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Mon, 6 Oct 2025 08:03:19 +0000 Message-ID: <3bbc4e6d-9f52-483c-a25d-166dca62fb25@intel.com> Date: Mon, 6 Oct 2025 13:33:05 +0530 User-Agent: Mozilla Thunderbird Subject: Re: REGRESSION on linux-next (next-20250919) To: Sean Christopherson , Dapeng Mi CC: "intel-gfx@lists.freedesktop.org" , "intel-xe@lists.freedesktop.org" , "Suresh Kumar Kurmi" , Jani Saarinen , , , References: <70b64347-2aca-4511-af78-a767d5fa8226@intel.com> <25af94f5-79e3-4005-964e-e77b1320a16e@linux.intel.com> Content-Language: en-GB From: "Borah, Chaitanya Kumar" In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: MA0PR01CA0123.INDPRD01.PROD.OUTLOOK.COM (2603:1096:a01:11d::6) To SJ1PR11MB6129.namprd11.prod.outlook.com (2603:10b6:a03:488::12) Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ1PR11MB6129:EE_|MN0PR11MB6159:EE_ X-MS-Office365-Filtering-Correlation-Id: 3a12f137-0f12-4d95-613f-08de04aecff3 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|366016|1800799024; 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I am Chaitanya from the linux graphics team in >>> Intel. >>> >>> This mail is regarding a regression we are seeing in our CI runs[1] on >>> linux-next repository. >>> >>> Since the version next-20250919 [2], we are seeing the following regression >>> >>> ````````````````````````````````````````````````````````````````````````````````` >>> <4>[ 10.973827] ------------[ cut here ]------------ >>> <4>[ 10.973841] WARNING: arch/x86/events/core.c:3089 at >>> perf_get_x86_pmu_capability+0xd/0xc0, CPU#15: (udev-worker)/386 >>> ... >>> <4>[ 10.974028] Call Trace: >>> <4>[ 10.974030] >>> <4>[ 10.974033] ? kvm_init_pmu_capability+0x2b/0x190 [kvm] >>> <4>[ 10.974154] kvm_x86_vendor_init+0x1b0/0x1a40 [kvm] >>> <4>[ 10.974248] vmx_init+0xdb/0x260 [kvm_intel] >>> <4>[ 10.974278] ? __pfx_vt_init+0x10/0x10 [kvm_intel] >>> <4>[ 10.974296] vt_init+0x12/0x9d0 [kvm_intel] >>> <4>[ 10.974309] ? __pfx_vt_init+0x10/0x10 [kvm_intel] >>> <4>[ 10.974322] do_one_initcall+0x60/0x3f0 >>> <4>[ 10.974335] do_init_module+0x97/0x2b0 >>> <4>[ 10.974345] load_module+0x2d08/0x2e30 >>> <4>[ 10.974349] ? __kernel_read+0x158/0x2f0 >>> <4>[ 10.974370] ? kernel_read_file+0x2b1/0x320 >>> <4>[ 10.974381] init_module_from_file+0x96/0xe0 >>> <4>[ 10.974384] ? init_module_from_file+0x96/0xe0 >>> <4>[ 10.974399] idempotent_init_module+0x117/0x330 >>> <4>[ 10.974415] __x64_sys_finit_module+0x73/0xe0 >>> ... >>> ````````````````````````````````````````````````````````````````````````````````` >>> Details log can be found in [3]. >>> >>> After bisecting the tree, the following patch [4] seems to be the first >>> "bad" commit >>> >>> ````````````````````````````````````````````````````````````````````````````````````````````````````````` >>> From 51f34b1e650fc5843530266cea4341750bd1ae37 Mon Sep 17 00:00:00 2001 >>> >>> From: Sean Christopherson >>> >>> Date: Wed, 6 Aug 2025 12:56:39 -0700 >>> >>> Subject: KVM: x86/pmu: Snapshot host (i.e. perf's) reported PMU capabilities >>> >>> Take a snapshot of the unadulterated PMU capabilities provided by perf so >>> that KVM can compare guest vPMU capabilities against hardware capabilities >>> when determining whether or not to intercept PMU MSRs (and RDPMC). >>> ````````````````````````````````````````````````````````````````````````````````````````````````````````` >>> >>> We also verified that if we revert the patch the issue is not seen. >>> >>> Could you please check why the patch causes this regression and provide >>> a fix if necessary? >> >> Hi