[PATCH v3 00/15] Ram blocks with resizeable anonymous allocations under POSIX

[David Hildenbrand]

This series is now based on [1]:
    "[PATCH v3 00/13] migrate/ram: Fix resizing RAM blocks while migrating"

We already allow resizable ram blocks for anonymous memory, however, they
are not actually resized. All memory is mmaped() R/W, including the memory
exceeding the used_length, up to the max_length.

When resizing, effectively only the boundary is moved. Implement actually
resizable anonymous allocations and make use of them in resizable ram
blocks when possible. Memory exceeding the used_length will be
inaccessible. Especially ram block notifiers require care.

Having actually resizable anonymous allocations (via mmap-hackery) allows
to reserve a big region in virtual address space and grow the
accessible/usable part on demand. Even if "/proc/sys/vm/overcommit_memory"
is set to "never" under Linux, huge reservations will succeed. If there is
not enough memory when resizing (to populate parts of the reserved region),
trying to resize will fail. Only the actually used size is reserved in the
OS.

Especially, memory notifiers already handle resizing by first removing
the old region, and then re-adding the resized region. prealloc is
currently not possible with resizable ram blocks. mlock() should continue
to work as is. Resizing is currently rare and must only happen on the
start of an incoming migration, or during resets. No code path (except
HAX and SEV ram block notifiers) should access memory outside of the usable
range - and if we ever find one, that one has to be fixed (I did not
identify any).

E.g., virtio-mem [2] wants to reserve big resizable memory regions and
grow the usable part on demand. I think this change is worth sending out
individually. I did excessive tests of this with virtio-mem (which makes
it very easy to trigger resizes), including precopy and postcopy migration.

Accompanied by a bunch of minor fixes and cleanups.

v2 -> v3:
- Rebased on current master/[1].
- "util: vfio-helpers: Factor out and fix processing of existing ram
   blocks"
-- moved to [1]
- "util: vfio-helpers: Remove Error parameter from qemu_vfio_undo_mapping()"
-- Better parch description
- "util/mmap-alloc: Factor out calculation of pagesize to mmap_pagesize()"
-- is now "util/mmap-alloc: Factor out calculation of the pagesize for the
   guard page"
-- Decided to keep special handling for the guard page for now
-- Dropped rb's
- "util/mmap-alloc: Prepare for resizeable mmaps"
-- No asserts sizes against the real page size
- "numa: Teach ram block notifiers about resizable ram blocks"
-- Split. One part is in [1], the other is now in "numa: Introduce
   ram_block_notifiers_support_resize()"
- "exec: Ram blocks with resizeable anonymous allocations under POSIX"
-- Call qemu_ram_apply_settings() only populated parts. Call it on
   freshly populated parts when growing.
- Minor changes

v1 -> v2:
- Add "util: vfio-helpers: Fix qemu_vfio_close()"
- Add "util: vfio-helpers: Remove Error parameter from
       qemu_vfio_undo_mapping()"
- Add "util: vfio-helpers: Factor out removal from
       qemu_vfio_undo_mapping()"
- "util/mmap-alloc: ..."
 -- Minor changes due to review feedback (e.g., assert alignment, return
    bool when resizing)
- "util: vfio-helpers: Implement ram_block_resized()"
 -- Reserve max_size in the IOVA address space.
 -- On resize, undo old mapping and do new mapping. We can later implement
    a new ioctl to resize the mapping directly.
- "numa: Teach ram block notifiers about resizable ram blocks"
 -- Pass size/max_size to ram block notifiers, which makes things easier an
    cleaner
- "exec: Ram blocks with resizable anonymous allocations under POSIX"
 -- Adapt to new ram block notifiers
 -- Shrink after notifying. Always trigger ram block notifiers on resizes
 -- Add a safety net that all ram block notifiers registered at runtime
    support resizes.

[1] https://lkml.kernel.org/r/address@hidden
[2] https://lore.kernel.org/kvm/address@hidden/

David Hildenbrand (15):
  util: vfio-helpers: Fix qemu_vfio_close()
  util: vfio-helpers: Remove Error parameter from
    qemu_vfio_undo_mapping()
  util: vfio-helpers: Factor out removal from qemu_vfio_undo_mapping()
  exec: Factor out setting ram settings (madvise ...) into
    qemu_ram_apply_settings()
  exec: Reuse qemu_ram_apply_settings() in qemu_ram_remap()
  exec: Drop "shared" parameter from ram_block_add()
  util/mmap-alloc: Factor out calculation of the pagesize for the guard
    page
  util/mmap-alloc: Factor out reserving of a memory region to
    mmap_reserve()
  util/mmap-alloc: Factor out populating of memory to mmap_populate()
  util/mmap-alloc: Prepare for resizeable mmaps
  util/mmap-alloc: Implement resizeable mmaps
  util: vfio-helpers: Implement ram_block_resized()
  util: oslib: Resizeable anonymous allocations under POSIX
  numa: Introduce ram_block_notifiers_support_resize()
  exec: Ram blocks with resizeable anonymous allocations under POSIX

 exec.c                    |  99 +++++++++++++++++-----
 hw/core/numa.c            |  19 +++++
 include/exec/cpu-common.h |   2 +
 include/exec/memory.h     |   8 ++
 include/exec/ramlist.h    |   1 +
 include/qemu/mmap-alloc.h |  21 +++--
 include/qemu/osdep.h      |   6 +-
 util/mmap-alloc.c         | 167 ++++++++++++++++++++++++--------------
 util/oslib-posix.c        |  37 ++++++++-
 util/oslib-win32.c        |  14 ++++
 util/trace-events         |   9 +-
 util/vfio-helpers.c       | 120 ++++++++++++++++++++-------
 12 files changed, 380 insertions(+), 123 deletions(-)

-- 
2.24.1