1 /*
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 #include <linux/export.h>
28
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
61 static unsigned long next_mmu_context;
62 static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
63
__init_new_context(void)64 unsigned long __init_new_context(void)
65 {
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;
74
75 return ctx;
76 }
77 EXPORT_SYMBOL_GPL(__init_new_context);
78
79 /*
80 * Set up the context for a new address space.
81 */
init_new_context(struct task_struct * t,struct mm_struct * mm)82 int init_new_context(struct task_struct *t, struct mm_struct *mm)
83 {
84 mm->context.id = __init_new_context();
85
86 return 0;
87 }
88
89 /*
90 * Free a context ID. Make sure to call this with preempt disabled!
91 */
__destroy_context(unsigned long ctx)92 void __destroy_context(unsigned long ctx)
93 {
94 clear_bit(ctx, context_map);
95 }
96 EXPORT_SYMBOL_GPL(__destroy_context);
97
98 /*
99 * We're finished using the context for an address space.
100 */
destroy_context(struct mm_struct * mm)101 void destroy_context(struct mm_struct *mm)
102 {
103 preempt_disable();
104 if (mm->context.id != NO_CONTEXT) {
105 __destroy_context(mm->context.id);
106 mm->context.id = NO_CONTEXT;
107 }
108 preempt_enable();
109 }
110
111 /*
112 * Initialize the context management stuff.
113 */
mmu_context_init(void)114 void __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 }
120