Masking CPU Flags Via Libvirt Xml Not Working?

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Hi,

Has anyone here managed to get cpu masking working via libvirt?
Intention to enable VM migrations between hosts of a different CPU
generation.

Inside my xml I’m providing the model as well as a list of features to specifically disable, but none of it seems to take any effect. On booting the VM I still see the disabled flags in /proc/cpuinfo


x86_64
Westmere












Doing a dumpxml against the domU once it’s booted leaves out the entire
section, leading me to think maybe libvirt is dropping it for some reason. I’ve got the above just in the main section.

Anyone have this working or able to offer some suggestions?

Thanks!

– Nathan

2 thoughts on - Masking CPU Flags Via Libvirt Xml Not Working?

  • To add to this, I’ve tried using the boot options to set the cpu mask instead:

    xen_commandline : dom0_mem 48M,max:2048M loglvl=all guest_loglvl=all cpuid_mask_ecx=0x009ee3fd cpuid_mask_edx=0xbfebfbff

    Unfortunately still no luck. There’s no errors in xm dmesg to indicate the settings were / weren’t applied, it simply doesn’t seem to do anything.

    – Nathan

  • Hi,

    I guess this is the wrong approach:

    Libvirt does manage cpu type in an xml file, you would have to alter this xml file:

    /usr/share/libvirt/cpu_map.xml

    HTH

    PS: Maybe add an feature request upstream to enable this for all libvirt users?

    I have seen this request quite some time on different mailing lists.

    Am 27.08.2014 20:08, schrieb Nathan March: