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=1794475836; b=wf96KN/l6or46/V/4riBzmwEm6qQbSDCfzbsgssWHYLlz7CL+EmgnQKQ24Iu4QkAEJEq ZJt9lpnJUGTqO9v63y+s6W97o95cRJ1ze+89n8+LpmK1H9a84lmi0rAYfCvxllqs6L888 mxNETmvaWA61COyEWDkZRTSot3lr+k7hwWOueOHVQrZYz6YzeLqmpCcK+/zZsir08QeMa cZNWhYQsSQOjjPtISr1mLr0fmf49M1RTkUf41qOYVmhRtXP9AeCZm4QbpHE4K7YFMvP6Y c/zk8VNl6MbpPjzt2gb+8NwASeACGkVa6/mZq5b+Twa3daIsTrVS15StKd3uAupPIUg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794475836; 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=0e9G5NVEpupIHAFHHKTSoDANySvZv3eOPYAS0FitsYQ=; b=sQxPL4yu0LlgO+Yq1jR90iziAy7NjYyz4P4+gx2ElM/kidyHe9uoADLGnMpZaiIeIAyH tVbwk2Yg6J/zGEDsgU7qYNJgqqPJkUCtWd2/uILSsGMv+pOZypYWsnS0YYL0IwKchWeWF mjbY9K4faAxq9268HdtGOjHJTvUa9XLQJBdH6enLXjeEKWpPWDRXJNYjreUPAq85kP7mo mtEdmJDgzkWFhnWKEG6hvf9T5IL32P6i4p/0RFYKC3Do3+SVBC1L5n69iRMq5Mqe9TZKv uk2N8Byrp+2hSavZwwYRfHLj4kxqQxVUZUw4RXZJEyXjudi9U28uAqmegDHboE9FxnQ== 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=fo4I2LHA; 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 BDD43606A31C; Thu, 12 Nov 2026 09:30:36 +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=fo4I2LHA Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2E6AC1F00A05; Thu, 12 Nov 2026 09:30:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794475836; bh=0e9G5NVEpupIHAFHHKTSoDANySvZv3eOPYAS0FitsYQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=fo4I2LHA0zZl3knSLUeE0hRwvNc8XGv3Rg43/4BSErdYyntyj/sQ6Ouwk/u11bS7I lsd8aAtZ5KVuS/TOcdCMY1l0D5xG2QF+dCvVihKbdwVK7N3JRwqwfW8KsjxGkZySse 4ZA7s454jngOb6cVLoif5+oUxq5/+u6K0dDYnCtCYqw1Hs4zUpg7/RFD1oObuBjR0M Fl9uqQEooRA7IxoJdZ9McqawAogG/BgIM4ZH1/dZy2b/SAlSMkuvf6BagIu1seecRL RiyMUUys9qpxM0hUIK0qtH3POk8zrhtTFEap/7Ahh/fFFPfBz0fig0/ImKOB2KxQhy clRzy5PKMQUKw== Message-ID: Date: Thu, 12 Nov 2026 10:30:29 +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] mm/memory: refuse to map page cache folios that are not uptodate To: "Kiryl Shutsemau (Meta)" , Andrew Morton , Pedro Falcato , Lorenzo Stoakes , "Matthew Wilcox (Oracle)" Cc: "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Hugh Dickins , Chris Mason , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com References: <20261111182445.656620-1-kas@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: <20261111182445.656620-1-kas@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/11/26 19:24, Kiryl Shutsemau (Meta) wrote: > A page cache folio that is not uptodate holds data that was never read > in or cleared. shmem fallocate(2), for one, adds such folios and clears > them only on first use. Mapping one hands userspace whatever the memory > held before. > > Each path that maps page cache checks for this itself: fault-around in > next_uptodate_folio(), a fault in filemap_fault() or shmem_get_folio(). > Nothing in the mapping code does, so a caller that misses the check > leaks stale memory silently. MADV_COLLAPSE did exactly that with > fallocated shmem THPs until recently. > > Warn and refuse the mapping in __do_fault() and do_set_pmd(). > > __do_fault() checks the folio ->fault() returned while it is still > locked. For CoW, that is the page cache folio that do_cow_fault() > copies from. do_set_pmd() covers MADV_COLLAPSE, which maps without a > fault. > > do_shared_fault() then unlocks the folio for ->page_mkwrite(). A > filesystem that clears PG_uptodate on a folio in the page cache is > buggy, so that window gets no check of its own. > > The fault gets SIGBUS, as for a folio that fails to read in. > MADV_COLLAPSE fails and leaves the range to be faulted in. > > Suggested-by: David Hildenbrand (Arm) > Signed-off-by: Kiryl Shutsemau (Meta) > --- Thanks! I'll wait a bit for more review brefore applying. Reviewed-by: David Hildenbrand (Arm) -- Cheers, David