### **Enable IOMMU**
***Set the kernel paramater depending on your CPU.*** \
For GRUB user, edit grub configuration.
| /etc/default/grub |
| ----- |
| `GRUB_CMDLINE_LINUX_DEFAULT="... intel_iommu=on iommu=pt ..."` |
| OR |
| `GRUB_CMDLINE_LINUX_DEFAULT="... amd_iommu=on iommu=pt ..."` |
***Generate grub.cfg***
```sh
grub-mkconfig -o /boot/grub/grub.cfg
```
Reboot your system for the changes to take effect.

### **Verify IOMMU**
***If you don't see any output when running following command, IOMMU is not functioning.***
```sh
dmesg | grep 'IOMMU enabled'
```

### **Install required tools**
<details>
  <summary><b>Gentoo Linux</b></summary>

  ```sh
  emerge -av qemu virt-manager libvirt ebtables dnsmasq
  ```
</details>

<details>
  <summary><b>Arch Linux</b></summary>

  ```sh
  pacman -S qemu libvirt edk2-ovmf virt-manager dnsmasq ebtables
  ```
</details>

<details>
  <summary><b>Fedora</b></summary>

  ```sh
  dnf install @virtualization
  ```
</details>

### **Enable required services**
<details>
  <summary><b>SystemD</b></summary>

  ```sh
  systemctl enable --now libvirtd
  ```
</details>

<details>
  <summary><b>OpenRC</b></summary>

  ```sh
  rc-update add libvirtd default
  rc-service libvirtd start
  ```
</details>

Sometimes, you might need to start default network manually.
```sh
virsh net-start default
virsh net-autostart default
```

### **Setup Guest OS**
***NOTE: You should replace win10 with your VM's name where applicable*** \
Download [virtio](https://fedorapeople.org/groups/virt/virtio-win/direct-downloads/stable-virtio/virtio-win.iso) driver. \
Launch ***virt-manager*** and create a new virtual machine. Select ***Customize before install*** on Final Step. \
In ***Overview*** section, set ***Chipset*** to ***Q35***, and ***Firmware*** to ***UEFI*** \
In ***CPUs*** section, set ***CPU model*** to ***host-passthrough***, and ***CPU Topology*** to whatever fits your system. \
For ***SATA*** disk of VM, set ***Disk Bus*** to ***virtio***. \
In ***NIC*** section, set ***Device Model*** to ***virtio*** \
Add Hardware > CDROM: virtio-win.iso \
Now, ***Begin Installation***. Windows can't detect the ***virtio disk***, so you need to ***Load Driver*** and select ***virtio-iso/amd64/win10*** when prompted. \
After successful installation of Windows, install virtio drivers from virtio CDROM.

### **Attaching PCI devices**
Remove Channel Spice, Display Spice, Video XQL, Sound ich* and other unnecessary devices. \
Now, click on ***Add Hardware***, select ***PCI Devices*** and add the PCI Host devices for your GPU's VGA and HDMI Audio \
Some GPU vBIOS needs to be patched for UEFI Support. \
----- TODO: vBIOS patching ------ \
To use patched vBIOS, edit VM's configuration to include patched vBIOS inside ***hostdev*** block of VGA

  ```sh
  mkdir /etc/libvirt/hooks
  touch /etc/libvirt/hooks/qemu
  chmod +x /etc/libvirt/hooks/qemu
  ```
  <table>
  <tr>
  <th>
  virsh edit win10
  </th>
  </tr>

  <tr>
  <td>

  ```xml
  ...
  <hostdev mode='subsystem' type='pci' managed='yes'>
    <source>
      ...
    </source>
    <rom file='/home/me/patched.rom'/>
    ...
  </hostdev>
  ...
  ```

  </td>
  </tr>
  </table>

### Libvirt Hooks
Libvirt hooks automate the process of running specific tasks during VM state change. \
More info at: [PassthroughPost](https://passthroughpo.st/simple-per-vm-libvirt-hooks-with-the-vfio-tools-hook-helper/)
<details>
  <summary><b>Create Libvirt Hook</b></summary>

  ```sh
  mkdir /etc/libvirt/hooks
  touch /etc/libvirt/hooks/qemu
  chmod +x /etc/libvirt/hooks/qemu
  ```
  <table>
  <tr>
  <th>
    /etc/libvirt/hooks/qemu
  </th>
  </tr>

