1*4882a593Smuzhiyun // SPDX-License-Identifier: GPL-2.0-or-later
2*4882a593Smuzhiyun /*
3*4882a593Smuzhiyun * This file contains the routines for handling the MMU on those
4*4882a593Smuzhiyun * PowerPC implementations where the MMU substantially follows the
5*4882a593Smuzhiyun * architecture specification. This includes the 6xx, 7xx, 7xxx,
6*4882a593Smuzhiyun * and 8260 implementations but excludes the 8xx and 4xx.
7*4882a593Smuzhiyun * -- paulus
8*4882a593Smuzhiyun *
9*4882a593Smuzhiyun * Derived from arch/ppc/mm/init.c:
10*4882a593Smuzhiyun * Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
11*4882a593Smuzhiyun *
12*4882a593Smuzhiyun * Modifications by Paul Mackerras (PowerMac) (paulus@cs.anu.edu.au)
13*4882a593Smuzhiyun * and Cort Dougan (PReP) (cort@cs.nmt.edu)
14*4882a593Smuzhiyun * Copyright (C) 1996 Paul Mackerras
15*4882a593Smuzhiyun *
16*4882a593Smuzhiyun * Derived from "arch/i386/mm/init.c"
17*4882a593Smuzhiyun * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
18*4882a593Smuzhiyun */
19*4882a593Smuzhiyun
20*4882a593Smuzhiyun #include <linux/mm.h>
21*4882a593Smuzhiyun #include <linux/init.h>
22*4882a593Smuzhiyun #include <linux/export.h>
23*4882a593Smuzhiyun
24*4882a593Smuzhiyun #include <asm/mmu_context.h>
25*4882a593Smuzhiyun
26*4882a593Smuzhiyun /*
27*4882a593Smuzhiyun * On 32-bit PowerPC 6xx/7xx/7xxx CPUs, we use a set of 16 VSIDs
28*4882a593Smuzhiyun * (virtual segment identifiers) for each context. Although the
29*4882a593Smuzhiyun * hardware supports 24-bit VSIDs, and thus >1 million contexts,
30*4882a593Smuzhiyun * we only use 32,768 of them. That is ample, since there can be
31*4882a593Smuzhiyun * at most around 30,000 tasks in the system anyway, and it means
32*4882a593Smuzhiyun * that we can use a bitmap to indicate which contexts are in use.
33*4882a593Smuzhiyun * Using a bitmap means that we entirely avoid all of the problems
34*4882a593Smuzhiyun * that we used to have when the context number overflowed,
35*4882a593Smuzhiyun * particularly on SMP systems.
36*4882a593Smuzhiyun * -- paulus.
37*4882a593Smuzhiyun */
38*4882a593Smuzhiyun #define NO_CONTEXT ((unsigned long) -1)
39*4882a593Smuzhiyun #define LAST_CONTEXT 32767
40*4882a593Smuzhiyun #define FIRST_CONTEXT 1
41*4882a593Smuzhiyun
42*4882a593Smuzhiyun /*
43*4882a593Smuzhiyun * This function defines the mapping from contexts to VSIDs (virtual
44*4882a593Smuzhiyun * segment IDs). We use a skew on both the context and the high 4 bits
45*4882a593Smuzhiyun * of the 32-bit virtual address (the "effective segment ID") in order
46*4882a593Smuzhiyun * to spread out the entries in the MMU hash table. Note, if this
47*4882a593Smuzhiyun * function is changed then arch/ppc/mm/hashtable.S will have to be
48*4882a593Smuzhiyun * changed to correspond.
49*4882a593Smuzhiyun *
50*4882a593Smuzhiyun *
51*4882a593Smuzhiyun * CTX_TO_VSID(ctx, va) (((ctx) * (897 * 16) + ((va) >> 28) * 0x111) \
52*4882a593Smuzhiyun * & 0xffffff)
53*4882a593Smuzhiyun */
54*4882a593Smuzhiyun
55*4882a593Smuzhiyun static unsigned long next_mmu_context;
56*4882a593Smuzhiyun static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
57*4882a593Smuzhiyun
__init_new_context(void)58*4882a593Smuzhiyun unsigned long __init_new_context(void)
59*4882a593Smuzhiyun {
60*4882a593Smuzhiyun unsigned long ctx = next_mmu_context;
61*4882a593Smuzhiyun
62*4882a593Smuzhiyun while (test_and_set_bit(ctx, context_map)) {
63*4882a593Smuzhiyun ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1, ctx);
64*4882a593Smuzhiyun if (ctx > LAST_CONTEXT)
65*4882a593Smuzhiyun ctx = 0;
66*4882a593Smuzhiyun }
67*4882a593Smuzhiyun next_mmu_context = (ctx + 1) & LAST_CONTEXT;
68*4882a593Smuzhiyun
69*4882a593Smuzhiyun return ctx;
70*4882a593Smuzhiyun }
71*4882a593Smuzhiyun EXPORT_SYMBOL_GPL(__init_new_context);
72*4882a593Smuzhiyun
73*4882a593Smuzhiyun /*
74*4882a593Smuzhiyun * Set up the context for a new address space.
75*4882a593Smuzhiyun */
init_new_context(struct task_struct * t,struct mm_struct * mm)76*4882a593Smuzhiyun int init_new_context(struct task_struct *t, struct mm_struct *mm)
77*4882a593Smuzhiyun {
78*4882a593Smuzhiyun mm->context.id = __init_new_context();
79*4882a593Smuzhiyun
80*4882a593Smuzhiyun return 0;
81*4882a593Smuzhiyun }
82*4882a593Smuzhiyun
83*4882a593Smuzhiyun /*
84*4882a593Smuzhiyun * Free a context ID. Make sure to call this with preempt disabled!
85*4882a593Smuzhiyun */
__destroy_context(unsigned long ctx)86*4882a593Smuzhiyun void __destroy_context(unsigned long ctx)
87*4882a593Smuzhiyun {
88*4882a593Smuzhiyun clear_bit(ctx, context_map);
89*4882a593Smuzhiyun }
90*4882a593Smuzhiyun EXPORT_SYMBOL_GPL(__destroy_context);
91*4882a593Smuzhiyun
92*4882a593Smuzhiyun /*
93*4882a593Smuzhiyun * We're finished using the context for an address space.
94*4882a593Smuzhiyun */
destroy_context(struct mm_struct * mm)95*4882a593Smuzhiyun void destroy_context(struct mm_struct *mm)
96*4882a593Smuzhiyun {
97*4882a593Smuzhiyun preempt_disable();
98*4882a593Smuzhiyun if (mm->context.id != NO_CONTEXT) {
99*4882a593Smuzhiyun __destroy_context(mm->context.id);
100*4882a593Smuzhiyun mm->context.id = NO_CONTEXT;
101*4882a593Smuzhiyun }
102*4882a593Smuzhiyun preempt_enable();
103*4882a593Smuzhiyun }
104*4882a593Smuzhiyun
105*4882a593Smuzhiyun /*
106*4882a593Smuzhiyun * Initialize the context management stuff.
107*4882a593Smuzhiyun */
mmu_context_init(void)108*4882a593Smuzhiyun void __init mmu_context_init(void)
109*4882a593Smuzhiyun {
110*4882a593Smuzhiyun /* Reserve context 0 for kernel use */
111*4882a593Smuzhiyun context_map[0] = (1 << FIRST_CONTEXT) - 1;
112*4882a593Smuzhiyun next_mmu_context = FIRST_CONTEXT;
113*4882a593Smuzhiyun }
114