Received: by 2002:a05:6a10:d5a5:0:0:0:0 with SMTP id gn37csp1464221pxb; Fri, 1 Oct 2021 11:08:26 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwANw6qV/k0QY4NWt6xseCbh5gbgi6dv1jmdXsxbaO3FAGrM3+P47veNd872PcmFZZt8vDX X-Received: by 2002:a17:907:9604:: with SMTP id gb4mr8015147ejc.142.1633111706586; Fri, 01 Oct 2021 11:08:26 -0700 (PDT) ARC-Seal: i=2; a=rsa-sha256; t=1633111706; cv=pass; d=google.com; s=arc-20160816; b=y0oad9A5j0rPtaWuEcuu1UVVq/fx86de+137Q/ewDYv62FmYR6ylrmlnFXW0XUz3M+ QMEyGkCrgjv6JW4BmiizeQqedxdpLDPOR25OGElegutUhrZ06Atz/tbL0g0VJiByD/mL g86/15lD87fRyQvqd1OE2PXgtpx13GgMcKoS79C/grcbZ0XWL0zp2s2yXq48J/PDrZBi RzdTjEqfYPBpze+6u7/nF7WG6g6Yh8NGX6+e1OaSHuYjCNjYU3C3kKsfZxK/fk0TYL96 gZboB0qQjDFJZNjx1sPS/bLwpP1CfFeVb/4oFhZAmEXQWTxlVbwpV1UEh0v4lkWWQHpk aC4Q== ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:mime-version:content-language :content-transfer-encoding:in-reply-to:user-agent:date:message-id :from:references:cc:to:subject:dkim-signature; bh=694OsMqbNw+F1LYcy2RPic5ojPA2PXMo0xi79fzFJjU=; b=hjyh2Jv76XLQhjzq/2It+/rmzs1zgaP72ux5m95xdMP+XbqXuyoBUwQgMAAKAbSwhj H+yMCiNPGkn8p4ehjjc2Jmy0jQoQ++NpeTWE4LVR2uiAU8XSVoT3UEkgeZXfZHWyc2Ky gOKNcXERSXoxmtrzkf0j+I3zj5ujaBLALT308rPqPyNX0jHeRF8DZmVt+RrF4YIoMixA m01xGQezXM4VI2a3AAVt/p+2p7qYxhkKunuSKabuoxXjTIvugW4dZiXfKPu5R/ujIvnj RZDYklAlPX7z7BbUd0dJV5O4ykvcDS4W4gY7J+Jtbb1n7uoQaVC6P8oK4DOmkH6/xRAH yWPA== ARC-Authentication-Results: i=2; mx.google.com; dkim=pass header.i=@intel.onmicrosoft.com header.s=selector2-intel-onmicrosoft-com header.b=SSSAAArq; arc=pass (i=1 spf=pass spfdomain=intel.com dkim=pass dkdomain=intel.com dmarc=pass fromdomain=intel.com); spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com Return-Path: Received: from vger.kernel.org (vger.kernel.org. [23.128.96.18]) by mx.google.com with ESMTP id g2si13861948ejt.1.2021.10.01.11.07.52; Fri, 01 Oct 2021 11:08:26 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@intel.onmicrosoft.com header.s=selector2-intel-onmicrosoft-com header.b=SSSAAArq; arc=pass (i=1 spf=pass spfdomain=intel.com dkim=pass dkdomain=intel.com dmarc=pass fromdomain=intel.com); spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1355622AbhJASGp (ORCPT + 99 others); Fri, 1 Oct 2021 14:06:45 -0400 Received: from mga04.intel.com ([192.55.52.120]:23676 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229576AbhJASGm (ORCPT ); Fri, 1 Oct 2021 14:06:42 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10124"; a="223618288" X-IronPort-AV: E=Sophos;i="5.85,339,1624345200"; d="scan'208";a="223618288" Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Oct 2021 11:04:28 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.85,339,1624345200"; d="scan'208";a="710069217" Received: from fmsmsx604.amr.corp.intel.com ([10.18.126.84]) by fmsmga005.fm.intel.com with ESMTP; 01 Oct 2021 11:04:28 -0700 Received: from fmsmsx612.amr.corp.intel.com (10.18.126.92) by fmsmsx604.amr.corp.intel.com (10.18.126.84) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2242.12; Fri, 1 Oct 2021 11:04:27 -0700 Received: from fmsmsx610.amr.corp.intel.com (10.18.126.90) by fmsmsx612.amr.corp.intel.com (10.18.126.92) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2242.12; Fri, 1 Oct 2021 11:04:27 -0700 Received: from fmsedg602.ED.cps.intel.com (10.1.192.136) by fmsmsx610.amr.corp.intel.com (10.18.126.90) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2242.12 via Frontend Transport; Fri, 1 Oct 2021 11:04:27 -0700 Received: from NAM10-DM6-obe.outbound.protection.outlook.com (104.47.58.108) by edgegateway.intel.com (192.55.55.71) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.1.2242.12; Fri, 1 Oct 2021 11:04:27 -0700 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=O4uTdiEAGPJuaqGLe2+xH1hWiQc6VEnD8XvD7RtP8Cejtji0K5kaS8SEJQS7P4vFkiPdRLJaBw1mRu6DWBX9DaurgM280KjXjH/wPqaaXw4oDoo1z5BZqMe6Am/pFp8l79pmPKUX7UaIuz2clgJXr2se16RXuUqxiKUePV1I1q0UtraS4nE2OZIC4Zst780iG1kdTiIg3C/ThAsSxMeZqJnvFyAfFb1sg8OwcSYwfQwMRMvBapR4nWKlGxFfAhvUBbHB1X+q2K1ryGXr078WElWsucOZosPC2u8ffurNkCdpUDs8wW/lvj2YcZ+a58ok5cjGnKLqFAdNqs4iZFpozQ== 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=694OsMqbNw+F1LYcy2RPic5ojPA2PXMo0xi79fzFJjU=; b=Kug/ygOJCt8qh1ZQv51Ll7zeK+EX3uGzQ3/ahBIxLRBfPG7cRvXlbf0A6wBV2740B5st9GGPVZmFwPPCUYbBbvNN6nmH9Vo5pV9s/83JkythmDurrjb+6wEMD1eN8wpnKy9aD5SlJMWd7EpGmcyVOjSYtmEEI40L5mPrnHGC+8hqFd0iIvHfXURx61Zk97YS3/hj5rN+5jWjOCLGv8SS24wk9ogzdcgt7cvSyw/LsPHufzql6szMiEF/gnBl8bRhftkOKC6Chxlww0+TTgMd36tWTKPQl9Lit9SGrhT+vEaJY/MwybHTYtZlQfY4Rmt+Pxmy1gYFDeF/EKz1BpVOLQ== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=intel.com; dmarc=pass action=none header.from=intel.com; dkim=pass header.d=intel.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel.onmicrosoft.com; s=selector2-intel-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=694OsMqbNw+F1LYcy2RPic5ojPA2PXMo0xi79fzFJjU=; b=SSSAAArqFoG9SybfbgN8xALCJIf64j976PfRcXQvWQrR6ikfLh9OgWOx61XzSkx7vBQbPxhSyfPY9aLRHBc20VpOwIQPzY0mvYeZepAkJkELMLVU/MJJZxc1bHY8YFaLOF3nz7WUbQvI47ksIyO2eQqgndA3Ive8LJ4XZflSg/A= Authentication-Results: vger.kernel.org; dkim=none (message not signed) header.d=none;vger.kernel.org; dmarc=none action=none header.from=intel.com; Received: from BYAPR11MB3320.namprd11.prod.outlook.com (2603:10b6:a03:18::25) by BYAPR11MB2936.namprd11.prod.outlook.com (2603:10b6:a03:8c::17) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4544.15; Fri, 1 Oct 2021 18:04:24 +0000 Received: from BYAPR11MB3320.namprd11.prod.outlook.com ([fe80::4167:f9ef:19b2:eaff]) by BYAPR11MB3320.namprd11.prod.outlook.com ([fe80::4167:f9ef:19b2:eaff%3]) with mapi id 15.20.4566.019; Fri, 1 Oct 2021 18:04:24 +0000 Subject: Re: [RFC PATCH 11/13] x86/uintr: Introduce uintr_wait() syscall To: Andy Lutomirski , Thomas Gleixner , the arch/x86 maintainers CC: Tony Luck , Dave Hansen , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Jens Axboe , Christian Brauner , "Peter Zijlstra (Intel)" , Shuah Khan , Arnd Bergmann , Jonathan Corbet , Raj Ashok , Jacob Pan , Gayatri Kammela , Zeng Guang , "Williams, Dan J" , Randy E Witt , "Shankar, Ravi V" , Ramesh Thomas , Linux API , , "Linux Kernel Mailing List" , References: <20210913200132.3396598-1-sohil.mehta@intel.com> <20210913200132.3396598-12-sohil.mehta@intel.com> <877dex7tgj.ffs@tglx> <87tui162am.ffs@tglx> <25ba1e1f-c05b-4b67-b547-6b5dbc958a2f@www.fastmail.com> <87pmsp5aqx.ffs@tglx> <0364c572-4bc2-4538-8d65-485dbfa81f0d@www.fastmail.com> From: Sohil Mehta Message-ID: Date: Fri, 1 Oct 2021 11:04:22 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Firefox/78.0 Thunderbird/78.14.0 In-Reply-To: <0364c572-4bc2-4538-8d65-485dbfa81f0d@www.fastmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-ClientProxiedBy: BY5PR03CA0018.namprd03.prod.outlook.com (2603:10b6:a03:1e0::28) To BYAPR11MB3320.namprd11.prod.outlook.com (2603:10b6:a03:18::25) MIME-Version: 1.0 Received: from [192.168.86.37] (73.222.31.188) by BY5PR03CA0018.namprd03.prod.outlook.com (2603:10b6:a03:1e0::28) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4566.14 via Frontend Transport; Fri, 1 Oct 2021 18:04:23 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 216b2c30-a73e-4c9d-da5f-08d98505e6c5 X-MS-TrafficTypeDiagnostic: BYAPR11MB2936: X-LD-Processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr,ExtFwd X-MS-Exchange-Transport-Forked: True X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:9508; 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:BYAPR11MB3320.namprd11.prod.outlook.com;PTR:;CAT:NONE;SFS:(4636009)(366004)(53546011)(38100700002)(7416002)(2616005)(86362001)(508600001)(956004)(83380400001)(316002)(31696002)(16576012)(186003)(2906002)(110136005)(54906003)(36756003)(26005)(66946007)(4326008)(31686004)(6486002)(66476007)(8676002)(66556008)(966005)(44832011)(8936002)(5660300002)(43740500002)(45980500001);DIR:OUT;SFP:1102; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?R2k4OUpRWUVFS2dpTC9iQ25yV29sWG9UVjZsTkVVd1dvVDE4Snc5VXZ0L0V5?= =?utf-8?B?ZGNwY0tUWGx1Y1pBcXI4VmdHWm95QWxrdDFuUytEOUV3MUFaajRTR2dDQVFM?= =?utf-8?B?a01BRHlVWkZOb2NtN1I4S1ZSOVo1VUFaajQ4bkp6UHQ0azNnWXMwWms2c1pw?= =?utf-8?B?TkNUTEhzYnRFdzFEdElUZjhYclVNZHJHZzUvV29vN3pvRjFoQlpUb3lRclU1?= =?utf-8?B?SXhPU3NHQldCSm13eXhVZjhVNE5sVWtLajdjb05UdUpOd2Vva0NuenUzaE5R?= =?utf-8?B?ZVdZUEFyYVZWNGQ2ZlAvNkJMN1hmaDdIOWlDVUpVcmdFMVpFVEkzc1NhRklV?= =?utf-8?B?eG1tbHFRN1lCQmVRZzNWcHBzVzBqVHFtS2hNV1pmbVZLLzJ6S1JrZFU0Zk1W?= =?utf-8?B?bFl4WjZrTWViZ2cyUU0wWWxLZXFOL0NjVlFGT1lWR2VjbkN6UVh3RUlNNDJV?= =?utf-8?B?ckFiOTBxaUFhRmxBMnVMRHE3azcrNHAweWhtUXM0RWc4VldpeGIzTG9xanZV?= =?utf-8?B?dSt2dkppcmVTUnJ0ejlwSW5jMWtHQm9sKzc1bDY4T3B0a3lOUlVTTkNYQXBP?= =?utf-8?B?V05wS0EwcmtURnV4cWVyQjMxbW9FZmRDc0JncjhOWm1aL0d2b0MvRkVtSWg0?= =?utf-8?B?bnN4eGlmU1lPZU55VjhWWDh3eHJ0clVjT3VPazdoMitSTjV0SzlXc211elBL?= =?utf-8?B?M2xkR1pzNFpIVzNlMlFwZTVEOHk3MFNjYm05SzdDUEhLdGtiSTRUNzFYSUVt?= =?utf-8?B?VDZhNVZUOTNJUjFOV09jQWpjWEJuMDZTbmEzMERPdFJmMWxQcmRmR083QUlC?= =?utf-8?B?cGllaGRJWGFqa1pUVHJWS3NRRUgraDhUbVkyUUY1YVc5SWhBUFZncS9saU9T?= =?utf-8?B?K1BGQkw0UGMycjhmTGJNa2wwV0lXTU5TcTAybWllK3RaQlAyNDFoNWNuNDBB?= =?utf-8?B?WStySjQ3QVZ1dU5vczVuQXhIR0pidGgzQk9ZbmlnckVJd0xWR1dzcjVhc3pJ?= =?utf-8?B?TFFielkzSk5IMmp2cTJoSjBEWnplZzBLejIvUTNXdkhkcjlqVTgxNWdIRzBo?= =?utf-8?B?RGJLaDlOVkRnRDhlQlBWOWZ0VTRtVTZqNDY5K3dudFJIZUpDZGRQeW40SHZx?= =?utf-8?B?MkRpc2JZZ0xJQk42b3ZOT0VXdHc3M2lSZE1aSlY3Vk5mZklpdVhuOEZiMUg5?= =?utf-8?B?VkY3d1ZyeWhZQTU5QUtqcGR2dUg2SWZRd2U2d2p6VFJoTGdvMUd2V2ZSQkdB?= =?utf-8?B?ZHZ2ZVJlN0QrS2kzUlFXWGtzaWdFY1RFa1RGbWl4RHI1bm91cEdTTWNvak40?