages;

        if (group && movable)
                group->present_movable_pages += nr_pages;
        else if (group && !movable)
                group->present_kernel_pages += nr_pages;
}

int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
                              struct zone *zone)
{
        unsigned long end_pfn = pfn + nr_pages;
        int ret, i;

        ret = kasan_add_zero_shadow(__va(PFN_PHYS(pfn)), PFN_PHYS(nr_pages));
        if (ret)
                return ret;

        move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_UNMOVABLE);

        for (i = 0; i < nr_pages; i++)
                SetPageVmemmapSelfHosted(pfn_to_page(pfn + i));

        /*
         * It might be that the vmemmap_pages fully span sections. If that is
         * the case, mark those sections online here as otherwise they will be
         * left offline.
         */
        if (nr_pages >= PAGES_PER_SECTION)
                online_mem_sections(pfn, ALIGN_DOWN(end_pfn, PAGES_PER_SECTION));

        return ret;
}

void mhp_deinit_memmap_on_memory(unsigned long pfn, unsigned long nr_pages)
{
        unsigned long end_pfn = pfn + nr_pages;

        /*
         * It might be that the vmemmap_pages fully span sections. If that is
         * the case, mark those sections offline here as otherwise they will be
         * left online.
         */
        if (nr_pages >= PAGES_PER_SECTION)
                offline_mem_sections(pfn, ALIGN_DOWN(end_pfn, PAGES_PER_SECTION));

        /*
         * The pages associated with this vmemmap have been offlined, so
         * we can reset its state here.
         */
        remove_pfn_range_from_zone(page_zone(pfn_to_page(pfn)), pfn, nr_pages);
        kasan_remove_zero_shadow(__va(PFN_PHYS(pfn)), PFN_PHYS(nr_pages));
}

int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
                       struct zone *zone, struct memory_group *group)
{
        unsigned long flags;
        int need_zonelists_rebuild = 0;
        const int nid = zone_to_nid(zone);
        int ret;
        struct memory_notify arg;

        /*
         * {on,off}lining is constrained to full memory sections (or more
         * precisely to memory blocks from the user space POV).
         * memmap_on_memory is an exception because it reserves initial part
         * of the physical memory space for vmemmaps. That space is pageblock
         * aligned.
         */
        if (WARN_ON_ONCE(!nr_pages ||
                         !IS_ALIGNED(pfn, pageblock_nr_pages) ||
                         !IS_ALIGNED(pfn + nr_pages, PAGES_PER_SECTION)))
                return -EINVAL;

        mem_hotplug_begin();

        /* associate pfn range with the zone */
        move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_ISOLATE);

        arg.start_pfn = pfn;
        arg.nr_pages = nr_pages;
        node_states_check_changes_online(nr_pages, zone, &arg);

        ret = memory_notify(MEM_GOING_ONLINE, &arg);
        ret = notifier_to_errno(ret);
        if (ret)
                goto failed_addition;

        /*
         * Fixup the number of isolated pageblocks before marking the sections
         * onlining, such that undo_isolate_page_range() works correctly.
         */
        spin_lock_irqsave(&zone->lock, flags);
        zone->nr_isolate_pageblock += nr_pages / pageblock_nr_pages;
        spin_unlock_irqrestore(&zone->lock, flags);

        /*
         * If this zone is not populated, then it is not in zonelist.
         * This means the page allocator ignores this zone.
         * So, zonelist must be updated after online.
         */
        if (!populated_zone(zone)) {
                need_zonelists_rebuild = 1;
                setup_zone_pageset(zone);
        }

        online_pages_range(pfn, nr_pages);
        adjust_present_page_count(pfn_to_page(pfn), group, nr_pages);

        node_states_set_node(nid, &arg);
        if (need_zonelists_rebuild)
                build_all_zonelists(NULL);

        /* Basic onlining is complete, allow allocation of onlined pages. */
        undo_isolate_page_range(pfn, pfn + nr_pages, MIGRATE_MOVABLE);

        /*
         * Freshly onlined pages aren't shuffled (e.g., all pages are placed to
         * the tail of the freelist when undoing isolation). Shuffle the whole
         * zone to make sure the just onlined pages are properly distributed
         * across the whole freelist - to create an initial shuffle.
         */
        shuffle_zone(zone);

        /* reinitialise watermarks and update pcp limits */
        init_per_zone_wmark_min();

        kswapd_run(nid);
        kcompactd_run(nid);

        writeback_set_ratelimit();

        memory_notify(MEM_ONLINE, &arg);
        mem_hotplug_done();
        return 0;

failed_addition:
        pr_debug("online_pages [mem %#010llx-%#010llx] failed\n",
                 (unsigned long long) pfn << PAGE_SHIFT,
                 (((unsigned long long) pfn + nr_pages) << PAGE_SHIFT) - 1);
        memory_notify(MEM_CANCEL_ONLINE, &arg);
        remove_pfn_range_from_zone(zone, pfn, nr_pages);
        mem_hotplug_done();
        return ret;
}

static void reset_node_present_pages(pg_data_t *pgdat)
{
        struct zone *z;

        for (z = pgdat->node_zones; z < pgdat->node_zones + MAX_NR_ZONES; z++)
                z->present_pages = 0;

        pgdat->node_present_pages = 0;
}

/* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
static pg_data_t __ref *hotadd_init_pgdat(int nid)
{
        struct pglist_data *pgdat;

        /*
         * NODE_DATA is preallocated (free_area_init) but its internal
         * state is not allocated completely. Add missing pieces.
         * Completely offline nodes stay around and they just need
         * reintialization.
         */
        pgdat = NODE_DATA(nid);

        /* init node's zones as empty zones, we don't have any present pages.*/
        free_area_init_core_hotplug(pgdat);

        /*
         * The node we allocated has no zone fallback lists. For avoiding
         * to access not-initialized zonelist, build here.
         */
        build_all_zonelists(pgdat);

        /*
         * When memory is hot-added, all the memory is in offline state. So
         * clear all zones' present_pages because they will be updated in
         * online_pages() and offline_pages().
         * TODO: should be in free_area_init_core_hotplug?
         */
        reset_node_managed_pages(pgdat);
        reset_node_present_pages(pgdat);

        return pgdat;
}

/*
 * __try_online_node - online a node if offlined
 * @nid: the node ID
 * @set_node_online: Whether we want to online the node
 * called by cpu_up() to online a node without onlined memory.
 *
 * Returns:
 * 1 -> a new node has been allocated
 * 0 -> the node is already online
 * -ENOMEM -> the node could not be allocated
 */
static int __try_online_node(int nid, bool set_node_online)
{
        pg_data_t *pgdat;
        int ret = 1;

        if (node_online(nid))
                return 0;

        pgdat = hotadd_init_pgdat(nid);
        if (!pgdat) {
                pr_err("Cannot online node %d due to NULL pgdat\n", nid);
                ret = -ENOMEM;
                goto out;
        }

        if (set_node_online) {
                node_set_online(nid);
                ret = register_one_node(nid);
                BUG_ON(ret);
        }
out:
        return ret;
}

/*
 * Users of this function always want to online/register the node
 */
int try_online_node(int nid)
{
        int ret;

        mem_hotplug_begin();
        ret =  __try_online_node(nid, true);
        mem_hotplug_done();
        return ret;
}

static int check_hotplug_memory_range(u64 start, u64 size)
{
        /* memory range must be block size aligned */
        if (!size || !IS_ALIGNED(start, memory_block_size_bytes()) ||
            !IS_ALIGNED(size, memory_block_size_bytes())) {
                pr_err("Block size [%#lx] unaligned hotplug range: start %#llx, size %#llx",
                       memory_block_size_bytes(), start, size);
                return -EINVAL;
        }

        return 0;
}

static int online_memory_block(struct memory_block *mem, void *arg)
{
        mem->online_type = mhp_default_online_type;
        return device_online(&mem->dev);
}

bool mhp_supports_memmap_on_memory(unsigned long size)
{
        unsigned long nr_vmemmap_pages = size / PAGE_SIZE;
        unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page);
        unsigned long remaining_size = size - vmemmap_size;

        /*
         * Besides having arch support and the feature enabled at runtime, we
         * need a few more assumptions to hold true:
         *
         * a) We span a single memory block: memory onlining/offlinin;g happens
         *    in memory block granularity. We don't want the vmemmap of online
         *    memory blocks to reside on offline memory blocks. In the future,
         *    we might want to support variable-sized memory blocks to make the
         *    feature more versatile.
         *
         * b) The vmemmap pages span complete PMDs: We don't want vmemmap code
         *    to populate memory from the altmap for unrelated parts (i.e.,
         *    other memory blocks)
         *
         * c) The vmemmap pages (and thereby the pages that will be exposed to
         *    the buddy) have to cover full pageblocks: memory onlining/offlining
         *    code requires applicable ranges to be page-aligned, for example, to
         *    set the migratetypes properly.
         *
         * TODO: Although we have a check here to make sure that vmemmap pages
         *       fully populate a PMD, it is not the right place to check for
         *       this. A much better solution involves improving vmemmap code
         *       to fallback to base pages when trying to populate vmemmap using
         *       altmap as an alternative source of memory, and we do not exactly
         *       populate a single PMD.
         */
        return mhp_memmap_on_memory() &&
               size == memory_block_size_bytes() &&
               IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
               IS_ALIGNED(remaining_size, (pageblock_nr_pages << PAGE_SHIFT));
}

