KVM: x86: Allow suppressing prints on RDMSR/WRMSR of unhandled MSRs

Some guests use these unhandled MSRs very frequently.
This cause dmesg to be populated with lots of aggregated messages on
usage of ignored MSRs. As ignore_msrs=true means that the user is
well-aware his guest use ignored MSRs, allow to also disable the
prints on their usage.

An example of such guest is ESXi which tends to access a lot to MSR
0x34 (MSR_SMI_COUNT) very frequently.

In addition, we have observed this to cause unnecessary delays to
guest execution. Such an example is ESXi which experience networking
delays in it's guests (L2 guests) because of these prints (even when
prints are rate-limited). This can easily be reproduced by pinging
from one L2 guest to another.  Once in a while, a peak in ping RTT
will be observed. Removing these unhandled MSR prints solves the
issue.

Because these prints can help diagnose issues with guests,
this commit only suppress them by a module parameter instead of
removing them from code entirely.

Signed-off-by: Eyal Moscovici <eyal.moscovici@oracle.com>
Reviewed-by: Liran Alon <liran.alon@oracle.com>
Reviewed-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
[Changed suppress_ignore_msrs_prints to report_ignored_msrs - Radim]
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

arch/x86/kvm/x86.c

@@ -107,6 +107,9 @@ EXPORT_SYMBOL_GPL(kvm_x86_ops);
 static bool __read_mostly ignore_msrs = 0;
 module_param(ignore_msrs, bool, S_IRUGO | S_IWUSR);
 
+static bool __read_mostly report_ignored_msrs = true;
+module_param(report_ignored_msrs, bool, S_IRUGO | S_IWUSR);
+
 unsigned int min_timer_period_us = 500;
 module_param(min_timer_period_us, uint, S_IRUGO | S_IWUSR);
 
@@ -2325,7 +2328,9 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		/* Drop writes to this legacy MSR -- see rdmsr
 		 * counterpart for further detail.
 		 */
-		vcpu_unimpl(vcpu, "ignored wrmsr: 0x%x data 0x%llx\n", msr, data);
+		if (report_ignored_msrs)
+			vcpu_unimpl(vcpu, "ignored wrmsr: 0x%x data 0x%llx\n",
+				msr, data);
 		break;
 	case MSR_AMD64_OSVW_ID_LENGTH:
 		if (!guest_cpuid_has(vcpu, X86_FEATURE_OSVW))
@@ -2362,8 +2367,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 				    msr, data);
 			return 1;
 		} else {
-			vcpu_unimpl(vcpu, "ignored wrmsr: 0x%x data 0x%llx\n",
-				    msr, data);
+			if (report_ignored_msrs)
+				vcpu_unimpl(vcpu,
+					"ignored wrmsr: 0x%x data 0x%llx\n",
+					msr, data);
 			break;
 		}
 	}
@@ -2581,7 +2588,9 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 					       msr_info->index);
 			return 1;
 		} else {
-			vcpu_unimpl(vcpu, "ignored rdmsr: 0x%x\n", msr_info->index);
+			if (report_ignored_msrs)
+				vcpu_unimpl(vcpu, "ignored rdmsr: 0x%x\n",
+					msr_info->index);
 			msr_info->data = 0;
 		}
 		break;