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b=wiUYqawRMVLTKAueTFawsS++DDQ6NdPUQA8IfWicJNVlsMm1FySVC81cvSUHkjz3IrrVb+Vp/WzXiOfuLV+5Jw5G445gro3QxUWn4HGKJBsRTdz16xlt65yOx30JKnk1i1OZX/fM2XZtxVkJoJR6loFEEPIi2AB7CYpHw2Uy1Lo= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from PH7PR12MB5712.namprd12.prod.outlook.com (2603:10b6:510:1e3::13) by DM4PR12MB6493.namprd12.prod.outlook.com (2603:10b6:8:b6::13) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.428.16; Mon, 21 Sep 2026 05:11:37 +0000 Received: from PH7PR12MB5712.namprd12.prod.outlook.com ([fe80::afe1:7dd0:ea71:b7e7]) by PH7PR12MB5712.namprd12.prod.outlook.com ([fe80::afe1:7dd0:ea71:b7e7%4]) with mapi id 15.21.0428.015; Mon, 21 Sep 2026 05:11:36 +0000 Message-ID: <727ec541-3bee-4e78-806d-587ca9261d51@amd.com> Date: Mon, 21 Sep 2026 10:41:29 +0530 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] KVM: x86/pmu: Don't retry a counter whose config was rejected To: Luka Absandze , seanjc@google.com, pbonzini@redhat.com Cc: tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, dwmw2@infradead.org, kvm@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260920155453.10836-1-absandze@amazon.de> Content-Language: en-US From: Sandipan Das In-Reply-To: <20260920155453.10836-1-absandze@amazon.de> Content-Type: text/plain; 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That is true for contention, e.g. the -EBUSY from > x86_reserve_hardware(), but not for a configuration the host PMU driver > rejects outright. A rejected config can never succeed on retry, so the > counter is reprogrammed on every PMU refresh for as long as the guest > leaves it enabled, and every attempt fails the same way. > > Re-arm only for the errnos that indicate a transient condition, i.e. > -EBUSY and -ENOMEM. > > Suggested-by: Sean Christopherson > Link: https://lore.kernel.org/all/20260916123315.89042-1-absandze@amazon.de/ > Signed-off-by: Luka Absandze > --- > v2: > - Use an allow-list of transient errnos (-EBUSY, -ENOMEM) rather than > excluding -EINVAL, and hoist 'r' out of the loop. Diff taken from > Sean's suggestion verbatim. [Sean] > - Reword the comment to say "fails on a transient condition". [Sean] > - v1: https://lore.kernel.org/all/20260918160006.61816-1-absandze@amazon.de/ > > diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c > index a7d60c8785cd..03a470c49a74 100644 > --- a/arch/x86/kvm/pmu.c > +++ b/arch/x86/kvm/pmu.c > @@ -662,7 +662,7 @@ void kvm_pmu_handle_event(struct kvm_vcpu *vcpu) > DECLARE_BITMAP(bitmap, X86_PMC_IDX_MAX); > struct kvm_pmu *pmu = vcpu_to_pmu(vcpu); > struct kvm_pmc *pmc; > - int bit; > + int bit, r; > > bitmap_copy(bitmap, pmu->reprogram_pmi, X86_PMC_IDX_MAX); > > @@ -676,12 +676,14 @@ void kvm_pmu_handle_event(struct kvm_vcpu *vcpu) > > kvm_for_each_pmc(pmu, pmc, bit, bitmap) { > /* > - * If reprogramming fails, e.g. due to contention, re-set the > - * reprogram bit, i.e. opportunistically try again on the next > - * PMU refresh. Don't make a new request as doing so can stall > - * the guest if reprogramming repeatedly fails. > + * If reprogramming fails on a transient condition, e.g. due to > + * contention, re-set the reprogram bit, i.e. opportunistically > + * try again on the next PMU refresh. Don't make a new request > + * as doing so can stall the guest if reprogramming repeatedly > + * fails. > */ > - if (reprogram_counter(pmc)) > + r = reprogram_counter(pmc); > + if (r == -EBUSY || r == -ENOMEM) > set_bit(pmc->idx, pmu->reprogram_pmi); > } > Reviewed-by: Sandipan Das