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>

diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index 427b056dfd3de5fc556a355042c16fa3914abb33..7f1810a3b5a4f1044f3742e97c76da1f325ea249 100644 (file)
--- 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 +37,8 @@ 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);
        }
 }
 

diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 8ad53c9d38b66ccfd9f0d993718537a544b581b3..17715d811b71c147b619d2de7d0ab3a3595a2712 100644 (file)
--- 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) != 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);
 
 /**