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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 50397C433EF for ; Mon, 18 Oct 2021 20:19:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3740C60F9E for ; Mon, 18 Oct 2021 20:19:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232805AbhJRUVZ (ORCPT ); Mon, 18 Oct 2021 16:21:25 -0400 Received: from esa4.hc3370-68.iphmx.com ([216.71.155.144]:16549 "EHLO esa4.hc3370-68.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230415AbhJRUVU (ORCPT ); Mon, 18 Oct 2021 16:21:20 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=citrix.com; s=securemail; t=1634588349; h=to:cc:references:from:subject:message-id:date: in-reply-to:content-transfer-encoding:mime-version; bh=e0WEoxviSomcfgv69YZIFtnnJemFellICfA4UqB9ER0=; b=NP3SMKYqFW724ReXq4sMcV021pLG/uzM+M3jnbIhocoXKzSQ7ShmuJ2V AR6lazh8R7IY4NodihECeRFy3Bhmp9o1yfRIZyQFqTcNYI0q9bEYI3Eux wzrUzElz7rXI8GnZIQlT8AVL/fZFXY3eZmgcY6KZheXqkAD2ATh0wmblv 8=; Authentication-Results: esa4.hc3370-68.iphmx.com; dkim=pass (signature verified) header.i=@citrix.onmicrosoft.com IronPort-SDR: 9+WH82c/lF1K25fdZtOYfpQKKcmWeJDlEqVIzMDI79TVkW6gH2oC99+wGRL5qym2Yf4SFASQ1p JnkOz9NM/dqzl5N+Za/LhH/8QgvMpwt7nJkz5mQ3m2YOTxNAJq7dOBAK0UcC/PIi8dvaQLQVbC Yf8PejmvwKaQbj+xLETPj4cUXK8chhwDC5SqeNe4vsCaWEmZlqjdM84HgBVa5Tpb4GW1tlNjpF KR5mCcUD2dQ186ndQO7EvWmVyKpCGMYHI2JcbmR35Br2mSOFHXmZTPcX5S8RMvQns8V0tjLSzc nqn/Zr2i/6KPDg1hXcseX39I X-SBRS: 5.1 X-MesageID: 57371604 X-Ironport-Server: esa4.hc3370-68.iphmx.com X-Remote-IP: 162.221.156.83 X-Policy: $RELAYED IronPort-Data: A9a23:d+ipa6p0f9ZEydS+cKl8hmBREQJeBmL/YxIvgKrLsJaIsI4StFCzt garIBnVbvyDZGTzfN0nPNyw8RwF78PSyddgTFBrriwyFi1E+ZuZCYyVIHmrMnLJJKUvbq7GA +byyDXkBJppJpMJjk71atANlZT4vE2xbuKU5NTsY0idfic5Dnd84f5fs7Rh2Ncx2YHpW1nlV e7a+KUzBnf0g1aYDUpMg06zgEsHUCPa4W5wUvQWPJinjXeG/5UnJMt3yZKZdhMUdrJ8DO+iL 9sv+Znilo/vE7XBPfv++lrzWhVirrc/pmFigFIOM0SpqkAqSiDfTs/XnRfTAKtao2zhojx/9 DlCncLgWB5xNerVotoiXyhnGgdQHfVGw6CSdBBTseTLp6HHW37lwvEoB0AqJ4wIvO1wBAmi9 9RBdmpLNErawbvrnvTrEYGAhex6RCXvFKoZtmtt0nfyCvE+TIqYa67L+cVZzHE7gcUm8fP2O pVCNmMxNEiojxtnOUkrMYI6rduUtnT0SHpYlmKRpKg77D2GpOB2+Oe0a4eEEjCQfu1Qn0CXo Urc8mj5Cw1cP9uaoRKZ/Xa8ruvOmz7nQoUUFa3++vMCqEWO2WEVIB0HWly95/K/4ma+Q9t3O V0I/TBopq83nGShVvH0Wxy1pi7CshN0c8FdGus44ymCza3b5wvfDW8BJhZROIIOt8IsQzEuk FiTkLvBAT1pra3QSn+H8LqQhS29NDJTLmIYYyIACwwf7LHLpJwviTrMQ8xlHarzicf6cRnqy iHMrDU3gbo7hMsHka68+DjvmC6lrJzEZhA66x+RXW+/6A59Iom/aOSA6lneq+5ALYKdT0Gal HEBl46V6+VmJYmAiCGXUs0MGr+z7vqIOTGahkRgd7E5/TOr6X+lfKhK7T1+LVsvOcEBERfje k7RtBhRooRSOnSqRaZyb8S6DMFC5ZnpB9njEN/UZ9xIa51ZfQqLuippYCatM3vFyRZ21/tlY NHCLJjqXS1y5blbICSeGbcMyOcggTkE+1zfdK/y6TqHibqleyvAIVsaC2emYuc85aKChQza9 