On 1/9/20 7:00 AM, Michal Hocko wrote:
> [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?
I have the same question as Michal. Did you see an issue where such a check
could help?
There is nothing wrong with the proposed code. However, it would be good to
know the reason for adding it. I started looking at all possible code paths
where this could apply. However, it would be better if you pointed out the
concern that caused you to create the patch.
--
Mike Kravetz
>
>> Signed-off-by: Li Xinhai <lixinhai.lxh@xxxxxxxxx>
>> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
>> ---
>> 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