/*
 * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
 * and online/offline operations (triggered e.g. by sysfs).
 *
 * we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG
 */
int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
{
        struct mhp_params params = { .pgprot = pgprot_mhp(PAGE_KERNEL) };
        enum memblock_flags memblock_flags = MEMBLOCK_NONE;
        struct vmem_altmap mhp_altmap = {};
        struct memory_group *group = NULL;
        u64 start, size;
        bool new_node = false;
        int ret;

        start = res->start;
        size = resource_size(res);

        ret = check_hotplug_memory_range(start, size);
        if (ret)
                return ret;

        if (mhp_flags & MHP_NID_IS_MGID) {
                group = memory_group_find_by_id(nid);
                if (!group)
                        return -EINVAL;
                nid = group->nid;
        }

        if (!node_possible(nid)) {
                WARN(1, "node %d was absent from the node_possible_map\n", nid);
                return -EINVAL;
        }

        mem_hotplug_begin();

        if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK)) {
                if (res->flags & IORESOURCE_SYSRAM_DRIVER_MANAGED)
                        memblock_flags = MEMBLOCK_DRIVER_MANAGED;
                ret = memblock_add_node(start, size, nid, memblock_flags);
                if (ret)
                        goto error_mem_hotplug_end;
        }

        ret = __try_online_node(nid, false);
        if (ret < 0)
                goto error;
        new_node = ret;

        /*
         * Self hosted memmap array
         */
        if (mhp_flags & MHP_MEMMAP_ON_MEMORY) {
                if (!mhp_supports_memmap_on_memory(size)) {
                        ret = -EINVAL;
                        goto error;
                }
                mhp_altmap.free = PHYS_PFN(size);
                mhp_altmap.base_pfn = PHYS_PFN(start);
                params.altmap = &mhp_altmap;
        }

        /* call arch's memory hotadd */
        ret = arch_add_memory(nid, start, size, &params);
        if (ret < 0)
                goto error;

        /* create memory block devices after memory was added */
        ret = create_memory_block_devices(start, size, mhp_altmap.alloc,
                                          group);
        if (ret) {
                arch_remove_memory(start, size, NULL);
                goto error;
        }

        if (new_node) {
                /* If sysfs file of new node can't be created, cpu on the node
                 * can't be hot-added. There is no rollback way now.
                 * So, check by BUG_ON() to catch it reluctantly..
                 * We online node here. We can't roll back from here.
                 */
                node_set_online(nid);
                ret = __register_one_node(nid);
                BUG_ON(ret);
        }

        register_memory_blocks_under_node(nid, PFN_DOWN(start),
                                          PFN_UP(start + size - 1),
                                          MEMINIT_HOTPLUG);

        /* create new memmap entry */
        if (!strcmp(res->name, "System RAM"))
                firmware_map_add_hotplug(start, start + size, "System RAM");

        /* device_online() will take the lock when calling online_pages() */
        mem_hotplug_done();

        /*
         * In case we're allowed to merge the resource, flag it and trigger
         * merging now that adding succeeded.
         */
        if (mhp_flags & MHP_MERGE_RESOURCE)
                merge_system_ram_resource(res);

        /* online pages if requested */
        if (mhp_default_online_type != MMOP_OFFLINE)
                walk_memory_blocks(start, size, NULL, online_memory_block);

        return ret;
error:
        if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK))
                memblock_remove(start, size);
error_mem_hotplug_end:
        mem_hotplug_done();
        return ret;
}

/* requires device_hotplug_lock, see add_memory_resource() */
int __ref __add_memory(int nid, u64 start, u64 size, mhp_t mhp_flags)
{
        struct resource *res;
        int ret;

        res = register_memory_resource(start, size, "System RAM");
        if (IS_ERR(res))
                return PTR_ERR(res);

        ret = add_memory_resource(nid, res, mhp_flags);
        if (ret < 0)
                release_memory_resource(res);
        return ret;
}

int add_memory(int nid, u64 start, u64 size, mhp_t mhp_flags)
{
        int rc;

        lock_device_hotplug();
        rc = __add_memory(nid, start, size, mhp_flags);
        unlock_device_hotplug();

        return rc;
}
EXPORT_SYMBOL_GPL(add_memory);

/*
 * Add special, driver-managed memory to the system as system RAM. Such
 * memory is not exposed via the raw firmware-provided memmap as system
 * RAM, instead, it is detected and added by a driver - during cold boot,
 * after a reboot, and after kexec.
 *
 * Reasons why this memory should not be used for the initial memmap of a
 * kexec kernel or for placing kexec images:
 * - The booting kernel is in charge of determining how this memory will be
 *   used (e.g., use persistent memory as system RAM)
 * - Coordination with a hypervisor is required before this memory
 *   can be used (e.g., inaccessible parts).
 *
 * For this memory, no entries in /sys/firmware/memmap ("raw firmware-provided
 * memory map") are created. Also, the created memory resource is flagged
 * with IORESOURCE_SYSRAM_DRIVER_MANAGED, so in-kernel users can special-case
 * this memory as well (esp., not place kexec images onto it).
 *
 * The resource_name (visible via /proc/iomem) has to have the format
 * "System RAM ($DRIVER)".
 */
int add_memory_driver_managed(int nid, u64 start, u64 size,
                              const char *resource_name, mhp_t mhp_flags)
{
        struct resource *res;
        int rc;

        if (!resource_name ||
            strstr(resource_name, "System RAM (") != resource_name ||
            resource_name[strlen(resource_name) - 1] != ')')
                return -EINVAL;

        lock_device_hotplug();

        res = register_memory_resource(start, size, resource_name);
        if (IS_ERR(res)) {
                rc = PTR_ERR(res);
                goto out_unlock;
        }

        rc = add_memory_resource(nid, res, mhp_flags);
        if (rc < 0)
                release_memory_resource(res);

out_unlock:
        unlock_device_hotplug();
        return rc;
}
EXPORT_SYMBOL_GPL(add_memory_driver_managed);

