Bug 1290324

Summary: libvirt should forbid set current cpu is 0 in xml
Product: Red Hat Enterprise Linux 7 Reporter: Luyao Huang <lhuang>
Component: libvirtAssignee: Peter Krempa <pkrempa>
Status: CLOSED ERRATA QA Contact: Virtualization Bugs <virt-bugs>
Severity: medium Docs Contact:
Priority: low    
Version: 7.2CC: dyuan, mzhan, pkrempa, rbalakri
Target Milestone: rc   
Target Release: ---   
Hardware: x86_64   
OS: Linux   
Whiteboard:
Fixed In Version: libvirt-1.3.2-1.el7 Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2016-11-03 18:49:33 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description Luyao Huang 2015-12-10 08:55:19 UTC 
Description of problem:

libvirt should forbid set current cpu to 0

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

libvirt-1.2.17-13.el7_2.2.x86_64
How reproducible:
100%

Steps to Reproduce:
1. prepare a inactive guest:

# virsh list --all
 Id    Name                           State
----------------------------------------------------
 -     RHEL71-lhuang-novhost          shut off

2. edit guest xml and make current cpu to 0:

  <vcpu placement='static' current='0'>16</vcpu>

# virsh edit RHEL71-lhuang-novhost
error: XML document failed to validate against schema: Unable to validate doc against /usr/share/libvirt/schemas/domain.rng
Extra element vcpu in interleave
Invalid sequence in interleave
Element domain failed to validate content

Failed. Try again? [y,n,i,f,?]:
Domain RHEL71-lhuang-novhost XML configuration edited.

3. check xml:

# virsh dumpxml RHEL71-lhuang-novhost | grep current
  <currentMemory unit='KiB'>1153433</currentMemory>
  <vcpu placement='static' current='0'>16</vcpu>

4. try to start this guest:

# virsh start RHEL71-lhuang-novhost
error: Failed to start domain RHEL71-lhuang-novhost
error: internal error: got wrong number of vCPU pids from QEMU monitor. got 16, wanted 0

5. try some command:

# virsh vcpupin RHEL71-lhuang-novhost
error: ncpumaps in virDomainGetVcpuPinInfo must be greater than zero
 
# virsh vcpuinfo RHEL71-lhuang-novhost
error: ncpumaps in virDomainGetVcpuPinInfo must be greater than zero

Actual results:

libvirt allow set current vcpu to 0, but it doesn't make sense 

Expected results:

forbid it

Additional info:
Comment 1 Peter Krempa 2016-01-25 16:55:52 UTC 
commit b3c91b8a50ac0d772f883e737252202d48658139
Author: Peter Krempa <pkrempa>
Date:   Wed Jan 6 16:27:45 2016 +0100

    qemu: process: Disallow VMs with 0 vcpus
    
    Counterintuitively the user would end up with a VM with maximum number
    of vCPUs available.
    
    Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1290324

v1.3.1-44-gb3c91b8
Comment 3 Luyao Huang 2016-08-09 01:54:46 UTC 
Verify this bug with libvirt-2.0.0-4.el7.x86_64:

1. edit guest with current vcpu = 0:

# virsh dumpxml r7 |grep current=
  <vcpu placement='static' current='0'>10</vcpu>

2. try to start guest and libvirt report an error:

# virsh start r7
error: Failed to start domain r7
error: unsupported configuration: Domain requires at least 1 vCPU

3. try other command:

# virsh vcpucount r7
maximum      config        10

# virsh vcpuinfo r7
error: ncpumaps in virDomainGetVcpuPinInfo must be greater than zero

# virsh vcpupin r7
VCPU: CPU Affinity
----------------------------------
   0: 0-23
   1: 0-23
   2: 0-23
   3: 0-23
   4: 0-23
   5: 0-23
   6: 0-23
   7: 0-23
   8: 0-23
   9: 0-23
Comment 5 errata-xmlrpc 2016-11-03 18:49:33 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHSA-2016-2577.html