1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * Copyright (C) 2010-2017 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
4 *
5 * membarrier system call
6 */
7 #include "sched.h"
8
9 /*
10 * Bitmask made from a "or" of all commands within enum membarrier_cmd,
11 * except MEMBARRIER_CMD_QUERY.
12 */
13 #ifdef CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE
14 #define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK \
15 (MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE \
16 | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE)
17 #else
18 #define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK 0
19 #endif
20
21 #define MEMBARRIER_CMD_BITMASK \
22 (MEMBARRIER_CMD_GLOBAL | MEMBARRIER_CMD_GLOBAL_EXPEDITED \
23 | MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED \
24 | MEMBARRIER_CMD_PRIVATE_EXPEDITED \
25 | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED \
26 | MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK)
27
28 static void ipi_mb(void *info)
29 {
30 smp_mb(); /* IPIs should be serializing but paranoid. */
31 }
32
33 static void ipi_sync_rq_state(void *info)
34 {
35 struct mm_struct *mm = (struct mm_struct *) info;
36
37 if (current->mm != mm)
38 return;
39 this_cpu_write(runqueues.membarrier_state,
40 atomic_read(&mm->membarrier_state));
41 /*
42 * Issue a memory barrier after setting
43 * MEMBARRIER_STATE_GLOBAL_EXPEDITED in the current runqueue to
44 * guarantee that no memory access following registration is reordered
45 * before registration.
46 */
47 smp_mb();
48 }
49
50 void membarrier_exec_mmap(struct mm_struct *mm)
51 {
52 /*
53 * Issue a memory barrier before clearing membarrier_state to
54 * guarantee that no memory access prior to exec is reordered after
55 * clearing this state.
56 */
57 smp_mb();
58 atomic_set(&mm->membarrier_state, 0);
59 /*
60 * Keep the runqueue membarrier_state in sync with this mm
61 * membarrier_state.
62 */
63 this_cpu_write(runqueues.membarrier_state, 0);
64 }
65
66 static int membarrier_global_expedited(void)
67 {
68 int cpu;
69 cpumask_var_t tmpmask;
70
71 if (num_online_cpus() == 1)
72 return 0;
73
74 /*
75 * Matches memory barriers around rq->curr modification in
76 * scheduler.
77 */
78 smp_mb(); /* system call entry is not a mb. */
79
80 if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
81 return -ENOMEM;
82
83 cpus_read_lock();
84 rcu_read_lock();
85 for_each_online_cpu(cpu) {
86 struct task_struct *p;
87
88 /*
89 * Skipping the current CPU is OK even through we can be
90 * migrated at any point. The current CPU, at the point
91 * where we read raw_smp_processor_id(), is ensured to
92 * be in program order with respect to the caller
93 * thread. Therefore, we can skip this CPU from the
94 * iteration.
95 */
96 if (cpu == raw_smp_processor_id())
97 continue;
98
99 if (!(READ_ONCE(cpu_rq(cpu)->membarrier_state) &
100 MEMBARRIER_STATE_GLOBAL_EXPEDITED))
101 continue;
102
103 /*
104 * Skip the CPU if it runs a kernel thread. The scheduler
105 * leaves the prior task mm in place as an optimization when
106 * scheduling a kthread.
107 */
108 p = rcu_dereference(cpu_rq(cpu)->curr);
109 if (p->flags & PF_KTHREAD)
110 continue;
111
112 __cpumask_set_cpu(cpu, tmpmask);
113 }
114 rcu_read_unlock();
115
116 preempt_disable();
117 smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
118 preempt_enable();
119
120 free_cpumask_var(tmpmask);
121 cpus_read_unlock();
122
123 /*
124 * Memory barrier on the caller thread _after_ we finished
125 * waiting for the last IPI. Matches memory barriers around
126 * rq->curr modification in scheduler.
