highmem.c

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/*
 * High memory handling common code and variables.
 *
 * (C) 1999 Andrea Arcangeli, SuSE GmbH, [email protected]
 *          Gerhard Wichert, Siemens AG, [email protected]
 *
 *
 * Redesigned the x86 32-bit VM architecture to deal with
 * 64-bit physical space. With current x86 CPUs this
 * means up to 64 Gigabytes physical RAM.
 *
 * Rewrote high memory support to move the page cache into
 * high memory. Implemented permanent (schedulable) kmaps
 * based on Linus' idea.
 *
 * Copyright (C) 1999 Ingo Molnar <[email protected]>
 */

#include <linux/mm.h>
#include <linux/export.h>
#include <linux/swap.h>
#include <linux/bio.h>
#include <linux/pagemap.h>
#include <linux/mempool.h>
#include <linux/blkdev.h>
#include <linux/init.h>
#include <linux/hash.h>
#include <linux/highmem.h>
#include <linux/kgdb.h>
#include <asm/tlbflush.h>


#if defined(CONFIG_HIGHMEM) || defined(CONFIG_X86_32)
DEFINE_PER_CPU(int, __kmap_atomic_idx);
#endif

/*
 * Virtual_count is not a pure "count".
 *  0 means that it is not mapped, and has not been mapped
 *    since a TLB flush - it is usable.
 *  1 means that there are no users, but it has been mapped
 *    since the last TLB flush - so we can't use it.
 *  n means that there are (n-1) current users of it.
 */
#ifdef CONFIG_HIGHMEM

unsigned long totalhigh_pages __read_mostly;
EXPORT_SYMBOL(totalhigh_pages);


EXPORT_PER_CPU_SYMBOL(__kmap_atomic_idx);

unsigned int nr_free_highpages (void)
{
    pg_data_t *pgdat;
    unsigned int pages = 0;

    for_each_online_pgdat(pgdat) {
        pages += zone_page_state(&pgdat->node_zones[ZONE_HIGHMEM],
            NR_FREE_PAGES);
        if (zone_movable_is_highmem())
            pages += zone_page_state(
                    &pgdat->node_zones[ZONE_MOVABLE],
                    NR_FREE_PAGES);
    }

    return pages;
}

static int pkmap_count[LAST_PKMAP];
static unsigned int last_pkmap_nr;
static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);

pte_t * pkmap_page_table;

static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);

/*
 * Most architectures have no use for kmap_high_get(), so let's abstract
 * the disabling of IRQ out of the locking in that case to save on a
 * potential useless overhead.
 */
#ifdef ARCH_NEEDS_KMAP_HIGH_GET
#define lock_kmap()             spin_lock_irq(&kmap_lock)
#define unlock_kmap()           spin_unlock_irq(&kmap_lock)
#define lock_kmap_any(flags)    spin_lock_irqsave(&kmap_lock, flags)
#define unlock_kmap_any(flags)  spin_unlock_irqrestore(&kmap_lock, flags)
#else
#define lock_kmap()             spin_lock(&kmap_lock)
#define unlock_kmap()           spin_unlock(&kmap_lock)
#define lock_kmap_any(flags)    \
        do { spin_lock(&kmap_lock); (void)(flags); } while (0)
#define unlock_kmap_any(flags)  \
        do { spin_unlock(&kmap_lock); (void)(flags); } while (0)
#endif

struct page *kmap_to_page(void *vaddr)
{
    unsigned long addr = (unsigned long)vaddr;

    if (addr >= PKMAP_ADDR(0) && addr < PKMAP_ADDR(LAST_PKMAP)) {
        int i = (addr - PKMAP_ADDR(0)) >> PAGE_SHIFT;
        return pte_page(pkmap_page_table[i]);
    }

    return virt_to_page(addr);
}

static void flush_all_zero_pkmaps(void)
{
    int i;
    int need_flush = 0;

    flush_cache_kmaps();

    for (i = 0; i < LAST_PKMAP; i++) {
        struct page *page;

