KVM: x86: Use static_call() for .vcpu_deliver_sipi_vector()

Define and use a static_call() for kvm_x86_ops.vcpu_deliver_sipi_vector(),
mostly so that the op is defined in kvm-x86-ops.h.  This will allow using
KVM_X86_OP in vendor code to wire up the implementation.  Any performance
gains eeked out by using static_call() is a happy bonus and not the
primary motiviation.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220128005208.4008533-6-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm-x86-ops.h

@@ -122,6 +122,7 @@ KVM_X86_OP_NULL(enable_direct_tlbflush)
 KVM_X86_OP_NULL(migrate_timers)
 KVM_X86_OP(msr_filter_changed)
 KVM_X86_OP_NULL(complete_emulated_msr)
+KVM_X86_OP(vcpu_deliver_sipi_vector)
 
 #undef KVM_X86_OP
 #undef KVM_X86_OP_NULL

arch/x86/kvm/lapic.c

@@ -2933,7 +2933,7 @@ int kvm_apic_accept_events(struct kvm_vcpu *vcpu)
 			/* evaluate pending_events before reading the vector */
 			smp_rmb();
 			sipi_vector = apic->sipi_vector;
-			kvm_x86_ops.vcpu_deliver_sipi_vector(vcpu, sipi_vector);
+			static_call(kvm_x86_vcpu_deliver_sipi_vector)(vcpu, sipi_vector);
 			vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
 		}
 	}