Andrew: This series has been fully reviewed, and contains minimal
changes compared to what is currently being tested in linux-next
diff between v7 and v8 can be viewe, here: [8]
Four patches have been dropped compared to v7: and are going to be sent
separately.
This series introduces the Live Update Orchestrator, a kernel subsystem
designed to facilitate live kernel updates using a kexec-based reboot.
This capability is critical for cloud environments, allowing hypervisors
to be updated with minimal downtime for running virtual machines. LUO
achieves this by preserving the state of selected resources, such as
memory, devices and their dependencies, across the kernel transition.
As a key feature, this series includes support for preserving memfd file
descriptors, which allows critical in-memory data, such as guest RAM or
any other large memory region, to be maintained in RAM across the kexec
reboot.
The other series that use LUO, are VFIO [1], IOMMU [2], and PCI [3]
preservations.
Github repo of this series [4].
The core of LUO is a framework for managing the lifecycle of preserved
resources through a userspace-driven interface. Key features include:
- Session Management
Userspace agent (i.e. luod [5]) creates named sessions, each
represented by a file descriptor (via centralized agent that controls
/dev/liveupdate). The lifecycle of all preserved resources within a
session is tied to this FD, ensuring automatic kernel cleanup if the
controlling userspace agent crashes or exits unexpectedly.
- File Preservation
A handler-based framework allows specific file types (demonstrated
here with memfd) to be preserved. Handlers manage the serialization,
restoration, and lifecycle of their specific file types.
- File-Lifecycle-Bound State
A new mechanism for managing shared global state whose lifecycle is
tied to the preservation of one or more files. This is crucial for
subsystems like IOMMU or HugeTLB, where multiple file descriptors may
depend on a single, shared underlying resource that must be preserved
only once.
- KHO Integration
LUO drives the Kexec Handover framework programmatically to pass its
serialized metadata to the next kernel. The LUO state is finalized and
added to the kexec image just before the reboot is triggered. In the
future this step will also be removed once stateless KHO is
merged [6].
- Userspace Interface
Control is provided via ioctl commands on /dev/liveupdate for creating
and retrieving sessions, as well as on session file descriptors for
managing individual files.
- Testing
The series includes a set of selftests, including userspace API
validation, kexec-based lifecycle tests for various session and file
scenarios, and a new in-kernel test module to validate the FLB logic.
Changelog since v7 [7]
- Collected Reviewed-by tags from Mike Rapoport, Pratyush Yadav.
- Addressed mostly nits. The diff can be viewed here [8].
[1] https://lore.kernel.org/all/20251018000713.677779-1-vipinsh@google.com/
[2] https://lore.kernel.org/linux-iommu/20250928190624.3735830-1-skhawaja@google.com
[3] https://lore.kernel.org/linux-pci/20250916-luo-pci-v2-0-c494053c3c08@kernel.org
[4] https://github.com/googleprodkernel/linux-liveupdate/tree/luo/v8
[5] https://tinyurl.com/luoddesign
[6] https://lore.kernel.org/all/20251020100306.2709352-1-jasonmiu@google.com
[7] https://lore.kernel.org/all/20251115233409.768044-1-pasha.tatashin@soleen.com
[8] https://github.com/soleen/linux/blob/luo/v8b03/diff.v7.v8
Pasha Tatashin (12):
liveupdate: luo_core: Live Update Orchestrato,
liveupdate: luo_core: integrate with KHO
