From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id DF735FD8770 for ; Tue, 17 Mar 2026 14:05:46 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 31B8E6B008C; Tue, 17 Mar 2026 10:05:46 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2F2F66B0092; Tue, 17 Mar 2026 10:05:46 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1E25B6B0093; Tue, 17 Mar 2026 10:05:46 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 0C6C36B008C for ; Tue, 17 Mar 2026 10:05:46 -0400 (EDT) Received: from smtpin12.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id A4225B70ED for ; Tue, 17 Mar 2026 14:05:45 +0000 (UTC) X-FDA: 84555728250.12.52CAC64 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf01.hostedemail.com (Postfix) with ESMTP id AEFB34000A for ; Tue, 17 Mar 2026 14:05:43 +0000 (UTC) Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Ri6T6pi1; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf01.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1773756343; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=GKS35ceZV45ppQEFdZWxUPfVmHQOGqA3wYGxWtozKwo=; b=iBAPMACfnsYpFopc41QVSQ6V/+mJYM45et5Df5BxbpjaIMuaa7bCXJvj8tI93FMIlnGu0D lZ8G36dF6jFcXaJT1Z5VRacVSMuvLSGonQYM7iNCEUCXfSZ5/qoNB1Bnbo/Y34PY0msSuK tCt2Cn2ah0/M6RovyBPH0xoSfkB79UE= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1773756343; a=rsa-sha256; cv=none; b=BejumQCmCRZBFCAuUjy38Rdj5LtqbtQzzq7/+ieLm7C1FRPNzM0Ae+2ohA0h6DNVrUydsy u8kaz9iPjQRvSCb7oSBtemuu9O9q+5JDDrALoRL7Tn/5MHBfkVIJvxzld6CqoqsMPGGNWg z7k7Oefqzy5CzmOWt1oNUt+/5CRQyyg= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Ri6T6pi1; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf01.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id AC440408A3; Tue, 17 Mar 2026 14:05:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CCB0EC4CEF7; Tue, 17 Mar 2026 14:05:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773756342; bh=1sbqgNXyu2WMmYk8by5cABtxizG2nxoEyafVwjmfq10=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Ri6T6pi1H13WvM/4/umOiNgP5i/JgzzB82JRb0t1zzGpdQMvyBN80YkgubPATmTO7 HP5xNuWKCERKeDfphiZH+/rsG31IKv3mM8+EuDxCJRXt4mKCw4faRzLtQwSyeAoeB0 JydOwImqSO4RryEZZIv8Homrp+uyrw6wFmvJn+bZ/tg2fmBi0APzds3464luEPdgJS FsZXK0XaJCDsU/YtwJ8wIeuLAlrNqIoFaIssiAcAWO/YR0Dgwf5Ge1W6+keCzILx7D idnwYlgz/mh7uCW1HreKv+tQHviGDo+jm/vcO+vRUcmYeXNwtM9OtNYTWj/yDB7odv 1pYtoIwTuf75A== Message-ID: <12804801-d4f9-42c9-8580-e3897efd15ef@kernel.org> Date: Tue, 17 Mar 2026 15:05:37 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/pagewalk: fix race between concurrent split and refault To: mboone@akamai.com, Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, stable@vger.kernel.org References: <20260317-pagewalk-check-pmd-refault-v1-1-f699a010f2b3@akamai.com> 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: <20260317-pagewalk-check-pmd-refault-v1-1-f699a010f2b3@akamai.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: AEFB34000A X-Stat-Signature: tswxpdi6gyuh1yrsqo6n9fd6eg1czyag X-Rspam-User: X-HE-Tag: 1773756343-35147 X-HE-Meta: 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 InTsiMFR +pChECzCoduWER5a5s9kqL1A9ak597JqNCjxDGsWohtZhwJq8/KiCrC3sLUZQZq5gX9uJ4vLHygi5kWjTk0QLltJ06hnY0HgqCZILf8w0IGNwyxW2rICA0NnqNOalU4XNgU7MM/SQl/k4wyDZgF7xJbAnUIBLh4Z5EC0v3dqajWCysdiP6Bv/g/OZsIpeQKGEYdkChlf3aNBsLawgIUaWzWUh8LRwL0TMZ8TSTmEiBiqE2CmMDBqd3KfE93qdgowacXitX+NP6up89upWK+m7zJDhg/NsqhZMPpLlIFZKlciU9tgC1Ow/ApGMMg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/17/26 