From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 37ADA3112C0; Thu, 18 Jun 2026 08:47:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781772446; cv=none; b=nEWg3XmBbPaW6qlMnc4BXFv7jYLl6SwtpWMOx7WrHk55vw9jDZM777609WKk98lsxZ5gmQNqFO16onAFpvj3EdKXgYGve7xW9MMdrqOXncdD7npCI8FKH45XsGRQAtvlZV0SvdKPzdz1X/1ObEqgLCZSukgjfkKHb06msg/8HMI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781772446; c=relaxed/simple; bh=cVYxPbKiCw8I6vWtZVfisPED329h8mPhpx51Bjwx8v0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=UisTGOx2qxpxHHRjY8tIOUvME4zRuNmOk6zOlTGTjo0kZvkJdMnez2TYa3hiQgxNZ4Z2Fro4ZIJ6tpuiqljmor1rPtBn+Nr5Iiq+5gEbLf65At4825jdDhBJsosUtc2oS9G+ZlTKOR4uuY4vHAD7nxcqgTOF0npxDfPjQOFWhHY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=h2napG4F; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="h2napG4F" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8AFEA1F000E9; Thu, 18 Jun 2026 08:47:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781772444; bh=CnSbWReKGTEDPoaUR3qOev0pPCPHLKT28K++dObk2Z4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=h2napG4FfR/yPntLk9yltjsnQ1tWjH6S5xgCqt9ov3q4oh5HWT9ILBcDj7n1lAKVS Gj3t0fhK8jL2HzUkqIXxVlJbp7Q5H9PYweet2l1FOjxfJbUE2mxdD6LdxTFYu4NXX6 3CH15FT9GJjMwegnFDDQjy+m3iw6Rs8AOxyjn4JNe7iiTFhUFaqhdtczAn5CB0620e pPSshravIhP7l0D5iSUrj5wwSnIgZqaQcL5XFFzakD5gK2RaVO0MDia0Ibp/yuCtpK OiMWdYA+VXlVBcibkICEFagANR9A52Ue+h6FmWNDLBk3aB/c7ddKRObfDVSlZw25Qc 8ZdFnDLdc/bFg== Message-ID: <41ef0dce-e973-4947-b5e3-150fdb07f1a6@kernel.org> Date: Thu, 18 Jun 2026 10:47:19 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] userfaultfd: prevent registration of special VMAs To: Mike Rapoport Cc: Andrew Morton , Linus Torvalds , Alexander Viro , Christian Brauner , Jan Kara , Oleg Nesterov , Peter Xu , vova tokarev , linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org References: <20260617194059.2529406-1-rppt@kernel.org> <5a993689-f730-406d-8515-8bb6025cc851@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/18/26 10:43, Mike Rapoport wrote: > On Thu, Jun 18, 2026 at 11:34:12AM +0300, Mike Rapoport wrote: >> On Thu, Jun 18, 2026 at 10:19:17AM +0200, David Hildenbrand (Arm) wrote: >>> >>> I'm sure you considered VM_SPECIAL, which additionally includes VM_DONTEXPAND. >>> >>> Would that be better, or what was the reason to allow VM_DONTEXPAND? >> >> By itself VM_DONTEXPAND won't matter, as uffd can't resize a VMA. >> But thinking more about it, it's better to make vma_can_userfault() more >> restrictive and just use VM_SPECIAL. > > Ah, hugetlb sets VM_DONTEXPAND, so it must me excluded to allow uffd with > hugetlb. > It would probably be cleaner to just allow hugetlb, and then check for VM_SPECIAL if not hugetlb. -- Cheers, David