source: mainline/genarch/src/mm/asid.c@ a60c748

/*
 * 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 (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);
}