s390/mcck: fix calculation of SIE critical section size
[linux-2.6-microblaze.git] / kernel / context_tracking.c
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Context tracking: Probe on high level context boundaries such as kernel
4  * and userspace. This includes syscalls and exceptions entry/exit.
5  *
6  * This is used by RCU to remove its dependency on the timer tick while a CPU
7  * runs in userspace.
8  *
9  *  Started by Frederic Weisbecker:
10  *
11  * Copyright (C) 2012 Red Hat, Inc., Frederic Weisbecker <fweisbec@redhat.com>
12  *
13  * Many thanks to Gilad Ben-Yossef, Paul McKenney, Ingo Molnar, Andrew Morton,
14  * Steven Rostedt, Peter Zijlstra for suggestions and improvements.
15  *
16  */
17
18 #include <linux/context_tracking.h>
19 #include <linux/rcupdate.h>
20 #include <linux/sched.h>
21 #include <linux/hardirq.h>
22 #include <linux/export.h>
23 #include <linux/kprobes.h>
24
25 #define CREATE_TRACE_POINTS
26 #include <trace/events/context_tracking.h>
27
28 DEFINE_STATIC_KEY_FALSE(context_tracking_key);
29 EXPORT_SYMBOL_GPL(context_tracking_key);
30
31 DEFINE_PER_CPU(struct context_tracking, context_tracking);
32 EXPORT_SYMBOL_GPL(context_tracking);
33
34 static noinstr bool context_tracking_recursion_enter(void)
35 {
36         int recursion;
37
38         recursion = __this_cpu_inc_return(context_tracking.recursion);
39         if (recursion == 1)
40                 return true;
41
42         WARN_ONCE((recursion < 1), "Invalid context tracking recursion value %d\n", recursion);
43         __this_cpu_dec(context_tracking.recursion);
44
45         return false;
46 }
47
48 static __always_inline void context_tracking_recursion_exit(void)
49 {
50         __this_cpu_dec(context_tracking.recursion);
51 }
52
53 /**
54  * context_tracking_enter - Inform the context tracking that the CPU is going
55  *                          enter user or guest space mode.
56  *
57  * This function must be called right before we switch from the kernel
58  * to user or guest space, when it's guaranteed the remaining kernel
59  * instructions to execute won't use any RCU read side critical section
60  * because this function sets RCU in extended quiescent state.
61  */
62 void noinstr __context_tracking_enter(enum ctx_state state)
63 {
64         /* Kernel threads aren't supposed to go to userspace */
65         WARN_ON_ONCE(!current->mm);
66
67         if (!context_tracking_recursion_enter())
68                 return;
69
70         if ( __this_cpu_read(context_tracking.state) != state) {
71                 if (__this_cpu_read(context_tracking.active)) {
72                         /*
73                          * At this stage, only low level arch entry code remains and
74                          * then we'll run in userspace. We can assume there won't be
75                          * any RCU read-side critical section until the next call to
76                          * user_exit() or rcu_irq_enter(). Let's remove RCU's dependency
77                          * on the tick.
78                          */
79                         if (state == CONTEXT_USER) {
80                                 instrumentation_begin();
81                                 trace_user_enter(0);
82                                 vtime_user_enter(current);
83                                 instrumentation_end();
84                         }
85                         rcu_user_enter();
86                 }
87                 /*
88                  * Even if context tracking is disabled on this CPU, because it's outside
89                  * the full dynticks mask for example, we still have to keep track of the
90                  * context transitions and states to prevent inconsistency on those of
91                  * other CPUs.
92                  * If a task triggers an exception in userspace, sleep on the exception
93                  * handler and then migrate to another CPU, that new CPU must know where
94                  * the exception returns by the time we call exception_exit().
95                  * This information can only be provided by the previous CPU when it called
96                  * exception_enter().
97                  * OTOH we can spare the calls to vtime and RCU when context_tracking.active
98                  * is false because we know that CPU is not tickless.
