From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id E7837C44501 for ; Tue, 14 Jul 2026 15:05:18 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 821196B00E2; Tue, 14 Jul 2026 11:05:17 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7F9606B00E3; Tue, 14 Jul 2026 11:05:17 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6C1FB6B00E4; Tue, 14 Jul 2026 11:05:17 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 48AE16B00E2 for ; Tue, 14 Jul 2026 11:05:17 -0400 (EDT) Received: from smtpin20.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id D1FC01A0433 for ; Tue, 14 Jul 2026 15:05:16 +0000 (UTC) X-FDA: 84987705432.20.CFFB19C Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf28.hostedemail.com (Postfix) with ESMTP id 462BFC0007 for ; Tue, 14 Jul 2026 15:05:15 +0000 (UTC) Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=crOD2NmJ; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf28.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=1784041515; 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=AYjyETDBZwm0j/cPjjIgSYujcuHtX92Lh9M1By4BrMc=; b=f7cGbrSNMC6hcboIL4oZwn+JqqgXbTF3lGUnLfCnU5YtCtYBeCoH0EDG5bPJqgGNX/fBrM n8rDUigk1YyOryj7KEAT/h/NAscv8minljmeY2+5nBVx8wauZy+3J/r2UhO/Cx2TyhxAKT l/mCQIXj2pQwYfD8vyjKzO1np17XEV4= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=crOD2NmJ; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf28.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=1784041515; b=2bq4ocplKdzOKt0Ly71TAFLL4Zy6A1TYt8SjjnsmcphDF0LDvvRhUAvk412zzREo1WlALp o1DXUyAxeN5OTqIF2svTt0bBGYWYfpJ/4nduIITX6xEf/vpob47yrdKu/jjIwY98qzFWLV 8p+i8lO6kjc1ULmOfWTOX8U+T6eqACU= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id B803C60103; Tue, 14 Jul 2026 15:05:14 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 24AA51F000E9; Tue, 14 Jul 2026 15:05:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784041514; bh=AYjyETDBZwm0j/cPjjIgSYujcuHtX92Lh9M1By4BrMc=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=crOD2NmJDWob7tNH4b0nB1FiZnokFnKZDkP0Ght7V6I9Wl8zmC+0pmKCW+kuXLlLH OdZHmkh/T/9BB42ZvoZwp60T/mYLQwb+uOSlwDUb+jGK/rXpggWk3voCs1+1oCHlIy LXTlYETzj3M++Bh5NzIk2buDSGg3fmS7KG1J0rfl/O/1fHossnuwmJ7LiswfHs+0P0 ffWQo61tvdjoVoC7hXSzokGWOo+sPo7j+/6Jfs2msT1jdScy1yBzSMh3QvyUVNtNcz 99aBb5YGUL9jfl1vNkXPGp7NC4uErRwi1ismiMLOqmhMcboruizzYkE3vXwJGQsEgm RUE53xPNgB+iQ== Date: Tue, 14 Jul 2026 16:04:52 +0100 From: "Lorenzo Stoakes (ARM)" To: Dave Hansen Cc: Kevin Brodsky , linux-mm@kvack.org, Andrew Morton , David Hildenbrand , "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 Subject: Re: [PATCH 03/22] mm: introduce MMF_KERNEL flag and set it for init_mm Message-ID: 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <71045fa8-89fe-4a0b-a05b-67e19ce89834@intel.com> X-Stat-Signature: mjkeyn11j7cu89uhtgxik1rbetwhge7j X-Rspamd-Queue-Id: 462BFC0007 X-Rspamd-Server: rspam01 X-Rspam-User: X-HE-Tag: 1784041515-57756 X-HE-Meta: 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 hrzeQM1a Nq3nS80K4+3qVB+LkdeB2TqnucbiK2cyS1NCItS7fvv144HICWNjL/8cufWTcOcqgkcPzUpf26WAVUtwhmwH27FfgsAOt3AdOCMfVgLjSCZ4Z1XxkJ4LBaHQ6+GdTKJhk3rBLhnTVq8ewpZiroTFhsnsWtyqCJA+jr4MltBSC4YhYgpCgf8wHDrYE2XfxnOJ+TrPAUfodOwIKI6GA27WDq8ibKLHm2XX58ix6MpU0YssHk4l7/hd00YP+77s6vnvwHcenU9dDnSu/qjwHoVSAunX8cog++4/8+9KwAcDrtjho4pEHXdk70827A5mWXCm2mhLn/k6CVR2qXUeZCgVicH9OMAHbjES6iD6PehykdCadHW/CJtK0FiSmpQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jul 14, 2026 at 07:47:43AM -0700, Dave Hansen wrote: > On 7/14/26 07:03, Kevin Brodsky wrote: > > +static inline bool mm_is_kernel(const struct mm_struct *mm) > > +{ > > + return mm && mm_flags_test(MMF_KERNEL, mm); > > +} > > 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. > > 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); } :) Cheers, Lorenzo