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highmem.c

/*
 *  highmem.c: virtual kernel memory mappings for high memory
 *
 *  Provides kernel-static versions of atomic kmap functions originally
 *  found as inlines in include/asm-sparc/highmem.h.  These became
 *  needed as kmap_atomic() and kunmap_atomic() started getting
 *  called from within modules.
 *  -- Tomas Szepe <szepe@pinerecords.com>, September 2002
 *
 *  But kmap_atomic() and kunmap_atomic() cannot be inlined in
 *  modules because they are loaded with btfixup-ped functions.
 */

/*
 * The use of kmap_atomic/kunmap_atomic is discouraged - kmap/kunmap
 * gives a more generic (and caching) interface. But kmap_atomic can
 * be used in IRQ contexts, so in some (very limited) cases we need it.
 *
 * XXX This is an old text. Actually, it's good to use atomic kmaps,
 * provided you remember that they are atomic and not try to sleep
 * with a kmap taken, much like a spinlock. Non-atomic kmaps are
 * shared by CPUs, and so precious, and establishing them requires IPI.
 * Atomic kmaps are lightweight and we may have NCPUS more of them.
 */
#include <linux/mm.h>
#include <linux/highmem.h>
#include <asm/pgalloc.h>
#include <asm/cacheflush.h>
#include <asm/tlbflush.h>
#include <asm/fixmap.h>

void *kmap_atomic(struct page *page, enum km_type type)
{
      unsigned long 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);

      idx = type + KM_TYPE_NR*smp_processor_id();
      vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);

/* XXX Fix - Anton */
#if 0
      __flush_cache_one(vaddr);
#else
      flush_cache_all();
#endif

#ifdef CONFIG_DEBUG_HIGHMEM
      BUG_ON(!pte_none(*(kmap_pte-idx)));
#endif
      set_pte(kmap_pte-idx, mk_pte(page, kmap_prot));
/* XXX Fix - Anton */
#if 0
      __flush_tlb_one(vaddr);
#else
      flush_tlb_all();
#endif

      return (void*) vaddr;
}

void kunmap_atomic(void *kvaddr, enum km_type type)
{
#ifdef CONFIG_DEBUG_HIGHMEM
      unsigned long vaddr = (unsigned long) kvaddr & PAGE_MASK;
      unsigned long 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));

/* XXX Fix - Anton */
#if 0
      __flush_cache_one(vaddr);
#else
      flush_cache_all();
#endif

      /*
       * 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);
/* XXX Fix - Anton */
#if 0
      __flush_tlb_one(vaddr);
#else
      flush_tlb_all();
#endif
#endif

      pagefault_enable();
}

/* We may be fed a pagetable here by ptep_to_xxx and others. */
struct page *kmap_atomic_to_page(void *ptr)
{
      unsigned long idx, vaddr = (unsigned long)ptr;
      pte_t *pte;

      if (vaddr < SRMMU_NOCACHE_VADDR)
            return virt_to_page(ptr);
      if (vaddr < PKMAP_BASE)
            return pfn_to_page(__nocache_pa(vaddr) >> PAGE_SHIFT);
      BUG_ON(vaddr < FIXADDR_START);
      BUG_ON(vaddr > FIXADDR_TOP);

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

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