powerpc/mm: Split mmu_context handling

This splits the mmu_context handling between 32-bit hash based
processors, 64-bit hash based processors and everybody else.  This is
preliminary work for adding SMP support for BookE processors.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 162 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 000000000000..00e02150abef
--- /dev/null
+++ b/arch/powerpc/mm/mmu_context_nohash.c
@@ -0,0 +1,162 @@
+/*
+ * 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.
+ *
+ */
+
+#include <linux/mm.h>
+#include <linux/init.h>
+
+#include <asm/mmu_context.h>
+#include <asm/tlbflush.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
+ */
+
+#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
+
+#else
+#error Unsupported processor type
+#endif
+
+static unsigned long next_mmu_context;
+static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
+static atomic_t nr_free_contexts;
+static struct mm_struct *context_mm[LAST_CONTEXT+1];
+static void steal_context(void);
+
+/* 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 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
+ */
+static void steal_context(void)
+{
+        struct mm_struct *mm;
+
+        /* 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);
+}
+
+
+/*
+ * Get a new mmu context for the address space described by `mm'.
+ */
+static inline void get_mmu_context(struct mm_struct *mm)
+{
+        unsigned long ctx;
+
+        if (mm->context.id != NO_CONTEXT)
+                return;
+
+        while (atomic_dec_if_positive(&nr_free_contexts) < 0)
+                steal_context();
+
+        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;
+        }
+        next_mmu_context = (ctx + 1) & LAST_CONTEXT;
+        mm->context.id = ctx;
+        context_mm[ctx] = mm;
+}
+
+void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next)
+{
+        get_mmu_context(next);
+
+        set_context(next->context.id, next->pgd);
+}
+
+/*
+ * Set up the context for a new address space.
+ */
+int init_new_context(struct task_struct *t, struct mm_struct *mm)
+{
+        mm->context.id = NO_CONTEXT;
+        return 0;
+}
+
+/*
+ * We're finished using the context for an address space.
+ */
+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);
+        }
+        preempt_enable();
+}
+
+
+/*
+ * Initialize the context management stuff.
+ */
+void __init mmu_context_init(void)
+{
+        /*
+         * 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_mmu_context = FIRST_CONTEXT;
+        atomic_set(&nr_free_contexts, LAST_CONTEXT - FIRST_CONTEXT + 1);
+}
+