I used QEMU for VFIO, GPU passthrough to a Win 10 guest for games. It worked really well. I passed an nvidia card, an ssd with the os/programs, and an hdd data disk from a Linux host (Gentoo).

Setting it up was somewhat difficult. When I did it there weren't many good guides for just exactly my situation, so I had to use many, many different resources to get it running. Based on some of the links others have posted here, there seems to be more out there on it now.

This was my last working startup script. I no longer recall why or even if any of these options were necessary or beneficial. At the time, it was just what worked. (Dual monitor, separate video cards for host and guest, L-CTRL+R-CTRL to pass mouse/keyboard control back and forth.) I haven't used this in quite a while, so I can't say if all of these options are still legit anymore.

  #!/bin/bash

  cp /usr/share/edk2-ovmf/OVMF_VARS.fd /tmp/my_vars.fd

  qemu-system-x86_64 \
        -enable-kvm \
        -m 16G \
        -cpu qemu64,hv_vendor_id=whatever,kvm=off,hv_relaxed,hv_spinlocks=0x1fff,hv_vapic,hv_time,smep=off \
        -smp cores=8,threads=1,sockets=1 \
        -machine q35,type=pc -vga std -display gtk \
        -drive if=pflash,format=raw,readonly,file=/usr/share/edk2-ovmf/OVMF_CODE.fd \
        -drive if=pflash,format=raw,file=/tmp/my_vars.fd \
        -drive file=/dev/disk/by-id/ata-Samsung_SSD_860_EVO_250GB_XXXXXXXXXXXXXXX,format=raw,if=virtio \
        -drive file=/dev/disk/by-id/ata-ST3000DM001-XXXXXXXXXXXXXXX,format=raw,if=virtio \
        -boot order=d \
        -object input-linux,id=kbd,evdev=/dev/input/by-id/usb-XXXXXXXXXXXXX_USB_Keyboard-event-kbd,grab_all=yes \
        -object input-linux,id=mouse,evdev=/dev/input/by-id/usb-XXXXXXXXXXXXXXXX-event-mouse \
        -device virtio-mouse-pci \
        -device virtio-keyboard-pci \
        -netdev user,id=user.0 -device e1000,netdev=user.0 \
        &