15:03, Max Boone via B4 Relay wrote: > From: Max Boone > > The splitting of a PUD entry in walk_pud_range() can race with > a concurrent thread refaulting the PUD leaf entry causing it to > try walking a PMD range that has disappeared. > > An example and reproduction of this is to try reading numa_maps of > a process while VFIO-PCI is setting up DMA (specifically the > vfio_pin_pages_remote call) on a large BAR for that process. > > This will trigger a kernel BUG: > vfio-pci 0000:03:00.0: enabling device (0000 -> 0002) > BUG: unable to handle page fault for address: ffffa23980000000 > PGD 0 P4D 0 > Oops: Oops: 0000 [#1] SMP NOPTI > ... > RIP: 0010:walk_pgd_range+0x3b5/0x7a0 > Code: 8d 43 ff 48 89 44 24 28 4d 89 ce 4d 8d a7 00 00 20 00 48 8b 4c 24 > 28 49 81 e4 00 00 e0 ff 49 8d 44 24 ff 48 39 c8 4c 0f 43 e3 <49> f7 06 > 9f ff ff ff 75 3b 48 8b 44 24 20 48 8b 40 28 48 85 c0 74 > RSP: 0018:ffffac23e1ecf808 EFLAGS: 00010287 > RAX: 00007f44c01fffff RBX: 00007f4500000000 RCX: 00007f44ffffffff > RDX: 0000000000000000 RSI: 000ffffffffff000 RDI: ffffffff93378fe0 > RBP: ffffac23e1ecf918 R08: 0000000000000004 R09: ffffa23980000000 > R10: 0000000000000020 R11: 0000000000000004 R12: 00007f44c0200000 > R13: 00007f44c0000000 R14: ffffa23980000000 R15: 00007f44c0000000 > FS: 00007fe884739580(0000) GS:ffff9b7d7a9c0000(0000) > knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: ffffa23980000000 CR3: 000000c0650e2005 CR4: 0000000000770ef0 > PKRU: 55555554 > Call Trace: > > __walk_page_range+0x195/0x1b0 > walk_page_vma+0x62/0xc0 > show_numa_map+0x12b/0x3b0 > seq_read_iter+0x297/0x440 > seq_read+0x11d/0x140 > vfs_read+0xc2/0x340 > ksys_read+0x5f/0xe0 > do_syscall_64+0x68/0x130 > ? get_page_from_freelist+0x5c2/0x17e0 > ? mas_store_prealloc+0x17e/0x360 > ? vma_set_page_prot+0x4c/0xa0 > ? __alloc_pages_noprof+0x14e/0x2d0 > ? __mod_memcg_lruvec_state+0x8d/0x140 > ? __lruvec_stat_mod_folio+0x76/0xb0 > ? __folio_mod_stat+0x26/0x80 > ? do_anonymous_page+0x705/0x900 > ? __handle_mm_fault+0xa8d/0x1000 > ? __count_memcg_events+0x53/0xf0 > ? handle_mm_fault+0xa5/0x360 > ? do_user_addr_fault+0x342/0x640 > ? arch_exit_to_user_mode_prepare.constprop.0+0x16/0xa0 > ? irqentry_exit_to_user_mode+0x24/0x100 > entry_SYSCALL_64_after_hwframe+0x76/0x7e > RIP: 0033:0x7fe88464f47e > Code: c0 e9 b6 fe ff ff 50 48 8d 3d be 07 0b 00 e8 69 01 02 00 66 0f 1f > 84 00 00 00 00 00 64 8b 04 25 18 00 00 00 85 c0 75 14 0f 05 <48> 3d 00 > f0 ff ff 77 5a c3 66 0f 1f 84 00 00 00 00 00 48 83 ec 28 > RSP: 002b:00007ffe6cd9a9b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 > RAX: ffffffffffffffda RBX: 0000000000020000 RCX: 00007fe88464f47e > RDX: 0000000000020000 RSI: 00007fe884543000 RDI: 0000000000000003 > RBP: 00007fe884543000 R08: 00007fe884542010 R09: 0000000000000000 > R10: fffffffffffffbc5 R11: 0000000000000246 R12: 0000000000000000 > R13: 0000000000000003 R14: 0000000000020000 R15: 0000000000020000 > > > Fix this by validating the PUD entry in walk_pmd_range() using a stable > snapshot (pudp_get()). If the PUD is not present or is a leaf, retry the > walk via ACTION_AGAIN instead of descending further. This mirrors the > retry logic in walk_pmd_range(). > > Fixes: a00cc7d9dd93 ("mm, x86: add support for PUD-sized transparent hugepages") > Cc: stable@vger.kernel.org > Co-developed-by: David Hildenbrand (Arm) > Signed-off-by: David Hildenbrand (Arm) > Signed-off-by: Max Boone > --- Acked-by: David Hildenbrand (Arm) -- Cheers, David