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Wed, 23 Sep 2026 07:05:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790147144; bh=WmR3kOZB3ACXfNo3laV3NfaLUopFF9HlVbP149Haq1Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=EAnwJUiAqyojRKJf9KNQTwXny7L+XnGgJ0trGGXwGUbbfY4A9uWcu9K0SsUiWOgmc yb41CHhlT/HBuBnzVyYR5/fQuSR3XjSBl9uXtd/UfutbvMg5gyAst3woO5CUYyXhGy AD976W51iwZLDg5mT7WlRmgWnW6l1yj7+OPvlJqhBDwYsyITZldKacOLPw8X3r5iwh xdzP0DsHgF0BxH20eqFZEB0DFdFfRS+stF04cj498KEixAmiiwoIiMX7fOO4v2ki3T qJvjlyssz0DhAO2ce9/8NcZk01mVg0oHHUpA2uecyxQvoQ0UuWqDvbZALG/EIOlt5M hZKVkk39Tca+Q== Date: Wed, 23 Sep 2026 08:05:21 +0100 From: "Lorenzo Stoakes (ARM)" To: Lance Yang Cc: akpm@linux-foundation.org, david@kernel.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, liam@infradead.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, usama.arif@linux.dev, kas@kernel.org, guoren@kernel.org, bcain@kernel.org, geert@linux-m68k.org, dinguyen@kernel.org, schuster.simon@siemens-energy.com, jonas@southpole.se, stefan.kristiansson@saunalahti.fi, shorne@gmail.com, dalias@libc.org, glaubitz@physik.fu-berlin.de, pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr, linux@armlinux.org.uk, vgupta@kernel.org, monstr@monstr.eu, chris@zankel.net, jcmvbkbc@gmail.com, will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, peterz@infradead.org, davem@davemloft.net, andreas@gaisler.com, richard.henderson@linaro.org, mattst88@gmail.com, linmag7@gmail.com, catalin.marinas@arm.com, mark.rutland@arm.com, chenhuacai@kernel.org, kernel@xen0n.name, tsbogend@alpha.franken.de, James.Bottomley@hansenpartnership.com, deller@gmx.de, maddy@linux.ibm.com, mpe@ellerman.id.au, chleroy@kernel.org, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, richard@nod.at, anton.ivanov@cambridgegreys.com, johannes@sipsolutions.net, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, arnd@arndb.de, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, jgg@ziepe.ca, jhubbard@nvidia.com, peterx@redhat.com, ysato@users.sourceforge.jp, shakeel.butt@linux.dev, corbet@lwn.net, rdunlap@infradead.org, 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, hughd@google.com, qi.zheng@linux.dev, linux-doc@vger.kernel.org Subject: Re: [PATCH v4 03/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for MMU riscv Message-ID: References: <20260922-rcu-pagetable-freeing-v4-3-fe1ad1f1e303@kernel.org> <20260923061551.84398-1-lance.yang@linux.dev> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260923061551.84398-1-lance.yang@linux.dev> On Wed, Sep 23, 2026 at 02:15:51PM +0800, Lance Yang wrote: > > On Tue, Sep 22, 2026 at 04:35:34PM +0100, Lorenzo Stoakes (ARM) wrote: > >Currently riscv gates MMU_GATHER_RCU_TABLE_FREE on CONFIG_SMP and > >CONFIG_MMU. > > > >Commit 69be3fb111e7 ("riscv: enable MMU_GATHER_RCU_TABLE_FREE for SMP && > >MMU") enabled CONFIG_MMU_GATHER_RCU_TABLE_FREE for CONFIG_SMP, CONFIG_MMU > >riscv builds. > > > >This is expressly for the safety of GUP-fast walkers (CONFIG_HAVE_GUP_FAST > >is enabled if CONFIG_MMU is enabled). > > > >Naturally a single core system does not encounter issues with software page > >table walkers being correctly synchronised across cores, as there is only a > >single core. > > > >However, CONFIG_PREEMPT_RCU is still available on a riscv UP system, so for > >a future RCU-only page table walker, this guarantee is required to prevent > >concurrent page table teardown. > > > >All page table freeing is already done via tlb_remove_ptdesc() so the > >conditions of CONFIG_MMU_GATHER_RCU_TABLE_FREE are already met. > > > >This forms part of an overall effort to switch every architecture to this > >mode. > > > >Acked-by: Kiryl Shutsemau (Meta) > >Signed-off-by: Lorenzo Stoakes (ARM) > >--- > > Yeah, for RISC-V, page-table freeing already goes through > tlb_remove_ptdesc() :) Tested on QEMU, no issues seen :) > > Tested-by: Lance Yang Thanks! :) A cheeky A-b tag possible too? :P -- Cheers, Lorenzo