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 // 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/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(vaddr);
 }
 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);
 
 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_local_page(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_local_page(page + i);
                 memset(kaddr + start2, 0, this_end - start2);
             }
             end2 -= this_end;
             start2 = 0;
         }
 
         if (kaddr) {
             kunmap_local(kaddr);
             flush_dcache_page(page + i);
         }
 
         if (!end1 && !end2)
             break;
     }
 
     BUG_ON((start1 | start2 | end1 | end2) != 0);
 }
 EXPORT_SYMBOL(zero_user_segments);
 #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(const 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;
                 break;
             }
         }
     }
 
     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);
                 break;
             }
         }
         spin_unlock_irqrestore(&pas->lock, flags);
     }
 
     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) */

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