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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 1570ACD4F54 for ; Wed, 20 May 2026 21:23:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=ZD8qPPFqgaVsJrT+bNhoJDKlvxEOAlYooRCBoZWKDeg=; b=ypsFoVwVto6zxQkHk7XrpIMtKA b8MKQdw55N0m1BKvIBxjr+CQ91LtsooyOiHQ8nsxqCmo4kEgnfwlfaHMViuBDfrc3rbVr4TGLf2Vg xdGwaQhesKTKxtsGBJtFkFoCmag1y4Lo57Cz95cADxy8W8Cr31891eYi4IB8wwrwQLDPltZYzkUAe 5Z+8ouydVngoxqITSt5XN0HHjv9zTUrTAq/ORioz0T8qaPWGLU6jhyUDSGIVcBB7Os83QFEfLjB4e JZ9UIO3rHwZRzenfir8CF20wDA//5HabXxlJBrjNXs4U48ejdVriT9kVD0qBusfv3eKWg1Hs2OeUR 4i+hPvuA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wPoNR-00000005pLN-3Gbd; Wed, 20 May 2026 21:22:53 +0000 Received: from sea.source.kernel.org ([172.234.252.31]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wPoNO-00000005pKO-41X7 for linux-arm-kernel@lists.infradead.org; Wed, 20 May 2026 21:22:52 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 5EEDD43A22; Wed, 20 May 2026 21:22:50 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 71DFD1F000E9; Wed, 20 May 2026 21:22:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779312170; bh=ZD8qPPFqgaVsJrT+bNhoJDKlvxEOAlYooRCBoZWKDeg=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=S5yhYWvBFRRzb7ajya43HMybpM6sLW0lPBQvPDR2wRsGnCzAsRKRuTyzVUhdCHS/m hXcSTjHoDGmfM05SPuXedm3o/TZXUnAsNvOndmOJdzLlTJAHoYuk/3UfgELKFcN6Pg vx+ThFNX3B1KnL2tBIsHjGZNwt7Gmn+CildY2rgO9eEuEMr7YS8FR8tEjHtY8htC6g UlzPdcM08Xww1Ekb4vltqOkE9lVLpR6QWjdei0XFf54taKesaUUqu+xliTluF0NZw7 CMyrZ6NaetCNwkoCITv8jwuuQPQSTcgmutsq7EdubZMntf92fEkFYC7vfPwLlnbBuG M3tf5YcnSuX8A== Message-ID: <029df55b-5542-4f8a-bf13-7649bd9454cd@kernel.org> Date: Wed, 20 May 2026 23:22:40 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/8] mm: Add ptep_try_install() for lockless empty-slot installs To: Alexei Starovoitov Cc: Tejun Heo , David Vernet , Andrea Righi , Changwoo Min , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Martin KaFai Lau , Kumar Kartikeya Dwivedi , Catalin Marinas , Will Deacon , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Andrew Morton , Mike Rapoport , Emil Tsalapatis , sched-ext@lists.linux.dev, bpf , X86 ML , linux-arm-kernel , linux-mm , LKML References: <20260517211232.1670594-1-tj@kernel.org> <20260517211232.1670594-2-tj@kernel.org> <9ba50fd2-077e-4291-9276-9adb18186873@kernel.org> <2f02d90d-cdc9-48ef-abe3-99e00f22595f@kernel.org> <297658c4ae2d6e7103f5968efc936224@kernel.org> <04b03066-86d3-4c0b-b077-307fd0f3bc9c@kernel.org> <5590fd3d-dae1-4070-b52f-bc40982ac678@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-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260520_142251_051290_78B700A4 X-CRM114-Status: GOOD ( 15.98 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org >> >> At least in apply_range_clear_cb() one could similarly switch to >> ptep_try_install() to at least have both these paths handle races in a >> reasonable way. (having to handle when ptep_try_install() is not really implemented) > > You mean to use ptep_get_and_clear() ? > Makes sense to me. Yes, using also an atomic to replace it. I recall that ptep_get_and_clear() might not be atomic, but I guess it is on the architectures where ptep_try_install() is currently implemented. > >> Anyhow, the documentation of ptep_try_install() must clearly spell out that this >> must be used very carefully, and only in special kernel page tables, never user >> page tables. There are likely other scenarios we should document (caller must >> prevent concurrent page table teardown somehow, and must be prepared to handle >> races if other code is not using atomics). >> >> To highlight that, we should likely consider adding a "kernel" in the name, like >> "ptep_try_install_kernel()". >> >> I am also not sure if "install" is the right terminology and whether it should >> instead be "ptep_try_set()". (set_pte_at is the non-atomic interface right now) > > I suggested using the ptep_try_set() name too :) > >> Further note that last time I talked to Linus about arch helpers, he preferred >> >> #define ptep_try_install ptep_try_install >> >> over __HAVE_ARCH_PTEP_TRY_INSTALL > > ok. > I guess __HAVE_ARCH_PTEP_GET_AND_CLEAR is legacy ? Yeah ... and we have plenty of legacy around :) -- Cheers, David