Re: [PATCH] KVM: x86/pmu: Update AMD PMC smaple period to fix guest NMI-watchdog

["wangyanan (Y)" <wangyanan55@huawei.com>]

helped to Cc stable@ list...

On 2022/3/29 21:46, Like Xu wrote:
> From: Like Xu <likexu@tencent.com>
>
> NMI-watchdog is one of the favorite features of kernel developers,
> but it does not work in AMD guest even with vPMU enabled and worse,
> the system misrepresents this capability via /proc.
>
> This is a PMC emulation error. KVM does not pass the latest valid
> value to perf_event in time when guest NMI-watchdog is running, thus
> the perf_event corresponding to the watchdog counter will enter the
> old state at some point after the first guest NMI injection, forcing
> the hardware register PMC0 to be constantly written to 0x800000000001.
>
> Meanwhile, the running counter should accurately reflect its new value
> based on the latest coordinated pmc->counter (from vPMC's point of view)
> rather than the value written directly by the guest.
>
> Fixes: 168d918f2643 ("KVM: x86: Adjust counter sample period after a wrmsr")
> Reported-by: Dongli Cao <caodongli@kingsoft.com>
> Signed-off-by: Like Xu <likexu@tencent.com>
> ---
>   arch/x86/kvm/pmu.h           | 9 +++++++++
>   arch/x86/kvm/svm/pmu.c       | 1 +
>   arch/x86/kvm/vmx/pmu_intel.c | 8 ++------
>   3 files changed, 12 insertions(+), 6 deletions(-)
Recently I also met the "NMI watchdog not working on AMD guest"
issue, I have tested this patch locally and it helps.

Reviewed-by: Yanan Wang <wangyanan55@huawei.com>
Tested-by: Yanan Wang <wangyanan55@huawei.com>

Thanks,
Yanan
> diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
> index 7a7b8d5b775e..5e7e8d163b98 100644
> --- a/arch/x86/kvm/pmu.h
> +++ b/arch/x86/kvm/pmu.h
> @@ -140,6 +140,15 @@ static inline u64 get_sample_period(struct kvm_pmc *pmc, u64 counter_value)
>   	return sample_period;
>   }
>   
> +static inline void pmc_update_sample_period(struct kvm_pmc *pmc)
> +{
> +	if (!pmc->perf_event || pmc->is_paused)
> +		return;
> +
> +	perf_event_period(pmc->perf_event,
> +			  get_sample_period(pmc, pmc->counter));
> +}
> +
>   void reprogram_gp_counter(struct kvm_pmc *pmc, u64 eventsel);
>   void reprogram_fixed_counter(struct kvm_pmc *pmc, u8 ctrl, int fixed_idx);
>   void reprogram_counter(struct kvm_pmu *pmu, int pmc_idx);
> diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
> index 24eb935b6f85..b14860863c39 100644
> --- a/arch/x86/kvm/svm/pmu.c
> +++ b/arch/x86/kvm/svm/pmu.c
> @@ -257,6 +257,7 @@ static int amd_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   	pmc = get_gp_pmc_amd(pmu, msr, PMU_TYPE_COUNTER);
>   	if (pmc) {
>   		pmc->counter += data - pmc_read_counter(pmc);
> +		pmc_update_sample_period(pmc);
>   		return 0;
>   	}
>   	/* MSR_EVNTSELn */
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index efa172a7278e..e64046fbcdca 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -431,15 +431,11 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   			    !(msr & MSR_PMC_FULL_WIDTH_BIT))
>   				data = (s64)(s32)data;
>   			pmc->counter += data - pmc_read_counter(pmc);
> -			if (pmc->perf_event && !pmc->is_paused)
> -				perf_event_period(pmc->perf_event,
> -						  get_sample_period(pmc, data));
> +			pmc_update_sample_period(pmc);
>   			return 0;
>   		} else if ((pmc = get_fixed_pmc(pmu, msr))) {
>   			pmc->counter += data - pmc_read_counter(pmc);
> -			if (pmc->perf_event && !pmc->is_paused)
> -				perf_event_period(pmc->perf_event,
> -						  get_sample_period(pmc, data));
> +			pmc_update_sample_period(pmc);
>   			return 0;
>   		} else if ((pmc = get_gp_pmc(pmu, msr, MSR_P6_EVNTSEL0))) {
>   			if (data == pmc->eventsel)