Qemu: Is it possible to have BOTH the virtual display and VGA passthrough in a Windows guest?

Question

This guy implies that it's possible to have both the virtual display and a VGA passthrough display device active at the same time..

I've tried this, both with libvirt and with the qemu commandline. I can have one display, or the other, but not both. No matter what I do, I get a code 43 on the passthrough device. But I'm using antique hardware (an old PCI Nvidia 8400GS), and that might be the problem.

Is this actually possible with a Linux host and Windows guest? Would you mind describing your hardware, and your configuration?

My ultimate goal is to duplicate the Spice virtual display as a duplicate/clone of the Nvidia physical display. That would allow me to run graphic-intensive applications on the hardware GPU, but still have all the convenience of a windowed virtual display.

Answer 1

Looking-glass doesn't precisely answer the question, but it solves the underlying problem nearly perfectly -- providing GPU-accelerated VM graphics on the host desktop with the host's HID devices. In alpha as of Dec 2017, but appears stable enough for everyday use on a single display.

Answer 2

This is not possible at present, the Spice display driver does not appear to support Windows 10's cross-adapter display cloning feature as of yet.

Code 43

Turns out that the other issue I was complaining about is due to an Nvidia "bug." When the driver detects virtualization, it throws a code 43. NVidia has stated that this is unintentional, but they're not planning on fixing it, either.

I solved this by downgrading my Nvidia driver to 337.88, and adding <kvm><hidden state='on'/></kvm> to my machine definition with virsh edit domname. Apparently it's possible to get more modern drivers working by deleting a bunch of hyperv functionality, but I haven't bothered yet.