NUMA CPUs do not appear in KVM guest the same as they do on a physical machine

Issue

• NUMA CPUs do not appear in KVM guest the same as they do on a physical machine

• Looking at the NUMA CPU list, a physical machine appears differently to a KVM guest, despite the fact NUMA nodes are configured in the guest XML

• Guest XML contains interleaved CPUs like:

  <cpu>
    <numa>
      <cell cpus='0,2,4,6,8,10,12,14,16,18,20,22' memory='524288'></cell>
      <cell cpus='1,3,5,7,9,11,13,15,17,19,21,23' memory='524288'></cell>
    </numa>
  </cpu>
  

• CPU Node list appears like:

  $ cat /sys/devices/system/node/node0/cpulist 
  0,2-23
  $ cat /sys/devices/system/node/node1/cpulist 
  1
  

  But the physical NUMA layout is:

  $ cat /sys/devices/system/node/node0/cpulist
  0,2,4,6,8,10,12,14,16,18,20,22
  $ cat /sys/devices/system/node/node1/cpulist
  1,3,5,7,9,11,13,15,17,19,21,23
  

• The numactl hardware layout shows all CPUs except one in a NUMA Node inside the guest.

• Starting a KVM guest on RHEL7 fails with:

  error: Failed to start domain guestname
  error: unsupported configuration: disjoint NUMA cpu ranges are not supported with this QEMU