When CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled, struct page
initialization is deferred to parallel kthreads that run later
in the boot process.
During KHO restoration, kho_preserved_memory_reserve() writes metadata
for each preserved memory region. However, if the struct page has not
been initialized, this write targets uninitialized memory, potentially
leading to errors like:
BUG: unable to handle page fault for address: ...
Fix this by introducing kho_get_preserved_page(), which ensures
all struct pages in a preserved region are initialized by calling
init_deferred_page() which is a no-op when the struct page is already
initialized.
Signed-off-by: Evangelos Petrongonas <[email protected]>
Co-developed-by: Michal Clapinski <[email protected]>
Signed-off-by: Michal Clapinski <[email protected]>
Reviewed-by: Pratyush Yadav (Google) <[email protected]>
Reviewed-by: Pasha Tatashin <[email protected]>
Reviewed-by: Mike Rapoport (Microsoft) <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Mike Rapoport (Microsoft) <[email protected]>
Decouple memfd preservation support from the core Live Update Orchestrator
configuration.
Previously, enabling CONFIG_LIVEUPDATE forced a dependency on CONFIG_SHMEM
and unconditionally compiled memfd_luo.o. However, Live Update may be
used for purposes that do not require memfd-backed memory preservation.
Introduce CONFIG_LIVEUPDATE_MEMFD to gate memfd_luo.o. This moves the
SHMEM and MEMFD_CREATE dependencies to the specific feature that needs
them, allowing the base LIVEUPDATE option to be selected independently of
shared memory support.
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Pasha Tatashin <[email protected]>
Reviewed-by: Pratyush Yadav <[email protected]>
Reviewed-by: Mike Rapoport (Microsoft) <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
The new memfd code fails to link without SHMEM:
aarch64-linux-ld: mm/memfd_luo.o: in function `memfd_luo_retrieve_folios':
memfd_luo.c:(.text.memfd_luo_retrieve_folios+0xdc): undefined reference to `shmem_add_to_page_cache'
memfd_luo.c:(.text.memfd_luo_retrieve_folios+0x11c): undefined reference to `shmem_inode_acct_blocks'
memfd_luo.c:(.text.memfd_luo_retrieve_folios+0x134): undefined reference to `shmem_recalc_inode'
Add a Kconfig dependency to disallow that configuration.
Link: https://lkml.kernel.org/r/[email protected]
Fixes: b3749f174d ("mm: memfd_luo: allow preserving memfd")
Signed-off-by: Arnd Bergmann <[email protected]>
Reviewed-by: Pratyush Yadav <[email protected]>
Acked-by: Mike Rapoport (Microsoft) <[email protected]>
Reviewed-by: Pasha Tatashin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Patch series "Live Update Orchestrator", v8.
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.
Introduce LUO, a mechanism intended to facilitate kernel updates while
keeping designated devices operational across the transition (e.g., via
kexec). The primary use case is updating hypervisors with minimal
disruption to running virtual machines. For userspace side of hypervisor
update we have copyless migration. LUO is for updating the kernel.
This initial patch lays the groundwork for the LUO subsystem.
Further functionality, including the implementation of state transition
logic, integration with KHO, and hooks for subsystems and file
descriptors, will be added in subsequent patches.
Create a character device at /dev/liveupdate.
A new uAPI header, <uapi/linux/liveupdate.h>, will define the necessary
structures. The magic number for IOCTL is registered in
Documentation/userspace-api/ioctl/ioctl-number.rst.
Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Link: https://lore.kernel.org/all/[email protected]/ [1]
Link: https://lore.kernel.org/linux-iommu/[email protected] [2]
Link: https://lore.kernel.org/linux-pci/[email protected] [3]
Link: https://github.com/googleprodkernel/linux-liveupdate/tree/luo/v8 [4]
Link: https://tinyurl.com/luoddesign [5]
Link: https://lore.kernel.org/all/[email protected] [6]
Link: https://lore.kernel.org/all/[email protected] [7]
Link: https://github.com/soleen/linux/blob/luo/v8b03/diff.v7.v8 [8]
Signed-off-by: Pasha Tatashin <[email protected]>
Reviewed-by: Pratyush Yadav <[email protected]>
Reviewed-by: Mike Rapoport (Microsoft) <[email protected]>
Tested-by: David Matlack <[email protected]>
Cc: Aleksander Lobakin <[email protected]>
Cc: Alexander Graf <[email protected]>
Cc: Alice Ryhl <[email protected]>
Cc: Andriy Shevchenko <[email protected]>
Cc: anish kumar <[email protected]>
Cc: Anna Schumaker <[email protected]>
Cc: Bartosz Golaszewski <[email protected]>
Cc: Bjorn Helgaas <[email protected]>
Cc: Borislav Betkov <[email protected]>
Cc: Chanwoo Choi <[email protected]>
Cc: Chen Ridong <[email protected]>
Cc: Chris Li <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Daniel Wagner <[email protected]>
Cc: Danilo Krummrich <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: David Jeffery <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Guixin Liu <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Ilpo Järvinen <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Ira Weiny <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Joanthan Cameron <[email protected]>
Cc: Joel Granados <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Lennart Poettering <[email protected]>
Cc: Leon Romanovsky <[email protected]>
Cc: Leon Romanovsky <[email protected]>
Cc: Lukas Wunner <[email protected]>
Cc: Marc Rutland <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Matthew Maurer <[email protected]>
Cc: Miguel Ojeda <[email protected]>
Cc: Myugnjoo Ham <[email protected]>
Cc: Parav Pandit <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Saeed Mahameed <[email protected]>
Cc: Samiullah Khawaja <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Stuart Hayes <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Thomas Gleinxer <[email protected]>
Cc: Thomas Weißschuh <[email protected]>
Cc: Vincent Guittot <[email protected]>
Cc: William Tu <[email protected]>
Cc: Yoann Congal <[email protected]>
Cc: Zijun Hu <[email protected]>
Cc: Pratyush Yadav <[email protected]>
Cc: Zhu Yanjun <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Currently, Kexec Handover must be explicitly enabled via the kernel
command line parameter `kho=on`.
For workloads that rely on KHO as a foundational requirement (such as the
upcoming Live Update Orchestrator), requiring an explicit boot parameter
adds redundant configuration steps.
Introduce CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT. When selected, KHO
defaults to enabled. This is equivalent to passing kho=on at boot. The
behavior can still be disabled at runtime by passing kho=off.
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Pasha Tatashin <[email protected]>
Reviewed-by: Mike Rapoport (Microsoft) <[email protected]>
Reviewed-by: Pratyush Yadav <[email protected]>
Cc: Alexander Graf <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Coiby Xu <[email protected]>
Cc: Dave Vasilevsky <[email protected]>
Cc: Eric Biggers <[email protected]>
Cc: Kees Cook <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Evangelos Petrongonas