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=-3.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED 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 25179C433E6 for ; Mon, 11 Jan 2021 19:02:50 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 9600522795 for ; Mon, 11 Jan 2021 19:02:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9600522795 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.65344.115758 (Exim 4.92) (envelope-from ) id 1kz2Sa-0006gc-P9; Mon, 11 Jan 2021 19:02:36 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 65344.115758; Mon, 11 Jan 2021 19:02:36 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kz2Sa-0006gV-LD; Mon, 11 Jan 2021 19:02:36 +0000 Received: by outflank-mailman (input) for mailman id 65344; Mon, 11 Jan 2021 19:02:35 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kz2SZ-0006gQ-QA for xen-devel@lists.xenproject.org; Mon, 11 Jan 2021 19:02:35 +0000 Received: from EUR03-DB5-obe.outbound.protection.outlook.com (unknown [40.107.4.52]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id f99ec949-aa35-413c-adb6-2341a1df69c7; Mon, 11 Jan 2021 19:02:33 +0000 (UTC) Received: from DB8PR06CA0014.eurprd06.prod.outlook.com (2603:10a6:10:100::27) by VI1PR08MB3968.eurprd08.prod.outlook.com (2603:10a6:803:e5::14) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3742.6; Mon, 11 Jan 2021 19:02:31 +0000 Received: from DB5EUR03FT032.eop-EUR03.prod.protection.outlook.com (2603:10a6:10:100:cafe::db) by DB8PR06CA0014.outlook.office365.com (2603:10a6:10:100::27) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3742.6 via Frontend Transport; Mon, 11 Jan 2021 19:02:30 +0000 Received: from 64aa7808-outbound-1.mta.getcheckrecipient.com (63.35.35.123) by DB5EUR03FT032.mail.protection.outlook.com (10.152.20.162) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3742.6 via Frontend Transport; Mon, 11 Jan 2021 19:02:30 +0000 Received: ("Tessian outbound 2b57fdd78668:v71"); Mon, 11 Jan 2021 19:02:30 +0000 Received: from 01d46b7c073c.2 by 64aa7808-outbound-1.mta.getcheckrecipient.com id 821F418F-765D-4024-B744-8E8DDC39DDB7.1; Mon, 11 Jan 2021 19:02:25 +0000 Received: from EUR05-DB8-obe.outbound.protection.outlook.com by 64aa7808-outbound-1.mta.getcheckrecipient.com with ESMTPS id 01d46b7c073c.2 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384); Mon, 11 Jan 2021 19:02:25 +0000 Received: from VE1PR08MB5696.eurprd08.prod.outlook.com (2603:10a6:800:1ae::15) by VI1PR08MB3471.eurprd08.prod.outlook.com (2603:10a6:803:7d::22) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3742.6; Mon, 11 Jan 2021 19:02:22 +0000 Received: from VE1PR08MB5696.eurprd08.prod.outlook.com ([fe80::c8bf:1301:3373:94a6]) by VE1PR08MB5696.eurprd08.prod.outlook.com ([fe80::c8bf:1301:3373:94a6%5]) with mapi id 15.20.3742.012; Mon, 11 Jan 2021 19:02:22 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: f99ec949-aa35-413c-adb6-2341a1df69c7 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=7xzt0osNr+WBVnFNzSOloMmM4TStk3mixaVvrOwFjpY=; b=9ZNlCr4no7/fy6WNtZY1pRQnsqDdy9S6bqdVj9zhkaCnGTege94To6xP5wgE98hcnw/TU5yY5Je789wz8sir3Gj60t3n1Slmb8KEku5XK3CRjFRpY7+xhj1hZ1auF2GbUbDBRoYvys2SNwOe9XwrvLMLSemKoOYnTxL7JypvVAc= X-MS-Exchange-Authentication-Results: spf=pass (sender IP is 63.35.35.123) smtp.mailfrom=arm.com; lists.xenproject.org; dkim=pass (signature was verified) header.d=armh.onmicrosoft.com;lists.xenproject.org; dmarc=pass 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; X-CheckRecipientChecked: true X-CR-MTA-CID: 1f95e82f7d98739c X-CR-MTA-TID: 64aa7808 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=Ki8XZ8Rv0nNjwZx1zBrkFp33S/172ZzX9Cl0UkI4Ot8yqa+kZzp+ZAj/vKpbsYyoO5T3XRMvjVosFtvatIWGR+PKQuGveiIcMMeRbh3z8CeouSU5prAPvFLjY5kCTHGQcokxPtjd7MtbSgavkIf43QOnEDToicjUco7VMnXHLO+hiA9dwPppZzbiFlwW6QnbpV5IKOl0XRLvNSMEFeZVkIjwzxFm5k5gaPsOjChERwq3eK97oCOLAoKi8+KRfV86wcxRISPptW9wYipCNzzXy5RHrBxzHvo/PIQNO7RphLqg7d+fpMP/hYMAH4Cfl9cWLE74yREG/N04hUoXPHExKw== 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=7xzt0osNr+WBVnFNzSOloMmM4TStk3mixaVvrOwFjpY=; b=UKRuN36k1kdVclOUzB7g0Hh+84hnuEcaH/eqvYQSziGeaPyctb8dch9ohZCZTelx339KZTW+MvkzlYS1GOrqqh7eXm4pw/5OBaD9cpE9W/ybyiIyZEAAcWbwkF3V9xqTAM4IRfk1e4PV84lSXIBYDmyMTx9uLGZWLOhVZnefDwGNMiAcmXtqUQYUJSqbbgDWCuQ6OSw2gKdoM5jRBNdn/dqgvfp9r3lEpouwAgikjIW3lBJwZ9OaqSSWJHUOZE/9qR1Qi6bQWtCm1QM4JlY+S2Y6LMaeIRB8yJAcq+b6h9hiwT560mr10UrmlZBYQlP0hy0qel+RahhT4cT3uAx97Q== 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=7xzt0osNr+WBVnFNzSOloMmM4TStk3mixaVvrOwFjpY=; b=9ZNlCr4no7/fy6WNtZY1pRQnsqDdy9S6bqdVj9zhkaCnGTege94To6xP5wgE98hcnw/TU5yY5Je789wz8sir3Gj60t3n1Slmb8KEku5XK3CRjFRpY7+xhj1hZ1auF2GbUbDBRoYvys2SNwOe9XwrvLMLSemKoOYnTxL7JypvVAc= From: Bertrand Marquis To: Julien Grall CC: Jan Beulich , Stefano Stabellini , "Volodymyr_Babchuk@epam.com" , Stefano Stabellini , "xen-devel@lists.xenproject.org" , Andre Przywara Subject: Re: [PATCH v2] xen/arm: do not read MVFR2 when is not defined Thread-Topic: [PATCH v2] xen/arm: do not read MVFR2 when is not defined Thread-Index: AQHW5fO/cBZB5l3jZkmpNH6hbDKrc6oiIY2AgAAasgCAAIUfgIAACBWAgAADOgA= Date: Mon, 11 Jan 2021 19:02:22 +0000 Message-ID: <9A54F469-6A90-46C8-8BC4-673F469240E7@arm.com> References: <20210108192243.25889-1-sstabellini@kernel.org> <7311f402-dd5d-7484-345a-ef62071adb58@xen.org> In-Reply-To: <7311f402-dd5d-7484-345a-ef62071adb58@xen.org> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: Apple Mail (2.3608.120.23.2.4) Authentication-Results-Original: xen.org; dkim=none (message not signed) header.d=none;xen.org; dmarc=none action=none header.from=arm.com; x-originating-ip: [217.140.99.251] x-ms-publictraffictype: Email X-MS-Office365-Filtering-HT: Tenant X-MS-Office365-Filtering-Correlation-Id: c816297d-27ba-4dfd-5775-08d8b663723b x-ms-traffictypediagnostic: VI1PR08MB3471:|VI1PR08MB3968: 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-MS-Exchange-SenderADCheck: 1 X-Microsoft-Antispam-Untrusted: BCL:0; X-Microsoft-Antispam-Message-Info-Original: 9WvHIVw5yB0B680KOsThG+v6/eZ8jq93XIPqbi1RncOA6iZuxnGslPItuWmH/P4/c8t/HGYQYEzQukbC3RY1J29xznZf7UBrNX0nCsOpLqA166C5t94rIjzvNvfHscraLezb4iOgoutM4g914UG0ZckjiP9iyD6q6CF8trv9VTnvu2nOZuUN6+OJ/lilYoOXolN5/uCMA5IW2iPv98BlRNX3448w0ugsMjbqujmtrJwNE6NwZOM32kuKhNHC3Vzj8RyzqbgScaZw8Pf4NaJswPoVeG5jqR2v1zhrrCYCIIq8GSuGsu2sNGqA5+N0S+gIawTK99Mjus1l2/uenbrIaMu29tepemleOrCDzIDi06fnuaomutHdKHWdXYJhdZ+zQvaB0gqG4O05dsUCojC/200JCjNVH1JN9hVwzEzhJa5fHJZkde24o6FAkuz7tp/A X-Forefront-Antispam-Report-Untrusted: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:VE1PR08MB5696.eurprd08.prod.outlook.com;PTR:;CAT:NONE;SFS:(4636009)(396003)(376002)(346002)(39830400003)(366004)(136003)(64756008)(6512007)(83380400001)(66446008)(4326008)(8936002)(54906003)(36756003)(66946007)(66556008)(316002)(71200400001)(478600001)(6916009)(76116006)(91956017)(86362001)(8676002)(2906002)(5660300002)(6486002)(26005)(186003)(6506007)(33656002)(53546011)(2616005)(66476007)(45980500001);DIR:OUT;SFP:1101; x-ms-exchange-antispam-messagedata: =?us-ascii?Q?nOYcZBQzIi7LX9hG3ySrTJ7cwy12VF9PlUhwzj5lXQDNJ03fE1mCV47/Qc6R?