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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,
Michael Ellerman0f369102014-07-10 12:29:24 +10005 * and 8260 implementations but excludes the 8xx and 4xx.
Benjamin Herrenschmidt5e696612008-12-18 19:13:24 +00006 * -- 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>
Paul Gortmaker93087942011-07-29 16:19:31 +100027#include <linux/export.h>
Benjamin Herrenschmidt5e696612008-12-18 19:13:24 +000028
29#include <asm/mmu_context.h>
30#include <asm/tlbflush.h>
31
32/*
33 * On 32-bit PowerPC 6xx/7xx/7xxx CPUs, we use a set of 16 VSIDs
34 * (virtual segment identifiers) for each context. Although the
35 * hardware supports 24-bit VSIDs, and thus >1 million contexts,
36 * we only use 32,768 of them. That is ample, since there can be
37 * at most around 30,000 tasks in the system anyway, and it means
38 * that we can use a bitmap to indicate which contexts are in use.
39 * Using a bitmap means that we entirely avoid all of the problems
40 * that we used to have when the context number overflowed,
41 * particularly on SMP systems.
42 * -- paulus.
43 */
44#define NO_CONTEXT ((unsigned long) -1)
45#define LAST_CONTEXT 32767
46#define FIRST_CONTEXT 1
47
48/*
49 * This function defines the mapping from contexts to VSIDs (virtual
50 * segment IDs). We use a skew on both the context and the high 4 bits
51 * of the 32-bit virtual address (the "effective segment ID") in order
52 * to spread out the entries in the MMU hash table. Note, if this
53 * function is changed then arch/ppc/mm/hashtable.S will have to be
54 * changed to correspond.
55 *
56 *
57 * CTX_TO_VSID(ctx, va) (((ctx) * (897 * 16) + ((va) >> 28) * 0x111) \
58 * & 0xffffff)
59 */
60
61static unsigned long next_mmu_context;
62static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
63
Alexander Grafc83ec262010-04-16 00:11:36 +020064unsigned long __init_new_context(void)
Benjamin Herrenschmidt5e696612008-12-18 19:13:24 +000065{
66 unsigned long ctx = next_mmu_context;
67
68 while (test_and_set_bit(ctx, context_map)) {
69 ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1, ctx);
70 if (ctx > LAST_CONTEXT)
71 ctx = 0;
72 }
73 next_mmu_context = (ctx + 1) & LAST_CONTEXT;
Alexander Grafc83ec262010-04-16 00:11:36 +020074
75 return ctx;
76}
77EXPORT_SYMBOL_GPL(__init_new_context);
78
79/*
80 * Set up the context for a new address space.
81 */
82int init_new_context(struct task_struct *t, struct mm_struct *mm)
83{
84 mm->context.id = __init_new_context();
Benjamin Herrenschmidt5e696612008-12-18 19:13:24 +000085
86 return 0;
87}
88
89/*
Alexander Grafc83ec262010-04-16 00:11:36 +020090 * Free a context ID. Make sure to call this with preempt disabled!
91 */
92void __destroy_context(unsigned long ctx)
93{
94 clear_bit(ctx, context_map);
95}
96EXPORT_SYMBOL_GPL(__destroy_context);
97
98/*
Benjamin Herrenschmidt5e696612008-12-18 19:13:24 +000099 * We're finished using the context for an address space.
100 */
101void destroy_context(struct mm_struct *mm)
102{
103 preempt_disable();
104 if (mm->context.id != NO_CONTEXT) {
Alexander Grafc83ec262010-04-16 00:11:36 +0200105 __destroy_context(mm->context.id);
Benjamin Herrenschmidt5e696612008-12-18 19:13:24 +0000106 mm->context.id = NO_CONTEXT;
107 }
108 preempt_enable();
109}
110
111/*
112 * Initialize the context management stuff.
113 */
114void __init mmu_context_init(void)
115{
116 /* Reserve context 0 for kernel use */
117 context_map[0] = (1 << FIRST_CONTEXT) - 1;
118 next_mmu_context = FIRST_CONTEXT;
119}