Thanks. I have sent a patch based off the tip here:

I also have a patch off libvirt-4.5 which I have tested on our HW. If needed, I 
can send that patch as well.


On Dec 2, 2019, 5:22 PM +0530, Daniel P. Berrangé <>, wrote:
On Wed, Nov 27, 2019 at 11:10:21AM +0000, Ani Sinha wrote:
Hi :

I see a commit in qemu that adds support for CLZERO but in CPUIDs. :

commit e900135dcfb676a4019dc206395e02db5d1de0d6
Author: Sebastian Andrzej Siewior <>
Date: Wed Sep 25 23:49:48 2019 +0200

i386: Add CPUID bit for CLZERO and XSAVEERPTR

The CPUID bits CLZERO and XSAVEERPTR are availble on AMD's ZEN platform
and could be passed to the guest.

Signed-off-by: Sebastian Andrzej Siewior <>
Signed-off-by: Paolo Bonzini <>

Is there a corresponding change in libvirt adding this capability? Libvirt 
complains when I add it manually in the vm xml:

# virsh create newvm.xml
error: Failed to create domain from newvm.xml
error: unsupported configuration: unknown CPU feature: clzero

# grep clzero newvm.xml
<feature policy='require' name='clzero'/>

Should we add it?

Yes, if it is supported by QEMU to expose to a guest, then it should be
added to libvirt too.

Presumably only needs add an addition to src/cpu_maps/x86_features.xml


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