Re: [PATCH v4 03/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for MMU riscv

[sashiko-bot@kernel.org]

> 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) <kas@kernel.org>
> Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260922-rcu-pagetable-freeing-v4-0-fe1ad1f1e303@kernel.org?part=3