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Commit 3aab4f50 authored by Rik van Riel's avatar Rik van Riel Committed by Frederic Weisbecker
Browse files

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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: default avatarRik 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: default avatarFrederic Weisbecker <fweisbec@gmail.com>
parent c467ea76

include/linux/context_tracking.h

+6 −3
Original line number Diff line number Diff line
@@ -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

+28 −15
Original line number Diff line number Diff line
@@ -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);



/**