Loading...
1/*
2 * linux/arch/arm/mm/context.c
3 *
4 * Copyright (C) 2002-2003 Deep Blue Solutions Ltd, all rights reserved.
5 * Copyright (C) 2012 ARM Limited
6 *
7 * Author: Will Deacon <will.deacon@arm.com>
8 *
9 * This program is free software; you can redistribute it and/or modify
10 * it under the terms of the GNU General Public License version 2 as
11 * published by the Free Software Foundation.
12 */
13#include <linux/init.h>
14#include <linux/sched.h>
15#include <linux/mm.h>
16#include <linux/smp.h>
17#include <linux/percpu.h>
18
19#include <asm/mmu_context.h>
20#include <asm/smp_plat.h>
21#include <asm/thread_notify.h>
22#include <asm/tlbflush.h>
23#include <asm/proc-fns.h>
24
25/*
26 * On ARMv6, we have the following structure in the Context ID:
27 *
28 * 31 7 0
29 * +-------------------------+-----------+
30 * | process ID | ASID |
31 * +-------------------------+-----------+
32 * | context ID |
33 * +-------------------------------------+
34 *
35 * The ASID is used to tag entries in the CPU caches and TLBs.
36 * The context ID is used by debuggers and trace logic, and
37 * should be unique within all running processes.
38 *
39 * In big endian operation, the two 32 bit words are swapped if accessed
40 * by non-64-bit operations.
41 */
42#define ASID_FIRST_VERSION (1ULL << ASID_BITS)
43#define NUM_USER_ASIDS ASID_FIRST_VERSION
44
45static DEFINE_RAW_SPINLOCK(cpu_asid_lock);
46static atomic64_t asid_generation = ATOMIC64_INIT(ASID_FIRST_VERSION);
47static DECLARE_BITMAP(asid_map, NUM_USER_ASIDS);
48
49static DEFINE_PER_CPU(atomic64_t, active_asids);
50static DEFINE_PER_CPU(u64, reserved_asids);
51static cpumask_t tlb_flush_pending;
52
53#ifdef CONFIG_ARM_ERRATA_798181
54void a15_erratum_get_cpumask(int this_cpu, struct mm_struct *mm,
55 cpumask_t *mask)
56{
57 int cpu;
58 unsigned long flags;
59 u64 context_id, asid;
60
61 raw_spin_lock_irqsave(&cpu_asid_lock, flags);
62 context_id = mm->context.id.counter;
63 for_each_online_cpu(cpu) {
64 if (cpu == this_cpu)
65 continue;
66 /*
67 * We only need to send an IPI if the other CPUs are
68 * running the same ASID as the one being invalidated.
69 */
70 asid = per_cpu(active_asids, cpu).counter;
71 if (asid == 0)
72 asid = per_cpu(reserved_asids, cpu);
73 if (context_id == asid)
74 cpumask_set_cpu(cpu, mask);
75 }
76 raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);
77}
78#endif
79
80#ifdef CONFIG_ARM_LPAE
81/*
82 * With LPAE, the ASID and page tables are updated atomicly, so there is
83 * no need for a reserved set of tables (the active ASID tracking prevents
84 * any issues across a rollover).
85 */
86#define cpu_set_reserved_ttbr0()
87#else
88static void cpu_set_reserved_ttbr0(void)
89{
90 u32 ttb;
91 /*
92 * Copy TTBR1 into TTBR0.
93 * This points at swapper_pg_dir, which contains only global
94 * entries so any speculative walks are perfectly safe.