        /*
         * zero means we don't have anything to do,
         * >1 means that it is still in use. Only
         * a count of 1 means that it is free but
         * needs to be unmapped
         */
        if (pkmap_count[i] != 1)
            continue;
        pkmap_count[i] = 0;

        /* sanity check */
        BUG_ON(pte_none(pkmap_page_table[i]));

        /*
         * Don't need an atomic fetch-and-clear op here;
         * no-one has the page mapped, and cannot get at
         * its virtual address (and hence PTE) without first
         * getting the kmap_lock (which is held here).
         * So no dangers, even with speculative execution.
         */
        page = pte_page(pkmap_page_table[i]);
        pte_clear(&init_mm, (unsigned long)page_address(page),
              &pkmap_page_table[i]);

        set_page_address(page, NULL);
        need_flush = 1;
    }
    if (need_flush)
        flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
}

void kmap_flush_unused(void)
{
    lock_kmap();
    flush_all_zero_pkmaps();
    unlock_kmap();
}

static inline unsigned long map_new_virtual(struct page *page)
{
    unsigned long vaddr;
    int count;

start:
    count = LAST_PKMAP;
    /* Find an empty entry */
    for (;;) {
        last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
        if (!last_pkmap_nr) {
            flush_all_zero_pkmaps();
            count = LAST_PKMAP;
        }
        if (!pkmap_count[last_pkmap_nr])
            break;  /* Found a usable entry */
        if (--count)
            continue;

        /*
         * Sleep for somebody else to unmap their entries
         */
        {
            DECLARE_WAITQUEUE(wait, current);

            __set_current_state(TASK_UNINTERRUPTIBLE);
            add_wait_queue(&pkmap_map_wait, &wait);
            unlock_kmap();
            schedule();
            remove_wait_queue(&pkmap_map_wait, &wait);
            lock_kmap();

            /* Somebody else might have mapped it while we slept */
            if (page_address(page))
                return (unsigned long)page_address(page);

            /* Re-start */
            goto start;
        }
    }
    vaddr = PKMAP_ADDR(last_pkmap_nr);
    set_pte_at(&init_mm, vaddr,
           &(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot));

    pkmap_count[last_pkmap_nr] = 1;
    set_page_address(page, (void *)vaddr);

    return vaddr;
}

void *kmap_high(struct page *page)
{
    unsigned long vaddr;

    /*
     * For highmem pages, we can't trust "virtual" until
     * after we have the lock.
     */
    lock_kmap();
    vaddr = (unsigned long)page_address(page);
    if (!vaddr)
        vaddr = map_new_virtual(page);
    pkmap_count[PKMAP_NR(vaddr)]++;
    BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 2);
    unlock_kmap();
    return (void*) vaddr;
}

EXPORT_SYMBOL(kmap_high);

#ifdef ARCH_NEEDS_KMAP_HIGH_GET

void *kmap_high_get(struct page *page)
{
    unsigned long vaddr, flags;

    lock_kmap_any(flags);
    vaddr = (unsigned long)page_address(page);
    if (vaddr) {
        BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 1);
        pkmap_count[PKMAP_NR(vaddr)]++;
    }
    unlock_kmap_any(flags);
    return (void*) vaddr;
}
#endif

void kunmap_high(struct page *page)
{
    unsigned long vaddr;
    unsigned long nr;
    unsigned long flags;
    int need_wakeup;

    lock_kmap_any(flags);
    vaddr = (unsigned long)page_address(page);
    BUG_ON(!vaddr);
    nr = PKMAP_NR(vaddr);

    /*
     * A count must never go down to zero
     * without a TLB flush!
     */
    need_wakeup = 0;
    switch (--pkmap_count[nr]) {
    case 0:
        BUG();
    case 1:
        /*
         * Avoid an unnecessary wake_up() function call.
         * The common case is pkmap_count[] == 1, but
         * no waiters.
         * The tasks queued in the wait-queue are guarded
         * by both the lock in the wait-queue-head and by
         * the kmap_lock.  As the kmap_lock is held here,
         * no need for the wait-queue-head's lock.  Simply
         * test if the queue is empty.
         */
        need_wakeup = waitqueue_active(&pkmap_map_wait);
    }
    unlock_kmap_any(flags);

