From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751287AbeEDA6a convert rfc822-to-8bit (ORCPT ); Thu, 3 May 2018 20:58:30 -0400 Received: from ozlabs.org ([203.11.71.1]:56505 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751126AbeEDA62 (ORCPT ); Thu, 3 May 2018 20:58:28 -0400 Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au From: Michael Ellerman To: Michal =?utf-8?Q?Such=C3=A1nek?= Cc: linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org, npiggin@gmail.com Subject: Re: [PATCH 4/6] powerpc/64s: Enable barrier_nospec based on firmware settings In-Reply-To: <20180502134128.4a31b0fc@kitsune.suse.cz> References: <20180424041559.32410-1-mpe@ellerman.id.au> <20180424041559.32410-4-mpe@ellerman.id.au> <20180426180258.04e6bee6@kitsune.suse.cz> <87vac7r5px.fsf@concordia.ellerman.id.au> <20180502134128.4a31b0fc@kitsune.suse.cz> Date: Fri, 04 May 2018 10:58:26 +1000 Message-ID: <87bmdw9qz1.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Michal Suchánek writes: > On Tue, 01 May 2018 21:11:06 +1000 > Michael Ellerman wrote: >> Michal Suchánek writes: >> > On Tue, 24 Apr 2018 14:15:57 +1000 >> > Michael Ellerman wrote: >> > >> >> From: Michal Suchanek >> >> >> >> Check what firmware told us and enable/disable the barrier_nospec >> >> as appropriate. >> >> >> >> We err on the side of enabling the barrier, as it's no-op on older >> >> systems, see the comment for more detail. >> >> >> >> Signed-off-by: Michael Ellerman >> ... >> > >> > I am missing the option for the barrier to be disabled by a kernel >> > commandline argument here. >> > >> > It does make sense to add a kernel parameter that is checked on >> > boot to be compatible with other platforms that implement one. >> >> No other platforms have an option to disable variant 1 mitigations, so >> there isn't an existing parameter we can use. > > Right, I was looking at an older implementation which turned off both > v1 and v2 with same parameter. In current kernel the v1 mitigation is > not turned off at all. Ah OK. >> Which is not to say we can't add one, but I wasn't sure if it was >> really worth it. > > The current thinking is that most performance relevant cases are > covered with array_nospec which has little overhead. The less code we > have for this the better ;-) Amen to that :) cheers