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=1793907813; b=fmE2iQccM9vShPDV0IRwKOmJKBL4Rq7l/bulGZJkipYhPyMW6NUCTpwuY8/EXr6VR8xP LKe+N5K7p0KHX8ctztKRcyQdwPGSXKFJ0lU61YhQG/xgwqRnDEwtlUbDyJP39uOEfGxcF pxwEW0tQUnom6RUZIuOBRdnx8Yn+nk2t8W4IzCKJZHfIxW2vbKIqVjPZBfHrxCsBpi/KV 9D9Bj34jyN896pGvCfNKO60wRa9iky7i0mKuOXIL5zKGjh2E50BAP9I6kFV1hE7QrJkJr 5NxiuJ/77kpR1Zpab8xvhWOPXmb6qZaphZFWjX3LrqlbrJvAzaUzkfk5rYSFa4MAWvg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793907813; 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=dTMunOvWx9vfj4dikKtc63lykbDUpZcV5Bu+Cvs6i4Q=; b=MU3KWu0zQZgdGih/pGfweW7FfzRNHd1q8yW9MZesOZpaMNakUyHyO4+ZY64tkpITNS/u 7hx8EYqnf7ipb+A8kgdYNrgvFwT7hXs9Q4VGIbdUb5gZ8IA2kfoddQEBVt9Hjxm9uR8W+ IwSWKNyWSFQOuewHYDIajUoOnCKkNU/oRC0D9fN73KU8PBgHnRF+aRQclPfpu2M+Q/SP6 Kks1gVY8zOPuPIrNccg38MB+4JA4IFcgOtYETE4B25cwP+NlEVPEJ+F2xrodzPBn1AGkj boERyL2Z9z/vZ6k8uVV7v7GxN1Cs1kEWyqUcAklwEKOtjpcy9CLM0mqCvdWUf0VOeaQ== 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="gzfK7/nF"; 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 9D40E606A6C4; Thu, 5 Nov 2026 19:43:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=gzfK7/nF Received: by smtp.kernel.org (Postfix) with ESMTPSA id AE29F1F008A1; Thu, 5 Nov 2026 19:43:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793907813; bh=dTMunOvWx9vfj4dikKtc63lykbDUpZcV5Bu+Cvs6i4Q=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=gzfK7/nFuPPtB7TuaDe3+Fc+p0bNF+u4OzPhpYnN6Pgry/ETk5WJw/bk6pxBpNtXo VakeLxhOZEHtnMaMA/tBF8ufO9+3k+q73OIS4DvkuLPDyKlT0XPBcxLnwnFQgGVYT6 iR5Ow3jhrstIzdB1yLOnqInMkHBiz6HeSWPrVT+6K396fgBqDeSDUbRl+mfkzr5Sf7 lQkvd+zApBq4+NcjVkx12fZytmu2Yg5o6q730thrkMasxcit1lT3Ddk8nk1Md+QKsO Am85USGObzeUurcYRcqOFtoGLhaGBp9Ox5CAXaSD+iylDf4nZrPOtjeu8rcQYYVov5 kHczTEJKgsa2w== Message-ID: <8c11d322-5b30-43ef-8d8f-1baab4a90332@kernel.org> Date: Thu, 5 Nov 2026 20:43:26 +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/swapfile: drop a large unmapped swap-in folio in unuse_pte() To: mt4022@columbia.edu, Andrew Morton , Chris Li , Kairui Song Cc: Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Youngjun Park , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org, tz2294@columbia.edu, stable@vger.kernel.org References: <20261105-swapin-large-unmapped-v3-1-d5906e4cf18d@columbia.edu> 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: <20261105-swapin-large-unmapped-v3-1-d5906e4cf18d@columbia.edu> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/5/26 18:19, Mani Tofigh via B4 Relay wrote: > From: Mani Tofigh > > Since commit f1879e8a0c60 ("mm, swap: never bypass the swap cache even > for SWP_SYNCHRONOUS_IO"), a fault can read a swapped-out mTHP range into > one large folio in the swap cache. The folio only becomes anon once > do_swap_page() maps all of it, so if the faulting PTE changes in the > meantime the folio stays in the swap cache while not being mapped or > anon: > > Task A (fault) Task B > do_swap_page() > /* swaps in large folio F */ > madvise(MADV_DONTNEED) > /* zaps the faulting PTE */ > /* PTE changed (F not mapped) */ > > swapoff then maps it, which marks all of its pages as mapped and > exclusive, and the next fault on one of the other PTEs crashes in > do_swap_page(): > > [ 6.424485] kernel BUG at mm/memory.c:5195! > [ 6.424503] Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI > [ 6.427654] CPU: 0 UID: 0 PID: 67 Comm: swapmthp Tainted: G W 7.3.0-17087-gd865f2677c44 #1 PREEMPT > [ 6.432665] RIP: 0010:do_swap_page+0x24eb/0x2fa0 > [ 6.451035] Call Trace: > [ 6.451567] > [ 6.453841] __handle_mm_fault+0x13b5/0x3b40 > [ 6.458525] handle_mm_fault+0x16f/0x480 > [ 6.461143] do_user_addr_fault+0x312/0xa30 > [ 6.462044] exc_page_fault+0x66/0xc0 > [ 6.462846] asm_exc_page_fault+0x26/0x30 > [ 6.476708] > > do_swap_page() already drops such a folio from the swap cache when it > can't map all of it. We move that check into a helper and use it in > unuse_pte() too, so swapoff drops the folio and swaps the entries in > again as small folios. With the fix, the next fault doesn't crash > anymore. > > This bug was identified and confirmed with the help of a deterministic > hypervisor currently under development. The C reproducer below however > hits it within about 1s. > > Fixes: f1879e8a0c60 ("mm, swap: never bypass the swap cache even for SWP_SYNCHRONOUS_IO") > Cc: stable@vger.kernel.org > Reviewed-by: Nhat Pham > Signed-off-by: Mani Tofigh > --- Acked-by: David Hildenbrand (Arm) -- Cheers, David