[RFC v2 PATCH 09/21] KVM: Go back to online CPU on VM exit by external interrupt

[Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>]

If the slave CPU receives an interrupt in running a guest, current
implementation must once go back to onilne CPUs to handle the interupt.

This behavior will be replaced by later patch, which introduces direct
interrupt handling mechanism by the guest.

Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
---

 arch/x86/include/asm/kvm_host.h |    1 +
 arch/x86/kvm/vmx.c              |    1 +
 arch/x86/kvm/x86.c              |    6 ++++++
 3 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 0ea04c9..af68ffb 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -358,6 +358,7 @@ struct kvm_vcpu_arch {
 	int sipi_vector;
 	u64 ia32_misc_enable_msr;
 	bool tpr_access_reporting;
+	bool interrupted;
 
 #ifdef CONFIG_SLAVE_CPU
 	/* slave cpu dedicated to this vcpu */
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 7bbfa01..d99bee6 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -4408,6 +4408,7 @@ static int handle_exception(struct kvm_vcpu *vcpu)
 
 static int handle_external_interrupt(struct kvm_vcpu *vcpu)
 {
+	vcpu->arch.interrupted = true;
 	++vcpu->stat.irq_exits;
 	return 1;
 }
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b62f59c..db0be81 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5566,6 +5566,12 @@ static void __vcpu_enter_guest_slave(void *_arg)
 			break;
 
 		/* determine if slave cpu can handle the exit alone */
+		if (vcpu->arch.interrupted) {
+			vcpu->arch.interrupted = false;
+			arg->ret = LOOP_ONLINE;
+			break;
+		}
+
 		r = vcpu_post_run(vcpu, arg->task, &arg->apf_pending);
 
 		if (r == LOOP_SLAVE &&