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

Stefan Hajnoczi
2025-09-19T21:27:02Z

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On Thu, Sep 18, 2025 at 03:25:59PM -0700, Cong Wang wrote:
> 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

What level of isolation does this patch series provide? What stops
kernel A from accessing kernel B's memory pages, sending interrupts to
its CPUs, etc?

> - 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..

This reminds me of Jailhouse, a partitioning hypervisor for Linux.
Jailhouse uses virtualization and other techniques to isolate CPUs,
allowing real-time workloads to run alongside Linux:
https://github.com/siemens/jailhouse

It would be interesting to hear your thoughts about where you want to go
with this series and how it compares with a partitioning hypervisor like
Jailhouse.

Thanks,
Stefan

>
> 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
>
> --
> 2.34.1
>

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