Frederic Weisbecker | 4eacdf1 | 2013-01-16 17:16:37 +0100 | [diff] [blame] | 1 | /* |
| 2 | * Context tracking: Probe on high level context boundaries such as kernel |
| 3 | * and userspace. This includes syscalls and exceptions entry/exit. |
| 4 | * |
| 5 | * This is used by RCU to remove its dependency on the timer tick while a CPU |
| 6 | * runs in userspace. |
| 7 | * |
| 8 | * Started by Frederic Weisbecker: |
| 9 | * |
| 10 | * Copyright (C) 2012 Red Hat, Inc., Frederic Weisbecker <fweisbec@redhat.com> |
| 11 | * |
| 12 | * Many thanks to Gilad Ben-Yossef, Paul McKenney, Ingo Molnar, Andrew Morton, |
| 13 | * Steven Rostedt, Peter Zijlstra for suggestions and improvements. |
| 14 | * |
| 15 | */ |
| 16 | |
Frederic Weisbecker | 91d1aa43 | 2012-11-27 19:33:25 +0100 | [diff] [blame] | 17 | #include <linux/context_tracking.h> |
| 18 | #include <linux/rcupdate.h> |
| 19 | #include <linux/sched.h> |
Frederic Weisbecker | 91d1aa43 | 2012-11-27 19:33:25 +0100 | [diff] [blame] | 20 | #include <linux/hardirq.h> |
Frederic Weisbecker | 6a61671 | 2012-12-16 20:00:34 +0100 | [diff] [blame] | 21 | #include <linux/export.h> |
Masami Hiramatsu | 4cdf77a | 2014-06-14 06:47:12 +0000 | [diff] [blame] | 22 | #include <linux/kprobes.h> |
Frederic Weisbecker | 91d1aa43 | 2012-11-27 19:33:25 +0100 | [diff] [blame] | 23 | |
Frederic Weisbecker | 1b6a259 | 2013-07-11 20:27:43 +0200 | [diff] [blame] | 24 | #define CREATE_TRACE_POINTS |
| 25 | #include <trace/events/context_tracking.h> |
| 26 | |
Andy Lutomirski | ed11a7f | 2015-11-12 12:59:01 -0800 | [diff] [blame] | 27 | DEFINE_STATIC_KEY_FALSE(context_tracking_enabled); |
Frederic Weisbecker | 48d6a81 | 2013-07-10 02:44:35 +0200 | [diff] [blame] | 28 | EXPORT_SYMBOL_GPL(context_tracking_enabled); |
Frederic Weisbecker | 65f382f | 2013-07-11 19:12:32 +0200 | [diff] [blame] | 29 | |
| 30 | DEFINE_PER_CPU(struct context_tracking, context_tracking); |
Frederic Weisbecker | 48d6a81 | 2013-07-10 02:44:35 +0200 | [diff] [blame] | 31 | EXPORT_SYMBOL_GPL(context_tracking); |
Frederic Weisbecker | 91d1aa43 | 2012-11-27 19:33:25 +0100 | [diff] [blame] | 32 | |
Frederic Weisbecker | aed5ed4 | 2015-05-06 18:04:23 +0200 | [diff] [blame] | 33 | static bool context_tracking_recursion_enter(void) |
| 34 | { |
| 35 | int recursion; |
| 36 | |
| 37 | recursion = __this_cpu_inc_return(context_tracking.recursion); |
| 38 | if (recursion == 1) |
| 39 | return true; |
| 40 | |
| 41 | WARN_ONCE((recursion < 1), "Invalid context tracking recursion value %d\n", recursion); |
| 42 | __this_cpu_dec(context_tracking.recursion); |
| 43 | |
| 44 | return false; |
| 45 | } |
| 46 | |
| 47 | static void context_tracking_recursion_exit(void) |
| 48 | { |
| 49 | __this_cpu_dec(context_tracking.recursion); |
| 50 | } |
| 51 | |
Frederic Weisbecker | 4eacdf1 | 2013-01-16 17:16:37 +0100 | [diff] [blame] | 52 | /** |
Rik van Riel | 3aab4f5 | 2015-02-10 15:27:50 -0500 | [diff] [blame] | 53 | * context_tracking_enter - Inform the context tracking that the CPU is going |
| 54 | * enter user or guest space mode. |
Frederic Weisbecker | 4eacdf1 | 2013-01-16 17:16:37 +0100 | [diff] [blame] | 55 | * |
| 56 | * This function must be called right before we switch from the kernel |
Rik van Riel | 3aab4f5 | 2015-02-10 15:27:50 -0500 | [diff] [blame] | 57 | * to user or guest space, when it's guaranteed the remaining kernel |
| 58 | * instructions to execute won't use any RCU read side critical section |
