Re: [PATCH v1 2/2] mm/hugetlb: fix uffd-wp handling for migration entries in hugetlb_change_protection()

[Mike Kravetz]

On 12/22/22 21:55, David Hildenbrand wrote:
> We have to update the uffd-wp SWP PTE bit independent of the type of
> migration entry. Currently, if we're unlucky and we want to install/clear
> the uffd-wp bit just while we're migrating a read-only mapped hugetlb page,
> we would miss to set/clear the uffd-wp bit.
> 
> Further, if we're processing a readable-exclusive
> migration entry and neither want to set or clear the uffd-wp bit, we
> could currently end up losing the uffd-wp bit. Note that the same would
> hold for writable migrating entries, however, having a writable
> migration entry with the uffd-wp bit set would already mean that
> something went wrong.
> 
> Note that the change from !is_readable_migration_entry ->
> writable_migration_entry is harmless and actually cleaner, as raised by
> Miaohe Lin and discussed in [1].
> 
> [1] https://lkml.kernel.org/r/90dd6a93-4500-e0de-2bf0-bf522c311b0c@xxxxxxxxxx
> 
> Fixes: 60dfaad65aa9 ("mm/hugetlb: allow uffd wr-protect none ptes")
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
>  mm/hugetlb.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)

Thanks,

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