= =?utf-8?B?RC8zWi81a2RoTW8vSklxM2FvU2U2MW5qRGNiK1lHVjZWMlVaOVBmUEF6ckNM?= =?utf-8?B?cENPUGEvQ0h6ZlR3ZVZ0eWdodlRZTlplSkJnTXYzTXMrNVIzRUdzVGpzWGRG?= =?utf-8?B?NGlWb0ZnM1BlMGtqTEtJTXlhR1FHUGdiWW5oMmdhWmxWMi9yaytPck13bTA2?= =?utf-8?B?dmwwcERRSXhXZlFwV09QZW9CVXFnS2J6dG0wNFhUcld4VFo2NFlXSWcyRHds?= =?utf-8?B?VEFvWGF0eUwvL0dNdHlpVktYS283Ry9RSktYcGNCeHR5LzZLcUxiT3U2eVFo?= =?utf-8?B?a2cxU2ZtQWNiTWxWb3d6Z1ViT3RtMnNWM05mUmRtbTdrbU9xRGE5UFBVM0I4?= =?utf-8?B?UnBxMWYyWGIvYlcxMlR2MGFYN1VwZ0l1bnRyTm1nd0ZNdVU5U0g5ZzkvL0Rn?= =?utf-8?Q?1kmBps8xfapdgrgAHBGAsB6L7Fatg9H19QsvgKi?= X-MS-Exchange-CrossTenant-Network-Message-Id: 216b2c30-a73e-4c9d-da5f-08d98505e6c5 X-MS-Exchange-CrossTenant-AuthSource: BYAPR11MB3320.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 01 Oct 2021 18:04:24.6610 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 9S99FOFHTUwVtnJ2PmtWvBpT+S5Axj2MhGEL+8nc1q7Ev7wEjy8RiuKpxB5pNLxjEXw8eCZLRXBLPjvZ6hpj4Q== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR11MB2936 X-OriginatorOrg: intel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/1/2021 8:13 AM, Andy Lutomirski wrote: > > I'm just reading TFM, which is some kind of dystopian fantasy. > > 11.8.2.4 XRSTORS > > Before restoring the user-interrupt state component, XRSTORS verifies that UINV is 0. If it is not, XRSTORS > causes a general-protection fault (#GP) before loading any part of the user-interrupt state component. (UINV > is IA32_UINTR_MISC[39:32]; XRSTORS does not check the contents of the remainder of that MSR.) > > So if UINV is set in the memory image and you XRSTORS five times in a row, the first one will work assuming UINV was zero. The second one will #GP. And: > > 11.8.2.3 XSAVES > After saving the user-interrupt state component, XSAVES clears UINV. (UINV is IA32_UINTR_MISC[39:32]; > XSAVES does not modify the remainder of that MSR.) > > So if we're running a UPID-enabled user task and we switch to a kernel thread, we do XSAVES and UINV is cleared. Then we switch back to the same task and don't do XRSTORS (or otherwise write IA32_UINTR_MISC) and UINV is still clear. Andy, I am still catching up with the rest of the discussion but I wanted to provide some input here. Have you had a chance to look at the discussion on this topic in patch 5? https://lore.kernel.org/lkml/87bl4fcxz8.ffs@tglx/ The pseudo code Thomas provided and my comments on the same cover the above situation. The UINV bits in the IA32_UINTR_MISC act as an on/off switch for detecting user interrupts (i.e. moving them from UPID.PIR to UIRR). When XSAVES saves UIRR into memory we want the switch to atomically turn off to stop detecting additional interrupts. When we restore the state back the hardware wants to be sure the switch is off before writing to UIRR. If not, the UIRR state could potentially be overwritten. That's how I understand the XSAVES/XRSTORS behavior. I can confirm with the hardware architects if you want more details here. Regarding the #GP trick proposal, I am planning to get some feedback from the hardware folks to see if any potential issues could arise. I am on a pre-planned break next week. I apologize (in advance) for the delay in responding. Thanks, Sohil