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 62491606A332 for ; Thu, 12 Nov 2026 23:59:12 +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=fChm8D0E Received: by kanga.kvack.org (Postfix) id 2F5846B0623; Thu, 12 Nov 2026 18:59:11 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 2CD856B0625; Thu, 12 Nov 2026 18:59:11 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1BDA86B0626; Thu, 12 Nov 2026 18:59:11 -0500 (EST) 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 E0F4E6B0623 for ; Thu, 12 Nov 2026 18:59:10 -0500 (EST) Received: from smtpin02.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 66ADBAA553 for ; Thu, 12 Nov 2026 23:59:10 +0000 (UTC) X-FDA: 85428135660.02.F405A5B Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf19.hostedemail.com (Postfix) with ESMTP id 9BDF31A0006 for ; Thu, 12 Nov 2026 23:59:08 +0000 (UTC) Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=fChm8D0E; spf=pass (imf19.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1794527948; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=WxgEX4388zF6U8KM4KgbrPSeQjWqRryJtZ/6cfDPpWs=; b=ENf4yqRKOAaj78Ez2ekzvnDxDZSJ/6uoIUYoOWKU5w40nEZ7U0LBsQYNgps60qCf/aiKPt QfOF1iE4/z3lvD1kfI6zK0d3eD3Gs1pxbfDVR7MdlpznmFi252lYkTsicSGTqYqMgz8iJZ /PJTanulNyvMWM33kbzc737dE7XZ+B4= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1794527948; b=AymR6lkGS3NCLAWlJTbItcyFBlcyoliYTPjhTCEUWqnYhc+r8s7NbsCc03y0v3OvtlQhEM J7hgZ4UwH6TO51L7JRxH58QNM0nAZmp2V19INo6owvu0m5n0n8FqzoFIXej+0d3cSpufJM USbQYzguuyRnheYJBgZhroXf8waR7sc= ARC-Authentication-Results: i=1; imf19.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=fChm8D0E; spf=pass (imf19.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 3F5D260EFD; Thu, 12 Nov 2026 23:59:07 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9B85D1F000C4; Thu, 12 Nov 2026 23:59:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794527946; bh=WxgEX4388zF6U8KM4KgbrPSeQjWqRryJtZ/6cfDPpWs=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=fChm8D0EaIVF/iA0odcAXXSgtLTuReq648ASLwVx75+fiP4hIn2IxqLOz393lT+YY dI8xkbOHhpkbeTDq49ki1fgPcIHoVyx1+iZ7zaGmN6hCbjsvGXdDGgiwJvYx3klF5e O5UVzIf7JepO57KRDdTFadPkEVTj5ipcuzLl84Jc8p4boWXZ7hEMKmtBfiA3xf1Stf a3XKSwLSu+8hq2nPVjCaLlJOWZVVtC6rH+jtL9Y5tn9d4ybEcMlJwSUsDYuHHrC4MU s1wQta+FgpLtpRPpuq1QPBR0dfJKP8XE5E9LXzW3BEYZwID1RrNmguRyzXA0OJAFs0 MmIfRR0TmzGFg== Message-ID: <0e3e876e-c3df-4660-ad89-a5f0fd7dedc8@kernel.org> Date: Fri, 13 Nov 2026 00:59:00 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/madvise: disallow guard region installation in uffd-armed VMAs To: "Lorenzo Stoakes (ARM)" , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Jann Horn , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Shuah Khan Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Tal Zussman , stable@vger.kernel.org References: <20261112-disallow-uffd-guard-install-v1-1-bcf8b1aaa72e@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20261112-disallow-uffd-guard-install-v1-1-bcf8b1aaa72e@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam09 X-Stat-Signature: 3twrx1auej34ee66hc9yn5tb8pg3chda X-Rspamd-Queue-Id: 9BDF31A0006 X-Rspam-User: X-HE-Tag: 1794527948-300804 X-HE-Meta: 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 m0pIAhPI rc3R3CuyYP+K51wEHyFG15Do/k3r4htm36CnXDvennILc9YDDMgKWV9fzS70tSbwZGxeKrY3yD4uGYxumNKruYPv3QbBjQ+En0+q8fE8iEsi1zFfKmMjih+BIW2upy3/Gu1PIjDBdUw3aPYCKwYGY95FeNAXrMo+5jeHgCBiD4DKNaDUJNXpPc1iWo9dW35Zf/KNcOGfSdb+xH8w9ZdvdH7iyFcEtSE/t+ZYp7akPxwsuMaN/kZkNjDtIcEe8BI4SrY+Z 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 11/12/26 18:38, Lorenzo Stoakes (ARM) wrote: > In order to establish guard regions, guard markers are installed in the > page tables of a mapped VMA. > > However, problems arise when one tries to combine this with registering a > VMA for userfaultfd, as such operations may themselves need to install page > table markers such as uffd-wp. How does this interact with UFFDIO_POISON markers that can outlive even userfaultfd registration? I'd assume it's just the same thing, just like having proper hwpoison marker in anon mappings, so it just works (uffd-wp will skip, guard installation will zap). > > When this installation is attempted the guard marker prevents these markers > being applied, which can lead to unexpected results (especially if the > guard regions are later removed.) > > This is especially problematic because guard region installation causes the > regions to be zapped first, meaning that the removal of userfaultfd-tracked > ranges will not be logged in this case. Again, similar to trying to uffd-wp-protect'ing a hwpoison marker (which will be ignored), and then zapping that. Isn't guard marker installation/removal just another form of zapping? So to me this all sounds like "if user space does something stupid, it's user space's fault". > > Therefore, disallow this. > > This makes sense as conceptually, guard regions mark a part of a VMA as > effectively unmapped at the page table level, and removing the markers is > like mapping the VMA again, over which operation uffd markers would in any > case be lost. Right, but that to me just says "on the parts of the VMA where you mess with guard markers, your uffd-wp protection is similarly ignored". So disallowing it entirely for a VMA, I am not sure. I could see use cases for that, although you might argue that user space should then register uffd-wp on the separate pieces. But then you get multiple VMAs again. -- Cheers, David