From: "Chen, Zide" <zide.chen@intel.com>
To: Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org, Jim Mattson <jmattson@google.com>,
Andi Kleen <ak@linux.intel.com>,
linux-kernel@vger.kernel.org, Mingwei Zhang <mizhang@google.com>,
Das Sandipan <Sandipan.Das@amd.com>,
Shukla Manali <Manali.Shukla@amd.com>,
Dapeng Mi <dapeng1.mi@linux.intel.com>,
Xudong Hao <xudong.hao@intel.com>
Subject: Re: [PATCH v8 5/8] KVM: x86/pmu: Support PERF_METRICS MSR in mediated vPMU
Date: Wed, 16 Sep 2026 16:32:51 -0500 [thread overview]
Message-ID: <1320a70d-4d92-45bb-9cca-5e86199b4cb1@intel.com> (raw)
In-Reply-To: <20260817183143.226156-6-zide.chen@intel.com>
On 8/17/2026 1:31 PM, Zide Chen wrote:
> @@ -395,6 +400,14 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> if (pmu->fixed_ctr_ctrl != data)
> reprogram_fixed_counters(pmu, data);
> break;
> + case MSR_PERF_METRICS:
> + /*
> + * Bits [63:32] are ignored on hardware that supports only
> + * level-1 metrics, but may be valid on hardware that supports
> + * level-2 metrics. Preserve guest writes verbatim.
> + */
That comment isn't correct. I've confirmed that MSR_PERF_METRICS[63:32]
isn't simply ignored on hardware that implements only the four level-1
Topdown metrics. Those bits are reserved, and KVM should reject non-zero
writes.
I'll post a fix in the next version. KVM will get the number of Topdown
metric events supported by the host CPU from perf/x86 and derive the
MSR_PERF_METRICS reserved-bit mask from that count, using it to reject
invalid writes.
next prev parent reply other threads:[~2026-09-16 21:32 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-17 18:31 [PATCH v8 0/8] KVM: x86/pmu: Add hardware Topdown metrics support Zide Chen
2026-08-17 18:31 ` [PATCH v8 1/8] KVM: x86/pmu: Do not map fixed counters >= 3 to generic perf events Zide Chen
2026-08-17 18:31 ` [PATCH v8 2/8] KVM: x86/pmu: Support Intel fixed counter 3 on mediated vPMU Zide Chen
2026-08-17 18:31 ` [PATCH v8 3/8] KVM: x86/pmu: Rename and move vcpu_get_perf_capabilities() to pmu.h Zide Chen
2026-08-17 18:31 ` [PATCH v8 4/8] KVM: x86/pmu: Snapshot host IA32_PERF_CAPABILITIES in kvm_host Zide Chen
2026-08-17 18:31 ` [PATCH v8 5/8] KVM: x86/pmu: Support PERF_METRICS MSR in mediated vPMU Zide Chen
2026-08-20 0:56 ` Mi, Dapeng
2026-09-16 21:32 ` Chen, Zide [this message]
2026-08-17 18:31 ` [PATCH v8 6/8] KVM: x86/pmu: Move RDPMC emulation into per-vendor callbacks Zide Chen
2026-08-19 3:14 ` Sandipan Das
2026-08-17 18:31 ` [PATCH v8 7/8] KVM: x86/pmu: Emulate RDPMC on performance metrics Zide Chen
2026-08-18 17:41 ` Andi Kleen
2026-08-18 18:30 ` Chen, Zide
2026-08-18 19:24 ` Andi Kleen
2026-08-18 19:59 ` Chen, Zide
2026-08-17 18:31 ` [PATCH v8 8/8] KVM: selftests: Add PERF_METRICS and fixed counter 3 tests Zide Chen
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