Re: [PATCH v2 2/4] mm/shmem: Support vm_uffd_ops API

Mike Rapoport
2025-06-29T08:51:42Z

On Fri, Jun 27, 2025 at 11:46:53AM -0400, Peter Xu wrote:
> Add support for the new vm_uffd_ops API for shmem. Note that this only
> introduces the support, the API is not yet used by core mm.
>
> Due to the tailored uffd_copy() API, shmem is extremely easy to support it
> by reusing the existing mfill function.
>
> It only needs a separate uffd_get_folio() definition but that's oneliner.
>
> Cc: Hugh Dickins <hughd@google.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>

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

> ---
> mm/shmem.c | 26 ++++++++++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 2b19965d27df..9a8b8dd4709b 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -3151,6 +3151,13 @@ static inline struct inode *shmem_get_inode(struct mnt_idmap *idmap,
> #endif /* CONFIG_TMPFS_QUOTA */
>
> #ifdef CONFIG_USERFAULTFD
> +
> +static int shmem_uffd_get_folio(struct inode *inode, pgoff_t pgoff,
> + struct folio **folio)
> +{
> + return shmem_get_folio(inode, pgoff, 0, folio, SGP_NOALLOC);
> +}
> +
> int shmem_mfill_atomic_pte(pmd_t *dst_pmd,
> struct vm_area_struct *dst_vma,
> unsigned long dst_addr,
> @@ -5194,6 +5201,19 @@ static int shmem_error_remove_folio(struct address_space *mapping,
> return 0;
> }
>
> +#ifdef CONFIG_USERFAULTFD
> +static const vm_uffd_ops shmem_uffd_ops = {
> + .uffd_features = __VM_UFFD_FLAGS,
> + .uffd_ioctls = BIT(_UFFDIO_COPY) |
> + BIT(_UFFDIO_ZEROPAGE) |
> + BIT(_UFFDIO_WRITEPROTECT) |
> + BIT(_UFFDIO_CONTINUE) |
> + BIT(_UFFDIO_POISON),
> + .uffd_get_folio = shmem_uffd_get_folio,
> + .uffd_copy = shmem_mfill_atomic_pte,
> +};
> +#endif
> +
> static const struct address_space_operations shmem_aops = {
> .dirty_folio = noop_dirty_folio,
> #ifdef CONFIG_TMPFS
> @@ -5296,6 +5316,9 @@ static const struct vm_operations_struct shmem_vm_ops = {
> .set_policy = shmem_set_policy,
> .get_policy = shmem_get_policy,
> #endif
> +#ifdef CONFIG_USERFAULTFD
> + .userfaultfd_ops = &shmem_uffd_ops,
> +#endif
> };
>
> static const struct vm_operations_struct shmem_anon_vm_ops = {
> @@ -5305,6 +5328,9 @@ static const struct vm_operations_struct shmem_anon_vm_ops = {
> .set_policy = shmem_set_policy,
> .get_policy = shmem_get_policy,
> #endif
> +#ifdef CONFIG_USERFAULTFD
> + .userfaultfd_ops = &shmem_uffd_ops,
> +#endif
> };
>
> int shmem_init_fs_context(struct fs_context *fc)
> --
> 2.49.0
>
>

--
Sincerely yours,
Mike.