From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932275AbcE0GRK (ORCPT ); Fri, 27 May 2016 02:17:10 -0400 Received: from mail-pf0-f196.google.com ([209.85.192.196]:35596 "EHLO mail-pf0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932228AbcE0GRF (ORCPT ); Fri, 27 May 2016 02:17:05 -0400 From: Minfei Huang To: bp@suse.de, pbonzini@redhat.com, luto@kernel.org, hpa@zytor.com, mingo@redhat.com, tglx@linutronix.de Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Minfei Huang Subject: [PATCH 1/3] pvclock: Add CPU barries to get correct version value Date: Fri, 27 May 2016 14:17:10 +0800 Message-Id: <1464329832-4638-1-git-send-email-mnghuan@gmail.com> X-Mailer: git-send-email 2.6.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Protocol for the "version" fields is: hypervisor raises it (making it uneven) before it starts updating the fields and raises it again (making it even) when it is done. Thus the guest can make sure the time values it got are consistent by checking the version before and after reading them. Add CPU barries after getting version value just like what function vread_pvclock does, because all of callees in this function is inline. Signed-off-by: Minfei Huang --- arch/x86/include/asm/pvclock.h | 2 ++ arch/x86/kernel/pvclock.c | 4 ++++ 2 files changed, 6 insertions(+) diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h index fdcc040..538ae94 100644 --- a/arch/x86/include/asm/pvclock.h +++ b/arch/x86/include/asm/pvclock.h @@ -85,6 +85,8 @@ unsigned __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src, u8 ret_flags; version = src->version; + /* Make the latest version visible */ + smp_rmb(); offset = pvclock_get_nsec_offset(src); ret = src->system_time + offset; diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c index 99bfc02..7f82fe0 100644 --- a/arch/x86/kernel/pvclock.c +++ b/arch/x86/kernel/pvclock.c @@ -66,6 +66,8 @@ u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src) do { version = __pvclock_read_cycles(src, &ret, &flags); + /* Make sure that the version double-check is last. */ + smp_rmb(); } while ((src->version & 1) || version != src->version); return flags & valid_flags; @@ -80,6 +82,8 @@ cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src) do { version = __pvclock_read_cycles(src, &ret, &flags); + /* Make sure that the version double-check is last. */ + smp_rmb(); } while ((src->version & 1) || version != src->version); if (unlikely((flags & PVCLOCK_GUEST_STOPPED) != 0)) { -- 2.6.3