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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5DEE3C982FA for ; Wed, 23 Sep 2026 09:07:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=cOlOuLp4JJld8Lea3u3C0mm+PqADpaz1Gc4+Uy0KLio=; b=d/K7pVawxm8V9L bR3NBVkDxOCou5Of1YlX41SxtM6hhzAasRXtprzhkuNLfgy3jFq16dWG8/KoofjatH9+A+lS5Tn3G QadkCXt+rHbxHgXLwFu9P1PeZ038aiPf+je27NpB7zgf8HocNw8lok68tgux2yxEmIlsWobnRns6X sOCAUs9T2OY+XbURlkUJLHMI/jz77Gu+0UAhUwz3VYv7XtU21JyLyq6HDQKEH55S5kIEt4WgDmkOC jiDJEti0gwBs6/ojv8m1IdnnVunZgKvBDHIkAZoU+NRjzr6VyUCQ8WyAYm6pBhFaGTY9EtUbpMBwg U+rXd623BeJPz5xXP/hw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1x9IwX-00000007fep-24o5; Wed, 23 Sep 2026 09:07:09 +0000 Received: from sea.source.kernel.org ([172.234.252.31]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1x9IwV-00000007feT-1DUd; Wed, 23 Sep 2026 09:07:07 +0000 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-Disposition: inline In-Reply-To: <72d1548a-a4ee-4832-b2ab-4bc82f1933f8@kernel.org> X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org 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 _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv