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  */
30 void *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 
48 static unsigned long next_mmu_context;
49 static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
50 
51 unsigned 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 }
64 EXPORT_SYMBOL_GPL(__init_new_context);
65 
66 /*
67  * Set up the context for a new address space.
68  */
69 int 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 (!kuep_is_disabled())
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  */
85 void __destroy_context(unsigned long ctx)
86 {
87 	clear_bit(ctx, context_map);
88 }
89 EXPORT_SYMBOL_GPL(__destroy_context);
90 
91 /*
92  * We're finished using the context for an address space.
93  */
94 void 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  */
107 void __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 
114 void 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 }
134 EXPORT_SYMBOL(switch_mmu_context);
135