Linux Kernel  3.7.1
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mmu_context_hash32.c
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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,
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 ([email protected])
10  *
11  * Modifications by Paul Mackerras (PowerMac) ([email protected])
12  * and Cort Dougan (PReP) ([email protected])
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 
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)) {
70  if (ctx > LAST_CONTEXT)
71  ctx = 0;
72  }
73  next_mmu_context = (ctx + 1) & LAST_CONTEXT;
74 
75  return ctx;
76 }
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 {
85 
86  return 0;
87 }
88 
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 }
97 
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) {
106  mm->context.id = NO_CONTEXT;
107  }
108  preempt_enable();
109 }
110 
111 /*
112  * Initialize the context management stuff.
113  */
115 {
116  /* Reserve context 0 for kernel use */
117  context_map[0] = (1 << FIRST_CONTEXT) - 1;
119 }