/*
 * mm/percpu.c - percpu memory allocator
 *
 * Copyright (C) 2009           SUSE Linux Products GmbH
 * Copyright (C) 2009           Tejun Heo <tj@kernel.org>
 *
 * This file is released under the GPLv2.
 *
 * This is percpu allocator which can handle both static and dynamic
 * areas.  Percpu areas are allocated in chunks.  Each chunk is
 * consisted of boot-time determined number of units and the first
 * chunk is used for static percpu variables in the kernel image
 * (special boot time alloc/init handling necessary as these areas
 * need to be brought up before allocation services are running).
 * Unit grows as necessary and all units grow or shrink in unison.
 * When a chunk is filled up, another chunk is allocated.
 *
 *  c0                           c1                         c2
 *  -------------------          -------------------        ------------
 * | u0 | u1 | u2 | u3 |        | u0 | u1 | u2 | u3 |      | u0 | u1 | u
 *  -------------------  ......  -------------------  ....  ------------
 *
 * Allocation is done in offset-size areas of single unit space.  Ie,
 * an area of 512 bytes at 6k in c1 occupies 512 bytes at 6k of c1:u0,
 * c1:u1, c1:u2 and c1:u3.  On UMA, units corresponds directly to
 * cpus.  On NUMA, the mapping can be non-linear and even sparse.
 * Percpu access can be done by configuring percpu base registers
 * according to cpu to unit mapping and pcpu_unit_size.
 *
 * There are usually many small percpu allocations many of them being
 * as small as 4 bytes.  The allocator organizes chunks into lists
 * according to free size and tries to allocate from the fullest one.
 * Each chunk keeps the maximum contiguous area size hint which is
 * guaranteed to be equal to or larger than the maximum contiguous
 * area in the chunk.  This helps the allocator not to iterate the
 * chunk maps unnecessarily.
 *
 * Allocation state in each chunk is kept using an array of integers
 * on chunk->map.  A positive value in the map represents a free
 * region and negative allocated.  Allocation inside a chunk is done
 * by scanning this map sequentially and serving the first matching
 * entry.  This is mostly copied from the percpu_modalloc() allocator.
 * Chunks can be determined from the address using the index field
 * in the page struct. The index field contains a pointer to the chunk.
 *
 * To use this allocator, arch code should do the followings.
 *
 * - define __addr_to_pcpu_ptr() and __pcpu_ptr_to_addr() to translate
 *   regular address to percpu pointer and back if they need to be
 *   different from the default
 *
 * - use pcpu_setup_first_chunk() during percpu area initialization to
 *   setup the first chunk containing the kernel static percpu area
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/bitmap.h>
#include <linux/bootmem.h>
#include <linux/err.h>
#include <linux/list.h>
#include <linux/log2.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/percpu.h>
#include <linux/pfn.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/vmalloc.h>
#include <linux/workqueue.h>
#include <linux/kmemleak.h>

#include <asm/cacheflush.h>
#include <asm/sections.h>
#include <asm/tlbflush.h>
#include <asm/io.h>

#define PCPU_SLOT_BASE_SHIFT            5       /* 1-31 shares the same slot */
#define PCPU_DFL_MAP_ALLOC              16      /* start a map with 16 ents */
#define PCPU_ATOMIC_MAP_MARGIN_LOW      32
#define PCPU_ATOMIC_MAP_MARGIN_HIGH     64
#define PCPU_EMPTY_POP_PAGES_LOW        2
#define PCPU_EMPTY_POP_PAGES_HIGH       4

#ifdef CONFIG_SMP
/* default addr <-> pcpu_ptr mapping, override in asm/percpu.h if necessary */
#ifndef __addr_to_pcpu_ptr
#define __addr_to_pcpu_ptr(addr)                                        \
        (void __percpu *)((unsigned long)(addr) -                       \
                          (unsigned long)pcpu_base_addr +               \
                          (unsigned long)__per_cpu_start)
#endif
#ifndef __pcpu_ptr_to_addr
#define __pcpu_ptr_to_addr(ptr)                                         \
        (void __force *)((unsigned long)(ptr) +                         \
                         (unsigned long)pcpu_base_addr -                \
                         (unsigned long)__per_cpu_start)
#endif
#else   /* CONFIG_SMP */
/* on UP, it's always identity mapped */
#define __addr_to_pcpu_ptr(addr)        (void __percpu *)(addr)
#define __pcpu_ptr_to_addr(ptr)         (void __force *)(ptr)
#endif  /* CONFIG_SMP */

struct pcpu_chunk {
        struct list_head        list;           /* linked to pcpu_slot lists */
        int                     free_size;      /* free bytes in the chunk */
        int                     contig_hint;    /* max contiguous size hint */
        void                    *base_addr;     /* base address of this chunk */

        int                     map_used;       /* # of map entries used before the sentry */
        int                     map_alloc;      /* # of map entries allocated */
        int                     *map;           /* allocation map */
        struct work_struct      map_extend_work;/* async ->map[] extension */

        void                    *data;          /* chunk data */
        int                     first_free;     /* no free below this */
        bool                    immutable;      /* no [de]population allowed */
        int                     nr_populated;   /* # of populated pages */
        unsigned long           populated[];    /* populated bitmap */
};

static int pcpu_unit_pages __read_mostly;
static int pcpu_unit_size __read_mostly;
static int pcpu_nr_units __read_mostly;
static int pcpu_atom_size __read_mostly;
static int pcpu_nr_slots __read_mostly;
static size_t pcpu_chunk_struct_size __read_mostly;

/* cpus with the lowest and highest unit addresses */
static unsigned int pcpu_low_unit_cpu __read_mostly;
static unsigned int pcpu_high_unit_cpu __read_mostly;

/* the address of the first chunk which starts with the kernel static area */
void *pcpu_base_addr __read_mostly;
EXPORT_SYMBOL_GPL(pcpu_base_addr);

static const int *pcpu_unit_map __read_mostly;          /* cpu -> unit */
const unsigned long *pcpu_unit_offsets __read_mostly;   /* cpu -> unit offset */

/* group information, used for vm allocation */
static int pcpu_nr_groups __read_mostly;
static const unsigned long *pcpu_group_offsets __read_mostly;
static const size_t *pcpu_group_sizes __read_mostly;

/*
 * The first chunk which always exists.  Note that unlike other
 * chunks, this one can be allocated and mapped in several different
 * ways and thus often doesn't live in the vmalloc area.
 */
static struct pcpu_chunk *pcpu_first_chunk;

/*
 * Optional reserved chunk.  This chunk reserves part of the first
 * chunk and serves it for reserved allocations.  The amount of
 * reserved offset is in pcpu_reserved_chunk_limit.  When reserved
 * area doesn't exist, the following variables contain NULL and 0
 * respectively.
 */
static struct pcpu_chunk *pcpu_reserved_chunk;
static int pcpu_reserved_chunk_limit;

static DEFINE_SPINLOCK(pcpu_lock);      /* all internal data structures */
static DEFINE_MUTEX(pcpu_alloc_mutex);  /* chunk create/destroy, [de]pop */

static struct list_head *pcpu_slot __read_mostly; /* chunk list slots */

/*
 * The number of empty populated pages, protected by pcpu_lock.  The
 * reserved chunk doesn't contribute to the count.
 */
static int pcpu_nr_empty_pop_pages;

/*
 * Balance work is used to populate or destroy chunks asynchronously.  We
 * try to keep the number of populated free pages between
 * PCPU_EMPTY_POP_PAGES_LOW and HIGH for atomic allocations and at most one
 * empty chunk.
 */
static void pcpu_balance_workfn(struct work_struct *work);
static DECLARE_WORK(pcpu_balance_work, pcpu_balance_workfn);
static bool pcpu_async_enabled __read_mostly;
static bool pcpu_atomic_alloc_failed;

static void pcpu_schedule_balance_work(void)
{
        if (pcpu_async_enabled)
                schedule_work(&pcpu_balance_work);
}

static bool pcpu_addr_in_first_chunk(void *addr)
{
        void *first_start = pcpu_first_chunk->base_addr;

        return addr >= first_start && addr < first_start + pcpu_unit_size;
}

static bool pcpu_addr_in_reserved_chunk(void *addr)
{
        void *first_start = pcpu_first_chunk->base_addr;

        return addr >= first_start &&
                addr < first_start + pcpu_reserved_chunk_limit;
}

static int __pcpu_size_to_slot(int size)
{
        int highbit = fls(size);        /* size is in bytes */
        return max(highbit - PCPU_SLOT_BASE_SHIFT + 2, 1);
}

static int pcpu_size_to_slot(int size)
{
        if (size == pcpu_unit_size)
                return pcpu_nr_slots - 1;
        return __pcpu_size_to_slot(size);
}

static int pcpu_chunk_slot(const struct pcpu_chunk *chunk)
{
        if (chunk->free_size < sizeof(int) || chunk->contig_hint < sizeof(int))
                return 0;

        return pcpu_size_to_slot(chunk->free_size);
}

/* set the pointer to a chunk in a page struct */
static void pcpu_set_page_chunk(struct page *page, struct pcpu_chunk *pcpu)
{
        page->index = (unsigned long)pcpu;
}

/* obtain pointer to a chunk from a page struct */
static struct pcpu_chunk *pcpu_get_page_chunk(struct page *page)
{
        return (struct pcpu_chunk *)page->index;
}

static int __maybe_unused pcpu_page_idx(unsigned int cpu, int page_idx)
{
        return pcpu_unit_map[cpu] * pcpu_unit_pages + page_idx;
}

static unsigned long pcpu_chunk_addr(struct pcpu_chunk *chunk,
                                     unsigned int cpu, int page_idx)
{
        return (unsigned long)chunk->base_addr + pcpu_unit_offsets[cpu] +
                (page_idx << PAGE_SHIFT);
}

static void __maybe_unused pcpu_next_unpop(struct pcpu_chunk *chunk,
                                           int *rs, int *re, int end)
{
        *rs = find_next_zero_bit(chunk->populated, end, *rs);
        *re = find_next_bit(chunk->populated, end, *rs + 1);
}

static void __maybe_unused pcpu_next_pop(struct pcpu_chunk *chunk,
                                         int *rs, int *re, int end)
{
        *rs = find_next_bit(chunk->populated, end, *rs);
        *re = find_next_zero_bit(chunk->populated, end, *rs + 1);
}