/*
 * Platforms should define arch_get_mappable_range() that provides
 * maximum possible addressable physical memory range for which the
 * linear mapping could be created. The platform returned address
 * range must adhere to these following semantics.
 *
 * - range.start <= range.end
 * - Range includes both end points [range.start..range.end]
 *
 * There is also a fallback definition provided here, allowing the
 * entire possible physical address range in case any platform does
 * not define arch_get_mappable_range().
 */
struct range __weak arch_get_mappable_range(void)
{
        struct range mhp_range = {
                .start = 0UL,
                .end = -1ULL,
        };
        return mhp_range;
}

struct range mhp_get_pluggable_range(bool need_mapping)
{
        const u64 max_phys = (1ULL << MAX_PHYSMEM_BITS) - 1;
        struct range mhp_range;

        if (need_mapping) {
                mhp_range = arch_get_mappable_range();
                if (mhp_range.start > max_phys) {
                        mhp_range.start = 0;
                        mhp_range.end = 0;
                }
                mhp_range.end = min_t(u64, mhp_range.end, max_phys);
        } else {
                mhp_range.start = 0;
                mhp_range.end = max_phys;
        }
        return mhp_range;
}
EXPORT_SYMBOL_GPL(mhp_get_pluggable_range);

bool mhp_range_allowed(u64 start, u64 size, bool need_mapping)
{
        struct range mhp_range = mhp_get_pluggable_range(need_mapping);
        u64 end = start + size;

        if (start < end && start >= mhp_range.start && (end - 1) <= mhp_range.end)
                return true;

        pr_warn("Hotplug memory [%#llx-%#llx] exceeds maximum addressable range [%#llx-%#llx]\n",
                start, end, mhp_range.start, mhp_range.end);
        return false;
}

#ifdef CONFIG_MEMORY_HOTREMOVE
/*
 * Scan pfn range [start,end) to find movable/migratable pages (LRU pages,
 * non-lru movable pages and hugepages). Will skip over most unmovable
 * pages (esp., pages that can be skipped when offlining), but bail out on
 * definitely unmovable pages.
 *
 * Returns:
 *      0 in case a movable page is found and movable_pfn was updated.
 *      -ENOENT in case no movable page was found.
 *      -EBUSY in case a definitely unmovable page was found.
 */
static int scan_movable_pages(unsigned long start, unsigned long end,
                              unsigned long *movable_pfn)
{
        unsigned long pfn;

        for (pfn = start; pfn < end; pfn++) {
                struct page *page, *head;
                unsigned long skip;

                if (!pfn_valid(pfn))
                        continue;
                page = pfn_to_page(pfn);
                if (PageLRU(page))
                        goto found;
                if (__PageMovable(page))
                        goto found;

                /*
                 * PageOffline() pages that are not marked __PageMovable() and
                 * have a reference count > 0 (after MEM_GOING_OFFLINE) are
                 * definitely unmovable. If their reference count would be 0,
                 * they could at least be skipped when offlining memory.
                 */
                if (PageOffline(page) && page_count(page))
                        return -EBUSY;

                if (!PageHuge(page))
                        continue;
                head = compound_head(page);
                /*
                 * This test is racy as we hold no reference or lock.  The
                 * hugetlb page could have been free'ed and head is no longer
                 * a hugetlb page before the following check.  In such unlikely
                 * cases false positives and negatives are possible.  Calling
                 * code must deal with these scenarios.
                 */
                if (HPageMigratable(head))
                        goto found;
                skip = compound_nr(head) - (page - head);
                pfn += skip - 1;
        }
        return -ENOENT;
found:
        *movable_pfn = pfn;
        return 0;
}

static int
do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
{
        unsigned long pfn;
        struct page *page, *head;
        int ret = 0;
        LIST_HEAD(source);
        static DEFINE_RATELIMIT_STATE(migrate_rs, DEFAULT_RATELIMIT_INTERVAL,
                                      DEFAULT_RATELIMIT_BURST);

        for (pfn = start_pfn; pfn < end_pfn; pfn++) {
                struct folio *folio;

                if (!pfn_valid(pfn))
                        continue;
                page = pfn_to_page(pfn);
                folio = page_folio(page);
                head = &folio->page;

                if (PageHuge(page)) {
                        pfn = page_to_pfn(head) + compound_nr(head) - 1;
                        isolate_hugetlb(head, &source);
                        continue;
                } else if (PageTransHuge(page))
                        pfn = page_to_pfn(head) + thp_nr_pages(page) - 1;

