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
