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Benjamin Herrenschmidt5e696612008-12-18 19:13:24 +00001/*
2 * This file contains the routines for handling the MMU on those
3 * PowerPC implementations where the MMU substantially follows the
4 * architecture specification. This includes the 6xx, 7xx, 7xxx,
5 * 8260, and POWER3 implementations but excludes the 8xx and 4xx.
6 * -- paulus
7 *
8 * Derived from arch/ppc/mm/init.c:
9 * Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
10 *
11 * Modifications by Paul Mackerras (PowerMac) (paulus@cs.anu.edu.au)
12 * and Cort Dougan (PReP) (cort@cs.nmt.edu)
13 * Copyright (C) 1996 Paul Mackerras
14 *
15 * Derived from "arch/i386/mm/init.c"
16 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
17 *
18 * This program is free software; you can redistribute it and/or
19 * modify it under the terms of the GNU General Public License
20 * as published by the Free Software Foundation; either version
21 * 2 of the License, or (at your option) any later version.
22 *
23 */
24
25#include <linux/mm.h>
26#include <linux/init.h>
27
28#include <asm/mmu_context.h>
29#include <asm/tlbflush.h>
30
31/*
32 * On 32-bit PowerPC 6xx/7xx/7xxx CPUs, we use a set of 16 VSIDs
33 * (virtual segment identifiers) for each context. Although the
34 * hardware supports 24-bit VSIDs, and thus >1 million contexts,
35 * we only use 32,768 of them. That is ample, since there can be
36 * at most around 30,000 tasks in the system anyway, and it means
37 * that we can use a bitmap to indicate which contexts are in use.
38 * Using a bitmap means that we entirely avoid all of the problems
39 * that we used to have when the context number overflowed,
40 * particularly on SMP systems.
41 * -- paulus.
42 */
43#define NO_CONTEXT ((unsigned long) -1)
44#define LAST_CONTEXT 32767
45#define FIRST_CONTEXT 1
46
47/*
48 * This function defines the mapping from contexts to VSIDs (virtual
49 * segment IDs). We use a skew on both the context and the high 4 bits
50 * of the 32-bit virtual address (the "effective segment ID") in order
51 * to spread out the entries in the MMU hash table. Note, if this
52 * function is changed then arch/ppc/mm/hashtable.S will have to be
53 * changed to correspond.
54 *
55 *
56 * CTX_TO_VSID(ctx, va) (((ctx) * (897 * 16) + ((va) >> 28) * 0x111) \
57 * & 0xffffff)
58 */
59
60static unsigned long next_mmu_context;
61static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
62
63
64/*
65 * Set up the context for a new address space.
66 */
67int init_new_context(struct task_struct *t, struct mm_struct *mm)
68{
69 unsigned long ctx = next_mmu_context;
70
71 while (test_and_set_bit(ctx, context_map)) {
72 ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1, ctx);
73 if (ctx > LAST_CONTEXT)
74 ctx = 0;
75 }
76 next_mmu_context = (ctx + 1) & LAST_CONTEXT;
77 mm->context.id = ctx;
78
79 return 0;
80}
81
82/*
83 * We're finished using the context for an address space.
84 */
85void destroy_context(struct mm_struct *mm)
86{
87 preempt_disable();
88 if (mm->context.id != NO_CONTEXT) {
89 clear_bit(mm->context.id, context_map);
90 mm->context.id = NO_CONTEXT;
91 }
92 preempt_enable();
93}
94
95/*
96 * Initialize the context management stuff.
97 */
98void __init mmu_context_init(void)
99{
100 /* Reserve context 0 for kernel use */
101 context_map[0] = (1 << FIRST_CONTEXT) - 1;
102 next_mmu_context = FIRST_CONTEXT;
103}