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=-5.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 E13A4C2B9F4 for ; Mon, 28 Jun 2021 10:20:09 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id ADA6461C6C for ; Mon, 28 Jun 2021 10:20:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org ADA6461C6C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=8dpuoeHaYoG1UIDJbgCH+M3nqhy/YAgY6t1kx2Nbsbw=; b=TQ+ElCLfuGNPBy fdYlGJP5wDbGG7BoTLVJI6bCbgT6UUF+GSwvM7Z/tUdfnwGvP9AynhcfRXTupTItTyK28zCJ2tTEf Y/yUcMihPK7G8UXvD+FyUEc6KaBNanyy+4ltrwPVJEI+JDWFi4srK+QKqtic03PYBRMibCSfvdsbW 1uOjK66X4mSXt2HMK9B1Xs180WIP7qb3N8/0y7C0O9NmNIkFkNLuaLhO+UA5scz0CjQerELkufT7z Ir446sEZKHFQDUViOP+TtgR3mppHrhwtTEHnGqxth5ufVtFC9jb9uxRPnOWFL8JyU4LzToYpZjIqP 9pzo5CLm7MTTz2xUncYA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1lxoL7-007bUo-Kv; Mon, 28 Jun 2021 10:18:05 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1lxoL4-007bU7-61 for linux-arm-kernel@lists.infradead.org; Mon, 28 Jun 2021 10:18:03 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id 79AB561C6A; Mon, 28 Jun 2021 10:18:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1624875481; bh=jExpMEEsbLYZtRU90t4PqHY/gE+UfwIf4Wl8ZwYtcW8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Prs7dPwHo0CiO4ViS2Cd/DLPbs5BJvM0GqeHoxtc1roa3BWLsKLVmD/5+Kg4y1lYh EUNg2MvKMieJ08mRJYWTtE/MUSf1LRdFyPjccfu9uNu7qy1Hm7s91Swsu826qpMbvp J/c1xLMutEDNaG+x4WZYtiabrNDLW0HzRgaZ+vygvsMsbkY/9A75+DXAwDYJ+ax/w1 TLCRYzL47GvVRqjUKYyCHCCp+IAnCwM9zeAkdIy6+ZzUzqy/7kynkQpHzCrSud8jm4 Z93KURR3pNoVSDnQ65gcZsfLeIWGZtX0Cyo8GuZ7rP8ST/SOlM3/RWXZ2x4qPCULFo kgscU/mqysLug== Date: Mon, 28 Jun 2021 11:17:57 +0100 From: Will Deacon To: Szabolcs Nagy Cc: Catalin Marinas , Peter Collingbourne , Vincenzo Frascino , Evgenii Stepanov , Linux ARM , Tejas Belagod Subject: Re: [PATCH v5] arm64: mte: allow async MTE to be upgraded to sync on a per-CPU basis Message-ID: <20210628101756.GB5503@willie-the-truck> References: <20210621151858.GC11552@arm.com> <20210621173902.GA29713@willie-the-truck> <20210621185036.GD11552@arm.com> <20210623085530.GF13058@arm.com> <20210624165228.GB25097@arm.com> <20210625092253.GJ13058@arm.com> <20210625120137.GC20835@arm.com> <20210625123959.GB3170@willie-the-truck> <20210625141438.GK13058@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210625141438.GK13058@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210628_031802_300848_6C78DBDF X-CRM114-Status: GOOD ( 38.66 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Jun 25, 2021 at 03:14:40PM +0100, Szabolcs Nagy wrote: > The 06/25/2021 13:39, Will Deacon wrote: > > On Fri, Jun 25, 2021 at 01:01:37PM +0100, Catalin Marinas wrote: > > > Thanks, that's useful. I guess since the _MTAG_ENABLE tunable is not > > > ABI, the user app can't rely on what the glibc has configured. Arguably, > > > since it's driven from outside the application (env), we could say the > > > same for sysfs, though for the glibc case, the user app is still be able > > > to override it before the first thread is created (or per-thread). I > > > assume glibc only issues the prctl() once, not for every new thread. > > note: in the end the tunable is like > > GLIBC_TUNABLES=glibc.mem.tagging=3 ./exe > > not _MTAG_ENABLE. > > and yes the setting comes from outside and glibc > calls prctl once. > > > > So we can document that the mode requested by the app is an indication, > > > the system may change it to another value (and back-port documentation > > > to 5.10). If we get a request from developers to honour a specific mode, > > > we can add a new PR_MTE_TCF_EXACT bit or something but it's not > > > essential we do it now. > > > > > > So if we allow the kernel to change the user requested mode (via sysfs), > > > I think we still have two more issues to clarify: > > > > > > 1. Do we allow only "upgrade" (for some meaning of this) or sysfs can > > > downgrade to a less strict mode. I'd go for upgrade here to a > > > stricter check as in Peter's patch. > > > > > > 2. Should the sysfs upgrade the PR_MTE_TCF_NONE? _MTAG_ENABLE does that, > > > so I'd say yes. > > > > > > Any other thoughts are welcome. > > > > As I mentioned before, I think the sysfs interface should offer: > > > > "task" : Honour whatever the task has asked for (default) > > "async" : Force async on this CPU > > "sync" : Force sync on this CPU > > > > I don't think we should upgrade PR_MTE_TCF_NONE unless we also have a "none" > > option in here. I originally suggested that, but in hindsight it feels like > > a bad idea because a task could SIGILL on migration. So what we're saying is > > that PR_MTE_TCF_SYNC and PR_MTE_TCF_ASYNC will always enable MTE on success, > > but the reporting mode is a hint. > > > > I don't think upgrade/downgrade makes a lot of sense given that the sysfs > > controls can be changed at any point in time. It should just be an override. > > > > This means that we can force async for CPUs where sync mode is horribly > > slow, whilst honouring the task's request on CPUs which are better > > implemented. > > i think a user should be able to ask for sync check > mode for a process and get an error if that's not > possible. Hmm. The question then is what do we do if the sysfs override is changed after the application has started running? Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel