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/*

 * 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/pagemap.h>

#include <linux/highmem.h>

#include <linux/swap.h>

#include <linux/slab.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.

 */

static int pkmap_count[LAST_PKMAP];

static unsigned int last_pkmap_nr;

static spinlock_cacheline_t kmap_lock_cacheline = {SPIN_LOCK_UNLOCKED};

#define kmap_lock  kmap_lock_cacheline.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_all();

        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 */

                if (pte_none(pkmap_page_table[i]))

                        BUG();

                /*

                 * 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(&pkmap_page_table[i]);

                page->virtual = NULL;

        }

        flush_tlb_all();

}

static inline unsigned long map_new_virtual(struct page *page, int nonblocking)

{

        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;

                if (nonblocking)

                        return 0;

                /*

                 * Sleep for somebody else to unmap their entries

                 */

                {

                        DECLARE_WAITQUEUE(wait, current);

                        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->virtual)

                                return (unsigned long) page->virtual;

                        /* Re-start */

                        goto start;

                }

        }

        vaddr = PKMAP_ADDR(last_pkmap_nr);

        set_pte(&(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot));

        pkmap_count[last_pkmap_nr] = 1;

        page->virtual = (void *) vaddr;

        return vaddr;

}

void *kmap_high(struct page *page, int nonblocking)

{

        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->virtual;

        if (!vaddr) {

                vaddr = map_new_virtual(page, nonblocking);

                if (!vaddr)

                        goto out;

        }

        pkmap_count[PKMAP_NR(vaddr)]++;

        if (pkmap_count[PKMAP_NR(vaddr)] < 2)

                BUG();

 out:

        spin_unlock(&kmap_lock);

        return (void*) vaddr;

}

void kunmap_high(struct page *page)

{

        unsigned long vaddr;

        unsigned long nr;

        int need_wakeup;

        spin_lock(&kmap_lock);

        vaddr = (unsigned long) page->virtual;

        if (!vaddr)

                BUG();

        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);

}

#define POOL_SIZE 32

/*

 * This lock gets no contention at all, normally.

 */

static spinlock_t emergency_lock = SPIN_LOCK_UNLOCKED;

int nr_emergency_pages;

static LIST_HEAD(emergency_pages);

int nr_emergency_bhs;

static LIST_HEAD(emergency_bhs);

/*

 * Simple bounce buffer support for highmem pages.

 * This will be moved to the block layer in 2.5.

 */

static inline void copy_from_high_bh (struct buffer_head *to,

                         struct buffer_head *from)

{

        struct page *p_from;

        char *vfrom;

        p_from = from->b_page;

        vfrom = kmap_atomic(p_from, KM_USER0);

        memcpy(to->b_data, vfrom + bh_offset(from), to->b_size);

        kunmap_atomic(vfrom, KM_USER0);

}

static inline void copy_to_high_bh_irq (struct buffer_head *to,

                         struct buffer_head *from)

{

        struct page *p_to;

        char *vto;

        unsigned long flags;

        p_to = to->b_page;

        __save_flags(flags);

        __cli();

        vto = kmap_atomic(p_to, KM_BOUNCE_READ);

        memcpy(vto + bh_offset(to), from->b_data, to->b_size);

        kunmap_atomic(vto, KM_BOUNCE_READ);

        __restore_flags(flags);

}

static inline void bounce_end_io (struct buffer_head *bh, int uptodate)

{

        struct page *page;

        struct buffer_head *bh_orig = (struct buffer_head *)(bh->b_private);

        unsigned long flags;

        bh_orig->b_end_io(bh_orig, uptodate);

        page = bh->b_page;

        spin_lock_irqsave(&emergency_lock, flags);

        if (nr_emergency_pages >= POOL_SIZE)

                __free_page(page);

        else {

                /*

                 * We are abusing page->list to manage

                 * the highmem emergency pool:

                 */

                list_add(&page->list, &emergency_pages);

                nr_emergency_pages++;

        }

        if (nr_emergency_bhs >= POOL_SIZE) {

#ifdef HIGHMEM_DEBUG

                /* Don't clobber the constructed slab cache */

                init_waitqueue_head(&bh->b_wait);

#endif

                kmem_cache_free(bh_cachep, bh);

        } else {

                /*

                 * Ditto in the bh case, here we abuse b_inode_buffers:

                 */

                list_add(&bh->b_inode_buffers, &emergency_bhs);

                nr_emergency_bhs++;

        }

        spin_unlock_irqrestore(&emergency_lock, flags);

}

static __init int init_emergency_pool(void)

{

        struct sysinfo i;

        si_meminfo(&i);

        si_swapinfo(&i);

        if (!i.totalhigh)

                return 0;

        spin_lock_irq(&emergency_lock);

        while (nr_emergency_pages < POOL_SIZE) {

                struct page * page = alloc_page(GFP_ATOMIC);

                if (!page) {

                        printk("couldn't refill highmem emergency pages");

