Re: [PATCH v3 1/5] mm/sparse-vmemmap: provide generic vmemmap_set_pmd() and vmemmap_check_pmd()

["David Hildenbrand (Arm)" <david@kernel.org>]

On 6/1/26 10:48, Muchun Song wrote:
> The two weak functions are currently no-ops on every architecture,
> forcing each platform that needs them to duplicate the same handful
> of lines.  Provide a generic implementation:
> 
> - vmemmap_set_pmd() simply sets a huge PMD with PAGE_KERNEL protection.
> 
> - vmemmap_check_pmd() verifies that the PMD is present and leaf,
>   then calls the existing vmemmap_verify() helper.
> 
> Architectures that need special handling can continue to override the
> weak symbols; everyone else gets the standard version for free.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
> v2->v3:
> - Replace BUG_ON() with WARN_ON_ONCE() in vmemmap_set_pmd()
> ---
>  mm/sparse-vmemmap.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> index 112ccf9c71ca..99e2be39671b 100644
> --- a/mm/sparse-vmemmap.c
> +++ b/mm/sparse-vmemmap.c
> @@ -386,12 +386,17 @@ int __meminit vmemmap_populate_hvo(unsigned long addr, unsigned long end,
>  void __weak __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
>  				      unsigned long addr, unsigned long next)
>  {
> +	WARN_ON_ONCE(!pmd_set_huge(pmd, virt_to_phys(p), PAGE_KERNEL));


Not sure if a VM_WARN_ON_ONCE() would be appropriate. (then, we have to move the
pmd_set_huge() out of the statement).

Acked-by: David Hildenbrand (Arm) <david@kernel.org>


-- 
Cheers,

David