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 DC89A3FA5D9; Tue, 21 Jul 2026 15:04:47 +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=1784646288; cv=none; b=M6I7YyTc6ABmbmG3zqecaJJxh3xt/HZjdYrBkh82HJmQpz1QJoKGTDmk3Hypr/XEEBkiWYsmuaVfpA8iIjdwUEVv/odS98JTBAk5LrJsHMX+GIDfN12xzTZ3gKx7Y+lxdOZYxox3RFqHPV0eCAwLrpdxSscmSGi+4UaJHT5ZqOs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784646288; c=relaxed/simple; bh=tkasnsPwJ6sjtkQXlt8f9BYnXKVn8k89fxNkeWsPYpg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=bzdbBn4UdRyyGuoP5sOwXYn1aF9dgqv7BU9vVJOCRV8JPpJKhQ1/CTh5ZEr1ewn09ZTArF/yj5VccX7fiJBWqY6u63tJwFkKLvdvsuu2npLWYtW7XMS8BdNxdBoZZHwoaM69bKvqWjl9jAOURB/XrdkqGVoVdkoTzjAIpBqEvKg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=A7zv8FYY; 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="A7zv8FYY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 253511F000E9; Tue, 21 Jul 2026 15:04:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784646287; bh=KvFlBOSAAN25BmqEyf7MAcVM6Drefi3m8EoY83MJzfk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=A7zv8FYYS3BagE62jjvD73Uo/224uS+6js4DUo1TwI40rxRLe9Jy+r9SjEyOaqeU5 rrJBY4oVg3W901xWvxUgvAaN9pRWVrH2l4W2I/qQ5dqtTJ7UGaFX2JCrkU4eOJlqcD jxL2cK2LvZK45Y/FKSigYw2lIsYEm8O2UBS6UV1NJX6apyOK6foKBUIuE2snq0pRW2 8XXBKWZtHyGR2+qVvCUv9YcmaWJjt6iRu03x4OeaKWzLsttCkNZ0wQAKhXTJ1cXNRV 6VmOsoQBDpTz9vZqaykrZj3UP9etcPWzq5QO5kU0Ljog+5Hjy2ATYcv4TUr/wX9mdf dN7NNkgocFuig== Message-ID: <0bab816d-5de9-4814-b97d-11e89322c413@kernel.org> Date: Tue, 21 Jul 2026 17:04:33 +0200 Precedence: bulk X-Mailing-List: linux-parisc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 03/22] mm: introduce MMF_KERNEL flag and set it for init_mm To: Kevin Brodsky , "Lorenzo Stoakes (ARM)" , Dave Hansen Cc: linux-mm@kvack.org, Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Pasha Tatashin , Russell King , Catalin Marinas , Will Deacon , Ryan Roberts , linux-arm-kernel@lists.infradead.org, Huacai Chen , loongarch@lists.linux.dev, "James E.J. Bottomley" , Helge Deller , linux-parisc@vger.kernel.org, Madhavan Srinivasan , Michael Ellerman , linuxppc-dev@lists.ozlabs.org, Paul Walmsley , Palmer Dabbelt , Albert Ou , linux-riscv@lists.infradead.org, Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Gerald Schaefer , linux-s390@vger.kernel.org, "David S. Miller" , Andreas Larsson , sparclinux@vger.kernel.org, Richard Weinberger , Anton Ivanov , Johannes Berg , linux-um@lists.infradead.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Ning Sun , x86@kernel.org, tboot-devel@lists.sourceforge.net, Ard Biesheuvel , Ilias Apalodimas , linux-efi@vger.kernel.org, Vishal Moola , Alistair Popple , "Matthew Wilcox (Oracle)" , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org References: <20260714-remove_pgtable_cdtor-v1-0-44be8a7685d7@arm.com> <20260714-remove_pgtable_cdtor-v1-3-44be8a7685d7@arm.com> <71045fa8-89fe-4a0b-a05b-67e19ce89834@intel.com> <5ce00109-c0ea-43f0-881d-f58a0fda8dcb@arm.com> 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: <5ce00109-c0ea-43f0-881d-f58a0fda8dcb@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/16/26 11:33, Kevin Brodsky wrote: > On 14/07/2026 17:04, Lorenzo Stoakes (ARM) wrote: >> On Tue, Jul 14, 2026 at 07:47:43AM -0700, Dave Hansen wrote: >>> Could we give this some nice comments explaining what a kernel mm is, >>> please? Part of the problem with the init_mm checks is that they're >>> magic and it's not always clear what's special about init_mm. > > Agreed, we need to define what this property means exactly, and your > comments on patch 14 show that extending it to efi_mm isn't necessarily > as benign as it appeared to me at first. > > My motivation really is about how page tables are handled (in particular > whether ptlocks are used), so as you suggested on patch 19 maybe this > flag should be narrower in scope, and the naming should reflect it. > Possibly MMF_KERNEL_PGTABLES? That's at least one thing that should be > true of all of init_mm, efi_mm and tboot_mm: their page tables use > kernel permissions, not user, and should follow the same rules including > not using ptlocks. > >>> Maybe start with this list? >>> >>> 1. There's only one of them. >>> 2. All kernel threads share it. tsk->mm is the same for all kernel >>> threads. >>> 3. It holds the reference copy of the kernel page tables >>> 4. Userspace can't be entered when it is the current mm >>> 5. It has different TLB flushing rules than userspace mms >>> >>> I _think_ those are universal across all architectures. >> Well point 1 isn't true of efimm or tboot_mm so we possibly need a better >> name :) >> >> "Special" is overloaded too much already. I quite like "eternal" so: >> >> static inline bool mm_is_eternal(const struct mm_struct *mm) >> { >> return mm && mm_flags_test(MMF_ETERNAL, mm); >> } > > Cheeky but why not! I do wonder whether this conveys the right idea > though. The main point of this flag is that page tables are > allocated/initialised/locked differently; in principle you could have a > temporary non-user mm. I mean, we talk about MMs that are not used for actual user space processes? IOW, the following: arch/x86/kernel/tboot.c:static struct mm_struct tboot_mm = { drivers/firmware/efi/efi.c:struct mm_struct efi_mm = { drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-test.c:static struct mm_struct sva_mm = { mm/init-mm.c:struct mm_struct init_mm = { So "user" vs. "kernel" is quite intuitive. Sure, there can be multiple "kernel" ones, but each with a distinct purpose (IOW, we don't have multiple init_mm MMs). -- Cheers, David