                /*
                 * HWPoison pages have elevated reference counts so the migration would
                 * fail on them. It also doesn't make any sense to migrate them in the
                 * first place. Still try to unmap such a page in case it is still mapped
                 * (e.g. current hwpoison implementation doesn't unmap KSM pages but keep
                 * the unmap as the catch all safety net).
                 */
                if (PageHWPoison(page)) {
                        if (WARN_ON(folio_test_lru(folio)))
                                folio_isolate_lru(folio);
                        if (folio_mapped(folio))
                                try_to_unmap(folio, TTU_IGNORE_MLOCK);
                        continue;
                }

                if (!get_page_unless_zero(page))
                        continue;
                /*
                 * We can skip free pages. And we can deal with pages on
                 * LRU and non-lru movable pages.
                 */
                if (PageLRU(page))
                        ret = isolate_lru_page(page);
                else
                        ret = isolate_movable_page(page, ISOLATE_UNEVICTABLE);
                if (!ret) { /* Success */
                        list_add_tail(&page->lru, &source);
                        if (!__PageMovable(page))
                                inc_node_page_state(page, NR_ISOLATED_ANON +
                                                    page_is_file_lru(page));

                } else {
                        if (__ratelimit(&migrate_rs)) {
                                pr_warn("failed to isolate pfn %lx\n", pfn);
                                dump_page(page, "isolation failed");
                        }
                }
                put_page(page);
        }
        if (!list_empty(&source)) {
                nodemask_t nmask = node_states[N_MEMORY];
                struct migration_target_control mtc = {
                        .nmask = &nmask,
                        .gfp_mask = GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL,
                };

                /*
                 * We have checked that migration range is on a single zone so
                 * we can use the nid of the first page to all the others.
                 */
                mtc.nid = page_to_nid(list_first_entry(&source, struct page, lru));

                /*
                 * try to allocate from a different node but reuse this node
                 * if there are no other online nodes to be used (e.g. we are
                 * offlining a part of the only existing node)
                 */
                node_clear(mtc.nid, nmask);
                if (nodes_empty(nmask))
                        node_set(mtc.nid, nmask);
                ret = migrate_pages(&source, alloc_migration_target, NULL,
                        (unsigned long)&mtc, MIGRATE_SYNC, MR_MEMORY_HOTPLUG, NULL);
                if (ret) {
                        list_for_each_entry(page, &source, lru) {
                                if (__ratelimit(&migrate_rs)) {
                                        pr_warn("migrating pfn %lx failed ret:%d\n",
                                                page_to_pfn(page), ret);
                                        dump_page(page, "migration failure");
                                }
                        }
                        putback_movable_pages(&source);
                }
        }

        return ret;
}

static int __init cmdline_parse_movable_node(char *p)
{
        movable_node_enabled = true;
        return 0;
}
early_param("movable_node", cmdline_parse_movable_node);

/* check which state of node_states will be changed when offline memory */
static void node_states_check_changes_offline(unsigned long nr_pages,
                struct zone *zone, struct memory_notify *arg)
{
        struct pglist_data *pgdat = zone->zone_pgdat;
        unsigned long present_pages = 0;
        enum zone_type zt;

        arg->status_change_nid = NUMA_NO_NODE;
        arg->status_change_nid_normal = NUMA_NO_NODE;

        /*
         * Check whether node_states[N_NORMAL_MEMORY] will be changed.
         * If the memory to be offline is within the range
         * [0..ZONE_NORMAL], and it is the last present memory there,
         * the zones in that range will become empty after the offlining,
         * thus we can determine that we need to clear the node from
         * node_states[N_NORMAL_MEMORY].
         */
        for (zt = 0; zt <= ZONE_NORMAL; zt++)
                present_pages += pgdat->node_zones[zt].present_pages;
        if (zone_idx(zone) <= ZONE_NORMAL && nr_pages >= present_pages)
                arg->status_change_nid_normal = zone_to_nid(zone);

        /*
         * We have accounted the pages from [0..ZONE_NORMAL); ZONE_HIGHMEM
         * does not apply as we don't support 32bit.
         * Here we count the possible pages from ZONE_MOVABLE.
         * If after having accounted all the pages, we see that the nr_pages
         * to be offlined is over or equal to the accounted pages,
         * we know that the node will become empty, and so, we can clear
         * it for N_MEMORY as well.
         */
        present_pages += pgdat->node_zones[ZONE_MOVABLE].present_pages;

        if (nr_pages >= present_pages)
                arg->status_change_nid = zone_to_nid(zone);
}

static void node_states_clear_node(int node, struct memory_notify *arg)
{
        if (arg->status_change_nid_normal >= 0)
                node_clear_state(node, N_NORMAL_MEMORY);

        if (arg->status_change_nid >= 0)
                node_clear_state(node, N_MEMORY);
}

static int count_system_ram_pages_cb(unsigned long start_pfn,
                                     unsigned long nr_pages, void *data)
{
        unsigned long *nr_system_ram_pages = data;