ddDKseHoylivP3Cjjr/qtFLcwhbRZQvLdWv8ZYPL7/cSuZzMDh5U6e5/F83R2Byc025fM/z9 XahRlQQ9lP7gXDWQelhQiE+MO2xNXqTQHRSAMDNAbpK8yV7CWpMxP1GH3fSQVXB3LYypRKTZ 6JdE/hs+twVFlz6F801NPERVrBKehWxnh6pNCG4ejU5dJMIb1WXoYO4L1a+rnVSVHvfWS4CT 1uIjFKzrX0rHFwKMSorQKj3kwPZUYY1yYqeoHck0vEMIR6xoeCG2gT6j+MtItFkFPkw7mDy6 upiOj9B/bOli9ZsqLHh3PnYx6/0Q7oWNhcLRAHzsOfpXRQ2C0L+mOesps7TJmuDPI41kY3/D dhoIwbUYKRWwgca7dAie1uppIpnj+bSS3Zh5l0MNF3AbkixC6MmJX+D3MJVsbZKyKMfsgyzM n9jMPEGUVlQEM+6QlMXOiQ/aeGPiaMdljXItKxnK0Tm/i5nurGAVBwKbRWLjSVcKppzMZ8kn rh96JJHtVTnh0p4KMuCgwBV63+Ici4KXZI4u8xIG4TskAcqlA1POMSOFi/s7ZiTQNxQKU12c CSMja/Piu0ElErPenY+D1bX2u9ZichcsRxG1gZadV+IhsDElrk82xgIqWY7SQFczxNm1eNvO zc0ax0pdPvWpzox3ZpNRWGhHQ1FFSa1wE2pxgtbjnDdQmmpSnfJcD83N9GS8R1L6GlbZDVao u2VkT63TTbwccjt9SIuQko5+ef7RNl8+wCeysCqG8OJQ8szbTb/2/L8YGMJr13sAN8rhV2Br u5vpb4iZar+PC8Wgqs6F4jFiuhAFEHafDRPEaN74acEPWDAYzXjizGBJne4dt5JO/GXo1SzD NZjJ54XWhmzvMpUQuv32ULYz2dIocMU IronPort-HdrOrdr: A9a23:qKSOXaPpfjUuE8BcTjujsMiBIKoaSvp037BK7S1MoNJuEvBw9v re+MjzsCWftN9/Yh4dcLy7VpVoIkmskKKdg7NhXotKNTOO0AeVxelZhrcKqAeQeREWmNQ96U 9hGZIOdeEZDzJB/LrHCN/TKade/DGFmprY+9s31x1WPGZXgzkL1XYDNu6ceHcGIjVuNN4CO7 e3wNFInDakcWR/VLXAOpFUN9Kz3uEijfjdEGY7OyI= X-IronPort-AV: E=Sophos;i="5.85,382,1624334400"; d="scan'208";a="57371604" ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=O6/bGCzVWiWkZeW14Cntvd7ZcDAjCM376qRm7qHWgVdStFopjbuIPGC7bH7cwrlshu/ftwpb3KAlxMBauTRoozwntNm1vQ+GRgNQxLEerH/clEurk6LTO6gRjTFI8nQ8M7mYUPDRAPTQ1QUHj7kYX0fpU0ZQdPPHVZuMqWFkO9X1IJFV4aZbwlM1dxWj7Uuf9pWTkIc5PxUelkfWTbJTBx+usgf9YedS9FkYUmzEMJkL5aO3ivyTx8MDUZURdnNUrqt4UnNpNpdzHQqDMJvznZjyXM72LQZ79dqWpopSBqTDaYn+S8tpSHJei5gIusX2SpVcYPns5c7TbxL0V9lrsA== 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-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=hSu1MkRiPyeVF66HHg2Trf9sGzHNSV3VcvMsEeEroIE=; b=NaxUUxUf+meAPQNSMYSFSDtvoCa5tGfAPsSd4vKHI9Fd8Y8g6WSWhxfJKbDXoQibGfaMPzfCnaAAH9Cduz+VwmmaPbGwtai7D/aIxm1ptOtsRlfo22wdtp3RyxW9FNoKUIKGb/0DbCwMZ2+8BpHkt5l+E4wk0F5XreE/Rt9W4RazG253YVHVkZG/KtzqSrkDYp6hVix4epGPqJV24AiI3e1NgjJqUctCq2favfyxtRoy0//C0NkLtKXsZAewfQGNNdvUoZ2l3o9Wy98nk419YAtJRj8FqIvnjfEizr93m/RSiFhARkfzJik9g46ZPJnJ+x1bevK2RNlC9Ly2ZQi4Bg== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=citrix.com; dmarc=pass action=none header.from=citrix.com; dkim=pass header.d=citrix.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.onmicrosoft.com; s=selector2-citrix-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=hSu1MkRiPyeVF66HHg2Trf9sGzHNSV3VcvMsEeEroIE=; b=dHMBDUi3lxK28DH8DDd/3cePRFxS9k2jIAnhv5ljwpLehn5GCiQMZKfCC2Nv3/WqK1IpyOM0Mh5nXcQf8FX+iR3w65lgicoQu0fNbUs4KCVsiq1d5vH4Kkas2mIzPcYPNejuhbmBeUo6Yz+ZP4/i4fUTk2CASgq8XLgwhb17xq0= To: Sean Christopherson , Borislav Petkov CC: Jane Malalane , LKML , , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Pu Wen , Paolo Bonzini , Peter Zijlstra , Yazen Ghannam , Brijesh Singh , Huang Rui , Andy Lutomirski , Kim Phillips , References: <20211013142230.10129-1-jane.malalane@citrix.com> From: Andrew Cooper Subject: Re: [PATCH v2] x86/cpu: Fix migration safety with X86_BUG_NULL_SEL Message-ID: <16b82fc8-fbcd-bca4-f290-ef96cd747a15@citrix.com> Date: Mon, 18 Oct 2021 21:18:53 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Language: en-GB X-ClientProxiedBy: LO2P265CA0468.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:a2::24) To BYAPR03MB3623.namprd03.prod.outlook.com (2603:10b6:a02:aa::12) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 2db98353-33ad-4a74-6303-08d99274862a X-MS-TrafficTypeDiagnostic: BYAPR03MB4743: X-MS-Exchange-Transport-Forked: True X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:3173; X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:BYAPR03MB3623.namprd03.prod.outlook.com;PTR:;CAT:NONE;SFS:(4636009)(366004)(66556008)(966005)(2906002)(53546011)(8936002)(316002)(6666004)(86362001)(956004)(31686004)(26005)(16576012)(508600001)(7416002)(54906003)(110136005)(5660300002)(38100700002)(186003)(82960400001)(31696002)(6486002)(4326008)(36756003)(8676002)(66476007)(2616005)(66946007)(43740500002)(45980500001);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?RndSR2FWbmxKS2tRSnk2eFJUNlFjU05nTU9JK1V5VDhMR0lOQU9YWnkrT1pi?= =?utf-8?B?OWxZTlpYdTN0WjZJTFBZZEFlaUZ3b2VQalkwaHQ3dG1kTmFGTEFBQkpvTjJj?= =?utf-8?B?c1E3YlUvano3citkYlRoQS9WTzNjTzBUT0FGWWcyeWdQYzc4RFk2cEdDZk1k?= =?utf-8?B?WTI0N0xZRWd4TjI4eGhxbUFwZll3OU1JUC9odURjNEJBU3llbis3c1N0NnRF?= =?utf-8?B?V0FKTVlRMEFndGZUWWc1cTZ0cUk5aUNKazc0UjJQUW4va2lXQlBZVHNydDV0?= =?utf-8?B?cmNOQXlGbWw1NTNQSFI4bk1qdkZ2VklkVzZ4YnppQXFVY2xjZFMzU1J1K1Nr?= =?utf-8?B?NWJnVU5GQVRiQ1J3bnIyTGhpRlRyR3NiUmU5ZUJCWlN4TWhEelFZeHFVeDN3?= =?utf-8?B?akJPNTZSSWJJVnN0eXYzK2dQTm96OFpiLzFLbjB1aXVvVThnYTVvSy8xSE5t?= =?utf-8?B?dWwwRUJCcEdRTGh3QWIzOEVmVGE0VDRwSEN6TFZ2bjgweVU2YmtzNW9odDYy?= =?utf-8?B?TFVsLzhZNU5PV2J5WjBoTkNJY2MrN3Fralh1WG1heERub2JpQWZqS2U5K0hy?= =?utf-8?B?UUVPZG43c1dzZm40NS9CS0lXMlJxQlg4Mk9vcTFoTmtTU2VXL2hHRUhyUDNQ?= =?utf-8?B?VWh0Q0M2NFpsRGxkSzVUZksvOWFVZmZoK1N0NFJpSWdQMm5mMyttRndYZjJI?= =?utf-8?B?MFdtdVdiSC9YcnhHR25DTjZ1R1dNRE9VOUtvTVZEcHllcStyVG1CNlZPNVdK?= =?utf-8?B?YTB4N1NQelIzdEVFczdac0xtaXRzWS9MOFVwazBsZE9NQ1BDNkVDUFJ0ODNo?= =?utf-8?B?RHNkTXVmQjNCMVU5U1Fadm5pcnVSREJuRFdFSWlOWGk4QzFWc1NPM2ZYUzJT?= =?utf-8?B?OUZPQWVJc1F2Rm9jWEMvYXAyeFRFcFBEbmpSYlJyUFNQMTg2dGJDNEs3MTNT?= =?utf-8?B?T2U5SVdNbjEzNzdvQ0RuSTNWR09vM0hubHl0ZGtoRmgvRjFXV2pjSzlyZXNK?= =?utf-8?B?TFVLbm1FNFY2ditSN0xWeU80R0FEekJOMS9aNlNZY2daVnk5ODFlSUVSdVFI?