Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753687AbeAFCwL (ORCPT + 1 other); Fri, 5 Jan 2018 21:52:11 -0500 Received: from mail-it0-f54.google.com ([209.85.214.54]:42669 "EHLO mail-it0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753558AbeAFCwJ (ORCPT ); Fri, 5 Jan 2018 21:52:09 -0500 X-Google-Smtp-Source: ACJfBotaejrvFrX2Kcuj2CdwrbO1Fo2oiHCQ9p+HK9EmrITFfEousVRpHBJ3vRA2fIt1PJhPXlFYjjeqQh6boTalKPE= MIME-Version: 1.0 In-Reply-To: <151520102670.32271.8447983009852138826.stgit@dwillia2-desk3.amr.corp.intel.com> References: <151520099201.32271.4677179499894422956.stgit@dwillia2-desk3.amr.corp.intel.com> <151520102670.32271.8447983009852138826.stgit@dwillia2-desk3.amr.corp.intel.com> From: Linus Torvalds Date: Fri, 5 Jan 2018 18:52:07 -0800 X-Google-Sender-Auth: TGEE9IX_WEASMkpM-emT_Ca-jsY Message-ID: Subject: Re: [PATCH 06/18] x86, barrier: stop speculation for failed access_ok To: Dan Williams Cc: Linux Kernel Mailing List , linux-arch@vger.kernel.org, Andi Kleen , Arnd Bergmann , Greg Kroah-Hartman , Peter Zijlstra , Network Development , "the arch/x86 maintainers" , Ingo Molnar , "H. Peter Anvin" , Thomas Gleixner , Alan Cox Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: On Fri, Jan 5, 2018 at 5:10 PM, Dan Williams wrote: > From: Andi Kleen > > When access_ok fails we should always stop speculating. > Add the required barriers to the x86 access_ok macro. Honestly, this seems completely bogus. The description is pure garbage afaik. The fact is, we have to stop speculating when access_ok() does *not* fail - because that's when we'll actually do the access. And it's that access that needs to be non-speculative. That actually seems to be what the code does (it stops speculation when __range_not_ok() returns false, but access_ok() is !__range_not_ok()). But the explanation is crap, and dangerous. Linus