Re: [PATCH 0/3] mm/uffd: Fix missing markers on hugetlb

[David Hildenbrand]

On 04.01.23 23:52, Peter Xu wrote:
> When James was developing the vma split fix for hugetlb pmd sharing, he
> found that hugetlb uffd-wp is broken with the test case he developed [1]:
>
> https://lore.kernel.org/r/CADrL8HWSym93=yNpTUdWebOEzUOTR2ffbfUk04XdK6O+PNJNoA@xxxxxxxxxxxxxx
>
> Missing hugetlb pgtable pages caused uffd-wp to lose message when vma split
> happens to be across a shared huge pmd range in the test.
>
> The issue is pgtable pre-allocation on hugetlb path was overlooked.  That
> was fixed in patch 1.

Nice timing, I stumbled over that while adjusting background snapshot 
code in QEMU and wondered why we are not allocating page tables in that 
case -- and wanted to ask you why :)

--
Thanks,

David / dhildenb