Can hardware be used directly by both host and guest?

Question

I am about to start experimenting with VT-d/PCI passthrough on my new coming-soon hardware known to support it, and wondering if it will be possible to use say video/audio hardware by both host and guest OSes at the same time, or will passing a piece of hardware through to guest mean that the host will have to bear without it for the time the guest is using it?

Ideally, the host will be Linux (OpenSUSE) with virtualization powered by KVM/QEMU, but should this render what I am hoping for impossible I would consider other OSes/hypervisors.

Typical use case: running video games or audio sequencers inside Windows guest while still being able to watch videos / play music on the host.

Answer 1

No.

Operating systems typically expect complete and sole access to hardware. In order to pass a device directly down to a guest it needs to be released from the control of the host. There are currently no means for device sharing between operating systems. It is listed as "pass through" rather than "sharing", "arbitration" or some other synonym for a reason.

Typically in the case of graphics cards this means you need one graphics card for the host and one for the guest. Using integrated graphics for the host can often allow you to pass a dedicated graphics card down to the guest.

This doesn't mean you cannot do what you want though. If you had two powerful dedicated cards then gaming on the host and guest should be possible. I'm not sure if integrated graphics can be passed down to the guest (not convinced it hangs off the PCIe, shared memory could cause problems as well) so you would probably need two fully fledged graphics cards in order to have significant graphics power in the host as well as the guest.