From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751146AbdAaHex (ORCPT ); Tue, 31 Jan 2017 02:34:53 -0500 Received: from mail-wm0-f67.google.com ([74.125.82.67]:32961 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750802AbdAaHe0 (ORCPT ); Tue, 31 Jan 2017 02:34:26 -0500 Date: Tue, 31 Jan 2017 08:34:10 +0100 From: Ingo Molnar To: "Robert O'Callahan" Cc: kvm@vger.kernel.org, Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] KVM: x86: never specify a sample period for virtualized in_tx_cp counters Message-ID: <20170131073410.GC11851@gmail.com> References: <20170131014813.15220-1-robert@ocallahan.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170131014813.15220-1-robert@ocallahan.org> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Robert O'Callahan wrote: > pmc_reprogram_counter() always sets a sample period based on the value of > pmc->counter. However, hsw_hw_config() rejects sample periods less than > 2^31 - 1. So for example, a KVM guest doing > perf stat -e r2005101c4 sleep 0 > will count some conditional branch events, deschedule the task, reschedule > the task, try to restore the guest PMU state for the task, in the host > reach pmc_reprogram_counter() with nonzero pmc->count, trigger EOPNOTSUPP > in hsw_hw_config(), print "kvm_pmu: event creation failed" in > pmc_reprogram_counter(), and silently (from the guest's point of view) stop > counting events. > > We fix event counting by forcing attr.sample_period to always be zero for > in_tx_cp counters. Sampling doesn't work, but it already didn't work and > can't be fixed without major changes to the approach in hsw_hw_config(). > > Signed-off-by: Robert O'Callahan > --- > arch/x86/kvm/pmu.c | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c > index 06ce377..af993d7 100644 > --- a/arch/x86/kvm/pmu.c > +++ b/arch/x86/kvm/pmu.c > @@ -113,12 +113,18 @@ static void pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type, > .config = config, > }; > > + attr.sample_period = (-pmc->counter) & pmc_bitmask(pmc); > + > if (in_tx) > attr.config |= HSW_IN_TX; > - if (in_tx_cp) > + if (in_tx_cp) { > + /* HSW_IN_TX_CHECKPOINTED is not supported with nonzero > + * period. Just clear the sample period so at least > + * allocating the counter doesn't fail. > + */ > + attr.sample_period = 0; > attr.config |= HSW_IN_TX_CHECKPOINTED; > - > - attr.sample_period = (-pmc->counter) & pmc_bitmask(pmc); > + } please use the customary (multi-line) comment style: /* * Comment ..... * ...... goes here. */ specified in Documentation/CodingStyle. Thanks, Ingo