/*
 * High memory handling common code and variables.
 *
 * (C) 1999 Andrea Arcangeli, SuSE GmbH, andrea@suse.de
 *          Gerhard Wichert, Siemens AG, Gerhard.Wichert@pdb.siemens.de
 *
 *
 * 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 <mingo@redhat.com>
 */

#include <linux/mm.h>
#include <linux/module.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/blktrace_api.h>
#include <asm/tlbflush.h>

/*
 * 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;

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);

        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);

static void flush_all_zero_pkmaps(void)
{
        int i;

        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);
        }
        flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
}

/* Flush all unused kmap mappings in order to remove stray
   mappings. */
void kmap_flush_unused(void)
{
        spin_lock(&kmap_lock);
        flush_all_zero_pkmaps();
        spin_unlock(&kmap_lock);
}

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);
                        spin_unlock(&kmap_lock);
                        schedule();
                        remove_wait_queue(&pkmap_map_wait, &wait);
                        spin_lock(&kmap_lock);

                        /* 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 fastcall *kmap_high(struct page *page)
{
        unsigned long vaddr;

        /*
         * For highmem pages, we can't trust "virtual" until
         * after we have the lock.
         *
         * We cannot call this from interrupts, as it may block
         */
        spin_lock(&kmap_lock);
        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);
        spin_unlock(&kmap_lock);
        return (void*) vaddr;
}

EXPORT_SYMBOL(kmap_high);

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

        spin_lock(&kmap_lock);
        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);
        }
        spin_unlock(&kmap_lock);

        /* 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(struct page *page)
{
        return &page_address_htable[hash_ptr(page, PA_HASH_ORDER)];
}

void *page_address(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) */