From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 36D30C433E3 for ; Wed, 22 Jul 2020 10:29:01 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id CF0ED20729 for ; Wed, 22 Jul 2020 10:29:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CF0ED20729 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 48F376B0003; Wed, 22 Jul 2020 06:29:00 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 43EAF6B0005; Wed, 22 Jul 2020 06:29:00 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 32E116B0006; Wed, 22 Jul 2020 06:29:00 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0242.hostedemail.com [216.40.44.242]) by kanga.kvack.org (Postfix) with ESMTP id 1AC816B0003 for ; Wed, 22 Jul 2020 06:29:00 -0400 (EDT) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id B935C8248047 for ; Wed, 22 Jul 2020 10:28:59 +0000 (UTC) X-FDA: 77065338798.16.home59_050d17b26f35 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin16.hostedemail.com (Postfix) with ESMTP id 2259F18535FEA for ; Wed, 22 Jul 2020 10:28:53 +0000 (UTC) X-HE-Tag: home59_050d17b26f35 X-Filterd-Recvd-Size: 2578 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf13.hostedemail.com (Postfix) with ESMTP for ; Wed, 22 Jul 2020 10:28:52 +0000 (UTC) Received: from gaia (unknown [95.146.230.158]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id BA4BF20729; Wed, 22 Jul 2020 10:28:49 +0000 (UTC) Date: Wed, 22 Jul 2020 11:28:47 +0100 From: Catalin Marinas To: Dave Martin Cc: Kevin Brodsky , linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, Szabolcs Nagy , Andrey Konovalov , Peter Collingbourne , linux-mm@kvack.org, Andrew Morton , Vincenzo Frascino , Will Deacon Subject: Re: [PATCH v7 18/29] arm64: mte: Allow user control of the tag check mode via prctl() Message-ID: <20200722102845.GA27540@gaia> References: <20200715170844.30064-1-catalin.marinas@arm.com> <20200715170844.30064-19-catalin.marinas@arm.com> <20200720170050.GJ30452@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200720170050.GJ30452@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Rspamd-Queue-Id: 2259F18535FEA X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Jul 20, 2020 at 06:00:50PM +0100, Dave P Martin wrote: > On Mon, Jul 20, 2020 at 04:30:35PM +0100, Kevin Brodsky wrote: > > On 15/07/2020 18:08, Catalin Marinas wrote: > > >+void mte_thread_switch(struct task_struct *next) > > >+{ > > >+ if (!system_supports_mte()) > > >+ return; > > >+ > > >+ /* avoid expensive SCTLR_EL1 accesses if no change */ > > >+ if (current->thread.sctlr_tcf0 != next->thread.sctlr_tcf0) > > > > I think this could be improved by checking whether `next` is a kernel > > thread, in which case thread.sctlr_tcf0 is 0 but there is no point in > > setting SCTLR_EL1.TCF0, since there should not be any access via TTBR0. > > Out of interest, do we have a nice way of testing for a kernel thread > now? > > I remember fpsimd_thread_switch() used to check for task->mm, but we > seem to have got rid of that at some point. set_mm() can defeat this, > and anyway the heavy lifting for FPSIMD is now deferred until returning > to userspace. I think a better way is (current->flags & PF_KTHREAD). kthread_use_mm() indeed changes current->mm. -- Catalin