Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932446AbcLBTgC (ORCPT ); Fri, 2 Dec 2016 14:36:02 -0500 Received: from mail-io0-f195.google.com ([209.85.223.195]:34373 "EHLO mail-io0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754166AbcLBTgA (ORCPT ); Fri, 2 Dec 2016 14:36:00 -0500 MIME-Version: 1.0 In-Reply-To: References: <0a21157c2233ba7d0781bbf07866b3f2d7e7c25d.1480638597.git.luto@kernel.org> <20161202180343.gehqor7lgtmzwqq3@pd.tnic> <20161202185008.tdziqrzi4a3axord@pd.tnic> <20161202192050.l5l3rcwems6hptub@pd.tnic> From: Linus Torvalds Date: Fri, 2 Dec 2016 11:35:58 -0800 X-Google-Sender-Auth: Tqv01iWvCAgWNFG90rJTlKIlOJg Message-ID: Subject: Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation To: Andy Lutomirski Cc: Borislav Petkov , Borislav Petkov , Andy Lutomirski , Peter Anvin , "the arch/x86 maintainers" , One Thousand Gnomes , "linux-kernel@vger.kernel.org" , Brian Gerst , Matthew Whitehead , Henrique de Moraes Holschuh , Peter Zijlstra , Andrew Cooper Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 733 Lines: 22 On Fri, Dec 2, 2016 at 11:30 AM, Andy Lutomirski wrote: > > How's this? Looks ok. I do think that > I suppose it could be an unconditional IRET-to-self, but that's a good > deal slower and not a whole lot simpler. Although if we start doing > it right, performance won't really matter here. Considering you already got the iret-to-self wrong in the first version, I really like the "one single unconditional version" so that everybody tests that _one_ thing and there isn't anything subtle going on. Hmm? And yes, if it turns out that performance matters, we almost certainly are doing something really wrong, and we shouldn't be using that sync_core() thing in that place anyway. Linus