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 995A7CA9EBB for ; Fri, 9 Oct 2026 20:24:06 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 555C46B008C; Fri, 9 Oct 2026 16:24:05 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 52DC76B0092; Fri, 9 Oct 2026 16:24:05 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 443126B0095; Fri, 9 Oct 2026 16:24:05 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 139336B008C for ; Fri, 9 Oct 2026 16:24:05 -0400 (EDT) Received: from smtpin20.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id A47961C3CBE for ; Fri, 9 Oct 2026 20:24:04 +0000 (UTC) X-FDA: 85304214408.20.8212236 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf22.hostedemail.com (Postfix) with ESMTP id C2B4FC000E for ; Fri, 9 Oct 2026 20:24:02 +0000 (UTC) Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=Eqg3X0hc; spf=pass (imf22.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1791577442; 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=wCWQOptUF8jyyHqMADNE6+YL1lMNmRc+Jp6ycI/TeyM=; b=rgOFNCxS/agHb6BcvoijwksxvIUa7XGnwGYT277Y7QFCEfAcMadVKbdZO6PzbaX9XDVrgp rNq6SqZeuXRYz5pg0ufs8e6jL7htGhtAq8WpKmCltwyF82FYJ7BBKbalAE5RtEydNhCKAd QQnPlL0Pvh+Mo1IvWw+igU/gKi2RnEg= ARC-Authentication-Results: i=1; imf22.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=Eqg3X0hc; spf=pass (imf22.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1791577442; b=ev159aDlT4DhneRfCxaZzSphyjpCMBqarsXpU4/9nsc2Xo+qDU2oFrDlnZK0mveJILng+v Ep+8A5W+0DDRnFJU6IHM2tyrXgRgQ3jwTtK4+770UlfCMAywswg0vg4QieEwzEWPcTAuzc sHANVF2CIw6P+5jcDhVEmls/D+S4Mls= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 4B2D74199C; Fri, 9 Oct 2026 20:24:01 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6D7791F000FF; Fri, 9 Oct 2026 20:23:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791577441; bh=wCWQOptUF8jyyHqMADNE6+YL1lMNmRc+Jp6ycI/TeyM=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Eqg3X0hcDl6uYeqx8paTuM4ul5j58X9NkSbvaiUbh3DZbjI0Nli2t1c3p5CYydvYp GDWlI5RahfJcXnkDAle0s7tUtplBeedzgpEenX+zpQKqsmpDoXBEnL1Q6gCyTcXlXk qmpadTTJJzn274+83PezcoAmemAEG7p/CrhOAX1wdmTkYh1vE28FxAsYTao5iGjey8 PORlHEJYdkAvMbd0JnRh9Ihn1PiKLYt13216sIw08UVYTI1s82l1YEK7Ty1Pa1UOM7 m6LVY7j437q4llZ8qLyElsoxfS9LmDc/1BGrHJkDLO1twn0ICCLRSmrnHzwWcruEDt 2lgN73spZM5aA== Message-ID: <8db35dc0-eb06-42e4-90f9-534522e810e1@kernel.org> Date: Fri, 9 Oct 2026 22:23:54 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/huge_memory: avoid transient none PMDs during lazyfree reclaim To: Zi Yan , Kyle Zeng , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , stable@vger.kernel.org References: <20261009165214.40212-2-kylebot@openai.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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: C2B4FC000E X-Rspam-User: X-Stat-Signature: f1xrhwnu7wss1mipuhngqoompc66t6p4 X-HE-Tag: 1791577442-46169 X-HE-Meta: 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 RYFR4B7l X4y8qXtE2Ej4hswyt5Gq08Xiwj9qsXhuWMbEn/zyBKNsShumMF8jgiT4dtRw3Td8eMBBuqMBCRh/BLemjr666LrwIbaDiEacvkLWYSPEpGShh/pvgr9qVbw7H6adX7xntYf5FLoSuFe9NItxRrIRYwxPraqf4fv+5ULFGUktkVreCXKQRg9t7TVPVK9Qe7Fax7eAHMFKNXaj6tMMbCJVVRIAIdr2EVCNo9nZjAL7VLgwtFEaaQsc1AuM3MSDS1Uqcv8e17iWRAlHhjOKPWef5ZS6xAUknPFaELgI8rj3E6+c8S2qWUHjHPn6IrXiW13JG58u8IUE7UI88YCx2o4bIbKKKbJURkICCOF/Z Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/9/26 