You just don't share certain devices, like Bluetooth. The "main" kernel will probably own the boot process and manage some devices exclusively. I think the real advantage is running certain applications isolated within a CPU subset, protected/contained behind a dedicated kernel. You don't have the slowdown of VMs, or have to fight against the isolation sieve that is docker.

Is there anything that says that multiple kernels will be responsible for owning the drivers for HW? It could be that one kernel owns the hardware while the rest speak to the main kernel using a communication channel. That's also presumably why KHO is a thing because you have to hand over when shutting down the kernel responsible for managing the driver.

IBM mainframes and Power servers have “partitions” (LPARs). My understanding of how they work, is they actually are software-based virtualisation, but the hypervisor is in the system firmware, not the OS. And some of the firmware is loaded from disk at boot-up, making it even closer to something like Xen-labelling it as “hardware” not “software” is more about marketing (and which internal teams own it within IBM) than than technical reality. Their mainframe partitioning system, PR/SM, apparently began life as a stripped-down version of VM/CMS, although I’m not sure how close the relationship between PR/SM and z/VM is in current releases.

This sounds like running multiple kernels in a shared security domain, which reduces the performance cost of transitions and sharing, but you lose the reliability and security advantages that a proper VM gives you. It reminds me of coLinux (essentially, a Linux kernel as a Windows NT device driver)

Does anyone have more details on how OpenVMS Galaxy was actually implemented? I believe it was available for both Alpha and Itanium, but not yet x86-64 (and probably never…)

This was underrated!

Nothing prevents it if you achieve code execution. But where it helps is scenarios like syscall / memory mapping exploits where a user process can only affect resources attached to their current kernel. For example https://dirtycow.ninja/ would have a limited scope.

mainline vs abandoned.

> - Improved fault isolation between different workloads

Yes.

It should be possible in theory, as long as both use the same communication interface. In practice, I think getting it to work on just one kernel is already a huge amount of work.

Docker is the wrong thing to compare against, especially considering it is an application and not a technology; the technology would be containerization. This competes against hardware virtualization support, if anything.