[Pkg-libvirt-maintainers] Bug#830857: libvirt-daemon: CPU feature cmt not found

[Ansgar Hegerfeld]

Package: libvirt-daemon
Version: 2.0.0-1
Severity: normal

Dear Maintainer,

after upgrading libvirt-daemon from 1.3.5-1 to 2.0.0-1 I am unable to 
start a virtual machine which is configured with these CPU settings:

<domain type='kvm'>
   <name>foobar</name>
   <uuid>05a431db-0927-4ce2-8fb9-2830c962fa2d</uuid>
   <memory unit='KiB'>1048576</memory>
   <currentMemory unit='KiB'>1048576</currentMemory>
   <vcpu placement='static'>4</vcpu>
   <resource>
     <partition>/machine</partition>
   </resource>
   <os>
     <type arch='x86_64' machine='pc-i440fx-2.1'>hvm</type>
     <bootmenu enable='yes'/>
   </os>
   <features>
     <acpi/>
     <apic/>
     <pae/>
   </features>
   <cpu mode='host-model'>
     <model fallback='allow'/>
   </cpu>
[...]

Important is the <cpu mode='host-model'>. With libvirt-daemon 1.3.5-1 
this worked just fine but now you receive an error like this after 
turning a machine (which was live migrated to the updated host) off and 
on again:

"qemu-system-x86_64: CPU feature cmt not found"

Starting the same machine with these settings works as expected:
   <cpu mode='custom' match='exact'>
     <model fallback='allow'>Haswell-noTSX</model>
   </cpu>

I think that this patch is causing the error for our CPUs (see below): 
http://libvirt.org/git/?p=libvirt.git;a=commit;h=f294b83ee632a6330f3a3045fbb5bcb9d9951c03

Does the E5-2630 really support CMT? Since I can't find any specific 
information for this it's hard to guess if it is a problem with the 
patch or with the Debian system - maybe we have to enable CMT here 
somehow? That's why I open this bug report here and not upstream.

Commenting this out in /usr/share/libvirt/cpu_map.xml solves the issue 
as a workaround:

<!--    <feature name='cmt'>
       <cpuid eax_in='0x07' ebx='0x00001000'/>
     </feature> -->

Best Regards,
Ansgar


cat /proc/cpuinfo
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 63
model name      : Intel(R) Xeon(R) CPU E5-2630 v3 @ 2.40GHz
stepping        : 2
microcode       : 0x27
cpu MHz         : 1200.000
cache size      : 20480 KB
physical id     : 0
siblings        : 16
core id         : 0
cpu cores       : 8
apicid          : 0
initial apicid  : 0
fpu             : yes
fpu_exception   : yes
cpuid level     : 15
wp              : yes
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 pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good 
nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 
monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid dca 
sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c 
rdrand lahf_lm abm epb tpr_shadow vnmi flexpriority ept vpid fsgsbase 
tsc_adjust bmi1 avx2 smep bmi2 erms invpcid cqm xsaveopt cqm_llc 
cqm_occup_llc dtherm ida arat pln pts
bugs            :
bogomips        : 4799.73
clflush size    : 64
cache_alignment : 64
address sizes   : 46 bits physical, 48 bits virtual
power management: