linux-kernel - [PATCH 7/7] kvm,rcu,nohz: use RCU extended quiescent state when running KVM guest

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Date:	Tue, 10 Mar 2015 15:37:18 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Alexander Graf <agraf@...e.de>,
	Luiz Capitulino <lcapitulino@...hat.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andy Lutomirski <luto@...capital.net>,
	Will deacon <will.deacon@....com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: [PATCH 7/7] kvm,rcu,nohz: use RCU extended quiescent state when running KVM guest

From: Rik van Riel <riel@...hat.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. Leave those calls
where they are, instead of moving them into the context tracking
code.

Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Signed-off-by: Rik van Riel <riel@...hat.com>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Will deacon <will.deacon@....com>
Cc: Marcelo Tosatti <mtosatti@...hat.com>
Cc: Christian Borntraeger <borntraeger@...ibm.com>
Cc: Luiz Capitulino <lcapitulino@...hat.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
---
 include/linux/context_tracking.h       | 6 ++++++
 include/linux/context_tracking_state.h | 1 +
 include/linux/kvm_host.h               | 3 ++-
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index 7f1810a..2821838 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -81,10 +81,16 @@ static inline void guest_enter(void)
 		vtime_guest_enter(current);
 	else
 		current->flags |= PF_VCPU;
+
+	if (context_tracking_is_enabled())
+		context_tracking_enter(CONTEXT_GUEST);
 }
 
 static inline void guest_exit(void)
 {
+	if (context_tracking_is_enabled())
+		context_tracking_exit(CONTEXT_GUEST);
+
 	if (vtime_accounting_enabled())
 		vtime_guest_exit(current);
 	else
diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
index ad44585..6b7b96a 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 {
 		CONTEXT_KERNEL = 0,
 		CONTEXT_USER,
+		CONTEXT_GUEST,
 	} state;
 };
 
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index d12b210..cc8c61c 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -766,7 +766,8 @@ 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)
-- 
2.1.4

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