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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On Tue, Sep 22, 2026 at 04:35:35PM +0100, Lorenzo Stoakes (ARM) wrote: >Commit a0ad5496b2b3 ("arm: mm: enable HAVE_RCU_TABLE_FREE logic") enabled >CONFIG_MMU_GATHER_RCU_TABLE_FREE (then named HAVE_RCU_TABLE_FREE) for SMP >arm architectures with LPAE enabled. > >Regardless of whether CONFIG_ARM_LPAE is enabled or not, the same page >table freeing functions __pte_free_tlb() and __pmd_free_tlb() are used. > >Non-LPAE PMD page tables are folded into the PGD and freed by >pgd_free() (PGD freeing is not part of mmu_gather page table freeing in any >case), so this is a noop in this case. > >Since commit 358d1c39c82a ("arm: convert various functions to use ptdescs") >both LPAE and non-LPAE PTE page table freeing uses tlb_remove_ptdesc(). > >Thus all page table freeing is performed under RCU with >CONFIG_MMU_GATHER_RCU_TABLE_FREE enabled for LPAE and non-LPAE and thus it >need not be gated on LPAE. > >A UP arm system can set CONFIG_PREEMPT_RCU, so a future pure RCU page >table walker requires MMU_GATHER_RCU_TABLE_FREE to be enabled on UP as >well, even if concurrent GUP fast is not possible there. > >Therefore, it is both safe and desirable to set >CONFIG_MMU_GATHER_RCU_TABLE_FREE for all MMU arm architectures (nommu does >not perform mmu_gather operations). > >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) >--- Tested under heavy page-table teardown load on qemu-system-arm, with and without ARM_LPAE. No issues seen :D Tested-by: Lance Yang Also, feel free to add: Acked-by: Lance Yang > arch/arm/Kconfig | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > >diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig >index 408aa58a2a5b..72b9afc6ae10 100644 >--- a/arch/arm/Kconfig >+++ b/arch/arm/Kconfig >@@ -134,7 +134,7 @@ config ARM > select HAVE_PERF_REGS > select HAVE_PERF_USER_STACK_DUMP > select HAVE_POSIX_CPU_TIMERS_TASK_WORK >- select MMU_GATHER_RCU_TABLE_FREE if SMP && ARM_LPAE >+ select MMU_GATHER_RCU_TABLE_FREE if MMU > select HAVE_REGS_AND_STACK_ACCESS_API > select HAVE_RSEQ > select HAVE_RUST if CPU_LITTLE_ENDIAN && CPU_32v7 && !KASAN > >-- >2.55.0 > > _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv