From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757758AbcIHNdm (ORCPT ); Thu, 8 Sep 2016 09:33:42 -0400 Received: from mx1.redhat.com ([209.132.183.28]:35608 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752737AbcIHNdk (ORCPT ); Thu, 8 Sep 2016 09:33:40 -0400 Subject: Re: [PATCH] x86, clock: Fix kvm guest tsc initialization To: Prarit Bhargava , linux-kernel@vger.kernel.org References: <1473340038-26432-1-git-send-email-prarit@redhat.com> Cc: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, Len Brown , "Peter Zijlstra (Intel)" , Borislav Petkov , Adrian Hunter , "Christopher S. Hall" , David Woodhouse , kvm@vger.kernel.org From: Paolo Bonzini Message-ID: <67c4faca-5c32-85de-10c2-59eff3c9fb87@redhat.com> Date: Thu, 8 Sep 2016 15:33:33 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: <1473340038-26432-1-git-send-email-prarit@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Thu, 08 Sep 2016 13:33:40 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/09/2016 15:07, Prarit Bhargava wrote: > When booting a kvm guest on AMD with the latest kernel the following > messages are displayed in the boot log: > > tsc: Unable to calibrate against PIT > tsc: HPET/PMTIMER calibration failed > > aa297292d708 ("x86/tsc: Enumerate SKL cpu_khz and tsc_khz via CPUID") > introduced a change to account for a difference in cpu and tsc frequencies for > Intel SKL processors. Before this change the native tsc set > x86_platform.calibrate_tsc to native_calibrate_tsc() which is a hardware > calibration of the tsc, and in tsc_init() executed > > tsc_khz = x86_platform.calibrate_tsc(); > cpu_khz = tsc_khz; > > The kvm code changed x86_platform.calibrate_tsc to kvm_get_tsc_khz() and > executed the same tsc_init() function. This meant that KVM guests did not > execute the native hardware calibration function. > > After aa297292d708, there are separate native calibrations for cpu_khz and > tsc_khz. The code sets x86_platform.calibrate_tsc to native_calibrate_tsc() > which is now an Intel specific calibration function , and > x86_platform.calibrate_cpu to native_calibrate_cpu() which is the "old" > native_calibrate_tsc() function (ie, the native hardware calibration > function). [...] > > The kvm code should not call the hardware initialization in > native_calibrate_cpu(), as it isn't applicable for kvm and it didn't do that > prior to aa297292d708. Setting x86_platform.calibrate_cpu to NULL is not > appropriate as cpu_khz_from_cpuid() must be called to get the correct > value of cpu_khz on Intel KVM guests. > > This patch resolves this issue by setting x86_platform.calibrate_cpu to > cpu_khz_from_cpuid() for KVM guests, which allows Intel KVM guests to get > the right cpu frequency. KVM guests don't have that CPUID leaf at all. kvm_get_tsc_khz can double as x86_platform.calibrate_cpu too for KVM guests, restoring the behavior prior to aa297292d708. Thanks, Paolo > Fixes: aa297292d708 ("x86/tsc: Enumerate SKL cpu_khz and tsc_khz via CPUID") > Signed-off-by: Prarit Bhargava > Cc: Paolo Bonzini > Cc: "Radim Krčmář" > Cc: Thomas Gleixner > Cc: Ingo Molnar > Cc: "H. Peter Anvin" > Cc: x86@kernel.org > Cc: Len Brown > Cc: "Peter Zijlstra (Intel)" > Cc: Borislav Petkov > Cc: Adrian Hunter > Cc: "Christopher S. Hall" > Cc: David Woodhouse > Cc: kvm@vger.kernel.org > --- > arch/x86/include/asm/tsc.h | 1 + > arch/x86/kernel/kvmclock.c | 1 + > arch/x86/kernel/tsc.c | 2 +- > 3 files changed, 3 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h > index 33b6365c22fe..1bfb3a14dad0 100644 > --- a/arch/x86/include/asm/tsc.h > +++ b/arch/x86/include/asm/tsc.h > @@ -37,6 +37,7 @@ extern int unsynchronized_tsc(void); > extern int check_tsc_unstable(void); > extern unsigned long native_calibrate_cpu(void); > extern unsigned long native_calibrate_tsc(void); > +extern unsigned long cpu_khz_from_cpuid(void); > extern unsigned long long native_sched_clock_from_tsc(u64 tsc); > > extern int tsc_clocksource_reliable; > diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c > index 1d39bfbd26bb..1fe23cff7c3e 100644 > --- a/arch/x86/kernel/kvmclock.c > +++ b/arch/x86/kernel/kvmclock.c > @@ -289,6 +289,7 @@ void __init kvmclock_init(void) > put_cpu(); > > x86_platform.calibrate_tsc = kvm_get_tsc_khz; > + x86_platform.calibrate_cpu = cpu_khz_from_cpuid; > x86_platform.get_wallclock = kvm_get_wallclock; > x86_platform.set_wallclock = kvm_set_wallclock; > #ifdef CONFIG_X86_LOCAL_APIC > diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c > index 78b9cb5a26af..9265ea8effe9 100644 > --- a/arch/x86/kernel/tsc.c > +++ b/arch/x86/kernel/tsc.c > @@ -699,7 +699,7 @@ unsigned long native_calibrate_tsc(void) > return crystal_khz * ebx_numerator / eax_denominator; > } > > -static unsigned long cpu_khz_from_cpuid(void) > +unsigned long cpu_khz_from_cpuid(void) > { > unsigned int eax_base_mhz, ebx_max_mhz, ecx_bus_mhz, edx; > >