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

[Peter Xu]

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. :)

> +			remainder -= pages_per_hpte;
> +			i += pages_per_hpte;
>  			spin_unlock(ptl);
>  			hugetlb_vma_unlock_read(vma);
>  			continue;
>  		}

-- 
Peter Xu