Re: [PATCH v1 5/5] mm, hwpoison: enable memory error handling on 1GB hugepage

["HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>]

On Wed, Jun 08, 2022 at 08:57:24PM +0800, Miaohe Lin wrote:
...
> >
> > I think that most of page table walker for user address space should first
> > check is_vm_hugetlb_page() and call hugetlb specific walking code for vma
> > with VM_HUGETLB.
> > copy_page_range() is a good example.  It calls copy_hugetlb_page_range()
> > for vma with VM_HUGETLB and the function should support hwpoison entry.
> > But I feel that I need testing for confirmation.
>
> Sorry, I missed it should be called from hugetlb variants.
>
> >
> > And I'm not sure that all other are prepared for non-present pud-mapping,
> > so I'll need somehow code inspection and testing for each.
>
> I browsed the code again, there still might be some problematic code paths:
>
> 1.For follow_pud_mask, !pud_present will mostly reach follow_pmd_mask(). This can be
> called for hugetlb page. (Note gup_pud_range is fixed at 15494520b776 ("mm: fix gup_pud_range"))
>
> 2.Even for huge_pte_alloc, pud_offset will be called in pud_alloc. So pudp will be an invalid pointer.
> And it will be de-referenced later.

Yes, these paths need to support non-present pud entry, so I'll update/add
the patches.  It seems that I did the similar work for pmd few years ago
(cbef8478bee5 ("mm/hugetlb: pmd_huge() returns true for non-present hugepage").

Thanks,
Naoya Horiguchi