// SPDX-License-Identifier: GPL-2.0

  /*
   * 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>

  #include <linux/vmalloc.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

  /*
   * Architecture with aliasing data cache may define the following family of
   * helper functions in its asm/highmem.h to control cache color of virtual
   * addresses where physical memory pages are mapped by kmap.
   */
  #ifndef get_pkmap_color
  
  /*
   * Determine color of virtual address where the page should be mapped.
   */
  static inline unsigned int get_pkmap_color(struct page *page)
  {
  	return 0;
  }
  #define get_pkmap_color get_pkmap_color
  
  /*
   * Get next index for mapping inside PKMAP region for page with given color.
   */
  static inline unsigned int get_next_pkmap_nr(unsigned int color)
  {
  	static unsigned int last_pkmap_nr;
  
  	last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
  	return last_pkmap_nr;
  }
  
  /*
   * Determine if page index inside PKMAP region (pkmap_nr) of given color
   * has wrapped around PKMAP region end. When this happens an attempt to
   * flush all unused PKMAP slots is made.
   */
  static inline int no_more_pkmaps(unsigned int pkmap_nr, unsigned int color)
  {
  	return pkmap_nr == 0;
  }
  
  /*
   * Get the number of PKMAP entries of the given color. If no free slot is
   * found after checking that many entries, kmap will sleep waiting for
   * someone to call kunmap and free PKMAP slot.
   */
  static inline int get_pkmap_entries_count(unsigned int color)
  {
  	return LAST_PKMAP;
  }
  
  /*
   * Get head of a wait queue for PKMAP entries of the given color.
   * Wait queues for different mapping colors should be independent to avoid
   * unnecessary wakeups caused by freeing of slots of other colors.
   */
  static inline wait_queue_head_t *get_pkmap_wait_queue_head(unsigned int color)
  {
  	static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
  
  	return &pkmap_map_wait;
  }
  #endif

  atomic_long_t _totalhigh_pages __read_mostly;
  EXPORT_SYMBOL(_totalhigh_pages);

  unsigned int __nr_free_highpages(void)

  {

  	struct zone *zone;

  	unsigned int pages = 0;

  	for_each_populated_zone(zone) {
  		if (is_highmem(zone))
  			pages += zone_page_state(zone, NR_FREE_PAGES);

  	}

  
  	return pages;
  }

  static int pkmap_count[LAST_PKMAP];

  static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);

  pte_t *pkmap_page_table;

  /*
   * 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));

  }

  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;

  	unsigned int last_pkmap_nr;
  	unsigned int color = get_pkmap_color(page);

  
  start:

  	count = get_pkmap_entries_count(color);

  	/* Find an empty entry */
  	for (;;) {

  		last_pkmap_nr = get_next_pkmap_nr(color);
  		if (no_more_pkmaps(last_pkmap_nr, color)) {

  			flush_all_zero_pkmaps();

  			count = get_pkmap_entries_count(color);

  		}
  		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);

  			wait_queue_head_t *pkmap_map_wait =
  				get_pkmap_wait_queue_head(color);

  
  			__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;

  	unsigned int color = get_pkmap_color(page);
  	wait_queue_head_t *pkmap_map_wait;

  	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.
  		 */

  		pkmap_map_wait = get_pkmap_wait_queue_head(color);
  		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);

  
  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
  void zero_user_segments(struct page *page, unsigned start1, unsigned end1,
  		unsigned start2, unsigned end2)
  {
  	unsigned int i;
  
  	BUG_ON(end1 > page_size(page) || end2 > page_size(page));

  	if (start1 >= end1)
  		start1 = end1 = 0;
  	if (start2 >= end2)
  		start2 = end2 = 0;

  	for (i = 0; i < compound_nr(page); i++) {
  		void *kaddr = NULL;

  		if (start1 >= PAGE_SIZE) {
  			start1 -= PAGE_SIZE;
  			end1 -= PAGE_SIZE;
  		} else {
  			unsigned this_end = min_t(unsigned, end1, PAGE_SIZE);

  			if (end1 > start1) {
  				kaddr = kmap_atomic(page + i);

  				memset(kaddr + start1, 0, this_end - start1);

