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c942fddf | 1 | // SPDX-License-Identifier: GPL-2.0-or-later |
22e4ebb9 MD |
2 | /* |
3 | * Copyright (C) 2010-2017 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | |
4 | * | |
5 | * membarrier system call | |
22e4ebb9 | 6 | */ |
325ea10c | 7 | #include "sched.h" |
22e4ebb9 MD |
8 | |
9 | /* | |
10 | * Bitmask made from a "or" of all commands within enum membarrier_cmd, | |
11 | * except MEMBARRIER_CMD_QUERY. | |
12 | */ | |
70216e18 | 13 | #ifdef CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE |
97fb7a0a IM |
14 | #define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK \ |
15 | (MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE \ | |
70216e18 MD |
16 | | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE) |
17 | #else | |
18 | #define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK 0 | |
19 | #endif | |
20 | ||
97fb7a0a IM |
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 \ | |
70216e18 | 26 | | MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK) |
22e4ebb9 MD |
27 | |
28 | static void ipi_mb(void *info) | |
29 | { | |
30 | smp_mb(); /* IPIs should be serializing but paranoid. */ | |
31 | } | |
32 | ||
227a4aad MD |
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 | ||
c5f58bd5 MD |
66 | static int membarrier_global_expedited(void) |
67 | { | |
68 | int cpu; | |
c5f58bd5 MD |
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 | ||
c172e0a3 MD |
80 | if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL)) |
81 | return -ENOMEM; | |
c5f58bd5 MD |
82 | |
83 | cpus_read_lock(); | |
227a4aad | 84 | rcu_read_lock(); |
c5f58bd5 MD |
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; | |
97fb7a0a | 98 | |
227a4aad MD |
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 | */ | |
154abafc | 108 | p = rcu_dereference(cpu_rq(cpu)->curr); |
227a4aad MD |
109 | if (p->flags & PF_KTHREAD) |
110 | continue; | |
111 | ||
c172e0a3 | 112 | __cpumask_set_cpu(cpu, tmpmask); |
c5f58bd5 | 113 | } |
227a4aad | 114 | rcu_read_unlock(); |
c172e0a3 MD |
115 | |
116 | preempt_disable(); | |
117 | smp_call_function_many(tmpmask, ipi_mb, NULL, 1); | |
118 | preempt_enable(); | |
119 | ||
120 | free_cpumask_var(tmpmask); | |
c5f58bd5 MD |
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 | ||
70216e18 | 132 | static int membarrier_private_expedited(int flags) |
22e4ebb9 MD |
133 | { |
134 | int cpu; | |
22e4ebb9 | 135 | cpumask_var_t tmpmask; |
c6d68c1c | 136 | struct mm_struct *mm = current->mm; |
22e4ebb9 | 137 | |
70216e18 MD |
138 | if (flags & MEMBARRIER_FLAG_SYNC_CORE) { |
139 | if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE)) | |
140 | return -EINVAL; | |
c6d68c1c | 141 | if (!(atomic_read(&mm->membarrier_state) & |
70216e18 MD |
142 | MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY)) |
143 | return -EPERM; | |
144 | } else { | |
c6d68c1c | 145 | if (!(atomic_read(&mm->membarrier_state) & |
70216e18 MD |
146 | MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY)) |
147 | return -EPERM; | |
148 | } | |
a961e409 | 149 | |
c6d68c1c | 150 | if (atomic_read(&mm->mm_users) == 1 || num_online_cpus() == 1) |
a961e409 | 151 | return 0; |
22e4ebb9 MD |
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 | ||
c172e0a3 MD |
159 | if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL)) |
160 | return -ENOMEM; | |
22e4ebb9 MD |
161 | |
162 | cpus_read_lock(); | |
227a4aad | 163 | rcu_read_lock(); |
22e4ebb9 MD |
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; | |
154abafc | 177 | p = rcu_dereference(cpu_rq(cpu)->curr); |
c172e0a3 MD |
178 | if (p && p->mm == mm) |
179 | __cpumask_set_cpu(cpu, tmpmask); | |
22e4ebb9 | 180 | } |
227a4aad | 181 | rcu_read_unlock(); |
c172e0a3 MD |
182 | |
183 | preempt_disable(); | |
184 | smp_call_function_many(tmpmask, ipi_mb, NULL, 1); | |
185 | preempt_enable(); | |
186 | ||
187 | free_cpumask_var(tmpmask); | |
22e4ebb9 MD |
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 */ | |
97fb7a0a | 196 | |
a961e409 MD |
197 | return 0; |
198 | } | |
199 | ||
227a4aad MD |
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 | ||
c172e0a3 | 243 | p = rcu_dereference(rq->curr); |
227a4aad MD |
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 | ||
c5f58bd5 MD |
259 | static int membarrier_register_global_expedited(void) |
260 | { | |
261 | struct task_struct *p = current; | |
262 | struct mm_struct *mm = p->mm; | |
227a4aad | 263 | int ret; |
c5f58bd5 MD |
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); | |
227a4aad MD |
269 | ret = sync_runqueues_membarrier_state(mm); |
270 | if (ret) | |
271 | return ret; | |
c5f58bd5 MD |
272 | atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY, |
273 | &mm->membarrier_state); | |
97fb7a0a | 274 | |
c5f58bd5 MD |
275 | return 0; |
276 | } | |
277 | ||
70216e18 | 278 | static int membarrier_register_private_expedited(int flags) |
a961e409 MD |
279 | { |
280 | struct task_struct *p = current; | |
281 | struct mm_struct *mm = p->mm; | |
227a4aad MD |
282 | int ready_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY, |
283 | set_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED, | |
284 | ret; | |
70216e18 MD |
285 | |
286 | if (flags & MEMBARRIER_FLAG_SYNC_CORE) { | |
287 | if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE)) | |
288 | return -EINVAL; | |
227a4aad MD |
289 | ready_state = |
290 | MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY; | |
70216e18 | 291 | } |
a961e409 MD |
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 | */ | |
227a4aad | 298 | if ((atomic_read(&mm->membarrier_state) & ready_state) == ready_state) |
c5f58bd5 | 299 | return 0; |
70216e18 | 300 | if (flags & MEMBARRIER_FLAG_SYNC_CORE) |
227a4aad MD |
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); | |
97fb7a0a | 307 | |
c5f58bd5 | 308 | return 0; |
22e4ebb9 MD |
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, | |
227a4aad MD |
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. | |
22e4ebb9 MD |
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()) | |
c5f58bd5 | 350 | cmd_mask &= ~MEMBARRIER_CMD_GLOBAL; |
22e4ebb9 MD |
351 | return cmd_mask; |
352 | } | |
c5f58bd5 MD |
353 | case MEMBARRIER_CMD_GLOBAL: |
354 | /* MEMBARRIER_CMD_GLOBAL is not compatible with nohz_full. */ | |
22e4ebb9 MD |
355 | if (tick_nohz_full_enabled()) |
356 | return -EINVAL; | |
357 | if (num_online_cpus() > 1) | |
78d125d3 | 358 | synchronize_rcu(); |
22e4ebb9 | 359 | return 0; |
c5f58bd5 MD |
360 | case MEMBARRIER_CMD_GLOBAL_EXPEDITED: |
361 | return membarrier_global_expedited(); | |
362 | case MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED: | |
363 | return membarrier_register_global_expedited(); | |
22e4ebb9 | 364 | case MEMBARRIER_CMD_PRIVATE_EXPEDITED: |
70216e18 | 365 | return membarrier_private_expedited(0); |
a961e409 | 366 | case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED: |
70216e18 MD |
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); | |
22e4ebb9 MD |
372 | default: |
373 | return -EINVAL; | |
374 | } | |
375 | } |