KVM: x86: Directly block (instead of "halting") UNINITIALIZED vCPUs

Go directly to kvm_vcpu_block() when handling the case where userspace
attempts to run an UNINITIALIZED vCPU.  The vCPU is not halted, nor is it
likely that halt-polling will be successful in this case.
Reviewed-by: David Matlack <dmatlack@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211009021236.4122790-18-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -10203,7 +10203,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 			r = -EINTR;
 			goto out;
 		}
-		kvm_vcpu_halt(vcpu);
+		kvm_vcpu_block(vcpu);
 		if (kvm_apic_accept_events(vcpu) < 0) {
 			r = 0;
 			goto out;