Merge branch 'akpm' (patches from Andrew)

Merge more updates from Andrew Morton:
 "The remainder of the main mm/ queue.

  143 patches.

  Subsystems affected by this patch series (all mm): pagecache, hugetlb,
  userfaultfd, vmscan, compaction, migration, cma, ksm, vmstat, mmap,
  kconfig, util, memory-hotplug, zswap, zsmalloc, highmem, cleanups, and
  kfence"

* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (143 commits)
  kfence: use power-efficient work queue to run delayed work
  kfence: maximize allocation wait timeout duration
  kfence: await for allocation using wait_event
  kfence: zero guard page after out-of-bounds access
  mm/process_vm_access.c: remove duplicate include
  mm/mempool: minor coding style tweaks
  mm/highmem.c: fix coding style issue
  btrfs: use memzero_page() instead of open coded kmap pattern
  iov_iter: lift memzero_page() to highmem.h
  mm/zsmalloc: use BUG_ON instead of if condition followed by BUG.
  mm/zswap.c: switch from strlcpy to strscpy
  arm64/Kconfig: introduce ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
  x86/Kconfig: introduce ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
  mm,memory_hotplug: add kernel boot option to enable memmap_on_memory
  acpi,memhotplug: enable MHP_MEMMAP_ON_MEMORY when supported
  mm,memory_hotplug: allocate memmap from the added memory range
  mm,memory_hotplug: factor out adjusting present pages into adjust_present_page_count()
  mm,memory_hotplug: relax fully spanned sections check
  drivers/base/memory: introduce memory_block_{online,offline}
  mm/memory_hotplug: remove broken locking of zone PCP structures during hot remove
  ...

3 files changed, 92 insertions, 41 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 0d48fbd9107f..a1266f33d6e6 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2804,6 +2804,23 @@
 			seconds.  Use this parameter to check at some
 			other rate.  0 disables periodic checking.
 
+	memory_hotplug.memmap_on_memory
+			[KNL,X86,ARM] Boolean flag to enable this feature.
+			Format: {on | off (default)}
+			When enabled, runtime hotplugged memory will
+			allocate its internal metadata (struct pages)
+			from the hotadded memory which will allow to
+			hotadd a lot of memory without requiring
+			additional memory to do so.
+			This feature is disabled by default because it
+			has some implication on large (e.g. GB)
+			allocations in some configurations (e.g. small
+			memory blocks).
+			The state of the flag can be read in
+			/sys/module/memory_hotplug/parameters/memmap_on_memory.
+			Note that even when enabled, there are a few cases where
+			the feature is not effective.
+
 	memtest=	[KNL,X86,ARM,PPC] Enable memtest
 			Format: <integer>
 			default : 0 <disable>
diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
index 5307f90738aa..05d51d2d8beb 100644
--- a/Documentation/admin-guide/mm/memory-hotplug.rst
+++ b/Documentation/admin-guide/mm/memory-hotplug.rst
@@ -357,6 +357,15 @@ creates ZONE_MOVABLE as following.
    Unfortunately, there is no information to show which memory block belongs
    to ZONE_MOVABLE. This is TBD.
 
+.. note::
+   Techniques that rely on long-term pinnings of memory (especially, RDMA and
+   vfio) are fundamentally problematic with ZONE_MOVABLE and, therefore, memory
+   hot remove. Pinned pages cannot reside on ZONE_MOVABLE, to guarantee that
+   memory can still get hot removed - be aware that pinning can fail even if
+   there is plenty of free memory in ZONE_MOVABLE. In addition, using
+   ZONE_MOVABLE might make page pinning more expensive, because pages have to be
+   migrated off that zone first.
+
 .. _memory_hotplug_how_to_offline_memory:
 
 How to offline memory
diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst
index 65eefa66c0ba..3aa38e8b8361 100644
--- a/Documentation/admin-guide/mm/userfaultfd.rst
+++ b/Documentation/admin-guide/mm/userfaultfd.rst
@@ -63,36 +63,36 @@ the generic ioctl available.
 
