KVM: LAPIC: Narrow down the kick target vCPU

The kick after setting KVM_REQ_PENDING_TIMER is used to handle the timer
fires on a different pCPU which vCPU is running on.  This kick costs about
1000 clock cycles and we don't need this when injecting already-expired
timer or when using the VMX preemption timer because
kvm_lapic_expired_hv_timer() is called from the target vCPU.
Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Message-Id: <1599731444-3525-6-git-send-email-wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/lapic.c

@@ -1642,7 +1642,9 @@ static void apic_timer_expired(struct kvm_lapic *apic, bool from_timer_fn)
 	}
 
 	atomic_inc(&apic->lapic_timer.pending);
-	kvm_set_pending_timer(vcpu);
+	kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu);
+	if (from_timer_fn)
+		kvm_vcpu_kick(vcpu);
 }
 
 static void start_sw_tscdeadline(struct kvm_lapic *apic)

arch/x86/kvm/x86.c

@@ -1774,12 +1774,6 @@ static s64 get_kvmclock_base_ns(void)
 }
 #endif
 
-void kvm_set_pending_timer(struct kvm_vcpu *vcpu)
-{
-	kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu);
-	kvm_vcpu_kick(vcpu);
-}
-
 static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
 {
 	int version;

arch/x86/kvm/x86.h

@@ -246,7 +246,6 @@ static inline bool kvm_vcpu_latch_init(struct kvm_vcpu *vcpu)
 	return is_smm(vcpu) || kvm_x86_ops.apic_init_signal_blocked(vcpu);
 }
 
-void kvm_set_pending_timer(struct kvm_vcpu *vcpu);
 void kvm_inject_realmode_interrupt(struct kvm_vcpu *vcpu, int irq, int inc_eip);
 
 void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr);