/*
* This file contains the routines for handling the MMU on those
* PowerPC implementations where the MMU is not using the hash
* table, such as 8xx, 4xx, BookE's etc...
*
* Copyright 2008 Ben Herrenschmidt <benh@kernel.crashing.org>
* IBM Corp.
*
* Derived from previous arch/powerpc/mm/mmu_context.c
* and arch/powerpc/include/asm/mmu_context.h
*
* 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; either version
* 2 of the License, or (at your option) any later version.
*
* TODO:
*
* - The global context lock will not scale very well
* - The maps should be dynamically allocated to allow for processors
* that support more PID bits at runtime
* - Implement flush_tlb_mm() by making the context stale and picking
* a new one
* - More aggressively clear stale map bits and maybe find some way to
* also clear mm->cpu_vm_mask bits when processes are migrated
*/
#undef DEBUG
#define DEBUG_STEAL_ONLY
#undef DEBUG_MAP_CONSISTENCY
/*#define DEBUG_CLAMP_LAST_CONTEXT 15 */
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/bootmem.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <asm/mmu_context.h>
#include <asm/tlbflush.h>
static unsigned int first_context, last_context;
static unsigned int next_context, nr_free_contexts;
static unsigned long *context_map;
static unsigned long *stale_map[NR_CPUS];
static struct mm_struct **context_mm;
static DEFINE_SPINLOCK(context_lock);
#define CTX_MAP_SIZE \
(sizeof(unsigned long) * (last_context / BITS_PER_LONG + 1))
/* Steal a context from a task that has one at the moment.
*
* This is used when we are running out of available PID numbers
* on the processors.
*
* This isn't an LRU system, it just frees up each context in
* turn (sort-of pseudo-random replacement :). This would be the
* place to implement an LRU scheme if anyone was motivated to do it.
* -- paulus
*
* For context stealing, we use a slightly different approach for
* SMP and UP. Basically, the UP one is simpler and doesn't use
* the stale map as we can just flush the local CPU
* -- benh
*/
#ifdef CONFIG_SMP
static unsigned int steal_context_smp(unsigned int id)
{
struct mm_struct *mm;
unsigned int cpu, max;
max = last_context - first_context;
/* Attempt to free next_context first and then loop until we manage */
while (max--) {
/* Pick up the victim mm */
mm = context_mm[id];
/* We have a candidate victim, check if it's active, on SMP
* we cannot steal active contexts
*/
if (mm->context.active) {
id++;
if (id > last_context)
id = first_context;
continue;
}
pr_devel("[%d] steal context %d from mm @%p\n",
smp_processor_id(), id, mm);
/* Mark this mm has having no context anymore */
mm->context.id = MMU_NO_CONTEXT;
/* Mark it stale on all CPUs that used this mm */
for_each_cpu(cpu, mm_cpumask(mm))
__set_bit(id, stale_map[cpu]);
return id;
}
/* This will happen if you have more CPUs than available contexts,
* all we can do here is wait a bit and try again
*/
spin_unlock(&context_lock);
cpu_relax();
spin_lock(&context_lock);
/* This will cause the caller to try again */
return MMU_NO_CONTEXT;
}
#endif /* CONFIG_SMP */
/* Note that this will also be called on SMP if all other CPUs are
* offlined, which means that it may be called for cpu != 0. For
* this to work, we somewhat assume that CPUs that are onlined
* come up with a fully clean TLB (or are cleaned when offlined)
*/
static unsigned int steal_context_up(unsigned int id)
{
struct mm_struct *mm;
int cpu = smp_processor_id();
/* Pick up the victim mm */
mm = context_mm[id];
