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-rw-r--r--arch/powerpc/mm/mmu_context_nohash.c397
1 files changed, 397 insertions, 0 deletions
diff --git a/arch/powerpc/mm/mmu_context_nohash.c b/arch/powerpc/mm/mmu_context_nohash.c
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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
+ */
+
+#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 spinlock_t context_lock = SPIN_LOCK_UNLOCKED;
+
+#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;
+
+ 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];
+
+ /* 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 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_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);
+
+ /* 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_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) {
+#ifndef DEBUG_STEAL_ONLY
+ pr_debug(" old context %p active was: %d\n",
+ prev, prev->context.active);
+#endif
+ 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);
+}
+
+/*
+ * 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 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++;
+ }
+ spin_unlock(&context_lock);
+}
+
+#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_debug("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_debug("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 %d 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;
+}
+
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