| 59 | * because this function sets RCU in extended quiescent state. |
Frederic Weisbecker | 4eacdf1 | 2013-01-16 17:16:37 +0100 | [diff] [blame] | 60 | */ |
Paolo Bonzini | d0e536d | 2015-10-28 02:39:56 +0100 | [diff] [blame] | 61 | void __context_tracking_enter(enum ctx_state state) |
Frederic Weisbecker | 91d1aa43 | 2012-11-27 19:33:25 +0100 | [diff] [blame] | 62 | { |
Frederic Weisbecker | 4eacdf1 | 2013-01-16 17:16:37 +0100 | [diff] [blame] | 63 | /* Kernel threads aren't supposed to go to userspace */ |
Frederic Weisbecker | 91d1aa43 | 2012-11-27 19:33:25 +0100 | [diff] [blame] | 64 | WARN_ON_ONCE(!current->mm); |
| 65 | |
Frederic Weisbecker | aed5ed4 | 2015-05-06 18:04:23 +0200 | [diff] [blame] | 66 | if (!context_tracking_recursion_enter()) |
Paolo Bonzini | d0e536d | 2015-10-28 02:39:56 +0100 | [diff] [blame] | 67 | return; |
Frederic Weisbecker | aed5ed4 | 2015-05-06 18:04:23 +0200 | [diff] [blame] | 68 | |
Rik van Riel | 3aab4f5 | 2015-02-10 15:27:50 -0500 | [diff] [blame] | 69 | if ( __this_cpu_read(context_tracking.state) != state) { |
Frederic Weisbecker | d65ec12 | 2013-07-11 23:59:33 +0200 | [diff] [blame] | 70 | if (__this_cpu_read(context_tracking.active)) { |
| 71 | /* |
| 72 | * At this stage, only low level arch entry code remains and |
| 73 | * then we'll run in userspace. We can assume there won't be |
| 74 | * any RCU read-side critical section until the next call to |
| 75 | * user_exit() or rcu_irq_enter(). Let's remove RCU's dependency |
| 76 | * on the tick. |
| 77 | */ |
Rik van Riel | 19fdd98 | 2015-02-10 15:27:52 -0500 | [diff] [blame] | 78 | if (state == CONTEXT_USER) { |
| 79 | trace_user_enter(0); |
| 80 | vtime_user_enter(current); |
| 81 | } |
Frederic Weisbecker | d65ec12 | 2013-07-11 23:59:33 +0200 | [diff] [blame] | 82 | rcu_user_enter(); |
| 83 | } |
Frederic Weisbecker | 4eacdf1 | 2013-01-16 17:16:37 +0100 | [diff] [blame] | 84 | /* |
Frederic Weisbecker | d65ec12 | 2013-07-11 23:59:33 +0200 | [diff] [blame] | 85 | * Even if context tracking is disabled on this CPU, because it's outside |
| 86 | * the full dynticks mask for example, we still have to keep track of the |
| 87 | * context transitions and states to prevent inconsistency on those of |
| 88 | * other CPUs. |
| 89 | * If a task triggers an exception in userspace, sleep on the exception |
| 90 | * handler and then migrate to another CPU, that new CPU must know where |
| 91 | * the exception returns by the time we call exception_exit(). |
| 92 | * This information can only be provided by the previous CPU when it called |
| 93 | * exception_enter(). |
| 94 | * OTOH we can spare the calls to vtime and RCU when context_tracking.active |
| 95 | * is false because we know that CPU is not tickless. |
Frederic Weisbecker | 4eacdf1 | 2013-01-16 17:16:37 +0100 | [diff] [blame] | 96 | */ |
Rik van Riel | 3aab4f5 | 2015-02-10 15:27:50 -0500 | [diff] [blame] | 97 | __this_cpu_write(context_tracking.state, state); |
Frederic Weisbecker | 91d1aa43 | 2012-11-27 19:33:25 +0100 | [diff] [blame] | 98 | } |
Frederic Weisbecker | aed5ed4 | 2015-05-06 18:04:23 +0200 | [diff] [blame] | 99 | context_tracking_recursion_exit(); |
Paolo Bonzini | d0e536d | 2015-10-28 02:39:56 +0100 | [diff] [blame] | 100 | } |
| 101 | NOKPROBE_SYMBOL(__context_tracking_enter); |
| 102 | EXPORT_SYMBOL_GPL(__context_tracking_enter); |
| 103 | |
| 104 | void context_tracking_enter(enum ctx_state state) |
| 105 | { |
