I have some dated equipment used to run an experimental apparatus. Unfortunately, that equipment will only run on WinXP using FireWire/IEEE1394, which is becoming more and more of a pain for us to maintain hardware-wise. Unfortunately we also don't have the money to replace this equipment. We discussed perhaps trying to virtualize the XP environment on a newer OS. I'd been reading about VFIO/IOMMU and figured maybe I could pass the FireWire PCI cards through and just do it that way.
Plus side - I got it to work. I installed XP with a QEMU-KVM hypervisor. Got it set up, passed the firewire cards through, and all was recognized in the VM, including when I attached the equipment to the FW cards. XP device manager saw that it was all there.
Unfortunately, I've found that the actual interaction with the hardware seems to be touchy at best. Things misbehave in weird, unexplainable ways. Some of those made me think that the guest OS wasn't communicating with the passed through cards correctly. This was surprising as I was under the impression that passed through cards were utilized directly by the guest OS without host OS intervention.
My question is basically - if I'm virtualizing an older system and passing through the various ports/cards needed, should it behave as if it were bare metal? Or are there circumstances where what the guest OS tries to do is not the same as if it were bare metal (I.E - the host OS changes something when the instruction leaves the VM)? As I said - I was under the impression that the guest OS was interacting with hardware directly, but experience has made me question if this is actually the case.
Part of the reason I want to know this is that there's other equipment that would be more dangerous or lead to damage of the equipment if it behaved unexpectedly (I.E Lasers where power is computer controlled) that uses other hardware interfaces. So, if there is a risk of what the guest OS thinks it's doing being disconnected from the actual reality, that's a safety risk that I want to understand before going forward.