                        break;

                }

                list_add(&page->list, &emergency_pages);

                nr_emergency_pages++;

        }

        while (nr_emergency_bhs < POOL_SIZE) {

                struct buffer_head * bh = kmem_cache_alloc(bh_cachep, SLAB_ATOMIC);

                if (!bh) {

                        printk("couldn't refill highmem emergency bhs");

                        break;

                }

                list_add(&bh->b_inode_buffers, &emergency_bhs);

                nr_emergency_bhs++;

        }

        spin_unlock_irq(&emergency_lock);

        printk("allocated %d pages and %d bhs reserved for the highmem bounces\n",

               nr_emergency_pages, nr_emergency_bhs);

        return 0;

}

__initcall(init_emergency_pool);

static void bounce_end_io_write (struct buffer_head *bh, int uptodate)

{

        bounce_end_io(bh, uptodate);

}

static void bounce_end_io_read (struct buffer_head *bh, int uptodate)

{

        struct buffer_head *bh_orig = (struct buffer_head *)(bh->b_private);

        if (uptodate)

                copy_to_high_bh_irq(bh_orig, bh);

        bounce_end_io(bh, uptodate);

}

struct page *alloc_bounce_page (void)

{

        struct list_head *tmp;

        struct page *page;

        page = alloc_page(GFP_NOHIGHIO);

        if (page)

                return page;

        /*

         * No luck. First, kick the VM so it doesn't idle around while

         * we are using up our emergency rations.

         */

        wakeup_bdflush();

repeat_alloc:

        /*

         * Try to allocate from the emergency pool.

         */

        tmp = &emergency_pages;

        spin_lock_irq(&emergency_lock);

        if (!list_empty(tmp)) {

                page = list_entry(tmp->next, struct page, list);

                list_del(tmp->next);

                nr_emergency_pages--;

        }

        spin_unlock_irq(&emergency_lock);

        if (page)

                return page;

        /* we need to wait I/O completion */

        run_task_queue(&tq_disk);

        yield();

        goto repeat_alloc;

}

struct buffer_head *alloc_bounce_bh (void)

{

        struct list_head *tmp;

        struct buffer_head *bh;

        bh = kmem_cache_alloc(bh_cachep, SLAB_NOHIGHIO);

        if (bh)

                return bh;

        /*

         * No luck. First, kick the VM so it doesn't idle around while

         * we are using up our emergency rations.

         */

        wakeup_bdflush();

repeat_alloc:

        /*

         * Try to allocate from the emergency pool.

         */

        tmp = &emergency_bhs;

        spin_lock_irq(&emergency_lock);

        if (!list_empty(tmp)) {

                bh = list_entry(tmp->next, struct buffer_head, b_inode_buffers);

                list_del(tmp->next);

                nr_emergency_bhs--;

        }

        spin_unlock_irq(&emergency_lock);

        if (bh)

                return bh;

        /* we need to wait I/O completion */

        run_task_queue(&tq_disk);

        yield();

        goto repeat_alloc;

}

struct buffer_head * create_bounce(int rw, struct buffer_head * bh_orig)

{

        struct page *page;

        struct buffer_head *bh;

        if (!PageHighMem(bh_orig->b_page))

                return bh_orig;

        bh = alloc_bounce_bh();

        /*

         * This is wasteful for 1k buffers, but this is a stopgap measure

         * and we are being ineffective anyway. This approach simplifies

         * things immensly. On boxes with more than 4GB RAM this should

         * not be an issue anyway.

         */

        page = alloc_bounce_page();

        set_bh_page(bh, page, 0);

        bh->b_next = NULL;

        bh->b_blocknr = bh_orig->b_blocknr;

        bh->b_size = bh_orig->b_size;

        bh->b_list = -1;

        bh->b_dev = bh_orig->b_dev;

        bh->b_count = bh_orig->b_count;

        bh->b_rdev = bh_orig->b_rdev;

        bh->b_state = bh_orig->b_state;

#ifdef HIGHMEM_DEBUG

        bh->b_flushtime = jiffies;

        bh->b_next_free = NULL;

        bh->b_prev_free = NULL;

        /* bh->b_this_page */

        bh->b_reqnext = NULL;

        bh->b_pprev = NULL;

#endif

        /* bh->b_page */

        if (rw == WRITE) {

                bh->b_end_io = bounce_end_io_write;

                copy_from_high_bh(bh, bh_orig);

        } else

                bh->b_end_io = bounce_end_io_read;

        bh->b_private = (void *)bh_orig;

        bh->b_rsector = bh_orig->b_rsector;

#ifdef HIGHMEM_DEBUG

        memset(&bh->b_wait, -1, sizeof(bh->b_wait));

#endif

        return bh;

}