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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.