Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755853AbcCUWLv (ORCPT ); Mon, 21 Mar 2016 18:11:51 -0400 Received: from one.firstfloor.org ([193.170.194.197]:38814 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751877AbcCUWLu (ORCPT ); Mon, 21 Mar 2016 18:11:50 -0400 Date: Mon, 21 Mar 2016 23:11:48 +0100 From: Andi Kleen To: Andy Lutomirski Cc: Andi Kleen , X86 ML , "linux-kernel@vger.kernel.org" Subject: Re: Updated version of RD/WR FS/GS BASE patchkit Message-ID: <20160321221148.GF5083@two.firstfloor.org> References: <1458576969-13309-1-git-send-email-andi@firstfloor.org> <20160321190322.GZ5083@two.firstfloor.org> <20160321194027.GB5083@two.firstfloor.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1115 Lines: 31 > So a patchset to enable these asinine new instructions needs to take > this into account, and the ABI issue needs to be addressed, even if What's the ABI issue? AFAIK we're perfectly consistent. > the answer is that the proposed code is fine. > > (Also, the existing code is fscked up. Guess what xor %eax, %eax; mov > %ax, %gs does to the base on AMD? The existing code is *wrong*, and I > don't want to see it get wronger.) I have no idea, but changing it is definitely not in scope for my patches. > > And no, I don't really care about programs detecting context switches. > I do, however, care about allowing non-determinism in things that > ought to behave deterministically. Writing a nonzero value to %gs and > then doing WRGSBASE is something that user code will be able to do > whether we like it or not, some shitty threading library is likely to > do this just to spite us, the the kernel needs to do *something* when > this happens. They will quickly notice it if there is a problem, so I don't think we need to worry about that. -Andi -- ak@linux.intel.com -- Speaking for myself only.