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 2D1FEF8D762 for ; Thu, 16 Apr 2026 18:32:31 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4D0796B008A; Thu, 16 Apr 2026 14:32:30 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 4A8006B0093; Thu, 16 Apr 2026 14:32:30 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3BD706B009E; Thu, 16 Apr 2026 14:32:30 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 2C2B46B008A for ; Thu, 16 Apr 2026 14:32:30 -0400 (EDT) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id BDD6BC2FB7 for ; Thu, 16 Apr 2026 18:32:29 +0000 (UTC) X-FDA: 84665264418.16.108695C Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf22.hostedemail.com (Postfix) with ESMTP id B2D63C0017 for ; Thu, 16 Apr 2026 18:32:27 +0000 (UTC) Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=YOjrVj0z; spf=pass (imf22.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=1776364347; 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=UUQJK9TvQdxTqynr8ROR9fKaZ+1jJhhYjQ1speiu7k4=; b=hokHknPTY4cbMmbYvm8ZUEUKUnByfcloFzf+8gE/WUClKy08FSXMwv/DZpUdU2DDL5kqsH hqPA8nynZjZa2+QyEBmv8iMbXY1Dbr/K7tSinwHMZDDx14EovMRYav4rD4UGR89hLNbrMh EkT3fArXgeNPAQdKnLfhCRjMOniqIVI= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1776364347; a=rsa-sha256; cv=none; b=EVmKgLOVhZNLfztC08NrfICS83It6HzSie3QVBjE++oDi5JVEKo48mqCaEDdZ/gxns0zqY V+zJYG4fwSPwNsDJ1/Yj8L5vGZP2MMcvrE4kBdfIz9qvt1jl+CSzSI78cXA4m+j4mgyFWW 8MvPL9/3Bkr5O38+js5MTgCivXTZJpc= ARC-Authentication-Results: i=1; imf22.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=YOjrVj0z; spf=pass (imf22.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 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 62B8743A2D; Thu, 16 Apr 2026 18:32:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0BDF7C2BCAF; Thu, 16 Apr 2026 18:32:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776364346; bh=cuaEVAsEImHzMRgmx5zy1ElIshNgZdC1LMYmjR+EZF8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=YOjrVj0zkuyJq4UJAR2lP/YzBG7O+jCdG706M15jBmDHS8e2++5PcpU0ovWXMbB1a 33+kZ1OAPsZVfuQ1d2eoozg0XaqoX7973YAjvOan9LfWEvs2LR26eBqQPOSHzMNW99 XC5v2EEC7+KtgR5XWdivrJkVZy8K04wlwava9tp82RdORo1GV1+KNPz6srG802iSX1 0BshNuFosNEh6xxtwDjoW/L2Ao5CMZppGnzZQl0mvXqpNbTte6/x3J5LjyoTMk1RB3 OKfYdF7ririrKNyTHNuiO925fzsqMRe2tQ9VZJUck7m49cPPZ66ZFLMkKQHkgUmsQd 4ErCtFqBERQQQ== Message-ID: <1a499781-1115-44bc-adbf-2ac3769354ca@kernel.org> Date: Thu, 16 Apr 2026 20:32:19 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC, PATCH 00/12] userfaultfd: working set tracking for VM guest memory To: Kiryl Shutsemau Cc: Andrew Morton , Peter Xu , Lorenzo Stoakes , Mike Rapoport , Suren Baghdasaryan , Vlastimil Babka , "Liam R . Howlett" , Zi Yan , Jonathan Corbet , Shuah Khan , Sean Christopherson , Paolo Bonzini , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, kvm@vger.kernel.org References: <20260414142354.1465950-1-kas@kernel.org> <55019037-4f1c-4d9c-83ee-3a844d8f3d5e@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-Stat-Signature: y8axw5c5qgipu1q4nse5g6sx31c79xtb X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: B2D63C0017 X-Rspam-User: X-HE-Tag: 1776364347-296894 X-HE-Meta: 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 7F6yTR+s vYoWSrNKQB/H0G97jr+NGa8HgOW7qDdd3X+zXFf/zUK0G3ChZSTt5122B6r1WsXUDr706kTBIM7gHbmqaW3GGYVKtlOvoWuHFLHcw0RiAM7901fO62Mha+lWCbD5A5ArZNb1YfnID9R0fW8Qcr6vzvhaI5NMSiklsOuPcbG/iw5rWkGSshM/MSm3P9bV25kbemO9lLDL0uDWiSvSCtkyrDkLTTsqPs1AE/WrKVOokrfmxZlHWg7n/MILnL3/xLkU7CUpGMd4yI5QY8mvRWnDo7JHSaRG+stad+Zu7 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/16/26 15:49, Kiryl Shutsemau wrote: > On Tue, Apr 14, 2026 at 06:10:44PM +0100, Kiryl Shutsemau wrote: >> On Tue, Apr 14, 2026 at 05:37:50PM +0200, David Hildenbrand (Arm) wrote: >>> >>> I would rather tackle this from the other direction: it's another form >>> of protection (like WP), not really a "minor" mode. >>> >>> Could we add a UFFDIO_REGISTER_MODE_RWP (or however we would call it) >>> and support it for anon+shmem, avoiding the zapping for shmem completely? >> >> I like this idea. >> >> It should be functionally equivalent, but your interface idea fits >> better with the rest. >> >> Thanks! Will give it a try. > > Here is an updated version: > > https://git.kernel.org/pub/scm/linux/kernel/git/kas/linux.git/log/?h=uffd/rfc-v2 > > will post after -rc1 is tagged. > > I like it more. It got substantially cleaner. I don't have time to look into the details just yet, but my thinking was that a) It would avoid the zap+refault b) We could reuse the uffd-wp PTE bit + marker to indicate/remember the protection, making it co-exist with NUMA hinting naturally. b) obviously means that we cannot use uffd-wp and uffd-rwp at the same time in the same uffd area. I guess that should be acceptable for the use cases we you should have in mind? But I also haven't taken a closer look at this patch set, whether you would already be using a PTE bit somehow (I suspect not :) ) -- Cheers, David