    /* do wake-up, if needed, race-free outside of the spin lock */
    if (need_wakeup)
        wake_up(&pkmap_map_wait);
}

EXPORT_SYMBOL(kunmap_high);
#endif

#if defined(HASHED_PAGE_VIRTUAL)

#define PA_HASH_ORDER   7

/*
 * Describes one page->virtual association
 */
struct page_address_map {
    struct page *page;
    void *virtual;
    struct list_head list;
};

/*
 * page_address_map freelist, allocated from page_address_maps.
 */
static struct list_head page_address_pool;  /* freelist */
static spinlock_t pool_lock;            /* protects page_address_pool */

/*
 * Hash table bucket
 */
static struct page_address_slot {
    struct list_head lh;            /* List of page_address_maps */
    spinlock_t lock;            /* Protect this bucket's list */
} ____cacheline_aligned_in_smp page_address_htable[1<<PA_HASH_ORDER];

static struct page_address_slot *page_slot(const struct page *page)
{
    return &page_address_htable[hash_ptr(page, PA_HASH_ORDER)];
}

void *page_address(const struct page *page)
{
    unsigned long flags;
    void *ret;
    struct page_address_slot *pas;

    if (!PageHighMem(page))
        return lowmem_page_address(page);

    pas = page_slot(page);
    ret = NULL;
    spin_lock_irqsave(&pas->lock, flags);
    if (!list_empty(&pas->lh)) {
        struct page_address_map *pam;

        list_for_each_entry(pam, &pas->lh, list) {
            if (pam->page == page) {
                ret = pam->virtual;
                goto done;
            }
        }
    }
done:
    spin_unlock_irqrestore(&pas->lock, flags);
    return ret;
}

EXPORT_SYMBOL(page_address);

void set_page_address(struct page *page, void *virtual)
{
    unsigned long flags;
    struct page_address_slot *pas;
    struct page_address_map *pam;

    BUG_ON(!PageHighMem(page));

    pas = page_slot(page);
    if (virtual) {      /* Add */
        BUG_ON(list_empty(&page_address_pool));

        spin_lock_irqsave(&pool_lock, flags);
        pam = list_entry(page_address_pool.next,
                struct page_address_map, list);
        list_del(&pam->list);
        spin_unlock_irqrestore(&pool_lock, flags);

        pam->page = page;
        pam->virtual = virtual;

        spin_lock_irqsave(&pas->lock, flags);
        list_add_tail(&pam->list, &pas->lh);
        spin_unlock_irqrestore(&pas->lock, flags);
    } else {        /* Remove */
        spin_lock_irqsave(&pas->lock, flags);
        list_for_each_entry(pam, &pas->lh, list) {
            if (pam->page == page) {
                list_del(&pam->list);
                spin_unlock_irqrestore(&pas->lock, flags);
                spin_lock_irqsave(&pool_lock, flags);
                list_add_tail(&pam->list, &page_address_pool);
                spin_unlock_irqrestore(&pool_lock, flags);
                goto done;
            }
        }
        spin_unlock_irqrestore(&pas->lock, flags);
    }
done:
    return;
}

static struct page_address_map page_address_maps[LAST_PKMAP];

void __init page_address_init(void)
{
    int i;

    INIT_LIST_HEAD(&page_address_pool);
    for (i = 0; i < ARRAY_SIZE(page_address_maps); i++)
        list_add(&page_address_maps[i].list, &page_address_pool);
    for (i = 0; i < ARRAY_SIZE(page_address_htable); i++) {
        INIT_LIST_HEAD(&page_address_htable[i].lh);
        spin_lock_init(&page_address_htable[i].lock);
    }
    spin_lock_init(&pool_lock);
}

#endif  /* defined(CONFIG_HIGHMEM) && !defined(WANT_PAGE_VIRTUAL) */