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=-2.3 required=3.0 tests=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 E6471C433E0 for ; Tue, 19 May 2020 16:11:04 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id AE3462075F for ; Tue, 19 May 2020 16:11:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AE3462075F 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 4514880007; Tue, 19 May 2020 12:11:04 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 42815900002; Tue, 19 May 2020 12:11:04 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 33DA480007; Tue, 19 May 2020 12:11:04 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0049.hostedemail.com [216.40.44.49]) by kanga.kvack.org (Postfix) with ESMTP id 1A260900002 for ; Tue, 19 May 2020 12:11:04 -0400 (EDT) Received: from smtpin24.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id CBCF49434 for ; Tue, 19 May 2020 16:11:03 +0000 (UTC) X-FDA: 76833957606.24.frogs99_6089b0b3a123c X-HE-Tag: frogs99_6089b0b3a123c X-Filterd-Recvd-Size: 3421 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf42.hostedemail.com (Postfix) with ESMTP for ; Tue, 19 May 2020 16:11:03 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6BCB830E; Tue, 19 May 2020 09:11:02 -0700 (PDT) Received: from gaia (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 60C603F305; Tue, 19 May 2020 09:11:00 -0700 (PDT) Date: Tue, 19 May 2020 17:10:58 +0100 From: Catalin Marinas To: Luis Machado Cc: Dave Martin , linux-arch@vger.kernel.org, Richard Earnshaw , Will Deacon , Omair Javaid , Szabolcs Nagy , Kevin Brodsky , linux-mm@kvack.org, Andrey Konovalov , Vincenzo Frascino , Peter Collingbourne , Alan Hayward , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v3 19/23] arm64: mte: Add PTRACE_{PEEK,POKE}MTETAGS support Message-ID: <20200519161057.GE20313@gaia> References: <20200421142603.3894-1-catalin.marinas@arm.com> <20200421142603.3894-20-catalin.marinas@arm.com> <20200513104849.GC2719@gaia> <3d2621ac-9d08-53ea-6c22-c62532911377@linaro.org> <20200513141147.GD2719@gaia> <20200518164723.GA5031@arm.com> <55fe4d37-23ae-a6b7-8db1-884aaf4a9b9c@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55fe4d37-23ae-a6b7-8db1-884aaf4a9b9c@linaro.org> User-Agent: Mutt/1.10.1 (2018-07-13) 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, May 18, 2020 at 02:12:24PM -0300, Luis Machado wrote: > On 5/18/20 1:47 PM, Dave Martin wrote: > > Wrinkle: just because MTE is "off", pages might still be mapped with > > PROT_MTE and have arbitrary tags set on them, and the debugger perhaps > > needs a way to know that. Currently grubbing around in /proc is the > > only way to discover that. Dunno whether it matters. > > That is the sort of thing that may confused the debugger. > > If MTE is "off" (and thus the debugger doesn't need to validate tags), then > the pages mapped with PROT_MTE that show up in /proc//smaps should be > ignored? There is no such thing as global MTE "off". If the HWCAP is present, a user program can map an address with PROT_MTE and access tags. Maybe it uses it for extra storage, you never know, doesn't have to be heap allocation related. > I'm looking for a precise way to tell if MTE is being used or not for a > particular process/thread. This, in turn, will tell debuggers when to look > for PROT_MTE mappings in /proc//smaps and when to validate tagged > addresses. > > So far my assumption was that MTE will always be "on" when HWCAP2_MTE is > present. So having HWCAP2_MTE means we have the NT_ARM_MTE regset and that > PROT_MTE pages have to be checked. Yes. I haven't figured out what to put in the regset yet, most likely the prctl value as it has other software-only controls like the tagged address ABI. -- Catalin