/*
 * (Un)populated page region iterators.  Iterate over (un)populated
 * page regions between @start and @end in @chunk.  @rs and @re should
 * be integer variables and will be set to start and end page index of
 * the current region.
 */
#define pcpu_for_each_unpop_region(chunk, rs, re, start, end)               \
        for ((rs) = (start), pcpu_next_unpop((chunk), &(rs), &(re), (end)); \
             (rs) < (re);                                                   \
             (rs) = (re) + 1, pcpu_next_unpop((chunk), &(rs), &(re), (end)))

#define pcpu_for_each_pop_region(chunk, rs, re, start, end)                 \
        for ((rs) = (start), pcpu_next_pop((chunk), &(rs), &(re), (end));   \
             (rs) < (re);                                                   \
             (rs) = (re) + 1, pcpu_next_pop((chunk), &(rs), &(re), (end)))

/**
 * pcpu_mem_zalloc - allocate memory
 * @size: bytes to allocate
 *
 * Allocate @size bytes.  If @size is smaller than PAGE_SIZE,
 * kzalloc() is used; otherwise, vzalloc() is used.  The returned
 * memory is always zeroed.
 *
 * CONTEXT:
 * Does GFP_KERNEL allocation.
 *
 * RETURNS:
 * Pointer to the allocated area on success, NULL on failure.
 */
static void *pcpu_mem_zalloc(size_t size)
{
        if (WARN_ON_ONCE(!slab_is_available()))
                return NULL;

        if (size <= PAGE_SIZE)
                return kzalloc(size, GFP_KERNEL);
        else
                return vzalloc(size);
}

/**
 * pcpu_mem_free - free memory
 * @ptr: memory to free
 *
 * Free @ptr.  @ptr should have been allocated using pcpu_mem_zalloc().
 */
static void pcpu_mem_free(void *ptr)
{
        kvfree(ptr);
}

/**
 * pcpu_count_occupied_pages - count the number of pages an area occupies
 * @chunk: chunk of interest
 * @i: index of the area in question
 *
 * Count the number of pages chunk's @i'th area occupies.  When the area's
 * start and/or end address isn't aligned to page boundary, the straddled
 * page is included in the count iff the rest of the page is free.
 */
static int pcpu_count_occupied_pages(struct pcpu_chunk *chunk, int i)
{
        int off = chunk->map[i] & ~1;
        int end = chunk->map[i + 1] & ~1;

        if (!PAGE_ALIGNED(off) && i > 0) {
                int prev = chunk->map[i - 1];

                if (!(prev & 1) && prev <= round_down(off, PAGE_SIZE))
                        off = round_down(off, PAGE_SIZE);
        }

        if (!PAGE_ALIGNED(end) && i + 1 < chunk->map_used) {
                int next = chunk->map[i + 1];
                int nend = chunk->map[i + 2] & ~1;

                if (!(next & 1) && nend >= round_up(end, PAGE_SIZE))
                        end = round_up(end, PAGE_SIZE);
        }

        return max_t(int, PFN_DOWN(end) - PFN_UP(off), 0);
}

/**
 * pcpu_chunk_relocate - put chunk in the appropriate chunk slot
 * @chunk: chunk of interest
 * @oslot: the previous slot it was on
 *
 * This function is called after an allocation or free changed @chunk.
 * New slot according to the changed state is determined and @chunk is
 * moved to the slot.  Note that the reserved chunk is never put on
 * chunk slots.
 *
 * CONTEXT:
 * pcpu_lock.
 */
static void pcpu_chunk_relocate(struct pcpu_chunk *chunk, int oslot)
{
        int nslot = pcpu_chunk_slot(chunk);

        if (chunk != pcpu_reserved_chunk && oslot != nslot) {
                if (oslot < nslot)
                        list_move(&chunk->list, &pcpu_slot[nslot]);
                else
                        list_move_tail(&chunk->list, &pcpu_slot[nslot]);
        }
}

/**
 * pcpu_need_to_extend - determine whether chunk area map needs to be extended
 * @chunk: chunk of interest
 * @is_atomic: the allocation context
 *
 * Determine whether area map of @chunk needs to be extended.  If
 * @is_atomic, only the amount necessary for a new allocation is
 * considered; however, async extension is scheduled if the left amount is
 * low.  If !@is_atomic, it aims for more empty space.  Combined, this
 * ensures that the map is likely to have enough available space to
 * accomodate atomic allocations which can't extend maps directly.
 *
 * CONTEXT:
 * pcpu_lock.
 *
 * RETURNS:
 * New target map allocation length if extension is necessary, 0
 * otherwise.
 */
static int pcpu_need_to_extend(struct pcpu_chunk *chunk, bool is_atomic)
{
        int margin, new_alloc;

        if (is_atomic) {
                margin = 3;

                if (chunk->map_alloc <
                    chunk->map_used + PCPU_ATOMIC_MAP_MARGIN_LOW &&
                    pcpu_async_enabled)
                        schedule_work(&chunk->map_extend_work);
        } else {
                margin = PCPU_ATOMIC_MAP_MARGIN_HIGH;
        }

        if (chunk->map_alloc >= chunk->map_used + margin)
                return 0;

        new_alloc = PCPU_DFL_MAP_ALLOC;
        while (new_alloc < chunk->map_used + margin)
                new_alloc *= 2;

        return new_alloc;
}

/**
 * pcpu_extend_area_map - extend area map of a chunk
 * @chunk: chunk of interest
 * @new_alloc: new target allocation length of the area map
 *
 * Extend area map of @chunk to have @new_alloc entries.
 *
 * CONTEXT:
 * Does GFP_KERNEL allocation.  Grabs and releases pcpu_lock.
 *
 * RETURNS:
 * 0 on success, -errno on failure.
 */
static int pcpu_extend_area_map(struct pcpu_chunk *chunk, int new_alloc)
{
        int *old = NULL, *new = NULL;
        size_t old_size = 0, new_size = new_alloc * sizeof(new[0]);
        unsigned long flags;

        new = pcpu_mem_zalloc(new_size);
        if (!new)
                return -ENOMEM;

        /* acquire pcpu_lock and switch to new area map */
        spin_lock_irqsave(&pcpu_lock, flags);

        if (new_alloc <= chunk->map_alloc)
                goto out_unlock;

        old_size = chunk->map_alloc * sizeof(chunk->map[0]);
        old = chunk->map;

        memcpy(new, old, old_size);

        chunk->map_alloc = new_alloc;
        chunk->map = new;
        new = NULL;

out_unlock:
        spin_unlock_irqrestore(&pcpu_lock, flags);

        /*
         * pcpu_mem_free() might end up calling vfree() which uses
         * IRQ-unsafe lock and thus can't be called under pcpu_lock.
         */
        pcpu_mem_free(old);
        pcpu_mem_free(new);

        return 0;
}

static void pcpu_map_extend_workfn(struct work_struct *work)
{
        struct pcpu_chunk *chunk = container_of(work, struct pcpu_chunk,
                                                map_extend_work);
        int new_alloc;

        spin_lock_irq(&pcpu_lock);
        new_alloc = pcpu_need_to_extend(chunk, false);
        spin_unlock_irq(&pcpu_lock);

        if (new_alloc)
                pcpu_extend_area_map(chunk, new_alloc);
}

/**
 * pcpu_fit_in_area - try to fit the requested allocation in a candidate area
 * @chunk: chunk the candidate area belongs to
 * @off: the offset to the start of the candidate area
 * @this_size: the size of the candidate area
 * @size: the size of the target allocation
 * @align: the alignment of the target allocation
 * @pop_only: only allocate from already populated region
 *
 * We're trying to allocate @size bytes aligned at @align.  @chunk's area
 * at @off sized @this_size is a candidate.  This function determines
 * whether the target allocation fits in the candidate area and returns the
 * number of bytes to pad after @off.  If the target area doesn't fit, -1
 * is returned.
 *
 * If @pop_only is %true, this function only considers the already
 * populated part of the candidate area.
 */
static int pcpu_fit_in_area(struct pcpu_chunk *chunk, int off, int this_size,
                            int size, int align, bool pop_only)
{
        int cand_off = off;

        while (true) {
                int head = ALIGN(cand_off, align) - off;
                int page_start, page_end, rs, re;

                if (this_size < head + size)
                        return -1;

                if (!pop_only)
                        return head;

                /*
                 * If the first unpopulated page is beyond the end of the
                 * allocation, the whole allocation is populated;
                 * otherwise, retry from the end of the unpopulated area.
                 */
                page_start = PFN_DOWN(head + off);
                page_end = PFN_UP(head + off + size);

                rs = page_start;
                pcpu_next_unpop(chunk, &rs, &re, PFN_UP(off + this_size));
                if (rs >= page_end)
                        return head;
                cand_off = re * PAGE_SIZE;
        }
}

/**
 * pcpu_alloc_area - allocate area from a pcpu_chunk
 * @chunk: chunk of interest
 * @size: wanted size in bytes
 * @align: wanted align
 * @pop_only: allocate only from the populated area
 * @occ_pages_p: out param for the number of pages the area occupies
 *
 * Try to allocate @size bytes area aligned at @align from @chunk.
 * Note that this function only allocates the offset.  It doesn't
 * populate or map the area.
 *
 * @chunk->map must have at least two free slots.
 *
 * CONTEXT:
 * pcpu_lock.
 *
 * RETURNS:
 * Allocated offset in @chunk on success, -1 if no matching area is
 * found.
 */
static int pcpu_alloc_area(struct pcpu_chunk *chunk, int size, int align,
                           bool pop_only, int *occ_pages_p)
{
        int oslot = pcpu_chunk_slot(chunk);
        int max_contig = 0;
        int i, off;
        bool seen_free = false;
        int *p;

        for (i = chunk->first_free, p = chunk->map + i; i < chunk->map_used; i++, p++) {
                int head, tail;
                int this_size;

                off = *p;
                if (off & 1)
                        continue;

                this_size = (p[1] & ~1) - off;

                head = pcpu_fit_in_area(chunk, off, this_size, size, align,
                                        pop_only);
                if (head < 0) {
                        if (!seen_free) {
                                chunk->first_free = i;
                                seen_free = true;
                        }
                        max_contig = max(this_size, max_contig);
                        continue;
                }

