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 B83C5C79FB9 for ; Thu, 10 Sep 2026 11:12:43 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D520A6B008C; Thu, 10 Sep 2026 07:12:42 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D01206B0093; Thu, 10 Sep 2026 07:12:42 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BCBB66B0096; Thu, 10 Sep 2026 07:12:42 -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 8CA9E6B008C for ; Thu, 10 Sep 2026 07:12:42 -0400 (EDT) Received: from smtpin08.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 2A83B1C246A for ; Thu, 10 Sep 2026 11:12:42 +0000 (UTC) X-FDA: 85197589764.08.6BAAB79 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf15.hostedemail.com (Postfix) with ESMTP id 65F93A0006 for ; Thu, 10 Sep 2026 11:12:40 +0000 (UTC) Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=XAA2AxP9; spf=pass (imf15.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=1789038760; 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=ERCd9oSGM6NphjvkvfR4ik7TZShb7N0/sLtNifxHmW4=; b=aYuKI9VMccO3oXbEgZWOGKMGbdaQPATmiRPVtfLYUXLSxacEwFxHY3k36KaTkMBAW76W6U 5SAYGJZQnpOrejvHFqn603WeCcBtG/HlAC67JkvIPEgsSOaFI9I+Er5NJFvkiR/c6Q5K8Y +/RUggfI5aNGXI1Ke9yYBqr/R9ptTaA= ARC-Authentication-Results: i=1; imf15.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=XAA2AxP9; spf=pass (imf15.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=1789038760; b=NywMmj3PN/qxcZxlJzp1AWx728aVPKJXG+hvpEREOmsjVvMjFsKkI4uiuMEAmyb/oKz0QT Yvwdozc9Wo/1IzMBnqz94/fae1nz44ELYjeiGWocpSglnr0l1SnBpYJJnB823Kc3DfSyio 3rh/v4lP398JM27WKzggZJboELhq62I= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 82FC441170; Thu, 10 Sep 2026 11:12:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B4ECB1F00893; Thu, 10 Sep 2026 11:12:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789038759; bh=ERCd9oSGM6NphjvkvfR4ik7TZShb7N0/sLtNifxHmW4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=XAA2AxP9wc3keOOWbFhRPVpf+EYxKxMasAJfXKjcAqAFuVSeVn1RDY4Gg9ZkUluVf n9pwpAydmxlkNOitfcepj28uyjlpttBuu7A4phufEbFGOKtzfugTxHl7+ssItL/GQj HJqh+ZELtkOt/9go2MSO372IFr6HppkrEGAHyYQH9y95v92CgUil/++DQ2G82I3a+9 8d7WwlCUuv4fbKea+9p2VnVIi8KGTwP1gD3LirxqJvH+dmiAPuGT6Ox5CfyrIybIPa w+bQJuF1/u7a6X6L3GlQWGV405kMeRAkPD+ghJsspAJGKwdZ8kbCeIEMW5928Iofp6 xjHWmpt+oHGhw== Message-ID: <52562b42-1186-4e44-90ab-7fb92a6dcb1e@kernel.org> Date: Thu, 10 Sep 2026 13:12:22 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC v3 00/21] mm: change behavior of pXdp_get()/pXd_page() in compile-time folded pgtable To: Yeoreum Yun , Russell King , Huacai Chen , WANG Xuerui , Thomas Bogendoerfer , Catalin Marinas , Will Deacon , Arnd Bergmann , Andrew Morton , Kairui Song , Qi Zheng , Shakeel Butt , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Johannes Weiner , Michal Hocko , Lorenzo Stoakes , Tianrui Zhao , Bibo Mao , Anup Patel , Atish Patra , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jonas Bonn , Stefan Kristiansson , Stafford Horne Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, kvm@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-openrisc@vger.kernel.org, Muhammad