From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758227Ab2IEJIq (ORCPT ); Wed, 5 Sep 2012 05:08:46 -0400 Received: from mail-bk0-f46.google.com ([209.85.214.46]:64623 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750964Ab2IEJIo (ORCPT ); Wed, 5 Sep 2012 05:08:44 -0400 Date: Wed, 5 Sep 2012 11:08:39 +0200 From: Ingo Molnar To: Peter Zijlstra Cc: "Yan, Zheng" , eranian@google.com, mingo@elte.hu, andi@firstfloor.org, avi@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] perf/x86: Disable uncore on virtualized CPU. Message-ID: <20120905090839.GA31992@gmail.com> References: <1345540117-14164-1-git-send-email-zheng.z.yan@intel.com> <20120905063524.GA20710@gmail.com> <1346834836.2600.3.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1346834836.2600.3.camel@twins> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Peter Zijlstra wrote: > 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. Ok, no objections. Thanks, Ingo