 The ``uffdio_api.features`` bitmask returned by the ``UFFDIO_API`` ioctl
 defines what memory types are supported by the ``userfaultfd`` and what
-events, except page fault notifications, may be generated.
-
-If the kernel supports registering ``userfaultfd`` ranges on hugetlbfs
-virtual memory areas, ``UFFD_FEATURE_MISSING_HUGETLBFS`` will be set in
-``uffdio_api.features``. Similarly, ``UFFD_FEATURE_MISSING_SHMEM`` will be
-set if the kernel supports registering ``userfaultfd`` ranges on shared
-memory (covering all shmem APIs, i.e. tmpfs, ``IPCSHM``, ``/dev/zero``,
-``MAP_SHARED``, ``memfd_create``, etc).
-
-The userland application that wants to use ``userfaultfd`` with hugetlbfs
-or shared memory need to set the corresponding flag in
-``uffdio_api.features`` to enable those features.
-
-If the userland desires to receive notifications for events other than
-page faults, it has to verify that ``uffdio_api.features`` has appropriate
-``UFFD_FEATURE_EVENT_*`` bits set. These events are described in more
-detail below in `Non-cooperative userfaultfd`_ section.
-
-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
+when invoking the ``UFFDIO_API`` ioctl, to request that those features be
+enabled if supported.
+
+Once the ``userfaultfd`` API 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
 uffdio_register structure accordingly. The ``uffdio_register.mode``
 bitmask will specify to the kernel which kind of faults to track for
-the range (``UFFDIO_REGISTER_MODE_MISSING`` would track missing
-pages). The ``UFFDIO_REGISTER`` ioctl will return the
+the range. The ``UFFDIO_REGISTER`` ioctl will return the
 ``uffdio_register.ioctls`` bitmask of ioctls that are suitable to resolve
 userfaults on the range registered. Not all ioctls will necessarily be
-supported for all memory types depending on the underlying virtual
-memory backend (anonymous memory vs tmpfs vs real filebacked
-mappings).
+supported for all memory types (e.g. anonymous memory vs. shmem vs.
+hugetlbfs), or all types of intercepted faults.
 
 Userland can use the ``uffdio_register.ioctls`` to manage the virtual
 address space in the background (to add or potentially also remove
@@ -100,21 +100,46 @@ memory from the ``userfaultfd`` registered range). This means a userfault
 could be triggering just before userland maps in the background the
 user-faulted page.
 
-The primary ioctl to resolve userfaults is ``UFFDIO_COPY``. That
-atomically copies a page into the userfault registered range and wakes
-up the blocked userfaults
-(unless ``uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE`` is set).
-Other ioctl works similarly to ``UFFDIO_COPY``. They're atomic as in
-guaranteeing that nothing can see an half copied page since it'll
-keep userfaulting until the copy has finished.
+Resolving Userfaults
+--------------------
+
+There are three basic ways to resolve userfaults:
+
+- ``UFFDIO_COPY`` atomically copies some existing page contents from
+  userspace.
+
+- ``UFFDIO_ZEROPAGE`` atomically zeros the new page.
+
+- ``UFFDIO_CONTINUE`` maps an existing, previously-populated page.
+
+These operations are atomic in the sense that they guarantee nothing can
+see a half-populated page, since readers will keep userfaulting until the
+operation has finished.
+
+By default, these wake up userfaults blocked on the range in question.
+They support a ``UFFDIO_*_MODE_DONTWAKE`` ``mode`` flag, which indicates
+that waking will be done separately at some later time.
+
+Which ioctl to choose depends on the kind of page fault, and what we'd
+like to do to resolve it:
+
+- For ``UFFDIO_REGISTER_MODE_MISSING`` faults, the fault needs to be
+  resolved by either providing a new page (``UFFDIO_COPY``), or mapping
+  the zero page (``UFFDIO_ZEROPAGE``). By default, the kernel would map
+  the zero page for a missing fault. With userfaultfd, userspace can
+  decide what content to provide before the faulting thread continues.
+
+- For ``UFFDIO_REGISTER_MODE_MINOR`` faults, there is an existing page (in
+  the page cache). Userspace has the option of modifying the page's
+  contents before resolving the fault. Once the contents are correct
+  (modified or not), userspace asks the kernel to map the page and let the
+  faulting thread continue with ``UFFDIO_CONTINUE``.
 
 Notes:
 
-- If you requested ``UFFDIO_REGISTER_MODE_MISSING`` when registering then
-  you must provide some kind of page in your thread after reading from
-  the uffd.  You must provide either ``UFFDIO_COPY`` or ``UFFDIO_ZEROPAGE``.
-  The normal behavior of the OS automatically providing a zero page on
-  an anonymous mmaping is not in place.
+- You can tell which kind of fault occurred by examining
+  ``pagefault.flags`` within the ``uffd_msg``, checking for the
+  ``UFFD_PAGEFAULT_FLAG_*`` flags.
 
 - None of the page-delivering ioctls default to the range that you
   registered with.  You must fill in all fields for the appropriate
@@ -122,9 +147,9 @@ Notes:
 
 - You get the address of the access that triggered the missing page
   event out of a struct uffd_msg that you read in the thread from the
-  uffd.  You can supply as many pages as you want with ``UFFDIO_COPY`` or
-  ``UFFDIO_ZEROPAGE``.  Keep in mind that unless you used DONTWAKE then
-  the first of any of those IOCTLs wakes up the faulting thread.
+  uffd.  You can supply as many pages as you want with these IOCTLs.
+  Keep in mind that unless you used DONTWAKE then the first of any of
+  those IOCTLs wakes up the faulting thread.
 
 - Be sure to test for all errors including
   (``pollfd[0].revents & POLLERR``).  This can happen, e.g. when ranges