Chapter 4. Getting started with virtualization on IBM Z

Prerequisites

• RHEL 8.6 or later is installed and registered on your host machine.

  Important

  If you already enabled virtualization on an IBM Z machine by using RHEL 8.5 or earlier, you should instead reconfigure your virtualization module and update your system. For instructions, see How virtualization on IBM Z differs from AMD64 and Intel 64.

• The following minimum system resources are available:

  • 6 GB free disk space for the host, plus another 6 GB for each intended VM.
  • 2 GB of RAM for the host, plus another 2 GB for each intended VM.
  • 4 CPUs on the host. VMs can generally run with a single assigned vCPU, but Red Hat recommends assigning 2 or more vCPUs per VM to avoid VMs becoming unresponsive during high load.
• Your IBM Z host system is using an IBM z14 CPU or later.

• RHEL 8 is installed on a logical partition (LPAR). In addition, the LPAR supports the start-interpretive execution (SIE) virtualization functions.

  To verify this, search for sie in your /proc/cpuinfo file.

  # grep sie /proc/cpuinfo
  features        : esan3 zarch stfle msa ldisp eimm dfp edat etf3eh highgprs te sie

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Troubleshooting

• If KVM virtualization is not supported by your host CPU, virt-host-validate generates the following output:

  QEMU: Checking for hardware virtualization: FAIL (Only emulated CPUs are available, performance will be significantly limited)

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  However, VMs on such a host system will fail to boot, rather than have performance problems.

  To work around this, you can change the <domain type> value in the XML configuration of the VM to qemu. Note, however, that Red Hat does not support VMs that use the qemu domain type, and setting this is highly discouraged in production environments.

Prerequisites

• You are using a RHEL 8.5 on IBM Z, with the virt:av module installed. To confirm that this is the case:

  # hostnamectl | grep "Operating System"
  Operating System: Red Hat Enterprise Linux 8.5 (Ootpa)
  # yum module list --installed
  [...]
  Advanced Virtualization for RHEL 8 IBM Z Systems (RPMs)
  Name                Stream                  Profiles                  Summary
  virt                av [e]                common [i]                Virtualization module

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Verification

• Ensure the virt module on your system is provided by the rhel stream.

  # yum module info virt
  
  Name             : virt
  Stream           : rhel [d][e][a]
  Version          : 8050020211203195115
  [...]

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• Device passthrough by using vfio
• Obtaining memory information by using virsh domstats and virsh memstat
• The memballoon and virtio-rng virtual devices
• Memory backing by using huge pages
• Live and non-live VM migrations
• Saving and restoring VMs
• VM snapshots, including memory snapshots (using the --memspec option)
• Full memory dumps. Instead, specify the --memory-only option for the virsh dump command.
• 248 or more vCPUs. The vCPU limit for secure guests is 247.
• Nested virtualization

• When setting up a VM on an IBM Z system, it is recommended to protect the guest OS from the "Spectre" vulnerability. To do so, use the virsh edit command to modify the VM’s XML configuration and configure its CPU in one of the following ways:

  • Use the host CPU model:

    <cpu mode='host-model' check='partial'>
      <model fallback='allow'/>
    </cpu>

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    This makes the ppa15 and bpb features available to the guest if the host supports them.

  • If using a specific host model, add the ppa15 and pbp features. The following example uses the zEC12 CPU model:

    <cpu mode='custom' match='exact' check='partial'>
        <model fallback='allow'>zEC12</model>
        <feature policy='force' name='ppa15'/>
        <feature policy='force' name='bpb'/>
    </cpu>

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    Note that when using the ppa15 feature with the z114 and z196 CPU models on a host machine that uses a z12 CPU, you also need to use the latest microcode level (bundle 95 or later).