20:17, Zi Yan wrote: > On Fri Oct 9, 2026 at 12:52 PM EDT, Kyle Zeng wrote: >> __discard_anon_folio_pmd_locked() clears and flushes a huge PMD before >> checking whether the folio can be discarded. If the folio was redirtied >> or has unexpected references, it restores the original PMD. Reclaim holds >> the PMD lock and the anon_vma read lock, but not the owning mmap_lock. >> >> Both zap_pmd_range() and mremap's get_old_pmd() can skip a none PMD >> without taking its lock. A concurrent munmap() or whole-VMA >> MREMAP_DONTUNMAP can therefore miss the PMD and later unlink the source >> VMA from its anon_vma, leaving a restored mapping behind. The anon_vma >> write lock taken by unlink_anon_vmas() waits for reclaim to finish, but >> does not repeat the skipped page-table walk. Once the remaining VMA >> links are removed, the folio's positive mapcount no longer guarantees a >> live anon_vma. Racing lazyfree reclaim against MREMAP_DONTUNMAP as an >> unprivileged user reproduces a KASAN use-after-free in >> folio_lock_anon_vma_read(). >> >> Use pmdp_invalidate() to keep a recognizable, non-none huge PMD while >> the discard can still fail. Concurrent unmap and move operations then >> have to synchronize on the PMD lock instead of skipping the mapping. >> Clear the invalidated PMD only after the dirty and reference checks have >> succeeded, before removing the rmap and withdrawing the deposited page >> table. The full invalidation retains the TLB flush required for the >> dirty and GUP-fast checks. >> >> Fixes: 735ecdfaf4e8 ("mm/vmscan: avoid split lazyfree THP during shrink_folio_list()") >> Cc: stable@vger.kernel.org >> Assisted-by: Codex:gpt-6-astra >> Signed-off-by: Kyle Zeng >> --- >> mm/huge_memory.c | 11 +++++++++-- >> 1 file changed, 9 insertions(+), 2 deletions(-) >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 1e5d68acf62a..20262195385a 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -3569,11 +3569,17 @@ static bool __discard_anon_folio_pmd_locked(struct vm_area_struct *vma, >> return false; >> } >> >> - orig_pmd = pmdp_huge_clear_flush(vma, addr, pmdp); >> + /* >> + * The discard may fail, so keep the PMD non-none until we're >> + * committed to discarding it. Otherwise, concurrent munmap() or >> + * mremap() can skip the PMD without taking the PTL and later unlink >> + * the VMA from its anon_vma despite a restored mapping. >> + */ >> + orig_pmd = pmdp_invalidate(vma, addr, pmdp); > > There are some gaps we need to close before getting this fix in: > > 1. GUP-fast cannot follow the invalidated PMD: riscv and LoongArch need > pmd_access_permitted() that requires _PAGE_PRESENT; s390's > pmdp_invalidate() needs a change. Ugh. We really need pmdp_invalidate() to have reasonable semantics. This whole PMD locking is a mess :( > > 2. sparc64's thp_pte_count can be imbalanced with this change (based on > Lance's offlist feedback). Ack. > > In addition, powerpc has a page table check issue similr to riscv, where riscv > fixed it with commit 9f4a88b8d01a6. This is not related to this issue > but discovered along with the investigation. Zi, do you have the capacity to take over this patch? -- Cheers, David