How to pass SSE4 to Libvirt KVM

Question

The box has X5570 cpus.

flags       : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm dca sse4_1 sse4_2 popcnt lahf_lm ida dtherm tpr_shadow vnmi flexpriority ept vpid

What I have tried:

<cpu mode='custom' match='exact' check='partial'>
    <model fallback='allow'>qemu64</model>
    <feature policy='require' name='sse4.2'/>
    <feature policy='disable' name='svm'/>
</cpu>

error: internal error Cannot find suitable CPU model for given data

Answer 1

If you do not need to migrate domains to a different host, you can just forego any customization:

<cpu>
  <topology sockets='1' dies='1' cores='2' threads='1'/>
</cpu>

Another method is to use host-passthru:

<cpu mode='host-passthrough'>
  <cache mode='passthrough'/>
  <feature policy='disable' name='lahf_lm'/>
  <!-- ... -->
</cpu>

You can find out more by looking at the reference.

Not sure what you’re trying to achieve by disabling SVM (AMD’s equivalent of VT-x). If it’s about nested virtualization, that doesn’t work anyway unless you enable it on your CPU vendor’s kvm kernel module.