From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753100AbcHHTNo (ORCPT ); Mon, 8 Aug 2016 15:13:44 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:35754 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753055AbcHHTNj (ORCPT ); Mon, 8 Aug 2016 15:13:39 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Minfei Huang , Paolo Bonzini Subject: [PATCH 4.4 31/68] pvclock: Add CPU barriers to get correct version value Date: Mon, 8 Aug 2016 21:11:06 +0200 Message-Id: <20160808180211.193761249@linuxfoundation.org> X-Mailer: git-send-email 2.9.2 In-Reply-To: <20160808180209.697765393@linuxfoundation.org> References: <20160808180209.697765393@linuxfoundation.org> User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Minfei Huang commit 749d088b8e7f4b9826ede02b9a043e417fa84aa1 upstream. 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. Fixes: 502dfeff239e8313bfbe906ca0a1a6827ac8481b Signed-off-by: Minfei Huang Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman --- arch/x86/include/asm/pvclock.h | 2 ++ arch/x86/kernel/pvclock.c | 4 ++++ 2 files changed, 6 insertions(+) --- a/arch/x86/include/asm/pvclock.h +++ b/arch/x86/include/asm/pvclock.h @@ -76,6 +76,8 @@ unsigned __pvclock_read_cycles(const str u8 ret_flags; version = src->version; + /* Make the latest version visible */ + smp_rmb(); offset = pvclock_get_nsec_offset(src); ret = src->system_time + offset; --- a/arch/x86/kernel/pvclock.c +++ b/arch/x86/kernel/pvclock.c @@ -66,6 +66,8 @@ u8 pvclock_read_flags(struct pvclock_vcp 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 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)) {