Re: [PATCH 1/6] mm/hugetlb: Fix uffd-wp during fork()

Mike Kravetz
2023-04-14T22:17:59Z

On 04/13/23 19:11, Peter Xu wrote:
> There're a bunch of things that were wrong:
>
> - Reading uffd-wp bit from a swap entry should use pte_swp_uffd_wp()
> rather than huge_pte_uffd_wp().

That was/is quite confusing to me at least.

>
> - When copying over a pte, we should drop uffd-wp bit when
> !EVENT_FORK (aka, when !userfaultfd_wp(dst_vma)).
>
> - When doing early CoW for private hugetlb (e.g. when the parent page was
> pinned), uffd-wp bit should be properly carried over if necessary.
>
> No bug reported probably because most people do not even care about these
> corner cases, but they are still bugs and can be exposed by the recent unit
> tests introduced, so fix all of them in one shot.
>
> Cc: linux-stable <stable@vger.kernel.org>
> Fixes: bc70fbf269fd ("mm/hugetlb: handle uffd-wp during fork()")
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> mm/hugetlb.c | 26 ++++++++++++++++----------
> 1 file changed, 16 insertions(+), 10 deletions(-)

No issues except losing information in pte entry as pointed out by Mika.

--
Mike Kravetz