Usama Anjum References: <20260902-dummy_ptxp3-v3-0-5d8f5b17c25c@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: <20260902-dummy_ptxp3-v3-0-5d8f5b17c25c@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 65F93A0006 X-Stat-Signature: dknnkp5beiohc187pp54665u8yicbpmy X-Rspam-User: X-HE-Tag: 1789038760-491683 X-HE-Meta: U2FsdGVkX19bluQdswAoBvE+T89BaKwZg9tM71iX5dM4WiXl0AY146dsbOIJdbtHMvtTjZCOv24SRt04h6+gi0VNTChsPRU/jQJdfN9DfR6h0LaXmNj87qFPh3fGcZPaTEcc6lE+9wC9S0fk3T11ChMXhekV8jDUGRfAQkY6kc0BCNsR7/EPCsMcsAnvw3KMbIp4kydlUzK3HcrcHSI2ZRmPJQuFslV0fBK4r8fXHrAe5tcjSRF1D6/OFzdT2kAE827K7VK96WuTeH34KsgZH0HtiIYpOyzSvUFIQ9dFQVijqoAI3a10VqecMZ45AkbYbKeEILrNsyl6jM+cGwfiWri+nnmfn9BhW7nE+OpjjYXEU4O/1ZW/ReBIKVVnS5zHVVawXQ5cfkSYeQik2ZhQ0krO3xta1yGot3in+MiHMKny1M6hdJaib2e8Z30kgyWeunLwdlTofTnCQOXsSNxNyNcX22DX4PSUi3s5FXBCga1ef92lYjHIuU1U3v2brvG/HCu4eFoi7kuoNLduRHwbqMflTGb+i0ATH/jRy/nZAyTMVnov4VCN8CEVULqsR1ZPS9gClcCaAgSA8nAs+5nrZjJGCx7AL+QTDVhZmezasiLRu3i+40zefJ+p8xtyvhSEAWt9kxMQWvCb8PbGoSXLRttnoy0zwOLsnPeAwMhsApYg0aLyAduqZDI5jsnNOV+PunDeQMoiVNpXYkHHlwIVqaZGi99oUsvTxO8nhXHHKCTdPr26d2+aDP8FJJf5/Gte/KrRl5cXQZb4jpeSqisOwtI6paA0NNJ253PSf8BkNwJpGOcxU4aEHZuZOoUUVmJDJSYKAO6DQk5gGXnRqaf0YX8rp/Y8P21J8Vf2mF5x9NAszT8674B6qUkepxXgkb0xSip4EBdwPLrCOeUXIDtaTehhts4JkMvvQuSWA0ckSOQm/OUM6gZl/Aj+tq0qlrqxxre3uSFuFMcm3acYuY2 9QkxNWYI /WNGGLsZs9bN9njFJVEoskL6QhvChEDvQPkiw0ZZUC9X2jkqPRLaSAxNTSUpUTcxBQN126xihury+VT4cv4B9V6VpYGrVpVhxZcssFAhdVHUrtt3goj4pfmxIhGK26QaVkv6bO141Lc+Ejr+q04IMFrwxq/Lj0jgGdOHRvqxidE3MxgufPvpMPhmzQnVp1un7qg/cyOR7fJeCSExCO3IX9BJ1ZD/YYXJEDD6RkovbmJIDRWiuo/bI5YaA0HCGFXUmJBBsmx6Nu0rXcJkeUjWY3rfFaweGI5xobx+jM6uS/alCtO+tDEiXiZIb6g== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/2/26 13:56, Yeoreum Yun wrote: > Using ptep_get() and its counterparts in common code is suboptimal on > kernel configurations with generic compile-time folded page tables. > By default, ptep_get() and its friends expands to READ_ONCE(), > forcing the compiler to emit a load even when the value is not used afterwards. > > This issue was recently reported by Christophe Leroy [1] for ppc32 > preventing futher code conversion to ptep_get()/pmdp_get()/... helper > and the same behavior can also be observed on arm64 when built with > 2- or 3-level page tables > > e.g) perf_get_page_size() in arm64 with CONFIG_PGTABLE_LEVEL=3: > > 00000000000052a0 : > ... > 52dc: d53b4234 mrs x20, DAIF > 52e0: d50343df msr DAIFSet, #0x3 > ... > 52fc: d35e9a69 ubfx x9, x19, #30, #9 /* pud_offset_lockless() */ > 5300: f9403508 ldr x8, [x8, #0x68] > 5304: f869790a ldr x10, [x8, x9, lsl #3] /* pudp_get() */ > 5308: f90007ea str x10, [sp, #0x8] > 530c: f8697908 ldr x8, [x8, x9, lsl #3] /* pudp_get() */ > ... > 5360: 90000009 adrp x9, 0x5000 > 5364: 92746908 and x8, x8, #0x7ffffff000 > 5368: d3557675 ubfx x21, x19, #21, #9 /* pmd_offset_lockless() */ > ... > 5394: f8757ac8 ldr x8, [x22, x21, lsl #3] /* pmdp_get() */ > > Though PGTABLE_LEVEL=3, since the pudp_get() still remain with > READ_ONCE(), there's redundant load for the pud which is folded. It would be good to include what it looks like with this series. -- Cheers, David