From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linutronix.de (193.142.43.55:993) by crypto-ml.lab.linutronix.de with IMAP4-SSL for ; 15 Oct 2019 13:06:38 -0000 Received: from mx1.redhat.com ([209.132.183.28]) by Galois.linutronix.de with esmtps (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1iKMX6-000081-FP for speck@linutronix.de; Tue, 15 Oct 2019 15:06:37 +0200 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 44AE88980F0 for ; Tue, 15 Oct 2019 13:06:30 +0000 (UTC) Received: from treble (ovpn-120-85.rdu2.redhat.com [10.10.120.85]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E14CF6012C for ; Tue, 15 Oct 2019 13:06:29 +0000 (UTC) Date: Tue, 15 Oct 2019 08:06:27 -0500 From: Josh Poimboeuf Subject: [MODERATED] Re: ***UNCHECKED*** Re: [PATCH v5 08/11] TAAv5 8 Message-ID: <20191015130627.7jkhqy2zrtm35ool@treble> References: <20191009131251.GD6616@dhcp22.suse.cz> <20191014210458.GF4957@zn.tnic> <20191015103454.GW317@dhcp22.suse.cz> MIME-Version: 1.0 In-Reply-To: <20191015103454.GW317@dhcp22.suse.cz> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit To: speck@linutronix.de List-ID: On Tue, Oct 15, 2019 at 12:34:54PM +0200, speck for Michal Hocko wrote: > OK, so what about this patch on top of Pawan's series? I have to say I am not > really entirely happy about yet another config option. In principle this > is not much different from the HT where we decided to stay enabled even > though it is vulnerable to side channels. But I do understand that much > more people will notice HT off than TSX off. > > Anyway here is the patch > --- > From 9666e91b63cd6213d362d04289e1bcbbe2050bc3 Mon Sep 17 00:00:00 2001 > From: Michal Hocko > Date: Tue, 15 Oct 2019 11:21:01 +0200 > Subject: [PATCH] x86, tsx: allow to set tsx=auto by a config option > > There is a general consensus that TSX usage is not largely spread while > the history shows there is a non trivial space for side channel attacks > possible. Therefore the tsx is disabled by default even on platforms > that might have a safe implementation of TSX according to the current > knowledge. This is a fair trade off to make. > > There are, however, workloads that really do benefit from using TSX and > updating to a newer kernel with TSX disabled might introduce a > noticeable regressions. This would be especially a problem for Linux > distributions which will provide TAA mitigations. > > Introduce X86_INTEL_ENABLE_SAFE_TSX config option to override the > default tsx=off semantic and make tsx=auto a default which is more > update friendly. > > Suggested-by: Borislav Petkov > Signed-off-by: Michal Hocko Since all (or most?) modern Intel CPUs are vulnerable to TAA, defaulting to tsx=auto would effectively be the same as defaulting to tsx=off, right? How does this help with regressions? -- Josh