highmem.c

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/*
 * Copyright 2010 Tilera Corporation. All Rights Reserved.
 *
 *   This program is free software; you can redistribute it and/or
 *   modify it under the terms of the GNU General Public License
 *   as published by the Free Software Foundation, version 2.
 *
 *   This program is distributed in the hope that it will be useful, but
 *   WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
 *   NON INFRINGEMENT.  See the GNU General Public License for
 *   more details.
 */

#include <linux/highmem.h>
#include <linux/module.h>
#include <linux/pagemap.h>
#include <asm/homecache.h>

#define kmap_get_pte(vaddr) \
    pte_offset_kernel(pmd_offset(pud_offset(pgd_offset_k(vaddr), (vaddr)),\
        (vaddr)), (vaddr))


void *kmap(struct page *page)
{
    void *kva;
    unsigned long flags;
    pte_t *ptep;

    might_sleep();
    if (!PageHighMem(page))
        return page_address(page);
    kva = kmap_high(page);

    /*
     * Rewrite the PTE under the lock.  This ensures that the page
     * is not currently migrating.
     */
    ptep = kmap_get_pte((unsigned long)kva);
    flags = homecache_kpte_lock();
    set_pte_at(&init_mm, kva, ptep, mk_pte(page, page_to_kpgprot(page)));
    homecache_kpte_unlock(flags);

    return kva;
}
EXPORT_SYMBOL(kmap);

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

/*
 * Describe a single atomic mapping of a page on a given cpu at a
 * given address, and allow it to be linked into a list.
 */
struct atomic_mapped_page {
    struct list_head list;
    struct page *page;
    int cpu;
    unsigned long va;
};

static spinlock_t amp_lock = __SPIN_LOCK_UNLOCKED(&amp_lock);
static struct list_head amp_list = LIST_HEAD_INIT(amp_list);

/*
 * Combining this structure with a per-cpu declaration lets us give
 * each cpu an atomic_mapped_page structure per type.
 */
struct kmap_amps {
    struct atomic_mapped_page per_type[KM_TYPE_NR];
};
static DEFINE_PER_CPU(struct kmap_amps, amps);

/*
 * Add a page and va, on this cpu, to the list of kmap_atomic pages,
 * and write the new pte to memory.  Writing the new PTE under the
 * lock guarantees that it is either on the list before migration starts
 * (if we won the race), or set_pte() sets the migrating bit in the PTE
 * (if we lost the race).  And doing it under the lock guarantees
 * that when kmap_atomic_fix_one_pte() comes along, it finds a valid
 * PTE in memory, iff the mapping is still on the amp_list.
 *
 * Finally, doing it under the lock lets us safely examine the page
 * to see if it is immutable or not, for the generic kmap_atomic() case.
 * If we examine it earlier we are exposed to a race where it looks
 * writable earlier, but becomes immutable before we write the PTE.
 */
static void kmap_atomic_register(struct page *page, int type,
                 unsigned long va, pte_t *ptep, pte_t pteval)
{
    unsigned long flags;
    struct atomic_mapped_page *amp;

    flags = homecache_kpte_lock();
    spin_lock(&amp_lock);

    /* With interrupts disabled, now fill in the per-cpu info. */
    amp = &__get_cpu_var(amps).per_type[type];
    amp->page = page;
    amp->cpu = smp_processor_id();
    amp->va = va;

    /* For generic kmap_atomic(), choose the PTE writability now. */
    if (!pte_read(pteval))
        pteval = mk_pte(page, page_to_kpgprot(page));

    list_add(&amp->list, &amp_list);
    set_pte(ptep, pteval);
    arch_flush_lazy_mmu_mode();

    spin_unlock(&amp_lock);
    homecache_kpte_unlock(flags);
}

/*
 * Remove a page and va, on this cpu, from the list of kmap_atomic pages.
 * Linear-time search, but we count on the lists being short.
 * We don't need to adjust the PTE under the lock (as opposed to the
 * kmap_atomic_register() case), since we're just unconditionally
 * zeroing the PTE after it's off the list.
 */
static void kmap_atomic_unregister(struct page *page, unsigned long va)
{
    unsigned long flags;
    struct atomic_mapped_page *amp;
    int cpu = smp_processor_id();
    spin_lock_irqsave(&amp_lock, flags);
    list_for_each_entry(amp, &amp_list, list) {
        if (amp->page == page && amp->cpu == cpu && amp->va == va)
            break;
    }
    BUG_ON(&amp->list == &amp_list);
    list_del(&amp->list);
    spin_unlock_irqrestore(&amp_lock, flags);
}

