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=-2.2 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MSGID_FROM_MTA_HEADER, SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,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 3DE07C433E0 for ; Fri, 15 May 2020 12:53:59 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B766920759 for ; Fri, 15 May 2020 12:53:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=armh.onmicrosoft.com header.i=@armh.onmicrosoft.com header.b="vOrhozJL"; dkim=pass (1024-bit key) header.d=armh.onmicrosoft.com header.i=@armh.onmicrosoft.com header.b="vOrhozJL" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B766920759 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 2E06F90000C; Fri, 15 May 2020 08:53:58 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 26A468E0005; Fri, 15 May 2020 08:53:58 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0E4D290000C; Fri, 15 May 2020 08:53:58 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0229.hostedemail.com [216.40.44.229]) by kanga.kvack.org (Postfix) with ESMTP id E403B8E0005 for ; Fri, 15 May 2020 08:53:57 -0400 (EDT) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id A77691F08 for ; Fri, 15 May 2020 12:53:57 +0000 (UTC) X-FDA: 76818945714.17.kick94_227489f75720f X-HE-Tag: kick94_227489f75720f X-Filterd-Recvd-Size: 12530 Received: from EUR05-DB8-obe.outbound.protection.outlook.com (mail-db8eur05on2078.outbound.protection.outlook.com [40.107.20.78]) by imf19.hostedemail.com (Postfix) with ESMTP for ; Fri, 15 May 2020 12:53:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=armh.onmicrosoft.com; s=selector2-armh-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=stnUWRg+rnNrzWma3EVekRGQliDkle5EU2+JAanlOO0=; b=vOrhozJLUjbB8OP5QYYL/Axc7SoArGrEMy+a54cCbfwd02LV7JpVI+JkW/HfwM4noOoMpVyBuSS/vhLtNA+Jqpp8yB4b3OvYt0pw4O6Q9/SCvAk8fcu+TMxAI86CQg5DqLVyvOJT7ME9L45f71pqkkEdX1L10RyjMmk44FJA/50= Received: from AM6P191CA0020.EURP191.PROD.OUTLOOK.COM (2603:10a6:209:8b::33) by AM0PR08MB4017.eurprd08.prod.outlook.com (2603:10a6:208:12a::14) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3000.24; Fri, 15 May 2020 12:53:53 +0000 Received: from AM5EUR03FT041.eop-EUR03.prod.protection.outlook.com (2603:10a6:209:8b:cafe::97) by AM6P191CA0020.outlook.office365.com (2603:10a6:209:8b::33) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3000.25 via Frontend Transport; Fri, 15 May 2020 12:53:53 +0000 Authentication-Results: spf=pass (sender IP is 63.35.35.123) smtp.mailfrom=arm.com; kvack.org; dkim=pass (signature was verified) header.d=armh.onmicrosoft.com;kvack.org; dmarc=bestguesspass action=none header.from=arm.com; Received-SPF: Pass (protection.outlook.com: domain of arm.com designates 63.35.35.123 as permitted sender) receiver=protection.outlook.com; client-ip=63.35.35.123; helo=64aa7808-outbound-1.mta.getcheckrecipient.com; Received: from 64aa7808-outbound-1.mta.getcheckrecipient.com (63.35.35.123) by AM5EUR03FT041.mail.protection.outlook.com (10.152.17.186) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3000.19 via Frontend Transport; Fri, 15 May 2020 12:53:52 +0000 Received: ("Tessian outbound 11763d234d54:v54"); Fri, 15 May 2020 12:53:52 +0000 X-CheckRecipientChecked: true X-CR-MTA-CID: bd20fb0878f121e3 X-CR-MTA-TID: 64aa7808 Received: from 135ebd315029.2 by 64aa7808-outbound-1.mta.getcheckrecipient.com id 85374A5A-381D-4505-90F0-20AD9B96B8E1.1; Fri, 15 May 2020 12:53:47 +0000 Received: from EUR05-AM6-obe.outbound.protection.outlook.com by 64aa7808-outbound-1.mta.getcheckrecipient.com with ESMTPS id 135ebd315029.2 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384); Fri, 15 May 2020 12:53:47 +0000 