KVM: x86: Clear "has_error_code", not "error_code", for RM exception injection

When injecting an exception into a vCPU in Real Mode, suppress the error
code by clearing the flag that tracks whether the error code is valid, not
by clearing the error code itself.  The "typo" was introduced by recent
fix for SVM's funky Paged Real Mode.

Opportunistically hoist the logic above the tracepoint so that the trace
is coherent with respect to what is actually injected (this was also the
behavior prior to the buggy commit).

Fixes: b97f0745 ("KVM: x86: determine if an exception has an error code only when injecting it.")
Cc: stable@vger.kernel.org
Cc: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230322143300.2209476-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -9908,13 +9908,20 @@ int kvm_check_nested_events(struct kvm_vcpu *vcpu)
 
 static void kvm_inject_exception(struct kvm_vcpu *vcpu)
 {
+	/*
+	 * Suppress the error code if the vCPU is in Real Mode, as Real Mode
+	 * exceptions don't report error codes.  The presence of an error code
+	 * is carried with the exception and only stripped when the exception
+	 * is injected as intercepted #PF VM-Exits for AMD's Paged Real Mode do
+	 * report an error code despite the CPU being in Real Mode.
+	 */
+	vcpu->arch.exception.has_error_code &= is_protmode(vcpu);
+
 	trace_kvm_inj_exception(vcpu->arch.exception.vector,
 				vcpu->arch.exception.has_error_code,
 				vcpu->arch.exception.error_code,
 				vcpu->arch.exception.injected);
 
-	if (vcpu->arch.exception.error_code && !is_protmode(vcpu))
-		vcpu->arch.exception.error_code = false;
 	static_call(kvm_x86_inject_exception)(vcpu);
 }