1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * This file contains the routines for handling the MMU on those
4 * PowerPC implementations where the MMU substantially follows the
5 * architecture specification. This includes the 6xx, 7xx, 7xxx,
6 * and 8260 implementations but excludes the 8xx and 4xx.
7 * -- paulus
8 *
9 * Derived from arch/ppc/mm/init.c:
10 * Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
11 *
12 * Modifications by Paul Mackerras (PowerMac) (paulus@cs.anu.edu.au)
13 * and Cort Dougan (PReP) (cort@cs.nmt.edu)
14 * Copyright (C) 1996 Paul Mackerras
15 *
16 * Derived from "arch/i386/mm/init.c"
17 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
18 */
19
20 #include <linux/mm.h>
21 #include <linux/init.h>
22 #include <linux/export.h>
23
24 #include <asm/mmu_context.h>
25
26 /*
27 * On 32-bit PowerPC 6xx/7xx/7xxx CPUs, we use a set of 16 VSIDs
28 * (virtual segment identifiers) for each context. Although the
29 * hardware supports 24-bit VSIDs, and thus >1 million contexts,
30 * we only use 32,768 of them. That is ample, since there can be
31 * at most around 30,000 tasks in the system anyway, and it means
32 * that we can use a bitmap to indicate which contexts are in use.
33 * Using a bitmap means that we entirely avoid all of the problems
34 * that we used to have when the context number overflowed,
35 * particularly on SMP systems.
36 * -- paulus.
37 */
38 #define NO_CONTEXT ((unsigned long) -1)
39 #define LAST_CONTEXT 32767
40 #define FIRST_CONTEXT 1
41
42 /*
43 * This function defines the mapping from contexts to VSIDs (virtual
44 * segment IDs). We use a skew on both the context and the high 4 bits
45 * of the 32-bit virtual address (the "effective segment ID") in order
46 * to spread out the entries in the MMU hash table. Note, if this
47 * function is changed then arch/ppc/mm/hashtable.S will have to be
48 * changed to correspond.
49 *
50 *
51 * CTX_TO_VSID(ctx, va) (((ctx) * (897 * 16) + ((va) >> 28) * 0x111) \
52 * & 0xffffff)
53 */
54
55 static unsigned long next_mmu_context;
56 static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
57
58 unsigned long __init_new_context(void)
59 {
60 unsigned long ctx = next_mmu_context;
61
62 while (test_and_set_bit(ctx, context_map)) {
63 ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1, ctx);
64 if (ctx > LAST_CONTEXT)
65 ctx = 0;
66 }
67 next_mmu_context = (ctx + 1) & LAST_CONTEXT;
68
69 return ctx;
70 }
71 EXPORT_SYMBOL_GPL(__init_new_context);
72
73 /*
74 * Set up the context for a new address space.
75 */
76 int init_new_context(struct task_struct *t, struct mm_struct *mm)
77 {
78 mm->context.id = __init_new_context();
79
80 return 0;
81 }
82
83 /*
84 * Free a context ID. Make sure to call this with preempt disabled!
85 */
86 void __destroy_context(unsigned long ctx)
87 {
88 clear_bit(ctx, context_map);
89 }
90 EXPORT_SYMBOL_GPL(__destroy_context);
91
92 /*
93 * We're finished using the context for an address space.
94 */
95 void destroy_context(struct mm_struct *mm)
96 {
97 preempt_disable();
98 if (mm->context.id != NO_CONTEXT) {
99 __destroy_context(mm->context.id);
100 mm->context.id = NO_CONTEXT;
101 }
102 preempt_enable();
103 }
104
105 /*
106 * Initialize the context management stuff.
107 */
108 void __init mmu_context_init(void)
109 {
110 /* Reserve context 0 for kernel use */
111 context_map[0] = (1 << FIRST_CONTEXT) - 1;
112 next_mmu_context = FIRST_CONTEXT;
113 }