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| author | Axel Rasmussen <axelrasmussen@google.com> | 2023-03-14 15:12:50 -0700 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2023-04-05 19:42:48 -0700 |
| commit | 0289184476c845968ad6ac9083c96cc0f75ca505 (patch) | |
| tree | 56e15e1e7c25c18711b1e6835ae86836dcfd8313 /Documentation/admin-guide/mm/userfaultfd.rst | |
| parent | d9712937037e0ce887920f321429826e9dbfd960 (diff) | |
| download | lwn-0289184476c845968ad6ac9083c96cc0f75ca505.tar.gz lwn-0289184476c845968ad6ac9083c96cc0f75ca505.zip | |
mm: userfaultfd: add UFFDIO_CONTINUE_MODE_WP to install WP PTEs
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.
Update Documentation/ to describe how these flags are used (neither the
COPY nor the new CONTINUE versions of this mode flag were described there
before).
[1]: https://patchwork.kernel.org/project/linux-mm/cover/20230218002819.1486479-1-jthoughton@google.com/
Link: https://lkml.kernel.org/r/20230314221250.682452-5-axelrasmussen@google.com
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Acked-by: Peter Xu <peterx@redhat.com>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nadav Amit <namit@vmware.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'Documentation/admin-guide/mm/userfaultfd.rst')
| -rw-r--r-- | Documentation/admin-guide/mm/userfaultfd.rst | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst index bd2226299583..7c304e432205 100644 --- a/Documentation/admin-guide/mm/userfaultfd.rst +++ b/Documentation/admin-guide/mm/userfaultfd.rst @@ -236,6 +236,14 @@ newer kernels, one can also detect the feature UFFD_FEATURE_WP_UNPOPULATED and set the feature bit in advance to make sure none ptes will also be write protected even upon anonymous memory. +When using ``UFFDIO_REGISTER_MODE_WP`` in combination with either +``UFFDIO_REGISTER_MODE_MISSING`` or ``UFFDIO_REGISTER_MODE_MINOR``, when +resolving missing / minor faults with ``UFFDIO_COPY`` or ``UFFDIO_CONTINUE`` +respectively, it may be desirable for the new page / mapping to be +write-protected (so future writes will also result in a WP fault). These ioctls +support a mode flag (``UFFDIO_COPY_MODE_WP`` or ``UFFDIO_CONTINUE_MODE_WP`` +respectively) to configure the mapping this way. + QEMU/KVM ======== |