                /*
                 * If head is small or the previous block is free,
                 * merge'em.  Note that 'small' is defined as smaller
                 * than sizeof(int), which is very small but isn't too
                 * uncommon for percpu allocations.
                 */
                if (head && (head < sizeof(int) || !(p[-1] & 1))) {
                        *p = off += head;
                        if (p[-1] & 1)
                                chunk->free_size -= head;
                        else
                                max_contig = max(*p - p[-1], max_contig);
                        this_size -= head;
                        head = 0;
                }

                /* if tail is small, just keep it around */
                tail = this_size - head - size;
                if (tail < sizeof(int)) {
                        tail = 0;
                        size = this_size - head;
                }

                /* split if warranted */
                if (head || tail) {
                        int nr_extra = !!head + !!tail;

                        /* insert new subblocks */
                        memmove(p + nr_extra + 1, p + 1,
                                sizeof(chunk->map[0]) * (chunk->map_used - i));
                        chunk->map_used += nr_extra;

                        if (head) {
                                if (!seen_free) {
                                        chunk->first_free = i;
                                        seen_free = true;
                                }
                                *++p = off += head;
                                ++i;
                                max_contig = max(head, max_contig);
                        }
                        if (tail) {
                                p[1] = off + size;
                                max_contig = max(tail, max_contig);
                        }
                }

                if (!seen_free)
                        chunk->first_free = i + 1;

                /* update hint and mark allocated */
                if (i + 1 == chunk->map_used)
                        chunk->contig_hint = max_contig; /* fully scanned */
                else
                        chunk->contig_hint = max(chunk->contig_hint,
                                                 max_contig);

                chunk->free_size -= size;
                *p |= 1;

                *occ_pages_p = pcpu_count_occupied_pages(chunk, i);
                pcpu_chunk_relocate(chunk, oslot);
                return off;
        }

        chunk->contig_hint = max_contig;        /* fully scanned */
        pcpu_chunk_relocate(chunk, oslot);

        /* tell the upper layer that this chunk has no matching area */
        return -1;
}

/**
 * pcpu_free_area - free area to a pcpu_chunk
 * @chunk: chunk of interest
 * @freeme: offset of area to free
 * @occ_pages_p: out param for the number of pages the area occupies
 *
 * Free area starting from @freeme to @chunk.  Note that this function
 * only modifies the allocation map.  It doesn't depopulate or unmap
 * the area.
 *
 * CONTEXT:
 * pcpu_lock.
 */
static void pcpu_free_area(struct pcpu_chunk *chunk, int freeme,
                           int *occ_pages_p)
{
        int oslot = pcpu_chunk_slot(chunk);
        int off = 0;
        unsigned i, j;
        int to_free = 0;
        int *p;

        freeme |= 1;    /* we are searching for <given offset, in use> pair */

        i = 0;
        j = chunk->map_used;
        while (i != j) {
                unsigned k = (i + j) / 2;
                off = chunk->map[k];
                if (off < freeme)
                        i = k + 1;
                else if (off > freeme)
                        j = k;
                else
                        i = j = k;
        }
        BUG_ON(off != freeme);

        if (i < chunk->first_free)
                chunk->first_free = i;

        p = chunk->map + i;
        *p = off &= ~1;
        chunk->free_size += (p[1] & ~1) - off;

        *occ_pages_p = pcpu_count_occupied_pages(chunk, i);

        /* merge with next? */
        if (!(p[1] & 1))
                to_free++;
        /* merge with previous? */
        if (i > 0 && !(p[-1] & 1)) {
                to_free++;
                i--;
                p--;
        }
        if (to_free) {
                chunk->map_used -= to_free;
                memmove(p + 1, p + 1 + to_free,
                        (chunk->map_used - i) * sizeof(chunk->map[0]));
        }

        chunk->contig_hint = max(chunk->map[i + 1] - chunk->map[i] - 1, chunk->contig_hint);
        pcpu_chunk_relocate(chunk, oslot);
}

static struct pcpu_chunk *pcpu_alloc_chunk(void)
{
        struct pcpu_chunk *chunk;

        chunk = pcpu_mem_zalloc(pcpu_chunk_struct_size);
        if (!chunk)
                return NULL;

        chunk->map = pcpu_mem_zalloc(PCPU_DFL_MAP_ALLOC *
                                                sizeof(chunk->map[0]));
        if (!chunk->map) {
                pcpu_mem_free(chunk);
                return NULL;
        }

        chunk->map_alloc = PCPU_DFL_MAP_ALLOC;
        chunk->map[0] = 0;
        chunk->map[1] = pcpu_unit_size | 1;
        chunk->map_used = 1;

        INIT_LIST_HEAD(&chunk->list);
        INIT_WORK(&chunk->map_extend_work, pcpu_map_extend_workfn);
        chunk->free_size = pcpu_unit_size;
        chunk->contig_hint = pcpu_unit_size;

        return chunk;
}

static void pcpu_free_chunk(struct pcpu_chunk *chunk)
{
        if (!chunk)
                return;
        pcpu_mem_free(chunk->map);
        pcpu_mem_free(chunk);
}

/**
 * pcpu_chunk_populated - post-population bookkeeping
 * @chunk: pcpu_chunk which got populated
 * @page_start: the start page
 * @page_end: the end page
 *
 * Pages in [@page_start,@page_end) have been populated to @chunk.  Update
 * the bookkeeping information accordingly.  Must be called after each
 * successful population.
 */
static void pcpu_chunk_populated(struct pcpu_chunk *chunk,
                                 int page_start, int page_end)
{
        int nr = page_end - page_start;

        lockdep_assert_held(&pcpu_lock);

        bitmap_set(chunk->populated, page_start, nr);
        chunk->nr_populated += nr;
        pcpu_nr_empty_pop_pages += nr;
}

/**
 * pcpu_chunk_depopulated - post-depopulation bookkeeping
 * @chunk: pcpu_chunk which got depopulated
 * @page_start: the start page
 * @page_end: the end page
 *
 * Pages in [@page_start,@page_end) have been depopulated from @chunk.
 * Update the bookkeeping information accordingly.  Must be called after
 * each successful depopulation.
 */
static void pcpu_chunk_depopulated(struct pcpu_chunk *chunk,
                                   int page_start, int page_end)
{
        int nr = page_end - page_start;

        lockdep_assert_held(&pcpu_lock);

        bitmap_clear(chunk->populated, page_start, nr);
        chunk->nr_populated -= nr;
        pcpu_nr_empty_pop_pages -= nr;
}

/*
 * Chunk management implementation.
 *
 * To allow different implementations, chunk alloc/free and
 * [de]population are implemented in a separate file which is pulled
 * into this file and compiled together.  The following functions
 * should be implemented.
 *
 * pcpu_populate_chunk          - populate the specified range of a chunk
 * pcpu_depopulate_chunk        - depopulate the specified range of a chunk
 * pcpu_create_chunk            - create a new chunk
 * pcpu_destroy_chunk           - destroy a chunk, always preceded by full depop
 * pcpu_addr_to_page            - translate address to physical address
 * pcpu_verify_alloc_info       - check alloc_info is acceptable during init
 */
static int pcpu_populate_chunk(struct pcpu_chunk *chunk, int off, int size);
static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk, int off, int size);
static struct pcpu_chunk *pcpu_create_chunk(void);
static void pcpu_destroy_chunk(struct pcpu_chunk *chunk);
static struct page *pcpu_addr_to_page(void *addr);
static int __init pcpu_verify_alloc_info(const struct pcpu_alloc_info *ai);

#ifdef CONFIG_NEED_PER_CPU_KM
#include "percpu-km.c"
#else
#include "percpu-vm.c"
#endif

/**
 * pcpu_chunk_addr_search - determine chunk containing specified address
 * @addr: address for which the chunk needs to be determined.
 *
 * RETURNS:
 * The address of the found chunk.
 */
static struct pcpu_chunk *pcpu_chunk_addr_search(void *addr)
{
        /* is it in the first chunk? */
        if (pcpu_addr_in_first_chunk(addr)) {
                /* is it in the reserved area? */
                if (pcpu_addr_in_reserved_chunk(addr))
                        return pcpu_reserved_chunk;
                return pcpu_first_chunk;
        }

        /*
         * The address is relative to unit0 which might be unused and
         * thus unmapped.  Offset the address to the unit space of the
         * current processor before looking it up in the vmalloc
         * space.  Note that any possible cpu id can be used here, so
         * there's no need to worry about preemption or cpu hotplug.
         */
        addr += pcpu_unit_offsets[raw_smp_processor_id()];
        return pcpu_get_page_chunk(pcpu_addr_to_page(addr));
}

/**
 * pcpu_alloc - the percpu allocator
 * @size: size of area to allocate in bytes
 * @align: alignment of area (max PAGE_SIZE)
 * @reserved: allocate from the reserved chunk if available
 * @gfp: allocation flags
 *
 * Allocate percpu area of @size bytes aligned at @align.  If @gfp doesn't
 * contain %GFP_KERNEL, the allocation is atomic.
 *
 * RETURNS:
 * Percpu pointer to the allocated area on success, NULL on failure.
 */
static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
                                 gfp_t gfp)
{
        static int warn_limit = 10;
        struct pcpu_chunk *chunk;
        const char *err;
        bool is_atomic = (gfp & GFP_KERNEL) != GFP_KERNEL;
        int occ_pages = 0;
        int slot, off, new_alloc, cpu, ret;
        unsigned long flags;
        void __percpu *ptr;

        /*
         * We want the lowest bit of offset available for in-use/free
         * indicator, so force >= 16bit alignment and make size even.
         */
        if (unlikely(align < 2))
                align = 2;

        size = ALIGN(size, 2);

        if (unlikely(!size || size > PCPU_MIN_UNIT_SIZE || align > PAGE_SIZE)) {
                WARN(true, "illegal size (%zu) or align (%zu) for percpu allocation\n",
                     size, align);
                return NULL;
        }

        spin_lock_irqsave(&pcpu_lock, flags);

        /* serve reserved allocations from the reserved chunk if available */
        if (reserved && pcpu_reserved_chunk) {
                chunk = pcpu_reserved_chunk;

                if (size > chunk->contig_hint) {
                        err = "alloc from reserved chunk failed";
                        goto fail_unlock;
                }

                while ((new_alloc = pcpu_need_to_extend(chunk, is_atomic))) {
                        spin_unlock_irqrestore(&pcpu_lock, flags);
                        if (is_atomic ||
                            pcpu_extend_area_map(chunk, new_alloc) < 0) {
                                err = "failed to extend area map of reserved chunk";
                                goto fail;
                        }
                        spin_lock_irqsave(&pcpu_lock, flags);
                }

                off = pcpu_alloc_area(chunk, size, align, is_atomic,
                                      &occ_pages);
                if (off >= 0)
                        goto area_found;

                err = "alloc from reserved chunk failed";
                goto fail_unlock;
        }

restart:
        /* search through normal chunks */
        for (slot = pcpu_size_to_slot(size); slot < pcpu_nr_slots; slot++) {
                list_for_each_entry(chunk, &pcpu_slot[slot], list) {
                        if (size > chunk->contig_hint)
                                continue;

                        new_alloc = pcpu_need_to_extend(chunk, is_atomic);
                        if (new_alloc) {
                                if (is_atomic)
                                        continue;
                                spin_unlock_irqrestore(&pcpu_lock, flags);
                                if (pcpu_extend_area_map(chunk,
                                                         new_alloc) < 0) {
                                        err = "failed to extend area map";
                                        goto fail;
                                }
                                spin_lock_irqsave(&pcpu_lock, flags);
                                /*
                                 * pcpu_lock has been dropped, need to
                                 * restart cpu_slot list walking.
                                 */
                                goto restart;
                        }

                        off = pcpu_alloc_area(chunk, size, align, is_atomic,
                                              &occ_pages);
                        if (off >= 0)
                                goto area_found;
                }
        }

        spin_unlock_irqrestore(&pcpu_lock, flags);

        /*
         * No space left.  Create a new chunk.  We don't want multiple
         * tasks to create chunks simultaneously.  Serialize and create iff
         * there's still no empty chunk after grabbing the mutex.
         */
        if (is_atomic)
                goto fail;

        mutex_lock(&pcpu_alloc_mutex);

        if (list_empty(&pcpu_slot[pcpu_nr_slots - 1])) {
                chunk = pcpu_create_chunk();
                if (!chunk) {
                        mutex_unlock(&pcpu_alloc_mutex);
                        err = "failed to allocate new chunk";
                        goto fail;
                }

                spin_lock_irqsave(&pcpu_lock, flags);
                pcpu_chunk_relocate(chunk, -1);
        } else {
                spin_lock_irqsave(&pcpu_lock, flags);
        }

        mutex_unlock(&pcpu_alloc_mutex);
        goto restart;

area_found:
        spin_unlock_irqrestore(&pcpu_lock, flags);

        /* populate if not all pages are already there */
        if (!is_atomic) {
                int page_start, page_end, rs, re;

                mutex_lock(&pcpu_alloc_mutex);

                page_start = PFN_DOWN(off);
                page_end = PFN_UP(off + size);

                pcpu_for_each_unpop_region(chunk, rs, re, page_start, page_end) {
                        WARN_ON(chunk->immutable);

                        ret = pcpu_populate_chunk(chunk, rs, re);

                        spin_lock_irqsave(&pcpu_lock, flags);
                        if (ret) {
                                mutex_unlock(&pcpu_alloc_mutex);
                                pcpu_free_area(chunk, off, &occ_pages);
                                err = "failed to populate";
                                goto fail_unlock;
                        }
                        pcpu_chunk_populated(chunk, rs, re);
                        spin_unlock_irqrestore(&pcpu_lock, flags);
                }

                mutex_unlock(&pcpu_alloc_mutex);
        }

        if (chunk != pcpu_reserved_chunk)
                pcpu_nr_empty_pop_pages -= occ_pages;

        if (pcpu_nr_empty_pop_pages < PCPU_EMPTY_POP_PAGES_LOW)
                pcpu_schedule_balance_work();

        /* clear the areas and return address relative to base address */
        for_each_possible_cpu(cpu)
                memset((void *)pcpu_chunk_addr(chunk, cpu, 0) + off, 0, size);

        ptr = __addr_to_pcpu_ptr(chunk->base_addr + off);
        kmemleak_alloc_percpu(ptr, size, gfp);
        return ptr;

fail_unlock:
        spin_unlock_irqrestore(&pcpu_lock, flags);
fail:
        if (!is_atomic && warn_limit) {
                pr_warn("allocation failed, size=%zu align=%zu atomic=%d, %s\n",
                        size, align, is_atomic, err);
                dump_stack();
                if (!--warn_limit)
                        pr_info("limit reached, disable warning\n");
        }
        if (is_atomic) {
                /* see the flag handling in pcpu_blance_workfn() */
                pcpu_atomic_alloc_failed = true;
                pcpu_schedule_balance_work();
        }
        return NULL;
}

/**
 * __alloc_percpu_gfp - allocate dynamic percpu area
 * @size: size of area to allocate in bytes
 * @align: alignment of area (max PAGE_SIZE)
 * @gfp: allocation flags
 *
 * Allocate zero-filled percpu area of @size bytes aligned at @align.  If
 * @gfp doesn't contain %GFP_KERNEL, the allocation doesn't block and can
 * be called from any context but is a lot more likely to fail.
 *
 * RETURNS:
 * Percpu pointer to the allocated area on success, NULL on failure.
 */
void __percpu *__alloc_percpu_gfp(size_t size, size_t align, gfp_t gfp)
{
        return pcpu_alloc(size, align, false, gfp);
}
EXPORT_SYMBOL_GPL(__alloc_percpu_gfp);

/**
 * __alloc_percpu - allocate dynamic percpu area
 * @size: size of area to allocate in bytes
 * @align: alignment of area (max PAGE_SIZE)
 *
 * Equivalent to __alloc_percpu_gfp(size, align, %GFP_KERNEL).
 */
void __percpu *__alloc_percpu(size_t size, size_t align)
{
        return pcpu_alloc(size, align, false, GFP_KERNEL);
}
EXPORT_SYMBOL_GPL(__alloc_percpu);

/**
 * __alloc_reserved_percpu - allocate reserved percpu area
 * @size: size of area to allocate in bytes
 * @align: alignment of area (max PAGE_SIZE)
 *
 * Allocate zero-filled percpu area of @size bytes aligned at @align
 * from reserved percpu area if arch has set it up; otherwise,
 * allocation is served from the same dynamic area.  Might sleep.
 * Might trigger writeouts.
 *
 * CONTEXT:
 * Does GFP_KERNEL allocation.
 *
 * RETURNS:
 * Percpu pointer to the allocated area on success, NULL on failure.
 */
void __percpu *__alloc_reserved_percpu(size_t size, size_t align)
{
        return pcpu_alloc(size, align, true, GFP_KERNEL);
}

/**
 * pcpu_balance_workfn - manage the amount of free chunks and populated pages
 * @work: unused
 *
 * Reclaim all fully free chunks except for the first one.
 */
static void pcpu_balance_workfn(struct work_struct *work)
{
        LIST_HEAD(to_free);
        struct list_head *free_head = &pcpu_slot[pcpu_nr_slots - 1];
        struct pcpu_chunk *chunk, *next;
        int slot, nr_to_pop, ret;

        /*
         * There's no reason to keep around multiple unused chunks and VM
         * areas can be scarce.  Destroy all free chunks except for one.
         */
        mutex_lock(&pcpu_alloc_mutex);
        spin_lock_irq(&pcpu_lock);

        list_for_each_entry_safe(chunk, next, free_head, list) {
                WARN_ON(chunk->immutable);

                /* spare the first one */
                if (chunk == list_first_entry(free_head, struct pcpu_chunk, list))
                        continue;

                list_move(&chunk->list, &to_free);
        }

        spin_unlock_irq(&pcpu_lock);

        list_for_each_entry_safe(chunk, next, &to_free, list) {
                int rs, re;

                pcpu_for_each_pop_region(chunk, rs, re, 0, pcpu_unit_pages) {
                        pcpu_depopulate_chunk(chunk, rs, re);
                        spin_lock_irq(&pcpu_lock);
                        pcpu_chunk_depopulated(chunk, rs, re);
                        spin_unlock_irq(&pcpu_lock);
                }
                pcpu_destroy_chunk(chunk);
        }

        /*
         * Ensure there are certain number of free populated pages for
         * atomic allocs.  Fill up from the most packed so that atomic
         * allocs don't increase fragmentation.  If atomic allocation
         * failed previously, always populate the maximum amount.  This
         * should prevent atomic allocs larger than PAGE_SIZE from keeping
         * failing indefinitely; however, large atomic allocs are not
         * something we support properly and can be highly unreliable and
         * inefficient.
         */
retry_pop:
        if (pcpu_atomic_alloc_failed) {
                nr_to_pop = PCPU_EMPTY_POP_PAGES_HIGH;
                /* best effort anyway, don't worry about synchronization */
                pcpu_atomic_alloc_failed = false;
        } else {
                nr_to_pop = clamp(PCPU_EMPTY_POP_PAGES_HIGH -
                                  pcpu_nr_empty_pop_pages,
                                  0, PCPU_EMPTY_POP_PAGES_HIGH);
        }

        for (slot = pcpu_size_to_slot(PAGE_SIZE); slot < pcpu_nr_slots; slot++) {
                int nr_unpop = 0, rs, re;

                if (!nr_to_pop)
                        break;

                spin_lock_irq(&pcpu_lock);
                list_for_each_entry(chunk, &pcpu_slot[slot], list) {
                        nr_unpop = pcpu_unit_pages - chunk->nr_populated;
                        if (nr_unpop)
                                break;
                }
                spin_unlock_irq(&pcpu_lock);

                if (!nr_unpop)
                        continue;

                /* @chunk can't go away while pcpu_alloc_mutex is held */
                pcpu_for_each_unpop_region(chunk, rs, re, 0, pcpu_unit_pages) {
                        int nr = min(re - rs, nr_to_pop);

                        ret = pcpu_populate_chunk(chunk, rs, rs + nr);
                        if (!ret) {
                                nr_to_pop -= nr;
                                spin_lock_irq(&pcpu_lock);
                                pcpu_chunk_populated(chunk, rs, rs + nr);
                                spin_unlock_irq(&pcpu_lock);
                        } else {
                                nr_to_pop = 0;
                        }

