Re: [PATCH v2] mm/page_vma_mapped.c: Detect mismatched pfn of hugetlbfs page in pfn_in_hpage()

[Michal Hocko <mhocko@kernel.org>]

[Cc Mike who is hugetlb maintainer]

On Thu 09-01-20 14:26:02, Li Xinhai wrote:
> check_pte is called for hugetlbfs page and comparing pfn in pfn_in_page,
> where pfn is compared in range [hpage_pfn, hpage_pfn+HPAGE_PMD_NR). For
> hugetlbfs page, pfn must equal to hpage_pfn, so catch it as bug if they
> are not equal.

Why do we need this? Would that help to debug any past bug?

> Signed-off-by: Li Xinhai <lixinhai.lxh@gmail.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
>  mm/page_vma_mapped.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
> index eff4b45..713aaed 100644
> --- a/mm/page_vma_mapped.c
> +++ b/mm/page_vma_mapped.c
> @@ -55,6 +55,7 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw)
>  static inline bool pfn_in_hpage(struct page *hpage, unsigned long pfn)
>  {
>  	unsigned long hpage_pfn = page_to_pfn(hpage);
> +	VM_BUG_ON_PAGE(PageHuge(hpage) && pfn != hpage_pfn, hpage);
>  
>  	/* THP can be referenced by any subpage */
>  	return pfn >= hpage_pfn && pfn - hpage_pfn < hpage_nr_pages(hpage);
> -- 
> 1.8.3.1
> 

-- 
Michal Hocko
SUSE Labs