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

[Mike Rapoport <rppt@kernel.org>]

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@iscas.ac.cn>
> ---
> 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.
 
> 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@iscas.ac.cn
> [2]: https://lore.kernel.org/linux-riscv/20260309-riscv-sparsemem-vmemmap-limits-v1-2-f40efe18e3cd@iscas.ac.cn
> ---
>  arch/riscv/mm/init.c | 6 ++++++
>  include/linux/mm.h   | 1 +
>  mm/sparse-vmemmap.c  | 6 ++++++
>  3 files changed, 13 insertions(+)
> 
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 706f43523935..cf9ae4099f82 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -1360,6 +1360,12 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
>  	 */
>  	return vmemmap_populate_hugepages(start, end, node, altmap);
>  }
> +
> +void __meminit vmemmap_populate_finalize(void)
> +{
> +	/* Avoid faults on cached non-present TLB entries. */
> +	mark_new_valid_map();
> +}
>  #endif
>  
>  #if defined(CONFIG_MMU) && defined(CONFIG_64BIT)
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 0b776907152e..65deccbd7e31 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -4882,6 +4882,7 @@ int vmemmap_populate_hugepages(unsigned long start, unsigned long end,
>  			       int node, struct vmem_altmap *altmap);
>  int vmemmap_populate(unsigned long start, unsigned long end, int node,
>  		struct vmem_altmap *altmap);
> +void vmemmap_populate_finalize(void);
>  int vmemmap_populate_hvo(unsigned long start, unsigned long end,
>  			 unsigned int order, struct zone *zone,
>  			 unsigned long headsize);
> 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.

>  struct page * __meminit __populate_section_memmap(unsigned long pfn,
>  		unsigned long nr_pages, int nid, struct vmem_altmap *altmap,
>  		struct dev_pagemap *pgmap)
> @@ -561,6 +565,8 @@ struct page * __meminit __populate_section_memmap(unsigned long pfn,
>  	else
>  		r = vmemmap_populate(start, end, nid, altmap);
>  
> +	vmemmap_populate_finalize();
> +
>  	if (r < 0)
>  		return NULL;
>  
> 
> ---
> base-commit: 254f49634ee16a731174d2ae34bc50bd5f45e731
> change-id: 20260525-mark-after-vmemmap-populate-68bd790839c9
> prerequisite-message-id: <20260303-handle-kfence-protect-spurious-fault-v2-0-f80d8354d79d@iscas.ac.cn>
> prerequisite-patch-id: fdc42f2647e21d111f44a6532887a6705cd470a9
> prerequisite-patch-id: 096fa339c84c36643ae4311fd8362dc63e23d950
> prerequisite-patch-id: 305c876a5f4a23a840a8142aea79b796ed297545
> prerequisite-patch-id: d78cb55d6a616b1170f06a401c8fd44acd11e5d5
> prerequisite-patch-id: b02b4a76e94f3e2821291d4c23b46f6e5ecf5203
> 
> Best regards,
> --  
> Vivian Wang <wangruikang@iscas.ac.cn>
> 

-- 
Sincerely yours,
Mike.