[RFC Patch 0/7] kernel: Introduce multikernel architecture support

Cong Wang
2025-09-18T22:26:20Z

This patch series introduces multikernel architecture support, enabling
multiple independent kernel instances to coexist and communicate on a
single physical machine. Each kernel instance can run on dedicated CPU
cores while sharing the underlying hardware resources.

The multikernel architecture provides several key benefits:
- Improved fault isolation between different workloads
- Enhanced security through kernel-level separation
- Better resource utilization than traditional VM (KVM, Xen etc.)
- Potential zero-down kernel update with KHO (Kernel Hand Over)

Architecture Overview:
The implementation leverages kexec infrastructure to load and manage
multiple kernel images, with each kernel instance assigned to specific
CPU cores. Inter-kernel communication is facilitated through a dedicated
IPI framework that allows kernels to coordinate and share information
when necessary.

Key Components:
1. Enhanced kexec subsystem with dynamic kimage tracking
2. Generic IPI communication framework for inter-kernel messaging
3. Architecture-specific CPU bootstrap mechanisms (only x86 so far)
4. Proc interface for monitoring loaded kernel instances

Patch Summary:

Patch 1/7: Introduces basic multikernel support via kexec, allowing
multiple kernel images to be loaded simultaneously.

Patch 2/7: Adds x86-specific SMP INIT trampoline for bootstrapping
CPUs with different kernel instances.

Patch 3/7: Introduces dedicated MULTIKERNEL_VECTOR for x86 inter-kernel
communication.

Patch 4/7: Implements generic multikernel IPI communication framework
for cross-kernel messaging and coordination.

Patch 5/7: Adds arch_cpu_physical_id() function to obtain physical CPU
identifiers for proper CPU management.

Patch 6/7: Replaces static kimage globals with dynamic linked list
infrastructure to support multiple kernel images.

Patch 7/7: Adds /proc/multikernel interface for monitoring and debugging
loaded kernel instances.

The implementation maintains full backward compatibility with existing
kexec functionality while adding the new multikernel capabilities.

IMPORTANT NOTES:

1) This is a Request for Comments (RFC) submission. While the core
architecture is functional, there are numerous implementation details
that need improvement. The primary goal is to gather feedback on the
high-level design and overall approach rather than focus on specific
coding details at this stage.

2) This patch series represents only the foundational framework for
multikernel support. It establishes the basic infrastructure and
communication mechanisms. We welcome the community to build upon
this foundation and develop their own solutions based on this
framework.

3) Testing has been limited to the author's development machine using
hard-coded boot parameters and specific hardware configurations.
Community testing across different hardware platforms, configurations,
and use cases would be greatly appreciated to identify potential
issues and improve robustness. Obviously, don't use this code beyond
testing.

This work enables new use cases such as running real-time kernels
alongside general-purpose kernels, isolating security-critical
applications, and providing dedicated kernel instances for specific
workloads etc..

Signed-off-by: Cong Wang <cwang@multikernel.io>

---

Cong Wang (7):
kexec: Introduce multikernel support via kexec
x86: Introduce SMP INIT trampoline for multikernel CPU bootstrap
x86: Introduce MULTIKERNEL_VECTOR for inter-kernel communication
kernel: Introduce generic multikernel IPI communication framework
x86: Introduce arch_cpu_physical_id() to obtain physical CPU ID
kexec: Implement dynamic kimage tracking
kexec: Add /proc/multikernel interface for kimage tracking

arch/powerpc/kexec/crash.c | 8 +-
arch/x86/include/asm/idtentry.h | 1 +
arch/x86/include/asm/irq_vectors.h | 1 +
arch/x86/include/asm/smp.h | 7 +
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/crash.c | 4 +-
arch/x86/kernel/head64.c | 5 +
arch/x86/kernel/idt.c | 1 +
arch/x86/kernel/setup.c | 3 +
arch/x86/kernel/smp.c | 15 ++
arch/x86/kernel/smpboot.c | 161 +++++++++++++
arch/x86/kernel/trampoline_64_bsp.S | 288 ++++++++++++++++++++++
arch/x86/kernel/vmlinux.lds.S | 6 +
include/linux/kexec.h | 22 +-
include/linux/multikernel.h | 81 +++++++
include/uapi/linux/kexec.h | 1 +
include/uapi/linux/reboot.h | 2 +-
init/main.c | 2 +
kernel/Makefile | 2 +-
kernel/kexec.c | 103 +++++++-
kernel/kexec_core.c | 359 ++++++++++++++++++++++++++++
kernel/kexec_file.c | 33 ++-
kernel/multikernel.c | 314 ++++++++++++++++++++++++
kernel/reboot.c | 10 +
24 files changed, 1411 insertions(+), 19 deletions(-)
create mode 100644 arch/x86/kernel/trampoline_64_bsp.S
create mode 100644 include/linux/multikernel.h
create mode 100644 kernel/multikernel.c

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2.34.1