From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755442Ab0LHO73 (ORCPT ); Wed, 8 Dec 2010 09:59:29 -0500 Received: from canuck.infradead.org ([134.117.69.58]:44727 "EHLO canuck.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755424Ab0LHO72 convert rfc822-to-8bit (ORCPT ); Wed, 8 Dec 2010 09:59:28 -0500 Subject: Re: perf hw in kexeced kernel broken in tip From: Peter Zijlstra To: Don Zickus Cc: "Eric W. Biederman" , Vivek Goyal , Yinghai Lu , Ingo Molnar , Jason Wessel , "linux-kernel@vger.kernel.org" , Haren Myneni In-Reply-To: <1291818005.28378.38.camel@laptop> References: <1291232292.32004.1969.camel@laptop> <20101201194644.GD2511@redhat.com> <1291232989.32004.1987.camel@laptop> <20101201195835.GE2511@redhat.com> <1291234036.32004.2008.camel@laptop> <20101202052321.GH18100@redhat.com> <1291275270.4023.20.camel@twins> <20101202161502.GL18100@redhat.com> <1291764620.2032.1293.camel@laptop> <20101208140103.GM21786@redhat.com> <1291818005.28378.38.camel@laptop> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Wed, 08 Dec 2010 15:59:16 +0100 Message-ID: <1291820356.28378.83.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2010-12-08 at 15:20 +0100, Peter Zijlstra wrote: > > I wonder if you should reverse these checks. If the bios has the perf > > counter enabled, there might be a high chance that it fails the first > > check and never gets to the actually bios checks. > > Ah, good point. Something like so.. --- Subject: perf, x86: Detect broken BIOSes From: Peter Zijlstra Date: Wed Dec 08 15:56:23 CET 2010 Some BIOSes use PMU resources, this is a bug. Try to detect this, warn about it, and further refuse to touch the PMU ourselves. Signed-off-by: Peter Zijlstra --- Index: linux-2.6/arch/x86/kernel/cpu/perf_event.c =================================================================== --- linux-2.6.orig/arch/x86/kernel/cpu/perf_event.c +++ linux-2.6/arch/x86/kernel/cpu/perf_event.c @@ -375,15 +375,51 @@ static void release_pmc_hardware(void) { static bool check_hw_exists(void) { u64 val, val_new = 0; - int ret = 0; + int i, reg, ret = 0; + /* + * Check to see if the BIOS enabled any of the counters, if so + * complain and bail. + */ + for (i = 0; i < x86_pmu.num_counters; i++) { + reg = x86_pmu.eventsel + i; + ret = rdmsrl_safe(reg, &val); + if (ret) + goto msr_fail; + if (val & ARCH_PERFMON_EVENTSEL_ENABLE) + goto bios_fail; + } + + for (i = 0; i < x86_pmu.num_counters_fixed; i++) { + reg = MSR_ARCH_PERFMON_FIXED_CTR_CTRL; + ret = rdmsrl_safe(reg, &val); + if (ret) + goto msr_fail; + if (val & (0x03 << i*4)) + goto bios_fail; + } + + /* + * Now write a value and read it back to see if it matches, + * this is needed to detect certain hardware emulators (qemu/kvm) + * that don't trap on the MSR access and always return 0s. + */ val = 0xabcdUL; - ret |= checking_wrmsrl(x86_pmu.perfctr, val); + ret = checking_wrmsrl(x86_pmu.perfctr, val); ret |= rdmsrl_safe(x86_pmu.perfctr, &val_new); if (ret || val != val_new) - return false; + goto msr_fail; return true; + +bios_fail: + printk(KERN_CONT "Broken BIOS detected, software events only.\n"); + printk(KERN_ERR FW_BUG "invalid MSR: %x=%Lx\n", reg, val); + return false; + +msr_fail: + printk(KERN_CONT "Broken PMU hardware detected, software events only.\n"); + return false; } static void reserve_ds_buffers(void); @@ -1378,10 +1414,8 @@ int __init init_hw_perf_events(void) pmu_check_apic(); /* sanity check that the hardware exists or is emulated */ - if (!check_hw_exists()) { - pr_cont("Broken PMU hardware detected, software events only.\n"); + if (!check_hw_exists()) return 0; - } pr_cont("%s PMU driver.\n", x86_pmu.name);