Commit 2ca8cf73 authored by Benjamin Herrenschmidt's avatar Benjamin Herrenschmidt Committed by Paul Mackerras

powerpc/mm: Rework context management for CPUs with no hash table

This reworks the context management code used by 4xx,8xx and
freescale BookE.  It adds support for SMP by implementing a
concept of stale context map to lazily flush the TLB on
processors where a context may have been invalidated.  This
also contains the ground work for generalizing such lazy TLB
flushing by just picking up a new PID and marking the old one
stale.  This will be implemented later.

This is a first implementation that uses a global spinlock.

Ideally, we should try to get at least the fast path (context ID
already assigned) lockless or limited to a per context lock,
but for now this will do.

I tried to keep the UP case reasonably simple to avoid adding
too much overhead to 8xx which does a lot of context stealing
since it effectively has only 16 PIDs available.
Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: default avatarKumar Gala <galak@kernel.crashing.org>
Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
parent 5e696617
......@@ -54,7 +54,8 @@
#ifndef __ASSEMBLY__
typedef struct {
unsigned long id;
unsigned int id;
unsigned int active;
unsigned long vdso_base;
} mm_context_t;
......
......@@ -56,7 +56,8 @@
extern unsigned int tlb_44x_hwater;
typedef struct {
unsigned long id;
unsigned int id;
unsigned int active;
unsigned long vdso_base;
} mm_context_t;
......
......@@ -137,7 +137,8 @@
#ifndef __ASSEMBLY__
typedef struct {
unsigned long id;
unsigned int id;
unsigned int active;
unsigned long vdso_base;
} mm_context_t;
#endif /* !__ASSEMBLY__ */
......
......@@ -76,7 +76,8 @@
#ifndef __ASSEMBLY__
typedef struct {
unsigned long id;
unsigned int id;
unsigned int active;
unsigned long vdso_base;
} mm_context_t;
#endif /* !__ASSEMBLY__ */
......
......@@ -29,6 +29,8 @@
#include <linux/mm.h>
#define MMU_NO_CONTEXT ((unsigned int)-1)
extern void _tlbie(unsigned long address, unsigned int pid);
extern void _tlbil_all(void);
extern void _tlbil_pid(unsigned int pid);
......
......@@ -14,13 +14,28 @@
* 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
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/init.h>
#include <asm/mmu_context.h>
#include <asm/tlbflush.h>
#include <linux/spinlock.h>
/*
* The MPC8xx has only 16 contexts. We rotate through them on each
......@@ -40,17 +55,14 @@
*/
#ifdef CONFIG_8xx
#define NO_CONTEXT 16
#define LAST_CONTEXT 15
#define FIRST_CONTEXT 0
#elif defined(CONFIG_4xx)
#define NO_CONTEXT 256
#define LAST_CONTEXT 255
#define FIRST_CONTEXT 1
#elif defined(CONFIG_E200) || defined(CONFIG_E500)
#define NO_CONTEXT 256
#define LAST_CONTEXT 255
#define FIRST_CONTEXT 1
......@@ -58,66 +70,208 @@
#error Unsupported processor type
#endif
static unsigned long next_mmu_context;
static unsigned int next_context, nr_free_contexts;
static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
static atomic_t nr_free_contexts;
static unsigned long stale_map[NR_CPUS][LAST_CONTEXT / BITS_PER_LONG + 1];
static struct mm_struct *context_mm[LAST_CONTEXT+1];
static void steal_context(void);
static spinlock_t context_lock = SPIN_LOCK_UNLOCKED;
/* Steal a context from a task that has one at the moment.
* This is only used on 8xx and 4xx and we presently assume that
* they don't do SMP. If they do then this will have to check
* whether the MM we steal is in use.
* We also assume that this is only used on systems that don't
* use an MMU hash table - this is true for 8xx and 4xx.
*
* 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
*/
static void steal_context(void)
#ifdef CONFIG_SMP
static unsigned int steal_context_smp(unsigned int id)
{
struct mm_struct *mm;
unsigned int cpu, max;
/* free up context `next_mmu_context' */
