[PATCH 1/5] context_tracking: generalize context tracking APIs to support user and guest

riel
2015-02-10T20:28:08Z

From: Rik van Riel <riel@redhat.com>

Split out the mechanism from context_tracking_user_enter and
context_tracking_user_exit into context_tracking_enter and
context_tracking_exit. Leave the old functions in order to avoid
breaking ARM, which calls these functions from assembler code,
and cannot easily use C enum parameters.

Add the expected ctx_state as a parameter to context_tracking_enter and
context_tracking_exit, allowing the same functions to not just track
kernel <> user space switching, but also kernel <> guest transitions.

Signed-off-by: Rik van Riel <riel@redhat.com>
---
include/linux/context_tracking.h | 8 +++++---
kernel/context_tracking.c | 43 ++++++++++++++++++++++++++--------------
2 files changed, 33 insertions(+), 18 deletions(-)

diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index 37b81bd51ec0..954253283709 100644
--- a/include/linux/context_tracking.h
+++ b/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 +37,7 @@ static inline enum ctx_state exception_enter(void)
return 0;

prev_ctx = this_cpu_read(context_tracking.state);
- context_tracking_user_exit();
+ context_tracking_exit(prev_ctx);

return prev_ctx;
}
@@ -43,8 +45,8 @@ 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 == IN_USER)
- context_tracking_user_enter();
+ if (prev_ctx != IN_KERNEL)
+ context_tracking_enter(prev_ctx);
}
}

diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 937ecdfdf258..38e38aeac8b9 100644
--- a/kernel/context_tracking.c
+++ b/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) != IN_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, IN_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(IN_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) == IN_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(IN_USER);
+}
NOKPROBE_SYMBOL(context_tracking_user_exit);

/**
--
1.9.3