highmem.c

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/*
 * highmem.c: virtual kernel memory mappings for high memory
 *
 * PowerPC version, stolen from the i386 version.
 *
 * Used in CONFIG_HIGHMEM systems for memory pages which
 * are not addressable by direct kernel virtual addresses.
 *
 * Copyright (C) 1999 Gerhard Wichert, Siemens AG
 *            [email protected]
 *
 *
 * Redesigned the x86 32-bit VM architecture to deal with
 * up to 16 Terrabyte physical memory. With current x86 CPUs
 * we now support up to 64 Gigabytes physical RAM.
 *
 * Copyright (C) 1999 Ingo Molnar <[email protected]>
 *
 * Reworked for PowerPC by various contributors. Moved from
 * highmem.h by Benjamin Herrenschmidt (c) 2009 IBM Corp.
 */

#include <linux/highmem.h>
#include <linux/module.h>

/*
 * 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.
 */
void *kmap_atomic_prot(struct page *page, pgprot_t prot)
{
    unsigned long vaddr;
    int idx, type;

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

    type = kmap_atomic_idx_push();
    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_at(&init_mm, vaddr, kmap_pte-idx, mk_pte(page, prot), 1);
    local_flush_tlb_page(NULL, vaddr);

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

void __kunmap_atomic(void *kvaddr)
{
    unsigned long vaddr = (unsigned long) kvaddr & PAGE_MASK;
    int type;

    if (vaddr < __fix_to_virt(FIX_KMAP_END)) {
        pagefault_enable();
        return;
    }

    type = kmap_atomic_idx();

#ifdef CONFIG_DEBUG_HIGHMEM
    {
        unsigned int idx;

        idx = type + KM_TYPE_NR * smp_processor_id();
        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_page(NULL, vaddr);
    }
#endif

    kmap_atomic_idx_pop();
    pagefault_enable();
}
EXPORT_SYMBOL(__kunmap_atomic);