                        if (!nr_to_pop)
                                break;
                }
        }

        if (nr_to_pop) {
                /* ran out of chunks to populate, create a new one and retry */
                chunk = pcpu_create_chunk();
                if (chunk) {
                        spin_lock_irq(&pcpu_lock);
                        pcpu_chunk_relocate(chunk, -1);
                        spin_unlock_irq(&pcpu_lock);
                        goto retry_pop;
                }
        }

        mutex_unlock(&pcpu_alloc_mutex);
}

/**
 * free_percpu - free percpu area
 * @ptr: pointer to area to free
 *
 * Free percpu area @ptr.
 *
 * CONTEXT:
 * Can be called from atomic context.
 */
void free_percpu(void __percpu *ptr)
{
        void *addr;
        struct pcpu_chunk *chunk;
        unsigned long flags;
        int off, occ_pages;

        if (!ptr)
                return;

        kmemleak_free_percpu(ptr);

        addr = __pcpu_ptr_to_addr(ptr);

        spin_lock_irqsave(&pcpu_lock, flags);

        chunk = pcpu_chunk_addr_search(addr);
        off = addr - chunk->base_addr;

        pcpu_free_area(chunk, off, &occ_pages);

        if (chunk != pcpu_reserved_chunk)
                pcpu_nr_empty_pop_pages += occ_pages;

        /* if there are more than one fully free chunks, wake up grim reaper */
        if (chunk->free_size == pcpu_unit_size) {
                struct pcpu_chunk *pos;

                list_for_each_entry(pos, &pcpu_slot[pcpu_nr_slots - 1], list)
                        if (pos != chunk) {
                                pcpu_schedule_balance_work();
                                break;
                        }
        }

        spin_unlock_irqrestore(&pcpu_lock, flags);
}
EXPORT_SYMBOL_GPL(free_percpu);

/**
 * is_kernel_percpu_address - test whether address is from static percpu area
 * @addr: address to test
 *
 * Test whether @addr belongs to in-kernel static percpu area.  Module
 * static percpu areas are not considered.  For those, use
 * is_module_percpu_address().
 *
 * RETURNS:
 * %true if @addr is from in-kernel static percpu area, %false otherwise.
 */
bool is_kernel_percpu_address(unsigned long addr)
{
#ifdef CONFIG_SMP
        const size_t static_size = __per_cpu_end - __per_cpu_start;
        void __percpu *base = __addr_to_pcpu_ptr(pcpu_base_addr);
        unsigned int cpu;

        for_each_possible_cpu(cpu) {
                void *start = per_cpu_ptr(base, cpu);

                if ((void *)addr >= start && (void *)addr < start + static_size)
                        return true;
        }
#endif
        /* on UP, can't distinguish from other static vars, always false */
        return false;
}

/**
 * per_cpu_ptr_to_phys - convert translated percpu address to physical address
 * @addr: the address to be converted to physical address
 *
 * Given @addr which is dereferenceable address obtained via one of
 * percpu access macros, this function translates it into its physical
 * address.  The caller is responsible for ensuring @addr stays valid
 * until this function finishes.
 *
 * percpu allocator has special setup for the first chunk, which currently
 * supports either embedding in linear address space or vmalloc mapping,
 * and, from the second one, the backing allocator (currently either vm or
 * km) provides translation.
 *
 * The addr can be translated simply without checking if it falls into the
 * first chunk. But the current code reflects better how percpu allocator
 * actually works, and the verification can discover both bugs in percpu
 * allocator itself and per_cpu_ptr_to_phys() callers. So we keep current
 * code.
 *
 * RETURNS:
 * The physical address for @addr.
 */
phys_addr_t per_cpu_ptr_to_phys(void *addr)
{
        void __percpu *base = __addr_to_pcpu_ptr(pcpu_base_addr);
        bool in_first_chunk = false;
        unsigned long first_low, first_high;
        unsigned int cpu;

        /*
         * The following test on unit_low/high isn't strictly
         * necessary but will speed up lookups of addresses which
         * aren't in the first chunk.
         */
        first_low = pcpu_chunk_addr(pcpu_first_chunk, pcpu_low_unit_cpu, 0);
        first_high = pcpu_chunk_addr(pcpu_first_chunk, pcpu_high_unit_cpu,
                                     pcpu_unit_pages);
        if ((unsigned long)addr >= first_low &&
            (unsigned long)addr < first_high) {
                for_each_possible_cpu(cpu) {
                        void *start = per_cpu_ptr(base, cpu);

                        if (addr >= start && addr < start + pcpu_unit_size) {
                                in_first_chunk = true;
                                break;
                        }
                }
        }

        if (in_first_chunk) {
                if (!is_vmalloc_addr(addr))
                        return __pa(addr);
                else
                        return page_to_phys(vmalloc_to_page(addr)) +
                               offset_in_page(addr);
        } else
                return page_to_phys(pcpu_addr_to_page(addr)) +
                       offset_in_page(addr);
}

/**
 * pcpu_alloc_alloc_info - allocate percpu allocation info
 * @nr_groups: the number of groups
 * @nr_units: the number of units
 *
 * Allocate ai which is large enough for @nr_groups groups containing
 * @nr_units units.  The returned ai's groups[0].cpu_map points to the
 * cpu_map array which is long enough for @nr_units and filled with
 * NR_CPUS.  It's the caller's responsibility to initialize cpu_map
 * pointer of other groups.
 *
 * RETURNS:
 * Pointer to the allocated pcpu_alloc_info on success, NULL on
 * failure.
 */
struct pcpu_alloc_info * __init pcpu_alloc_alloc_info(int nr_groups,
                                                      int nr_units)
{
        struct pcpu_alloc_info *ai;
        size_t base_size, ai_size;
        void *ptr;
        int unit;

        base_size = ALIGN(sizeof(*ai) + nr_groups * sizeof(ai->groups[0]),
                          __alignof__(ai->groups[0].cpu_map[0]));
        ai_size = base_size + nr_units * sizeof(ai->groups[0].cpu_map[0]);

        ptr = memblock_virt_alloc_nopanic(PFN_ALIGN(ai_size), 0);
        if (!ptr)
                return NULL;
        ai = ptr;
        ptr += base_size;

        ai->groups[0].cpu_map = ptr;

        for (unit = 0; unit < nr_units; unit++)
                ai->groups[0].cpu_map[unit] = NR_CPUS;

        ai->nr_groups = nr_groups;
        ai->__ai_size = PFN_ALIGN(ai_size);

        return ai;
}

/**
 * pcpu_free_alloc_info - free percpu allocation info
 * @ai: pcpu_alloc_info to free
 *
 * Free @ai which was allocated by pcpu_alloc_alloc_info().
 */
void __init pcpu_free_alloc_info(struct pcpu_alloc_info *ai)
{
        memblock_free_early(__pa(ai), ai->__ai_size);
}

/**
 * pcpu_dump_alloc_info - print out information about pcpu_alloc_info
 * @lvl: loglevel
 * @ai: allocation info to dump
 *
 * Print out information about @ai using loglevel @lvl.
 */
static void pcpu_dump_alloc_info(const char *lvl,
                                 const struct pcpu_alloc_info *ai)
{
        int group_width = 1, cpu_width = 1, width;
        char empty_str[] = "--------";
        int alloc = 0, alloc_end = 0;
        int group, v;
        int upa, apl;   /* units per alloc, allocs per line */

        v = ai->nr_groups;
        while (v /= 10)
                group_width++;

        v = num_possible_cpus();
        while (v /= 10)
                cpu_width++;
        empty_str[min_t(int, cpu_width, sizeof(empty_str) - 1)] = '\0';

        upa = ai->alloc_size / ai->unit_size;
        width = upa * (cpu_width + 1) + group_width + 3;
        apl = rounddown_pow_of_two(max(60 / width, 1));

        printk("%spcpu-alloc: s%zu r%zu d%zu u%zu alloc=%zu*%zu",
               lvl, ai->static_size, ai->reserved_size, ai->dyn_size,
               ai->unit_size, ai->alloc_size / ai->atom_size, ai->atom_size);

        for (group = 0; group < ai->nr_groups; group++) {
                const struct pcpu_group_info *gi = &ai->groups[group];
                int unit = 0, unit_end = 0;

                BUG_ON(gi->nr_units % upa);
                for (alloc_end += gi->nr_units / upa;
                     alloc < alloc_end; alloc++) {
                        if (!(alloc % apl)) {
                                pr_cont("\n");
                                printk("%spcpu-alloc: ", lvl);
                        }
                        pr_cont("[%0*d] ", group_width, group);

                        for (unit_end += upa; unit < unit_end; unit++)
                                if (gi->cpu_map[unit] != NR_CPUS)
                                        pr_cont("%0*d ",
                                                cpu_width, gi->cpu_map[unit]);
                                else
                                        pr_cont("%s ", empty_str);
                }
        }
        pr_cont("\n");
}

