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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id D0EDAC54E64 for ; Mon, 25 Mar 2024 15:54:29 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 64DFD6B0085; Mon, 25 Mar 2024 11:54:29 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5FCAA6B0087; Mon, 25 Mar 2024 11:54:29 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 477BD6B0088; Mon, 25 Mar 2024 11:54:29 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 3903A6B0085 for ; Mon, 25 Mar 2024 11:54:29 -0400 (EDT) Received: from smtpin25.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 0C7801C0A26 for ; Mon, 25 Mar 2024 15:54:29 +0000 (UTC) X-FDA: 81936008658.25.D7B0FBB Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.12]) by imf27.hostedemail.com (Postfix) with ESMTP id 2A2C44001D for ; Mon, 25 Mar 2024 15:54:24 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=AOf3XWv1; spf=pass (imf27.hostedemail.com: domain of dan.j.williams@intel.com designates 192.198.163.12 as permitted sender) smtp.mailfrom=dan.j.williams@intel.com; dmarc=pass (policy=none) header.from=intel.com; arc=reject ("signature check failed: fail, {[1] = sig:microsoft.com:reject}") ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1711382065; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=2d/pJgsi7JkTWhbTQTCOu4qVz6zK8Jmh5WOoj+GH714=; b=T1cWmnl/7LC77vYeyiPPKf2ubfKODEFssuuOx5CKxWLHERJxcc670jSlql6YcAt/jYJpED KyBZk0qfHjq/qd/NBScRdpOs/bGW70Pq8tEJ3fSLY47c55+uK6Gh5jrM2CJMHvIweRii8z KACX2AqfBRiBzK8m+tjtrBq+HKZvhJo= ARC-Seal: i=2; s=arc-20220608; d=hostedemail.com; t=1711382065; a=rsa-sha256; cv=fail; b=KkRRxXrryFcw0q9/4NcXYwxykASHF23nqlUsu8lA9fVuD2gJz40nNBM+h3ZIJIeJW8Co5F +oJ6ZOfeRu3O04nalLGos+cy3LjuJdpKVHPeZMAmY6JKdXgm15A6dpvyzllZjJF/mdGt/M gE4u55iEU6lb1fOpynONoWUFjOdiTS8= ARC-Authentication-Results: i=2; imf27.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=AOf3XWv1; spf=pass (imf27.hostedemail.com: domain of dan.j.williams@intel.com designates 192.198.163.12 as permitted sender) smtp.mailfrom=dan.j.williams@intel.com; dmarc=pass (policy=none) header.from=intel.com; arc=reject ("signature check failed: fail, {[1] = sig:microsoft.com:reject}") DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1711382065; x=1742918065; h=date:from:to:cc:subject:message-id:references: in-reply-to:mime-version; bh=wJNrOF6n5v50elvbyscLgb6i4uPE/7PLSKLt4cxl7xA=; b=AOf3XWv1+I4VV5Q5FPes7XDz4tnms8G40viYZC8Xf8dnQJGNEPv0SSQm w9lt550dXM/pmrln2Th96xvBDdvQYDLel+4ca4wn3QwAqENU88CeHmwrG 7+gvnyymkLR+n0X8omkHXhdy2H0R+hk4ep1i1EcoBiwi98v+gTRnsUj7x +eeyhoyvkekACzKfAraV6O/gwyzFKSzxQKUOXX/RQ61N84GEBtxaMBKUp QTvquxOPqni2FafHKRRpjaXLOY/mlpr5VX/Zyg+KvrCrt7yJuXnBPqkxe 5/o1W3D+aJJp1YP7ubtGMrKatlKVbOBPda5yEUrUgmvvW0j9p51XzPM91 A==; X-IronPort-AV: E=McAfee;i="6600,9927,11024"; a="10170470" X-IronPort-AV: E=Sophos;i="6.07,153,1708416000"; d="scan'208";a="10170470" Received: from orviesa006.jf.intel.com ([10.64.159.146]) by fmvoesa106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Mar 2024 08:54:14 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.07,153,1708416000"; d="scan'208";a="16087721" Received: from fmsmsx602.amr.corp.intel.com ([10.18.126.82]) by orviesa006.jf.intel.com with ESMTP/TLS/AES256-GCM-SHA384; 25 Mar 2024 08:54:14 -0700 Received: from fmsmsx612.amr.corp.intel.com (10.18.126.92) by fmsmsx602.amr.corp.intel.com (10.18.126.82) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.35; Mon, 