From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757029Ab2BMPqh (ORCPT ); Mon, 13 Feb 2012 10:46:37 -0500 Received: from mx1.redhat.com ([209.132.183.28]:9546 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756953Ab2BMPqg (ORCPT ); Mon, 13 Feb 2012 10:46:36 -0500 From: Igor Mammedov To: linux-kernel@vger.kernel.org Cc: kvm@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, jacob.jun.pan@linux.intel.com, alan@linux.intel.com, feng.tang@intel.com, konrad.wilk@oracle.com, avi@redhat.com, glommer@redhat.com, johnstul@us.ibm.com, riel@redhat.com, tj@kernel.org, kosaki.motohiro@jp.fujitsu.com, akpm@linux-foundation.org, amit.shah@redhat.com Subject: [PATCH RFC] pvclock: Make pv_clock more robust and fixup it if overflow happens Date: Mon, 13 Feb 2012 16:45:59 +0100 Message-Id: <1329147959-22472-1-git-send-email-imammedo@redhat.com> In-Reply-To: <20120213130727.GA8052@amt.cnet> References: <20120213130727.GA8052@amt.cnet> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Instead of hunting misterious stalls/hungs all over the kernel when overflow occurs at pvclock.c:pvclock_get_nsec_offset u64 delta = native_read_tsc() - shadow->tsc_timestamp; and introducing hooks when places of unexpected access found, pv_clock should be initialized for the calling cpu if overflow condition is detected. Signed-off-by: Igor Mammedov --- arch/x86/kernel/pvclock.c | 18 +++++++++++++++--- 1 files changed, 15 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c index 42eb330..b486756 100644 --- a/arch/x86/kernel/pvclock.c +++ b/arch/x86/kernel/pvclock.c @@ -41,9 +41,14 @@ void pvclock_set_flags(u8 flags) valid_flags = flags; } -static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow) +static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow, + bool *overflow) { - u64 delta = native_read_tsc() - shadow->tsc_timestamp; + u64 delta; + u64 tsc = native_read_tsc(); + u64 shadow_timestamp = shadow->tsc_timestamp; + *overflow = tsc < shadow_timestamp; + delta = tsc - shadow_timestamp; return pvclock_scale_delta(delta, shadow->tsc_to_nsec_mul, shadow->tsc_shift); } @@ -94,12 +99,19 @@ cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src) unsigned version; cycle_t ret, offset; u64 last; + bool overflow; do { version = pvclock_get_time_values(&shadow, src); barrier(); - offset = pvclock_get_nsec_offset(&shadow); + offset = pvclock_get_nsec_offset(&shadow, &overflow); ret = shadow.system_timestamp + offset; + if (unlikely(overflow)) { + memset(src, 0, sizeof(*src)); + barrier(); + x86_cpuinit.early_percpu_clock_init(); + continue; + } barrier(); } while (version != src->version); -- 1.7.7.6