admin-guide/mm/userfaultfd.rst

20 Userfaults are delivered and resolved through the ``userfaultfd`` syscall.
22 The ``userfaultfd`` (aside from registering and unregistering virtual
29    registered in the ``userfaultfd`` that allows userland to efficiently
36 ``userfaultfd`` runtime load never takes the mmap_lock for writing).
42 The ``userfaultfd`` once opened by invoking the syscall, can also be
46 (well of course unless they later try to use the ``userfaultfd``
53 When first opened the ``userfaultfd`` must be enabled invoking the
65 defines what memory types are supported by the ``userfaultfd`` and what
70   detail below in the `Non-cooperative userfaultfd`_ section.
87 Once the ``userfaultfd`` API has been enabled the ``UFFDIO_REGISTER``
89 bitmask) to register a memory range in the ``userfaultfd`` by setting the
100 memory from the ``userfaultfd`` registered range). This means a userfault
130   the zero page for a missing fault. With userfaultfd, userspace can
192 QEMU/KVM is using the ``userfaultfd`` syscall to implement postcopy live
196 ``userfaultfd`` abstraction is generic enough that not a single line of
218 ioctls on the ``userfaultfd`` in order to map the received pages into the
222 poll() to the ``userfaultfd`` in parallel. When a ``POLLIN`` event is
224 the ``userfaultfd`` and receives the fault address (or ``-EAGAIN`` in case the
252 Non-cooperative userfaultfd
255 When the ``userfaultfd`` is monitored by an external manager, the manager
263 	enable ``userfaultfd`` hooks for fork(). When this feature is
264 	enabled, the ``userfaultfd`` context of the parent process is
267 	``userfaultfd`` context in the ``uffd_msg.fork``.
289 ``userfaultfd`` manager. In the former case, the virtual memory is
291 ``userfaultfd``, and if a page fault occurs in that area it will be
296 ``userfaultfd`` context for such area disappears too and the manager will
304 soon as manager executes read(). The ``userfaultfd`` manager should
313 single threaded non-cooperative ``userfaultfd`` manager implementations. A
315 ``userfaultfd`` feature to facilitate multithreading enhancements of the