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=jTnxrjxFbDjHXO7hiXEANI1RPrc3B6nmagfB6EWtGjlKrazgxKD7Kp6PKx09PtC7CKVlWUZKoWwsfbM4CmKE6JKLIx9Q11+hlERLcgIGXiDNyT4ekrS5QOMN1tfOkoOFPJlfpn8cC1wmYi+tQoqlnUX47UGqACqEWIWPJhcMjhMb3wW+mjdfP0TKjZp8BnXsl9KkmctOj60rs33n22JZ+6bI1c4Lz85DtRAhF85EsLXH+sUmH2j7WffF/2yk11v46LRhEDEC1koMpxIQeW+/xqPMqg2zGYtS4D87NKnsX+1xLByffCGzkpZXxKNcB2Lg38KRS0vvg5K4sG32HIL22Q== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=stnUWRg+rnNrzWma3EVekRGQliDkle5EU2+JAanlOO0=; b=DiX4/Ky7LCJQ17pmeXuH6Mr+48G8ni8tAReQTvB+lpasVDz1Xmlu2HKYfYoO9S/eE7v8CHtgwlqazrPB2z1RR59EQ/GzNstkIjyUYRY5dhUeQV8nFOl7dgB9x35gwl9UGHfgJ9FjtjTM4Jm+y2Va/gfAQXxT+fwkikpASYQwSKqWo78PPT7VkPulIERahqVYt2E1WaUsdYegzceis1nNZMZnYurugBoI2KbYh4FYYBl5x0dLMJF41siQpCMEWdwe1yeulzYoXzf1YQBfTc9+RrGjRp9kqyZJF6hOAcmdl1g51imqXw8C8Tt1C05WbMo4EXV/MdHxxJ+y9DEbCzHgSQ== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=arm.com; dmarc=pass action=none header.from=arm.com; dkim=pass header.d=arm.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=armh.onmicrosoft.com; s=selector2-armh-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=stnUWRg+rnNrzWma3EVekRGQliDkle5EU2+JAanlOO0=; b=vOrhozJLUjbB8OP5QYYL/Axc7SoArGrEMy+a54cCbfwd02LV7JpVI+JkW/HfwM4noOoMpVyBuSS/vhLtNA+Jqpp8yB4b3OvYt0pw4O6Q9/SCvAk8fcu+TMxAI86CQg5DqLVyvOJT7ME9L45f71pqkkEdX1L10RyjMmk44FJA/50= Authentication-Results-Original: arm.com; dkim=none (message not signed) header.d=none;arm.com; dmarc=none action=none header.from=arm.com; Received: from AM6PR08MB3047.eurprd08.prod.outlook.com (2603:10a6:209:4c::23) by AM6PR08MB3862.eurprd08.prod.outlook.com (2603:10a6:20b:8c::28) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3000.25; Fri, 15 May 2020 12:53:44 +0000 Received: from AM6PR08MB3047.eurprd08.prod.outlook.com ([fe80::49fd:6ded:4da7:8862]) by AM6PR08MB3047.eurprd08.prod.outlook.com ([fe80::49fd:6ded:4da7:8862%7]) with mapi id 15.20.2979.033; Fri, 15 May 2020 12:53:44 +0000 Date: Fri, 15 May 2020 13:53:32 +0100 From: Szabolcs Nagy To: Catalin Marinas Cc: Dave Martin , linux-arch@vger.kernel.org, Richard Earnshaw , Andrey Konovalov , Kevin Brodsky , Peter Collingbourne , linux-mm@kvack.org, Vincenzo Frascino , Will Deacon , linux-arm-kernel@lists.infradead.org, nd@arm.com Subject: Re: [PATCH v3 23/23] arm64: mte: Add Memory Tagging Extension documentation Message-ID: <20200515125332.GF27289@arm.com> References: <20200430162316.GJ2717@gaia> <20200504164617.GK30377@arm.com> <20200511164018.GC19176@gaia> <20200513154845.GT21779@arm.com> <20200514113722.GA1907@gaia> <20200515103839.GA22393@gaia> <20200515111359.GC27289@arm.com> <20200515112740.GB22393@gaia> <20200515120433.GE27289@arm.com> <20200515121343.GC22393@gaia> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200515121343.GC22393@gaia> User-Agent: Mutt/1.9.4 (2018-02-28) X-ClientProxiedBy: SN6PR08CA0021.namprd08.prod.outlook.com (2603:10b6:805:66::34) To AM6PR08MB3047.eurprd08.prod.outlook.com (2603:10a6:209:4c::23) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from arm.com (217.140.106.55) by SN6PR08CA0021.namprd08.prod.outlook.com (2603:10b6:805:66::34) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3000.20 via Frontend Transport; Fri, 15 May 2020 12:53:39 +0000 X-Originating-IP: [217.140.106.55] X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-HT: Tenant X-MS-Office365-Filtering-Correlation-Id: ad586766-8fbb-409c-e37f-08d7f8cf0569 X-MS-TrafficTypeDiagnostic: AM6PR08MB3862:|AM0PR08MB4017: X-MS-Exchange-Transport-Forked: True X-Microsoft-Antispam-PRVS: x-checkrecipientrouted: true NoDisclaimer: true X-MS-Oob-TLC-OOBClassifiers: OLM:10000;OLM:10000; X-Forefront-PRVS: 04041A2886 X-MS-Exchange-SenderADCheck: 1 X-Microsoft-Antispam-Untrusted: BCL:0; X-Microsoft-Antispam-Message-Info-Original: hLzO3fSMBPbkP8zlp0v4LdsUj4l2Y7AZcDdRIi5ln16z7ovj07LSh2yhEuAw98XNDbiR4KXNI/s9zBELVNmNqp9EpKDxXtbNgnZB4k0opLLxgDy872BXXHpVHgk1r7tZAqQJWwqozG8stHGZlri5V5YgB5VHv8eZYsFjJNfWtHAMcH2wXpeIHIX3XHUTSWWuoSNpzHzj0ZFvQhqA6qI4SD6FwWZ5JnFSC0rXXAS9kJ2drhD9rRsPn8GBgRkqyKGKENnqHgP3RcdIOWdZXKJDtOtyuNWzHXU/mk4h7ibIah4cBX1tCs9F4uwfQxwQlYF2V2m/p9YIe8wRE58gjDcA4gzyhO3toI2Nm0ZwUcW6/3PS3jftiUSIpbELhGTzNSGFAr4Wg9JNfgemrQtk7+DFRwHhl0OZrBKN/ieNg6/ciNWf1goDMJGeIDwy5k+bLiok X-Forefront-Antispam-Report-Untrusted: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:AM6PR08MB3047.eurprd08.prod.outlook.com;PTR:;CAT:NONE;SFTY:;SFS:(4636009)(136003)(376002)(346002)(366004)(39860400002)(396003)(6636002)(478600001)(66946007)(6666004)(54906003)(26005)(66476007)(186003)(316002)(66556008)(2906002)(2616005)(44832011)(16526019)(956004)(8886007)(6862004)(55016002)(4326008)(36756003)(8676002)(5660300002)(8936002)(86362001)(1076003)(37006003)(33656002)(52116002)(7696005);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM6PR08MB3862 Original-Authentication-Results: arm.com; dkim=none (message not signed) header.d=none;arm.com; dmarc=none action=none header.from=arm.com; X-EOPAttributedMessage: 0 X-MS-Exchange-Transport-CrossTenantHeadersStripped: AM5EUR03FT041.eop-EUR03.prod.protection.outlook.com X-Forefront-Antispam-Report: CIP:63.35.35.123;CTRY:IE;LANG:en;SCL:1;SRV:;IPV:CAL;SFV:NSPM;H:64aa7808-outbound-1.mta.getcheckrecipient.com;PTR:ec2-63-35-35-123.eu-west-1.compute.amazonaws.com;CAT:NONE;SFTY:;SFS:(4636009)(136003)(39860400002)(396003)(346002)(376002)(46966005)(47076004)(2906002)(36906005)(6666004)(1076003)(8886007)(4326008)(316002)(5660300002)(6862004)(356005)(82740400003)(6636002)(81166007)(36756003)(54906003)(37006003)(82310400002)(7696005)(33656002)(336012)(44832011)(86362001)(70206006)(478600001)(2616005)(26005)(956004)(186003)(16526019)(55016002)(70586007)(8936002)(8676002);DIR:OUT;SFP:1101; X-MS-Office365-Filtering-Correlation-Id-Prvs: 25cafa1f-93e1-42ed-c2eb-08d7f8cf0027 X-Forefront-PRVS: 04041A2886 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 15 May 2020 12:53:52.8399 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: ad586766-8fbb-409c-e37f-08d7f8cf0569 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[63.35.35.123];Helo=[64aa7808-outbound-1.mta.getcheckrecipient.com] X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM0PR08MB4017 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: The 05/15/2020 13:13, Catalin Marinas wrote: > On Fri, May 15, 2020 at 01:04:33PM +0100, Szabolcs Nagy wrote: > > The 05/15/2020 12:27, Catalin Marinas wrote: > > > Thanks Szabolcs. While we are at this, no-one so far asked for the > > > GCR_EL1.RRND to be exposed to user (and this implies RGSR_EL1.SEED). > > > Since RRND=1 guarantees a distribution "no worse" than that of RRND=0, I > > > thought there isn't much point in exposing this configuration to the > > > user. The only advantage of RRND=0 I see is that the kernel can change > > > > it seems RRND=1 is the impl specific algorithm. > > Yes, that's the implementation specific algorithm which shouldn't be > worse than the standard one. > > > > the seed randomly but, with only 4 bits per tag, it really doesn't > > > matter much. > > > > > > Anyway, mentioning it here in case anyone is surprised later about the > > > lack of RRND configurability. > > > > i'm not familiar with how irg works. > > It generates a random tag based on some algorithm. > > > is the seed per process state that's set up at process startup in some > > way? or shared (and thus effectively irg is non-deterministic in > > userspace)? > > The seed is only relevant if the standard algorithm is used (RRND=0). i wanted to understand if we can get deterministic irg behaviour in user space (which may be useful for debugging to get reproducible tag failures). i guess if no control is exposed that means non- deterministic irg. i think this is fine.