/*
   * 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/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 = PKMAP_NR(addr);
  		return pte_page(pkmap_page_table[i]);
  	}
  
  	return virt_to_page(addr);
  }
  EXPORT_SYMBOL(kmap_to_page);
  
  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, PKMAP_ADDR(i), &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));
  }
  
  /**
   * kmap_flush_unused - flush all unused kmap mappings in order to remove stray mappings
   */
  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;
  }
  
  /**
   * kmap_high - map a highmem page into memory
   * @page: &struct page to map
   *
   * Returns the page's virtual memory address.
   *
   * We cannot call this from interrupts, as it may block.
   */
  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
  /**
   * kmap_high_get - pin a highmem page into memory
   * @page: &struct page to pin
   *
   * Returns the page's current virtual memory address, or NULL if no mapping
   * exists.  If and only if a non null address is returned then a
   * matching call to kunmap_high() is necessary.
   *
   * This can be called from any context.
   */
  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
  
  /**
   * kunmap_high - unmap a highmem page into memory
   * @page: &struct page to unmap
   *
   * If ARCH_NEEDS_KMAP_HIGH_GET is not defined then this may be called
   * only from user context.
   */
  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;
  };
  
  static struct page_address_map page_address_maps[LAST_PKMAP];
  
  /*
   * 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)];
  }
  
  /**
   * page_address - get the mapped virtual address of a page
   * @page: &struct page to get the virtual address of
   *
   * Returns the page's virtual address.
   */
  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);
  
  /**
   * set_page_address - set a page's virtual address
   * @page: &struct page to set
   * @virtual: virtual address to use
   */
  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 */
  		pam = &page_address_maps[PKMAP_NR((unsigned long)virtual)];
  		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);
  				goto done;
  			}
  		}
  		spin_unlock_irqrestore(&pas->lock, flags);
  	}
  done:
  	return;
  }
  
  void __init page_address_init(void)
  {
  	int i;
  
  	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);
  	}
  }
  
  #endif	/* defined(CONFIG_HIGHMEM) && !defined(WANT_PAGE_VIRTUAL) */