Bug 1355857 - CPU feature cmt not found with 2.0.0-1
Summary: CPU feature cmt not found with 2.0.0-1
Alias: None
Product: Virtualization Tools
Classification: Community
Component: libvirt
Version: unspecified
Hardware: x86_64
OS: Linux
Target Milestone: ---
Assignee: Jiri Denemark
QA Contact:
Depends On:
Blocks: 1365500
TreeView+ depends on / blocked
Reported: 2016-07-12 18:20 UTC by redhatbugreports_541234
Modified: 2016-08-10 12:30 UTC (History)
6 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
: 1365500 (view as bug list)
Last Closed: 2016-08-10 12:30:13 UTC

Attachments (Terms of Use)

System ID Priority Status Summary Last Updated
Debian BTS 830857 None None None 2016-07-12 18:20:28 UTC

Description redhatbugreports_541234 2016-07-12 18:20:29 UTC
Description of problem:
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 <cpu mode='host-model'>. With libvirt-daemon 1.3.5-1 this worked just fine. Now you receive an error like that one below when turning a machine (which was live migrated to the updated host) off and on again.

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

I think that this patch is causing the error for our CPUs (see below): 

Does the E5-2630 really support CMT? Since I can't find any specific 
information for this (it's missing here: http://www.intel.de/content/www/de/de/communications/cache-monitoring-cache-allocation-technologies.html) it's hard to guess if it is a problem with the 
patch or with the system - maybe we have to enable CMT here somehow?

As far as I understand this topic (http://www.spinics.net/linux/fedora/libvir/msg132822.html) this error is by design but shouldn't be the "mode='host-model'" support dropped since it cause errors? Maybe someone can explain this here :-)

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,

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
1. Create a virtual machine with this CPU configuration:

<domain type='kvm'>
  <memory unit='KiB'>1048576</memory>
  <currentMemory unit='KiB'>1048576</currentMemory>
  <vcpu placement='static'>4</vcpu>
    <type arch='x86_64' machine='pc-i440fx-2.1'>hvm</type>
    <bootmenu enable='yes'/>
  <cpu mode='host-model'>
    <model fallback='allow'/>

2. Start virtual machine

Actual results:
Start fails with this error:
"qemu-system-x86_64: CPU feature cmt not found"

Expected results:
Virtual machine should start without errors

Additional info:
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:

Comment 1 Jiri Denemark 2016-08-09 13:59:41 UTC
Patches sent upstream for review: https://www.redhat.com/archives/libvir-list/2016-August/msg00486.html

Comment 2 Jiri Denemark 2016-08-10 12:30:13 UTC
This bug is now fixed in libvirt.git by

commit dbb14bb0f1316d92c89541fca816c91dce0dc8fb
Refs: v2.1.0-108-gdbb14bb
Author:     Jiri Denemark <jdenemar@redhat.com>
AuthorDate: Tue Jun 28 10:51:41 2016 +0200
Commit:     Jiri Denemark <jdenemar@redhat.com>
CommitDate: Wed Aug 10 14:25:24 2016 +0200

    cpu_x86: Introduce x86FeatureIsMigratable

    Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
 src/cpu/cpu_x86.c | 37 +++++++++++++++++++++++--------------
 1 file changed, 23 insertions(+), 14 deletions(-)

commit 1ac897a15da11d1bfca2642bce3b0beaad32bcf1
Refs: v2.1.0-109-g1ac897a
Author:     Jiri Denemark <jdenemar@redhat.com>
AuthorDate: Tue Jun 28 11:12:41 2016 +0200
Commit:     Jiri Denemark <jdenemar@redhat.com>
CommitDate: Wed Aug 10 14:25:24 2016 +0200

    cpu_x86: Properly drop non-migratable features

    By removing a non-migratable feature in a for loop we would fail to drop
    every second non-migratable feature if the features array contained
    several of them in a row.

    Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
 src/cpu/cpu_x86.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

commit 58ba240df89a7dd7bff16ebb65d9aadd49fb8bbb
Refs: v2.1.0-110-g58ba240
Author:     Jiri Denemark <jdenemar@redhat.com>
AuthorDate: Tue Aug 9 15:03:20 2016 +0200
Commit:     Jiri Denemark <jdenemar@redhat.com>
CommitDate: Wed Aug 10 14:25:24 2016 +0200

    tests: Add a test for host-model CPU with CMT feature

    The generated command line wouldn't work since QEMU doesn't know what
    'cmt' is. The following patch will fix this issue.


    Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
 tests/qemuxml2argvdata/qemuxml2argv-cpu-host-model-cmt.args | 22 ++++++++++++++++++++++
 tests/qemuxml2argvdata/qemuxml2argv-cpu-host-model-cmt.xml  | 19 +++++++++++++++++++
 tests/qemuxml2argvtest.c                                    |  1 +
 tests/testutilsqemu.c                                       |  1 +
 4 files changed, 43 insertions(+)

commit 300f668c665f1ec0f834917fe8a58b5991322441
Refs: v2.1.0-111-g300f668
Author:     Jiri Denemark <jdenemar@redhat.com>
AuthorDate: Tue Aug 9 15:15:20 2016 +0200
Commit:     Jiri Denemark <jdenemar@redhat.com>
CommitDate: Wed Aug 10 14:25:24 2016 +0200

    cpu_x86: Fix host-model CPUs on hosts with CMT

    Since the introduction of CMT features (commit v1.3.5-461-gf294b83)
    starting a domain with host-model CPU on a host which supports CMT fails
    because QEMU complains about unknown 'cmt' feature:

        qemu-system-x86_64: CPU feature cmt not found


    Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
 src/cpu/cpu_x86.c                                           | 8 ++++++--
 tests/qemuxml2argvdata/qemuxml2argv-cpu-host-model-cmt.args | 2 +-
 2 files changed, 7 insertions(+), 3 deletions(-)

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