KVM: x86: report negative values from wrmsr emulation to userspace

This will allow the KVM to report such errors (e.g -ENOMEM)
to the userspace.
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20201001112954.6258-3-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/emulate.c

@@ -3712,10 +3712,10 @@ static int em_wrmsr(struct x86_emulate_ctxt *ctxt)
 	if (r == X86EMUL_IO_NEEDED)
 		return r;
 
-	if (r)
+	if (r > 0)
 		return emulate_gp(ctxt, 0);
 
-	return X86EMUL_CONTINUE;
+	return r < 0 ? X86EMUL_UNHANDLEABLE : X86EMUL_CONTINUE;
 }
 
 static int em_rdmsr(struct x86_emulate_ctxt *ctxt)

arch/x86/kvm/x86.c

@@ -1737,13 +1737,16 @@ int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu)
 	r = kvm_set_msr(vcpu, ecx, data);
 
 	/* MSR write failed? See if we should ask user space */
-	if (r && kvm_set_msr_user_space(vcpu, ecx, data, r)) {
+	if (r && kvm_set_msr_user_space(vcpu, ecx, data, r))
 		/* Bounce to user space */
 		return 0;
-	}
+
+	/* Signal all other negative errors to userspace */
+	if (r < 0)
+		return r;
 
 	/* MSR write failed? Inject a #GP */
-	if (r) {
+	if (r > 0) {
 		trace_kvm_msr_write_ex(ecx, data);
 		kvm_inject_gp(vcpu, 0);
 		return 1;