From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH v4 24/26] arm64: mte: Introduce early param to disable MTE support Date: Mon, 18 May 2020 12:31:03 +0100 Message-ID: <20200518113103.GA32394@willie-the-truck> References: <20200515171612.1020-1-catalin.marinas@arm.com> <20200515171612.1020-25-catalin.marinas@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail.kernel.org ([198.145.29.99]:57762 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726855AbgERLbJ (ORCPT ); Mon, 18 May 2020 07:31:09 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Vladimir Murzin Cc: Catalin Marinas , linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, Szabolcs Nagy , Andrey Konovalov , Kevin Brodsky , Peter Collingbourne , linux-mm@kvack.org, Vincenzo Frascino , Dave P Martin On Mon, May 18, 2020 at 12:26:30PM +0100, Vladimir Murzin wrote: > On 5/15/20 6:16 PM, Catalin Marinas wrote: > > For performance analysis it may be desirable to disable MTE altogether > > via an early param. Introduce arm64.mte_disable and, if true, filter out > > the sanitised ID_AA64PFR1_EL1.MTE field to avoid exposing the HWCAP to > > user. > > > > Signed-off-by: Catalin Marinas > > Cc: Will Deacon > > --- > > > > Notes: > > New in v4. > > > > Documentation/admin-guide/kernel-parameters.txt | 4 ++++ > > arch/arm64/kernel/cpufeature.c | 11 +++++++++++ > > 2 files changed, 15 insertions(+) > > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > > index f2a93c8679e8..7436e7462b85 100644 > > --- a/Documentation/admin-guide/kernel-parameters.txt > > +++ b/Documentation/admin-guide/kernel-parameters.txt > > @@ -373,6 +373,10 @@ > > arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards > > Format: ,, > > > > + arm64.mte_disable= > > + [ARM64] Disable Linux support for the Memory > > + Tagging Extension (both user and in-kernel). > > + > > Should it really to take parameter (on/off/true/false)? It may lead to expectation > that arm64.mte_disable=false should enable MT and, yes, double negatives make it > look ugly, so if we do need parameter, can it be arm64.mte=on/off/true/false? I don't think "performance analysis" is a good justification for this parameter tbh. We don't tend to add these options for other architectural features, and I don't see why MTE is any different in this regard. Will