RHEV/KVM: how are the CPU models mapped to the CPU flags?

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原文链接：https://access.redhat.com/solutions/2574771

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本文详细介绍了在Red Hat Enterprise Linux (RHEL) 和 KVM 虚拟化环境中，如何查找CPU模型与特征标志之间的映射。文章解释了如何在/usr/share/libvirt/cpu_map.xml中找到这些映射，并提供了如何启用或禁用特定CPU特征的方法。此外，还列出了Sandy Bridge、Haswell、Broadwell和Opteron G5等CPU模型所支持的特征。

https://access.redhat.com/solutions/2574771

RHEV/KVM: how are the CPU models mapped to the CPU flags?

SOLUTION IN PROGRESS - 已更新 2016年八月26日12:25 -

English

环境

Red Hat Virtualization 4
Red Hat Enterprise Virtualization 3
Red Hat Enterprise Linux 7
Red Hat Enterprise Linux 6
- libvirt
- qemu-kvm

问题

Where can I find the mapping between CPU models and flags for Virtualization?
How can I enabled or disable a specific feature/flag?
Which CPU flags are enabled when I select Sandy Bridge?
Which CPU flags are enabled when I select Haswell?
Which CPU flags are enabled when I select Broadwell?
Which CPU flags are enabled when I select Opteron_G5?

决议

The definitions are stored in /usr/share/libvirt/cpu_map.xml.

Raw

$ cat /usr/share/libvirt/cpu_map.xml | egrep 'Opteron_G5|Broadwell' -A5
    <model name='Broadwell'>
      <vendor name='Intel'/>
      <feature name='3dnowprefetch'/>
      <feature name='adx'/>
      <feature name='aes'/>
      <feature name='apic'/>
      ...
--
    <model name='Opteron_G5'>
      <vendor name='AMD'/>
      <feature name='3dnowprefetch'/>
      <feature name='abm'/>
      <feature name='aes'/>
      <feature name='apic'/>
      ...

NOTE: the below is not valid for Red Hat Virtualization. It's only intended for RHEL KVM.

To enable or disable a specific flag, edit the VM definition using virsh edit <vm name> and edit the cpu section of the xml with:

Raw

  <cpu ....>
    <feature policy='policy' name='flag'/>
  </cpu>

Where flag is the feature, such as vmx. And policy is one of the below:

Policy	Description
force	The virtual CPU will claim the feature is supported regardless of it being supported by host CPU.
require	Guest creation will fail unless the feature is supported by host CPU.
optional	The feature will be supported by virtual CPU if and only if it is supported by host CPU.
disable	The feature will not be supported by virtual CPU.
forbid	Guest creation will fail if the feature is supported by host CPU.

For example, to require the vmx feature to be passed to the Virtual Machine CPU:

Raw

  <cpu ....>
    <feature policy='require' name='vmx'/>
  </cpu>