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 * Room for two PTE pointers, usually the kernel and current user pointers
28 * to their respective root page table.
29 */
30void *abatron_pteptrs[2];
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
48static unsigned long next_mmu_context;
49static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
50
51unsigned long __init_new_context(void)
52{
53	unsigned long ctx = next_mmu_context;
54
55	while (test_and_set_bit(ctx, context_map)) {
56		ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1, ctx);
57		if (ctx > LAST_CONTEXT)
58			ctx = 0;
59	}
60	next_mmu_context = (ctx + 1) & LAST_CONTEXT;
61
62	return ctx;
63}
64EXPORT_SYMBOL_GPL(__init_new_context);
65
66/*
67 * Set up the context for a new address space.
68 */
69int init_new_context(struct task_struct *t, struct mm_struct *mm)
70{
71	mm->context.id = __init_new_context();
72	mm->context.sr0 = CTX_TO_VSID(mm->context.id, 0);
73
74	if (IS_ENABLED(CONFIG_PPC_KUEP))
75		mm->context.sr0 |= SR_NX;
76	if (!kuap_is_disabled())
77		mm->context.sr0 |= SR_KS;
78
79	return 0;
80}
81
82/*
83 * Free a context ID. Make sure to call this with preempt disabled!
84 */
85void __destroy_context(unsigned long ctx)
86{
87	clear_bit(ctx, context_map);
88}
89EXPORT_SYMBOL_GPL(__destroy_context);
90
91/*
92 * We're finished using the context for an address space.
93 */
94void destroy_context(struct mm_struct *mm)
95{
96	preempt_disable();
97	if (mm->context.id != NO_CONTEXT) {
98		__destroy_context(mm->context.id);
99		mm->context.id = NO_CONTEXT;
100	}
101	preempt_enable();
102}
103
104/*
105 * Initialize the context management stuff.
106 */
107void __init mmu_context_init(void)
108{
109	/* Reserve context 0 for kernel use */
110	context_map[0] = (1 << FIRST_CONTEXT) - 1;
111	next_mmu_context = FIRST_CONTEXT;
112}
113
114void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next, struct task_struct *tsk)
115{
116	long id = next->context.id;
117
118	if (id < 0)
119		panic("mm_struct %p has no context ID", next);
120
121	isync();
122
123	update_user_segments(next->context.sr0);
124
125	if (IS_ENABLED(CONFIG_BDI_SWITCH))
126		abatron_pteptrs[1] = next->pgd;
127
128	if (!mmu_has_feature(MMU_FTR_HPTE_TABLE))
129		mtspr(SPRN_SDR1, rol32(__pa(next->pgd), 4) & 0xffff01ff);
130
131	mb();	/* sync */
132	isync();
133}
134EXPORT_SYMBOL(switch_mmu_context);
135