Hector Martin

you should join our discord! we are planning to use PongoOS, our toy kernel, in EL2, and use it to virtualize a GIC to boot UEFI (which will run in EL1). @never_released

this should simplify things quite a bit..

Sounds interesting, though is it worth the extra latency of adding a virtualized shim for interrupts? I mean, I've written custom interrupt controllers for Linux...

i think the extra latency is low cost enough to not really matter and the advantages of not having to port OSes to the oddball platform are worth the cost

Sure, if it works and doesn't end up being a user experience compromise down the line, that's fine.

What made us seriously think about it is that M1 is new enough to have nested virtualisation, so that the thin hypervisor for this can still expose the full CPU feature set to the guest.

Yeah, that's a big one. Though nested virt usually has a nontrivial perf cost, but it depends on the implementation. E.g. what is the cost of the extra pagetable level (which presumably at least can be using very large pages)?

But anyway, there is always time to ditch the virtualization if it becomes the limiting factor, so I'm not too worried about that. Crossporting drivers back into the kernel is trivial compared to, like, GPU support (assuming the license permits).