On Thu, Mar 9, 2023 at 1:11 AM Mike Rapoport rppt@kernel.org wrote:
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.
Acked-by: Peter Xu peterx@redhat.com Signed-off-by: Axel Rasmussen axelrasmussen@google.com
Acked-by: Mike Rapoport (IBM) rppt@kernel.org
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.
Funny enough, neither flag is mentioned in Documentation/ today - I'll add a short passage about both.
Happy to update the man pages as well, I'll send that patch separately.
Thanks for reviewing!
__u64 mode; /*-- Sincerely yours, Mike.