context_tracing: Fix guest accounting with native vtime

1) If context tracking is enabled with native vtime accounting (which
combo is useless except for dev testing), we call vtime_guest_enter()
and vtime_guest_exit() on host <-> guest switches. But those are stubs
in this configurations. As a result, cputime is not correctly flushed
on kvm context switches.

2) If context tracking runs but is disabled on some CPUs, those
CPUs end up calling __guest_enter/__guest_exit which in turn
call vtime_account_system(). We don't want to call this because we
run in tick based accounting for these CPUs.

Refactor the guest_enter/guest_exit code such that all combinations
finally work.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Kevin Hilman <khilman@linaro.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 942835c12ae5..1f47119c5b09 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -141,12 +141,13 @@ void user_exit(void)
 	local_irq_restore(flags);
 }
 
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
 void guest_enter(void)
 {
 	if (vtime_accounting_enabled())
 		vtime_guest_enter(current);
 	else
-		__guest_enter();
+		current->flags |= PF_VCPU;
 }
 EXPORT_SYMBOL_GPL(guest_enter);
 
@@ -155,9 +156,10 @@ void guest_exit(void)
 	if (vtime_accounting_enabled())
 		vtime_guest_exit(current);
 	else
-		__guest_exit();
+		current->flags &= ~PF_VCPU;
 }
 EXPORT_SYMBOL_GPL(guest_exit);
+#endif /* CONFIG_VIRT_CPU_ACCOUNTING_GEN */
 
 
 /**