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Chapter 23. Feature support and limitations in RHEL 10 virtualization

This document provides information about feature support and restrictions in Red Hat Enterprise Linux 10 (RHEL 10) virtualization.

23.1. How RHEL virtualization support works

A set of support limitations applies to virtualization in Red Hat Enterprise Linux 10 (RHEL 10). This means that when you use certain features or exceed a certain amount of allocated resources when using virtual machines in RHEL 10, Red Hat will provide only limited support for these guests unless you have a specific subscription plan.

Features listed in Recommended features in RHEL 10 virtualization have been tested and certified by Red Hat to work with the KVM hypervisor on a RHEL 10 system. Therefore, they are fully supported and recommended for use in virtualization in RHEL 10.

Features listed in Unsupported features in RHEL 10 virtualization may work, but are not supported and not intended for use in RHEL 10. Therefore, Red Hat strongly recommends not using these features in RHEL 10 with KVM.

Resource allocation limits in RHEL 10 virtualization lists the maximum amount of specific resources supported on a KVM guest in RHEL 10. Guests that exceed these limits are considered as Technology Preview by Red Hat.

In addition, unless stated otherwise, all features and solutions used by the documentation for RHEL 10 virtualization are supported. However, some of these have not been completely tested and therefore may not be fully optimized.

Important

Many of these limitations do not apply to other virtualization solutions provided by Red Hat, such as OpenShift Virtualization or Red Hat OpenStack Platform (RHOSP).

23.3. Unsupported features in RHEL 10 virtualization

The following features are not supported by the KVM hypervisor included with Red Hat Enterprise Linux 10 (RHEL 10):

Important

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 below.

For support details of the respective virtualization solutions, consult the relevant documentation.

Host system architectures

RHEL 10 with KVM is not supported on any host architectures that are not listed in Recommended features in RHEL 10 virtualization.

Guest operating systems

KVM virtual machines (VMs) that use the following guest operating systems (OSs) are not supported on a RHEL 10 host:

  • Windows 8.1 and earlier
  • Windows Server 2012 R2 and earlier
  • macOS
  • Solaris for x86 systems
  • Any operating system released before 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 10 hypervisor (such as the QEMU emulator or the libvirt package).

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 as virsh iface-start and virsh iface-destroy
  • virsh blkdeviotune
  • virsh snapshot-* commands that do not support external snapshots. For details, see Support limitations for virtual machine snapshots.

The QEMU command line

QEMU is an essential component of the virtualization architecture in RHEL 10, but it is difficult to manage manually, and improper QEMU configurations might 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. However, the qemu-img utility is supported for management of virtual disk images.

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 10. Note that adding vCPUs to a running VM, or vCPU hot plug, is supported.

RDMA-based migration

In RHEL 10, migrating virtual machines (VMs) by using Remote Direct Memory Access (RDMA) is no longer supported. Therefore, Red Hat highly discourages using the rdma URI for VM migration.

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 10.

To set up I/O throttling in RHEL 10, 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 more information, see Red Hat Knowledgebase solutions 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 10.

Other solutions:

  • Storage live migration is supported in RHOSP, but with some limitations. For details, see Migrate a Volume.

vHost Data Path Acceleration

On RHEL 10 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 10 does not support the implementation of a user-space vHost interface.

Other solutions:

  • vhost-user is supported in RHOSP, but only for virtio-net interfaces. For more information, see the Red Hat Knowledgebase solution virtio-net implementation and vhost user ports.
  • OpenShift Virtualization supports vhost-user as 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 10. As a consequence, Windows Cluster is not supported in RHEL 10.

virtio-crypto

Using the virtio-crypto device in RHEL 10 is not supported and RHEL strongly discourages its use.

Note that virtio-crypto devices are also not supported in any other virtualization solution provided by Red Hat.

virtio-multitouch-device, virtio-multitouch-pci

Using the virtio-multitouch-device and virtio-multitouch-pci devices in RHEL 10 is not supported and RHEL strongly discourages their use.

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 10, and Red Hat highly discourages its use.

Other solutions: * Use 3rd party backup solutions instead.

net_failover

Using the net_failover driver to set up an automated network device failover mechanism is not supported in RHEL 10.

Note that net_failover 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'>
    Copy to Clipboard

  • The configuration file of a KVM guest contains the following line: 

    <domain type='kvm'>
    Copy to Clipboard

SR-IOV InfiniBand networking devices

Attaching InfiniBand networking devices to VMs using Single-root I/O virtualization (SR-IOV) is not supported.

SGIO

Attaching SCSI devices to VMs by using SCSI generic I/O (SGIO) is not supported on RHEL 10. To detect whether your VM has an attached SGIO device, check the VM configuration for the following lines: 

<disk type="block" device="lun">
Copy to Clipboard 
<hostdev mode='subsystem' type='scsi'>
Copy to Clipboard

23.4. Resource allocation limits in RHEL 10 virtualization

The following limits apply to virtualized resources that can be allocated to a single KVM virtual machine (VM) on a Red Hat Enterprise Linux 10 (RHEL 10) host. If you VM exceeds these limits, it is considered a Technology Preview by Red Hat.

Important

Many of these limitations do not apply to other virtualization solutions provided by Red Hat, such as OpenShift Virtualization or Red Hat OpenStack Platform (RHOSP).

Maximum vCPUs per VM

For the maximum amount of vCPUs and memory that is supported on a single VM running on a RHEL 10 host, see: Virtualization limits for Red Hat Enterprise Linux with KVM

PCI devices per VM

RHEL 10 supports 32 PCI device slots per VM bus, and 8 PCI functions per device slot. This gives a theoretical maximum of 256 PCI functions per bus when multi-function capabilities are enabled in the VM, and no PCI bridges are used.

Each PCI bridge adds a new bus, potentially enabling another 256 device addresses. However, some buses do not make all 256 device addresses available for the user; for example, the root bus has several built-in devices occupying slots.

Virtualized IDE devices

KVM is limited to a maximum of 4 virtualized IDE devices per VM.

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