/* Helper routine for kmap_atomic_fix_kpte(), below. */
static void kmap_atomic_fix_one_kpte(struct atomic_mapped_page *amp,
                     int finished)
{
    pte_t *ptep = kmap_get_pte(amp->va);
    if (!finished) {
        set_pte(ptep, pte_mkmigrate(*ptep));
        flush_remote(0, 0, NULL, amp->va, PAGE_SIZE, PAGE_SIZE,
                 cpumask_of(amp->cpu), NULL, 0);
    } else {
        /*
         * Rewrite a default kernel PTE for this page.
         * We rely on the fact that set_pte() writes the
         * present+migrating bits last.
         */
        pte_t pte = mk_pte(amp->page, page_to_kpgprot(amp->page));
        set_pte(ptep, pte);
    }
}

/*
 * This routine is a helper function for homecache_fix_kpte(); see
 * its comments for more information on the "finished" argument here.
 *
 * Note that we hold the lock while doing the remote flushes, which
 * will stall any unrelated cpus trying to do kmap_atomic operations.
 * We could just update the PTEs under the lock, and save away copies
 * of the structs (or just the va+cpu), then flush them after we
 * release the lock, but it seems easier just to do it all under the lock.
 */
void kmap_atomic_fix_kpte(struct page *page, int finished)
{
    struct atomic_mapped_page *amp;
    unsigned long flags;
    spin_lock_irqsave(&amp_lock, flags);
    list_for_each_entry(amp, &amp_list, list) {
        if (amp->page == page)
            kmap_atomic_fix_one_kpte(amp, finished);
    }
    spin_unlock_irqrestore(&amp_lock, flags);
}

/*
 * kmap_atomic/kunmap_atomic is significantly faster than kmap/kunmap
 * because the kmap code must perform a global TLB invalidation when
 * the kmap pool wraps.
 *
 * Note that they may be slower than on x86 (etc.) because unlike on
 * those platforms, we do have to take a global lock to map and unmap
 * pages on Tile (see above).
 *
 * 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_prot(struct page *page, pgprot_t prot)
{
    unsigned long vaddr;
    int idx, type;
    pte_t *pte;

    /* even !CONFIG_PREEMPT needs this, for in_atomic in do_page_fault */
    pagefault_disable();

    /* Avoid icache flushes by disallowing atomic executable mappings. */
    BUG_ON(pte_exec(prot));

    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);
    pte = kmap_get_pte(vaddr);
    BUG_ON(!pte_none(*pte));

    /* Register that this page is mapped atomically on this cpu. */
    kmap_atomic_register(page, type, vaddr, pte, mk_pte(page, prot));

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

void *kmap_atomic(struct page *page)
{
    /* PAGE_NONE is a magic value that tells us to check immutability. */
    return kmap_atomic_prot(page, PAGE_NONE);
}
EXPORT_SYMBOL(kmap_atomic);

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

    if (vaddr >= __fix_to_virt(FIX_KMAP_END) &&
        vaddr <= __fix_to_virt(FIX_KMAP_BEGIN)) {
        pte_t *pte = kmap_get_pte(vaddr);
        pte_t pteval = *pte;
        int idx, type;

        type = kmap_atomic_idx();
        idx = type + KM_TYPE_NR*smp_processor_id();

        /*
         * Force other mappings to Oops if they try to access this pte
         * without first remapping it.  Keeping stale mappings around
         * is a bad idea.
         */
        BUG_ON(!pte_present(pteval) && !pte_migrating(pteval));
        kmap_atomic_unregister(pte_page(pteval), vaddr);
        kpte_clear_flush(pte, vaddr);
        kmap_atomic_idx_pop();
    } else {
        /* Must be a lowmem page */
        BUG_ON(vaddr < PAGE_OFFSET);
        BUG_ON(vaddr >= (unsigned long)high_memory);
    }

    arch_flush_lazy_mmu_mode();
    pagefault_enable();
}
EXPORT_SYMBOL(__kunmap_atomic);

/*
 * This API is supposed to allow us to map memory without a "struct page".
 * Currently we don't support this, though this may change in the future.
 */
void *kmap_atomic_pfn(unsigned long pfn)
{
    return kmap_atomic(pfn_to_page(pfn));
}
void *kmap_atomic_prot_pfn(unsigned long pfn, pgprot_t prot)
{
    return kmap_atomic_prot(pfn_to_page(pfn), prot);
}

struct page *kmap_atomic_to_page(void *ptr)
{
    pte_t *pte;
    unsigned long vaddr = (unsigned long)ptr;

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

    pte = kmap_get_pte(vaddr);
    return pte_page(*pte);
}