/* if we shouldn't free context 0, don't... */
if (next_mmu_context < FIRST_CONTEXT)
next_mmu_context = FIRST_CONTEXT;
mm = context_mm[next_mmu_context];
flush_tlb_mm(mm);
destroy_context(mm);
}
again:
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];
/*
* Get a new mmu context for the address space described by `mm'.
/* 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_debug("[%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_mask_nr(cpu, mm->cpu_vm_mask)
__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);
goto again;
}
#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 inline void get_mmu_context(struct mm_struct *mm)
static unsigned int steal_context_up(unsigned int id)
{
unsigned long ctx;
struct mm_struct *mm;
int cpu = smp_processor_id();
if (mm->context.id != NO_CONTEXT)
return;
/* Pick up the victim mm */
mm = context_mm[id];
pr_debug("[%d] steal context %d from mm @%p\n", cpu, id, mm);
/* Mark this mm has having no context anymore */
mm->context.id = MMU_NO_CONTEXT;
/* Flush the TLB for that context */
local_flush_tlb_mm(mm);
while (atomic_dec_if_positive(&nr_free_contexts) < 0)
steal_context();
/* XXX This clear should ultimately be part of local_flush_tlb_mm */
__clear_bit(id, stale_map[cpu]);
ctx = next_mmu_context;
while (test_and_set_bit(ctx, context_map)) {
ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1, ctx);
if (ctx > LAST_CONTEXT)
ctx = 0;
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;
}
next_mmu_context = (ctx + 1) & LAST_CONTEXT;
mm->context.id = ctx;
context_mm[ctx] = mm;
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());
}
#else
static void context_check_map(void) { }
#endif
void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next)
{
get_mmu_context(next);
unsigned int id, cpu = smp_processor_id();
unsigned long *map;
set_context(next->context.id, next->pgd);
/* No lockless fast path .. yet */
spin_lock(&context_lock);
#ifndef DEBUG_STEAL_ONLY
pr_debug("[%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) {
WARN_ON(prev->context.active < 1);
prev->context.active--;
}
#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);
goto stolen;
}
#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_debug("[%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_debug("[%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);
}
/*
......@@ -125,7 +279,9 @@ void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next)
*/
int init_new_context(struct task_struct *t, struct mm_struct *mm)
{
mm->context.id = NO_CONTEXT;
mm->context.id = MMU_NO_CONTEXT;
mm->context.active = 0;
return 0;
}
......@@ -134,13 +290,25 @@ int init_new_context(struct task_struct *t, struct mm_struct *mm)
*/
void destroy_context(struct mm_struct *mm)
{
preempt_disable();
if (mm->context.id != NO_CONTEXT) {
clear_bit(mm->context.id, context_map);
mm->context.id = NO_CONTEXT;
atomic_inc(&nr_free_contexts);
unsigned int id;
if (mm->context.id == MMU_NO_CONTEXT)
return;
WARN_ON(mm->context.active != 0);
spin_lock(&context_lock);
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;
context_mm[id] = NULL;
#endif
nr_free_contexts++;
}
preempt_enable();
spin_unlock(&context_lock);
}
......@@ -149,6 +317,12 @@ void destroy_context(struct mm_struct *mm)
*/
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;
/*
* Some processors have too few contexts to reserve one for
* init_mm, and require using context 0 for a normal task.
......@@ -156,7 +330,7 @@ void __init mmu_context_init(void)
* This code assumes FIRST_CONTEXT < 32.
*/
context_map[0] = (1 << FIRST_CONTEXT) - 1;
next_mmu_context = FIRST_CONTEXT;
atomic_set(&nr_free_contexts, LAST_CONTEXT - FIRST_CONTEXT + 1);
next_context = FIRST_CONTEXT;
nr_free_contexts = LAST_CONTEXT - FIRST_CONTEXT + 1;
}
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