liveupdate: kvm: guest_memfd preservation

Hello,
This is Non-RFC patch series for guest_memfd preservation. After
having multiple discussion across hypervisor liveupdate meeting,
guest_memfd bi-weekly meeting, the design for the basic support of
guest_memfd preservation is final. This series is going to include
guest_memfd which are fully shared and does not support private mem
and backed by PAGE_SIZE pages.

Steps to test:
1. Compile Kernel with CONFIG_LIVEUPDATE_GUEST_MEMFD=y
2. boot kernel with command line: kho=on liveupdate=on
3. run the following kselftest
	$ .selftests/kvm/guest_memfd_preservation_test --stage 1
	$ <kexec> --reuse-cmdline
	$ .selftests/kvm/guest_memfd_preservation_test --stage 2

NOTE: Assert the following:
	$ ls /dev/liveupdate
	$ ls /dev/kvm
	$ dmesg | grep liveupdate # (should have kvm_vm_luo &&
		# guest_memfd_luo handler registered)

The changes are rebased on:
	kvm/next + liveupdate/next (merge) + [3] + [4] + [5]
	Where,
	[3]: luo: conversion of serialized_data to KHOSER_PTR
	[4]: luo: APIs to retrieve file internally from session
	[5]: selftests: liveupdate sefltests library
Here is the github repo:
	https://github.com/tar-unix/linux/tree/gmem-pre

V3 <- RFC V2 [2]
1. Finalize the design
2. resolve sashiko reported bugs
3. Use of KHOSER_PTR instead of raw serialized_data as per [3]

RFC V2 [2] <- RFC V1 [1]
1. Removed mem_attr_array as it is not needed for fully-shared
2. Removed pre-faulted condition
3. Added vm_type preservation for ARM64.
4. Removed liveupdate_get_file_incoming api patch as it is sent
   separately [4] by Samiullah.

[1] https://lore.kernel.org/all/cover.1779080766.git.tarunsah...
[2] https://lore.kernel.org/all/c054ba0fb2639932bbe354420d3f4...
[3] https://lore.kernel.org/all/20260622111215.4157974-1-taru...
[4] https://lore.kernel.org/all/20260613012521.835490-1-skhaw...
[5] https://lore.kernel.org/all/20260612214512.464146-1-vipin...

Tarun Sahu (9):
  liveupdate: Add LIVEUPDATE_GUEST_MEMFD config option
  kvm: Prepare core VM structs and helpers for LUO support
  kvm: kvm_luo: Allow kvm preservation with LUO
  kvm: guest_memfd: Move internal definitions and helper to new header
  kvm: guest_memfd: Add support for freezing and unfreezing mappings
  kvm: guest_memfd_luo: add support for guest_memfd preservation
  docs: add documentation for guest_memfd preservation via LUO
  selftests: kvm: Split ____vm_create() to expose init helpers
  selftests: kvm: Add guest_memfd_preservation_test

 Documentation/core-api/liveupdate.rst         |   1 +
 Documentation/liveupdate/vmm.rst              | 107 ++++
 MAINTAINERS                                   |  14 +
 include/linux/kho/abi/kvm.h                   | 106 ++++
 include/linux/kvm_host.h                      |  14 +
 kernel/liveupdate/Kconfig                     |  15 +
 tools/testing/selftests/kvm/Makefile.kvm      |   6 +-
 .../kvm/guest_memfd_preservation_test.c       | 236 +++++++++
 .../testing/selftests/kvm/include/kvm_util.h  |   2 +
 tools/testing/selftests/kvm/lib/kvm_util.c    |  26 +-
 virt/kvm/Makefile.kvm                         |   1 +
 virt/kvm/guest_memfd.c                        | 185 +++++--
 virt/kvm/guest_memfd.h                        |  44 ++
 virt/kvm/guest_memfd_luo.c                    | 497 ++++++++++++++++++
 virt/kvm/kvm_luo.c                            | 195 +++++++
 virt/kvm/kvm_main.c                           |  94 +++-
 virt/kvm/kvm_mm.h                             |  15 +
 17 files changed, 1477 insertions(+), 81 deletions(-)
 create mode 100644 Documentation/liveupdate/vmm.rst
 create mode 100644 include/linux/kho/abi/kvm.h
 create mode 100644 tools/testing/selftests/kvm/guest_memfd_preservation_test.c
 create mode 100644 virt/kvm/guest_memfd.h
 create mode 100644 virt/kvm/guest_memfd_luo.c
 create mode 100644 virt/kvm/kvm_luo.c

-- 
2.55.0.rc0.786.g65d90a0328-goog