Recs.
Updated
A device driver that allows hardware to be used directly by a virtual machine to achive close to native performance
Specs
Pros
Cons
Con Requires two GPUs if using a graphical environment on host machine
Since the hardware is attached to the virtual machine, it cannot be used outside of it, meaning two GPUs are required if using a graphical environment. IGPUs (integrated GPUs, usually included in consumer grade CPUs) can of course also be used.
Con Requires a separate video output
While a VFIO virtual machine can be run in windowed mode, it does not perform at near native performance while doing so, a second monitor output is required in order to display the GPU output with near native performance. This can for example be achived using a secondary monitor, or by plugging both your host and virtual machine video output into the same monitor and switching between them with a button if it supports it.
Con Some games might not allow it
One game, in particular, Counter-Strike: Global Offensive, does not allow its users to play the game using a VFIO setup. This could, however, be overcome by playing it on your host machine, since the game runs on Linux. Then you could either rely on your secondary graphics card to run the game on your host machine or rebind your primary GPU to the host machine.