  			}

  			end1 -= this_end;
  			start1 = 0;
  		}
  
  		if (start2 >= PAGE_SIZE) {
  			start2 -= PAGE_SIZE;
  			end2 -= PAGE_SIZE;
  		} else {
  			unsigned this_end = min_t(unsigned, end2, PAGE_SIZE);

  			if (end2 > start2) {
  				if (!kaddr)
  					kaddr = kmap_atomic(page + i);

  				memset(kaddr + start2, 0, this_end - start2);

  			}

  			end2 -= this_end;
  			start2 = 0;
  		}
  
  		if (kaddr) {
  			kunmap_atomic(kaddr);
  			flush_dcache_page(page + i);
  		}
  
  		if (!end1 && !end2)
  			break;
  	}
  
  	BUG_ON((start1 | start2 | end1 | end2) != 0);
  }
  EXPORT_SYMBOL(zero_user_segments);
  #endif /* CONFIG_TRANSPARENT_HUGEPAGE */

  #endif /* CONFIG_HIGHMEM */
  
  #ifdef CONFIG_KMAP_LOCAL
  
  #include <asm/kmap_size.h>

  /*

   * With DEBUG_KMAP_LOCAL the stack depth is doubled and every second

   * slot is unused which acts as a guard page
   */

  #ifdef CONFIG_DEBUG_KMAP_LOCAL

  # define KM_INCR	2
  #else
  # define KM_INCR	1
  #endif

  static inline int kmap_local_idx_push(void)
  {

  	WARN_ON_ONCE(in_hardirq() && !irqs_disabled());

  	current->kmap_ctrl.idx += KM_INCR;
  	BUG_ON(current->kmap_ctrl.idx >= KM_MAX_IDX);
  	return current->kmap_ctrl.idx - 1;

  }
  
  static inline int kmap_local_idx(void)
  {

  	return current->kmap_ctrl.idx - 1;

  }
  
  static inline void kmap_local_idx_pop(void)
  {

  	current->kmap_ctrl.idx -= KM_INCR;
  	BUG_ON(current->kmap_ctrl.idx < 0);

  }
  
  #ifndef arch_kmap_local_post_map
  # define arch_kmap_local_post_map(vaddr, pteval)	do { } while (0)
  #endif

  #ifndef arch_kmap_local_pre_unmap
  # define arch_kmap_local_pre_unmap(vaddr)		do { } while (0)
  #endif
  
  #ifndef arch_kmap_local_post_unmap
  # define arch_kmap_local_post_unmap(vaddr)		do { } while (0)
  #endif
  
  #ifndef arch_kmap_local_map_idx
  #define arch_kmap_local_map_idx(idx, pfn)	kmap_local_calc_idx(idx)
  #endif
  
  #ifndef arch_kmap_local_unmap_idx
  #define arch_kmap_local_unmap_idx(idx, vaddr)	kmap_local_calc_idx(idx)
  #endif
  
  #ifndef arch_kmap_local_high_get
  static inline void *arch_kmap_local_high_get(struct page *page)
  {
  	return NULL;
  }
  #endif

  #ifndef arch_kmap_local_set_pte
  #define arch_kmap_local_set_pte(mm, vaddr, ptep, ptev)	\
  	set_pte_at(mm, vaddr, ptep, ptev)
  #endif

  /* Unmap a local mapping which was obtained by kmap_high_get() */

  static inline bool kmap_high_unmap_local(unsigned long vaddr)

  {
  #ifdef ARCH_NEEDS_KMAP_HIGH_GET

  	if (vaddr >= PKMAP_ADDR(0) && vaddr < PKMAP_ADDR(LAST_PKMAP)) {

  		kunmap_high(pte_page(pkmap_page_table[PKMAP_NR(vaddr)]));

  		return true;
  	}

  #endif

  	return false;