99                  */
100                 __this_cpu_write(context_tracking.state, state);
101         }
102         context_tracking_recursion_exit();
103 }
104 EXPORT_SYMBOL_GPL(__context_tracking_enter);
105
106 void context_tracking_enter(enum ctx_state state)
107 {
108         unsigned long flags;
109
110         /*
111          * Some contexts may involve an exception occuring in an irq,
112          * leading to that nesting:
113          * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
114          * This would mess up the dyntick_nesting count though. And rcu_irq_*()
115          * helpers are enough to protect RCU uses inside the exception. So
116          * just return immediately if we detect we are in an IRQ.
117          */
118         if (in_interrupt())
119                 return;
120
121         local_irq_save(flags);
122         __context_tracking_enter(state);
123         local_irq_restore(flags);
124 }
125 NOKPROBE_SYMBOL(context_tracking_enter);
126 EXPORT_SYMBOL_GPL(context_tracking_enter);
127
128 void context_tracking_user_enter(void)
129 {
130         user_enter();
131 }
132 NOKPROBE_SYMBOL(context_tracking_user_enter);
133
134 /**
135  * context_tracking_exit - Inform the context tracking that the CPU is
136  *                         exiting user or guest mode and entering the kernel.
137  *
138  * This function must be called after we entered the kernel from user or
139  * guest space before any use of RCU read side critical section. This
140  * potentially include any high level kernel code like syscalls, exceptions,
141  * signal handling, etc...
142  *
143  * This call supports re-entrancy. This way it can be called from any exception
144  * handler without needing to know if we came from userspace or not.
145  */
146 void noinstr __context_tracking_exit(enum ctx_state state)
147 {
148         if (!context_tracking_recursion_enter())
149                 return;
150
151         if (__this_cpu_read(context_tracking.state) == state) {
152                 if (__this_cpu_read(context_tracking.active)) {
153                         /*
154                          * We are going to run code that may use RCU. Inform
155                          * RCU core about that (ie: we may need the tick again).
156                          */
157                         rcu_user_exit();
158                         if (state == CONTEXT_USER) {
159                                 instrumentation_begin();
160                                 vtime_user_exit(current);
161                                 trace_user_exit(0);
162                                 instrumentation_end();
163                         }
164                 }
165                 __this_cpu_write(context_tracking.state, CONTEXT_KERNEL);
166         }
167         context_tracking_recursion_exit();
168 }
169 EXPORT_SYMBOL_GPL(__context_tracking_exit);
170
171 void context_tracking_exit(enum ctx_state state)
172 {
173         unsigned long flags;
174
175         if (in_interrupt())
176                 return;
177
178         local_irq_save(flags);
179         __context_tracking_exit(state);
180         local_irq_restore(flags);
181 }
182 NOKPROBE_SYMBOL(context_tracking_exit);
183 EXPORT_SYMBOL_GPL(context_tracking_exit);
184
185 void context_tracking_user_exit(void)
186 {
187         user_exit();
188 }
189 NOKPROBE_SYMBOL(context_tracking_user_exit);
190
191 void __init context_tracking_cpu_set(int cpu)
192 {
193         static __initdata bool initialized = false;
194
195         if (!per_cpu(context_tracking.active, cpu)) {
196                 per_cpu(context_tracking.active, cpu) = true;
197                 static_branch_inc(&context_tracking_key);
198         }
199
200         if (initialized)
201                 return;
202
203 #ifdef CONFIG_HAVE_TIF_NOHZ
204         /*
205          * Set TIF_NOHZ to init/0 and let it propagate to all tasks through fork
206          * This assumes that init is the only task at this early boot stage.
207          */
208         set_tsk_thread_flag(&init_task, TIF_NOHZ);
209 #endif
210         WARN_ON_ONCE(!tasklist_empty());
211
212         initialized = true;
213 }
214
215 #ifdef CONFIG_CONTEXT_TRACKING_FORCE
216 void __init context_tracking_init(void)
217 {
218         int cpu;
219
220         for_each_possible_cpu(cpu)
221                 context_tracking_cpu_set(cpu);
222 }
223 #endif