KVM: VMX: Drop unnecessary PI logic to handle impossible conditions

Drop sanity checks on the validity of the previous pCPU when handling
vCPU block/unlock for posted interrupts.  The intention behind the sanity
checks is to avoid memory corruption in case of a race or incorrect locking,
but the code has been stable for a few years now and the checks get in
the way of eliminating kvm_vcpu.pre_cpu.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211009021236.4122790-23-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/posted_intr.c

@@ -123,12 +123,10 @@ static void __pi_post_block(struct kvm_vcpu *vcpu)
 	} while (cmpxchg64(&pi_desc->control, old.control,
 			   new.control) != old.control);
 
-	if (!WARN_ON_ONCE(vcpu->pre_pcpu == -1)) {
-		spin_lock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
-		list_del(&vcpu->blocked_vcpu_list);
-		spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
-		vcpu->pre_pcpu = -1;
-	}
+	spin_lock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
+	list_del(&vcpu->blocked_vcpu_list);
+	spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
+	vcpu->pre_pcpu = -1;
 }
 
 /*
@@ -156,14 +154,12 @@ int pi_pre_block(struct kvm_vcpu *vcpu)
 
 	WARN_ON(irqs_disabled());
 	local_irq_disable();
-	if (!WARN_ON_ONCE(vcpu->pre_pcpu != -1)) {
-		vcpu->pre_pcpu = vcpu->cpu;
-		spin_lock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
-		list_add_tail(&vcpu->blocked_vcpu_list,
-			      &per_cpu(blocked_vcpu_on_cpu,
-				       vcpu->pre_pcpu));
-		spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
-	}
+
+	vcpu->pre_pcpu = vcpu->cpu;
+	spin_lock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
+	list_add_tail(&vcpu->blocked_vcpu_list,
+		      &per_cpu(blocked_vcpu_on_cpu, vcpu->pre_pcpu));
+	spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
 
 	do {
 		old.control = new.control = pi_desc->control;