From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 48A7E3DD525 for ; Tue, 31 Mar 2026 14:43:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774968227; cv=none; b=PqugVngaMrFZ1p17HNUnnV+NOpR5ahjdItTAgAp087+51j/3Ujvjah1Jv5DpOBAS20yFqX76IyZiCadu4tbPK2j5aa22itM2XDH8smd6ltkJ8+0U39dO/gQusgDR5oXnwSD6mKtM/ENbMklx9GPig/N0RBOaXmy0GJOObdsQXeE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774968227; c=relaxed/simple; bh=qBD4i79Tp2F9U9XawLdp4ZrTkKT14MKydi831kGtOyo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=rkCKcibRNw43UCPYrRbbHuH8jOqmFgpUfV53aJzqo9sotlUyGh/iZZdgiKpEqQN65C8AQEB6NOv/2ULtMk7QmC08/r+j8LBxbq+KCuf5RLM+jpjhS9ZqAE7ALcZtkJvo3AzHdG8fGyiZY4oUpkTRW9oDRGN/tLCMcVKdH5jWl/8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=kBIdHv+L; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="kBIdHv+L" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 67A9DC19423; Tue, 31 Mar 2026 14:43:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774968226; bh=qBD4i79Tp2F9U9XawLdp4ZrTkKT14MKydi831kGtOyo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=kBIdHv+Lf0bPUm2yWcsb6x8qhJhnOHxXxpvVynAn5WMhjZCPZHHf1FeCdmzfTKKu+ MaFX9P6fonG8XdQku1NQ0SS1GkcGhoW4r16tJ4y1ffAw19SdHGUmNy5vho7KZ9Mqtr uC6BEDuVzpqgutz3lrWXgJtzDW5XT3Y4v041/GN23kuQxAHmQUs+g4FVcvW9Nk4xk9 BDgYIHueMZrByDZaq0UOwFFbCIAqBTSDEmLGv3wPURvrDRQ2GkrGRRIIIBJ+2+c3Af WGuQhlovtB7Xds9AV4vlkCW6hzF2EINK5coQDp7PTpc6Q1ouGQzpNkyrEr+vBgvKlT JB2qAuorprZNg== From: Sasha Levin To: stable@vger.kernel.org Cc: Jinjiang Tu , "David Hildenbrand (Arm)" , "Lorenzo Stoakes (Oracle)" , Barry Song , Kefeng Wang , Liam Howlett , Michal Hocko , Mike Rapoport , Nanyong Sun , Ryan Roberts , Suren Baghdasaryan , Vlastimil Babka , Andrew Morton , Sasha Levin Subject: [PATCH 5.10.y] mm/huge_memory: fix folio isn't locked in softleaf_to_folio() Date: Tue, 31 Mar 2026 10:43:42 -0400 Message-ID: <20260331144342.2532713-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026033040-unscathed-uncurled-5f6b@gregkh> References: <2026033040-unscathed-uncurled-5f6b@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Jinjiang Tu [ Upstream commit 4c5e7f0fcd592801c9cc18f29f80fbee84eb8669 ] On arm64 server, we found folio that get from migration entry isn't locked in softleaf_to_folio(). This issue triggers when mTHP splitting and zap_nonpresent_ptes() races, and the root cause is lack of memory barrier in softleaf_to_folio(). The race is as follows: CPU0 CPU1 deferred_split_scan() zap_nonpresent_ptes() lock folio split_folio() unmap_folio() change ptes to migration entries __split_folio_to_order() softleaf_to_folio() set flags(including PG_locked) for tail pages folio = pfn_folio(softleaf_to_pfn(entry)) smp_wmb() VM_WARN_ON_ONCE(!folio_test_locked(folio)) prep_compound_page() for tail pages In __split_folio_to_order(), smp_wmb() guarantees page flags of tail pages are visible before the tail page becomes non-compound. smp_wmb() should be paired with smp_rmb() in softleaf_to_folio(), which is missed. As a result, if zap_nonpresent_ptes() accesses migration entry that stores tail pfn, softleaf_to_folio() may see the updated compound_head of tail page before page->flags. This issue will trigger VM_WARN_ON_ONCE() in pfn_swap_entry_folio() because of the race between folio split and zap_nonpresent_ptes() leading to a folio incorrectly undergoing modification without a folio lock being held. This is a BUG_ON() before commit 93976a20345b ("mm: eliminate further swapops predicates"), which in merged in v6.19-rc1. To fix it, add missing smp_rmb() if the softleaf entry is migration entry in softleaf_to_folio() and softleaf_to_page(). [tujinjiang@huawei.com: update function name and comments] Link: https://lkml.kernel.org/r/20260321075214.3305564-1-tujinjiang@huawei.com Link: https://lkml.kernel.org/r/20260319012541.4158561-1-tujinjiang@huawei.com Fixes: e9b61f19858a ("thp: reintroduce split_huge_page()") Signed-off-by: Jinjiang Tu Acked-by: David Hildenbrand (Arm) Reviewed-by: Lorenzo Stoakes (Oracle) Cc: Barry Song Cc: Kefeng Wang Cc: Liam Howlett Cc: Michal Hocko Cc: Mike Rapoport Cc: Nanyong Sun Cc: Ryan Roberts Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: Signed-off-by: Andrew Morton [ adapted upstream leafops.h changes to swapops.h ] Signed-off-by: Sasha Levin --- include/linux/swapops.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/include/linux/swapops.h b/include/linux/swapops.h index 0d429a102d417..e62ef6fe81fab 100644 --- a/include/linux/swapops.h +++ b/include/linux/swapops.h @@ -197,6 +197,12 @@ static inline unsigned long migration_entry_to_pfn(swp_entry_t entry) static inline struct page *migration_entry_to_page(swp_entry_t entry) { struct page *p = pfn_to_page(swp_offset(entry)); + /* + * Ensure we do not race with split, which might alter tail pages + * into new folios and thus result in observing an unlocked page. + * This matches the write barrier in __split_huge_page_tail(). + */ + smp_rmb(); /* * Any use of migration entries may only occur while the * corresponding page is locked -- 2.53.0