From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794432943; b=ttYs3m+DkcOYNfo9Yl0ul6gFmv3hsBpElSZzMHgT9cjdeelP33/BpC/Qc0NzrU4LwKTf is32t0Ut63r5oRazzqnfQyJPgXcGN9a6QCvXU8YiymEsjpyYFz3g/Wkbobytg7cJAZfXG p3PJeXU4kYSK7zKy8qqEilq0s0q+exmWtBVkaIjh9Lz17bFTbFp0SDJ9SEp0ZN5VCCsHg AphpNW7uPakEJ1WaTrCfuLQvToIMxGkOAfL7hXm8VXdYQPEcrfuPWNpdBUnuq0F14qOJo 1B8fIw5J2VW2VRBQ0IoVjsfHtitnEQqfF1kjr/BBwTqtACvMLLRJ8bM7Ey6N2QhqvNg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794432943; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=GiLrJsK0i/ckXgWaDlbef6TGeEOzJ1BPFASM5Mf1Dm0=; b=iBb5WwNwqiJNVwWDQK1FnrCs1o0yfIgCs5rUBXLr4NAPyCsHl1sVgJowbmsqJKhOnHyV zkc2DfmTDwL6GVkjYje4zmFuQw5ZSU8q9ZoWXMBqp0vwbhDkTuAm5Kz3x0nOWVmzwXfmQ NwVIjPpKhFiOjpn49xCA4mMv3uztfvqTG0YFbN+nX4ppisHlRjTSVTWJ8Uou31vrk3WgN PoJxqnAWxwr2Jj8RBX4D44wwg6AX4G+1o7VMCrQUA6wIgyU+/rAiGi0Ki0zlVwElaCXhF tYKP+VNOY7Mj6XzyJlWEyL7n53KQ3VtdDpGOVOYYOAHzsiQsQblD7kYhQv7sewVRdpQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=TQyowssI; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A3BDF606A321 for ; Wed, 11 Nov 2026 21:35:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=TQyowssI Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0B5761F00A05; Wed, 11 Nov 2026 21:35:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794432943; bh=GiLrJsK0i/ckXgWaDlbef6TGeEOzJ1BPFASM5Mf1Dm0=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=TQyowssIWW+ldhbXHt3ypnihvJY5A2V8A1ANyggKEptG/EKnniGrg0vMcNbDWRxpM i/K1Jqbjg0PKNkaMzI9cYXiqL60QROS9FkYFDVY/AOGa7uqFqrQi05tzQDAh5By8V1 fvr3qr2TkFfEx6gIKUJbXu7bXksFRI11IHQgncEMfvVgMck+Me5vklonxrkX3WqKDx IibRBU/J5lj9H63TRIzC/wPCdGWNFLgCEGIjDN6zFndiUvXRA4DltB5+eQ1RfClMiT 45GyZ85VVFDJeQ9h+N02CT2I1yfVLT59Ohc0PNkK/j5NInFd0ple3lV86gx7130wWi CpzhVNiOBej3A== Message-ID: <72f286d5-3f1d-4350-b463-09f7b320cacf@kernel.org> Date: Wed, 11 Nov 2026 22:35:34 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [SECURITY] mm: khugepaged collapse_file() drops RWP PTE markers To: Linus Torvalds Cc: Kiryl Shutsemau , Tal Zussman , n3rd <18670333770@163.com>, "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "akpm@linux-foundation.org" , "ljs@kernel.org" , "ziy@nvidia.com" , Mike Rapoport , "peterx@redhat.com" , "security@kernel.org" , "Jose A. Perez de Azpillaga" References: <606cae9e.bbec5.1a1c54f4f9f.Coremail.18670333770@163.com> <60541e98-b1f0-4f92-a155-8a29c0bb17dc@kernel.org> <44abb8ef-7711-4ad0-be9f-ca47206892a3@columbia.edu> <856cdf21-7982-475a-b244-a7ceff4eb6aa@kernel.org> <71e24630-4c71-4518-a9b7-68cf3597ce80@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 On 11/11/26 21:55, Linus Torvalds wrote: > On Wed, 11 Nov 2026 at 12:20, David Hildenbrand (Arm) wrote: >> >> It would be a lot more consistent if we'd just add marker support. Or is there a >> good reason why that is explicitly not wanted? > > Let's not help people do things that won't work on older kernels for > no real gain. Uffd folks usually indicate such things through new uffd features. > > Is there an actual real-life user that would care and be enormously > helped by such a thing and it would increase performance or something? > That sounds very unlikely, since presumably re-faulting never happens > in practice, so just tracking it in user space is "free". > > In the absence of some real load with a real argument for it, please > let's just document existing behavior to the fact that you need to > simply see the re-faulting of these things.. Just to express why I would even dare proposing to implement something in userfaultfd: in Kiryl's series we abstracted the uffd-wp PTE bit to a uffd PTE bit, which made things more generic. Abstracting uffd-wp markers to uffd markers would similarly make things more generic. A quick codex prompt tells me: 90 insertions, 95 deletions. But most changes are documentation either way, so that doesn't reflect reality. Now let's ignore what I wrote above, I just polished another uffd fix and most fixes I looked at throughout the last days were uffd related, which is starting to get annoying. So yes, no new uffd features. -- Cheers, David