kexec: call liveupdate_reboot() before kexec
liveupdate: luo_session: add sessions support
liveupdate: luo_core: add user interface
liveupdate: luo_file: implement file systems callbacks
liveupdate: luo_session: Add ioctls for file preservation
docs: add luo documentation
MAINTAINERS: add liveupdate entry
selftests/liveupdate: Add userspace API selftests
selftests/liveupdate: Add simple kexec-based selftest for LUO
selftests/liveupdate: Add kexec test for multiple and empty sessions
Pratyush Yadav (6):
mm: shmem: use SHMEM_F_* flags instead of VM_* flags
mm: shmem: allow freezing inode mapping
mm: shmem: export some functions to internal.h
liveupdate: luo_file: add private argument to store runtime state
mm: memfd_luo: allow preserving memfd
docs: add documentation for memfd preservation via LUO
Documentation/core-api/index.rst | 1 +
Documentation/core-api/liveupdate.rst | 61 ++
Documentation/mm/index.rst | 1 +
Documentation/mm/memfd_preservation.rst | 23 +
Documentation/userspace-api/index.rst | 1 +
.../userspace-api/ioctl/ioctl-number.rst | 2 +
Documentation/userspace-api/liveupdate.rst | 20 +
MAINTAINERS | 16 +
include/linux/kho/abi/luo.h | 166 ++++
include/linux/kho/abi/memfd.h | 77 ++
include/linux/liveupdate.h | 138 +++
include/linux/shmem_fs.h | 23 +
include/uapi/linux/liveupdate.h | 216 +++++
kernel/kexec_core.c | 5 +
kernel/liveupdate/Kconfig | 21 +
kernel/liveupdate/Makefile | 7 +
kernel/liveupdate/luo_core.c | 450 +++++++++
kernel/liveupdate/luo_file.c | 889 ++++++++++++++++++
kernel/liveupdate/luo_internal.h | 110 +++
kernel/liveupdate/luo_session.c | 646 +++++++++++++
mm/Makefile | 1 +
mm/internal.h | 6 +
mm/memfd_luo.c | 516 ++++++++++
mm/shmem.c | 49 +-
tools/testing/selftests/Makefile | 1 +
tools/testing/selftests/liveupdate/.gitignore | 9 +
tools/testing/selftests/liveupdate/Makefile | 34 +
tools/testing/selftests/liveupdate/config | 11 +
.../testing/selftests/liveupdate/do_kexec.sh | 16 +
.../testing/selftests/liveupdate/liveupdate.c | 348 +++++++
.../selftests/liveupdate/luo_kexec_simple.c | 89 ++
.../selftests/liveupdate/luo_multi_session.c | 162 ++++
.../selftests/liveupdate/luo_test_utils.c | 266 ++++++
.../selftests/liveupdate/luo_test_utils.h | 44 +
34 files changed, 4407 insertions(+), 18 deletions(-)
create mode 100644 Documentation/core-api/liveupdate.rst
create mode 100644 Documentation/mm/memfd_preservation.rst
create mode 100644 Documentation/userspace-api/liveupdate.rst
create mode 100644 include/linux/kho/abi/luo.h
create mode 100644 include/linux/kho/abi/memfd.h
create mode 100644 include/linux/liveupdate.h
create mode 100644 include/uapi/linux/liveupdate.h
create mode 100644 kernel/liveupdate/luo_core.c
create mode 100644 kernel/liveupdate/luo_file.c
create mode 100644 kernel/liveupdate/luo_internal.h
create mode 100644 kernel/liveupdate/luo_session.c
create mode 100644 mm/memfd_luo.c
create mode 100644 tools/testing/selftests/liveupdate/.gitignore
create mode 100644 tools/testing/selftests/liveupdate/Makefile
create mode 100644 tools/testing/selftests/liveupdate/config
create mode 100755 tools/testing/selftests/liveupdate/do_kexec.sh
create mode 100644 tools/testing/selftests/liveupdate/liveupdate.c
create mode 100644 tools/testing/selftests/liveupdate/luo_kexec_simple.c
create mode 100644 tools/testing/selftests/liveupdate/luo_multi_session.c
create mode 100644 tools/testing/selftests/liveupdate/luo_test_utils.c
create mode 100644 tools/testing/selftests/liveupdate/luo_test_utils.h
base-commit: 2cb7e27ffe3e3e1d8a837026462ebca22cba3b4f
--
2.52.0.460.gd25c4c69ec-goog