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[RFC PATCH 2/2] KVM: x86: use __kvm_guest_exit

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This gains ~20 clock cycles per vmexit.  On Intel there is no need
anymore to enable the interrupts in vmx_handle_external_intr, since we
are using the "acknowledge interrupt on exit" feature.  AMD needs to do
that temporarily, and must be careful to avoid the interrupt shadow.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/svm.c |  6 ++++++
 arch/x86/kvm/vmx.c |  4 +---
 arch/x86/kvm/x86.c | 11 ++---------
 3 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 5ff292778110..5bfdbbf1ce79 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -4935,6 +4935,12 @@ out:
 static void svm_handle_external_intr(struct kvm_vcpu *vcpu)
 {
 	local_irq_enable();
+	/*
+	 * We must execute an instruction with interrupts enabled, so
+	 * the "cli" doesn't fall right on the interrupt shadow.
+	 */
+	asm("nop");
+	local_irq_disable();
 }
 
 static void svm_sched_in(struct kvm_vcpu *vcpu, int cpu)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 4e9657730bf6..a46bce9e3683 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -8544,7 +8544,6 @@ static void vmx_handle_external_intr(struct kvm_vcpu *vcpu)
 			"push %[sp]\n\t"
 #endif
 			"pushf\n\t"
-			"orl $0x200, (%%" _ASM_SP ")\n\t"
 			__ASM_SIZE(push) " $%c[cs]\n\t"
 			"call *%[entry]\n\t"
 			:
@@ -8557,8 +8556,7 @@ static void vmx_handle_external_intr(struct kvm_vcpu *vcpu)
 			[ss]"i"(__KERNEL_DS),
 			[cs]"i"(__KERNEL_CS)
 			);
-	} else
-		local_irq_enable();
+	}
 }
 
 static bool vmx_has_high_real_mode_segbase(void)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7e3041ef050f..cc741b68139c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6706,21 +6706,13 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 
 	kvm_put_guest_xcr0(vcpu);
 
-	/* Interrupt is enabled by handle_external_intr() */
 	kvm_x86_ops->handle_external_intr(vcpu);
 
 	++vcpu->stat.exits;
 
-	/*
-	 * We must have an instruction between local_irq_enable() and
-	 * kvm_guest_exit(), so the timer interrupt isn't delayed by
-	 * the interrupt shadow.  The stat.exits increment will do nicely.
-	 * But we need to prevent reordering, hence this barrier():
-	 */
-	barrier();
-
-	kvm_guest_exit();
+	__kvm_guest_exit();
 
+	local_irq_enable();
 	preempt_enable();
 
 	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
-- 
1.8.3.1

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[RFC PATCH 0/2] KVM: x86: guest exit microoptimization Paolo Bonzini <pbonzini@redhat.com> - 2016-06-16 10:30 +0200
  [RFC PATCH 2/2] KVM: x86: use __kvm_guest_exit Paolo Bonzini <pbonzini@redhat.com> - 2016-06-16 10:30 +0200
    Re: [RFC PATCH 2/2] KVM: x86: use __kvm_guest_exit David Matlack <dmatlack@google.com> - 2016-06-16 18:50 +0200
      Re: [RFC PATCH 2/2] KVM: x86: use __kvm_guest_exit Paolo Bonzini <pbonzini@redhat.com> - 2016-06-16 18:50 +0200
        Re: [RFC PATCH 2/2] KVM: x86: use __kvm_guest_exit David Matlack <dmatlack@google.com> - 2016-06-16 19:10 +0200
          Re: [RFC PATCH 2/2] KVM: x86: use __kvm_guest_exit Paolo Bonzini <pbonzini@redhat.com> - 2016-06-16 19:30 +0200
    Re: [RFC PATCH 2/2] KVM: x86: use __kvm_guest_exit Bandan Das <bsd@redhat.com> - 2016-06-17 00:10 +0200
      Re: [RFC PATCH 2/2] KVM: x86: use __kvm_guest_exit Paolo Bonzini <pbonzini@redhat.com> - 2016-06-17 07:30 +0200

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