95 */
96 asm volatile(
97 " mrc p15, 0, %0, c2, c0, 1 @ read TTBR1\n"
98 " mcr p15, 0, %0, c2, c0, 0 @ set TTBR0\n"
99 : "=r" (ttb));
100 isb();
101}
102#endif
103
104#ifdef CONFIG_PID_IN_CONTEXTIDR
105static int contextidr_notifier(struct notifier_block *unused, unsigned long cmd,
106 void *t)
107{
108 u32 contextidr;
109 pid_t pid;
110 struct thread_info *thread = t;
111
112 if (cmd != THREAD_NOTIFY_SWITCH)
113 return NOTIFY_DONE;
114
115 pid = task_pid_nr(thread->task) << ASID_BITS;
116 asm volatile(
117 " mrc p15, 0, %0, c13, c0, 1\n"
118 " and %0, %0, %2\n"
119 " orr %0, %0, %1\n"
120 " mcr p15, 0, %0, c13, c0, 1\n"
121 : "=r" (contextidr), "+r" (pid)
122 : "I" (~ASID_MASK));
123 isb();
124
125 return NOTIFY_OK;
126}
127
128static struct notifier_block contextidr_notifier_block = {
129 .notifier_call = contextidr_notifier,
130};
131
132static int __init contextidr_notifier_init(void)
133{
134 return thread_register_notifier(&contextidr_notifier_block);
135}
136arch_initcall(contextidr_notifier_init);
137#endif
138
139static void flush_context(unsigned int cpu)
140{
141 int i;
142 u64 asid;
143
144 /* Update the list of reserved ASIDs and the ASID bitmap. */
145 bitmap_clear(asid_map, 0, NUM_USER_ASIDS);
146 for_each_possible_cpu(i) {
147 asid = atomic64_xchg(&per_cpu(active_asids, i), 0);
148 /*
149 * If this CPU has already been through a
150 * rollover, but hasn't run another task in
151 * the meantime, we must preserve its reserved
152 * ASID, as this is the only trace we have of
153 * the process it is still running.
154 */
155 if (asid == 0)
156 asid = per_cpu(reserved_asids, i);
157 __set_bit(asid & ~ASID_MASK, asid_map);
158 per_cpu(reserved_asids, i) = asid;
159 }
160
161 /* Queue a TLB invalidate and flush the I-cache if necessary. */
162 cpumask_setall(&tlb_flush_pending);
163
164 if (icache_is_vivt_asid_tagged())
165 __flush_icache_all();
166}
167
168static bool check_update_reserved_asid(u64 asid, u64 newasid)
169{
170 int cpu;
171 bool hit = false;
172
173 /*
174 * Iterate over the set of reserved ASIDs looking for a match.
175 * If we find one, then we can update our mm to use newasid
176 * (i.e. the same ASID in the current generation) but we can't
177 * exit the loop early, since we need to ensure that all copies
178 * of the old ASID are updated to reflect the mm. Failure to do
179 * so could result in us missing the reserved ASID in a future
180 * generation.
181 */
182 for_each_possible_cpu(cpu) {
183 if (per_cpu(reserved_asids, cpu) == asid) {
184 hit = true;
185 per_cpu(reserved_asids, cpu) = newasid;
186 }
187 }
188
189 return hit;
190}
191
192static u64 new_context(struct mm_struct *mm, unsigned int cpu)
193{
194 static u32 cur_idx = 1;
195 u64 asid = atomic64_read(&mm->context.id);
196 u64 generation = atomic64_read(&asid_generation);
197
198 if (asid != 0) {
199 u64 newasid = generation | (asid & ~ASID_MASK);
200
201 /*
202 * If our current ASID was active during a rollover, we
203 * can continue to use it and this was just a false alarm.
204 */
205 if (check_update_reserved_asid(asid, newasid))
206 return newasid;
207
208 /*
209 * We had a valid ASID in a previous life, so try to re-use
210 * it if possible.,
211 */
212 asid &= ~ASID_MASK;
213 if (!__test_and_set_bit(asid, asid_map))
214 return newasid;
215 }
216
217 /*
218 * Allocate a free ASID. If we can't find one, take a note of the
219 * currently active ASIDs and mark the TLBs as requiring flushes.
220 * We always count from ASID #1, as we reserve ASID #0 to switch
221 * via TTBR0 and to avoid speculative page table walks from hitting
222 * in any partial walk caches, which could be populated from
223 * overlapping level-1 descriptors used to map both the module
224 * area and the userspace stack.