  <tr>
  <td>

  ```sh
  #!/bin/bash

GUEST_NAME="$1"
HOOK_NAME="$2"
STATE_NAME="$3"
MISC="${@:4}"

BASEDIR="$(dirname $0)"

HOOKPATH="$BASEDIR/qemu.d/$GUEST_NAME/$HOOK_NAME/$STATE_NAME"
set -e # If a script exits with an error, we should as well.

if [ -f "$HOOKPATH" ]; then
  eval \""$HOOKPATH"\" "$@"
elif [ -d "$HOOKPATH" ]; then
  while read file; do
    eval \""$file"\" "$@"
  done <<< "$(find -L "$HOOKPATH" -maxdepth 1 -type f -executable -print;)"
fi
  ```

  </td>
  </tr>
  </table>
</details>

<details>
  <summary><b>Create Start Script</b></summary>

  ```sh
  mkdir -p /etc/libvirt/hooks/qemu.d/win10/prepare/begin
  touch /etc/libvirt/hooks/qemu.d/win10/prepare/begin/start.sh
  chmod +x /etc/libvirt/hooks/qemu.d/win10/prepare/begin/start.sh
  ```
  <table>
  <tr>
  <th>
    /etc/libvirt/hooks/qemu.d/win10/prepare/begin/start.sh
  </th>
  </tr>

  <tr>
  <td>

  ```sh
#!/bin/bash
set -x

# Stop display manager
systemctl stop display-manager
# rc-service display-manager stop

# Unbind EFI Framebuffer
echo efi-framebuffer.0 > /sys/bus/platform/drivers/efi-framebuffer/unbind

# Unload NVIDIA kernel modules
modprobe -r nvidia_drm nvidia_modeset nvidia_uvm nvidia

# Unload AMD kernel module
# modprobe -r amdgpu

# Detach GPU devices from host
# Use your GPU and HDMI Audio PCI host device
virsh nodedev-detach pci_0000_01_00_0
virsh nodedev-detach pci_0000_01_00_1

# Load vfio module
modprobe vfio-pci
  ```

  </td>
  </tr>
  </table>
</details>

<details>
  <summary><b>Create Stop Script</b></summary>

  ```sh
  mkdir -p /etc/libvirt/hooks/qemu.d/win10/release/end
  touch /etc/libvirt/hooks/qemu.d/win10/release/end/stop.sh
  chmod +x /etc/libvirt/hooks/qemu.d/win10/release/end/stop.sh
  ```
  <table>
  <tr>
  <th>
    /etc/libvirt/hooks/qemu.d/win10/release/end/stop.sh
  </th>
  </tr>

  <tr>
  <td>

  ```sh
#!/bin/bash
set -x

# Unload vfio module
modprobe -r vfio-pci

# Attach GPU devices to host
# Use your GPU and HDMI Audio PCI host device
virsh nodedev-reattach pci_0000_01_00_0
virsh nodedev-reattach pci_0000_01_00_1

# Rebind framebuffer to host
echo "efi-framebuffer.0" > /sys/bus/platform/drivers/efi-framebuffer/bind

# Load NVIDIA kernel modules
modprobe nvidia_drm
modprobe nvidia_modeset
modprobe nvidia_uvm
modprobe nvidia

# Load AMD kernel module
# modprobe amdgpu

# Restart Display Manager
systemctl start display-manager
# rc-service display-manager start
  ```

  </td>
  </tr>
  </table>
</details>

### **See Also**
> [Single GPU Passthrough by joeknock90](https://github.com/joeknock90/Single-GPU-Passthrough)<br/>
> [Single GPU Passthrough by YuriAlek](https://gitlab.com/YuriAlek/vfio)<br/>
> [ArchLinux PCI Passthrough](https://wiki.archlinux.org/index.php/PCI_passthrough_via_OVMF)<br/>
> [Gentoo GPU Passthrough](https://wiki.gentoo.org/wiki/GPU_passthrough_with_libvirt_qemu_kvm)<br/>