  }
  
  static inline int kmap_local_calc_idx(int idx)
  {
  	return idx + KM_MAX_IDX * smp_processor_id();
  }
  
  static pte_t *__kmap_pte;

  static pte_t *kmap_get_pte(unsigned long vaddr, int idx)

  {

  	if (IS_ENABLED(CONFIG_KMAP_LOCAL_NON_LINEAR_PTE_ARRAY))
  		/*
  		 * Set by the arch if __kmap_pte[-idx] does not produce
  		 * the correct entry.
  		 */
  		return virt_to_kpte(vaddr);

  	if (!__kmap_pte)
  		__kmap_pte = virt_to_kpte(__fix_to_virt(FIX_KMAP_BEGIN));

  	return &__kmap_pte[-idx];

  }
  
  void *__kmap_local_pfn_prot(unsigned long pfn, pgprot_t prot)
  {

  	pte_t pteval, *kmap_pte;

  	unsigned long vaddr;
  	int idx;

  	/*
  	 * Disable migration so resulting virtual address is stable

  	 * across preemption.

  	 */
  	migrate_disable();

  	preempt_disable();
  	idx = arch_kmap_local_map_idx(kmap_local_idx_push(), pfn);
  	vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);

  	kmap_pte = kmap_get_pte(vaddr, idx);
  	BUG_ON(!pte_none(*kmap_pte));

  	pteval = pfn_pte(pfn, prot);

  	arch_kmap_local_set_pte(&init_mm, vaddr, kmap_pte, pteval);

  	arch_kmap_local_post_map(vaddr, pteval);

  	current->kmap_ctrl.pteval[kmap_local_idx()] = pteval;

  	preempt_enable();
  
  	return (void *)vaddr;
  }
  EXPORT_SYMBOL_GPL(__kmap_local_pfn_prot);
  
  void *__kmap_local_page_prot(struct page *page, pgprot_t prot)
  {
  	void *kmap;

  	/*
  	 * To broaden the usage of the actual kmap_local() machinery always map
  	 * pages when debugging is enabled and the architecture has no problems
  	 * with alias mappings.
  	 */
  	if (!IS_ENABLED(CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP) && !PageHighMem(page))

  		return page_address(page);
  
  	/* Try kmap_high_get() if architecture has it enabled */
  	kmap = arch_kmap_local_high_get(page);
  	if (kmap)
  		return kmap;
  
  	return __kmap_local_pfn_prot(page_to_pfn(page), prot);
  }
  EXPORT_SYMBOL(__kmap_local_page_prot);
  
  void kunmap_local_indexed(void *vaddr)
  {
  	unsigned long addr = (unsigned long) vaddr & PAGE_MASK;

  	pte_t *kmap_pte;

  	int idx;
  
  	if (addr < __fix_to_virt(FIX_KMAP_END) ||
  	    addr > __fix_to_virt(FIX_KMAP_BEGIN)) {

  		if (IS_ENABLED(CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP)) {
  			/* This _should_ never happen! See above. */
  			WARN_ON_ONCE(1);
  			return;
  		}

  		/*
  		 * Handle mappings which were obtained by kmap_high_get()
  		 * first as the virtual address of such mappings is below
  		 * PAGE_OFFSET. Warn for all other addresses which are in
  		 * the user space part of the virtual address space.
  		 */
  		if (!kmap_high_unmap_local(addr))
  			WARN_ON_ONCE(addr < PAGE_OFFSET);

  		return;
  	}
  
  	preempt_disable();
  	idx = arch_kmap_local_unmap_idx(kmap_local_idx(), addr);
  	WARN_ON_ONCE(addr != __fix_to_virt(FIX_KMAP_BEGIN + idx));

  	kmap_pte = kmap_get_pte(addr, idx);

  	arch_kmap_local_pre_unmap(addr);

  	pte_clear(&init_mm, addr, kmap_pte);

  	arch_kmap_local_post_unmap(addr);

  	current->kmap_ctrl.pteval[kmap_local_idx()] = __pte(0);

  	kmap_local_idx_pop();
  	preempt_enable();

  	migrate_enable();

