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>

1 files changed, 28 insertions, 15 deletions

diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 8ad53c9d38b6..17715d811b71 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) != 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);
 
 /**