From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from DM5PR21CU001.outbound.protection.outlook.com (mail-centralusazon11011050.outbound.protection.outlook.com [52.101.62.50]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0F912364EB7; Wed, 8 Apr 2026 07:04:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=52.101.62.50 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775631845; cv=fail; b=fiefgF4IwiUs0q+QEbsmNq7l+mygn4SXZOnOWywfU66xUdB53h5qVjxQHityAiPqi3s8gaKh9EdJytOanaFZDwbCPN1WdvJAHQG4IkAQ4qSOdyX9jZdUlh5bb8TsosuUbVRUC/TSo3RKmkqw49lURfe5Xm1kXxoTU65xaHXZG+c= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775631845; c=relaxed/simple; bh=SQB+YrQ9BTfSze1katwVhTB3Z81pGJNmrQpDoG0E00s=; h=Content-Type:Date:Message-Id:From:To:Cc:Subject:References: In-Reply-To:MIME-Version; b=XcFsZVOU34ENKRo50TkRkun1BiEBOOnvOUlrIpGjKuZlLaP0chrvCXOQ/zl4reX7DIwe0iCk91WPh3vrZsiZq+ESd+DZHQPSvIfQgQUhlWQqlaC2FOSAwkS8mGJCqjup/Wl3QMNsY/FB4qiprxW7mwU1n7oeLjBAjTpjHESH3Fo= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com; spf=fail smtp.mailfrom=nvidia.com; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b=YR2gWBZl; arc=fail smtp.client-ip=52.101.62.50 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=nvidia.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b="YR2gWBZl" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=OuXzxHarW9Usyz2Y42gL5dLB4D8TSDVWMyYpz4o5lhe1u8OHJOvNHbsljLbIPMS3zPdJGWWRNJ1lmeK4Vk289RfzuO5lRx62zBR9j5Vcfxh9/AFmfya1XICaUbru92RPw6fHMoSmfMc6paBHX7EkroRQ25AyJamq1+MvujUffkUAvekua5wqGVTOriXt9P517znBtA6mTq78FswwXim7cjPfKxLiJ/rb7dCfzroNdVr13ZiBUdbwMVvX5llnFtKICb7PtSCgWYW5PPfXTZaf2v4atunGxP4OYoH4dng7t/x1jiZQMDGXoTtMEpI+T8dNaR5njB62rmO0EGRdcG+PlQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector10001; 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=QutQ3CdynSj67ZC1105GCYUZGUGuk4BvqWikYEe2YQw=; b=LJr33xsj8Ggl39A8jVGzGCewhnjEZzg4dNAmLsOEmz5LLraMfZSTH5/jr1BYDi+8O+m7RgV0vsu/x2aJHhZ20iFvK4ERFz/8n3zApZ/J4IcfeLYqY1rnxiSoW4K79t6ewbcX3gBGmwAZwBXIqIEKVwkC2gi47KTiYYwEjPoiMJh6BW8XG0xmfD0y2Mm3say2QosWqayO4t9kCkT7VnYj3Kp5RjJPntSJiH4x4v8yJfHDm+1a1FFfCx0mtwkTyQif3t3XpOYU5CrV8io/OZjTYwQjAy0yG9gbLw+asNDcY0jBXYdqwbdjMYKKLUTNOtp05qoYf79ze2CupRQGc7ErtQ== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=nvidia.com; dmarc=pass action=none header.from=nvidia.com; dkim=pass header.d=nvidia.