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=-5.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,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 D71C2C433DF for ; Sat, 22 Aug 2020 11:33:01 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 9FBA820738 for ; Sat, 22 Aug 2020 11:33:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="fxAj/3Ri" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9FBA820738 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com 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=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject: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=fVfISv8jRrIdoBXgucrI6fTIDALIos8Ihk1d1iYEMhA=; b=fxAj/3RifnwB0B/MUmpxuMMlC oouH8L3FJMWes1zYhvFGo6CpOeq8whlsDfPSp9ULssgrfoyeVG+HjDt3l/LJonNXS8qy1CpRN+hig qw6K7KXyK67+ajHQGt8vGk46Vvx8mpor84TIAaE6bhc9KJrnIpKlMuFMvyzGIUgUFPwPMz3YVvDyQ Sq0Ip46AoxfXIH73Qq+me9LaauNcNjuh2leSvHBm5FPn1Kw4Aho2qa4vZ9uRAYIRgwUN1z3CWUK2M eiliIhk10ZIX4DsrsuLor90ZT3tCjMAxyEKDUIIG+jSYxiq7yB96L2Zw96SMhFKREsqq9kKrUrdwu b6YVJXS9w==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1k9RkR-0006Yh-SH; Sat, 22 Aug 2020 11:31:47 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1k9RkO-0006Y9-4W for linux-arm-kernel@lists.infradead.org; Sat, 22 Aug 2020 11:31:44 +0000 Received: from gaia (unknown [95.146.230.145]) (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 CE41820738; Sat, 22 Aug 2020 11:31:40 +0000 (UTC) Date: Sat, 22 Aug 2020 12:31:38 +0100 From: Catalin Marinas To: Paul Eggert Subject: Re: [PATCH v7 29/29] arm64: mte: Add Memory Tagging Extension documentation Message-ID: <20200822113138.GC16635@gaia> References: <20200728145350.GR7127@arm.com> <20200728195957.GA31698@gaia> <20200803124309.GC14398@arm.com> <20200807151906.GM6750@gaia> <20200810141309.GK14398@arm.com> <20200811172038.GB1429@gaia> <20200812124520.GP14398@arm.com> <20200819095453.GA86@DESKTOP-O1885NU.localdomain> <20200820164313.GL29343@arm.com> <80a8937b-6e48-44ce-221c-84c6d27b211d@cs.ucla.edu> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <80a8937b-6e48-44ce-221c-84c6d27b211d@cs.ucla.edu> 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-20200822_073144_265413_09AB194F X-CRM114-Status: GOOD ( 18.66 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, Richard Earnshaw , Vincenzo Frascino , libc-alpha@sourceware.org, Szabolcs Nagy , Andrey Konovalov , Kevin Brodsky , Peter Collingbourne , linux-mm@kvack.org, Matthew Malcomson , Andrew Morton , nd@arm.com, Will Deacon , Dave Martin , linux-arm-kernel@lists.infradead.org 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 Thu, Aug 20, 2020 at 10:27:43AM -0700, Paul Eggert wrote: > On 8/20/20 9:43 AM, Szabolcs Nagy wrote: > > the compat issue with this is existing code > > using pointer top bits which i assume faults > > when dereferenced with the mte checks enabled. > > (although this should be very rare since > > top byte ignore on deref is aarch64 specific.) > > Does anyone know of significant aarch64-specific application code that > depends on top byte ignore? I would think it's so rare (nonexistent?) as to > not be worth worrying about. Apart from the LLVM hwasan feature, I'm not aware of code relying on the top byte ignore. There were discussions in the past to use it with some JITs but I'm not sure they ever materialised. I think the Mozilla JS engine uses (used?) additional bits on top of a pointer but they are masked out before the access. > Even in the bad old days when Emacs used pointer top bits for typechecking, > it carefully removed those bits before dereferencing. Any other > reasonably-portable application would have to do the same of course. I agree. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel