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/*
 * Copyright (C) 2006 Jakub Jermar
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * ASID management.
 *
 * Modern processor architectures optimize TLB utilization
 * by using ASIDs (a.k.a. memory contexts on sparc64 and
 * region identifiers on ia64). These ASIDs help to associate
 * each TLB item with an address space, thus making
 * finer-grained TLB invalidation possible.
 *
 * Unfortunatelly, there are usually less ASIDs available than
 * there can be unique as_t structures (i.e. address spaces
 * recognized by the kernel).
 *
 * When system runs short of ASIDs, it will attempt to steal
 * ASID from an address space that has not been active for
 * a while.
 *
 * Architectures that don't have hardware support for address
 * spaces do not compile with this file.
 */

#include <mm/asid.h>
#include <mm/as.h>
#include <mm/tlb.h>
#include <arch/mm/asid.h>
#include <synch/spinlock.h>
#include <arch.h>
#include <list.h>
#include <debug.h>

/**
 * asidlock protects both the asids_allocated counter
 * and the list of address spaces that were already
 * assigned ASID.
 */
SPINLOCK_INITIALIZE(asidlock);

static count_t asids_allocated = 0;

/**
 * List of address spaces with assigned ASID.
 * When the system runs short of allocable
 * ASIDS, inactive address spaces are guaranteed
 * to be at the beginning of the list.
 */
LIST_INITIALIZE(as_with_asid_head);


/** Allocate free address space identifier.
 *
 * This code depends on the fact that ASIDS_ALLOCABLE
 * is greater than number of supported CPUs.
 *
 * @return New ASID.
 */
asid_t asid_get(void)
{
    ipl_t ipl;
    asid_t asid;
    link_t *tmp;
    as_t *as;

    /*
     * Check if there is an unallocated ASID.
     */
    
    ipl = interrupts_disable();
    spinlock_lock(&asidlock);
    if (ASID_STEALING_ENABLED && asids_allocated == ASIDS_ALLOCABLE) {

        /*
         * All ASIDs are already allocated.
         * Resort to stealing.
         */
        
        /*
         * Remove the first item on the list.
         * It is guaranteed to belong to an
         * inactive address space.
         */
        tmp = as_with_asid_head.next;
        ASSERT(tmp != &as_with_asid_head);
        list_remove(tmp);
        
        as = list_get_instance(tmp, as_t, as_with_asid_link);
        spinlock_lock(&as->lock);

        /*
         * Steal the ASID.
         * Note that the stolen ASID is not active.
         */
        asid = as->asid;
        ASSERT(asid != ASID_INVALID);

        /*
         * Notify the address space from wich the ASID
         * was stolen by invalidating its asid member.
         */
        as->asid = ASID_INVALID;
        spinlock_unlock(&as->lock);

        /*
         * Get the system rid of the stolen ASID.
         */
        tlb_shootdown_start(TLB_INVL_ASID, asid, 0, 0);
        tlb_shootdown_finalize();
        tlb_invalidate_asid(asid);
    } else {

        /*
         * There is at least one unallocated ASID.
         * Find it and assign it.
         */

        asid = asid_find_free();
        asids_allocated++;
    }
    
    spinlock_unlock(&asidlock);
    interrupts_restore(ipl);
    
    return asid;
}

/** Release address space identifier.
 *
 * This code relies on architecture
 * dependent functionality.
 *
 * @param asid ASID to be released.
 */
void asid_put(asid_t asid)
{
    ipl_t ipl;

    ipl = interrupts_disable();
    spinlock_lock(&asidlock);

    asids_allocated--;
    asid_put_arch(asid);
    
    spinlock_unlock(&asidlock);
    interrupts_restore(ipl);
}

/** Install ASID.
 *
 * This function is to be executed on each address space switch.
 *
 * @param as Address space.
 */
void asid_install(as_t *as)
{
    ipl_t ipl;
    
    ipl = interrupts_disable();
    spinlock_lock(&asidlock);
    spinlock_lock(&as->lock);
    
    if (as->asid != ASID_KERNEL) {
        if (as->asid != ASID_INVALID) {
            /*
             * This address space has valid ASID.
             * Remove 'as' from the list of address spaces
             * with assigned ASID, so that it can be later
             * appended to the tail of the same list.
             * This is to prevent stealing of ASIDs from
             * recently installed address spaces.
             */
            list_remove(&as->as_with_asid_link);
        } else {
            spinlock_unlock(&as->lock);
            spinlock_unlock(&asidlock);
    
            /*
             * This address space doesn't have ASID assigned.
             * It was stolen or the address space is being
             * installed for the first time.
             * Allocate new ASID for it.
             */
            as->asid = asid_get();
            spinlock_lock(&asidlock);
            spinlock_lock(&as->lock);
        }
    
        /*
         * Now it is sure that 'as' has ASID.
         * It is therefore appended to the list
         * of address spaces from which it can
         * be stolen.
         */
        list_append(&as->as_with_asid_link, &as_with_asid_head);
    }
    
    spinlock_unlock(&as->lock);
    spinlock_unlock(&asidlock);
    interrupts_restore(ipl);
}