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Wed, 23 Sep 2026 06:16:01 +0000 X-Mizu-Trace-ID: 4b4ce70d101944f5 X-Migadu-Flow: FLOW_OUT From: Lance Yang To: ljs@kernel.org 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, lance.yang@linux.dev, 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 Date: Wed, 23 Sep 2026 14:15:51 +0800 Message-ID: <20260923061551.84398-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20260922-rcu-pagetable-freeing-v4-3-fe1ad1f1e303@kernel.org> References: <20260922-rcu-pagetable-freeing-v4-3-fe1ad1f1e303@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: nbmks5s1a6bg9pxiin3guyk3f8ustn96 X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 51381A0005 X-HE-Tag: 1790144165-743796 X-HE-Meta: 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 1wkCSuY+ iP1uOzLTEAG1s6VVH1eSA7AT6hrLwJT9bVqL7MSEdrDV9CIH5Bttt418DIzR73WkwFv0SKACdfIQEEu0ErITvuyQJsa34R71MmsHhPROeRwqyni/IuawKOGUC4F8TY600RhkzvLpM18/UM+V8O68xAMdPTDTVUmaVusudZpBQfy+gd1K9WSWv9a84Dea9fLxv8ww7K5vwOsArhCv4LGTZ/EgNiiArPCeKyie6EXvkmcMGToQc3/qy2qOu5yHKF/eeU4Z2+snh4Jg1bK9sQZPdoGH9dE/U7CEA0P0V9DGtxcB0YUE7r6ckGYzOPJcGorCppkhLO6IbdFR9B7571EvoOtzLVvxUsquPUnbfr/zvXEV85ByZbXklXbYVbO0Hkn83CWdy Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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