admin-guide/mm/userfaultfd.rst

10 Userfaults allow the implementation of on-demand paging from userland
38 Vmas are not suitable for page- (or hugepage) granular fault tracking
48 is a corner case that would currently return ``-EBUSY``).
68 - The ``UFFD_FEATURE_EVENT_*`` flags indicate that various other events
70   detail below in the `Non-cooperative userfaultfd`_ section.
72 - ``UFFD_FEATURE_MISSING_HUGETLBFS`` and ``UFFD_FEATURE_MISSING_SHMEM``
78 - ``UFFD_FEATURE_MINOR_HUGETLBFS`` indicates that the kernel supports
102 user-faulted page.
105 --------------------
109 - ``UFFDIO_COPY`` atomically copies some existing page contents from
112 - ``UFFDIO_ZEROPAGE`` atomically zeros the new page.
114 - ``UFFDIO_CONTINUE`` maps an existing, previously-populated page.
117 see a half-populated page, since readers will keep userfaulting until the
127 - For ``UFFDIO_REGISTER_MODE_MISSING`` faults, the fault needs to be
131   decide what content to provide before the faulting thread continues.
133 - For ``UFFDIO_REGISTER_MODE_MINOR`` faults, there is an existing page (in
141 - You can tell which kind of fault occurred by examining
145 - None of the page-delivering ioctls default to the range that you
149 - You get the address of the access that triggered the missing page
155 - Be sure to test for all errors including
160 ---------------------------
183 difference between writes into a WP area and into a !WP area.  The
224 the ``userfaultfd`` and receives the fault address (or ``-EAGAIN`` in case the
241 doesn't need to keep any per-page state bitmap relative to the live
242 migration around and a single per-page bitmap has to be maintained in
252 Non-cooperative userfaultfd
271 	non-cooperative process moves a virtual memory area to a
303 asynchronously and the non-cooperative process resumes execution as
307 return ``-ENOSPC`` when the monitored process exits at the time of
308 ``UFFDIO_COPY``, and ``-ENOENT``, when the non-cooperative process has changed
313 single threaded non-cooperative ``userfaultfd`` manager implementations. A