Re: [PATCH v4 1/4] mm: Introduce vm_uffd_ops API

[David Hildenbrand]

On 15.10.25 01:14, Peter Xu wrote:
> Currently, most of the userfaultfd features are implemented directly in the
> core mm.  It will invoke VMA specific functions whenever necessary.  So far
> it is fine because it almost only interacts with shmem and hugetlbfs.
>
> Introduce a generic userfaultfd API extension for vm_operations_struct,
> so that any code that implements vm_operations_struct (including kernel
> modules that can be compiled separately from the kernel core) can support
> userfaults without modifying the core files.
>
> With this API applied, if a module wants to support userfaultfd, the
> module should only need to properly define vm_uffd_ops and hook it to
> vm_operations_struct, instead of changing anything in core mm.
>
> This API will not work for anonymous memory. Handling of userfault
> operations for anonymous memory remains unchanged in core mm.
>
> Due to a security concern while reviewing older versions of this series
> [1], uffd_copy() will be temprorarily removed.  IOW, MISSING-capable memory
> types can only be hard-coded and implemented in mm/.  It would also affect
> UFFDIO_COPY and UFFDIO_ZEROPAGE.  Other functions should still be able to
> be provided from vm_uffd_ops.
>
> Introduces the API only so that existing userfaultfd users can be moved
> over without breaking them.
>
> [1] https://lore.kernel.org/all/20250627154655.2085903-1-peterx@xxxxxxxxxx/
>
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> ---

Acked-by: David Hildenbrand <david@xxxxxxxxxx>

--
Cheers

David / dhildenb