/**
 * pcpu_setup_first_chunk - initialize the first percpu chunk
 * @ai: pcpu_alloc_info describing how to percpu area is shaped
 * @base_addr: mapped address
 *
 * Initialize the first percpu chunk which contains the kernel static
 * perpcu area.  This function is to be called from arch percpu area
 * setup path.
 *
 * @ai contains all information necessary to initialize the first
 * chunk and prime the dynamic percpu allocator.
 *
 * @ai->static_size is the size of static percpu area.
 *
 * @ai->reserved_size, if non-zero, specifies the amount of bytes to
 * reserve after the static area in the first chunk.  This reserves
 * the first chunk such that it's available only through reserved
 * percpu allocation.  This is primarily used to serve module percpu
 * static areas on architectures where the addressing model has
 * limited offset range for symbol relocations to guarantee module
 * percpu symbols fall inside the relocatable range.
 *
 * @ai->dyn_size determines the number of bytes available for dynamic
 * allocation in the first chunk.  The area between @ai->static_size +
 * @ai->reserved_size + @ai->dyn_size and @ai->unit_size is unused.
 *
 * @ai->unit_size specifies unit size and must be aligned to PAGE_SIZE
 * and equal to or larger than @ai->static_size + @ai->reserved_size +
 * @ai->dyn_size.
 *
 * @ai->atom_size is the allocation atom size and used as alignment
 * for vm areas.
 *
 * @ai->alloc_size is the allocation size and always multiple of
 * @ai->atom_size.  This is larger than @ai->atom_size if
 * @ai->unit_size is larger than @ai->atom_size.
 *
 * @ai->nr_groups and @ai->groups describe virtual memory layout of
 * percpu areas.  Units which should be colocated are put into the
 * same group.  Dynamic VM areas will be allocated according to these
 * groupings.  If @ai->nr_groups is zero, a single group containing
 * all units is assumed.
 *
 * The caller should have mapped the first chunk at @base_addr and
 * copied static data to each unit.
 *
 * If the first chunk ends up with both reserved and dynamic areas, it
 * is served by two chunks - one to serve the core static and reserved
 * areas and the other for the dynamic area.  They share the same vm
 * and page map but uses different area allocation map to stay away
 * from each other.  The latter chunk is circulated in the chunk slots
 * and available for dynamic allocation like any other chunks.
 *
 * RETURNS:
 * 0 on success, -errno on failure.
 */
int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
                                  void *base_addr)
{
        static int smap[PERCPU_DYNAMIC_EARLY_SLOTS] __initdata;
        static int dmap[PERCPU_DYNAMIC_EARLY_SLOTS] __initdata;
        size_t dyn_size = ai->dyn_size;
        size_t size_sum = ai->static_size + ai->reserved_size + dyn_size;
        struct pcpu_chunk *schunk, *dchunk = NULL;
        unsigned long *group_offsets;
        size_t *group_sizes;
        unsigned long *unit_off;
        unsigned int cpu;
        int *unit_map;
        int group, unit, i;

#define PCPU_SETUP_BUG_ON(cond) do {                                    \
        if (unlikely(cond)) {                                           \
                pr_emerg("failed to initialize, %s\n", #cond);          \
                pr_emerg("cpu_possible_mask=%*pb\n",                    \
                         cpumask_pr_args(cpu_possible_mask));           \
                pcpu_dump_alloc_info(KERN_EMERG, ai);                   \
                BUG();                                                  \
        }                                                               \
} while (0)

        /* sanity checks */
        PCPU_SETUP_BUG_ON(ai->nr_groups <= 0);
#ifdef CONFIG_SMP
        PCPU_SETUP_BUG_ON(!ai->static_size);
        PCPU_SETUP_BUG_ON(offset_in_page(__per_cpu_start));
#endif
        PCPU_SETUP_BUG_ON(!base_addr);
        PCPU_SETUP_BUG_ON(offset_in_page(base_addr));
        PCPU_SETUP_BUG_ON(ai->unit_size < size_sum);
        PCPU_SETUP_BUG_ON(offset_in_page(ai->unit_size));
        PCPU_SETUP_BUG_ON(ai->unit_size < PCPU_MIN_UNIT_SIZE);
        PCPU_SETUP_BUG_ON(ai->dyn_size < PERCPU_DYNAMIC_EARLY_SIZE);
        PCPU_SETUP_BUG_ON(pcpu_verify_alloc_info(ai) < 0);

        /* process group information and build config tables accordingly */
        group_offsets = memblock_virt_alloc(ai->nr_groups *
                                             sizeof(group_offsets[0]), 0);
        group_sizes = memblock_virt_alloc(ai->nr_groups *
                                           sizeof(group_sizes[0]), 0);
        unit_map = memblock_virt_alloc(nr_cpu_ids * sizeof(unit_map[0]), 0);
        unit_off = memblock_virt_alloc(nr_cpu_ids * sizeof(unit_off[0]), 0);

        for (cpu = 0; cpu < nr_cpu_ids; cpu++)
                unit_map[cpu] = UINT_MAX;

        pcpu_low_unit_cpu = NR_CPUS;
        pcpu_high_unit_cpu = NR_CPUS;

        for (group = 0, unit = 0; group < ai->nr_groups; group++, unit += i) {
                const struct pcpu_group_info *gi = &ai->groups[group];

                group_offsets[group] = gi->base_offset;
                group_sizes[group] = gi->nr_units * ai->unit_size;

                for (i = 0; i < gi->nr_units; i++) {
                        cpu = gi->cpu_map[i];
                        if (cpu == NR_CPUS)
                                continue;

                        PCPU_SETUP_BUG_ON(cpu >= nr_cpu_ids);
                        PCPU_SETUP_BUG_ON(!cpu_possible(cpu));
                        PCPU_SETUP_BUG_ON(unit_map[cpu] != UINT_MAX);

                        unit_map[cpu] = unit + i;
                        unit_off[cpu] = gi->base_offset + i * ai->unit_size;

                        /* determine low/high unit_cpu */
                        if (pcpu_low_unit_cpu == NR_CPUS ||
                            unit_off[cpu] < unit_off[pcpu_low_unit_cpu])
                                pcpu_low_unit_cpu = cpu;
                        if (pcpu_high_unit_cpu == NR_CPUS ||
                            unit_off[cpu] > unit_off[pcpu_high_unit_cpu])
                                pcpu_high_unit_cpu = cpu;
                }
        }
        pcpu_nr_units = unit;

        for_each_possible_cpu(cpu)
                PCPU_SETUP_BUG_ON(unit_map[cpu] == UINT_MAX);

        /* we're done parsing the input, undefine BUG macro and dump config */
#undef PCPU_SETUP_BUG_ON
        pcpu_dump_alloc_info(KERN_DEBUG, ai);

        pcpu_nr_groups = ai->nr_groups;
        pcpu_group_offsets = group_offsets;
        pcpu_group_sizes = group_sizes;
        pcpu_unit_map = unit_map;
        pcpu_unit_offsets = unit_off;

        /* determine basic parameters */
        pcpu_unit_pages = ai->unit_size >> PAGE_SHIFT;
        pcpu_unit_size = pcpu_unit_pages << PAGE_SHIFT;
        pcpu_atom_size = ai->atom_size;
        pcpu_chunk_struct_size = sizeof(struct pcpu_chunk) +
                BITS_TO_LONGS(pcpu_unit_pages) * sizeof(unsigned long);

        /*
         * Allocate chunk slots.  The additional last slot is for
         * empty chunks.
         */
        pcpu_nr_slots = __pcpu_size_to_slot(pcpu_unit_size) + 2;
        pcpu_slot = memblock_virt_alloc(
                        pcpu_nr_slots * sizeof(pcpu_slot[0]), 0);
        for (i = 0; i < pcpu_nr_slots; i++)
                INIT_LIST_HEAD(&pcpu_slot[i]);

        /*
         * Initialize static chunk.  If reserved_size is zero, the
         * static chunk covers static area + dynamic allocation area
         * in the first chunk.  If reserved_size is not zero, it
         * covers static area + reserved area (mostly used for module
         * static percpu allocation).
         */
        schunk = memblock_virt_alloc(pcpu_chunk_struct_size, 0);
        INIT_LIST_HEAD(&schunk->list);
        INIT_WORK(&schunk->map_extend_work, pcpu_map_extend_workfn);
        schunk->base_addr = base_addr;
        schunk->map = smap;
        schunk->map_alloc = ARRAY_SIZE(smap);
        schunk->immutable = true;
        bitmap_fill(schunk->populated, pcpu_unit_pages);
        schunk->nr_populated = pcpu_unit_pages;

        if (ai->reserved_size) {
                schunk->free_size = ai->reserved_size;
                pcpu_reserved_chunk = schunk;
                pcpu_reserved_chunk_limit = ai->static_size + ai->reserved_size;
        } else {
                schunk->free_size = dyn_size;
                dyn_size = 0;                   /* dynamic area covered */
        }
        schunk->contig_hint = schunk->free_size;

        schunk->map[0] = 1;
        schunk->map[1] = ai->static_size;
        schunk->map_used = 1;
        if (schunk->free_size)
                schunk->map[++schunk->map_used] = ai->static_size + schunk->free_size;
        schunk->map[schunk->map_used] |= 1;

        /* init dynamic chunk if necessary */
        if (dyn_size) {
                dchunk = memblock_virt_alloc(pcpu_chunk_struct_size, 0);
                INIT_LIST_HEAD(&dchunk->list);
                INIT_WORK(&dchunk->map_extend_work, pcpu_map_extend_workfn);
                dchunk->base_addr = base_addr;
                dchunk->map = dmap;
                dchunk->map_alloc = ARRAY_SIZE(dmap);
                dchunk->immutable = true;
                bitmap_fill(dchunk->populated, pcpu_unit_pages);
                dchunk->nr_populated = pcpu_unit_pages;

                dchunk->contig_hint = dchunk->free_size = dyn_size;
                dchunk->map[0] = 1;
                dchunk->map[1] = pcpu_reserved_chunk_limit;
                dchunk->map[2] = (pcpu_reserved_chunk_limit + dchunk->free_size) | 1;
                dchunk->map_used = 2;
        }

        /* link the first chunk in */
        pcpu_first_chunk = dchunk ?: schunk;
        pcpu_nr_empty_pop_pages +=
                pcpu_count_occupied_pages(pcpu_first_chunk, 1);
        pcpu_chunk_relocate(pcpu_first_chunk, -1);

        /* we're done */
        pcpu_base_addr = base_addr;
        return 0;
}

#ifdef CONFIG_SMP

const char * const pcpu_fc_names[PCPU_FC_NR] __initconst = {
        [PCPU_FC_AUTO]  = "auto",
        [PCPU_FC_EMBED] = "embed",
        [PCPU_FC_PAGE]  = "page",
};

enum pcpu_fc pcpu_chosen_fc __initdata = PCPU_FC_AUTO;

static int __init percpu_alloc_setup(char *str)
{
        if (!str)
                return -EINVAL;

        if (0)
                /* nada */;
#ifdef CONFIG_NEED_PER_CPU_EMBED_FIRST_CHUNK
        else if (!strcmp(str, "embed"))
                pcpu_chosen_fc = PCPU_FC_EMBED;
#endif
#ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
        else if (!strcmp(str, "page"))
                pcpu_chosen_fc = PCPU_FC_PAGE;
#endif
        else
                pr_warn("unknown allocator %s specified\n", str);

        return 0;
}
early_param("percpu_alloc", percpu_alloc_setup);

/*
 * pcpu_embed_first_chunk() is used by the generic percpu setup.
 * Build it if needed by the arch config or the generic setup is going
 * to be used.
 */
#if defined(CONFIG_NEED_PER_CPU_EMBED_FIRST_CHUNK) || \
        !defined(CONFIG_HAVE_SETUP_PER_CPU_AREA)
#define BUILD_EMBED_FIRST_CHUNK
#endif

/* build pcpu_page_first_chunk() iff needed by the arch config */
#if defined(CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK)
#define BUILD_PAGE_FIRST_CHUNK
#endif

/* pcpu_build_alloc_info() is used by both embed and page first chunk */
#if defined(BUILD_EMBED_FIRST_CHUNK) || defined(BUILD_PAGE_FIRST_CHUNK)
/**
 * pcpu_build_alloc_info - build alloc_info considering distances between CPUs
 * @reserved_size: the size of reserved percpu area in bytes
 * @dyn_size: minimum free size for dynamic allocation in bytes
 * @atom_size: allocation atom size
 * @cpu_distance_fn: callback to determine distance between cpus, optional
 *
 * This function determines grouping of units, their mappings to cpus
 * and other parameters considering needed percpu size, allocation
 * atom size and distances between CPUs.
 *
 * Groups are always multiples of atom size and CPUs which are of
 * LOCAL_DISTANCE both ways are grouped together and share space for
 * units in the same group.  The returned configuration is guaranteed
 * to have CPUs on different nodes on different groups and >=75% usage
 * of allocated virtual address space.
 *
 * RETURNS:
 * On success, pointer to the new allocation_info is returned.  On
 * failure, ERR_PTR value is returned.
 */
static struct pcpu_alloc_info * __init pcpu_build_alloc_info(
                                size_t reserved_size, size_t dyn_size,
                                size_t atom_size,
                                pcpu_fc_cpu_distance_fn_t cpu_distance_fn)
{
        static int group_map[NR_CPUS] __initdata;
        static int group_cnt[NR_CPUS] __initdata;
        const size_t static_size = __per_cpu_end - __per_cpu_start;
        int nr_groups = 1, nr_units = 0;
        size_t size_sum, min_unit_size, alloc_size;
        int upa, max_upa, uninitialized_var(best_upa);  /* units_per_alloc */
        int last_allocs, group, unit;
        unsigned int cpu, tcpu;
        struct pcpu_alloc_info *ai;
        unsigned int *cpu_map;

        /* this function may be called multiple times */
        memset(group_map, 0, sizeof(group_map));
        memset(group_cnt, 0, sizeof(group_cnt));

        /* calculate size_sum and ensure dyn_size is enough for early alloc */
        size_sum = PFN_ALIGN(static_size + reserved_size +
                            max_t(size_t, dyn_size, PERCPU_DYNAMIC_EARLY_SIZE));
        dyn_size = size_sum - static_size - reserved_size;

        /*
         * Determine min_unit_size, alloc_size and max_upa such that
         * alloc_size is multiple of atom_size and is the smallest
         * which can accommodate 4k aligned segments which are equal to
         * or larger than min_unit_size.
         */
        min_unit_size = max_t(size_t, size_sum, PCPU_MIN_UNIT_SIZE);

        alloc_size = roundup(min_unit_size, atom_size);
        upa = alloc_size / min_unit_size;
        while (alloc_size % upa || (offset_in_page(alloc_size / upa)))
                upa--;
        max_upa = upa;

        /* group cpus according to their proximity */
        for_each_possible_cpu(cpu) {
                group = 0;
        next_group:
                for_each_possible_cpu(tcpu) {
                        if (cpu == tcpu)
                                break;
                        if (group_map[tcpu] == group && cpu_distance_fn &&
                            (cpu_distance_fn(cpu, tcpu) > LOCAL_DISTANCE ||
                             cpu_distance_fn(tcpu, cpu) > LOCAL_DISTANCE)) {
                                group++;
                                nr_groups = max(nr_groups, group + 1);
                                goto next_group;
                        }
                }
                group_map[cpu] = group;
                group_cnt[group]++;
        }

        /*
         * Expand unit size until address space usage goes over 75%
         * and then as much as possible without using more address
         * space.
         */
        last_allocs = INT_MAX;
        for (upa = max_upa; upa; upa--) {
                int allocs = 0, wasted = 0;

                if (alloc_size % upa || (offset_in_page(alloc_size / upa)))
                        continue;

                for (group = 0; group < nr_groups; group++) {
                        int this_allocs = DIV_ROUND_UP(group_cnt[group], upa);
                        allocs += this_allocs;
                        wasted += this_allocs * upa - group_cnt[group];
                }

                /*
                 * Don't accept if wastage is over 1/3.  The
                 * greater-than comparison ensures upa==1 always
                 * passes the following check.
                 */
                if (wasted > num_possible_cpus() / 3)
                        continue;

                /* and then don't consume more memory */
                if (allocs > last_allocs)
                        break;
                last_allocs = allocs;
                best_upa = upa;
        }
        upa = best_upa;

        /* allocate and fill alloc_info */
        for (group = 0; group < nr_groups; group++)
                nr_units += roundup(group_cnt[group], upa);

        ai = pcpu_alloc_alloc_info(nr_groups, nr_units);
        if (!ai)
                return ERR_PTR(-ENOMEM);
        cpu_map = ai->groups[0].cpu_map;

        for (group = 0; group < nr_groups; group++) {
                ai->groups[group].cpu_map = cpu_map;
                cpu_map += roundup(group_cnt[group], upa);
        }

        ai->static_size = static_size;
        ai->reserved_size = reserved_size;
        ai->dyn_size = dyn_size;
        ai->unit_size = alloc_size / upa;
        ai->atom_size = atom_size;
        ai->alloc_size = alloc_size;

        for (group = 0, unit = 0; group_cnt[group]; group++) {
                struct pcpu_group_info *gi = &ai->groups[group];

                /*
                 * Initialize base_offset as if all groups are located
                 * back-to-back.  The caller should update this to
                 * reflect actual allocation.
                 */
                gi->base_offset = unit * ai->unit_size;

                for_each_possible_cpu(cpu)
                        if (group_map[cpu] == group)
                                gi->cpu_map[gi->nr_units++] = cpu;
                gi->nr_units = roundup(gi->nr_units, upa);
                unit += gi->nr_units;
        }
        BUG_ON(unit != nr_units);

        return ai;
}
#endif /* BUILD_EMBED_FIRST_CHUNK || BUILD_PAGE_FIRST_CHUNK */

#if defined(BUILD_EMBED_FIRST_CHUNK)
/**
 * pcpu_embed_first_chunk - embed the first percpu chunk into bootmem
 * @reserved_size: the size of reserved percpu area in bytes
 * @dyn_size: minimum free size for dynamic allocation in bytes
 * @atom_size: allocation atom size
 * @cpu_distance_fn: callback to determine distance between cpus, optional
 * @alloc_fn: function to allocate percpu page
 * @free_fn: function to free percpu page
 *
 * This is a helper to ease setting up embedded first percpu chunk and
 * can be called where pcpu_setup_first_chunk() is expected.
 *
 * If this function is used to setup the first chunk, it is allocated
 * by calling @alloc_fn and used as-is without being mapped into
 * vmalloc area.  Allocations are always whole multiples of @atom_size
 * aligned to @atom_size.
 *
 * This enables the first chunk to piggy back on the linear physical
 * mapping which often uses larger page size.  Please note that this
 * can result in very sparse cpu->unit mapping on NUMA machines thus
 * requiring large vmalloc address space.  Don't use this allocator if
 * vmalloc space is not orders of magnitude larger than distances
 * between node memory addresses (ie. 32bit NUMA machines).
 *
 * @dyn_size specifies the minimum dynamic area size.
 *
 * If the needed size is smaller than the minimum or specified unit
 * size, the leftover is returned using @free_fn.
 *
 * RETURNS:
 * 0 on success, -errno on failure.
 */
int __init pcpu_embed_first_chunk(size_t reserved_size, size_t dyn_size,
                                  size_t atom_size,
                                  pcpu_fc_cpu_distance_fn_t cpu_distance_fn,
                                  pcpu_fc_alloc_fn_t alloc_fn,
                                  pcpu_fc_free_fn_t free_fn)
{
        void *base = (void *)ULONG_MAX;
        void **areas = NULL;
        struct pcpu_alloc_info *ai;
        size_t size_sum, areas_size, max_distance;
        int group, i, rc;

        ai = pcpu_build_alloc_info(reserved_size, dyn_size, atom_size,
                                   cpu_distance_fn);
        if (IS_ERR(ai))
                return PTR_ERR(ai);

        size_sum = ai->static_size + ai->reserved_size + ai->dyn_size;
        areas_size = PFN_ALIGN(ai->nr_groups * sizeof(void *));

        areas = memblock_virt_alloc_nopanic(areas_size, 0);
        if (!areas) {
                rc = -ENOMEM;
                goto out_free;
        }

        /* allocate, copy and determine base address */
        for (group = 0; group < ai->nr_groups; group++) {
                struct pcpu_group_info *gi = &ai->groups[group];
                unsigned int cpu = NR_CPUS;
                void *ptr;

                for (i = 0; i < gi->nr_units && cpu == NR_CPUS; i++)
                        cpu = gi->cpu_map[i];
                BUG_ON(cpu == NR_CPUS);

                /* allocate space for the whole group */
                ptr = alloc_fn(cpu, gi->nr_units * ai->unit_size, atom_size);
                if (!ptr) {
                        rc = -ENOMEM;
                        goto out_free_areas;
                }
                /* kmemleak tracks the percpu allocations separately */
                kmemleak_free(ptr);
                areas[group] = ptr;

                base = min(ptr, base);
        }

        /*
         * Copy data and free unused parts.  This should happen after all
         * allocations are complete; otherwise, we may end up with
         * overlapping groups.
         */
        for (group = 0; group < ai->nr_groups; group++) {
                struct pcpu_group_info *gi = &ai->groups[group];
                void *ptr = areas[group];

                for (i = 0; i < gi->nr_units; i++, ptr += ai->unit_size) {
                        if (gi->cpu_map[i] == NR_CPUS) {
                                /* unused unit, free whole */

                                free_fn(ptr, ai->unit_size);
                                continue;
                        }
                        /* copy and return the unused part */
                        memcpy(ptr, __per_cpu_load, ai->static_size);
                        free_fn(ptr + size_sum, ai->unit_size - size_sum);
                }
        }

