Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756202AbcLBHel (ORCPT ); Fri, 2 Dec 2016 02:34:41 -0500 Received: from mail-wj0-f193.google.com ([209.85.210.193]:34251 "EHLO mail-wj0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751296AbcLBHek (ORCPT ); Fri, 2 Dec 2016 02:34:40 -0500 Date: Fri, 2 Dec 2016 08:34:35 +0100 From: Ingo Molnar To: Borislav Petkov Cc: Andy Lutomirski , x86@kernel.org, One Thousand Gnomes , "linux-kernel@vger.kernel.org" , Brian Gerst , Matthew Whitehead , Henrique de Moraes Holschuh , Linus Torvalds , Andrew Morton , "H. Peter Anvin" , Thomas Gleixner , Peter Zijlstra Subject: Re: [PATCH 4/4] x86/asm: Change sync_core() to use MOV to CR2 to serialize Message-ID: <20161202073435.GA14396@gmail.com> References: <46816abe4f68ac3eb9b80231bf64ba8edcebc2f7.1480536936.git.luto@kernel.org> <20161201092228.calajwwv4k4k4l6f@pd.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161201092228.calajwwv4k4k4l6f@pd.tnic> 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 Content-Length: 1403 Lines: 36 * Borislav Petkov wrote: > On Wed, Nov 30, 2016 at 12:34:55PM -0800, Andy Lutomirski wrote: > > Aside from being excessively slow, CPUID is problematic: Linux runs > > on a handful of CPUs that don't have CPUID. MOV to CR2 is always > > available, so use it instead. > > > > Signed-off-by: Andy Lutomirski > > --- > > arch/x86/include/asm/processor.h | 31 ++++++++----------------------- > > 1 file changed, 8 insertions(+), 23 deletions(-) > > Looks nice. > > I'm wondering if we should leave this one in tip for an additional cycle > to have it tested on more hw. I know, it is architectural and so on but > who knows what every implementation actually does... I think -tip and "upstream of the day" mostly gets tested on relatively recent x86 hardware - proven by the fact that these regressions are many months old. The reason v4.9 got extra testing is the announced Long Term Support (LTS) aspect: more, older, weirder hardware is being tested because it's going to be a very popular base kernel. So the best option would be to get these fixes into -tip, make sure it's sane all around and works on hardware that gets tested on bleeding edge kernels, then push it upstream sooner rather than later and also have Cc:stable tags on the obvious fixes, and handle any eventual fallout as it happens. That's the best we can do I think. Thanks, Ingo