Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932321AbcLBS3L (ORCPT ); Fri, 2 Dec 2016 13:29:11 -0500 Received: from mail-io0-f193.google.com ([209.85.223.193]:36052 "EHLO mail-io0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751711AbcLBS3H (ORCPT ); Fri, 2 Dec 2016 13:29:07 -0500 MIME-Version: 1.0 In-Reply-To: <20161202180343.gehqor7lgtmzwqq3@pd.tnic> References: <0a21157c2233ba7d0781bbf07866b3f2d7e7c25d.1480638597.git.luto@kernel.org> <20161202180343.gehqor7lgtmzwqq3@pd.tnic> From: Linus Torvalds Date: Fri, 2 Dec 2016 10:27:29 -0800 X-Google-Sender-Auth: EOytVMwcXlKCJe88_yByaYeVqrs Message-ID: Subject: Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation To: Borislav Petkov Cc: Andy Lutomirski , Peter Anvin , "the arch/x86 maintainers" , One Thousand Gnomes , Borislav Petkov , "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: 752 Lines: 22 On Fri, Dec 2, 2016 at 10:03 AM, Borislav Petkov wrote: > > SNB: > * before: > * after: I suspect it's entirely invisible on raw hardware. But quite possibly more noticeable in a VM that takes slow faults for every case. But yes, even there is' probably not *that* noticeable. I'd prefer to get rid of them just because I don't like voodoo programming. If there is no actual reason for "sync_core()", we shouldn't have one there. Even if it were entirely free and the compiler optimized it away because the compiler was so smart that it would see that it's pointless, it's misleading and wrong on a source level. That is, of course, assuming that there is no really subtle reason why that stupid sync_core() is there. Linus