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 94C0EC98307 for ; Wed, 23 Sep 2026 09:07:10 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A58316B0088; Wed, 23 Sep 2026 05:07:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A0A4F6B0092; Wed, 23 Sep 2026 05:07:09 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8F7826B0093; Wed, 23 Sep 2026 05:07:09 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 6F3B86B0088 for ; Wed, 23 Sep 2026 05:07:09 -0400 (EDT) Received: from smtpin26.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 046E4160755 for ; Wed, 23 Sep 2026 09:07:08 +0000 (UTC) X-FDA: 85244447778.26.5889256 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf31.hostedemail.com (Postfix) with ESMTP id 6606D20005 for ; Wed, 23 Sep 2026 09:07:07 +0000 (UTC) Authentication-Results: imf31.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=bAwdkSD5; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf31.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1790154427; b=8q+MQeVJbmN+uxOieThD+ONpXYqi0SC2g0+jLksNFgLtUEMlLuUowmrCojsT9Lyc/yW93O HArpkPx7mufuMk1GEp1ypTiZZ+YTbUYYAxge7BrFuki9KTW/FgtU/b+WOSiEwXVKCUAeBA ObDBw7oxuVVof3qgVgZwPUcxTJBd+RA= ARC-Authentication-Results: i=1; imf31.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=bAwdkSD5; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf31.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 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=1790154427; 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=ijxX8jmbmIhLUVAlgpu4wGN9OCs93woylxUncz1YJO8=; b=b8FlzaPxEAqp/AYhkKQkKB8wnmODFNfGRNgv2e7o1yc5yMxu4AEwxngqT37B0J5GvPWzYt fx8iXgtaR20vyuUeQm3KkU6hbLAdWD/rXh7LchiFFR9m3prmrI6PBo7m/ZtEPpfkjK5BXL yt1n+qaNWRYoXGv/7MM+qwisT8hoEIs= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 9813F405A6; Wed, 23 Sep 2026 09:07:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4CF911F000FF; Wed, 23 Sep 2026 09:06:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790154426; bh=ijxX8jmbmIhLUVAlgpu4wGN9OCs93woylxUncz1YJO8=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=bAwdkSD5tOW3uSVWxMzm2cuxEOctSvm7upiBz52QQgLh1Fp9Rd2BrR27jhHQIGX1D 03FLfGYqnqMpsgrwWg6NuY3wCZsFPfpnaSn7FT0wD73NSlHIvsYvEi/JGXmdHhyYBh Efd2lHjnpvzCYvE6IamlA1AxLWKWSLywhDW2Z+KgjD3ZcL9lyDJcNXeZYMDQpwFfPx WXdI3juP8lJmxxiGyfzOaeA5OwQifsTbNhZfOL7TC941WNds3R6K7uUmYZvvKOCLY9 sirrE3GI0tMMCEVeeeA/BxuD/c1QG59rgcina6NubfQn1BvO6FmOYDPEJFO456rfNZ PVwkGIBGoLtpA== Date: Wed, 23 Sep 2026 10:06:43 +0100 From: "Lorenzo Stoakes (ARM)" To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Guo Ren , Brian Cain , Geert Uytterhoeven , Dinh Nguyen , Simon Schuster , Jonas Bonn , Stefan Kristiansson , Stafford Horne , Rich Felker , John Paul Adrian Glaubitz , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Russell King , Vineet Gupta , Michal Simek , Chris Zankel , Max Filippov , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Peter Zijlstra , "David S. Miller" , Andreas Larsson , Richard Henderson , Matt Turner , Magnus Lindholm , Catalin Marinas , Mark Rutland , Huacai Chen , WANG Xuerui , Thomas Bogendoerfer , "James E.J. Bottomley" , Helge Deller , Madhavan Srinivasan , Michael Ellerman , "Christophe Leroy (CS GROUP)" , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Richard Weinberger , Anton Ivanov , Johannes Berg , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Arnd Bergmann , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jason Gunthorpe , John Hubbard , Peter Xu , Yoshinori Sato , Shakeel Butt , Jonathan Corbet , Randy Dunlap , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-openrisc@vger.kernel.org, linux-sh@vger.kernel.org, linux-riscv@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-snps-arc@lists.infradead.org, linux-arch@vger.kernel.org, sparclinux@vger.kernel.org, linux-alpha@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-um@lists.infradead.org, Hugh Dickins , Qi Zheng , linux-doc@vger.kernel.org Subject: Re: [PATCH v4 11/12] mm: make userland page table freeing RCU-safe Message-ID: References: <20260922-rcu-pagetable-freeing-v4-0-fe1ad1f1e303@kernel.org> <20260922-rcu-pagetable-freeing-v4-11-fe1ad1f1e303@kernel.org> <72d1548a-a4ee-4832-b2ab-4bc82f1933f8@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <72d1548a-a4ee-4832-b2ab-4bc82f1933f8@kernel.org> X-Rspamd-Server: rspam06 X-Stat-Signature: 7cp5o198kz45rm8ey4ij95eneazszrpw X-Rspam-User: X-Rspamd-Queue-Id: 6606D20005 X-HE-Tag: 1790154427-31379 X-HE-Meta: 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 hmv8xyj4 td56MuJWtWRxDmzbtbWQlhUN9xE47qaO3rXupq9cQZ8VoSDZXi9pNGFjn2RSefIp5PE5/5i6ddsk0l7NUwt+XolpSYmUov/aSo/u8Eyf8CbadE6fs+V/Eo/JXCct9uBJYxUTh0S8HP5Sv2+urTaZdr8o+7sKYsfcpsELnMz+BpB69SSM6m4io0tRc12Vfz5e79CO0kY1+tvKG1rdr0Yfp/AEM08iFp+O/Ltn8fqjSPsbJFT30Y1P+lpcWBC+RKCQX9X7hcQdMVtZcGDeYsBmRv4xkUpq25U11Yed+XZ8hqInlUgUQohtMrCrsUwdQNxg6k+8SSomRJVx65ouJN5UmTLgMm9BlhsJAZpgJ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Sep 23, 2026 at 11:04:17AM +0200, David Hildenbrand (Arm) wrote: > On 9/22/26 17:35, Lorenzo Stoakes (ARM) wrote: > > The patch subject confused me at first: that's not what the patch is doing, no? > Previous patches did that, and now you're just removing the leftovers? > > Maybe I'm missing something that this patch does along the lines of teaching the > code to be RCU-safe. It is the final piece that makes that the case, so I think it's OK to allow oneself a nice subject line? No? :) If people are confused they can read the commit message which goes into some detail. > > > Now every architecture has been converted to support > > CONFIG_MMU_GATHER_RCU_TABLE_FREE, this configuration option no longer makes > > any sense to keep around. > > > > Therefore remove it, and remove all the dead code that existed for > > !CONFIG_MMU_GATHER_RCU_TABLE_FREE architectures previously. > > > > Additionally, CONFIG_MMU_GATHER_TABLE_FREE is no longer necessary, as all > > architectures instead use CONFIG_HAVE_ARCH_TLB_REMOVE_TABLE when a custom > > __tlb_remove_table() is required, so remove this too. > > > > A number of architectures only enabled CONFIG_MMU_GATHER_RCU_TABLE_FREE if > > CONFIG_MMU was set, however the mmu_gather logic only actually does > > something meaningful if CONFIG_MMU is set (mmu_gather.c is only compiled in > > this case, for instance). > > > > As a result, there's no need to gate any of this logic on CONFIG_MMU > > explicitly. > > > > CONFIG_PT_RECLAIM however does have a strict dependency on CONFIG_MMU, so > > make this dependency explicit. > > > > Additionally, correct comments to remove references to non-RCU page table > > gathering and make it clear that this is not 'semi-RCU', nor has it been > > since commit 1fb3d8c20bfa ("mm/mmu_gather: replace IPI with > > synchronize_rcu() when batch allocation fails"). > > > > With this change in place the kernel policy is now that userspace page > > tables are freed after an RCU grace period, and thus it is now safe to > > unconditionally perform page table walks under RCU, safe in the knowledge > > that page tables will not be freed underneath the walker. > > > > This is all that is guaranteed, however, so naturally it is still incumbent > > upon page table walkers to ensure that the page table entries are as > > expected. > > > > Acked-by: Kiryl Shutsemau (Meta) > > Signed-off-by: Lorenzo Stoakes (ARM) > > > [...] > > > --- a/mm/Kconfig > > +++ b/mm/Kconfig > > @@ -1465,7 +1465,7 @@ config HAVE_ARCH_TLB_REMOVE_TABLE > > > > config PT_RECLAIM > > def_bool y > > - depends on MMU_GATHER_RCU_TABLE_FREE && !HAVE_ARCH_TLB_REMOVE_TABLE > > + depends on MMU && !HAVE_ARCH_TLB_REMOVE_TABLE > > help > > Try to reclaim empty user page table pages in paths other than munmap > > and exit_mmap path. > > $ git grep PT_RECLAIM > mm/Kconfig:config PT_RECLAIM > mm/memory.c: if (!IS_ENABLED(CONFIG_PT_RECLAIM)) > mm/mmu_gather.c:#ifdef CONFIG_PT_RECLAIM > mm/mmu_gather.c:#endif /* CONFIG_PT_RECLAIM */ > > whereby all files are MMU-only. > > Makes sense. > > > Very nice > > Acked-by: David Hildenbrand (Arm) Thanks. > > -- > Cheers, > > David -- Cheers, Lorenzo