25 Mar 2024 08:54:13 -0700 Received: from FMSEDG603.ED.cps.intel.com (10.1.192.133) 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 15.1.2507.35 via Frontend Transport; Mon, 25 Mar 2024 08:54:12 -0700 Received: from NAM11-CO1-obe.outbound.protection.outlook.com (104.47.56.169) by edgegateway.intel.com (192.55.55.68) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.1.2507.35; Mon, 25 Mar 2024 08:54:12 -0700 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=GIexsBoqu/R49VJNkCkhr7uHSUz2m7OQDMxJYEUbIwOxJqr5rIV7hQ5mmE7RcaHVr+ypARTgxDtYcux35uDoZd9LrSsC3N9ddzn46A+/MPDKzn2y7eEMckYfJquSX77L01Dym9pTY1oOWM0sKEHiIH+dAWh8jaj57tRLP0/hwbdh7HDqYyBoVv3w21M4HPndsIZRpow56MKRdr51uQlewnuCNygt+W7fOvtlDERIr0YKgTQBFXebYfUfrUj79Ofw5bDTyz0dsZM7K1NDkMKuKBI3yNW+yabm534HcRmRjLBuDDCWop0zw88vyY7Gr/nKTDHNBgGL785iZW0A3/lrkQ== 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=2d/pJgsi7JkTWhbTQTCOu4qVz6zK8Jmh5WOoj+GH714=; b=ODuict6Gt8buQclm76PUXGvhWAPKyaNGl/E5w1uVqSgZmHhr+odnc7bs6DU4Ws0vZQdxVzxOauLC+ZRVS+o7VmOBuCnKO5gYFzJymFB5pSxaEk0s1zBk+iIXCzZIyXkSLsf6RyDdjjGj+DqOOk0Hfq7bChAtaHr+95xP0Pfl3zcdvCNRdbiUYifYtMjLj2tGf9tqcDZ1rlcctZD2E/a4N81yCrF9tldzAiUTsIWF4HNdoFyMjxiBPKh23Mn/LYEzR6Ws27oxZf2d1OMHz1F/Lqqu+IAWftXY8PWTJ3pfTf46VPMg95xrzwXdlcECwxu0AL0gRxtPls3mAnOHqc5OAA== 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 Received: from PH8PR11MB8107.namprd11.prod.outlook.com (2603:10b6:510:256::6) by DS0PR11MB7264.namprd11.prod.outlook.com (2603:10b6:8:13b::5) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.7409.32; Mon, 25 Mar 2024 15:54:10 +0000 Received: from PH8PR11MB8107.namprd11.prod.outlook.com ([fe80::82fd:75df:40d7:ed71]) by PH8PR11MB8107.namprd11.prod.outlook.com ([fe80::82fd:75df:40d7:ed71%4]) with mapi id 15.20.7409.028; Mon, 25 Mar 2024 15:54:10 +0000 Date: Mon, 25 Mar 2024 08:54:06 -0700 From: Dan Williams To: Ben Cheatham , Dan Williams , , CC: , , , , , , , Subject: Re: [RFC PATCH 0/6] Implement initial CXL Timeout & Isolation support Message-ID: <66019e1ec2153_2690d29440@dwillia2-mobl3.amr.corp.intel.com.notmuch> References: <20240215194048.141411-1-Benjamin.Cheatham@amd.com> <65cea1bc6ac0c_5e9bf294ed@dwillia2-xfh.jf.intel.com.notmuch> <1287adbe-364f-431c-b33f-9d73e7829b6c@amd.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <1287adbe-364f-431c-b33f-9d73e7829b6c@amd.com> X-ClientProxiedBy: MW4PR03CA0081.namprd03.prod.outlook.com (2603:10b6:303:b6::26) To PH8PR11MB8107.namprd11.prod.outlook.com (2603:10b6:510:256::6) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH8PR11MB8107:EE_|DS0PR11MB7264:EE_ X-MS-Office365-Filtering-Correlation-Id: 66b4eec5-f477-4e92-fe17-08dc4ce3cf2c X-LD-Processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr 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:PH8PR11MB8107.namprd11.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230031)(1800799015)(366007)(376005);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?9n+GnqqsGOhtox76C/jyV6p26s1g+nzFBmeylDWi+4bxfhC6NvYwSJSJp277?= =?us-ascii?Q?kEhWu75s+UmXOllmMIeaEY2VqY/l5s8lNb+bvkG8WMWmmwzm1e1RNXAu0UV+?= =?us-ascii?Q?+jmMVMmyvrySVW5lCTkz2dGmtKqr9MQ5SN0VJJceYHR995k3irqgz+I5WyKi?= =?us-ascii?Q?zZcsaVFRh9CVon1I0MPp33MN95VQgNpfm6Vz4xS3WcRnygQZKMrlfx+TMv9k?= =?us-ascii?Q?hxML6VQeAi3Y9tUbUGT1TMTyPZ1OckkGszyheBE/mdojhBU2Amg8X0FUtcS7?= =?us-ascii?Q?Lbd0TmeS7fT9mC+byuoZbbn5pcQT+BEu4kJWhG5R+ke7mP5kVEwb7OaAd8yM?