From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794721373; b=QK4I15hqEBEItUGyKW8uKrM/nAXb9m9k7lolSXYzZolMWaGR+TmKurRSihVn458SRtha Vk9xhHcktOAOwzztybxMHF90FTwnkzdocp1ozdTsLXsQGT5MvGCh2AHh4U4n98rWZSMBN 3esh9EY94r939I6XD/N/ASclj7u5xADy1cFzlWstSTqMXIVICy4gMQyd0xzl9GoVpHXy7 PWGs0ikNCt3kywUTOqf+m503W1Eg2CMA0XGFRQdGeAg9/0aRACuG9SBfSBDnP2WX158sL AemsQTl2BvYWNjFOLNt75H3JDa/qj5hfjfs8OX1uoTWtKL7mWv78VLcFFrFuV+mMBGA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794721373; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=nyBkJVwlUhwTxJyGO+bv5cKEFN7sPZnmNLTwTWcdOtQ=; b=Z9alVZeG8A62p/SayIthW4wRDybdjfOoLpUdcq6r5ism2/KkZLnv349zHEzIVwyiNE/b MaEipuElHppXPvTUx75ahyNGSMsTk1ddmbTAMrkpds98LLpPPb3AI8t69rL0oHUzxmItr uNXHhUbLauCiUQ8TBLyfNFTWvctmOn6FnC+bP93Zd6iaio28E/EJc4XJ09t34+it0HIG4 2YtxHrEdZOSkv0iCEkkLRhBpSrT+2Kc3yJZLiEYetkJ0Cl9KunazwsK6ZBroWHDW5+xNV nbbj8NBkNKHGiNxTxvSmUrP5QQzw1G8z5JhxSJ+Th+Ds5YxOYt173xfs/P7JQqJRfVQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b="LCGBC/PO"; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4D529606A329; Sun, 15 Nov 2026 05:42:53 +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=LCGBC/PO Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9B9FE1F000C4; Sun, 15 Nov 2026 05:42:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794721372; bh=nyBkJVwlUhwTxJyGO+bv5cKEFN7sPZnmNLTwTWcdOtQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=LCGBC/POf5Gn/rnspd1Eu2NhGBKKHCC5PeEenTKJRyjA1UBFCM1dny8zz0QppLOUM HUiWHTNDTXtwkwW1OQyWllS/gQ2v0jl/x5WpfwxLL+0Q1BzwRwMyIlkhwZlBlvE/Nd u783YyJBqEacJoSMuwJIlCy0bup1mHkGTtHTODpEBhAfROGZ8kPKWfgrFdV+YB5MFy QY5pke4h0wswcPg0lWCW9z7Rv2iPlZabnpStD0oVk2erJMzkbG57hrs/O/pJjgnnkB qIXZaGwq/OZ4+T05gvgbrOOtA288S3SeslMygDVYek2efEcTJVgcLvbLaxObJC7QL+ TWu2cBtCMwfug== Date: Sun, 15 Nov 2026 07:42:40 +0200 From: Mike Rapoport To: "David Hildenbrand (Arm)" Cc: Jonathan Corbet , Shuah Khan , Randy Dunlap , Andrew Morton , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Pedro Falcato , 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> X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261107-b4-uffd_marker_loss-v1-1-82926b22704c@kernel.org> On Sat, Nov 07, 2026 at 12:51:05AM +0100, 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) Acked-by: Mike Rapoport (Microsoft) > --- > Documentation/filesystems/proc.rst | 1 + > fs/proc/task_mmu.c | 3 +++ > include/linux/mm.h | 45 ++++++++++++++++++++++++-------------- > include/linux/userfaultfd_k.h | 7 ++++-- > include/trace/events/mmflags.h | 9 +++++++- > mm/Kconfig | 1 + > mm/khugepaged.c | 9 ++++---- > mm/userfaultfd.c | 3 +++ > tools/testing/vma/include/dup.h | 20 ++++++++++++----- > 9 files changed, 70 insertions(+), 28 deletions(-) -- Sincerely yours, Mike.