pr_devel("[%d] steal context %d from mm @%p\n", cpu, id, mm);
/* Flush the TLB for that context */
local_flush_tlb_mm(mm);
/* Mark this mm has having no context anymore */
mm->context.id = MMU_NO_CONTEXT;
/* XXX This clear should ultimately be part of local_flush_tlb_mm */
__clear_bit(id, stale_map[cpu]);
return id;
}
#ifdef DEBUG_MAP_CONSISTENCY
static void context_check_map(void)
{
unsigned int id, nrf, nact;
nrf = nact = 0;
for (id = first_context; id <= last_context; id++) {
int used = test_bit(id, context_map);
if (!used)
nrf++;
if (used != (context_mm[id] != NULL))
pr_err("MMU: Context %d is %s and MM is %p !\n",
id, used ? "used" : "free", context_mm[id]);
if (context_mm[id] != NULL)
nact += context_mm[id]->context.active;
}
if (nrf != nr_free_contexts) {
pr_err("MMU: Free context count out of sync ! (%d vs %d)\n",
nr_free_contexts, nrf);
nr_free_contexts = nrf;
}
if (nact > num_online_cpus())
pr_err("MMU: More active contexts than CPUs ! (%d vs %d)\n",
nact, num_online_cpus());
if (first_context > 0 && !test_bit(0, context_map))
pr_err("MMU: Context 0 has been freed !!!\n");
}
#else
static void context_check_map(void) { }
#endif
void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next)
{
unsigned int id, cpu = smp_processor_id();
unsigned long *map;
/* No lockless fast path .. yet */
spin_lock(&context_lock);
#ifndef DEBUG_STEAL_ONLY
pr_devel("[%d] activating context for mm @%p, active=%d, id=%d\n",
cpu, next, next->context.active, next->context.id);
#endif
#ifdef CONFIG_SMP
/* Mark us active and the previous one not anymore */
next->context.active++;
if (prev) {
#ifndef DEBUG_STEAL_ONLY
pr_devel(" old context %p active was: %d\n",
prev, prev->context.active);
#endif
WARN_ON(prev->context.active < 1);
prev->context.active--;
}
again:
#endif /* CONFIG_SMP */
/* If we already have a valid assigned context, skip all that */
id = next->context.id;
if (likely(id != MMU_NO_CONTEXT))
goto ctxt_ok;
/* We really don't have a context, let's try to acquire one */
id = next_context;
if (id > last_context)
id = first_context;
map = context_map;
/* No more free contexts, let's try to steal one */
if (nr_free_contexts == 0) {
#ifdef CONFIG_SMP
if (num_online_cpus() > 1) {
id = steal_context_smp(id);
if (id == MMU_NO_CONTEXT)
goto again;
}
#endif /* CONFIG_SMP */
id = steal_context_up(id);
goto stolen;
}
nr_free_contexts--;
/* We know there's at least one free context, try to find it */
while (__test_and_set_bit(id, map)) {
id = find_next_zero_bit(map, last_context+1, id);
if (id > last_context)
id = first_context;
}
stolen:
next_context = id + 1;
context_mm[id] = next;
next->context.id = id;
#ifndef DEBUG_STEAL_ONLY
pr_devel("[%d] picked up new id %d, nrf is now %d\n",
cpu, id, nr_free_contexts);
#endif
context_check_map();
ctxt_ok:
/* If that context got marked stale on this CPU, then flush the
* local TLB for it and unmark it before we use it
*/
if (test_bit(id, stale_map[cpu])) {
pr_devel("[%d] flushing stale context %d for mm @%p !\n",
cpu, id, next);
local_flush_tlb_mm(next);
/* XXX This clear should ultimately be part of local_flush_tlb_mm */
__clear_bit(id, stale_map[cpu]);
}
/* Flick the MMU and release lock */
set_context(id, next->pgd);
spin_unlock(&context_lock);
}
/*
* Set up the context for a new address space.
*/
int init_new_context(struct task_struct *t, struct mm_struct *mm)
{
mm->context.id = MMU_NO_CONTEXT;
mm->context.active = 0;
return 0;
}
/*
* We're finished using the context for an address space.
