Re: [PATCH] riscv: mm: Call mark_new_valid_map() after hotplugging vmemmap

[Vivian Wang]

Hi Mike,

Thanks for your review.

On 6/1/26 15:13, Mike Rapoport wrote:
> Hi,
>
> On Mon, May 25, 2026 at 12:23:29PM +0800, Vivian Wang wrote:
>> section_activate() creates new mappings in the vmemmap range without
>> flushing TLB, which may cause faults on some RISC-V implementations that
>> cache non-present PTEs and crashes.
>>
>> This seems to be most easily reproduced with DEBUG_VM=y and
>> PAGE_POISONING=y, which causes these newly mapped struct pages to be
>> poisoned i.e. written to immediately after mapping.
>>
>> Add a hook vmemmap_populate_finalize() in __populate_section_memmap(),
>> and implement it as calling mark_new_valid_map() on RISC-V, which
>> arranges for the exception handler to deal with these faults if they
>> happen.
>>
>> Signed-off-by: Vivian Wang <wangruikang@xxxxxxxxxxx>
>> ---
>> I'm not sure if this is the right place to add this hook. I didn't add
>> it to vmemmap_populate because it doesn't seem to be called in all
>> cases. Please advise.
> Indeed it looks like we'd need a new hook to let architectures run
> post-populate actions.
>
> The explanation that says why a new hook is needed should be a part of the
> changelog.
>  

I will reorganize this in v2.

>> Depends on my earlier kfence fixes for mark_new_valid_map() [1].
>>
>> Found while testing AMD_HSA/ZONE_DEVICE on SpacemiT K3. Using
>> ZONE_DEVICE requires another fix [2].
>>
>> [1]: https://lore.kernel.org/linux-riscv/20260303-handle-kfence-protect-spurious-fault-v2-0-f80d8354d79d@xxxxxxxxxxx
>> [2]: https://lore.kernel.org/linux-riscv/20260309-riscv-sparsemem-vmemmap-limits-v1-2-f40efe18e3cd@xxxxxxxxxxx
>> ---
>>  arch/riscv/mm/init.c | 6 ++++++
>>  include/linux/mm.h   | 1 +
>>  mm/sparse-vmemmap.c  | 6 ++++++
>>  3 files changed, 13 insertions(+)

[...]

>> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
>> index 6eadb9d116e4..2b860d2b1703 100644
>> --- a/mm/sparse-vmemmap.c
>> +++ b/mm/sparse-vmemmap.c
>> @@ -544,6 +544,10 @@ static int __meminit vmemmap_populate_compound_pages(unsigned long start_pfn,
>>  
>>  #endif
>>  
>> +void __weak __meminit vmemmap_populate_finalize(void)
>> +{
>> +}
>> +
> The existing hooks in sparse-vmemmap use #ifdef <hook> rather than __weak
> functions. Take a look at vmemmap_can_optimize() and
> vmemmap_populate_compound_pages().
>
> Let's keep it consistent.

I wasn't sure since it seems that both styles exist in this file.

I will change it to #ifdef in v2, as that seems to be preferable.

Vivian "dramforever" Wang

> [...]