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

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Message-ID: <20250924190316.GA8709@fedora>
Date: Wed, 24 Sep 2025 15:03:16 -0400
From: Stefan Hajnoczi <stefanha@...hat.com>
To: Cong Wang <xiyou.wangcong@...il.com>
Cc: David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org,
	pasha.tatashin@...een.com, Cong Wang <cwang@...tikernel.io>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Baoquan He <bhe@...hat.com>, Alexander Graf <graf@...zon.com>,
	Mike Rapoport <rppt@...nel.org>,
	Changyuan Lyu <changyuanl@...gle.com>, kexec@...ts.infradead.org,
	linux-mm@...ck.org, multikernel@...ts.linux.dev
Subject: Re: [RFC Patch 0/7] kernel: Introduce multikernel architecture
 support

On Wed, Sep 24, 2025 at 11:28:04AM -0700, Cong Wang wrote:
> On Wed, Sep 24, 2025 at 5:51 AM Stefan Hajnoczi <stefanha@...hat.com> wrote:
> >
> > On Wed, Sep 24, 2025 at 01:38:31PM +0200, David Hildenbrand wrote:
> > > > >
> > > > > Two more points:
> > > > >
> > > > > 1) Security lockdown. Security lockdown transforms multikernel from
> > > > > "0-day means total compromise" to "0-day means single workload
> > > > > compromise with rapid recovery." This is still a significant improvement
> > > > > over containers where a single kernel 0-day compromises everything
> > > > > simultaneously.
> > > >
> > > > I don't follow. My understanding is that multikernel currently does not
> > > > prevent spawned kernels from affecting each other, so a kernel 0-day in
> > > > multikernel still compromises everything?
> > >
> > > I would assume that if there is no enforced isolation by the hardware (e.g.,
> > > virtualization, including partitioning hypervisors like jailhouse, pkvm etc)
> > > nothing would stop a kernel A to access memory assigned to kernel B.
> > >
> > > And of course, memory is just one of the resources that would not be
> > > properly isolated.
> > >
> > > Not sure if encrypting memory per kernel would really allow to not let other
> > > kernels still damage such kernels.
> > >
> > > Also, what stops a kernel to just reboot the whole machine? Happy to learn
> > > how that will be handled such that there is proper isolation.
> >
> > The reason I've been asking about the fault isolation and security
> > statements in the cover letter is because it's unclear:
> > 1. What is implemented today in multikernel.
> > 2. What is on the roadmap for multikernel.
> > 3. What is out of scope for multikernel.
> >
> > Cong: Can you clarify this? If the answer is that fault isolation and
> > security are out of scope, then this discussion can be skipped.
> 
> It is my pleasure. The email is too narrow, therefore I wrote a
> complete document for you:
> https://docs.google.com/document/d/1yneO6O6C_z0Lh3A2QyT8XsH7ZrQ7-naGQT-rpdjWa_g/edit?usp=sharing
> 
> I hope it answers all of the above questions and provides a clear
> big picture. If not, please let me know.
> 
> (If you need edit permission for the above document, please just
> request, I will approve.)

Thanks, that gives a nice overview!

I/O Resource Allocation part will be interesting. Restructuring existing
device drivers to allow spawned kernels to use specific hardware queues
could be a lot of work and very device-specific. I guess a small set of
devices can be supported initially and then it can grow over time.

This also reminds me of VFIO/mdev devices, which would be another
solution to the same problem, but equally device-specific and also a lot
of work to implement the devices that spawned kernels see.

Anyway, I look forward to seeing how this develops.

Stefan

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