FreeBSD/Linux Kernel Cross Reference
sys/mm/highmem.c

     /*
      * 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) */

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