= =?utf-8?B?MUQvQkUwUnFaM0t5d09nR1BMZ3QrMkVCVkZ1cy83cW9UWWloL2lKSFRUTmxW?= =?utf-8?B?ZGNpMVQ4WWJZV1J5a2NGT2dTTlJhYkFVL0hRNlZyemliei9aekxiNlJwcW14?= =?utf-8?B?dERqQlk0L2pGSm8xQ1JJVEQzTXUrT29qWnlIWFMwVk5TODgrdlphZWhkNDVW?= =?utf-8?B?d1NZYXkwV0c3cHk2dHcveUtHRWdteTI5UmRpc1gvd3MwVno1YnZIbnB4bTE5?= =?utf-8?B?eFdYdGc4M1hYVzVCS25DY0YzNHRjVWRTWEVncWhERlBBYWxVZEswbzlwRWhH?= =?utf-8?B?Q2RQVWRxa2RLYVZRWjNFWkNjWDJodDBjVHdtcmNaZjlOS29VWDFHTHBtZ2VV?= =?utf-8?B?N2VHSmhyNG9mMlZmL0FLMWdlZy9VdkFNM3JXUXgvT0JBV2w5UnZXNWFJdDF0?= =?utf-8?B?S1pXODRGMlBNTWRuemYvUWYyeWZRL1pZK2NwQkRTa1VKdGhTTXV4dzFHbkZw?= =?utf-8?B?aEkzMFZ0MEsxWlNtR1VuTklXLzlFR0pleXh4d0hpZmhzYU5xYlBmNldsbTdP?= =?utf-8?B?M04xbVdTcEtkMm5UYnp4V3NPRkNTdG9WMllyWU90UTd0UjJsY0NBUkdnN0JK?= =?utf-8?B?eWdGSGxUMy9yZWFMSFRPMnlraGxPTy9tMit3bnNKQlZhM2EwY2c2TkFieFZz?= =?utf-8?Q?3XEvoTCZ/V4kpdABdUom8aGp5zlNYOmC7dq5x+W?= X-MS-Exchange-CrossTenant-Network-Message-Id: 2db98353-33ad-4a74-6303-08d99274862a X-MS-Exchange-CrossTenant-AuthSource: BYAPR03MB3623.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Oct 2021 20:19:01.6071 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 335836de-42ef-43a2-b145-348c2ee9ca5b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: +ppQRtMOEU2V66dRDYTg6sG5Z+96IJqqDgP+fdzywo8zeQ51L/wsRReOt+8hYrC4g5waxx5pQBW8epYvSG/6lI90IL4XfXwG3cmYWpdoHJ4= X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR03MB4743 X-OriginatorOrg: citrix.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 18/10/2021 21:05, Sean Christopherson wrote: > On Mon, Oct 18, 2021, Borislav Petkov wrote: >> On Mon, Oct 18, 2021 at 07:29:41PM +0000, Sean Christopherson wrote: >>> I agree. If the argument for this patch is that the kernel can be migr= ated to >>> older hardware, then it stands to reason that the kernel could also be = migrated >>> to a different CPU vendor entirely. E.g. start on Intel, migrate to Ze= n1, kaboom. >> Migration across vendors? Really, that works? >> >> I'll believe it only when I see it with my own eyes. > There are plenty of caveats, but it is feasible. KVM even has a few patc= hes that > came about specifically to support cross-vendor migration, e.g. commit ad= c2a23734ac > ("KVM: nSVM: improve SYSENTER emulation on AMD"). http://developer.amd.com/wordpress/media/2012/10/CrossVendorMigration.pdf Yeah - it really did work back in the day.=C2=A0 For Xen PV guests, it stil= l largely works today, because the most obvious vendor specifics were already abstracted away in the PV ABI. Of course, none of this has remotely survived the speculation apocalypse.=C2=A0 A cross-vendor VM has 0 chance of getting speculation safety working. ~Andrew