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

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Message-ID: <20250924125101.GA562097@fedora>
Date: Wed, 24 Sep 2025 08:51:01 -0400
From: Stefan Hajnoczi <stefanha@...hat.com>
To: David Hildenbrand <david@...hat.com>
Cc: Cong Wang <xiyou.wangcong@...il.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 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.

Thanks,
Stefan

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