        *nr_system_ram_pages += nr_pages;
        return 0;
}

int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
                        struct zone *zone, struct memory_group *group)
{
        const unsigned long end_pfn = start_pfn + nr_pages;
        unsigned long pfn, system_ram_pages = 0;
        const int node = zone_to_nid(zone);
        unsigned long flags;
        struct memory_notify arg;
        char *reason;
        int ret;

        /*
         * {on,off}lining is constrained to full memory sections (or more
         * precisely to memory blocks from the user space POV).
         * memmap_on_memory is an exception because it reserves initial part
         * of the physical memory space for vmemmaps. That space is pageblock
         * aligned.
         */
        if (WARN_ON_ONCE(!nr_pages ||
                         !IS_ALIGNED(start_pfn, pageblock_nr_pages) ||
                         !IS_ALIGNED(start_pfn + nr_pages, PAGES_PER_SECTION)))
                return -EINVAL;

        mem_hotplug_begin();

        /*
         * Don't allow to offline memory blocks that contain holes.
         * Consequently, memory blocks with holes can never get onlined
         * via the hotplug path - online_pages() - as hotplugged memory has
         * no holes. This way, we e.g., don't have to worry about marking
         * memory holes PG_reserved, don't need pfn_valid() checks, and can
         * avoid using walk_system_ram_range() later.
         */
        walk_system_ram_range(start_pfn, nr_pages, &system_ram_pages,
                              count_system_ram_pages_cb);
        if (system_ram_pages != nr_pages) {
                ret = -EINVAL;
                reason = "memory holes";
                goto failed_removal;
        }

        /*
         * We only support offlining of memory blocks managed by a single zone,
         * checked by calling code. This is just a sanity check that we might
         * want to remove in the future.
         */
        if (WARN_ON_ONCE(page_zone(pfn_to_page(start_pfn)) != zone ||
                         page_zone(pfn_to_page(end_pfn - 1)) != zone)) {
                ret = -EINVAL;
                reason = "multizone range";
                goto failed_removal;
        }

        /*
         * Disable pcplists so that page isolation cannot race with freeing
         * in a way that pages from isolated pageblock are left on pcplists.
         */
        zone_pcp_disable(zone);
        lru_cache_disable();

        /* set above range as isolated */
        ret = start_isolate_page_range(start_pfn, end_pfn,
                                       MIGRATE_MOVABLE,
                                       MEMORY_OFFLINE | REPORT_FAILURE,
                                       GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL);
        if (ret) {
                reason = "failure to isolate range";
                goto failed_removal_pcplists_disabled;
        }

        arg.start_pfn = start_pfn;
        arg.nr_pages = nr_pages;
        node_states_check_changes_offline(nr_pages, zone, &arg);

        ret = memory_notify(MEM_GOING_OFFLINE, &arg);
        ret = notifier_to_errno(ret);
        if (ret) {
                reason = "notifier failure";
                goto failed_removal_isolated;
        }

        do {
                pfn = start_pfn;
                do {
                        if (signal_pending(current)) {
                                ret = -EINTR;
                                reason = "signal backoff";
                                goto failed_removal_isolated;
                        }

                        cond_resched();

                        ret = scan_movable_pages(pfn, end_pfn, &pfn);
                        if (!ret) {
                                /*
                                 * TODO: fatal migration failures should bail
                                 * out
                                 */
                                do_migrate_range(pfn, end_pfn);
                        }
                } while (!ret);

                if (ret != -ENOENT) {
                        reason = "unmovable page";
                        goto failed_removal_isolated;
                }

                /*
                 * Dissolve free hugepages in the memory block before doing
                 * offlining actually in order to make hugetlbfs's object
                 * counting consistent.
                 */
                ret = dissolve_free_huge_pages(start_pfn, end_pfn);
                if (ret) {
                        reason = "failure to dissolve huge pages";
                        goto failed_removal_isolated;
                }

                ret = test_pages_isolated(start_pfn, end_pfn, MEMORY_OFFLINE);

        } while (ret);

        /* Mark all sections offline and remove free pages from the buddy. */
        __offline_isolated_pages(start_pfn, end_pfn);
        pr_debug("Offlined Pages %ld\n", nr_pages);

        /*
         * The memory sections are marked offline, and the pageblock flags
         * effectively stale; nobody should be touching them. Fixup the number
         * of isolated pageblocks, memory onlining will properly revert this.
         */
        spin_lock_irqsave(&zone->lock, flags);
        zone->nr_isolate_pageblock -= nr_pages / pageblock_nr_pages;
        spin_unlock_irqrestore(&zone->lock, flags);

        lru_cache_enable();
        zone_pcp_enable(zone);

        /* removal success */
        adjust_managed_page_count(pfn_to_page(start_pfn), -nr_pages);
        adjust_present_page_count(pfn_to_page(start_pfn), group, -nr_pages);

