context_tracking: Generalize context tracking APIs to support user and guest

Generalize the context tracking APIs to support various nature of
contexts. This is performed by splitting out the mechanism from
context_tracking_user_enter and context_tracking_user_exit into
context_tracking_enter and context_tracking_exit.

The nature of the context we track is now detailed in a ctx_state
parameter pushed to these APIs, allowing the same functions to not just
track kernel <> user space switching, but also kernel <> guest transitions.

But leave the old functions in order to avoid breaking ARM, which calls
these functions from assembler code, and cannot easily use C enum
parameters.

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Will deacon <will.deacon@arm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

include/linux/context_tracking.h

@@ -10,6 +10,8 @@
 #ifdef CONFIG_CONTEXT_TRACKING
 extern void context_tracking_cpu_set(int cpu);
 
+extern void context_tracking_enter(enum ctx_state state);
+extern void context_tracking_exit(enum ctx_state state);
 extern void context_tracking_user_enter(void);
 extern void context_tracking_user_exit(void);
 extern void __context_tracking_task_switch(struct task_struct *prev,
@@ -35,7 +37,8 @@ static inline enum ctx_state exception_enter(void)
 		return 0;
 
 	prev_ctx = this_cpu_read(context_tracking.state);
-	context_tracking_user_exit();
+	if (prev_ctx != CONTEXT_KERNEL)
+		context_tracking_exit(prev_ctx);
 
 	return prev_ctx;
 }
@@ -43,8 +46,8 @@ static inline enum ctx_state exception_enter(void)
 static inline void exception_exit(enum ctx_state prev_ctx)
 {
 	if (context_tracking_is_enabled()) {
-		if (prev_ctx == CONTEXT_USER)
-			context_tracking_user_enter();
+		if (prev_ctx != CONTEXT_KERNEL)
+			context_tracking_enter(prev_ctx);
 	}
 }
 

kernel/context_tracking.c

@@ -39,15 +39,15 @@ void context_tracking_cpu_set(int cpu)
 }
 
 /**
- * context_tracking_user_enter - Inform the context tracking that the CPU is going to
- *                               enter userspace mode.
+ * context_tracking_enter - Inform the context tracking that the CPU is going
+ *                          enter user or guest space mode.
  *
  * This function must be called right before we switch from the kernel
- * to userspace, when it's guaranteed the remaining kernel instructions
- * to execute won't use any RCU read side critical section because this
- * function sets RCU in extended quiescent state.
+ * to user or guest space, when it's guaranteed the remaining kernel
+ * instructions to execute won't use any RCU read side critical section
+ * because this function sets RCU in extended quiescent state.
  */
-void context_tracking_user_enter(void)
+void context_tracking_enter(enum ctx_state state)
 {
 	unsigned long flags;
 
@@ -75,7 +75,7 @@ void context_tracking_user_enter(void)
 	WARN_ON_ONCE(!current->mm);
 
 	local_irq_save(flags);
-	if ( __this_cpu_read(context_tracking.state) != CONTEXT_USER) {
+	if ( __this_cpu_read(context_tracking.state) != state) {
 		if (__this_cpu_read(context_tracking.active)) {
 			trace_user_enter(0);
 			/*
@@ -101,24 +101,31 @@ void context_tracking_user_enter(void)
 		 * OTOH we can spare the calls to vtime and RCU when context_tracking.active
 		 * is false because we know that CPU is not tickless.
 		 */
-		__this_cpu_write(context_tracking.state, CONTEXT_USER);
+		__this_cpu_write(context_tracking.state, state);
 	}
 	local_irq_restore(flags);
 }
+NOKPROBE_SYMBOL(context_tracking_enter);
+
+void context_tracking_user_enter(void)
+{
+	context_tracking_enter(CONTEXT_USER);
+}
 NOKPROBE_SYMBOL(context_tracking_user_enter);
 
 /**
- * context_tracking_user_exit - Inform the context tracking that the CPU is
- *                              exiting userspace mode and entering the kernel.
+ * context_tracking_exit - Inform the context tracking that the CPU is
+ *                         exiting user or guest mode and entering the kernel.
  *
- * This function must be called after we entered the kernel from userspace
- * before any use of RCU read side critical section. This potentially include
- * any high level kernel code like syscalls, exceptions, signal handling, etc...
+ * This function must be called after we entered the kernel from user or
+ * guest space before any use of RCU read side critical section. This
+ * potentially include any high level kernel code like syscalls, exceptions,
+ * signal handling, etc...
  *
  * This call supports re-entrancy. This way it can be called from any exception
  * handler without needing to know if we came from userspace or not.
  */
-void context_tracking_user_exit(void)
+void context_tracking_exit(enum ctx_state state)
 {
 	unsigned long flags;
 
@@ -129,7 +136,7 @@ void context_tracking_user_exit(void)
 		return;
 
 	local_irq_save(flags);
-	if (__this_cpu_read(context_tracking.state) == CONTEXT_USER) {
+	if (__this_cpu_read(context_tracking.state) == state) {
 		if (__this_cpu_read(context_tracking.active)) {
 			/*
 			 * We are going to run code that may use RCU. Inform
@@ -143,6 +150,12 @@ void context_tracking_user_exit(void)
 	}
 	local_irq_restore(flags);
 }
+NOKPROBE_SYMBOL(context_tracking_exit);
+
+void context_tracking_user_exit(void)
+{
+	context_tracking_exit(CONTEXT_USER);
+}
 NOKPROBE_SYMBOL(context_tracking_user_exit);
 
 /**