225 */
226 asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, cur_idx);
227 if (asid == NUM_USER_ASIDS) {
228 generation = atomic64_add_return(ASID_FIRST_VERSION,
229 &asid_generation);
230 flush_context(cpu);
231 asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, 1);
232 }
233
234 __set_bit(asid, asid_map);
235 cur_idx = asid;
236 cpumask_clear(mm_cpumask(mm));
237 return asid | generation;
238}
239
240void check_and_switch_context(struct mm_struct *mm, struct task_struct *tsk)
241{
242 unsigned long flags;
243 unsigned int cpu = smp_processor_id();
244 u64 asid;
245
246 if (unlikely(mm->context.vmalloc_seq != init_mm.context.vmalloc_seq))
247 __check_vmalloc_seq(mm);
248
249 /*
250 * We cannot update the pgd and the ASID atomicly with classic
251 * MMU, so switch exclusively to global mappings to avoid
252 * speculative page table walking with the wrong TTBR.
253 */
254 cpu_set_reserved_ttbr0();
255
256 asid = atomic64_read(&mm->context.id);
257 if (!((asid ^ atomic64_read(&asid_generation)) >> ASID_BITS)
258 && atomic64_xchg(&per_cpu(active_asids, cpu), asid))
259 goto switch_mm_fastpath;
260
261 raw_spin_lock_irqsave(&cpu_asid_lock, flags);
262 /* Check that our ASID belongs to the current generation. */
263 asid = atomic64_read(&mm->context.id);
264 if ((asid ^ atomic64_read(&asid_generation)) >> ASID_BITS) {
265 asid = new_context(mm, cpu);
266 atomic64_set(&mm->context.id, asid);
267 }
268
269 if (cpumask_test_and_clear_cpu(cpu, &tlb_flush_pending)) {
270 local_flush_bp_all();
271 local_flush_tlb_all();
272 }
273
274 atomic64_set(&per_cpu(active_asids, cpu), asid);
275 cpumask_set_cpu(cpu, mm_cpumask(mm));
276 raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);
277
278switch_mm_fastpath:
279 cpu_switch_mm(mm->pgd, mm);
280}
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * linux/arch/arm/mm/context.c
4 *
5 * Copyright (C) 2002-2003 Deep Blue Solutions Ltd, all rights reserved.
6 * Copyright (C) 2012 ARM Limited
7 *
8 * Author: Will Deacon <will.deacon@arm.com>
9 */
10#include <linux/init.h>
11#include <linux/sched.h>
12#include <linux/mm.h>
13#include <linux/smp.h>
14#include <linux/percpu.h>
15
16#include <asm/mmu_context.h>
17#include <asm/smp_plat.h>
18#include <asm/thread_notify.h>
19#include <asm/tlbflush.h>
20#include <asm/proc-fns.h>
21
22/*
23 * On ARMv6, we have the following structure in the Context ID:
24 *
25 * 31 7 0
26 * +-------------------------+-----------+
27 * | process ID | ASID |
28 * +-------------------------+-----------+
29 * | context ID |
30 * +-------------------------------------+
31 *
32 * The ASID is used to tag entries in the CPU caches and TLBs.
33 * The context ID is used by debuggers and trace logic, and
34 * should be unique within all running processes.
35 *
36 * In big endian operation, the two 32 bit words are swapped if accessed
37 * by non-64-bit operations.
38 */
39#define ASID_FIRST_VERSION (1ULL << ASID_BITS)
40#define NUM_USER_ASIDS ASID_FIRST_VERSION
41
42static DEFINE_RAW_SPINLOCK(cpu_asid_lock);
43static atomic64_t asid_generation = ATOMIC64_INIT(ASID_FIRST_VERSION);
44static DECLARE_BITMAP(asid_map, NUM_USER_ASIDS);
45
46static DEFINE_PER_CPU(atomic64_t, active_asids);
47static DEFINE_PER_CPU(u64, reserved_asids);
48static cpumask_t tlb_flush_pending;
49
50#ifdef CONFIG_ARM_ERRATA_798181
51void a15_erratum_get_cpumask(int this_cpu, struct mm_struct *mm,
52 cpumask_t *mask)
53{
54 int cpu;
55 unsigned long flags;
56 u64 context_id, asid;
57
58 raw_spin_lock_irqsave(&cpu_asid_lock, flags);
59 context_id = mm->context.id.counter;
60 for_each_online_cpu(cpu) {
61 if (cpu == this_cpu)
62 continue;
63 /*
64 * We only need to send an IPI if the other CPUs are
65 * running the same ASID as the one being invalidated.