        /* reinitialise watermarks and update pcp limits */
        init_per_zone_wmark_min();

        if (!populated_zone(zone)) {
                zone_pcp_reset(zone);
                build_all_zonelists(NULL);
        }

        node_states_clear_node(node, &arg);
        if (arg.status_change_nid >= 0) {
                kswapd_stop(node);
                kcompactd_stop(node);
        }

        writeback_set_ratelimit();

        memory_notify(MEM_OFFLINE, &arg);
        remove_pfn_range_from_zone(zone, start_pfn, nr_pages);
        mem_hotplug_done();
        return 0;

failed_removal_isolated:
        /* pushback to free area */
        undo_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE);
        memory_notify(MEM_CANCEL_OFFLINE, &arg);
failed_removal_pcplists_disabled:
        lru_cache_enable();
        zone_pcp_enable(zone);
failed_removal:
        pr_debug("memory offlining [mem %#010llx-%#010llx] failed due to %s\n",
                 (unsigned long long) start_pfn << PAGE_SHIFT,
                 ((unsigned long long) end_pfn << PAGE_SHIFT) - 1,
                 reason);
        mem_hotplug_done();
        return ret;
}

static int check_memblock_offlined_cb(struct memory_block *mem, void *arg)
{
        int ret = !is_memblock_offlined(mem);
        int *nid = arg;

        *nid = mem->nid;
        if (unlikely(ret)) {
                phys_addr_t beginpa, endpa;

                beginpa = PFN_PHYS(section_nr_to_pfn(mem->start_section_nr));
                endpa = beginpa + memory_block_size_bytes() - 1;
                pr_warn("removing memory fails, because memory [%pa-%pa] is onlined\n",
                        &beginpa, &endpa);

                return -EBUSY;
        }
        return 0;
}

static int get_nr_vmemmap_pages_cb(struct memory_block *mem, void *arg)
{
        /*
         * If not set, continue with the next block.
         */
        return mem->nr_vmemmap_pages;
}

static int check_cpu_on_node(int nid)
{
        int cpu;

        for_each_present_cpu(cpu) {
                if (cpu_to_node(cpu) == nid)
                        /*
                         * the cpu on this node isn't removed, and we can't
                         * offline this node.
                         */
                        return -EBUSY;
        }

        return 0;
}

static int check_no_memblock_for_node_cb(struct memory_block *mem, void *arg)
{
        int nid = *(int *)arg;

        /*
         * If a memory block belongs to multiple nodes, the stored nid is not
         * reliable. However, such blocks are always online (e.g., cannot get
         * offlined) and, therefore, are still spanned by the node.
         */
        return mem->nid == nid ? -EEXIST : 0;
}

/**
 * try_offline_node
 * @nid: the node ID
 *
 * Offline a node if all memory sections and cpus of the node are removed.
 *
 * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
 * and online/offline operations before this call.
 */
void try_offline_node(int nid)
{
        int rc;

        /*
         * If the node still spans pages (especially ZONE_DEVICE), don't
         * offline it. A node spans memory after move_pfn_range_to_zone(),
         * e.g., after the memory block was onlined.
         */
        if (node_spanned_pages(nid))
                return;

        /*
         * Especially offline memory blocks might not be spanned by the
         * node. They will get spanned by the node once they get onlined.
         * However, they link to the node in sysfs and can get onlined later.
         */
        rc = for_each_memory_block(&nid, check_no_memblock_for_node_cb);
        if (rc)
                return;

        if (check_cpu_on_node(nid))
                return;

        /*
         * all memory/cpu of this node are removed, we can offline this
         * node now.
         */
        node_set_offline(nid);
        unregister_one_node(nid);
}
EXPORT_SYMBOL(try_offline_node);

static int __ref try_remove_memory(u64 start, u64 size)
{
        struct vmem_altmap mhp_altmap = {};
        struct vmem_altmap *altmap = NULL;
        unsigned long nr_vmemmap_pages;
        int rc = 0, nid = NUMA_NO_NODE;

        BUG_ON(check_hotplug_memory_range(start, size));

        /*
         * All memory blocks must be offlined before removing memory.  Check
         * whether all memory blocks in question are offline and return error
         * if this is not the case.
         *
         * While at it, determine the nid. Note that if we'd have mixed nodes,
         * we'd only try to offline the last determined one -- which is good
         * enough for the cases we care about.
         */
        rc = walk_memory_blocks(start, size, &nid, check_memblock_offlined_cb);
        if (rc)
                return rc;

        /*
         * We only support removing memory added with MHP_MEMMAP_ON_MEMORY in
         * the same granularity it was added - a single memory block.
         */
        if (mhp_memmap_on_memory()) {
                nr_vmemmap_pages = walk_memory_blocks(start, size, NULL,
                                                      get_nr_vmemmap_pages_cb);
                if (nr_vmemmap_pages) {
                        if (size != memory_block_size_bytes()) {
                                pr_warn("Refuse to remove %#llx - %#llx,"
                                        "wrong granularity\n",
                                        start, start + size);
                                return -EINVAL;
                        }

                        /*
                         * Let remove_pmd_table->free_hugepage_table do the
                         * right thing if we used vmem_altmap when hot-adding
                         * the range.
                         */
                        mhp_altmap.alloc = nr_vmemmap_pages;
                        altmap = &mhp_altmap;
                }
        }

