Bug 1631754

Description of problem:

I was able to reproduce this issue in my test environment: 

Installed a RHEL 7.5 KVM HOST. 

Further installed a RHEL 6.9 vm with 1 Core, 2 Threads, below are the outputs on it. 

# uname -a
Linux rhel610 2.6.32-696.el6.x86_64 #1 SMP Tue Feb 21 00:53:17 EST 2017 x86_64 x86_64 x86_64 GNU/Linux

# uname -r
2.6.32-696.el6.x86_64

# lscpu
Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                2
On-line CPU(s) list:   0,1  <<<<<<<
Thread(s) per core:    2  <<<<<<< 
Core(s) per socket:    1
Socket(s):             1
NUMA node(s):          1
Vendor ID:             GenuineIntel
CPU family:            6
Model:                 60
Model name:            Intel Core Processor (Haswell)
Stepping:              1
CPU MHz:               2397.222
BogoMIPS:              4794.44
Hypervisor vendor:     KVM
Virtualization type:   full
L1d cache:             32K
L1i cache:             32K
L2 cache:              4096K
NUMA node0 CPU(s):     0,1

# Then ran yum update -y on the machine and rebooted it: 

# uname -r
2.6.32-754.3.5.el6.x86_64

# uname -a
Linux rhel610 2.6.32-754.3.5.el6.x86_64 #1 SMP Thu Aug 9 11:56:22 EDT 2018 x86_64 x86_64 x86_64 GNU/Linux

# lscpu 
Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                2
On-line CPU(s) list:   0  <<<<<<<
Off-line CPU(s) list:  1   <<<<<<<
Thread(s) per core:    1   <<<<<<<
Core(s) per socket:    1
Socket(s):             1
NUMA node(s):          1
Vendor ID:             GenuineIntel
CPU family:            6
Model:                 60
Model name:            Intel Core Processor (Haswell)
Stepping:              1
CPU MHz:               2397.222
BogoMIPS:              4794.44
Hypervisor vendor:     KVM
Virtualization type:   full
L1d cache:             32K
L1i cache:             32K
L2 cache:              4096K
NUMA node0 CPU(s):     0



How reproducible:


Steps to Reproduce:
1. Installed a RHEL 7.5 kvm host
2. Then installed RHEL 6.9 vm with 1 Core, 2 Threads, verify this in lscpu command 
3. Upgrade the system to latest version i.e RHEL 6.10, after upgrading see only 1 thread and cpu, see highlighted part here.  

Actual results:

Got: 1 Core, 1 Thread after upgrade to 2.6.32-754.3.5.el6.x86_64

Expected results:

Expected: 1 Core, 2 Threads after the upgrade

Additional info: 

Customer have tested this on Hypervisor with RHEL 6 and Hypervisor with RHEL 7 both the same issue is seen.