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
new file mode 100644
index 00000000000..52a0cfc38b6
--- /dev/null
+++ b/arch/powerpc/mm/mmu_context_nohash.c
@@ -0,0 +1,397 @@
+/*
+ * 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;
+}
+