From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 3D132471D03; Tue, 28 Jul 2026 19:26:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785266787; cv=none; b=k/l/K15MwyBG97NqiANRB/AA+5iXvUEiqsklsunXDdg4613ifvRe9KJ8U785IRSFCt5SuzmZmOJnVRiBT+TaKTKydrTRUCTEttyUPw4JfFOYRJmLfqlelpuw0Hh5CLqK96BA4LD7ieKAHsI3RbFnc6vhnAjrPMyGwC3Jtxjtyis= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785266787; c=relaxed/simple; bh=t3PUtazpRGqw1bmR2BviNtX9wa1tr+1RO8d6vzdFsRY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=aSu0jOW4MO6kOYP7i9BiHtEgZSFteDZDPS2EALGv1SecwCnlr49L/2rtusW6rbdy8V9xMkE5ZY9Whcpgtprvf3vgyxm93uUVyozMgCcDohPN6cTLyyV4rctuja44MFcJAdE+3pVjm7AW3s22zx5FJzJcHL/V8U9s8lht+LqcMNc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Wk+Dy2Ld; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Wk+Dy2Ld" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 55FCD1F000E9; Tue, 28 Jul 2026 19:26:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785266786; bh=B9zPErIOkKOvWU4JJG+dspgkrLmx8WSjgAIhjf1cHOk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Wk+Dy2LdjSS++FUG8ogDF9T7pT+EAMTNcB05WeR4hXNaXglCVPisWY+LtMICE7Ccn wg89k4Kvgy+wj1Z+MYeBAhF/fpDBT5QBmapIlx+G9nPNFi+PtoCZcgFGdFDnLbAXt0 xB9tb7u8wQORuyWEL/5BRGQ2JQ2k9CqZ2ZVyyUj8/EZCr1Qepptpcml/7TGdY1D8nm GSTIcvePc1fP69qF+FthXNV/zsYPQIg7psEdREpgXn9BbFwQhb7/ZitQjH5BdGIeL5 10/HbxBCKZnA9MQ0tzrL6PXNOGh1zI0y/tMqhlx3SWm/HNYuS05o09qLSvFYiNKTIz dUsn/WiERIxzg== Message-ID: <2c19247e-bee6-45f4-a353-2fcc60db26e6@kernel.org> Date: Tue, 28 Jul 2026 21:26:06 +0200 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 00/11] mm: distinguish PTE table storage from PTE values To: Muhammad Usama Anjum , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , David Airlie , Simona Vetter , Dimitri Sivanich , Arnd Bergmann , Greg Kroah-Hartman , "James E.J. Bottomley" , Helge Deller , Juergen Gross , Stefano Stabellini , Muchun Song , Oscar Salvador , Andrew Morton , "Liam R. Howlett" , Lorenzo Stoakes , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Peter Zijlstra , Andrey Ryabinin , Pasha Tatashin , Chris Li , Kairui Song , Uladzislau Rezki , Steven Rostedt , Masami Hiramatsu , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , SJ Park , "Matthew Wilcox (Oracle)" , Jan Kara , Jason Gunthorpe , Leon Romanovsky , Miaohe Lin , Dennis Zhou , Tejun Heo , Christoph Lameter , Mike Rapoport , Johannes Weiner , ziy@nvidia.com, pfalcato@suse.de, agordeev@linux.ibm.com, ryan.roberts@arm.com Cc: linux-kernel@vger.kernel.org, intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-parisc@vger.kernel.org, xen-devel@lists.xenproject.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, kasan-dev@googlegroups.com, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-perf-users@vger.kernel.org, damon@lists.linux.dev References: <20260727164715.2866609-1-usama.anjum@arm.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260727164715.2866609-1-usama.anjum@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/27/26 18:46, Muhammad Usama Anjum wrote: > Hi, > > pte_t currently describes both a logical PTE value and an element stored in > a PTE table. Consequently, pte_t * can point either to a standalone value, > often a stack copy, or to a PTE-table slot. The compiler cannot distinguish > these cases. A value pointer can therefore be passed to an interface that > expects table storage, while table storage can be read by direct > dereference instead of the architecture accessor. > > This series begins a staged conversion at the PTE level. It introduces > hw_pte_t as the element type for PTE-table storage and converts generic MM > to use hw_pte_t *. Logical PTE values remain pte_t. Interfaces that > intentionally return a value through pte_t *, such as install_pte, remain > value interfaces; the relevant parameters are named ptentp to make that > distinction explicit. > > The generic definition aliases hw_pte_t to pte_t, so this series preserves > the representation and behaviour of every architecture. ptep_get() keeps > its existing READ_ONCE() semantics and converts the stored element through > __pte_from_hw(). An architecture can later define a distinct hw_pte_t and > convert its PTE interfaces to make the distinction compiler-enforced. > Architecture PTE implementations and most architecture code are > deliberately left for those later opt-in conversions. > > Here, hw_pte_t identifies PTE-table storage rather than table lifetime: > complete PTE tables use hw_pte_t whether or not they are currently linked > into a page-table hierarchy, while standalone copied values use pte_t. The > distinction between complete but unlinked tables and hardware-reachable > tables was raised during discussion and remains an important point for > review. > > PMD, PUD, P4D and PGD storage are deliberately out of scope. They can be > converted in later series after the PTE boundary is agreed, avoiding the > PMD-specific cases that made an all-level conversion difficult to review. > > Most mechanical pointer conversions were generated with the Coccinelle > script included below, then audited and fixed by hand. > > This series does not add a second ptep_get_once() accessor and does not > remove or replace STRICT_MM_TYPECHECKS. Do you have a pointer at the arm64 part, so people can get a feeling for how an actual hw_pte_t implementation can look like. -- Cheers, David