        /* remove memmap entry */
        firmware_map_remove(start, start + size, "System RAM");

        /*
         * Memory block device removal under the device_hotplug_lock is
         * a barrier against racing online attempts.
         */
        remove_memory_block_devices(start, size);

        mem_hotplug_begin();

        arch_remove_memory(start, size, altmap);

        if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK)) {
                memblock_phys_free(start, size);
                memblock_remove(start, size);
        }

        release_mem_region_adjustable(start, size);

        if (nid != NUMA_NO_NODE)
                try_offline_node(nid);

        mem_hotplug_done();
        return 0;
}

/**
 * __remove_memory - Remove memory if every memory block is offline
 * @start: physical address of the region to remove
 * @size: size of the region to remove
 *
 * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
 * and online/offline operations before this call, as required by
 * try_offline_node().
 */
void __remove_memory(u64 start, u64 size)
{

        /*
         * trigger BUG() if some memory is not offlined prior to calling this
         * function
         */
        if (try_remove_memory(start, size))
                BUG();
}

/*
 * Remove memory if every memory block is offline, otherwise return -EBUSY is
 * some memory is not offline
 */
int remove_memory(u64 start, u64 size)
{
        int rc;

        lock_device_hotplug();
        rc = try_remove_memory(start, size);
        unlock_device_hotplug();

        return rc;
}
EXPORT_SYMBOL_GPL(remove_memory);

static int try_offline_memory_block(struct memory_block *mem, void *arg)
{
        uint8_t online_type = MMOP_ONLINE_KERNEL;
        uint8_t **online_types = arg;
        struct page *page;
        int rc;

        /*
         * Sense the online_type via the zone of the memory block. Offlining
         * with multiple zones within one memory block will be rejected
         * by offlining code ... so we don't care about that.
         */
        page = pfn_to_online_page(section_nr_to_pfn(mem->start_section_nr));
        if (page && zone_idx(page_zone(page)) == ZONE_MOVABLE)
                online_type = MMOP_ONLINE_MOVABLE;

        rc = device_offline(&mem->dev);
        /*
         * Default is MMOP_OFFLINE - change it only if offlining succeeded,
         * so try_reonline_memory_block() can do the right thing.
         */
        if (!rc)
                **online_types = online_type;

        (*online_types)++;
        /* Ignore if already offline. */
        return rc < 0 ? rc : 0;
}

static int try_reonline_memory_block(struct memory_block *mem, void *arg)
{
        uint8_t **online_types = arg;
        int rc;

        if (**online_types != MMOP_OFFLINE) {
                mem->online_type = **online_types;
                rc = device_online(&mem->dev);
                if (rc < 0)
                        pr_warn("%s: Failed to re-online memory: %d",
                                __func__, rc);
        }

        /* Continue processing all remaining memory blocks. */
        (*online_types)++;
        return 0;
}

/*
 * Try to offline and remove memory. Might take a long time to finish in case
 * memory is still in use. Primarily useful for memory devices that logically
 * unplugged all memory (so it's no longer in use) and want to offline + remove
 * that memory.
 */
int offline_and_remove_memory(u64 start, u64 size)
{
        const unsigned long mb_count = size / memory_block_size_bytes();
        uint8_t *online_types, *tmp;
        int rc;

        if (!IS_ALIGNED(start, memory_block_size_bytes()) ||
            !IS_ALIGNED(size, memory_block_size_bytes()) || !size)
                return -EINVAL;

        /*
         * We'll remember the old online type of each memory block, so we can
         * try to revert whatever we did when offlining one memory block fails
         * after offlining some others succeeded.
         */
        online_types = kmalloc_array(mb_count, sizeof(*online_types),
                                     GFP_KERNEL);
        if (!online_types)
                return -ENOMEM;
        /*
         * Initialize all states to MMOP_OFFLINE, so when we abort processing in
         * try_offline_memory_block(), we'll skip all unprocessed blocks in
         * try_reonline_memory_block().
         */
        memset(online_types, MMOP_OFFLINE, mb_count);

        lock_device_hotplug();

        tmp = online_types;
        rc = walk_memory_blocks(start, size, &tmp, try_offline_memory_block);

        /*
         * In case we succeeded to offline all memory, remove it.
         * This cannot fail as it cannot get onlined in the meantime.
         */
        if (!rc) {
                rc = try_remove_memory(start, size);
                if (rc)
                        pr_err("%s: Failed to remove memory: %d", __func__, rc);
        }

        /*
         * Rollback what we did. While memory onlining might theoretically fail
         * (nacked by a notifier), it barely ever happens.
         */
        if (rc) {
                tmp = online_types;
                walk_memory_blocks(start, size, &tmp,
                                   try_reonline_memory_block);
        }
        unlock_device_hotplug();

        kfree(online_types);
        return rc;
}
EXPORT_SYMBOL_GPL(offline_and_remove_memory);
#endif /* CONFIG_MEMORY_HOTREMOVE */