Re: [PATCH v3 4/4] hugetlb/userfaultfd: Unshare all pmds for hugetlbfs when register wp

[Mike Kravetz]

On 2/18/21 1:55 PM, Peter Xu wrote:
> Huge pmd sharing for hugetlbfs is racy with userfaultfd-wp because
> userfaultfd-wp is always based on pgtable entries, so they cannot be shared.
> 
> Walk the hugetlb range and unshare all such mappings if there is, right before
> UFFDIO_REGISTER will succeed and return to userspace.
> 
> This will pair with want_pmd_share() in hugetlb code so that huge pmd sharing
> is completely disabled for userfaultfd-wp registered range.
> 
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> ---
>  fs/userfaultfd.c        |  4 ++++
>  include/linux/hugetlb.h |  3 +++
>  mm/hugetlb.c            | 51 +++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 58 insertions(+)

Thanks,
Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
-- 
Mike Kravetz