/*
* 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 <adt/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);
}