Chaitanya, >> >> I suppose you found this warning on a hybrid client platform, right? It >> looks the warning is triggered by the below WARN_ON_ONCE() in >> perf_get_x86_pmu_capability() function. >> >>   if (WARN_ON_ONCE(cpu_feature_enabled(X86_FEATURE_HYBRID_CPU)) || >>         !x86_pmu_initialized()) { >>         memset(cap, 0, sizeof(*cap)); >>         return; >>     } >> >> The below change should fix it (just building, not test it). I would run a >> full scope vPMU test after I come back from China national day's holiday. > > I have access to a hybrid system, I'll also double check there (though I'm 99.9% > certain you've got it right). > >> Thanks. >> >> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c >> index cebce7094de8..6d87c25226d8 100644 >> --- a/arch/x86/kvm/pmu.c >> +++ b/arch/x86/kvm/pmu.c >> @@ -108,8 +108,6 @@ void kvm_init_pmu_capability(struct kvm_pmu_ops *pmu_ops) >>         bool is_intel = boot_cpu_data.x86_vendor == X86_VENDOR_INTEL; >>         int min_nr_gp_ctrs = pmu_ops->MIN_NR_GP_COUNTERS; >> >> -       perf_get_x86_pmu_capability(&kvm_host_pmu); >> - >>         /* >>          * Hybrid PMUs don't play nice with virtualization without careful >>          * configuration by userspace, and KVM's APIs for reporting supported >> @@ -120,6 +118,8 @@ void kvm_init_pmu_capability(struct kvm_pmu_ops *pmu_ops) >>                 enable_pmu = false; >> >>         if (enable_pmu) { >> +               perf_get_x86_pmu_capability(&kvm_host_pmu); >> + >>                 /* >>                  * WARN if perf did NOT disable hardware PMU if the number of >>                  * architecturally required GP counters aren't present, i.e. if > > If we go this route, then the !enable_pmu path should explicitly zero kvm_host_pmu > so that the behavior is consistent userspace loads kvm.ko with enable_pmu=0, > versus enable_pmu being cleared because of lack of support. > > if (!enable_pmu) { > memset(&kvm_host_pmu, 0, sizeof(kvm_host_pmu)); > memset(&kvm_pmu_cap, 0, sizeof(kvm_pmu_cap)); > return; > } > > The alternative would be keep kvm_host_pmu valid at all times for !HYBRID, which > is what I intended with the bad patch, but that too would lead to inconsistent > behavior. So I think it makes sense to go with Dapeng's approach; we can always > revisit this if some future thing in KVM _needs_ kvm_host_pmu even with enable_pmu=0. > > if (cpu_feature_enabled(X86_FEATURE_HYBRID_CPU)) { > enable_pmu = false; > memset(&kvm_host_pmu, 0, sizeof(kvm_host_pmu)); > } else { > perf_get_x86_pmu_capability(&kvm_host_pmu); > } Thank you for your responses. Following change fixes the issue for us. diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c index 40ac4cb44ed2..487ad19a236e 100644 --- a/arch/x86/kvm/pmu.c +++ b/arch/x86/kvm/pmu.c @@ -108,16 +108,18 @@ void kvm_init_pmu_capability(const struct kvm_pmu_ops *pmu_ops) bool is_intel = boot_cpu_data.x86_vendor == X86_VENDOR_INTEL; int min_nr_gp_ctrs = pmu_ops->MIN_NR_GP_COUNTERS; - perf_get_x86_pmu_capability(&kvm_host_pmu); - /* * Hybrid PMUs don't play nice with virtualization without careful * configuration by userspace, and KVM's APIs for reporting supported * vPMU features do not account for hybrid PMUs. Disable vPMU support * for hybrid PMUs until KVM gains a way to let userspace opt-in. */ - if (cpu_feature_enabled(X86_FEATURE_HYBRID_CPU)) + if (cpu_feature_enabled(X86_FEATURE_HYBRID_CPU)) { enable_pmu = false; + memset(&kvm_host_pmu, 0, sizeof(kvm_host_pmu)); + } else { + perf_get_x86_pmu_capability(&kvm_host_pmu); + } Regards Chaitanya