Bit of an odd situation, I've installed Windows Server 2022 (desktop experience) on a server, installed MegaStorage MSM and the relevant drivers from Supermicro and any Windows updates. When I install the role HyperV (just the Windows feature Hyper V, not any VMs), my host goes from 8c16t to 1c1t. I thought it might be a visual bug, but it runs like a snail stuck in syrup, so it seems like it's running on 1c. The L1 and L2 caches reported by Task Manager are also altered, but the reported caches are 1/8s of total cache, so it fits the core reduction.
I'm not experienced with Server 2022, and I've only really set up HyperV and VMs on Windows 7/10/11 as well as VirtualBox previously, so it's entirely possible this is amateur hour and I've forgotten to set/install something basic and obvious.
As for the usual suspects, I've double checked BIOS settings (originally set by the hardware supplier) and everything VT-related looks enabled. The msconfig -> Boot -> Advanced -> "Number Of Processors" check box is unchecked.
I suppose maybe the correct way to do it is to use HyperV 2019 (since MS has not released a 2022 version) as the host, and use my licensed 2022 as the guest VM, I'll try that next as the supplier suggested it might be a Server 2022 software issue.
The system in question:
Motherboard: Supermicro X11SPL-F running 3.6 BIOS
CPU: Intel Xeon Silver 4208SP 8c16t
RAM: 16GB DDR4 3200MHz ECC Registered 2Rx8 Samsung x4
Controller: Avago/Broadcom/LSI/whatever the flavour of the month SAS9341-8i
Storage: 2x Samsung PM883 SSD 960GB running RAID1
Here are screenshots of the feature list, Task Manager and Device Manager before and after: https://ibb.co/v1mP8Zn https://ibb.co/6Z6xj7C
Update: I installed Windows Server 2019 (evaluation edition, no license) and this doesn't happen at all. HyperV goes in, CPU remains 8c16t. I upgraded that install with HyperV enabled from Server 2019 (eval) to Server 2022 (licensed) and the upgrade reduces my host CPU to 1c1t.
#2: Edit: Corrected feature to role.
I went through the logs and there's an error being thrown just after HyperV is installed.
Event 97: "Hypervisor processor startup failed (APIC ID 0x0) due to CPUID feature validation error. Further processors in the system were not started. Leaf 0x1, register 0x2 feature mismatch: BSP has features 0x77FEFBF7; AP has features 0x0". I see other people have reported this error for previous Windows Server versions.
My exact CPU specs are:
Processor Name: Intel(R) Xeon(R) Silver 4208 CPU @ 2.10GHz
Type : 0 Family : 6
Model : 55
Stepping : 7
Revision: 500320A