From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1425706AbcFHTpR (ORCPT ); Wed, 8 Jun 2016 15:45:17 -0400 Received: from mx2.suse.de ([195.135.220.15]:32828 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161609AbcFHTpP (ORCPT ); Wed, 8 Jun 2016 15:45:15 -0400 Date: Wed, 8 Jun 2016 21:45:09 +0200 From: Borislav Petkov To: Roman Kagan , Minfei Huang Cc: linux-kernel@vger.kernel.org, "Denis V. Lunev" , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, Andy Lutomirski , Paolo Bonzini Subject: Re: [PATCH] x86:pvclock: add missing barriers Message-ID: <20160608194509.GE4094@pd.tnic> References: <1465409499-23166-1-git-send-email-rkagan@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1465409499-23166-1-git-send-email-rkagan@virtuozzo.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 08, 2016 at 09:11:39PM +0300, Roman Kagan wrote: > Gradual removal of excessive barriers in pvclock reading functions > (commits 502dfeff239e8313bfbe906ca0a1a6827ac8481b, > a3eb97bd80134ba07864ca00747466c02118aca1) ended up removing too much: > although rdtsc is now orderd WRT other loads, there's no protection > against the compiler reordering the loads of ->version with the loads of > other fields. > > E.g. on my system gcc-5.3.1 generates code which loads ->system_time and > ->flags outside of the ->version test loop. > > (Re)introduce the compiler barriers around accesses to the contents of > pvclock. While at this, make the function a bit more compact by > removing unnecessary local variables. > > Signed-off-by: Roman Kagan > Cc: Thomas Gleixner > Cc: Ingo Molnar > Cc: "H. Peter Anvin" > Cc: x86@kernel.org > Cc: Andy Lutomirski > Cc: Borislav Petkov > Cc: Paolo Bonzini > Cc: stable@vger.kernel.org > --- > arch/x86/include/asm/pvclock.h | 17 +++++------------ > 1 file changed, 5 insertions(+), 12 deletions(-) > > diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h > index fdcc040..65c4de2 100644 > --- a/arch/x86/include/asm/pvclock.h > +++ b/arch/x86/include/asm/pvclock.h > @@ -80,18 +80,11 @@ static __always_inline > unsigned __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src, > cycle_t *cycles, u8 *flags) > { > - unsigned version; > - cycle_t ret, offset; > - u8 ret_flags; > - > - version = src->version; > - > - offset = pvclock_get_nsec_offset(src); > - ret = src->system_time + offset; > - ret_flags = src->flags; > - > - *cycles = ret; > - *flags = ret_flags; > + unsigned version = src->version; > + barrier(); > + *cycles = src->system_time + pvclock_get_nsec_offset(src); > + *flags = src->flags; > + barrier(); > return version; I have a similar patchset in my mbox starting here: https://lkml.kernel.org/r/1464329832-4638-1-git-send-email-mnghuan@gmail.com Care to take a look? Thanks. -- Regards/Gruss, Boris. SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) --