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=1794384364; b=B+SSwJhjQu+CUXBCvLUifHuTiWzNTkQoNQ8bB/XrDv5FiFptkzym5HwBX6YfVAN5pbHh 6AW9Lpe2bPZys8u/ihVazNBzXVAI94PGpNqyLbedyEoxHflwVG9Hz7y6KqNP2uFdk91Ay SZ22DlP/dWOtP+dSqEBiBWVLcoOPGXRrd1aZ93CoDi78c/wk/J4pdCvTKOHH9933KnE98 ZU/10a7kazr0Ju5uxOmIRsbTKwIkjCMxYORS9zsMDvJzXPBFMVGyfZALRwSdnnywCFsby MAafLgPmjDx8KDTNhJpfXAF7dyCVIdSDiumXxWtlBCloNUWyndEFjAGHKizp1LPKCuQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794384364; 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=LdKcGRF+Thd2B4nVWmeKuOcWRtPqdSv0jcsrCZK/1Fg=; b=oJnbecluuOR5Zg9dGeuVVO+/89qK1t11vL4tKRwJDxeYEDR8F8ssmCf76AmHFapTsFkh 7cLFyb6+02wkjCjQFZ8aSJYtZ79lFihplHsPuVUuWJRlCMqaJ34Bycr02X0FWuD0bKg5u +YrfA7eAsPZV6taJSVHhY53L730OyKtVwISbtA9gpLJ6UeVpm6i1teGgHG6z6ru/Q9fm1 zSz8XvT4HmXAzRpM1ODa/1HT+ei7Kp6hdRLZB3HWEXw7aSuKC44qZKXh1XWn59765UA5q jagoFWu1Ih6VvBBr8r3TAUel6e+HUIwgDxgwv1AqW8hNpQ2EUWA/hSf0Ch5Ap1LUM5w== 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=Vl6uSg+5; 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 5ECE9606A32D; Wed, 11 Nov 2026 08:06:04 +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=Vl6uSg+5 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 73A1E1F00A08; Wed, 11 Nov 2026 08:05:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794384364; bh=LdKcGRF+Thd2B4nVWmeKuOcWRtPqdSv0jcsrCZK/1Fg=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Vl6uSg+5H3MQjU0G8UEBAvxxx48dToHk8qFJy0CRWT5rG45kg0zUz6Q5BzBvivoYP 9ls8MupqlwHXysP3k/yldpoy3uQLkl79v/euvRQqxIR168ip5B8Y6IXWPcgW3wqhxy Bu3Tglve+PkvXEWu4oZ9HAB9UXKrbwEVqvFuOJktFXjtrarjOXe2qPtNBHe1l6oAIO WhvGrgGLEkSUi0qCmEnJlkIGJZQ1wwaJmwlyLXZqi5h37ZzFi2CgPsrwMiQlmjKkCE 4ZB1xN/onBQU+0NuVvUq+c4nsHbU0SxTd2ikrQLFJFvqr7SgXO0mgEPuLvBZm2eNF1 YFp/CXjWnLQNQ== Message-ID: <7698b32c-eb47-46d9-8ebb-337aa575d062@kernel.org> Date: Wed, 11 Nov 2026 09:05:54 +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 v2 2/2] mm/memory: refuse to map page cache folios that are not uptodate To: "Kiryl Shutsemau (Meta)" , Andrew Morton , Pedro Falcato Cc: Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , "Matthew Wilcox (Oracle)" , Hugh Dickins , Chris Mason , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com References: <20261109120403.82361-1-kas@kernel.org> <20261109120403.82361-3-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: <20261109120403.82361-3-kas@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/9/26 13:04, 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. do_shared_fault() unlocks it for ->page_mkwrite(), and a > writeback error can clear PG_uptodate after that; that case retries the > fault instead. For CoW, __do_fault() sees the page cache folio that > do_cow_fault() copies from. do_set_pmd() covers MADV_COLLAPSE, which > maps without a fault. > > 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) > --- Reviewed-by: David Hildenbrand (Arm) How do we proceed with patch #1 (on which this patch relies on :) )? -- Cheers, David