KVM: x86: Refactor handling of SIPI_RECEIVED when setting MP_STATE

Convert the incoming mp_state to INIT_RECIEVED instead of manually calling
kvm_set_mp_state() to make it more obvious that the SIPI_RECEIVED logic is
translating the incoming state to KVM's internal tracking, as opposed to
being some entirely unique flow.

Opportunistically add a comment to explain what the code is doing.

No functional change intended.

Link: https://lore.kernel.org/r/20250605195018.539901-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

arch/x86/kvm/x86.c

@@ -11929,11 +11929,17 @@ int kvm_arch_vcpu_ioctl_set_mpstate(struct kvm_vcpu *vcpu,
 		goto out;
 	}
 
+	/*
+	 * SIPI_RECEIVED is obsolete and no longer used internally; KVM instead
+	 * leaves the vCPU in INIT_RECIEVED (Wait-For-SIPI) and pends the SIPI.
+	 * Translate SIPI_RECEIVED as appropriate for backwards compatibility.
+	 */
 	if (mp_state->mp_state == KVM_MP_STATE_SIPI_RECEIVED) {
-		kvm_set_mp_state(vcpu, KVM_MP_STATE_INIT_RECEIVED);
+		mp_state->mp_state = KVM_MP_STATE_INIT_RECEIVED;
 		set_bit(KVM_APIC_SIPI, &vcpu->arch.apic->pending_events);
-	} else
-		kvm_set_mp_state(vcpu, mp_state->mp_state);
+	}
+
+	kvm_set_mp_state(vcpu, mp_state->mp_state);
 	kvm_make_request(KVM_REQ_EVENT, vcpu);
 
 	ret = 0;