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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id E497DC43602 for ; Tue, 7 Jul 2026 13:17:47 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 989C36B00A1; Tue, 7 Jul 2026 09:17:45 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8EBC06B00A2; Tue, 7 Jul 2026 09:17:45 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7B4556B00A3; Tue, 7 Jul 2026 09:17:45 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 4BC796B00A1 for ; Tue, 7 Jul 2026 09:17:45 -0400 (EDT) Received: from smtpin29.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay07.hostedemail.com (Postfix) with ESMTP id C04F6168D24 for ; Tue, 7 Jul 2026 13:17:44 +0000 (UTC) X-FDA: 84962032848.29.90B314A Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf07.hostedemail.com (Postfix) with ESMTP id E135140002 for ; Tue, 7 Jul 2026 13:17:42 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=ekBlEtaX; spf=pass (imf07.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1783430263; b=RvbEoXJTrD27mNagqmpsebCS1LcckIkNNOGkiNZ5S4NsE0dOUvzK5Plv/PJjYI9UQYulnU ObNuH/cKeXLuisuKhB66qso96mCgbvREnv8kypJDdASbD7JwbtDaxA+kHRMSkzjEHGC01K nhOTpdk4NVw07wzTx+uVGgCOXj+gUYU= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=ekBlEtaX; spf=pass (imf07.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1783430263; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=5p98PRn2cxjDk+JJlvD1wzmliW0l2W8nSc95PJxuTqs=; b=Bkkv8zeX/anP4dPR/FAbUWvqV4heiB1WZpVS/g3GqpY9+apYGGDOaHdMu2uEBoEEiyO6oD nLezjJ/VMNgdiYr/Mgz6n/6AQvIlec5f/QhbRf4P34jLIT4SlTmzy38QKmJfKwfRQ4j41a MvUheD88nAMRNaX+Rw7yUfZE8x8QeSU= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 1D68443D6C; Tue, 7 Jul 2026 13:17:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0D1D01F0155E; Tue, 7 Jul 2026 13:17:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783430262; bh=5p98PRn2cxjDk+JJlvD1wzmliW0l2W8nSc95PJxuTqs=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ekBlEtaXKEYUfjDrvSvzpx89vlzX8XAx0GfpW4nUJOaQ3SRolAmuk/Y7CfTfPGgJ7 JP8faT51OLBKI00vsvtQZWw9WIZOFJ3rVlmmw4hHsISJu7I7SgSszbErKQ1L870E8d KIls4KWjd6p/bXVbraoj9gw0JDhauAiy1T2Ba16ZZW274Vbl+qZ+0JC+Qgt9C12Fxs vwHJ02whL36oG1D1TQm/f57N0ubo2JltZ/dSnWg49uXAigoG4zbLnXj1TDipXQh/i6 ou8ugFM8ohRJLocIx6s+ZM7/hodfALjZxDkmwUMVIbVeNlu0X6hQMWJfwQ5uzJLzfr vrbb7unCQNidw== Message-ID: <4bfeb697-9c1f-4316-96bb-9bfd66f959df@kernel.org> Date: Tue, 7 Jul 2026 15:17:37 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: mm: opaque hardware page-table entry handles To: Muhammad Usama Anjum Cc: linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , Ryan Roberts , Anshuman Khandual , Catalin Marinas , Will Deacon , Samuel Holland References: <74182e50-b54f-4d2d-a27f-3a59a538d6bc@arm.com> <31d36023-d728-4eee-90f8-158c7066f565@kernel.org> 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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: E135140002 X-Stat-Signature: rkq99194e8rq734b3m4ezoytpf9edrxf X-HE-Tag: 1783430262-954560 X-HE-Meta: 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 LD1zGfKa 0y2vPzQRcw8PTpHOsegwDhZLwR+4j3PhRS9q3lR2p90bTjAFj59nfIUEy4b9qZe/SYwZC5huarEvc9niShGnNUra2XTJYvpg4AlHRokeWEZwB5Zto2Ata6g58uSXE1s/TSv7iHPWyDsJrLBglnj3jToCWv2cDamPePAZnQoOyFqRgaFhbM9Ist7Qj2Qbmx0QfhR7ziQ3DbK9BJ0dzqvlkbvltPktq0MiYDDFLDTaewUfDvJ9mv0nnH5t6MgjqeSrk+A0hMV3Dnh5zeFxQy+4kn5ngpW1x4TzlQ9nW Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: [...] >> >> typedef struct { >> pte_t __pte; >> } hw_pte_t; >> >> And then simply use >> >> hw_pte_t *hptep; > Make sense. So you have suggested to just hide put pte_t inside a structure > instead of complex structure of pointer. I've tried to implement and it reduces > churn enormously. Right. And for most architectures we can probable leave both types be the same under the hood. So we'd only have to convert common code first, and can then e.g., look into making architectures that care about the difference (e.g., arm64) actually have it be two separate types. Just an idea to further reduce the churn and limit it only to core code (because I saw some very ugly stuff in some arch code that would make such a conversion harder). [...] >> Why do we need this and what would we use it for? > The idea was that there should be two different functions to read value. Let's > leave this out of the first initial series. It is complicating the original > proposal. Right, let's leave that out for now. I'm currently working with Levi on an approach that tries to avoid the overhead due to READ_ONCE with folded page tables. [1] We're still struggling with some bits, but looks like we can make it fly and have it be fairly robust. With that, maybe there is no reason left to have separate pXXp_get() vs. pXXp_get_once(). TBD :) [1] https://lore.kernel.org/all/08ecabe9-0664-4aea-82fb-f9cb1739f762@kernel.org/ [...] >> >> I'm still not sure about the _once() really, and if we need that right now. We >> survived without is so far, why do we need it now? > The idea is to convert all current pXXp_get() to pXXp_get_once() and convert raw > dereference to pXXp_get(). Let's keep this idea separate for the other work. Let's > discuss it later sometime again later. Sounds good. -- Cheers, David