= =?us-ascii?Q?8m621crP9+AAJUvcO1dAfLpiXvUysAshkLNcPrCitysRL0SJHV52M4N3d6Mg?= =?us-ascii?Q?XNwL3mJ5I0HMIrbdEIT2dy3u4KMQukW8GYgGELwondb9B6AVGJgNWU5DODMk?= =?us-ascii?Q?l35/fakdia9SLEJa6oGO3S7/LkQtSrlkpe/U9SVhJn/s1vOb9eYMN4/xobOO?= =?us-ascii?Q?0J1rxhzW9jf5roTwV6rl47nX946k9t5izt8oGaTqnSsz6iriHfjJupZrxI72?= =?us-ascii?Q?NyCKzttILUsuaNnImoWNd9EzcZmMJ4zos1Nd/ZmwDhGG9ior//hnRESjuWA0?= =?us-ascii?Q?wDGsOpfia2haUd/TJXNo6jOgbr9nwkQbuY7hfIp+TDCTRt6wcEyzekzK/uQ3?= =?us-ascii?Q?ey4flLLYFlWWE8F6VYZ+oai6vx5WHCsZ+i4wbToW84ejqmFphHPRB3R2BpCX?= =?us-ascii?Q?QxZ+fdclk2MBm2o15wAdKh54jzhPYsY9sptgrOAsgeU91TPRhjF/2LrnFBGc?= =?us-ascii?Q?FKAkfS5Y08yqVsYPtuwzK7xinDKv797EgjsmEvr8XliVYkCR/IbTsmiwtZ6P?= =?us-ascii?Q?6rO5fPl4pJQOH+/HBUlwmYbX7O70/2Pxqg+Hh8e/HvwuqiRcHM8qzLNx7zZ0?= =?us-ascii?Q?nOdjYZxhQexH6QTX7rCM0Jc9Beiw3wOgnaCml6f0ec6DoTQTFE/JTuAOZQI4?= =?us-ascii?Q?eN4Lk4YEI1Czb5D28CbkmVAJd7vnc3dLsYR0MpCKBorHet9RIu8ffmhn3IC0?= =?us-ascii?Q?1u8ZcR2Pt9+aA1VIYmdZ2launyOEYCDS5zBpjLfJY+GTbHM0H4wQF4bKmmuf?= =?us-ascii?Q?oLWWZNMl0C8RQ+Btt7WvDB1HHJG4dD5cT/+9041VtLmI+lsOW/M9m66C6A2A?= =?us-ascii?Q?QkyXQ+aCqB9Y5+VLwPF+9T0jedC0LkKkM7JxGbP5VZGXgEqhBtZeR8SfvPbq?= =?us-ascii?Q?jn7wqvl1FyF4f385ugKiTjslvWcqvk0oWm1QSgkloxmJZXW8nEeoQfNMPQLL?= =?us-ascii?Q?wlBa+ErsLUrHl1pn1JDVNQqG12dfIPJrVMMjdFSq4XAYadUyGJI3lV3XJF7D?= =?us-ascii?Q?jiy6KRpMtqiIustZYDqFalbeRYk+0Gm5Czod8lYIqRaB9MPyHTtbDKLrmbMJ?= =?us-ascii?Q?b3DkQD6PVJe3yf6chY9KGJbB4uC5NELV7avTthPXlMr65/M+o1Dy0RKDTv14?= =?us-ascii?Q?mx4xNZAIH+FJBcV/4vtEKmwg1VW+zrD15CUbQSsl5RAOwO8IS5Xmj3HBc3Gd?= =?us-ascii?Q?CZ/P13sTavCkrh5JHZCo5ylYtGbAhjt4kaGY7xNi2IjcrnZ5bMne+S9TesHa?= =?us-ascii?Q?Bg=3D=3D?= X-MS-Exchange-CrossTenant-Network-Message-Id: 66b4eec5-f477-4e92-fe17-08dc4ce3cf2c X-MS-Exchange-CrossTenant-AuthSource: PH8PR11MB8107.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Mar 2024 15:54:09.8544 (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: j7sQTccnw+SRBsSfJp5jpImHWVGVDJJNd4NrOkb97D5yjRW+a+XlAymQU7+awmgNsvc4nzPZJDZooKyUof554w8oQedYSVDdavf1H9GI/dM= X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS0PR11MB7264 X-OriginatorOrg: intel.com X-Rspamd-Queue-Id: 2A2C44001D X-Rspam-User: X-Stat-Signature: 3m6iaypbfmuu4u1d9wz4r99qkctzaar6 X-Rspamd-Server: rspam03 X-HE-Tag: 1711382064-876785 X-HE-Meta: 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 sfoY8lA8 xrkkf+kVcLsnsG9C0ggD/BlTEnOw1KiDxKieqWqCWQ8PLQ3oEiCdL/fedTAx9JL+iEZaRVlHu58sb0oh8r98ITIysT0hJvkAu2LCCGQABDUB5RtNa6i9VvUScxQsjTBwvtmnezGUPX37U3BmKXSfBCc73okQk5fuZXb07/LIVfQMIqPysEw8fhEharyjf6xfE2C30Gi07k3rEIjq9Nn42520eZUkb+VsyItmFiY2rRbWFFf/YLEdCkXco3w== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Ben Cheatham wrote: > Hey Dan, > > Sorry that I went radio silent on this, I've been thinking about the approach to take > from here on out. More below! > > On 2/15/24 5:43 PM, Dan Williams wrote: > > [snip] > > >> The series also introduces a PCIe port bus driver dependency on the CXL > >> core. I expect to be able to remove that when when my team submits > >> patches for a future rework of the PCIe port bus driver. > > > > We have time to wait for that work to settle. Do not make the job harder > > in the near term by adding one more dependency to unwind. > > > > For sure, I'll withhold any work I do that touches the port bus driver > until that's sent upstream. I'll send anything that doesn't touch > the port driver, i.e. CXL region changes, as RFC as well. > > [snip] > > > So if someone