Re: [External] [PATCH] userfaultfd: hugetlbfs: fix new flag usage in error path

[Muchun Song]

On Sat, May 22, 2021 at 7:40 AM Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:
>
> In commit d6995da31122 ("hugetlb: use page.private for hugetlb specific
> page flags") the use of PagePrivate to indicate a reservation count
> should be restored at free time was changed to the hugetlb specific flag
> HPageRestoreReserve.  Changes to a userfaultfd error path as well as a
> VM_BUG_ON() in remove_inode_hugepages() were overlooked.
>
> Users could see incorrect hugetlb reserve counts if they experience an
> error with a UFFDIO_COPY operation.  Specifically, this would be the
> result of an unlikely copy_huge_page_from_user error.  There is not an
> increased chance of hitting the VM_BUG_ON.
>
> Fixes: d6995da31122 ("hugetlb: use page.private for hugetlb specific page flags")
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>

Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>

Thanks Mike.