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|
/*
* 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
*/
//#define DEBUG_MAP_CONSISTENCY
//#define DEBUG_CLAMP_LAST_CONTEXT 31
//#define DEBUG_HARDER
/* We don't use DEBUG because it tends to be compiled in always nowadays
* and this would generate way too much output
*/
#ifdef DEBUG_HARDER
#define pr_hard(args...) printk(KERN_DEBUG args)
#define pr_hardcont(args...) printk(KERN_CONT args)
#else
#define pr_hard(args...) do { } while(0)
#define pr_hardcont(args...) do { } while(0)
#endif
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/memblock.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/slab.h>
#include <asm/mmu_context.h>
#include <asm/tlbflush.h>
#include "mmu_decl.h"
/*
* 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
*
* The IBM 47x core supports 16-bit PIDs, thus 65535 contexts. We should
* normally never have to steal though the facility is present if needed.
* -- BenH
*/
#define FIRST_CONTEXT 1
#ifdef DEBUG_CLAMP_LAST_CONTEXT
#define LAST_CONTEXT DEBUG_CLAMP_LAST_CONTEXT
#elif defined(CONFIG_PPC_8xx)
#define LAST_CONTEXT 16
#elif defined(CONFIG_PPC_47x)
#define LAST_CONTEXT 65535
#else
#define LAST_CONTEXT 255
#endif
static unsigned int next_context, nr_free_contexts;
static unsigned long *context_map;
#ifdef CONFIG_SMP
static unsigned long *stale_map[NR_CPUS];
#endif
static struct mm_struct **context_mm;
static DEFINE_RAW_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, i;
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_hardcont(" | steal %d from 0x%p", 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 threaded
* implementations, we set it on all threads on each core
* represented in the mask. A future implementation will use
* a core map instead but this will do for now.
*/
for_each_cpu(cpu, mm_cpumask(mm)) {
for (i = cpu_first_thread_sibling(cpu);
i <= cpu_last_thread_sibling(cpu); i++) {
if (stale_map[i])
__set_bit(id, stale_map[i]);
}
cpu = i - 1;
}
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
*/
raw_spin_unlock(&context_lock);
cpu_relax();
raw_spin_lock(&context_lock);
/* This will cause the caller to try again */
return MMU_NO_CONTEXT;
}
#endif /* CONFIG_SMP */
static unsigned int steal_all_contexts(void)
{
struct mm_struct *mm;
#ifdef CONFIG_SMP
int cpu = smp_processor_id();
#endif
unsigned int id;
for (id = FIRST_CONTEXT; id <= LAST_CONTEXT; id++) {
/* Pick up the victim mm */
mm = context_mm[id];
pr_hardcont(" | steal %d from 0x%p", id, mm);
/* Mark this mm as having no context anymore */
mm->context.id = MMU_NO_CONTEXT;
if (id != FIRST_CONTEXT) {
context_mm[id] = NULL;
__clear_bit(id, context_map);
#ifdef DEBUG_MAP_CONSISTENCY
mm->context.active = 0;
#endif
}
#ifdef CONFIG_SMP
__clear_bit(id, stale_map[cpu]);
#endif
}
/* Flush the TLB for all contexts (not to be used on SMP) */
_tlbil_all();
nr_free_contexts = LAST_CONTEXT - FIRST_CONTEXT;
return FIRST_CONTEXT;
}
/* 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;
#ifdef CONFIG_SMP
int cpu = smp_processor_id();
#endif
/* Pick up the victim mm */
mm = context_mm[id];
pr_hardcont(" | steal %d from 0x%p", 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 */
#ifdef CONFIG_SMP
__clear_bit(id, stale_map[cpu]);
#endif
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,
struct task_struct *tsk)
{
unsigned int id;
#ifdef CONFIG_SMP
unsigned int i, cpu = smp_processor_id();
#endif
unsigned long *map;
/* No lockless fast path .. yet */
raw_spin_lock(&context_lock);
pr_hard("[%d] activating context for mm @%p, active=%d, id=%d",
cpu, next, next->context.active, next->context.id);
#ifdef CONFIG_SMP
/* Mark us active and the previous one not anymore */
next->context.active++;
if (prev) {
pr_hardcont(" (old=0x%p a=%d)", prev, prev->context.active);
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)) {
#ifdef DEBUG_MAP_CONSISTENCY
if (context_mm[id] != next)
pr_err("MMU: mm 0x%p has id %d but context_mm[%d] says 0x%p\n",
next, id, id, context_mm[id]);
#endif
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;
goto stolen;
}
#endif /* CONFIG_SMP */
if (IS_ENABLED(CONFIG_PPC_8xx))
id = steal_all_contexts();
else
id = steal_context_up(id);
goto stolen;
}
nr_free_contexts--;
/* We know there's at least one free context, try to find it */
while (
|