context_tracking: avoid irq_save/irq_restore on guest entry and exit

guest_enter and guest_exit must be called with interrupts disabled,
since they take the vtime_seqlock with write_seq{lock,unlock}.
Therefore, it is not necessary to check for exceptions, nor to
save/restore the IRQ state, when context tracking functions are
called by guest_enter and guest_exit.

Split the body of context_tracking_entry and context_tracking_exit
out to __-prefixed functions, and use them from KVM.

Rik van Riel has measured this to speed up a tight vmentry/vmexit
loop by about 2%.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Tested-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index 6ef136ff0897..68b575afe5f5 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -10,6 +10,10 @@
 #ifdef CONFIG_CONTEXT_TRACKING
 extern void context_tracking_cpu_set(int cpu);
 
+/* Called with interrupts disabled.  */
+extern void __context_tracking_enter(enum ctx_state state);
+extern void __context_tracking_exit(enum ctx_state state);
+
 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);
@@ -88,13 +92,13 @@ static inline void guest_enter(void)
 		current->flags |= PF_VCPU;
 
 	if (context_tracking_is_enabled())
-		context_tracking_enter(CONTEXT_GUEST);
+		__context_tracking_enter(CONTEXT_GUEST);
 }
 
 static inline void guest_exit(void)
 {
 	if (context_tracking_is_enabled())
-		context_tracking_exit(CONTEXT_GUEST);
+		__context_tracking_exit(CONTEXT_GUEST);
 
 	if (vtime_accounting_enabled())
 		vtime_guest_exit(current);