[PATCH v5 3/9] mm/mremap: Use pmd/pud_poplulate to update page table entries

[Peter Xu]

On Wed, May 19, 2021 at 10:16:07AM +0530, Aneesh Kumar K.V wrote:
> > On Thu, Apr 22, 2021 at 11:13:17AM +0530, Aneesh Kumar K.V wrote:
> >> pmd/pud_populate is the right interface to be used to set the respective
> >> page table entries. Some architectures like ppc64 do assume that set_pmd/pud_at
> >> can only be used to set a hugepage PTE. Since we are not setting up a hugepage
> >> PTE here, use the pmd/pud_populate interface.

[1]

> Can you try this change?
> 
> modified   mm/mremap.c
> @@ -279,7 +279,7 @@ static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
>  	pmd_clear(old_pmd);
>  
>  	VM_BUG_ON(!pmd_none(*new_pmd));
> -	pmd_populate(mm, new_pmd, (pgtable_t)pmd_page_vaddr(pmd));
> +	pmd_populate(mm, new_pmd, pmd_pgtable(pmd));
>  
>  	if (new_ptl != old_ptl)
>  		spin_unlock(new_ptl);

I reported this issue today somewhere else:

https://lore.kernel.org/linux-mm/YKVemB5DuSqLFmmz@t490s/

And came to this same line after the bisection.

This seems to work at least for my userfaultfd test on shmem, however I don't
fully understand the commit message [1] on: How do we guarantee we're not
moving a thp pte?

-- 
Peter Xu