[PATCH] KVM: Clear pv eoi pending bit only when it is set

[Li RongQing <lirongqing@baidu.com>]

clear pv eoi pending bit only when it is set, to avoid calling
pv_eoi_put_user()

and this can speed pv_eoi_clr_pending about 300 nsec on AMD EPYC
most of the time

Signed-off-by: Li RongQing <lirongqing@baidu.com>
---
 arch/x86/kvm/lapic.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 76fb009..c434f70 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -694,9 +694,9 @@ static void pv_eoi_set_pending(struct kvm_vcpu *vcpu)
 	__set_bit(KVM_APIC_PV_EOI_PENDING, &vcpu->arch.apic_attention);
 }
 
-static void pv_eoi_clr_pending(struct kvm_vcpu *vcpu)
+static void pv_eoi_clr_pending(struct kvm_vcpu *vcpu, bool pending)
 {
-	if (pv_eoi_put_user(vcpu, KVM_PV_EOI_DISABLED) < 0) {
+	if (pending && pv_eoi_put_user(vcpu, KVM_PV_EOI_DISABLED) < 0) {
 		printk(KERN_WARNING "Can't clear EOI MSR value: 0x%llx\n",
 			   (unsigned long long)vcpu->arch.pv_eoi.msr_val);
 		return;
@@ -2693,7 +2693,8 @@ static void apic_sync_pv_eoi_from_guest(struct kvm_vcpu *vcpu,
 	 * While this might not be ideal from performance point of view,
 	 * this makes sure pv eoi is only enabled when we know it's safe.
 	 */
-	pv_eoi_clr_pending(vcpu);
+	pv_eoi_clr_pending(vcpu, pending);
+
 	if (pending)
 		return;
 	vector = apic_set_eoi(apic);
-- 
1.7.1