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VMs also don't always require hardware virtualization - Alibaba's PVM https://lkml.org/lkml/2024/2/26/1263 https://lkml.org/lkml/2024/2/26/1263 didn't get upstr
by mappu 1y ago
VMs also don't always require hardware virtualization - Alibaba's PVM https://lkml.org/lkml/2024/2/26/1263 https://lkml.org/lkml/2024/2/26/1263 didn't get upstreamed, but, theoretically the MMU is all you need for complete isolation. This kind of idea is also how VM software worked before VT-x was introduced. And of course QEMU has the TCG which works with no kernel support at all.
- SirGiggles 1y agoI think you could also add Xen to that list. IIRC, the old Xen PV mode was purely paravirtualized without using any hardware extensions.
- eru 1y agoYes, Xen was big on paravirtualisation but started supporting the other kinds pretty soon, too. (At least they were supported around 2009-2012, when I was working on XenServer.)
- SirGiggles 1y agoI think things are swinging back the other way if I have understood the more recent PVHv2 stuff correctly.
- 01HNNWZ0MV43FF 1y agoIn my experience TCG (or any method that doesn't require root / admin power) is pretty slow. But I'd be happy to be wrong about that, for an odd project I have
- eru 1y agoIt depends a bit on your workload. If you have a pure computation workload, without much IO, TCG etc doesn't need to be slow.
- johncolanduoni 1y agoIt also depends on the architectures. x86 on ARM is tough to do efficiently because of the memory model differences. One of the keys to Rosetta 2 being so good was being able to make the underlying ARM processor obey the x86 memory model (even though it was still executing ARM instructions).