Re: [PATCH v2 3/4] mm/hugetlb: Support vm_uffd_ops API

Mike Rapoport
2025-06-29T08:52:25Z

On Fri, Jun 27, 2025 at 11:46:54AM -0400, Peter Xu wrote:
> Add support for the new vm_uffd_ops API for hugetlb. Note that this only
> introduces the support, the API is not yet used by core mm.
>
> Due to legacy reasons, it's still not trivial to move hugetlb completely to
> the API (like shmem). But it will still use uffd_features and uffd_ioctls
> properly on the API because that's pretty general.
>
> Cc: Muchun Song <muchun.song@linux.dev>
> Cc: Oscar Salvador <osalvador@suse.de>
> Signed-off-by: Peter Xu <peterx@redhat.com>

Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

> ---
> mm/hugetlb.c | 19 +++++++++++++++++++
> 1 file changed, 19 insertions(+)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 11d5668ff6e7..ccd2be152d36 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5457,6 +5457,22 @@ static vm_fault_t hugetlb_vm_op_fault(struct vm_fault *vmf)
> return 0;
> }
>
> +#ifdef CONFIG_USERFAULTFD
> +static const vm_uffd_ops hugetlb_uffd_ops = {
> + .uffd_features = __VM_UFFD_FLAGS,
> + /* _UFFDIO_ZEROPAGE not supported */
> + .uffd_ioctls = BIT(_UFFDIO_COPY) |
> + BIT(_UFFDIO_WRITEPROTECT) |
> + BIT(_UFFDIO_CONTINUE) |
> + BIT(_UFFDIO_POISON),
> + /*
> + * Hugetlbfs still has its own hard-coded handler in userfaultfd,
> + * due to limitations similar to vm_operations_struct.fault().
> + * TODO: generalize it to use the API functions.
> + */
> +};
> +#endif
> +
> /*
> * When a new function is introduced to vm_operations_struct and added
> * to hugetlb_vm_ops, please consider adding the function to shm_vm_ops.
> @@ -5470,6 +5486,9 @@ const struct vm_operations_struct hugetlb_vm_ops = {
> .close = hugetlb_vm_op_close,
> .may_split = hugetlb_vm_op_split,
> .pagesize = hugetlb_vm_op_pagesize,
> +#ifdef CONFIG_USERFAULTFD
> + .userfaultfd_ops = &hugetlb_uffd_ops,
> +#endif
> };
>
> static pte_t make_huge_pte(struct vm_area_struct *vma, struct folio *folio,
> --
> 2.49.0
>

--
Sincerely yours,
Mike.