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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?sBO4Y3HF4VQ/+B6d0CcrjisNxyQa+IIbHHgOx2gAQKoULJHr3gnH8hfLjWt/?= =?us-ascii?Q?nr3Inh3ugzAOxS3FDZlkZrihIXeNIsDJ1fv+c+kP86zj+RaXH0z0JchjxmOp?= =?us-ascii?Q?ZeFLazcsNEaZaCS1LwxwB3FmyjOjYjI00jboVKma0GltfomMYnvHg6mvkYhk?= =?us-ascii?Q?O59LHtJC1u8zq9WLVGZhLs8oiEHimvf/6Au72tqDv2DyrornEWutWrHPmi5P?= =?us-ascii?Q?4zjdolwTMnZllbQsItTzJf4cBIYm4LIxHdxMmMIqOP5WxcSjFcHidmfkcwEz?= =?us-ascii?Q?WM0jZjRXGBrlLieYu3/6hFvXanhsLLabr2BsW8X7c1mUrC01/JpnaAl2PHsW?= =?us-ascii?Q?eyEU+uHFeb6wxHKZPIdPI51Yye9h98eeygl4TRLjgWSZ1ekuqWKE/y+a/ZII?= =?us-ascii?Q?d+odcCIUT8etoVTsVPlJb3SKoPAJISfThhAOGc/e2hHcLZBSJy0qi1U+JBYI?= =?us-ascii?Q?lcXmlewNb9PoI6wut+SrFoX91SjR82U5wslkSsQsZHlBTcOdAfKz6P12fJdw?= =?us-ascii?Q?UuiwptAldsGOJQUiw8ihndz6jEOI72thGtGU8lmRyn+b/kM49QCbYHy3ehZ/?= =?us-ascii?Q?8xMaSXUDvsu4w0mvWe5M5XD9TsdSSRPDbYbonCBmL4EVi/ZEOF1VEY1r35pN?= =?us-ascii?Q?5OKlDFIuixJSN+Wm2Xx7i5SuTg4RiyJ7n+AV2Qf5+XCDBbqNNJK8ceHEttqJ?= =?us-ascii?Q?NaqY/n0JnJWIfth1qsaAWJpBpG7IrGmj59C5lvCGGr4eh0ssE6EWeX8LCGgh?= =?us-ascii?Q?fS7CUa3Lu3Yfk8ERpong+ZxiY3Xr/QFWt+6vfsNrbXvxiePoXDusrADIxY28?= =?us-ascii?Q?SQSM53pkvmlInstvFplIp2gnX/0cW033vCrsESipPgKu9kwu2DM0SxQPtKJz?= =?us-ascii?Q?s9wo3F1C5cOvfB8LFY/rOcYUAw7FY+r8e7U0nPrLg97T14iTylF9evVrDbTy?= =?us-ascii?Q?2phGfP/gIJ2iVooqX6pOujFfYnARgQp9SZTAPl8S26GH47Xmlou7ripqmw6N?= =?us-ascii?Q?jSwn7s1gM6qG1uXedpoI1D57xTJikLJSVLYViZh80apeyIKn1uHKon1wFCJj?= =?us-ascii?Q?QnYm9l+YKTyNHRHKUAm/IO5dX5CUc1Kkwk1GBFKY+z+9J92KqKThnCej1jFL?= =?us-ascii?Q?Bp5r9dwEjzqbCNf2aIyzoV9+KfFK+UuDG5SL056iFlchAFGHMTdXtNoYdr9Z?= =?us-ascii?Q?cmcBxDvdYvSWRofFNTK/8z2aSAjKvFRDOfguFGx0DqnXLlgoZRnwTVM4PWBz?= =?us-ascii?Q?wZ2HVVxt0q5RowFoxF3pM2JAoRXS/f0Q8akh+5GYLNliOE5M3GhrzNWAzDyS?= =?us-ascii?Q?HR4a6G/xPtfSURHLyiT2W5VQQSXGLHq4Ogg5iuphrbKWFFUuYrlcy8mgZw6K?= =?us-ascii?Q?Nh0EfeoWO/fsgNWs5W1gALNWym0S11Ycthcl1eaebe2aQ0vAVK44Ek1GxUj8?= =?us-ascii?Q?1aLys2el5t0dGMa/ZS4LaE6Ieg4Oci7jHUUAz2bGvv42X8fh8cxPJDgsQ5aw?= =?us-ascii?Q?huRO7UBjieSvzgjwsfd3IZ//BDPndZZywboNuKzppqQ8rvzL8ZJ3mwoxWRGa?= =?us-ascii?Q?F6vPdiV8de8w8aljqtVBbSaZJtNTQRYSgJAwo75Y?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 91b6a8ba-45b3-4b22-e5ed-08dbcb3a25a5 X-MS-Exchange-CrossTenant-AuthSource: LV2PR12MB5869.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 12 Oct 2023 15:44:40.5063 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: GXRr415bNy4O0USnq63oii2zKkOsjYnxQqgYzjYNxmBYLLzGUxZmzITF311Q36Fl X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS7PR12MB6142 On Thu, Oct 12, 2023 at 03:48:08PM +0100, Will Deacon wrote: > I guess my wider point is that I'm not convinced that non-cacheable is > actually much better and I think we're going way off the deep end looking > at what particular implementations do and trying to justify to ourselves > that non-cacheable is safe, even though it's still a normal memory type > at the end of the day. When we went over this with ARM it became fairly clear there wasn't an official statement that Device-* is safe from uncontained failures. For instance, looking at the actual IP, our architects pointed out that ARM IP already provides ways for Device-* to trigger uncontained failures today. We then mutually concluded that KVM safe implementations must already be preventing uncontained failures for Device-* at the system level and that same prevention will carry over to NormalNC as well. IMHO, this seems to be a gap where ARM has not fully defined when uncontained failures are allowed and left that as an implementation choice. In other words, KVM safety around uncontained failure is not a property that can be reasoned about from the ARM architecture alone. > The current wording talks about use-cases (I get this) and error containment > (it's a property of the system) but doesn't talk at all about why Normal-NC > is the right result. Given that Device-* and NormalNC are equally implementation defined with regards to uncontained failures, NormalNC allows more VM functionality. Further, we have a broad agreement that this use case is important, and that NormalNC is the correct way to adress it. I think you are right to ask for more formality from ARM team but also we shouldn't hold up fixing real functional bugs in real shipping server ARM products. Jason 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B6951CDB46E for ; Thu, 12 Oct 2023 15:45:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:In-Reply-To:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=gKb7ROzwjyCntVAtT/ylYWp9Xak/pkCvbpHrWVUyvcg=; b=LQFc7XngXmQmEw ZgMbAyBI8N0HB0Qs3MdWRbSu+llWzSxsdjbaCKE1jKaOuRhfUq52k+doCy6EMwDY724ixywaxlCTk 5dqCQHBKDotXVYMPMXk5/9y0cj6a3lB2jltsvDsPpPZQ80VCHpIye0HweRPLok8ceKqLRwe5BWyLS 76YUZsrD9bX0dWdAdm2DgDyO7De6xJeEgN+oELbAVaVL1LmDhNYXqDccnoN+Xvt039sjUI9sl29RK zi9n9wIegkISC88yn/m7weO9+wYtaiVN4t3vEAGJS07a1V5LPocLqN0gZlEzKFHshg3fu3LTNNwrG +/zpSMeY1tyO9mLTEoiQ==; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Oct 12, 2023 at 03:48:08PM +0100, Will Deacon wrote: > I guess my wider point is that I'm not convinced that non-cacheable is > actually much better and I think we're going way off the deep end looking > at what particular implementations do and trying to justify to ourselves > that non-cacheable is safe, even though it's still a normal memory type > at the end of the day. When we went over this with ARM it became fairly clear there wasn't an official statement that Device-* is safe from uncontained failures. For instance, looking at the actual IP, our architects pointed out that ARM IP already provides ways for Device-* to trigger uncontained failures today. We then mutually concluded that KVM safe implementations must already be preventing uncontained failures for Device-* at the system level and that same prevention will carry over to NormalNC as well. IMHO, this seems to be a gap where ARM has not fully defined when uncontained failures are allowed and left that as an implementation choice. In other words, KVM safety around uncontained failure is not a property that can be reasoned about from the ARM architecture alone. > The current wording talks about use-cases (I get this) and error containment > (it's a property of the system) but doesn't talk at all about why Normal-NC > is the right result. Given that Device-* and NormalNC are equally implementation defined with regards to uncontained failures, NormalNC allows more VM functionality. Further, we have a broad agreement that this use case is important, and that NormalNC is the correct way to adress it. I think you are right to ask for more formality from ARM team but also we shouldn't hold up fixing real functional bugs in real shipping server ARM products. Jason _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel