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=1794494350; b=syuK/tQ7+IlFIBnLz62ktARKGAJ1Sl39AJxIFVFoh3j2ieW7MCKslLD+WisITRZP/C+x Gty6aB+6qZDuEfjGdWp678YzKREZtIE04YzdRjOe+QNgixUqTgZPb6Dje78fc9VZjF5BF g1BkjTekDuOPK3SE4VxEvv1W+JTpwWxLZDxiFlETWeAHebY+9b4X2BHLEimpTsa7F0IZ1 iu/n/cxgIRkZad0IPywu5P6LeRDtYHETaN/gbVcanERojdgZFbLHOL8UH9vvEFT40xtT/ rZir2aaxmKHFJOatCHO3JbRYWvqGhZcmfbVl3l+6YWIjbKWTHRRIeeCpfOqBIc9jc5w== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794494350; 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=JPCGNF/jEMU9xJrqkGIaHxvjMBqA0bWCrPxQL0nBrZo=; b=TCerqJjsusRR8ZdB6binPJzKLS0OOi5839sbGJ9UQIl72/dhcgeIlvkFX9nEAKKJWqyA OAYHJlS/L9x+arT4ld6xAh7sWyuVkM5xWQUDm/c4nexQFLbJWNub/2BTA9Si8RLGL+Sly qhnFfHzDWYEVs3gp6x/FSTEqJMtvj+Izl1PkSnSibTBCjDY1x6P7CSQjGAZCEw8pJy9gi zMvSmdmI4Ps6gyhqRAbIWDjorO68AMuKR3tYday4jSRt2rk26HE6JnqtulUXIEYYdBwtX LK6uOT2cGJLTmVdwFtGw5hciA/GpmfDnaWfZCpcRuXxIyXpsrWNe1uRlSzmgP1YfDtA== 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="f8mnD/IJ"; 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 EDBE5606A321; Thu, 12 Nov 2026 14:39:09 +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=f8mnD/IJ Received: by smtp.kernel.org (Postfix) with ESMTPSA id 38F651F00A0A; Thu, 12 Nov 2026 14:38:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794494349; bh=JPCGNF/jEMU9xJrqkGIaHxvjMBqA0bWCrPxQL0nBrZo=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=f8mnD/IJDys4pA4TeVplHqPuVUfXqGCBlqTLjIenB7gApydQVzgQ7FKsApOjymKoG uoxlhVqbleJeLcQbHt5sG3/YCao8omJde+LI+Zry9Zf+D7eJQ43/cy9LfzDcI/BP6n 59jf7Yk0E6oQ4ndx2WarOOMIOHOscf4lgBvg30XKqlVusvQHhnKQ56hfSOLHFXtqsO EvolT6DBDg4yO5pVhjYeYQQWWjGT7i8guvwpRcR7e7ysv6z3Wdrle0pzptbwklFN6w +hGHxd06iIp13iFBvUdxsoi8NV3KZFViRrZXNgUMAuxDnN60aj3/GIZ6wIZUduAG+I LxvkBDtRNAxDw== Message-ID: <1aa2d6a0-0104-4f94-821f-3a8a74636028@kernel.org> Date: Thu, 12 Nov 2026 15:38:45 +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: [PATCH v3 1/9] mm: limit pagecache folio refcount when mapping pages To: Pedro Falcato Cc: Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , "Matthew Wilcox (Oracle)" , Jan Kara , Andrew Morton , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Matthew Brost , Joshua Hahn , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Peter Xu , Johannes Weiner , Song Liu , Rik van Riel , Miklos Szeredi , Alexander Viro , Christian Brauner , Hugh Dickins , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Peter Zijlstra , Arnd Bergmann , Jason Gunthorpe , Kevin Tian , "Joerg Roedel (AMD)" , Robin Murphy , Steve Sistare , John Hubbard , "Jose A. Perez de Azpillaga" , Josef Bacik , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Neal Cardwell , Kuniyuki Iwashima , Linus Torvalds , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, fuse-devel@lists.linux.dev, linux-arch@vger.kernel.org, iommu@lists.linux.dev, netdev@vger.kernel.org, Chris Mason , stable@vger.kernel.org References: <20261110-refcount_overflow_stable-v3-0-318625d63a98@kernel.org> <20261110-refcount_overflow_stable-v3-1-318625d63a98@kernel.org> <86206f64-fefa-4a13-95bc-eddf756eecc8@kernel.org> <2f9b90fd-fe50-4afa-ab59-0c4a00e5e276@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 11/12/26 15:26, Pedro Falcato wrote: > On Thu, Nov 12, 2026 at 03:16:00PM +0100, David Hildenbrand (Arm) wrote: >> On 11/12/26 15:06, Pedro Falcato wrote: >>> >>> Alright. >>> >>> >>> Yes. As far as I know, it's always fine, even under NMI. But definitely fine >>> with IRQs disabled. >>> >>> >>> I had the impression we had some stuff in-tree that isn't marked as GPL. But a quick >>> grep shows that everything is either GPL or dual-licensed. >>> >>> In any case, yes, this will quite possibly break debug builds for people OOT. >>> I think folio_get() might be a bit too ubiquitous to do this to. >> >> Thinking again, folio_get() should not be affected, it rightfully only checks >> for a refcount underflow (when we exceed the limit + headroom). So only >> try_get_page() is affected, which OOT very likely doesn't use. > > Aha, yes, you're right. I mixed up your folio_get() change. Would it make sense > to VM_WARN_ON() on this as well, or does the <= 0 check cover us already? <=0 is sufficient for folio_get(). There are valid cases where we can exceed the limit into the rather large headroom (e.g., reaching the limit through page table mappings, then performing harmless read/write that take bounded references for a short time). -- Cheers, David