22.3. Unsupported features in RHEL 9 virtualization
The following features are not supported by the KVM hypervisor included with Red Hat Enterprise Linux 9 (RHEL 9):
Many of these limitations may not apply to other virtualization solutions provided by Red Hat, such as OpenShift Virtualization or Red Hat OpenStack Platform (RHOSP).
Features supported by other virtualization solutions are described as such in the following paragraphs.
Host system architectures
RHEL 9 with KVM is not supported on any host architectures that are not listed in Recommended features in RHEL 9 virtualization.
Notably, the 64-bit ARM architecture (ARM 64) is provided only as a Technology Preview for KVM virtualization on RHEL 9, and Red Hat therefore discourages its use in production environments.
Guest operating systems
KVM virtual machines (VMs) using the following guest operating systems (OSs) on a RHEL 9 host are not supported:
- Microsoft Windows 8.1 and earlier
- Microsoft Windows Server 2008 R2 and earlier
- macOS
- Solaris for x86 systems
- Any OS released prior to 2009
For a list of guest OSs supported on RHEL hosts and other virtualization solutions, see Certified Guest Operating Systems in Red Hat OpenStack Platform, Red Hat Virtualization, OpenShift Virtualization and Red Hat Enterprise Linux with KVM.
Creating VMs in containers
Red Hat does not support creating KVM virtual machines in any type of container that includes the elements of the RHEL 9 hypervisor (such as the QEMU emulator or the libvirt package).
Other solutions:
- To create VMs in containers, Red Hat recommends using the OpenShift Virtualization offering.
Specific virsh commands and options
Not every parameter that you can use with the virsh utility has been tested and certified as production-ready by Red Hat. Therefore, any virsh commands and options that are not explicitly recommended by Red Hat documentation may not work correctly, and Red Hat recommends not using them in your production environment.
Notably, unsupported virsh commands include the following:
-
virsh iface-*commands, such asvirsh iface-startandvirsh iface-destroy -
virsh blkdeviotune -
virsh snapshot-*commands, such asvirsh snapshot-createandvirsh snapshot-revert
The QEMU command line
QEMU is an essential component of the virtualization architecture in RHEL 9, but it is difficult to manage manually, and improper QEMU configurations may cause security vulnerabilities. Therefore, using qemu-* command-line utilities, such as qemu-kvm is not supported by Red Hat.
Instead, use libvirt utilities, such as virt-install, virt-xml, and supported virsh commands, as these orchestrate QEMU according to the best practices.
vCPU hot unplug
Removing a virtual CPU (vCPU) from a running VM, also referred to as a vCPU hot unplug, is not supported in RHEL 9.
Memory hot unplug
Removing a memory device attached to a running VM, also referred to as a memory hot unplug, is unsupported in RHEL 9.
QEMU-side I/O throttling
Using the virsh blkdeviotune utility to configure maximum input and output levels for operations on virtual disk, also known as QEMU-side I/O throttling, is not supported in RHEL 9.
To set up I/O throttling in RHEL 9, use virsh blkiotune. This is also known as libvirt-side I/O throttling. For instructions, see Disk I/O throttling in virtual machines.
Other solutions:
- QEMU-side I/O throttling is also supported in RHOSP. For details, see Setting Resource Limitation on Disk and the Use Quality-of-Service Specifications section in the RHOSP Storage Guide.
- In addition, OpenShift Virtualizaton supports QEMU-side I/O throttling as well.
Storage live migration
Migrating a disk image of a running VM between hosts is not supported in RHEL 9.
Other solutions:
- Storage live migration is also supported in RHOSP, but with some limitations. For details, see Migrate a Volume.
- It is also possible live-migrate VM storage when using OpenShift Virtualization. For more infrmation, see Virtual machine live migration.
Live snapshots
Creating or loading a snapshot of a running VM, also referred to as a live snapshot, is not supported in RHEL 9.
In addition, note that non-live VM snapshots are deprecated in RHEL 9. Therefore, creating or loading a snapshot of a shut-down VM is supported, but Red Hat recommends not using it.
Other solutions:
- RHOSP also supports live snapshots. For details, see Importing virtual machines into the overcloud.
vHost Data Path Acceleration
On RHEL 9 hosts, it is possible to configure vHost Data Path Acceleration (vDPA) for virtio devices, but Red Hat currently does not support this feature, and strongly discourages its use in production environments.
vhost-user
RHEL 9 does not support the implementation of a user-space vHost interface.
Other solutions:
-
vhost-useris supported in RHOSP, but only forvirtio-netinterfaces. For details, see virtio-net implementation and vhost user ports. -
OpenShift Virtualization supports
vhost-useras well.
S3 and S4 system power states
Suspending a VM to the Suspend to RAM (S3) or Suspend to disk (S4) system power states is not supported. Note that these features are disabled by default, and enabling them will make your VM not supportable by Red Hat.
Note that the S3 and S4 states are also currently not supported in any other virtualization solution provided by Red Hat.
S3-PR on a multipathed vDisk
SCSI3 persistent reservation (S3-PR) on a multipathed vDisk is not supported in RHEL 9. As a consequence, Windows Cluster is not supported in RHEL 9.
virtio-crypto
Using the virtio-crypto device in RHEL 9 is not supported and its use is therefore highly discouraged.
Note that virtio-crypto devices are also not supported in any other virtualization solution provided by Red Hat.
Incremental live backup
Configuring a VM backup that only saves VM changes since the last backup, also known as incremental live backup, is not supported in RHEL 9, and Red Hat highly discourages its use.
net_failover
Using the net_failover driver to set up an automated network device failover mechanism is not supported in RHEL 9.
Note that net_failover is also currently not supported in any other virtualization solution provided by Red Hat.
Multi-FD migration
Migrating VMs using multiple file descriptors (FDs), also known as multi-FD migration, is not supported in RHEL 9.
Note that multi-FD migrations are also currently not supported in any other virtualization solution provided by Red Hat.
NVMe devices
Attaching Non-volatile Memory express (NVMe) devices to VMs as a PCIe device with PCI-passthrough is not supported.
Note that attaching NVMe devices to VMs is also currently not supported in any other virtualization solution provided by Red Hat.
TCG
QEMU and libvirt include a dynamic translation mode using the QEMU Tiny Code Generator (TCG). This mode does not require hardware virtualization support. However, TCG is not supported by Red Hat.
TCG-based guests can be recognized by examining its XML configuration, for example using the virsh dumpxml command.
The configuration file of a TCG guest contains the following line:
<domain type='qemu'>
The configuration file of a KVM guest contains the following line:
<domain type='kvm'>
SR-IOV InfiniBand networking devices
Attaching InfiniBand networking devices to VMs using Single-root I/O virtualization (SR-IOV) is not supported.
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