  }
  EXPORT_SYMBOL(kunmap_local_indexed);

  
  /*
   * Invoked before switch_to(). This is safe even when during or after
   * clearing the maps an interrupt which needs a kmap_local happens because
   * the task::kmap_ctrl.idx is not modified by the unmapping code so a
   * nested kmap_local will use the next unused index and restore the index
   * on unmap. The already cleared kmaps of the outgoing task are irrelevant
   * because the interrupt context does not know about them. The same applies
   * when scheduling back in for an interrupt which happens before the
   * restore is complete.
   */
  void __kmap_local_sched_out(void)
  {
  	struct task_struct *tsk = current;

  	pte_t *kmap_pte;

  	int i;
  
  	/* Clear kmaps */
  	for (i = 0; i < tsk->kmap_ctrl.idx; i++) {
  		pte_t pteval = tsk->kmap_ctrl.pteval[i];
  		unsigned long addr;
  		int idx;
  
  		/* With debug all even slots are unmapped and act as guard */

  		if (IS_ENABLED(CONFIG_DEBUG_KMAP_LOCAL) && !(i & 0x01)) {

  			WARN_ON_ONCE(pte_val(pteval) != 0);

  			continue;
  		}
  		if (WARN_ON_ONCE(pte_none(pteval)))
  			continue;
  
  		/*
  		 * This is a horrible hack for XTENSA to calculate the
  		 * coloured PTE index. Uses the PFN encoded into the pteval
  		 * and the map index calculation because the actual mapped
  		 * virtual address is not stored in task::kmap_ctrl.
  		 * For any sane architecture this is optimized out.
  		 */
  		idx = arch_kmap_local_map_idx(i, pte_pfn(pteval));
  
  		addr = __fix_to_virt(FIX_KMAP_BEGIN + idx);

  		kmap_pte = kmap_get_pte(addr, idx);

  		arch_kmap_local_pre_unmap(addr);

  		pte_clear(&init_mm, addr, kmap_pte);

  		arch_kmap_local_post_unmap(addr);
  	}
  }
  
  void __kmap_local_sched_in(void)
  {
  	struct task_struct *tsk = current;

  	pte_t *kmap_pte;

  	int i;
  
  	/* Restore kmaps */
  	for (i = 0; i < tsk->kmap_ctrl.idx; i++) {
  		pte_t pteval = tsk->kmap_ctrl.pteval[i];
  		unsigned long addr;
  		int idx;
  
  		/* With debug all even slots are unmapped and act as guard */

  		if (IS_ENABLED(CONFIG_DEBUG_KMAP_LOCAL) && !(i & 0x01)) {

  			WARN_ON_ONCE(pte_val(pteval) != 0);

  			continue;
  		}
  		if (WARN_ON_ONCE(pte_none(pteval)))
  			continue;
  
  		/* See comment in __kmap_local_sched_out() */
  		idx = arch_kmap_local_map_idx(i, pte_pfn(pteval));
  		addr = __fix_to_virt(FIX_KMAP_BEGIN + idx);

  		kmap_pte = kmap_get_pte(addr, idx);
  		set_pte_at(&init_mm, addr, kmap_pte, pteval);

  		arch_kmap_local_post_map(addr, pteval);
  	}
  }
  
  void kmap_local_fork(struct task_struct *tsk)
  {
  	if (WARN_ON_ONCE(tsk->kmap_ctrl.idx))
  		memset(&tsk->kmap_ctrl, 0, sizeof(tsk->kmap_ctrl));
  }

  #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(HASHED_PAGE_VIRTUAL) */