[PATCH 5/6] kvm,rcu,nohz: use RCU extended quiescent state when running KVM guest

[riel@redhat.com]

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

The host kernel is not doing anything while the CPU is executing
a KVM guest VCPU, so it can be marked as being in an extended
quiescent state, identical to that used when running user space
code.

The only exception to that rule is when the host handles an
interrupt, which is already handled by the irq code, which
calls rcu_irq_enter and rcu_irq_exit.

The guest_enter and guest_exit functions already switch vtime
accounting independent of context tracking, so leave those calls
where they are, instead of moving them into the context tracking
code.

Signed-off-by: Rik van Riel <riel@redhat.com>
---
 include/linux/context_tracking.h       | 8 +++++++-
 include/linux/context_tracking_state.h | 1 +
 include/linux/kvm_host.h               | 3 ++-
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index 29d7fecb365a..c70d7e760061 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -43,7 +43,7 @@ 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)
+		if (prev_ctx != IN_KERNEL)
 			context_tracking_enter(prev_ctx);
 	}
 }
@@ -74,6 +74,9 @@ static inline void context_tracking_init(void) { }
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
 static inline void guest_enter(void)
 {
+	if (context_tracking_is_enabled())
+		context_tracking_enter(IN_GUEST);
+
 	if (vtime_accounting_enabled())
 		vtime_guest_enter(current);
 	else
@@ -86,6 +89,9 @@ static inline void guest_exit(void)
 		vtime_guest_exit(current);
 	else
 		current->flags &= ~PF_VCPU;
+
+	if (context_tracking_is_enabled())
+		context_tracking_exit(IN_GUEST);
 }
 
 #else
diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
index 97a81225d037..f3ef027af749 100644
--- a/include/linux/context_tracking_state.h
+++ b/include/linux/context_tracking_state.h
@@ -15,6 +15,7 @@ struct context_tracking {
 	enum ctx_state {
 		IN_KERNEL = 0,
 		IN_USER,
+		IN_GUEST,
 	} state;
 };
 
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 26f106022c88..c7828a6a9614 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -772,7 +772,8 @@ static inline void kvm_guest_enter(void)
 	 * one time slice). Lets treat guest mode as quiescent state, just like
 	 * we do with user-mode execution.
 	 */
-	rcu_virt_note_context_switch(smp_processor_id());
+	if (!context_tracking_cpu_is_enabled())
+		rcu_virt_note_context_switch(smp_processor_id());
 }
 
 static inline void kvm_guest_exit(void)
-- 
1.9.3