On Thu, Feb 4, 2021 at 11:57 AM Randy Dunlap [off-list ref] wrote:

Hi Axel-

one typo found:

On 2/4/21 10:34 AM, Axel Rasmussen wrote:

quoted

Reword / reorganize things a little bit into "lists", so new features /
modes / ioctls can sort of just be appended.

Good plan.

quoted

Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
---
 Documentation/admin-guide/mm/userfaultfd.rst | 107 ++++++++++++-------
 1 file changed, 66 insertions(+), 41 deletions(-)

diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst
index 65eefa66c0ba..cfd3daf59d0e 100644
--- a/Documentation/admin-guide/mm/userfaultfd.rst
+++ b/Documentation/admin-guide/mm/userfaultfd.rst

[snip]

quoted

-
-Once the ``userfaultfd`` has been enabled the ``UFFDIO_REGISTER`` ioctl should
-be invoked (if present in the returned ``uffdio_api.ioctls`` bitmask) to
-register a memory range in the ``userfaultfd`` by setting the
+events, except page fault notifications, may be generated:
+
+- The ``UFFD_FEATURE_EVENT_*`` flags indicate that various other events
+  other than page faults are supported. These events are described in more
+  detail below in the `Non-cooperative userfaultfd`_ section.
+
+- ``UFFD_FEATURE_MISSING_HUGETLBFS`` and ``UFFD_FEATURE_MISSING_SHMEM``
+  indicate that the kernel supports ``UFFDIO_REGISTER_MODE_MISSING``
+  registrations for hugetlbfs and shared memory (covering all shmem APIs,
+  i.e. tmpfs, ``IPCSHM``, ``/dev/zero``, ``MAP_SHARED``, ``memfd_create``,
+  etc) virtual memory areas, respectively.
+
+- ``UFFD_FEATURE_MINOR_HUGETLBFS`` indicates that the kernel supports
+  ``UFFDIO_REGISTER_MODE_MINOR`` registration for hugetlbfs virtual memory
+  areas.
+
+The userland application should set the feature flags it intends to use

(ah, userspace has moved to userland temporarily. :)

For better or worse, other parts of the document I'm not touching also
use this wording. Maybe we should s/userland/userspace/g, but perhaps
better done as a separate commit to keep this diff focused?
Anecdotally, the use of "userland" doesn't seem to be completely
unprecedented (e.g. grep -r "userland" | wc -l yields 566 matches in
the kernel tree).

I don't have strong feelings, and I was amused by picturing some
Shire-esque countryside with a friendly sign that reads: ~userland
welcomes you~. :)

quoted

+when envoking the ``UFFDIO_API`` ioctl, to request that those features be

        invoking

Whoops! Will send a new version with this fix. Thanks!

quoted

+enabled if supported.

thanks.
--
~Randy