From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.7 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 2876F7D2F0 for ; Fri, 23 Aug 2019 16:32:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2436766AbfHWQcx (ORCPT ); Fri, 23 Aug 2019 12:32:53 -0400 Received: from foss.arm.com ([217.140.110.172]:36952 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390061AbfHWQcx (ORCPT ); Fri, 23 Aug 2019 12:32:53 -0400 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 2435328; Fri, 23 Aug 2019 09:32:53 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7280E3F246; Fri, 23 Aug 2019 09:32:51 -0700 (PDT) Date: Fri, 23 Aug 2019 17:32:49 +0100 From: Dave Martin To: Catalin Marinas Cc: linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, Szabolcs Nagy , Andrey Konovalov , Kevin Brodsky , Will Deacon , linux-mm@kvack.org, Andrew Morton , Vincenzo Frascino , Will Deacon , Dave Hansen , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v9 3/3] arm64: Relax Documentation/arm64/tagged-pointers.rst Message-ID: <20190823163247.GG27757@arm.com> References: <20190821164730.47450-1-catalin.marinas@arm.com> <20190821164730.47450-4-catalin.marinas@arm.com> <20190821173352.yqfgaozi7nfhcofg@willie-the-truck> <20190821184649.GD27757@arm.com> <20190822155531.GB55798@arrakis.emea.arm.com> <20190822163723.GF27757@arm.com> <20190823161912.GJ29387@arrakis.emea.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190823161912.GJ29387@arrakis.emea.arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Fri, Aug 23, 2019 at 05:19:13PM +0100, Catalin Marinas wrote: > On Thu, Aug 22, 2019 at 05:37:23PM +0100, Dave P Martin wrote: > > On Thu, Aug 22, 2019 at 04:55:32PM +0100, Catalin Marinas wrote: > > > On Wed, Aug 21, 2019 at 07:46:51PM +0100, Dave P Martin wrote: [...] > > > > sigaltstack() is interesting, since we don't support tagged stacks. > > > > > > We should support tagged SP with the new ABI as they'll be required for > > > MTE. sigaltstack() and clone() are the two syscalls that come to mind > > > here. > > > > > > > Do we keep the ss_sp tag in the kernel, but squash it when delivering > > > > a signal to the alternate stack? > > > > > > We don't seem to be doing any untagging, so we just just use whatever > > > the caller asked for. We may need a small test to confirm. > > > > If we want to support tagged SP, then I guess we shouldn't be squashing > > the tag anywhere. A test for that would be sensible to have. > > I hacked the sas.c kselftest to use a tagged stack and works fine, the > SP register has a tagged address on the signal handler. Cool... [...] > > > > There is no foolproof rule, unless we can rewrite history... > > > > > > I would expect the norm to be the preservation of tags with a few > > > exceptions. The only ones I think where we won't preserve the tags are > > > mmap, mremap, brk (apart from the signal stuff already mentioned in the > > > current tagged-pointers.rst doc). > > > > > > So I can remove this paragraph altogether and add a note in part 3 of > > > the tagged-address-abi.rst document that mmap/mremap/brk do not preserve > > > the tag information. > > > > Deleting text is always a good idea ;) > > I'm going this route ;). [reply deleted] Cheers ---Dave