| 106 | unsigned long flags; |
| 107 | |
| 108 | /* |
| 109 | * Some contexts may involve an exception occuring in an irq, |
| 110 | * leading to that nesting: |
| 111 | * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit() |
| 112 | * This would mess up the dyntick_nesting count though. And rcu_irq_*() |
| 113 | * helpers are enough to protect RCU uses inside the exception. So |
| 114 | * just return immediately if we detect we are in an IRQ. |
| 115 | */ |
| 116 | if (in_interrupt()) |
| 117 | return; |
| 118 | |
| 119 | local_irq_save(flags); |
| 120 | __context_tracking_enter(state); |
Frederic Weisbecker | 91d1aa43 | 2012-11-27 19:33:25 +0100 | [diff] [blame] | 121 | local_irq_restore(flags); |
| 122 | } |
Rik van Riel | 3aab4f5 | 2015-02-10 15:27:50 -0500 | [diff] [blame] | 123 | NOKPROBE_SYMBOL(context_tracking_enter); |
Rik van Riel | efc1e2c | 2015-02-10 15:27:53 -0500 | [diff] [blame] | 124 | EXPORT_SYMBOL_GPL(context_tracking_enter); |
Rik van Riel | 3aab4f5 | 2015-02-10 15:27:50 -0500 | [diff] [blame] | 125 | |
| 126 | void context_tracking_user_enter(void) |
| 127 | { |
Paolo Bonzini | f70cd6b | 2015-10-28 02:39:55 +0100 | [diff] [blame] | 128 | user_enter(); |
Rik van Riel | 3aab4f5 | 2015-02-10 15:27:50 -0500 | [diff] [blame] | 129 | } |
Masami Hiramatsu | 4cdf77a | 2014-06-14 06:47:12 +0000 | [diff] [blame] | 130 | NOKPROBE_SYMBOL(context_tracking_user_enter); |
Frederic Weisbecker | 91d1aa43 | 2012-11-27 19:33:25 +0100 | [diff] [blame] | 131 | |
Frederic Weisbecker | 4eacdf1 | 2013-01-16 17:16:37 +0100 | [diff] [blame] | 132 | /** |
Rik van Riel | 3aab4f5 | 2015-02-10 15:27:50 -0500 | [diff] [blame] | 133 | * context_tracking_exit - Inform the context tracking that the CPU is |
| 134 | * exiting user or guest mode and entering the kernel. |
Frederic Weisbecker | 4eacdf1 | 2013-01-16 17:16:37 +0100 | [diff] [blame] | 135 | * |
Rik van Riel | 3aab4f5 | 2015-02-10 15:27:50 -0500 | [diff] [blame] | 136 | * This function must be called after we entered the kernel from user or |
| 137 | * guest space before any use of RCU read side critical section. This |
| 138 | * potentially include any high level kernel code like syscalls, exceptions, |
| 139 | * signal handling, etc... |
Frederic Weisbecker | 4eacdf1 | 2013-01-16 17:16:37 +0100 | [diff] [blame] | 140 | * |
| 141 | * This call supports re-entrancy. This way it can be called from any exception |
| 142 | * handler without needing to know if we came from userspace or not. |
| 143 | */ |
Paolo Bonzini | d0e536d | 2015-10-28 02:39:56 +0100 | [diff] [blame] | 144 | void __context_tracking_exit(enum ctx_state state) |
Frederic Weisbecker | 91d1aa43 | 2012-11-27 19:33:25 +0100 | [diff] [blame] | 145 | { |
Frederic Weisbecker | aed5ed4 | 2015-05-06 18:04:23 +0200 | [diff] [blame] | 146 | if (!context_tracking_recursion_enter()) |
Paolo Bonzini | d0e536d | 2015-10-28 02:39:56 +0100 | [diff] [blame] | 147 | return; |
Frederic Weisbecker | aed5ed4 | 2015-05-06 18:04:23 +0200 | [diff] [blame] | 148 | |
Rik van Riel | 3aab4f5 | 2015-02-10 15:27:50 -0500 | [diff] [blame] | 149 | if (__this_cpu_read(context_tracking.state) == state) { |
Frederic Weisbecker | d65ec12 | 2013-07-11 23:59:33 +0200 | [diff] [blame] | 150 | if (__this_cpu_read(context_tracking.active)) { |
| 151 | /* |
| 152 | * We are going to run code that may use RCU. Inform |
| 153 | * RCU core about that (ie: we may need the tick again). |
| 154 | */ |
| 155 | rcu_user_exit(); |