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=Nvidia.com; s=selector2; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=QutQ3CdynSj67ZC1105GCYUZGUGuk4BvqWikYEe2YQw=; b=YR2gWBZlY96RtUZKYda0UoWAX/o3zRtl6naMNUSIAnXTR/g5EvaNGfyTdkJQ9bLsTMtFsv3LMRZAiU2siO0Y3xYDYtWfeNBeAmhxxpstcfERQfgtzrLm0lDzbgd4apGJXtY0zhVe/ujmmyFRpJgkMsDe8De5yrpK0HKSJHcCX4gSj++c+SFkUb3Uf4TSzZ5+jAkmMgcAhQ3bfxY0b271FwKEPrqG1JTSzsdJzWpIrsiANGPEX9dvHHRUH5cmBNfV8rc9ZvDWPR2XBczYhnqut33K2IYFqngJ2S5Kqfxe6Oo5UusN4kOwzVQJzC00aX4tV7+DHZH42ahM3V2Wmjo31w== Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nvidia.com; Received: from CH2PR12MB3990.namprd12.prod.outlook.com (2603:10b6:610:28::18) by PH7PR12MB8055.namprd12.prod.outlook.com (2603:10b6:510:268::10) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9769.21; Wed, 8 Apr 2026 07:03:59 +0000 Received: from CH2PR12MB3990.namprd12.prod.outlook.com ([fe80::7de1:4fe5:8ead:5989]) by CH2PR12MB3990.namprd12.prod.outlook.com ([fe80::7de1:4fe5:8ead:5989%4]) with mapi id 15.20.9769.018; Wed, 8 Apr 2026 07:03:59 +0000 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Wed, 08 Apr 2026 16:03:54 +0900 Message-Id: From: "Alexandre Courbot" To: "Joel Fernandes" Cc: "Eliot Courtney" , , "Miguel Ojeda" , "Boqun Feng" , "Gary Guo" , "Bjorn Roy Baron" , "Benno Lossin" , "Andreas Hindborg" , "Alice Ryhl" , "Trevor Gross" , "Danilo Krummrich" , "Dave Airlie" , "Daniel Almeida" , "Koen Koning" , , , "Nikola Djukic" , "Maarten Lankhorst" , "Maxime Ripard" , "Thomas Zimmermann" , "David Airlie" , "Simona Vetter" , "Jonathan Corbet" , "Alex Deucher" , "Christian Koenig" , "Jani Nikula" , "Joonas Lahtinen" , "Rodrigo Vivi" , "Tvrtko Ursulin" , "Huang Rui" , "Matthew Auld" , "Matthew Brost" , "Lucas De Marchi" , "Thomas Hellstrom" , "Helge Deller" , "Alex Gaynor" , "Boqun Feng" , "John Hubbard" , "Alistair Popple" , "Timur Tabi" , "Edwin Peer" , "Andrea Righi" , "Andy Ritger" , "Zhi Wang" , "Balbir Singh" , "Philipp Stanner" , "Elle Rhumsaa" , , , , , , , Subject: Re: [PATCH v10 12/21] gpu: nova-core: mm: Add unified page table entry wrapper enums References: <20260311004008.2208806-1-joelagnelf@nvidia.com> <20260331212048.2229260-1-joelagnelf@nvidia.com> <20260331212048.2229260-13-joelagnelf@nvidia.com> <5db2aab1-4b65-486e-ad9b-27a108bdb0d6@nvidia.com> <537a8c5a-3885-4c47-99f6-963b48ddf87d@nvidia.com> In-Reply-To: <537a8c5a-3885-4c47-99f6-963b48ddf87d@nvidia.com> X-ClientProxiedBy: OS7PR01CA0153.jpnprd01.prod.outlook.com (2603:1096:604:24d::7) To CH2PR12MB3990.namprd12.prod.outlook.com (2603:10b6:610:28::18) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PR12MB3990:EE_|PH7PR12MB8055:EE_ X-MS-Office365-Filtering-Correlation-Id: 383e0f28-834d-4218-de67-08de953d0188 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|10070799003|7416014|376014|56012099003|22082099003|18002099003; X-Microsoft-Antispam-Message-Info: rzFS6rTZvqUDpiwWHXi2W0V3uh5PEOT9ZgsX3+WqkdExvTDntSp7C13ImQ56PsO//qyTtnZ4joYnO7jncP9k0BkdPJ5RLMX6E49V8F9+2+Jepi+C8kldXniy4WVMnYExmLEV5M06G3Ru9f2Syjw1mqpkk40gPBBu2LOc6OQf2fJrWJ5SKaDTlkhA5mvrLt+XtsRPwxW5IJ93uZI8d47S6unVHM3658XIMIJA4BiJiylhYTOB2W54FWObkGc9YFLSfxX4dDDtiTojDceE2f8amuwHaa/OaqDjO2KUttjpnYllQ5KQs1eEH/P+VpnJBIXUp+ivgyXGZTJJD3Dv4NKXtn0UgN34lsCNNd4MVwn0BH0EvmHiHYHj/Zy1w2ysBzatAl0OuG6m590z55OMqn11eZQrRGVd/Nx/yBf/Ymnii3KsibsrEzO3ctKg4ZRIeJF3NukpcXMKonf+1DeOeb9RcSdFHsDc7KNqWdXjgrfsBedeYNI9CaQrWOgySP/n8l0A4cRDqI9UfyisGEVfekSwbq6i8oJ640e55KhSDSJA27YnLCbDnjMMWxQKNFF+nQiK76c95sQP5aVSQIew+lGw6c1vZX5OQsdfKaqDTN/eKVKDqwhmL0d4PjBSI19pQuocXZyrMzXz7D09Vow35eDEYKgh89kyeAV4wzHOrD1jUaQ/qvuVt1keCRLD58W7GV5JB6oUIHPGlPzbjHzlOtuv8i19Ihyic5pRod0XnOUX5ds= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:CH2PR12MB3990.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(366016)(10070799003)(7416014)(376014)(56012099003)(22082099003)(18002099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 2 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?SXFiQnAwTnpBYVEwT0EwOTlTcHNWUmNpYm5QaUVYSVNWbTlib1RQZCs1V0tO?= =?utf-8?B?bWQ1ME0veWJ6VnJpOTdiSFlrSW9waEZyZmpXSTZVbDdZeEhNSGhXcnVrYUho?= =?utf-8?B?M2pycDlCTXJROU5vUzVkZk9PV0xXclJ5VzUrNjU3YThBT0FHditad04yaS9H?= =?utf-8?B?TklBdDNiM1JXZzBWb1dUNWNpZkRMcXNvUlZiUDlGeUt1UVNldnpGNWN3WVdW?= =?utf-8?B?bnFWNTFYbkRocXI4WnhNdS8xNUQzSlZGTEs5OVVYWEk2SUNZZE93ekRtVjVO?= =?utf-8?B?cmdxeXh4WFdRWWNCVVkyay9LSHpLS0NmbENvRkJnWXF6NDNFSjE3MGlJRTA4?= =?utf-8?B?WmlEWHlLVS9MRlVXOHFyNlM5cWsvSEJwS2NLWnpYSGw5K05kOUllWW8reDBh?= =?utf-8?B?cG56OXhnb1hlWk5SODRCOE01NGN2b3FML2I4WFlwUXl4WE5qQUxhS1JodkJJ?= =?utf-8?B?RVFjQTdMTGVjZ3doRzIxNmp2SkoyaEd4b1RRNFBUaUNKckZDbzNsbWVJcHRV?= =?utf-8?B?akFkRlBwdFdHVlFUSXNoVlpTZXVieVlLTkppMTRWdUlaOVBLRkNqMnZxOFVQ?= =?utf-8?B?dnhKRkRQOGtEdG0xSXl4QUZFUjY5WkwzQ002YWxEZzBndGF6TmwzaGt3L3VV?= =?utf-8?B?Sytpejk4aUhZaWdQeHVpaWIvczAvWnpTSWEyd1FxZmNTNlo2WHBSdEc1bm5F?= =?utf-8?B?MnlMRFBZNUVUT2N1OFpaR21DMkZTQXI0WEVrRzl5c0FUZ3lFckJXOGtUdTV4?= =?utf-8?B?WkxyRW9seENrZzcvbHdxZEpTUlIzcjY1SmtCQkl0YVQvbzR6SGFoQS9lamFz?= =?utf-8?B?S0h4VlZpQWhPWXFmcTNHQUhmV3F6RHFoM1dhaGYwbitZaWNlRjh0VnpJQW5C?= =?utf-8?B?SGVNWEZ0eUtRbWVhOURjYmhJSUpseEdiaHNHVUF1djRvelRIYzFVT01jV3VZ?= =?utf-8?B?ZjdDWXdrZzNDQ0w4cnN6cDlNWEFGVkpqTkwwUi9HdGR5dUgwOGlwdVZjL2ZK?= =?utf-8?B?eW84bkFLRzBUbGhBazV5RzZYaU92S0NCQ0hhdml6bmJBTEhZckIzUUI4Q2hN?= =?utf-8?B?blFrL0FLVFd6ck9ZcVhFam9GNzVUeFJubUtZTXAzL1NKMldYNEJCbk1ZWTk2?= =?utf-8?B?Q2UxT0RsVzMvK2Z5UjlGQjh1UW90Y3FVREx3TXdHQVcvMHlmMmJYNTRrTWw1?= =?utf-8?B?TzNyT0FEU2pzMlB0WUt0WHZQampYWUhMbjJKNGdPY0ZvNU5tRW1RZXJRUFM4?= =?utf-8?B?RWZSOE1VRDE3QXJmcUdxOWtBeDFmTklVc1U3dHNqMGhGQUV2R0FQMXhvc0VO?= =?utf-8?B?VFY5TGo3bU02TmMwVXljZ3pIQUVRTGhPNzJmSXgrQWVOYnQxQVo0Tmc0VStB?= =?utf-8?B?NDVzTW5SNzIwNDlOb01SRmhsTk5yblpiL25yMUxjdFhYem54bWJzWWs5ejFr?= =?utf-8?B?a0hLeTdBRnI5OEJuSURkSjU4TW9GdXFzMkJ2U212WDl6WmNKQ24xUXBqcHpG?