        /* base address is now known, determine group base offsets */
        max_distance = 0;
        for (group = 0; group < ai->nr_groups; group++) {
                ai->groups[group].base_offset = areas[group] - base;
                max_distance = max_t(size_t, max_distance,
                                     ai->groups[group].base_offset);
        }
        max_distance += ai->unit_size;

        /* warn if maximum distance is further than 75% of vmalloc space */
        if (max_distance > VMALLOC_TOTAL * 3 / 4) {
                pr_warn("max_distance=0x%zx too large for vmalloc space 0x%lx\n",
                        max_distance, VMALLOC_TOTAL);
#ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
                /* and fail if we have fallback */
                rc = -EINVAL;
                goto out_free;
#endif
        }

        pr_info("Embedded %zu pages/cpu @%p s%zu r%zu d%zu u%zu\n",
                PFN_DOWN(size_sum), base, ai->static_size, ai->reserved_size,
                ai->dyn_size, ai->unit_size);

        rc = pcpu_setup_first_chunk(ai, base);
        goto out_free;

out_free_areas:
        for (group = 0; group < ai->nr_groups; group++)
                if (areas[group])
                        free_fn(areas[group],
                                ai->groups[group].nr_units * ai->unit_size);
out_free:
        pcpu_free_alloc_info(ai);
        if (areas)
                memblock_free_early(__pa(areas), areas_size);
        return rc;
}
#endif /* BUILD_EMBED_FIRST_CHUNK */

#ifdef BUILD_PAGE_FIRST_CHUNK
/**
 * pcpu_page_first_chunk - map the first chunk using PAGE_SIZE pages
 * @reserved_size: the size of reserved percpu area in bytes
 * @alloc_fn: function to allocate percpu page, always called with PAGE_SIZE
 * @free_fn: function to free percpu page, always called with PAGE_SIZE
 * @populate_pte_fn: function to populate pte
 *
 * This is a helper to ease setting up page-remapped first percpu
 * chunk and can be called where pcpu_setup_first_chunk() is expected.
 *
 * This is the basic allocator.  Static percpu area is allocated
 * page-by-page into vmalloc area.
 *
 * RETURNS:
 * 0 on success, -errno on failure.
 */
int __init pcpu_page_first_chunk(size_t reserved_size,
                                 pcpu_fc_alloc_fn_t alloc_fn,
                                 pcpu_fc_free_fn_t free_fn,
                                 pcpu_fc_populate_pte_fn_t populate_pte_fn)
{
        static struct vm_struct vm;
        struct pcpu_alloc_info *ai;
        char psize_str[16];
        int unit_pages;
        size_t pages_size;
        struct page **pages;
        int unit, i, j, rc;

        snprintf(psize_str, sizeof(psize_str), "%luK", PAGE_SIZE >> 10);

        ai = pcpu_build_alloc_info(reserved_size, 0, PAGE_SIZE, NULL);
        if (IS_ERR(ai))
                return PTR_ERR(ai);
        BUG_ON(ai->nr_groups != 1);
        BUG_ON(ai->groups[0].nr_units != num_possible_cpus());

        unit_pages = ai->unit_size >> PAGE_SHIFT;

        /* unaligned allocations can't be freed, round up to page size */
        pages_size = PFN_ALIGN(unit_pages * num_possible_cpus() *
                               sizeof(pages[0]));
        pages = memblock_virt_alloc(pages_size, 0);

        /* allocate pages */
        j = 0;
        for (unit = 0; unit < num_possible_cpus(); unit++)
                for (i = 0; i < unit_pages; i++) {
                        unsigned int cpu = ai->groups[0].cpu_map[unit];
                        void *ptr;

                        ptr = alloc_fn(cpu, PAGE_SIZE, PAGE_SIZE);
                        if (!ptr) {
                                pr_warn("failed to allocate %s page for cpu%u\n",
                                        psize_str, cpu);
                                goto enomem;
                        }
                        /* kmemleak tracks the percpu allocations separately */
                        kmemleak_free(ptr);
                        pages[j++] = virt_to_page(ptr);
                }

        /* allocate vm area, map the pages and copy static data */
        vm.flags = VM_ALLOC;
        vm.size = num_possible_cpus() * ai->unit_size;
        vm_area_register_early(&vm, PAGE_SIZE);

        for (unit = 0; unit < num_possible_cpus(); unit++) {
                unsigned long unit_addr =
                        (unsigned long)vm.addr + unit * ai->unit_size;

                for (i = 0; i < unit_pages; i++)
                        populate_pte_fn(unit_addr + (i << PAGE_SHIFT));

                /* pte already populated, the following shouldn't fail */
                rc = __pcpu_map_pages(unit_addr, &pages[unit * unit_pages],
                                      unit_pages);
                if (rc < 0)
                        panic("failed to map percpu area, err=%d\n", rc);

                /*
                 * FIXME: Archs with virtual cache should flush local
                 * cache for the linear mapping here - something
                 * equivalent to flush_cache_vmap() on the local cpu.
                 * flush_cache_vmap() can't be used as most supporting
                 * data structures are not set up yet.
                 */

                /* copy static data */
                memcpy((void *)unit_addr, __per_cpu_load, ai->static_size);
        }

        /* we're ready, commit */
        pr_info("%d %s pages/cpu @%p s%zu r%zu d%zu\n",
                unit_pages, psize_str, vm.addr, ai->static_size,
                ai->reserved_size, ai->dyn_size);

        rc = pcpu_setup_first_chunk(ai, vm.addr);
        goto out_free_ar;

enomem:
        while (--j >= 0)
                free_fn(page_address(pages[j]), PAGE_SIZE);
        rc = -ENOMEM;
out_free_ar:
        memblock_free_early(__pa(pages), pages_size);
        pcpu_free_alloc_info(ai);
        return rc;
}
#endif /* BUILD_PAGE_FIRST_CHUNK */

#ifndef CONFIG_HAVE_SETUP_PER_CPU_AREA
/*
 * Generic SMP percpu area setup.
 *
 * The embedding helper is used because its behavior closely resembles
 * the original non-dynamic generic percpu area setup.  This is
 * important because many archs have addressing restrictions and might
 * fail if the percpu area is located far away from the previous
 * location.  As an added bonus, in non-NUMA cases, embedding is
 * generally a good idea TLB-wise because percpu area can piggy back
 * on the physical linear memory mapping which uses large page
 * mappings on applicable archs.
 */
unsigned long __per_cpu_offset[NR_CPUS] __read_mostly;
EXPORT_SYMBOL(__per_cpu_offset);

static void * __init pcpu_dfl_fc_alloc(unsigned int cpu, size_t size,
                                       size_t align)
{
        return  memblock_virt_alloc_from_nopanic(
                        size, align, __pa(MAX_DMA_ADDRESS));
}

static void __init pcpu_dfl_fc_free(void *ptr, size_t size)
{
        memblock_free_early(__pa(ptr), size);
}

void __init setup_per_cpu_areas(void)
{
        unsigned long delta;
        unsigned int cpu;
        int rc;

        /*
         * Always reserve area for module percpu variables.  That's
         * what the legacy allocator did.
         */
        rc = pcpu_embed_first_chunk(PERCPU_MODULE_RESERVE,
                                    PERCPU_DYNAMIC_RESERVE, PAGE_SIZE, NULL,
                                    pcpu_dfl_fc_alloc, pcpu_dfl_fc_free);
        if (rc < 0)
                panic("Failed to initialize percpu areas.");

        delta = (unsigned long)pcpu_base_addr - (unsigned long)__per_cpu_start;
        for_each_possible_cpu(cpu)
                __per_cpu_offset[cpu] = delta + pcpu_unit_offsets[cpu];
}
#endif  /* CONFIG_HAVE_SETUP_PER_CPU_AREA */

#else   /* CONFIG_SMP */

/*
 * UP percpu area setup.
 *
 * UP always uses km-based percpu allocator with identity mapping.
 * Static percpu variables are indistinguishable from the usual static
 * variables and don't require any special preparation.
 */
void __init setup_per_cpu_areas(void)
{
        const size_t unit_size =
                roundup_pow_of_two(max_t(size_t, PCPU_MIN_UNIT_SIZE,
                                         PERCPU_DYNAMIC_RESERVE));
        struct pcpu_alloc_info *ai;
        void *fc;

        ai = pcpu_alloc_alloc_info(1, 1);
        fc = memblock_virt_alloc_from_nopanic(unit_size,
                                              PAGE_SIZE,
                                              __pa(MAX_DMA_ADDRESS));
        if (!ai || !fc)
                panic("Failed to allocate memory for percpu areas.");
        /* kmemleak tracks the percpu allocations separately */
        kmemleak_free(fc);

        ai->dyn_size = unit_size;
        ai->unit_size = unit_size;
        ai->atom_size = unit_size;
        ai->alloc_size = unit_size;
        ai->groups[0].nr_units = 1;
        ai->groups[0].cpu_map[0] = 0;

        if (pcpu_setup_first_chunk(ai, fc) < 0)
                panic("Failed to initialize percpu areas.");
}

#endif  /* CONFIG_SMP */

/*
 * First and reserved chunks are initialized with temporary allocation
 * map in initdata so that they can be used before slab is online.
 * This function is called after slab is brought up and replaces those
 * with properly allocated maps.
 */
void __init percpu_init_late(void)
{
        struct pcpu_chunk *target_chunks[] =
                { pcpu_first_chunk, pcpu_reserved_chunk, NULL };
        struct pcpu_chunk *chunk;
        unsigned long flags;
        int i;

        for (i = 0; (chunk = target_chunks[i]); i++) {
                int *map;
                const size_t size = PERCPU_DYNAMIC_EARLY_SLOTS * sizeof(map[0]);

                BUILD_BUG_ON(size > PAGE_SIZE);

                map = pcpu_mem_zalloc(size);
                BUG_ON(!map);

                spin_lock_irqsave(&pcpu_lock, flags);
                memcpy(map, chunk->map, size);
                chunk->map = map;
                spin_unlock_irqrestore(&pcpu_lock, flags);
        }
}

/*
 * Percpu allocator is initialized early during boot when neither slab or
 * workqueue is available.  Plug async management until everything is up
 * and running.
 */
static int __init percpu_enable_async(void)
{
        pcpu_async_enabled = true;
        return 0;
}
subsys_initcall(percpu_enable_async);