wiki/virt/host/modules.md

title	description	published	date	tags	editor	dateCreated
Kernel modules		true	2023-02-08T18:42:56.268Z		markdown	2021-11-13T11:58:03.276Z

Host configuration and information

Section under construction {.is-warning}

IOMMU-enablement

By default, Linux distributions do not generally enable IOMMU groups, a prerequisite to share real hardware to virtual machines using modern virtualization techniques.

With GRUB as a bootloader

• For Intel CPUs, the following command adds the necessary bits:

# sed -i 's/\(quiet\)/\1 intel_iommu=on iommu=pt rd.driver.pre=vfio-pci/i' /etc/default/grub # Load kernel modules in GRUB.

iommu=pt makes sure that only devices that can be pass to a virtual machine will be flagged as such. rd.driver.pre=vfio-pci makes sure that the vfio-pci driver is loaded early in the boot process. {.is-info}

• For AMD CPUs, IOMMU groups are created by default, so the command is a bit different:

# sed -i 's/\(quiet\)/\1 iommu=pt rd.driver.pre=vfio-pci/i' /etc/default/grub # Load kernel modules in GRUB.

• It should then look like this:

$ cat /etc/default/grub

Then, one needs to regenerate GRUB.

• On Debian-based distributions:

# update-grub

With systemd-boot as a bootloader

Section under construction {.is-warning}

Nested virtualization

Nested virtualization is rarely enabled on Linux distributions.

• For Intel-based CPUs:

echo "options kvm_intel nested=1" >> /etc/modprobe.d/kvm.conf

• For AMD-based CPUs:

echo "options kvm_amd nested=1" >> /etc/modprobe.d/kvm.conf

VMCS Shadowing (Intel-only)

• Enabling VMCS shadowing may give a performance boost on Haswell CPUs and later. Append that enable_shadow_vmcs=1 to kvm.conf. It should look like that:

cat /etc/modprobe.d/kvm.conf
options kvm_intel nested=1 enable_shadow_vmcs=1

Virtualization-related kernel modules

This list is only concerned about kernel modules that relates to virtualization. Their description can be found using the modinfo command.

kvm_intel # "" 
kvm_amd # ""
kvm # Kernel virtual machine module for Linux

vfio_pci # "VFIO PCI - User Level meta-driver"
vfio_virqfd # "IRQFD support for VFIO bus drivers"
vfio_iommu_type1 # "Type1 IOMMU driver for VFIO"
vfio # "VFIO - User Level meta-driver"
vfio_mdev # "VFIO based driver for Mediated device"    

mdev # "Mediated device Core Driver"

vhost_net # "Host kernel accelerator for virtio net"
vhost # "Host kernel accelerator for virtio"
vhost_iotlb # "VHOST IOTLB"

tap # ""
tun # "Universal TUN/TAP device driver"

virtio_net # "Virtio network driver"
virtio_balloon # "Virtio balloon driver"
virtio_blk # "Virtio block driver"
virtio_console # "Virtio console driver"
virtio_scsi # "Virtio SCSI HBA driver"
virtio_gpu # "Virtio GPU driver"
virtio_dma_buf #

qemu_fw_cfg # "QEMU fw_cfg sysfs support"
irqbypass # "IRQ bypass manager utility module"
net_failover # "Failover driver for Paravirtual drivers"
failover # "Generic failover infrastructure/interface"

Ressources

• https://storpool.com/blog/nested-virtualization-with-kvm-and-opennebula/

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