= =?utf-8?B?QjZHd3JpU2k2Y3VCOTIxdXB5Z29CdjRmU2JMaWRWN0ROZjROUWIzOWhSWEtp?= =?utf-8?B?NmZjc2dUelNpUndOcTJQcTcrbjhyRWlXSjJYSEdXcmVGS2RBaUpPTktnaG4v?= =?utf-8?B?V2ZRWkY5clFORFV6VFhVNXdobm96QXgwTXJMNkp3ck5XelN1WHlLTkZ2SGVt?= =?utf-8?B?Q1VNWEpjM3JGSEozTlNXWGdYTnIwTjRtbXBKR0laa3N2SjhHSzY2VUhBME51?= =?utf-8?B?Vmc1bE91Zm9DKzlBZHlTSVIvY2NaNnNCS0xsYi9UUWtLZEJqcEgwVTRUT0pO?= =?utf-8?B?bTExaHBERjI2M3Zob2FZdTJMempPY3gvdGVzYmhlQjYzcHZUazFITzJBSHRQ?= =?utf-8?B?dE9uWml6bkFPSjRabWMwTjcxb2hDZmJkWWxTN0xIcXJMQkVzQ0FuYndURGhz?= =?utf-8?B?T0xnSHdyaHFKaVdDdEtJMzhuYnIvRlJWano0UkUyS01TQTgyS3BrUWZyQWcy?= =?utf-8?B?Z1hscGpiT3F0RmE4TUx6S3UvRTVodUU0Sys3MjVnTDUyQzBRbWtna1dFUFk0?= =?utf-8?B?VzNVMW9hWko0eVhhVXhDMGR6UG9PQ2YzNm56bDF6L2lkVGNja2hlN20yazFB?= =?utf-8?B?cEd1aGlkZk5BcVpmQlBuaUowUVc5RE1ZUUtsNm85RUhzY2dsRERSbTdmMXNG?= =?utf-8?B?ZUM5eC9mVnRLT0NCcHpvdEU1VUtoR1RCT0RpSU03L2tzNkNqZmZoTFV6VDZj?= =?utf-8?B?SGpUUjZSR2ZFcURQM28zWmFDcEMydk9Xdzl2VXkxbW5uZmU5VUc2aEpMYXVh?= =?utf-8?B?anZ4RGJOUm1vUjA4MlNHS1hoeXBlak1hTENmaGFndUtDZEhKNCtvOXRlUnpU?= =?utf-8?Q?Q9PcPYau7wCRIs4fuh3bvmfqGtCWfzGDlLHRQZQ9lfisB?= X-MS-Exchange-AntiSpam-MessageData-1: gItelP6aPABccg== X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 383e0f28-834d-4218-de67-08de953d0188 X-MS-Exchange-CrossTenant-AuthSource: CH2PR12MB3990.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Apr 2026 07:03:58.9146 (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: 5SV7SQfyl2ZUWI0I7leiMrt3jnb1RZEk98TyxNDXjA66n6KoDRoRJwadQqvOTL2wEqHWqa5es+9TsECkAYH2VQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR12MB8055 On Tue Apr 7, 2026 at 10:59 PM JST, Joel Fernandes wrote: > Hi Eliot, > > On 4/7/2026 9:42 AM, Eliot Courtney wrote: >> On Tue Apr 7, 2026 at 6:55 AM JST, Joel Fernandes wrote: >>>>> + /// Compute upper bound on page table pages needed for `num_virt= _pages`. >>>>> + /// >>>>> + /// Walks from PTE level up through PDE levels, accumulating the= tree. >>>>> + pub(crate) fn pt_pages_upper_bound(&self, num_virt_pages: usize)= -> usize { >>>>> + let mut total =3D 0; >>>>> + >>>>> + // PTE pages at the leaf level. >>>>> + let pte_epp =3D self.entries_per_page(self.pte_level()); >>>>> + let mut pages_at_level =3D num_virt_pages.div_ceil(pte_epp); >>>>> + total +=3D pages_at_level; >>>>> + >>>>> + // Walk PDE levels bottom-up (reverse of pde_levels()). >>>>> + for &level in self.pde_levels().iter().rev() { >>>>> + let epp =3D self.entries_per_page(level); >>>>> + >>>>> + // How many pages at this level do we need to point to >>>>> + // the previous pages_at_level? >>>>> + pages_at_level =3D pages_at_level.div_ceil(epp); >>>>> + total +=3D pages_at_level; >>>>> + } >>>>> + >>>>> + total >>>>> + } >>>>> +} >>>>> + >>>> >>>> We have a lot of matches on