Rik van Riel | 19fdd98 | 2015-02-10 15:27:52 -0500 | [diff] [blame] | 156 | if (state == CONTEXT_USER) { |
| 157 | vtime_user_exit(current); |
| 158 | trace_user_exit(0); |
| 159 | } |
Frederic Weisbecker | d65ec12 | 2013-07-11 23:59:33 +0200 | [diff] [blame] | 160 | } |
Frederic Weisbecker | c467ea7 | 2015-03-04 18:06:33 +0100 | [diff] [blame] | 161 | __this_cpu_write(context_tracking.state, CONTEXT_KERNEL); |
Frederic Weisbecker | 91d1aa43 | 2012-11-27 19:33:25 +0100 | [diff] [blame] | 162 | } |
Frederic Weisbecker | aed5ed4 | 2015-05-06 18:04:23 +0200 | [diff] [blame] | 163 | context_tracking_recursion_exit(); |
Paolo Bonzini | d0e536d | 2015-10-28 02:39:56 +0100 | [diff] [blame] | 164 | } |
| 165 | NOKPROBE_SYMBOL(__context_tracking_exit); |
| 166 | EXPORT_SYMBOL_GPL(__context_tracking_exit); |
| 167 | |
| 168 | void context_tracking_exit(enum ctx_state state) |
| 169 | { |
| 170 | unsigned long flags; |
| 171 | |
| 172 | if (in_interrupt()) |
| 173 | return; |
| 174 | |
| 175 | local_irq_save(flags); |
| 176 | __context_tracking_exit(state); |
Frederic Weisbecker | 91d1aa43 | 2012-11-27 19:33:25 +0100 | [diff] [blame] | 177 | local_irq_restore(flags); |
| 178 | } |
Rik van Riel | 3aab4f5 | 2015-02-10 15:27:50 -0500 | [diff] [blame] | 179 | NOKPROBE_SYMBOL(context_tracking_exit); |
Rik van Riel | efc1e2c | 2015-02-10 15:27:53 -0500 | [diff] [blame] | 180 | EXPORT_SYMBOL_GPL(context_tracking_exit); |
Rik van Riel | 3aab4f5 | 2015-02-10 15:27:50 -0500 | [diff] [blame] | 181 | |
| 182 | void context_tracking_user_exit(void) |
| 183 | { |
Paolo Bonzini | f70cd6b | 2015-10-28 02:39:55 +0100 | [diff] [blame] | 184 | user_exit(); |
Rik van Riel | 3aab4f5 | 2015-02-10 15:27:50 -0500 | [diff] [blame] | 185 | } |
Masami Hiramatsu | 4cdf77a | 2014-06-14 06:47:12 +0000 | [diff] [blame] | 186 | NOKPROBE_SYMBOL(context_tracking_user_exit); |
Frederic Weisbecker | 91d1aa43 | 2012-11-27 19:33:25 +0100 | [diff] [blame] | 187 | |
Frederic Weisbecker | fafe870 | 2015-05-06 18:04:24 +0200 | [diff] [blame] | 188 | void __init context_tracking_cpu_set(int cpu) |
Frederic Weisbecker | 91d1aa43 | 2012-11-27 19:33:25 +0100 | [diff] [blame] | 189 | { |
Frederic Weisbecker | fafe870 | 2015-05-06 18:04:24 +0200 | [diff] [blame] | 190 | static __initdata bool initialized = false; |
| 191 | |
| 192 | if (!per_cpu(context_tracking.active, cpu)) { |
| 193 | per_cpu(context_tracking.active, cpu) = true; |
Andy Lutomirski | ed11a7f | 2015-11-12 12:59:01 -0800 | [diff] [blame] | 194 | static_branch_inc(&context_tracking_enabled); |
Frederic Weisbecker | fafe870 | 2015-05-06 18:04:24 +0200 | [diff] [blame] | 195 | } |
| 196 | |
| 197 | if (initialized) |
| 198 | return; |
| 199 | |
| 200 | /* |
| 201 | * Set TIF_NOHZ to init/0 and let it propagate to all tasks through fork |
| 202 | * This assumes that init is the only task at this early boot stage. |
| 203 | */ |
| 204 | set_tsk_thread_flag(&init_task, TIF_NOHZ); |
| 205 | WARN_ON_ONCE(!tasklist_empty()); |
| 206 | |
| 207 | initialized = true; |
Frederic Weisbecker | 91d1aa43 | 2012-11-27 19:33:25 +0100 | [diff] [blame] | 208 | } |
Frederic Weisbecker | 65f382f | 2013-07-11 19:12:32 +0200 | [diff] [blame] | 209 | |
| 210 | #ifdef CONFIG_CONTEXT_TRACKING_FORCE |
| 211 | void __init context_tracking_init(void) |
| 212 | { |
| 213 | int cpu; |
| 214 | |
| 215 | for_each_possible_cpu(cpu) |
| 216 | context_tracking_cpu_set(cpu); |
| 217 | } |
| 218 | #endif |