127 */
128 smp_mb(); /* exit from system call is not a mb */
129 return 0;
130 }
131
132 static int membarrier_private_expedited(int flags)
133 {
134 int cpu;
135 cpumask_var_t tmpmask;
136 struct mm_struct *mm = current->mm;
137
138 if (flags & MEMBARRIER_FLAG_SYNC_CORE) {
139 if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
140 return -EINVAL;
141 if (!(atomic_read(&mm->membarrier_state) &
142 MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY))
143 return -EPERM;
144 } else {
145 if (!(atomic_read(&mm->membarrier_state) &
146 MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY))
147 return -EPERM;
148 }
149
150 if (atomic_read(&mm->mm_users) == 1 || num_online_cpus() == 1)
151 return 0;
152
153 /*
154 * Matches memory barriers around rq->curr modification in
155 * scheduler.
156 */
157 smp_mb(); /* system call entry is not a mb. */
158
159 if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
160 return -ENOMEM;
161
162 cpus_read_lock();
163 rcu_read_lock();
164 for_each_online_cpu(cpu) {
165 struct task_struct *p;
166
167 /*
168 * Skipping the current CPU is OK even through we can be
169 * migrated at any point. The current CPU, at the point
170 * where we read raw_smp_processor_id(), is ensured to
171 * be in program order with respect to the caller
172 * thread. Therefore, we can skip this CPU from the
173 * iteration.
174 */
175 if (cpu == raw_smp_processor_id())
176 continue;
177 p = rcu_dereference(cpu_rq(cpu)->curr);
178 if (p && p->mm == mm)
179 __cpumask_set_cpu(cpu, tmpmask);
180 }
181 rcu_read_unlock();
182
183 preempt_disable();
184 smp_call_function_many(tmpmask, ipi_mb, NULL, 1);
185 preempt_enable();
186
187 free_cpumask_var(tmpmask);
188 cpus_read_unlock();
189
190 /*
191 * Memory barrier on the caller thread _after_ we finished
192 * waiting for the last IPI. Matches memory barriers around
193 * rq->curr modification in scheduler.
194 */
195 smp_mb(); /* exit from system call is not a mb */
196
197 return 0;
198 }
199
200 static int sync_runqueues_membarrier_state(struct mm_struct *mm)
201 {
202 int membarrier_state = atomic_read(&mm->membarrier_state);
203 cpumask_var_t tmpmask;
204 int cpu;
205
206 if (atomic_read(&mm->mm_users) == 1 || num_online_cpus() == 1) {
207 this_cpu_write(runqueues.membarrier_state, membarrier_state);
208
209 /*
210 * For single mm user, we can simply issue a memory barrier
211 * after setting MEMBARRIER_STATE_GLOBAL_EXPEDITED in the
212 * mm and in the current runqueue to guarantee that no memory
213 * access following registration is reordered before
214 * registration.
215 */
216 smp_mb();
217 return 0;
218 }
219
220 if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
221 return -ENOMEM;
222
223 /*
224 * For mm with multiple users, we need to ensure all future
225 * scheduler executions will observe @mm's new membarrier
226 * state.
227 */
228 synchronize_rcu();
229
230 /*
231 * For each cpu runqueue, if the task's mm match @mm, ensure that all
232 * @mm's membarrier state set bits are also set in in the runqueue's
233 * membarrier state. This ensures that a runqueue scheduling
234 * between threads which are users of @mm has its membarrier state
235 * updated.
236 */
237 cpus_read_lock();
238 rcu_read_lock();
239 for_each_online_cpu(cpu) {
240 struct rq *rq = cpu_rq(cpu);
241 struct task_struct *p;
242
243 p = rcu_dereference(rq->curr);
244 if (p && p->mm == mm)
245 __cpumask_set_cpu(cpu, tmpmask);
246 }
247 rcu_read_unlock();
248
249 preempt_disable();
250 smp_call_function_many(tmpmask, ipi_sync_rq_state, mm, 1);
251 preempt_enable();
252
253 free_cpumask_var(tmpmask);
254 cpus_read_unlock();
255
256 return 0;
257 }
258
259 static int membarrier_register_global_expedited(void)
260 {
261 struct task_struct *p = current;
262 struct mm_struct *mm = p->mm;
263 int ret;
264
265 if (atomic_read(&mm->membarrier_state) &
266 MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY)
267 return 0;
268 atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED, &mm->membarrier_state);
269 ret = sync_runqueues_membarrier_state(mm);
270 if (ret)
271 return ret;
272 atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY,
273 &mm->membarrier_state);
274
275 return 0;
276 }
277
278 static int membarrier_register_private_expedited(int flags)
279 {
280 struct task_struct *p = current;
281 struct mm_struct *mm = p->mm;
282 int ready_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY,
283 set_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED,
284 ret;
285
286 if (flags & MEMBARRIER_FLAG_SYNC_CORE) {
287 if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE))
288 return -EINVAL;
289 ready_state =
290 MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY;
291 }
292
293 /*
294 * We need to consider threads belonging to different thread
295 * groups, which use the same mm. (CLONE_VM but not
296 * CLONE_THREAD).
