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727 jermar 1
/*
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 * Copyright (C) 2006 Jakub Jermar
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 * All rights reserved.
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 *
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 * Redistribution and use in source and binary forms, with or without
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 * modification, are permitted provided that the following conditions
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 * are met:
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 *
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 * - Redistributions of source code must retain the above copyright
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 *   notice, this list of conditions and the following disclaimer.
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 * - Redistributions in binary form must reproduce the above copyright
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 *   notice, this list of conditions and the following disclaimer in the
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 *   documentation and/or other materials provided with the distribution.
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 * - The name of the author may not be used to endorse or promote products
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 *   derived from this software without specific prior written permission.
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 *
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 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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 */
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/*
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 * ASID management.
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 *
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 * Modern processor architectures optimize TLB utilization
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 * by using ASIDs (a.k.a. memory contexts on sparc64 and
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 * region identifiers on ia64). These ASIDs help to associate
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 * each TLB item with an address space, thus making
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 * finer-grained TLB invalidation possible.
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 *
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 * Unfortunatelly, there are usually less ASIDs available than
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 * there can be unique as_t structures (i.e. address spaces
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 * recognized by the kernel).
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 *
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 * When system runs short of ASIDs, it will attempt to steal
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 * ASID from an address space that has not been active for
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 * a while.
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 *
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 * Architectures that don't have hardware support for address
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 * spaces do not compile with this file.
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 */
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#include <mm/asid.h>
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#include <mm/as.h>
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#include <mm/tlb.h>
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#include <arch/mm/asid.h>
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#include <synch/spinlock.h>
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#include <arch.h>
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#include <list.h>
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#include <debug.h>
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/**
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 * asidlock protects both the asids_allocated counter
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 * and the list of address spaces that were already
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 * assigned ASID.
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 */
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SPINLOCK_INITIALIZE(asidlock);
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static count_t asids_allocated = 0;
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/**
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 * List of address spaces with assigned ASID.
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 * When the system runs short of allocable
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 * ASIDS, inactive address spaces are guaranteed
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 * to be at the beginning of the list.
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 */
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LIST_INITIALIZE(as_with_asid_head);
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/** Allocate free address space identifier.
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 *
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 * This code depends on the fact that ASIDS_ALLOCABLE
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 * is greater than number of supported CPUs.
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 *
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 * @return New ASID.
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 */
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asid_t asid_get(void)
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{
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    ipl_t ipl;
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    asid_t asid;
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    link_t *tmp;
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    as_t *as;
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    /*
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     * Check if there is an unallocated ASID.
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     */
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    ipl = interrupts_disable();
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    spinlock_lock(&asidlock);
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    if (asids_allocated == ASIDS_ALLOCABLE) {
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        /*
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         * All ASIDs are already allocated.
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         * Resort to stealing.
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         */
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        /*
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         * Remove the first item on the list.
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         * It is guaranteed to belong to an
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         * inactive address space.
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         */
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        tmp = as_with_asid_head.next;
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        ASSERT(tmp != &as_with_asid_head);
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        list_remove(tmp);
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        as = list_get_instance(tmp, as_t, as_with_asid_link);
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        spinlock_lock(&as->lock);
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        /*
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         * Steal the ASID.
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         * Note that the stolen ASID is not active.
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         */
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        asid = as->asid;
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        ASSERT(asid != ASID_INVALID);
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        /*
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         * Notify the address space from wich the ASID
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         * was stolen by invalidating its asid member.
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         */
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        as->asid = ASID_INVALID;
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        spinlock_unlock(&as->lock);
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        /*
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         * Get the system rid of the stolen ASID.
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         */
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        tlb_shootdown_start(TLB_INVL_ASID, asid, 0, 0);
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        tlb_shootdown_finalize();
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        tlb_invalidate_asid(asid);
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    } else {
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        /*
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         * There is at least one unallocated ASID.
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         * Find it and assign it.
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         */
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        asid = asid_find_free();
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        asids_allocated++;
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    }
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    spinlock_unlock(&asidlock);
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    interrupts_restore(ipl);
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    return asid;
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}
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/** Release address space identifier.
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 *
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 * This code relies on architecture
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 * dependent functionality.
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 *
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 * @param asid ASID to be released.
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 */
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void asid_put(asid_t asid)
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{
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    ipl_t ipl;
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    ipl = interrupts_disable();
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    spinlock_lock(&asidlock);
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    asids_allocated--;
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    asid_put_arch(asid);
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    spinlock_unlock(&asidlock);
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    interrupts_restore(ipl);
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}
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/** Install ASID.
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 *
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 * This function is to be executed on each address space switch.
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 *
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 * @param as Address space.
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 */
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void asid_install(as_t *as)
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{
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    ipl_t ipl;
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    ipl = interrupts_disable();
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    spinlock_lock(&asidlock);
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    spinlock_lock(&as->lock);
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    if (as->asid != ASID_KERNEL) {
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        if (as->asid != ASID_INVALID) {
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            /*
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             * This address space has valid ASID.
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             * Remove 'as' from the list of address spaces
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             * with assigned ASID, so that it can be later
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             * appended to the tail of the same list.
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             * This is to prevent stealing of ASIDs from
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             * recently installed address spaces.
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             */
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            list_remove(&as->as_with_asid_link);
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        } else {
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            spinlock_unlock(&as->lock);
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            spinlock_unlock(&asidlock);
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            /*
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             * This address space doesn't have ASID assigned.
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             * It was stolen or the address space is being
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             * installed for the first time.
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             * Allocate new ASID for it.
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             */
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            as->asid = asid_get();
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            spinlock_lock(&asidlock);
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            spinlock_lock(&as->lock);
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        }
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        /*
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         * Now it is sure that 'as' has ASID.
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         * It is therefore appended to the list
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         * of address spaces from which it can
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         * be stolen.
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         */
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        list_append(&as->as_with_asid_link, &as_with_asid_head);
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    }
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    spinlock_unlock(&as->lock);
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    spinlock_unlock(&asidlock);
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    interrupts_restore(ipl);
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}