From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 87C01606A323 for ; Wed, 28 Oct 2026 11:41:03 +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=PiZ+2Gl5 Received: by kanga.kvack.org (Postfix) id A6FB76B05B3; Wed, 28 Oct 2026 07:41:02 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A20BD6B05B5; Wed, 28 Oct 2026 07:41:02 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 937196B05B6; Wed, 28 Oct 2026 07:41:02 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 6D1116B05B3 for ; Wed, 28 Oct 2026 07:41:02 -0400 (EDT) Received: from smtpin09.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay09.hostedemail.com (Postfix) with ESMTP id EB87280A56 for ; Wed, 28 Oct 2026 11:41:01 +0000 (UTC) X-FDA: 85371843522.09.5827E48 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf16.hostedemail.com (Postfix) with ESMTP id 44A20180003 for ; Wed, 28 Oct 2026 11:41:00 +0000 (UTC) Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=PiZ+2Gl5; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf16.hostedemail.com: domain of pratyush@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=pratyush@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793187660; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=Jlnfz7M1ITZw2qIEVKqbY+WjiMkAWf1Tu97ZUZ93IN0=; b=Yrd32I6ifwTf0frrHqaw8k2WCoXKPpixpZDWNJlbgZ6ysy9t3Sr0xHT7XCD0ext3MinpGa u/CWK0z05nuo3hvOkReSi7U1KaHS8WwJNSkQISqcjM7hQ2dz25cPDWB+0JOLrmncVZ7XPy opsB41BN24ig2azIs7cTPoDtIXCwQzc= ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=PiZ+2Gl5; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf16.hostedemail.com: domain of pratyush@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=pratyush@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793187660; b=KPeNYPLYCLwWpl1oPiG6YL6T0UmZ4xnzU9PJDfSyNkgyJrwbtvIomx2UaReW7byXV0ZMzN tKwQNglvMapDu61Q08eLBWeTdyqDkzQ3+8rpNmw3SMIKwRP/pEOuMOfxv/OPIHHtkXu0bt IevX4DbVyqV08yhVvK+lusY7xxQES7Y= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 6372942D52; Wed, 28 Oct 2026 11:40:59 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A41CA1F01825; Wed, 28 Oct 2026 11:40:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793187659; bh=Jlnfz7M1ITZw2qIEVKqbY+WjiMkAWf1Tu97ZUZ93IN0=; h=From:To:Cc:Subject:In-Reply-To:References:Date; b=PiZ+2Gl5kc0jJSeKMLoj7fOmlVIOFgswoanYFqn1DWdsQBEuhQPix9JVy9oWukGPG +F4YsgXNS1WGjwV30hoP8na9F/N7Eb7122WwInn552HizyxxW3YaCESCfroMU6yjAm VSLYDm5acEbC8X+0g/aR2w/YcyxdJoeMZDvuNVvBD2N8xDX/JIOe5gr86tQJIXfRoq 39Z0YQ1Uj9IsiFhECBTs0uTCctxqUM5+Y5krqY7Am0KOxTRvkUfV1a6g8jHytioWqL s93d076CkgIdrXOUk2WhEjj/95/4ACkRiIc76P4JQh7Skxr0Cekil6YVf24aF8v9MO VTNrBK9m2sErA== From: Pratyush Yadav To: "David Hildenbrand (Arm)" Cc: Pratyush Yadav , Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, Chris Mason , stable@vger.kernel.org Subject: Re: [PATCH 20/46] mm/gup: fix clearing folios in memfd_pin_folios() In-Reply-To: (David Hildenbrand's message of "Tue, 27 Oct 2026 20:20:43 +0100") References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-20-6f74bec9a5bb@kernel.org> <2vxzbj8fp4sn.fsf@kernel.org> Date: Wed, 28 Oct 2026 12:40:48 +0100 Message-ID: <2vxzld7injcv.fsf@kernel.org> User-Agent: Gnus/5.13 (Gnus v5.13) X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 44A20180003 X-Stat-Signature: mpyo3aetsw8nd4t53ti1i1b38m4t1jp6 X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793187660-351953 X-HE-Meta: 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 Ui8LbMuS e4wGvJV5d2g1C2PwUAqEFUvdKCbz8amg9LGpuUQPpiIJbt6MsIXt8XCsqIfEU2M+8maCq3Eehi8QZlDx1vo463FmA+gZrOhvkfcXHpKo0UH6QNe9cnOHyAmaNtq0WOqrQ8CQMlmTLiEaLo+biaaqFVQe4BRk7rNeDFTzLSbQiTnxD8K2ND0Q4leYkOqwY3V2MNu5WsAboMI6kI0hCQhOG+HSyGJ1K1YyQ8NnUggmda6ApaSbT8rWQq7ye/CGv/pbBddY3tBaNlI1SVUBdc2kn2iDVcZ/PxoUMgBDFlQFCi4JMX3iFatgQ9iorr57sft+Lekmzq0UW6pM8oROojcBghmEncK9jLaUj973q6+wnSG1BNSU= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Tue, Oct 27 2026, David Hildenbrand (Arm) wrote: > On 10/27/26 16:00, Pratyush Yadav wrote: >> On Tue, Oct 27 2026, David Hildenbrand (Arm) wrote: >> >>> From: Chris Mason >>> >>> memfd_pin_folios() pins folios obtained directly from the page cache >>> without checking whether they are uptodate. However, shmem fallocate() >>> can leave newly allocated folios uncleared and not uptodate. Callers >>> such as udmabuf can then expose uninitialized memory to userspace. >>> >>> Clear non-uptodate folios and mark them uptodate under the folio lock >>> before returning them to the caller. >>> >>> Fix generated by an LLM and sent by Chris Mason in private. >>> >>> Fixes: 89c1905d9c14 ("mm/gup: introduce memfd_pin_folios() for pinning memfd folios") >>> Cc: stable@vger.kernel.org >>> Signed-off-by: Chris Mason >>> [ david: simplify description and comment ] >>> Signed-off-by: David Hildenbrand (Arm) >>> --- >>> mm/gup.c | 14 ++++++++++++++ >>> 1 file changed, 14 insertions(+) >>> >>> diff --git a/mm/gup.c b/mm/gup.c >>> index efc9aa2654625..47e7ae152cdf1 100644 >>> --- a/mm/gup.c >>> +++ b/mm/gup.c >>> @@ -3516,6 +3516,20 @@ long memfd_pin_folios(struct file *memfd, loff_t start, loff_t end, >>> goto err; >>> } >>> >>> + /* >>> + * fallocate() can leave folios in the >>> + * page cache that were never cleared. >>> + */ >>> + if (!folio_test_uptodate(folio)) { >>> + folio_lock(folio); >>> + if (!folio_test_uptodate(folio)) { >>> + folio_zero_range(folio, 0, folio_size(folio)); >>> + flush_dcache_folio(folio); >>> + folio_mark_uptodate(folio); >>> + } >>> + folio_unlock(folio); >>> + } >>> + >> >> Nit: this logic is repeated in a couple places in shmem.c and in >> memfd_luo.c. Perhaps it deserves a helper? >> >> Anyway, sounds like an important fix so don't make my nitpick stop you >> from landing this if you don't want to bother. > > Thanks! yeah, I had the same thought when trying to improve this. We should have > an easier way to just not hand out unzeroed folios outside of shmem core > functions in the first place ... Normally this should use shmem_read_folio() to get all the folios, which does zero the folios before handing them out. I guess memfd_pin_folios() uses filemap_get_folios_contig() for performance reasons. It does the lookup under RCU and doesn't need to take the folio lock. Perhaps we need a shmem_get_folios_contig()? -- Regards, Pratyush Yadav