linux-kernel - Re: [PATCH v2] KVM: x86/pmu: Fix available_event_types check for REF_CPU

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Date:   Fri, 7 Jan 2022 17:48:55 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Like Xu <like.xu.linux@...il.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] KVM: x86/pmu: Fix available_event_types check for
 REF_CPU_CYCLES event

On 1/5/22 06:15, Like Xu wrote:
> From: Like Xu <likexu@...cent.com>
> 
> According to CPUID 0x0A.EBX bit vector, the event [7] should be the
> unrealized event "Topdown Slots" instead of the *kernel* generalized
> common hardware event "REF_CPU_CYCLES", so we need to skip the cpuid
> unavaliblity check in the intel_pmc_perf_hw_id() for the last
> REF_CPU_CYCLES event and update the confusing comment.
> 
> If the event is marked as unavailable in the Intel guest CPUID
> 0AH.EBX leaf, we need to avoid any perf_event creation, whether
> it's a gp or fixed counter. To distinguish whether it is a rejected
> event or an event that needs to be programmed with PERF_TYPE_RAW type,
> a new special returned value of "PERF_COUNT_HW_MAX + 1" is introduced.
> 
> Fixes: 62079d8a43128 ("KVM: PMU: add proper support for fixed counter 2")
> Signed-off-by: Like Xu <likexu@...cent.com>
> ---
> v1 -> v2 Changelog:
> - Refine comment based on commit c1d6f42f1a42;
> - Squash the idea "avoid event creation for rejected hw_config" into this commit;
> - Squash the idea "PERF_COUNT_HW_MAX + 1" into this commit;
> 
> Previous:
> https://lore.kernel.org/kvm/20211112095139.21775-3-likexu@tencent.com/
> 
>   arch/x86/kvm/pmu.c           |  3 +++
>   arch/x86/kvm/vmx/pmu_intel.c | 18 ++++++++++++------
>   2 files changed, 15 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> index 8abdadb7e22a..e632693a2266 100644
> --- a/arch/x86/kvm/pmu.c
> +++ b/arch/x86/kvm/pmu.c
> @@ -109,6 +109,9 @@ static void pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type,
>   		.config = config,
>   	};
>   
> +	if (type == PERF_TYPE_HARDWARE && config >= PERF_COUNT_HW_MAX)
> +		return;
> +
>   	attr.sample_period = get_sample_period(pmc, pmc->counter);
>   
>   	if (in_tx)
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index 5e0ac57d6d1b..ffccfd9823c0 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -21,7 +21,6 @@
>   #define MSR_PMC_FULL_WIDTH_BIT      (MSR_IA32_PMC0 - MSR_IA32_PERFCTR0)
>   
>   static struct kvm_event_hw_type_mapping intel_arch_events[] = {
> -	/* Index must match CPUID 0x0A.EBX bit vector */
>   	[0] = { 0x3c, 0x00, PERF_COUNT_HW_CPU_CYCLES },
>   	[1] = { 0xc0, 0x00, PERF_COUNT_HW_INSTRUCTIONS },
>   	[2] = { 0x3c, 0x01, PERF_COUNT_HW_BUS_CYCLES  },
> @@ -29,6 +28,7 @@ static struct kvm_event_hw_type_mapping intel_arch_events[] = {
>   	[4] = { 0x2e, 0x41, PERF_COUNT_HW_CACHE_MISSES },
>   	[5] = { 0xc4, 0x00, PERF_COUNT_HW_BRANCH_INSTRUCTIONS },
>   	[6] = { 0xc5, 0x00, PERF_COUNT_HW_BRANCH_MISSES },
> +	/* The above index must match CPUID 0x0A.EBX bit vector */
>   	[7] = { 0x00, 0x03, PERF_COUNT_HW_REF_CPU_CYCLES },
>   };
>   
> @@ -75,11 +75,17 @@ static unsigned int intel_pmc_perf_hw_id(struct kvm_pmc *pmc)
>   	u8 unit_mask = (pmc->eventsel & ARCH_PERFMON_EVENTSEL_UMASK) >> 8;
>   	int i;
>   
> -	for (i = 0; i < ARRAY_SIZE(intel_arch_events); i++)
> -		if (intel_arch_events[i].eventsel == event_select &&
> -		    intel_arch_events[i].unit_mask == unit_mask &&
> -		    (pmc_is_fixed(pmc) || pmu->available_event_types & (1 << i)))
> -			break;
> +	for (i = 0; i < ARRAY_SIZE(intel_arch_events); i++) {
> +		if (intel_arch_events[i].eventsel != event_select ||
> +		    intel_arch_events[i].unit_mask != unit_mask)
> +			continue;
> +
> +		/* disable event that reported as not present by cpuid */
> +		if ((i < 7) && !(pmu->available_event_types & (1 << i)))
> +			return PERF_COUNT_HW_MAX + 1;
> +
> +		break;
> +	}
>   
>   	if (i == ARRAY_SIZE(intel_arch_events))
>   		return PERF_COUNT_HW_MAX;

Queued, thanks.

Paolo