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highmem.c

#include <linux/module.h>
#include <linux/highmem.h>
#include <linux/smp.h>
#include <asm/fixmap.h>
#include <asm/tlbflush.h>

static pte_t *kmap_pte;

unsigned long highstart_pfn, highend_pfn;

void *__kmap(struct page *page)
{
      void *addr;

      might_sleep();
      if (!PageHighMem(page))
            return page_address(page);
      addr = kmap_high(page);
      flush_tlb_one((unsigned long)addr);

      return addr;
}
EXPORT_SYMBOL(__kmap);

void __kunmap(struct page *page)
{
      BUG_ON(in_interrupt());
      if (!PageHighMem(page))
            return;
      kunmap_high(page);
}
EXPORT_SYMBOL(__kunmap);

/*
 * kmap_atomic/kunmap_atomic is significantly faster than kmap/kunmap because
 * no global lock is needed and because the kmap code must perform a global TLB
 * invalidation when the kmap pool wraps.
 *
 * However when holding an atomic kmap is is not legal to sleep, so atomic
 * kmaps are appropriate for short, tight code paths only.
 */

void *__kmap_atomic(struct page *page, enum km_type type)
{
      enum fixed_addresses idx;
      unsigned long vaddr;

      /* even !CONFIG_PREEMPT needs this, for in_atomic in do_page_fault */
      pagefault_disable();
      if (!PageHighMem(page))
            return page_address(page);

      debug_kmap_atomic(type);
      idx = type + KM_TYPE_NR*smp_processor_id();
      vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
#ifdef CONFIG_DEBUG_HIGHMEM
      BUG_ON(!pte_none(*(kmap_pte - idx)));
#endif
      set_pte(kmap_pte-idx, mk_pte(page, PAGE_KERNEL));
      local_flush_tlb_one((unsigned long)vaddr);

      return (void*) vaddr;
}
EXPORT_SYMBOL(__kmap_atomic);

void __kunmap_atomic(void *kvaddr, enum km_type type)
{
#ifdef CONFIG_DEBUG_HIGHMEM
      unsigned long vaddr = (unsigned long) kvaddr & PAGE_MASK;
      enum fixed_addresses idx = type + KM_TYPE_NR*smp_processor_id();

      if (vaddr < FIXADDR_START) { // FIXME
            pagefault_enable();
            return;
      }

      BUG_ON(vaddr != __fix_to_virt(FIX_KMAP_BEGIN + idx));

      /*
       * force other mappings to Oops if they'll try to access
       * this pte without first remap it
       */
      pte_clear(&init_mm, vaddr, kmap_pte-idx);
      local_flush_tlb_one(vaddr);
#endif

      pagefault_enable();
}
EXPORT_SYMBOL(__kunmap_atomic);

/*
 * This is the same as kmap_atomic() but can map memory that doesn't
 * have a struct page associated with it.
 */
void *kmap_atomic_pfn(unsigned long pfn, enum km_type type)
{
      enum fixed_addresses idx;
      unsigned long vaddr;

      pagefault_disable();

      debug_kmap_atomic(type);
      idx = type + KM_TYPE_NR*smp_processor_id();
      vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
      set_pte(kmap_pte-idx, pfn_pte(pfn, PAGE_KERNEL));
      flush_tlb_one(vaddr);

      return (void*) vaddr;
}

struct page *__kmap_atomic_to_page(void *ptr)
{
      unsigned long idx, vaddr = (unsigned long)ptr;
      pte_t *pte;

      if (vaddr < FIXADDR_START)
            return virt_to_page(ptr);

      idx = virt_to_fix(vaddr);
      pte = kmap_pte - (idx - FIX_KMAP_BEGIN);
      return pte_page(*pte);
}

void __init kmap_init(void)
{
      unsigned long kmap_vstart;

      /* cache the first kmap pte */
      kmap_vstart = __fix_to_virt(FIX_KMAP_BEGIN);
      kmap_pte = kmap_get_fixmap_pte(kmap_vstart);
}

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