KVM: x86: handle MSR_IA32_DEBUGCTLMSR with report_ignored_msrs

Windows2016 guest tries to enable LBR by setting the corresponding bits
in MSR_IA32_DEBUGCTLMSR. KVM does not emulate MSR_IA32_DEBUGCTLMSR and
spams the host kernel logs with error messages like:

	kvm [...]: vcpu1, guest rIP: 0xfffff800a8b687d3 kvm_set_msr_common: MSR_IA32_DEBUGCTLMSR 0x1, nop"

This patch fixes this by enabling error logging only with
'report_ignored_msrs=1'.
Signed-off-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
Message-Id: <20201105153932.24316-1-pankaj.gupta.linux@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -3065,9 +3065,9 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 			/* Values other than LBR and BTF are vendor-specific,
 			   thus reserved and should throw a #GP */
 			return 1;
-		}
-		vcpu_unimpl(vcpu, "%s: MSR_IA32_DEBUGCTLMSR 0x%llx, nop\n",
-			    __func__, data);
+		} else if (report_ignored_msrs)
+			vcpu_unimpl(vcpu, "%s: MSR_IA32_DEBUGCTLMSR 0x%llx, nop\n",
+				    __func__, data);
 		break;
 	case 0x200 ... 0x2ff:
 		return kvm_mtrr_set_msr(vcpu, msr, data);