says, "yes I can tolerate losing a root port at a time and > > I can tolerate deploying my workloads with userspace memory management, > > and this is preferable to a reboot", then maybe Linux should entertain > > CXL Error Isolation. Until such an end use case gains clear uptake it > > seems too early to worry about plumbing the notification mechanism. > > So in my mind the primary use case for this feature is in a > server/data center environment. Losing a root port and the attached > memory is definitely preferable to a reboot in this environment, so I > think that isolation would still be useful even if it isn't > plug-and-play. That is not sufficient. This feature needs an implementation partner to work through the caveats. > I agree with your assessment of what has to happen before we can make > this feature work. From what I understand these are the main > requirements for making isolation work: Requirement 1 is "Find customer". > 1. The memory region can't be onlined as System RAM > 2. The region needs to be mapped as device-dax > 3. There need to be safeguards such that someone can't remap the > region to System RAM with error isolation enabled (added by me) No, this policy does not belong in the kernel. > Considering these all have to do with mm, I think that's a good place > to start. What I'm thinking of starting with is adding a module > parameter (or config option) to enable isolation for CXL dax regions > by default, as well as a sysfs option for toggling error isolation for > the CXL region. When the module parameter is specified, the CXL region > driver would create the region as a device-dax region by default > instead of onlining the region as system RAM. The sysfs would allow > toggling error isolation for CXL regions that are already device-dax. No, definitely not going to invent module paramter policy for this. The policy to not online dax regions is already available. > That would cover requirements 1 & 2, but would still allow someone to > reconfigure the region as a system RAM region with error isolation > still enabled using sysfs/daxctl. To make sure the this doesn't > happen, my plan is to have the CXL region driver automatically disable > error isolation when the underlying memory region is going offline, > then check to make sure the memory isn't onlined as System RAM before > re-enabling isolation. Why would you ever need to disable isolation? If it is present it at least nominally allows software to keep running vs hang awaiting a watchdog-timer reboot. > So, with that in mind, isolation would most likely go from something > that is enabled by default when compiled in to a feature for > correctly-configured CXL regions that has to be enabled by the end > user. If that is sounds good, here's what my roadmap would be going > forward: Again, this needs a customer to weigh the mitigations that the kernel needs to carry. > 1. Enable creating device-dax mapped CXL regions by default Already exists. > 2. Add support for checking a CXL region meets the requirements > for enabling isolation (i.e. all devices in > dax region(s) are device-dax) Regions should not know or care if isolation is enabled, the implications are identical to force unbinding the region driver. > 3. Add back in the error isolation enablement and notification > mechanisms in this patch series Not until it is clear that this feature has deployment value.