On Wed, Mar 08, 2023 at 02:19:32PM -0800, Axel Rasmussen wrote:
> UFFDIO_COPY already has UFFDIO_COPY_MODE_WP, so when installing a new
> PTE to resolve a missing fault, one can install a write-protected one.
> This is useful when using UFFDIO_REGISTER_MODE_{MISSING,WP} in
> combination.
>
> This was motivated by testing HugeTLB HGM [1], and in particular its
> interaction with userfaultfd features. Existing userfaultfd code
> supports using WP and MINOR modes together (i.e. you can register an
> area with both enabled), but without this CONTINUE flag the combination
> is in practice unusable.
>
> So, add an analogous UFFDIO_CONTINUE_MODE_WP, which does the same thing
> as UFFDIO_COPY_MODE_WP, but for *minor* faults.
>
> Update the selftest to do some very basic exercising of the new flag.
>
> [1]: https://patchwork.kernel.org/project/linux-mm/cover/20230218002819.1486479-1-jthoughton@xxxxxxxxxx/
>
> Acked-by: Peter Xu <peterx@xxxxxxxxxx>
> Signed-off-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Acked-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
> ---
> fs/userfaultfd.c | 8 ++++++--
> include/linux/userfaultfd_k.h | 3 ++-
> include/uapi/linux/userfaultfd.h | 7 +++++++
> mm/userfaultfd.c | 5 +++--
> tools/testing/selftests/mm/userfaultfd.c | 4 ++++
> 5 files changed, 22 insertions(+), 5 deletions(-)
>
> diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
> index 005e5e306266..14059a0861bf 100644
> --- a/include/uapi/linux/userfaultfd.h
> +++ b/include/uapi/linux/userfaultfd.h
> @@ -297,6 +297,13 @@ struct uffdio_writeprotect {
> struct uffdio_continue {
> struct uffdio_range range;
> #define UFFDIO_CONTINUE_MODE_DONTWAKE ((__u64)1<<0)
> + /*
> + * UFFDIO_CONTINUE_MODE_WP will map the page write protected on
> + * the fly. UFFDIO_CONTINUE_MODE_WP is available only if the
> + * write protected ioctl is implemented for the range
> + * according to the uffdio_register.ioctls.
> + */
> +#define UFFDIO_CONTINUE_MODE_WP ((__u64)1<<1)
Please add the description of the new flag to Documentation/ and to the
userfaultfd man pages.
> __u64 mode;
>
> /*
--
Sincerely yours,
Mike.
