From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from black.elm.relay.mailchannels.net (black.elm.relay.mailchannels.net [23.83.212.19]) by sourceware.org (Postfix) with ESMTPS id 017BF3857804 for ; Mon, 30 Nov 2020 06:28:21 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 017BF3857804 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=gotplt.org Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=siddhesh@gotplt.org X-Sender-Id: dreamhost|x-authsender|siddhesh@gotplt.org Received: from relay.mailchannels.net (localhost [127.0.0.1]) by relay.mailchannels.net (Postfix) with ESMTP id 615C37015B5; Mon, 30 Nov 2020 06:28:20 +0000 (UTC) Received: from pdx1-sub0-mail-a90.g.dreamhost.com (100-96-22-165.trex.outbound.svc.cluster.local [100.96.22.165]) (Authenticated sender: dreamhost) by relay.mailchannels.net (Postfix) with ESMTPA id C110F701671; Mon, 30 Nov 2020 06:28:19 +0000 (UTC) X-Sender-Id: dreamhost|x-authsender|siddhesh@gotplt.org Received: from pdx1-sub0-mail-a90.g.dreamhost.com (pop.dreamhost.com [64.90.62.162]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384) by 0.0.0.0:2500 (trex/5.18.10); Mon, 30 Nov 2020 06:28:20 +0000 X-MC-Relay: Neutral X-MailChannels-SenderId: dreamhost|x-authsender|siddhesh@gotplt.org X-MailChannels-Auth-Id: dreamhost X-Scare-Quick: 4616c2cb7d5f7150_1606717700097_1955938548 X-MC-Loop-Signature: 1606717700097:3029953321 X-MC-Ingress-Time: 1606717700096 Received: from pdx1-sub0-mail-a90.g.dreamhost.com (localhost [127.0.0.1]) by pdx1-sub0-mail-a90.g.dreamhost.com (Postfix) with ESMTP id 690147F25D; Sun, 29 Nov 2020 22:28:19 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=gotplt.org; h=subject:to :cc:references:from:message-id:date:mime-version:in-reply-to :content-type:content-transfer-encoding; s=gotplt.org; bh=fCTb2E 6np7rTjqsU4geUPDErVek=; b=BKqO2YwR2KyUZGg4L1bmhHzHYodqAlrGksra3Y l9c+HIx3AB8O1hoI6GHdlENU6xEglX5W/SALclIJP8rNT7oegmb3VU255FDnddzq iLiuJYuNcm8mSCvGjSXzcn9hYF/PsqhELIZg3Xt+fqhwbuiFY8DM//UVdwD6/D/i FtWvI= Received: from [192.168.1.111] (unknown [1.186.101.110]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: siddhesh@gotplt.org) by pdx1-sub0-mail-a90.g.dreamhost.com (Postfix) with ESMTPSA id BDE827E5FA; Sun, 29 Nov 2020 22:28:16 -0800 (PST) Subject: Re: [PATCH v3 2/8] elf: Add a tunable to control use of tagged memory To: "H.J. Lu" , Richard Earnshaw Cc: GNU C Library , Richard Earnshaw References: <20201123154236.25809-1-rearnsha@arm.com> <2a2cbd34-8dbc-34af-c5ee-b7d0ef5b48a7@gotplt.org> <26b8b11e-919a-b6e0-ff5f-51e724faffb2@foss.arm.com> <8ddb9604-5a6d-a656-0585-57a1b26c39f6@gotplt.org> <87e8b15f-8c86-4b2c-a5e4-3e70631ea505@gotplt.org> <23a8ad00-a376-48ae-cc6a-2684261146a1@foss.arm.com> <6173c59d-ee67-9499-ac61-c2dd37b56c67@foss.arm.com> <1938dee9-f8e5-ca9a-8f28-efb3ac91bf61@gotplt.org> <23462613-48c0-9fdf-aa89-18c98d9c6656@gotplt.org> <70937aae-cb56-50ad-dd1d-7e6b335ac927@gotplt.org> X-DH-BACKEND: pdx1-sub0-mail-a90 From: Siddhesh Poyarekar Message-ID: <8c33b27c-f088-3e0a-6314-776f8c173415@gotplt.org> Date: Mon, 30 Nov 2020 11:58:11 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=2.2 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, NICE_REPLY_A, RCVD_IN_BARRACUDACENTRAL, RCVD_IN_BL_SPAMCOP_NET, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=no autolearn_force=no version=3.4.2 X-Spam-Level: ** X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 30 Nov 2020 06:28:23 -0000 On 11/28/20 12:07 AM, H.J. Lu wrote: >>> The memory tag implementation should be independent of tunables. >>> Tunables should just turn on and off a few bits in the memory tag >>> implementation. Make the memory tag implementation depend on >>> tunables seems wrong to me. That comment seems to suggest that you'd like to see finer grained control over memory tagging in tunables. Could you elaborate on that? If you're suggesting splitting up or adding more tunables, could you suggest the splits you'd like to see? >> That shouldn't matter. The tunables are documented as not being stable >> and nothing else is exposed to the user; so if we want to change things >> later, there's nothing to stop that. >> > > This is not a good user experience and makes it harder to backport. I think that's only partly true. Backporting changes to the *meaning* of tunables can be hard to backport, but simply flipping the default isn't quite in the same category. Siddhesh