KVM: x86: WARN and reject KVM_RUN if vCPU's MP_STATE is SIPI_RECEIVED

WARN if KVM_RUN is reached with a vCPU's mp_state set to SIPI_RECEIVED, as
KVM no longer uses SIPI_RECEIVED internally, and should morph SIPI_RECEIVED
into INIT_RECEIVED with a pending SIPI if userspace forces SIPI_RECEIVED.

See commit 66450a2 ("KVM: x86: Rework INIT and SIPI handling") for
more history and details.

Link: https://lore.kernel.org/r/20250605195018.539901-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

arch/x86/kvm/x86.c

@@ -11568,6 +11568,20 @@ static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
 	trace_kvm_fpu(0);
 }
 
+static int kvm_x86_vcpu_pre_run(struct kvm_vcpu *vcpu)
+{
+	/*
+	 * SIPI_RECEIVED is obsolete; KVM leaves the vCPU in Wait-For-SIPI and
+	 * tracks the pending SIPI separately.  SIPI_RECEIVED is still accepted
+	 * by KVM_SET_VCPU_EVENTS for backwards compatibility, but should be
+	 * converted to INIT_RECEIVED.
+	 */
+	if (WARN_ON_ONCE(vcpu->arch.mp_state == KVM_MP_STATE_SIPI_RECEIVED))
+		return -EINVAL;
+
+	return kvm_x86_call(vcpu_pre_run)(vcpu);
+}
+
 int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 {
 	struct kvm_queued_exception *ex = &vcpu->arch.exception;
@@ -11670,7 +11684,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 		goto out;
 	}
 
-	r = kvm_x86_call(vcpu_pre_run)(vcpu);
+	r = kvm_x86_vcpu_pre_run(vcpu);
 	if (r <= 0)
 		goto out;