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Howlett" , Mike Rapoport , Anshuman Khandual , Catalin Marinas , Will Deacon , Samuel Holland , linux-s390@vger.kernel.org Subject: Re: mm: opaque hardware page-table entry handles To: "David Hildenbrand (Arm)" , Alexander Gordeev References: <74182e50-b54f-4d2d-a27f-3a59a538d6bc@arm.com> <31d36023-d728-4eee-90f8-158c7066f565@kernel.org> <4bfeb697-9c1f-4316-96bb-9bfd66f959df@kernel.org> <6110202c-057b-4701-8c04-1a76ee7bb9ab@arm.com> <20260721124057.2820903Adf-agordeev@linux.ibm.com> <3c21586c-0ffe-4ebc-97f1-803e8acfc5c1@arm.com> <716f73c1-41cc-48a5-b0e1-a47403a30da1@kernel.org> Content-Language: en-US From: Muhammad Usama Anjum In-Reply-To: <716f73c1-41cc-48a5-b0e1-a47403a30da1@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: LO3P123CA0032.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:388::8) To VI1PR08MB3421.eurprd08.prod.outlook.com (2603:10a6:803:80::16) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-TrafficTypeDiagnostic: VI1PR08MB3421:EE_|PAWPR08MB10973:EE_|AM3PEPF0000A79A:EE_|AMDPR08MB11508:EE_ X-MS-Office365-Filtering-Correlation-Id: 3fe14330-8f29-4ebb-25a2-08dee8dc3c78 x-checkrecipientrouted: true NoDisclaimer: true X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam-Untrusted: BCL:0;ARA:13230040|1800799024|366016|7416014|376014|23010399003|18002099003|22082099003|4143699003|11063799006|10067099003|56012099006; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: EfROl10OGV8zCSeqHdPpYq3ow2lVeSGecm/impmA7wzt+LPtapgiruEXBa8tVCWtQa7Rxvu6FZuP28hnoyDYAyU9J/b+0Ulp1UhgKRCjm52S3QtpNcSJ6w4MyLzSI+pQ64UIbarpM2FPPozLn+dpU+qVEdz+0Ze1Xfb8dvYamBXhL8xCtgmxwKC6K1vWrrR7jnYiYh1Zd8sIlcBFGBR7o0j8Q24AybgkE8QGtFpRik5NpH70iC8M38a1QHdMNcKUYzWxU1U2wy1Nshdb9zPdF6+OdteHE/I+rO5lxQ9e0v79YnNt4VDPGQRB/nsiMkabJB3WlspwmVBM+QdI65XoRrjsDQ0lU/XOOujpa5saJE2rKarEyT0/hOWprLRU7Tap4h/vW8+p0k7MHmGfWpdpwcm+0PuskK1kiKr8XFbGnxu2RDHKmkpeCqKxXVva+M40 X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 23 Jul 2026 17:02:53.7252 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 3fe14330-8f29-4ebb-25a2-08dee8dc3c78 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: AM3PEPF0000A79A.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AMDPR08MB11508 On 23/07/2026 5:38 pm, David Hildenbrand (Arm) wrote: > >> So after the conversion, it doesn't makes sense to keep STRICT_MM_TYPECHECKS >> around. Please correct me if I'm wrong. >> >> This brings another thing in my mind that in ideal world we would just >> turn STRICT_MM_TYPECHECKS on for all arches all the time. But the problem >> with it is that STRICT_MM_TYPECHECKS defines pte_t which will stay double >> meaning still. So we want sort of STRICT_MM_TYPECHECKS with different name >> and separate stack and hardware types. > > I think STRICT_MM_TYPECHECKS is also to avoid catching when passing a pte_t into > a function that consumes a pmd_t, and vice versa. > > STRICT_MM_TYPECHECKS makes the compiler generate worse code today, which is why > we don't enable it always. > >> >>> >>> We would like to keep it, and I guess some other architectures too. >> David had summarized it well. We'll convert generic code to use hw_p*_t >> types which would be typedef to p*_t for those architectures which don't >> care about. But if an architecture wants to interpret these types >> differently or want to make sure the type is enforced and not directly >> dereferenced, they need to convert the arch code a well. But it can be >> done slowly. > > I think what Alexander meant is: they want to keep STRICT_MM_TYPECHECKS (or > something that achieves something similar :) ). So as long as that keeps on > working, all good :) Thank you for clarifying. It has been a month since I started this discussion. We don't have any disagreement on it. Should I proceed to post first part patch series considering most people must already have viewed these emails and are on-board with it? -- Thanks, Usama