*/
void destroy_context(struct mm_struct *mm)
{
unsigned long flags;
unsigned int id;
if (mm->context.id == MMU_NO_CONTEXT)
return;
WARN_ON(mm->context.active != 0);
spin_lock_irqsave(&context_lock, flags);
id = mm->context.id;
if (id != MMU_NO_CONTEXT) {
__clear_bit(id, context_map);
mm->context.id = MMU_NO_CONTEXT;
#ifdef DEBUG_MAP_CONSISTENCY
mm->context.active = 0;
#endif
context_mm[id] = NULL;
nr_free_contexts++;
}
spin_unlock_irqrestore(&context_lock, flags);
}
#ifdef CONFIG_SMP
static int __cpuinit mmu_context_cpu_notify(struct notifier_block *self,
unsigned long action, void *hcpu)
{
unsigned int cpu = (unsigned int)(long)hcpu;
/* We don't touch CPU 0 map, it's allocated at aboot and kept
* around forever
*/
if (cpu == 0)
return NOTIFY_OK;
switch (action) {
case CPU_ONLINE:
case CPU_ONLINE_FROZEN:
pr_devel("MMU: Allocating stale context map for CPU %d\n", cpu);
stale_map[cpu] = kzalloc(CTX_MAP_SIZE, GFP_KERNEL);
break;
#ifdef CONFIG_HOTPLUG_CPU
case CPU_DEAD:
case CPU_DEAD_FROZEN:
pr_devel("MMU: Freeing stale context map for CPU %d\n", cpu);
kfree(stale_map[cpu]);
stale_map[cpu] = NULL;
break;
#endif
}
return NOTIFY_OK;
}
static struct notifier_block __cpuinitdata mmu_context_cpu_nb = {
.notifier_call = mmu_context_cpu_notify,
};
#endif /* CONFIG_SMP */
/*
* Initialize the context management stuff.
*/
void __init mmu_context_init(void)
{
/* Mark init_mm as being active on all possible CPUs since
* we'll get called with prev == init_mm the first time
* we schedule on a given CPU
*/
init_mm.context.active = NR_CPUS;
/*
* The MPC8xx has only 16 contexts. We rotate through them on each
* task switch. A better way would be to keep track of tasks that
* own contexts, and implement an LRU usage. That way very active
* tasks don't always have to pay the TLB reload overhead. The
* kernel pages are mapped shared, so the kernel can run on behalf
* of any task that makes a kernel entry. Shared does not mean they
* are not protected, just that the ASID comparison is not performed.
* -- Dan
*
* The IBM4xx has 256 contexts, so we can just rotate through these
* as a way of "switching" contexts. If the TID of the TLB is zero,
* the PID/TID comparison is disabled, so we can use a TID of zero
* to represent all kernel pages as shared among all contexts.
* -- Dan
*/
if (mmu_has_feature(MMU_FTR_TYPE_8xx)) {
first_context = 0;
last_context = 15;
} else {
first_context = 1;
last_context = 255;
}
#ifdef DEBUG_CLAMP_LAST_CONTEXT
last_context = DEBUG_CLAMP_LAST_CONTEXT;
#endif
/*
* Allocate the maps used by context management
*/
context_map = alloc_bootmem(CTX_MAP_SIZE);
context_mm = alloc_bootmem(sizeof(void *) * (last_context + 1));
stale_map[0] = alloc_bootmem(CTX_MAP_SIZE);
#ifdef CONFIG_SMP
register_cpu_notifier(&mmu_context_cpu_nb);
#endif
printk(KERN_INFO
"MMU: Allocated %zu bytes of context maps for %d contexts\n",
2 * CTX_MAP_SIZE + (sizeof(void *) * (last_context + 1)),
last_context - first_context + 1);
/*
* Some processors have too few contexts to reserve one for
* init_mm, and require using context 0 for a normal task.
* Other processors reserve the use of context zero for the kernel.
* This code assumes first_context < 32.
*/
context_map[0] = (1 << first_context) - 1;
next_context = first_context;
nr_free_contexts = last_context - first_context + 1;
}