297 */
298 if ((atomic_read(&mm->membarrier_state) & ready_state) == ready_state)
299 return 0;
300 if (flags & MEMBARRIER_FLAG_SYNC_CORE)
301 set_state |= MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE;
302 atomic_or(set_state, &mm->membarrier_state);
303 ret = sync_runqueues_membarrier_state(mm);
304 if (ret)
305 return ret;
306 atomic_or(ready_state, &mm->membarrier_state);
307
308 return 0;
309 }
310
311 /**
312 * sys_membarrier - issue memory barriers on a set of threads
313 * @cmd: Takes command values defined in enum membarrier_cmd.
314 * @flags: Currently needs to be 0. For future extensions.
315 *
316 * If this system call is not implemented, -ENOSYS is returned. If the
317 * command specified does not exist, not available on the running
318 * kernel, or if the command argument is invalid, this system call
319 * returns -EINVAL. For a given command, with flags argument set to 0,
320 * if this system call returns -ENOSYS or -EINVAL, it is guaranteed to
321 * always return the same value until reboot. In addition, it can return
322 * -ENOMEM if there is not enough memory available to perform the system
323 * call.
324 *
325 * All memory accesses performed in program order from each targeted thread
326 * is guaranteed to be ordered with respect to sys_membarrier(). If we use
327 * the semantic "barrier()" to represent a compiler barrier forcing memory
328 * accesses to be performed in program order across the barrier, and
329 * smp_mb() to represent explicit memory barriers forcing full memory
330 * ordering across the barrier, we have the following ordering table for
331 * each pair of barrier(), sys_membarrier() and smp_mb():
332 *
333 * The pair ordering is detailed as (O: ordered, X: not ordered):
334 *
335 * barrier() smp_mb() sys_membarrier()
336 * barrier() X X O
337 * smp_mb() X O O
338 * sys_membarrier() O O O
339 */
340 SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
341 {
342 if (unlikely(flags))
343 return -EINVAL;
344 switch (cmd) {
345 case MEMBARRIER_CMD_QUERY:
346 {
347 int cmd_mask = MEMBARRIER_CMD_BITMASK;
348
349 if (tick_nohz_full_enabled())
350 cmd_mask &= ~MEMBARRIER_CMD_GLOBAL;
351 return cmd_mask;
352 }
353 case MEMBARRIER_CMD_GLOBAL:
354 /* MEMBARRIER_CMD_GLOBAL is not compatible with nohz_full. */
355 if (tick_nohz_full_enabled())
356 return -EINVAL;
357 if (num_online_cpus() > 1)
358 synchronize_rcu();
359 return 0;
360 case MEMBARRIER_CMD_GLOBAL_EXPEDITED:
361 return membarrier_global_expedited();
362 case MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED:
363 return membarrier_register_global_expedited();
364 case MEMBARRIER_CMD_PRIVATE_EXPEDITED:
365 return membarrier_private_expedited(0);
366 case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED:
367 return membarrier_register_private_expedited(0);
368 case MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE:
369 return membarrier_private_expedited(MEMBARRIER_FLAG_SYNC_CORE);
370 case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE:
371 return membarrier_register_private_expedited(MEMBARRIER_FLAG_SYNC_CORE);
372 default:
373 return -EINVAL;
374 }
375 }