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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, | |
0f369103 | 5 | * and 8260 implementations but excludes the 8xx and 4xx. |
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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> | |
93087948 | 27 | #include <linux/export.h> |
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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 | ||
c83ec269 | 64 | unsigned long __init_new_context(void) |
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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; | |
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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 | */ | |
82 | int init_new_context(struct task_struct *t, struct mm_struct *mm) | |
83 | { | |
84 | mm->context.id = __init_new_context(); | |
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85 | |
86 | return 0; | |
87 | } | |
88 | ||
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89 | /* |
90 | * Free a context ID. Make sure to call this with preempt disabled! | |
91 | */ | |
92 | void __destroy_context(unsigned long ctx) | |
93 | { | |
94 | clear_bit(ctx, context_map); | |
95 | } | |
96 | EXPORT_SYMBOL_GPL(__destroy_context); | |
97 | ||
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98 | /* |
99 | * We're finished using the context for an address space. | |
100 | */ | |
101 | void destroy_context(struct mm_struct *mm) | |
102 | { | |
103 | preempt_disable(); | |
104 | if (mm->context.id != NO_CONTEXT) { | |
c83ec269 | 105 | __destroy_context(mm->context.id); |
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106 | mm->context.id = NO_CONTEXT; |
107 | } | |
108 | preempt_enable(); | |
109 | } | |
110 | ||
111 | /* | |
112 | * Initialize the context management stuff. | |
113 | */ | |
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 | } |