From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756547Ab2IEIrh (ORCPT ); Wed, 5 Sep 2012 04:47:37 -0400 Received: from merlin.infradead.org ([205.233.59.134]:55421 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752011Ab2IEIre convert rfc822-to-8bit (ORCPT ); Wed, 5 Sep 2012 04:47:34 -0400 Message-ID: <1346834836.2600.3.camel@twins> Subject: Re: [PATCH] perf/x86: Disable uncore on virtualized CPU. From: Peter Zijlstra To: Ingo Molnar Cc: "Yan, Zheng" , eranian@google.com, mingo@elte.hu, andi@firstfloor.org, avi@redhat.com, linux-kernel@vger.kernel.org Date: Wed, 05 Sep 2012 10:47:16 +0200 In-Reply-To: <20120905063524.GA20710@gmail.com> References: <1345540117-14164-1-git-send-email-zheng.z.yan@intel.com> <20120905063524.GA20710@gmail.com> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2012-09-05 at 08:35 +0200, Ingo Molnar wrote: > * Yan, Zheng wrote: > > > From: "Yan, Zheng" > > > > Initializing uncore PMU on virtualized CPU may hang the kernel. > > This is because kvm does not emulate the entire hardware. Thers > > are lots of uncore related MSRs, making kvm enumerate them all > > is a non-trival task. So just disable uncore on virtualized CPU. > > > > Signed-off-by: Yan, Zheng > > --- > > arch/x86/kernel/cpu/perf_event_intel_uncore.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/arch/x86/kernel/cpu/perf_event_intel_uncore.c b/arch/x86/kernel/cpu/perf_event_intel_uncore.c > > index 0a55710..2f005ba 100644 > > --- a/arch/x86/kernel/cpu/perf_event_intel_uncore.c > > +++ b/arch/x86/kernel/cpu/perf_event_intel_uncore.c > > @@ -2898,6 +2898,9 @@ static int __init intel_uncore_init(void) > > if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) > > return -ENODEV; > > > > + if (cpu_has_hypervisor) > > + return -ENODEV; > > + > > ret = uncore_pci_init(); > > if (ret) > > goto fail; > > Cannot the presence of the uncore hardware be detected in a > cleaner fashion, via the PCI config space and such? No, part of the uncore PMUs are in MSR space and aren't discoverable. CPUID model checks + hard assumptions of presence are all that we are left with. Now Avi suggested we teach KVM about these MSRs and then modify the uncore driver to test if the MSRs actually work -- as in retain values written to them and aren't always 0. That's a larger patch though, partly because enumerating the gazillion MSRs consumed by the various uncore PMUs is a tedious job, and we can always do this later. This patch is a minimal patch to at least make things 'work' for now.