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 79CB2606A323 for ; Sat, 14 Nov 2026 17:58:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=N8mR7pat Received: by kanga.kvack.org (Postfix) id 78F886B00EF; Sat, 14 Nov 2026 12:58:53 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 73F326B05B1; Sat, 14 Nov 2026 12:58:53 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 62EE96B05B2; Sat, 14 Nov 2026 12:58:53 -0500 (EST) 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 454B16B00EF for ; Sat, 14 Nov 2026 12:58:53 -0500 (EST) Received: from smtpin23.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id A6BFA1C22DA for ; Sat, 14 Nov 2026 17:58:52 +0000 (UTC) X-FDA: 85434485304.23.FA021FE Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf13.hostedemail.com (Postfix) with ESMTP id 08BA520006 for ; Sat, 14 Nov 2026 17:58:50 +0000 (UTC) Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=N8mR7pat; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf13.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1794679131; 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=/HQvy3Bf+SmAOhrQqSVfFUq9G41+E/cdawcP+LkvJ7k=; b=E5tMiFjRiI5XuC/IEk1oq9hbvqyPBerrb7KvFNqDn3SlG6AmDhclO71Zot2OPni2J+YDfk nd2ZYmMh7RTqttZnTgxP01fH8dmBXojfM0pyXgpXhqy7dXYkk4yoeeI0778qUeKowTz7tP NWNhAC/aAum8a4Unju1loziq+YxNTdc= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=N8mR7pat; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf13.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1794679131; b=jfQ9n9GOYuq4Qc08ZoSUECED1wJ47eVh50lVctxeXjIweWh8lAoa+vBsOC7pMYf3Q70llN vslOU/WQpWLMQz9YVieAjqgYACQs/x/2yMzxyen73GrySjVOpEJDivyY2d93IFITrLlMcK Wtbrjl+VZ4WYP7wd8Gn+qMM1GQJ6oJQ= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 6330560D70; Sat, 14 Nov 2026 17:58:50 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1C3851F000C4; Sat, 14 Nov 2026 17:58:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794679130; bh=/HQvy3Bf+SmAOhrQqSVfFUq9G41+E/cdawcP+LkvJ7k=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=N8mR7pat/AgWFEZudjyHd7qJBB0qQTOZWAzhwI7OKAco/3FMbPxpm7r6J9z2NrL5K zZXPUFSkOwIalYeVT18FocvsBKg96UZd5zOLhGAflrdGsckEbf+bMqkdTquefCO1wP eSUTsPFlNyU/yvae/e7nKC/z5iHwTytOrnpqjJW9Nrh3KEwZiH8M/G2j3RGSZILKyi x0TDM8U7JFia1yyzVyYUvzq1uCt2k3vFI8O/t0subTSzLfoKO0LUQjthEzGudkGUNP qQcj6uLH38Z0cXP+LUByAoxmrAp62uB/S9dh9+AR0xOn7VtX0Rgf5A+K3ipjRgzwK0 svq8hq1b/3v4w== Date: Sat, 14 Nov 2026 17:58:40 +0000 From: "Lorenzo Stoakes (ARM)" To: "David Hildenbrand (Arm)" Cc: Jonathan Corbet , Shuah Khan , Randy Dunlap , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Jann Horn , Pedro Falcato , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Peter Xu , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Axel Rasmussen , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] mm/userfaultfd: prevent poison marker loss Message-ID: References: <20261107-b4-uffd_marker_loss-v1-0-82926b22704c@kernel.org> <20261107-b4-uffd_marker_loss-v1-1-82926b22704c@kernel.org> <822c1c7e-bfdf-4570-bf30-08f187e7253d@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <822c1c7e-bfdf-4570-bf30-08f187e7253d@kernel.org> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 08BA520006 X-Stat-Signature: t59yxruz9476nuwc6zj9erjmuuaqz93b X-Rspam-User: X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1794679130-173670 X-HE-Meta: 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 vDSp5Gzo DCTKrKVFed2lRy0vF44oQd3aljcfZN3xzb6oENTW19XK4wLAnYK2yMw89hGTMB+gMAjUoEhwgDLOu/YcUkf8Mbvgv5qRgH+Is/fQSHPCLoHDzfJb3yXnLOtElQvBM+SkB69sbls9D6LOnZO6WWYuStURx78N+laJPaNNZ/zc6cy0QQ3DmsUG586ZT6MiidcOi1TMjnDrD5dqTMOLJg2DaDmOhos2pF6qSnub1DauZ11hqRUcM4Hk1dbpY1CB/DMonRO8maNY3/u2wMsdOZza15T+k+A== 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 Sat, Nov 14, 2026 at 04:39:44PM +0100, David Hildenbrand (Arm) wrote: > On 11/7/26 00:51, David Hildenbrand (Arm) wrote: > > Unregistering userfaultfd leaves poison markers in the page tables. > > However, once unregistered, hugetlb PMD tables can be shared again. > > > > Further, shmem page-table retraction can discard poison markers even > > while registered in missing mode, and fork() can skip copying page > > tables containing poison markers. > > > > To fix it, add VM_MAYBE_UFFD_POISON and set it before installing poison > > markers. Preserve it across unregistration, splits, merges and fork(), > > just like we do with guard markers. > > > > Use the new atomic VMA flag to disable PMD sharing and page-table > > retraction, and to force page-table copying during fork(). > > > > Move VM_UFFD_WP to bit 44 and make HAVE_ARCH_USERFAULTFD_WP depend on > > 64BIT, freeing bit 12 for the new flag on both 32-bit and 64-bit systems. > > Expose the flag as "up" in smaps. > > > > Losing poison markers, while unpleasant, is not really fatal, and the > > use case is rather a niche thing. In addition, we rely on the atomic > > VMA flags infrastructure ... so let's not CC stable. > > > > Fixes: fc71884a5f59 ("mm: userfaultfd: add new UFFDIO_POISON ioctl") > > Fixes: 8a13897fb0da ("mm: userfaultfd: support UFFDIO_POISON for hugetlbfs") > > Signed-off-by: David Hildenbrand (Arm) > > --- > > Ping on this one. Ack, will have a look. > > -- > Cheers, > > David -- Cheers, Lorenzo