= =?us-ascii?Q?il0jL3dqu2DgXJmDN8onG8/8oEU78orAMJYdT2JDglj3jVGR6230Xa0wHdKA?= =?us-ascii?Q?LSal92nfJvJgbvME6YUc21qCAx6a8MWfGsCcqtGhJfdXeVKRX+ML8PKh39X6?= =?us-ascii?Q?saaU0yjUqyRGp4GmK1Bvs6Qd76JPayjQkEeN/Ney8JM2SVYym28WlIuPeq87?= =?us-ascii?Q?didSytVdbgdXX/dSJRFA7CJt1/cFuTBCZRqfS+vaQsSZLsohhfzz5NMXD5Dk?= =?us-ascii?Q?rfML25CKNGa/xCccSJrRG6Nji5vlNjWjnpbKO1W1dY6+1OTD9r3IuV+QU5YC?= =?us-ascii?Q?PjtF+LmsH2ie0r8MpIqZzTy1Pj4LfTo/wRTnt8ELhFtDSEama2QLu9SJjjkH?= =?us-ascii?Q?olys+N627dLGGHbcR8WJ6MhyQ2i7TxZfy1oYjr/28r47CysCyOyod5OQz+2i?= =?us-ascii?Q?MPUw3wrywEzbmbUvx1aPpSfCCI+WD6b7tqmwt+3gRL9kXS30q4UbEISotG8A?= =?us-ascii?Q?tZtObe6rQPsOQG2sXlv2u1mdpAPeDfVVj66weExhGbKb6fucjGwZdXRv+1Au?= =?us-ascii?Q?/s6FywVdUOdA6LK01skta48he/7ugeCZHW5ZfiMwANl5n8ItWX8QYOBa9L7Z?= =?us-ascii?Q?wcT98aeAKufttGVfFaOgCUdTY0QAD+jg/LjUC7m5YE/m1Q5MIfmyjIKIL7lo?= =?us-ascii?Q?C+hEtLq7Pp5ilwVtG8/8T7CGGFPcZtf1tODfJckWfGmmBX/Qt/oZRVKMV+sz?= =?us-ascii?Q?xW8bc6TnGjWXp6Iwi0DD/iMRMiIkzHBAhr+JwFH/vidr0aQyzytkfo4F88bC?= =?us-ascii?Q?ZXNHIWJgk0vFFaVVymykvG/3NcF6U3Un26qDgB564br4KSkEzqzOzMXUlIC0?= =?us-ascii?Q?TfNObfrz+Bo1Fe5AxnFKhgBRNeYf7JPKwpn/3SkNp08VUPmTqhpPCra5zrTF?= =?us-ascii?Q?CCCO5xz02dGsiX5NRLse14UJEogkO+BVFOWEIJWtmhe2n8bguTi8k0KUf7JI?= =?us-ascii?Q?o6YC?= Content-Type: text/plain; charset="us-ascii" Content-ID: <461A80DDABBBE94FA12ECF8E95EC9F20@eurprd08.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI1PR08MB3471 Original-Authentication-Results: xen.org; dkim=none (message not signed) header.d=none;xen.org; dmarc=none action=none header.from=arm.com; X-EOPAttributedMessage: 0 X-MS-Exchange-Transport-CrossTenantHeadersStripped: DB5EUR03FT032.eop-EUR03.prod.protection.outlook.com X-MS-Office365-Filtering-Correlation-Id-Prvs: 2f9a3ceb-2d07-44b6-b178-08d8b6636d5a X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 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;SFS:(4636009)(39850400004)(136003)(376002)(396003)(346002)(46966006)(6486002)(2906002)(83380400001)(316002)(70586007)(54906003)(478600001)(70206006)(36756003)(8936002)(82740400003)(6512007)(81166007)(356005)(26005)(186003)(34020700004)(8676002)(2616005)(336012)(6506007)(53546011)(86362001)(5660300002)(82310400003)(33656002)(4326008)(6862004)(47076005);DIR:OUT;SFP:1101; X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 Jan 2021 19:02:30.7374 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: c816297d-27ba-4dfd-5775-08d8b663723b 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-AuthSource: DB5EUR03FT032.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI1PR08MB3968 Hi Julien, > On 11 Jan 2021, at 18:50, Julien Grall wrote: >=20 > On 11/01/2021 18:21, Bertrand Marquis wrote: >> Hi Julien, >=20 > Hi Bertrand, >=20 >> Sorry for the delay but I was on holiday until today. >=20 > Welcome back! No worries. >=20 >>> On 11 Jan 2021, at 10:25, Julien Grall wrote: >>>=20 >>> Hi Jan, >>>=20 >>> On 11/01/2021 08:49, Jan Beulich wrote: >>>> On 08.01.2021 20:22, Stefano Stabellini wrote: >>>>> MVFR2 is not available on ARMv7. It is available on ARMv8 aarch32 and >>>>> aarch64. If Xen reads MVFR2 on ARMv7 it could