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

[Lance Yang <lance.yang@linux.dev>]

On 2026/9/23 15:05, Lorenzo Stoakes (ARM) wrote:
> 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) <kas@kernel.org>
>>> Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
>>> ---
>>
>> Yeah, for RISC-V, page-table freeing already goes through
>> tlb_remove_ptdesc() :) Tested on QEMU, no issues seen :)
>>
>> Tested-by: Lance Yang <lance.yang@linux.dev>
> 
> Thanks! :)

Cheers!

> A cheeky A-b tag possible too? :P

Sure thing! Here it is :D

Acked-by: Lance Yang <lance.yang@linux.dev>