66 */
67 asid = per_cpu(active_asids, cpu).counter;
68 if (asid == 0)
69 asid = per_cpu(reserved_asids, cpu);
70 if (context_id == asid)
71 cpumask_set_cpu(cpu, mask);
72 }
73 raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);
74}
75#endif
76
77#ifdef CONFIG_ARM_LPAE
78/*
79 * With LPAE, the ASID and page tables are updated atomicly, so there is
80 * no need for a reserved set of tables (the active ASID tracking prevents
81 * any issues across a rollover).
82 */
83#define cpu_set_reserved_ttbr0()
84#else
85static void cpu_set_reserved_ttbr0(void)
86{
87 u32 ttb;
88 /*
89 * Copy TTBR1 into TTBR0.
90 * This points at swapper_pg_dir, which contains only global
91 * entries so any speculative walks are perfectly safe.
92 */
93 asm volatile(
94 " mrc p15, 0, %0, c2, c0, 1 @ read TTBR1\n"
95 " mcr p15, 0, %0, c2, c0, 0 @ set TTBR0\n"
96 : "=r" (ttb));
97 isb();
98}
99#endif
100
101#ifdef CONFIG_PID_IN_CONTEXTIDR
102static int contextidr_notifier(struct notifier_block *unused, unsigned long cmd,
103 void *t)
104{
105 u32 contextidr;
106 pid_t pid;
107 struct thread_info *thread = t;
108
109 if (cmd != THREAD_NOTIFY_SWITCH)
110 return NOTIFY_DONE;
111
112 pid = task_pid_nr(thread_task(thread)) << ASID_BITS;
113 asm volatile(
114 " mrc p15, 0, %0, c13, c0, 1\n"
115 " and %0, %0, %2\n"
116 " orr %0, %0, %1\n"
117 " mcr p15, 0, %0, c13, c0, 1\n"
118 : "=r" (contextidr), "+r" (pid)
119 : "I" (~ASID_MASK));
120 isb();
121
122 return NOTIFY_OK;
123}
124
125static struct notifier_block contextidr_notifier_block = {
126 .notifier_call = contextidr_notifier,
127};
128
129static int __init contextidr_notifier_init(void)
130{
131 return thread_register_notifier(&contextidr_notifier_block);
132}
133arch_initcall(contextidr_notifier_init);
134#endif
135
136static void flush_context(unsigned int cpu)
137{
138 int i;
139 u64 asid;
140
141 /* Update the list of reserved ASIDs and the ASID bitmap. */
142 bitmap_clear(asid_map, 0, NUM_USER_ASIDS);
143 for_each_possible_cpu(i) {
144 asid = atomic64_xchg(&per_cpu(active_asids, i), 0);
145 /*
146 * If this CPU has already been through a
147 * rollover, but hasn't run another task in
148 * the meantime, we must preserve its reserved
149 * ASID, as this is the only trace we have of
150 * the process it is still running.
151 */
152 if (asid == 0)
153 asid = per_cpu(reserved_asids, i);
154 __set_bit(asid & ~ASID_MASK, asid_map);
155 per_cpu(reserved_asids, i) = asid;
156 }
157
158 /* Queue a TLB invalidate and flush the I-cache if necessary. */
159 cpumask_setall(&tlb_flush_pending);
160
161 if (icache_is_vivt_asid_tagged())
162 __flush_icache_all();
163}
164
165static bool check_update_reserved_asid(u64 asid, u64 newasid)
166{
167 int cpu;
168 bool hit = false;
169
170 /*
171 * Iterate over the set of reserved ASIDs looking for a match.
172 * If we find one, then we can update our mm to use newasid
173 * (i.e. the same ASID in the current generation) but we can't
174 * exit the loop early, since we need to ensure that all copies
175 * of the old ASID are updated to reflect the mm. Failure to do
176 * so could result in us missing the reserved ASID in a future
177 * generation.
178 */
179 for_each_possible_cpu(cpu) {
180 if (per_cpu(reserved_asids, cpu) == asid) {
181 hit = true;
182 per_cpu(reserved_asids, cpu) = newasid;
183 }
184 }
185
186 return hit;
187}
188
189static u64 new_context(struct mm_struct *mm, unsigned int cpu)
190{
191 static u32 cur_idx = 1;
192 u64 asid = atomic64_read(&mm->context.id);
193 u64 generation = atomic64_read(&asid_generation);
194
195 if (asid != 0) {
196 u64 newasid = generation | (asid & ~ASID_MASK);
197
198 /*
199 * If our current ASID was active during a rollover, we
200 * can continue to use it and this was just a false alarm.
201 */
202 if (check_update_reserved_asid(asid, newasid))
203 return newasid;
204
205 /*
206 * We had a valid ASID in a previous life, so try to re-use
207 * it if possible.,
208 */
209 asid &= ~ASID_MASK;
210 if (!__test_and_set_bit(asid, asid_map))
211 return newasid;
212 }
213
214 /*
215 * Allocate a free ASID. If we can't find one, take a note of the
216 * currently active ASIDs and mark the TLBs as requiring flushes.
217 * We always count from ASID #1, as we reserve ASID #0 to switch
218 * via TTBR0 and to avoid speculative page table walks from hitting
219 * in any partial walk caches, which could be populated from
220 * overlapping level-1 descriptors used to map both the module
221 * area and the userspace stack.
222 */
223 asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, cur_idx);
224 if (asid == NUM_USER_ASIDS) {
225 generation = atomic64_add_return(ASID_FIRST_VERSION,
226 &asid_generation);
227 flush_context(cpu);
228 asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, 1);
229 }
230
231 __set_bit(asid, asid_map);
232 cur_idx = asid;
233 cpumask_clear(mm_cpumask(mm));
234 return asid | generation;
235}
236
237void check_and_switch_context(struct mm_struct *mm, struct task_struct *tsk)
238{
239 unsigned long flags;
240 unsigned int cpu = smp_processor_id();
241 u64 asid;
242
243 check_vmalloc_seq(mm);
244
245 /*
246 * We cannot update the pgd and the ASID atomicly with classic
247 * MMU, so switch exclusively to global mappings to avoid
248 * speculative page table walking with the wrong TTBR.
249 */
250 cpu_set_reserved_ttbr0();
251
252 asid = atomic64_read(&mm->context.id);
253 if (!((asid ^ atomic64_read(&asid_generation)) >> ASID_BITS)
254 && atomic64_xchg(&per_cpu(active_asids, cpu), asid))
255 goto switch_mm_fastpath;
256
257 raw_spin_lock_irqsave(&cpu_asid_lock, flags);
258 /* Check that our ASID belongs to the current generation. */
259 asid = atomic64_read(&mm->context.id);
260 if ((asid ^ atomic64_read(&asid_generation)) >> ASID_BITS) {
261 asid = new_context(mm, cpu);
262 atomic64_set(&mm->context.id, asid);
263 }
264
265 if (cpumask_test_and_clear_cpu(cpu, &tlb_flush_pending)) {
266 local_flush_bp_all();
267 local_flush_tlb_all();
268 }
269
270 atomic64_set(&per_cpu(active_asids, cpu), asid);
271 cpumask_set_cpu(cpu, mm_cpumask(mm));
272 raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);
273
274switch_mm_fastpath:
275 cpu_switch_mm(mm->pgd, mm);
276}