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

[Stefan Hajnoczi <stefanha@redhat.com>]

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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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