the MMU version here (and below in Pte, Pd= e, >>>> DualPde). What about making MmuVersion into a trait (e.g. Mmu) with >>>> associated types for Pte, Pde, DualPde which can implement traits >>>> defining their common operations too? >>> >>> I coded this up and it did not look pretty, there's not much LOC saving= s and the >>> code becomes harder to read because of parametrization of several funct= ions. Also: >>=20 >> Thanks for looking into it. Sorry to be a bother, but would you have a >> branch around with the code? I'm curious what didn't look good about it. > > Sorry but I already mentioned that above, the parameterizing of dozens of > function call sites, 3-4 new traits (because each struct like > Pte/Pde/DualPde etc each need their own trait which different MMU version= s > implement) etc. The code because hard to read and readability is the top > critical criteria for me - I am personally strictly against "Lets use shi= ny > features in language at the cost of making code unreadable". Because that > translates into bugs and nightmare for maintainability. After a quick look I'd say that having a trait here would actually be *good* for correctness and maintainability. The current design implies that every operation on a page table (most likely using the walker) goes through a branching point. Just looking at `PtWalk::read_pte_at_level`, there are already at least 6 `if version =3D=3D 2 { } else { }` branches that all resolve to the same result. Include walking down the PDEs and you have at least a dozen of these just to resolve a virtual address. I know CPUs are fast, but this is still wasted cycles for no good reason. If you use a trait here, and make `PtWalk` generic against it, you can optimize this away. We had a similar situation when we introduced Turing support and the v2 ucode header, and tried both approaches: the trait-based one was slightly shorter, and arguably more readable. But the main argument to use a trait here IMO is that it enables associated types and constants. That's particularly critical since some equivalent fields have different lengths between v2 and v3. An associated `Bounded` type for these would force the caller to validate the length of these fields before calling a non-fallible operation, which is exactly the level of caution that we want when dealing with page tables. In order to fully benefit from it, we will need the bitfield macro from the `kernel` crate so the PDE/PTE fields can be `Bounded`, I will try to make it available quickly in a patch that you can depend on. But long story short, and although I need to dive deeper into the code, this looks like a good candidate for using a trait and associated types.