Re: [PATCH 19/46] hugetlb: add HGM support for follow_hugetlb_page

[James Houghton]

On Thu, Jan 12, 2023 at 1:02 PM Peter Xu <peterx@xxxxxxxxxx> wrote:
>
> On Thu, Jan 05, 2023 at 10:18:17AM +0000, James Houghton wrote:
> > @@ -6731,22 +6746,22 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
> >                * and skip the same_page loop below.
> >                */
> >               if (!pages && !vmas && !pfn_offset &&
> > -                 (vaddr + huge_page_size(h) < vma->vm_end) &&
> > -                 (remainder >= pages_per_huge_page(h))) {
> > -                     vaddr += huge_page_size(h);
> > -                     remainder -= pages_per_huge_page(h);
> > -                     i += pages_per_huge_page(h);
> > +                 (vaddr + pages_per_hpte < vma->vm_end) &&
> > +                 (remainder >= pages_per_hpte)) {
> > +                     vaddr += pages_per_hpte;
>
> This silently breaks hugetlb GUP.. should be
>
>                         vaddr += hugetlb_pte_size(&hpte);
>
> It caused misterious MISSING events when I'm playing with this tree, and
> I'm surprised it rooted here.  So far the most time consuming one. :)

Thanks Peter!! And the `vaddr + pages_per_hpte < vma->vm_end` should
be `vaddr + hugetlb_pte_size(&hpte) < vma->vm_end` too.