On 08/11/2017 13:32, Eyal Moscovici wrote:
> 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.
For this particular MSR, it can be a good idea to implement it actually. :)
Paolo
> 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@xxxxxxxxxx>
> Reviewed-by: Liran Alon <liran.alon@xxxxxxxxxx>
> Reviewed-by: Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx>
> Signed-off-by: Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 17 +++++++++++++----
> 1 file changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 03869eb..21c0059 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -107,6 +107,9 @@
> static bool __read_mostly ignore_msrs = 0;
> module_param(ignore_msrs, bool, S_IRUGO | S_IWUSR);
>
> +static bool __read_mostly suppress_ignore_msrs_prints = false;
> +module_param(suppress_ignore_msrs_prints, bool, S_IRUGO | S_IWUSR);
> +
> unsigned int min_timer_period_us = 500;
> module_param(min_timer_period_us, uint, S_IRUGO | S_IWUSR);
>
> @@ -2317,7 +2320,9 @@ 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 (!suppress_ignore_msrs_prints)
> + 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))
> @@ -2354,8 +2359,10 @@ 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 (!suppress_ignore_msrs_prints)
> + vcpu_unimpl(vcpu,
> + "ignored wrmsr: 0x%x data 0x%llx\n",
> + msr, data);
> break;
> }
> }
> @@ -2573,7 +2580,9 @@ 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 (!suppress_ignore_msrs_prints)
> + vcpu_unimpl(vcpu, "ignored rdmsr: 0x%x\n",
> + msr_info->index);
> msr_info->data = 0;
> }
> break;
>
