KVM: VMX: optimize APIC EOI

[Marcelo Tosatti <mtosatti@redhat.com>]

Use information provided in exit_qualification to shortcut EOI path.

Reduces EOI latency from 4k to 2k cycles on Nehalem.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Index: kvm/arch/x86/kvm/lapic.c
===================================================================
--- kvm.orig/arch/x86/kvm/lapic.c
+++ kvm/arch/x86/kvm/lapic.c
@@ -1279,3 +1279,9 @@ int kvm_hv_vapic_msr_read(struct kvm_vcp
 
 	return 0;
 }
+
+void kvm_lapic_set_eoi(struct kvm_vcpu *vcpu)
+{
+	apic_set_eoi(vcpu->arch.apic);
+}
+EXPORT_SYMBOL_GPL(kvm_lapic_set_eoi);
Index: kvm/arch/x86/kvm/lapic.h
===================================================================
--- kvm.orig/arch/x86/kvm/lapic.h
+++ kvm/arch/x86/kvm/lapic.h
@@ -52,6 +52,8 @@ int kvm_x2apic_msr_read(struct kvm_vcpu 
 int kvm_hv_vapic_msr_write(struct kvm_vcpu *vcpu, u32 msr, u64 data);
 int kvm_hv_vapic_msr_read(struct kvm_vcpu *vcpu, u32 msr, u64 *data);
 
+void kvm_lapic_set_eoi(struct kvm_vcpu *vcpu);
+
 static inline bool kvm_hv_vapic_assist_page_enabled(struct kvm_vcpu *vcpu)
 {
 	return vcpu->arch.hv_vapic & HV_X64_MSR_APIC_ASSIST_PAGE_ENABLE;
Index: kvm/arch/x86/kvm/vmx.c
===================================================================
--- kvm.orig/arch/x86/kvm/vmx.c
+++ kvm/arch/x86/kvm/vmx.c
@@ -3395,6 +3395,17 @@ static int handle_wbinvd(struct kvm_vcpu
 
 static int handle_apic_access(struct kvm_vcpu *vcpu)
 {
+	unsigned long exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
+	int access_type, offset;
+
+	access_type = (exit_qualification >> 12) & 0xf;
+	offset = exit_qualification & 0xfff;
+	if (access_type == 1 && offset == APIC_EOI) {
+		kvm_lapic_set_eoi(vcpu);
+		skip_emulated_instruction(vcpu);
+		return 1;
+	}
+
 	return emulate_instruction(vcpu, 0, 0, 0) == EMULATE_DONE;
 }