crash. >>>>>=20 >>>>> Avoid the issue by doing the following: >>>>>=20 >>>>> - define MVFR2_MAYBE_UNDEFINED on arm32 >>>>> - if MVFR2_MAYBE_UNDEFINED, do not attempt to read MVFR2 in Xen >>>>> - keep the 3rd register_t in struct cpuinfo_arm.mvfr on arm32 so that= a >>>>> guest read to the register returns '0' instead of crashing the gues= t. >>>>>=20 >>>>> '0' is an appropriate value to return to the guest because it is defi= ned >>>>> as "no support for miscellaneous features". >>>>>=20 >>>>> Aarch64 Xen is not affected by this patch. >>>> But it looks to also be affected by ... >>>=20 >>> AFAICT, the smoke test passed on Laxton0 (AMD Seattle) [1] over the wee= k-end. >>>=20 >>>>> Fixes: 9cfdb489af81 ("xen/arm: Add ID registers and complete cpuinfo"= ) >>>> ... this, faulting (according to osstest logs) early during boot on >>>=20 >>> The xen-unstable flight [2] ran on Rochester0 (Cavium Thunder-X). So th= is has something to do with the platform. >>>=20 >>> The main difference is AMD Seattle supports AArch32 while Cavium Thunde= r-X doesn't. >>>=20 >>>> 000000000025D314 mrs x1, id_pfr2_el1 >>> This register contains information for the AArch32 state. >>>=20 >>> AFAICT, the Arm Arm back to at least ARM DDI 0487A.j (published in 2016= ) described the encoding as Read-Only. So I am not sure why we receive an U= NDEF here, the more it looks like ID_PFR{0, 1}_EL1 were correctly accessed. >>>=20 >>> Andre, Bertrand, do you have any clue? >> I will double check this but my understanding when I checked this was th= at it would be possible to read with an unknown value but should not genera= te an UNDEF. >>>=20 >>> However, most of the AArch32 ID registers are UNKNOWN on platform not i= mplementing AArch32. So we may want to conditionally skip the access to AAr= ch32 state. >> We could skip aarch32 registers on platforms not supporting aarch32 but = we will still have to provide values to a guest trying to access them so mi= ght be better to return what is returned by the hardware. >=20 > Per the Arm Arm, the value of the registers may changed at any time. IOW,= two read of the sytem registers may return different values. >=20 > IIRC, the original intent of the series was to provide sanitized value of= the ID registers. So I think it would be unwise to let the guest using the= values. >=20 > Instead, I would suggest to implement them as RAZ. Works for me. >=20 >> Now if some platforms are generating an UNDEF we need to understand in w= hat cases and behave the same way for the guest. >=20 > I am not entirely sure what you mean by platforms here. >=20 > If you mean any platform conforming with the Arm Arm, then I agree with y= our statement. >=20 > However, if you refer to platform that may not follow the Arm Arm, then I= disagree. We should try to expose a sane interface to the guest whenever i= t is possible. >=20 > In this case, I would bet the hardware would not even allow us to trap th= e ID_PFR2. Although, I haven't tried it. >=20 >> Do i understand it right that on Cavium which has no aarch32 support the= access is generating an UNDEF ? >=20 > Yes. The UNDEF will happen when trying to read ID_PFR2_EL1. Interestingly= , it doesn't happen when reading ID_PFR{0, 1}_EL1. So this smells like a si= licon bug. Sounds like the ifdef ARM64 should be something like if (!cavium) Cheers Bertrand >=20 > Cheers, >=20 > --=20 > Julien Grall