On Fri, May 06, 2022 at 12:07:13PM -0700, Mike Kravetz wrote: > On 5/3/22 03:03, Gerald Schaefer wrote: > > On Tue, 3 May 2022 10:19:46 +0800 > > Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> wrote: > >> On 5/2/2022 10:02 PM, Gerald Schaefer wrote: [...] > >> Please see previous code, we'll use the original pte value to check if > >> it is uffd-wp armed, and if need to mark it dirty though the hugetlbfs > >> is set noop_dirty_folio(). > >> > >> pte_install_uffd_wp_if_needed(vma, address, pvmw.pte, pteval); > > > > Uh, ok, that wouldn't work on s390, but we also don't have > > CONFIG_PTE_MARKER_UFFD_WP / HAVE_ARCH_USERFAULTFD_WP set, so > > I guess we will be fine (for now). > > > > Still, I find it a bit unsettling that pte_install_uffd_wp_if_needed() > > would work on a potential hugetlb *pte, directly de-referencing it > > instead of using huge_ptep_get(). > > > > The !pte_none(*pte) check at the beginning would be broken in the > > hugetlb case for s390 (not sure about other archs, but I think s390 > > might be the only exception strictly requiring huge_ptep_get() > > for de-referencing hugetlb *pte pointers). We could have used is_vm_hugetlb_page(vma) within the helper so as to properly use either generic pte or hugetlb version of pte fetching. We may want to conditionally do set_[huge_]pte_at() too at the end. I could prepare a patch for that even if it's not really anything urgently needed. I assume that won't need to block this patchset since we need the pteval for pte_dirty() check anyway and uffd-wp definitely needs it too. Thanks, -- Peter Xu
