Preserving guest memory across kexec [LWN.net]

Preserving guest memory across kexec

Posted May 21, 2022 15:05 UTC (Sat) by developer122 (guest, #152928)
In reply to: Preserving guest memory across kexec by developer122
Parent article: Preserving guest memory across kexec

The extreme example is one where the OS can replace itself while userspace continues on running CPU-bound load. Having the microkernel replace itself and pick back up without any downtime at all, unless perhaps a program tries to make a call.

Dunno that it would be possible on current hardware though, with existing interrupt controllers and memory paging.

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Preserving guest memory across kexec

Posted May 22, 2022 7:37 UTC (Sun) by Wol (subscriber, #4433) [Link] (3 responses)

Bear in mind you are describing 1980s technology ...

I've stood next to a system where my friend said "if I pull out this board no-one will notice except the engineers monitoring the system ..." he was pointing at the CPU ...

and the OS was just another replaceable component same as ...

Cheers,
Wol

Preserving guest memory across kexec

Posted May 26, 2022 2:54 UTC (Thu) by developer122 (guest, #152928) [Link] (2 responses)

Perhaps, but we stopped building anything to support that *in the 80's.* All the Dell and HP and Supermicro boxes are glorified PCs.

At the same time, the only reason that was possible was because of virtualization. All the "OSs" were running in logical partitions aka hardware VMs. If you lost the hypervisor then the system went down, and the base hypervisor firmware was impossible to replace (often because it's in ROM).

Preserving guest memory across kexec

Posted May 26, 2022 9:19 UTC (Thu) by Wol (subscriber, #4433) [Link] (1 responses)

Well, yes there was a lot of - not exactly custom - hardware in there, but I guess to upgrade the hypervisor they could quite possibly just have replaced the CPU boards. I don't remember any reference to rom-based hypervisors, though ...

Cheers,
Wol

Preserving guest memory across kexec

Posted May 30, 2022 0:42 UTC (Mon) by developer122 (guest, #152928) [Link]

From what I recall, the LPARS on IBM or domains on Sun SPARC were managed by firmware loaded from the system board itself, into either a main CPU or a service processor.