From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755199AbdBNRrx (ORCPT ); Tue, 14 Feb 2017 12:47:53 -0500 Received: from mail.kernel.org ([198.145.29.136]:41016 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753156AbdBNRrp (ORCPT ); Tue, 14 Feb 2017 12:47:45 -0500 Date: Tue, 14 Feb 2017 14:47:34 -0300 From: Arnaldo Carvalho de Melo To: Alexander Shishkin Cc: Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, vince@deater.net, eranian@google.com, Arnaldo Carvalho de Melo , Borislav Petkov , Thomas Gleixner Subject: Re: [PATCH 2/2] perf/x86/intel/pt: Fail event creation if VMX operation is on Message-ID: <20170214174734.GC4458@kernel.org> References: <20170214132416.26400-1-alexander.shishkin@linux.intel.com> <20170214132416.26400-3-alexander.shishkin@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170214132416.26400-3-alexander.shishkin@linux.intel.com> X-Url: http://acmel.wordpress.com User-Agent: Mutt/1.7.1 (2016-10-04) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Em Tue, Feb 14, 2017 at 03:24:16PM +0200, Alexander Shishkin escreveu: > On systems where PT does not coexist with VMX, users get confused when > PT turns up with no data because they forgot they're running a kvm > session at the same time. > > This patch adds a preemptive check for any active VMX operations that > will fail event creation. This does not provide any guarantees or > protection against racing with a kvm starting in parallel, but is > intended to serve as a hint for the user. If VMXON happens after an > event had been created, the event will still produce an empty trace. > > Signed-off-by: Alexander Shishkin > Reported-by: Andi Kleen Yeah, I saw that as well, and Andi told me about this limitation, so, for quite a while now, everytime I need to test PT on the only machine I have with it, I have to stop my kvm sessions :-\ Thanks for working on this! - Arnaldo > --- > arch/x86/events/intel/pt.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c > index 9372fa4549..b1490a879c 100644 > --- a/arch/x86/events/intel/pt.c > +++ b/arch/x86/events/intel/pt.c > @@ -1444,6 +1444,20 @@ static void pt_event_destroy(struct perf_event *event) > > static int pt_event_init(struct perf_event *event) > { > + int cpu, vmx_on = 0; > + > + get_online_cpus(); > + for_each_online_cpu(cpu) { > + struct pt *pt = per_cpu_ptr(&pt_ctx, cpu); > + > + if (READ_ONCE(pt->vmx_on)) > + vmx_on++; > + } > + put_online_cpus(); > + > + if (vmx_on) > + return -EBUSY; > + > if (event->attr.type != pt_pmu.pmu.type) > return -ENOENT; > > -- > 2.11.0