Re: [PATCH 5.4] KVM: x86/svm: Account for family 17h event renumberings in amd_pmc_perf_hw_id

[Paolo Bonzini <pbonzini@redhat.com>]

On 5/8/22 18:54, Kyle Huey wrote:
> From: Kyle Huey <me@kylehuey.com>
> 
> commit 5eb849322d7f7ae9d5c587c7bc3b4f7c6872cd2f upstream
> 
> Zen renumbered some of the performance counters that correspond to the
> well known events in perf_hw_id. This code in KVM was never updated for
> that, so guest that attempt to use counters on Zen that correspond to the
> pre-Zen perf_hw_id values will silently receive the wrong values.
> 
> This has been observed in the wild with rr[0] when running in Zen 3
> guests. rr uses the retired conditional branch counter 00d1 which is
> incorrectly recognized by KVM as PERF_COUNT_HW_STALLED_CYCLES_BACKEND.
> 
> [0] https://rr-project.org/
> 
> Signed-off-by: Kyle Huey <me@kylehuey.com>
> Message-Id: <20220503050136.86298-1-khuey@kylehuey.com>
> Cc: stable@vger.kernel.org
> [Check guest family, not host. - Paolo]
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> [Backport to 5.4: adjusted context]
> Signed-off-by: Kyle Huey <me@kylehuey.com>
> ---
>   arch/x86/kvm/pmu_amd.c | 28 +++++++++++++++++++++++++---
>   1 file changed, 25 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/pmu_amd.c b/arch/x86/kvm/pmu_amd.c
> index 6bc656abbe66..3ccfd1abcbad 100644
> --- a/arch/x86/kvm/pmu_amd.c
> +++ b/arch/x86/kvm/pmu_amd.c
> @@ -44,6 +44,22 @@ static struct kvm_event_hw_type_mapping amd_event_mapping[] = {
>   	[7] = { 0xd1, 0x00, PERF_COUNT_HW_STALLED_CYCLES_BACKEND },
>   };
>   
> +/* duplicated from amd_f17h_perfmon_event_map. */
> +static struct kvm_event_hw_type_mapping amd_f17h_event_mapping[] = {
> +	[0] = { 0x76, 0x00, PERF_COUNT_HW_CPU_CYCLES },
> +	[1] = { 0xc0, 0x00, PERF_COUNT_HW_INSTRUCTIONS },
> +	[2] = { 0x60, 0xff, PERF_COUNT_HW_CACHE_REFERENCES },
> +	[3] = { 0x64, 0x09, PERF_COUNT_HW_CACHE_MISSES },
> +	[4] = { 0xc2, 0x00, PERF_COUNT_HW_BRANCH_INSTRUCTIONS },
> +	[5] = { 0xc3, 0x00, PERF_COUNT_HW_BRANCH_MISSES },
> +	[6] = { 0x87, 0x02, PERF_COUNT_HW_STALLED_CYCLES_FRONTEND },
> +	[7] = { 0x87, 0x01, PERF_COUNT_HW_STALLED_CYCLES_BACKEND },
> +};
> +
> +/* amd_pmc_perf_hw_id depends on these being the same size */
> +static_assert(ARRAY_SIZE(amd_event_mapping) ==
> +	     ARRAY_SIZE(amd_f17h_event_mapping));
> +
>   static unsigned int get_msr_base(struct kvm_pmu *pmu, enum pmu_type type)
>   {
>   	struct kvm_vcpu *vcpu = pmu_to_vcpu(pmu);
> @@ -130,17 +146,23 @@ static unsigned amd_find_arch_event(struct kvm_pmu *pmu,
>   				    u8 event_select,
>   				    u8 unit_mask)
>   {
> +	struct kvm_event_hw_type_mapping *event_mapping;
>   	int i;
>   
> +	if (guest_cpuid_family(pmc->vcpu) >= 0x17)
> +		event_mapping = amd_f17h_event_mapping;
> +	else
> +		event_mapping = amd_event_mapping;
> +
>   	for (i = 0; i < ARRAY_SIZE(amd_event_mapping); i++)
> -		if (amd_event_mapping[i].eventsel == event_select
> -		    && amd_event_mapping[i].unit_mask == unit_mask)
> +		if (event_mapping[i].eventsel == event_select
> +		    && event_mapping[i].unit_mask == unit_mask)
>   			break;
>   
>   	if (i == ARRAY_SIZE(amd_event_mapping))
>   		return PERF_COUNT_HW_MAX;
>   
> -	return amd_event_mapping[i].event_type;
> +	return event_mapping[i].event_type;
>   }
>   
>   /* return PERF_COUNT_HW_MAX as AMD doesn't have fixed events */

Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Thanks,

Paolo