Pxe boot issue with VM using UEFI BIOS + x86-64-v* CPU type

[deebsr]

So it seems like we are seeing an issue where if we have a VM that uses UEFI BIOS type but also with any of the x86-64-v* CPU types we don't see any Pxe boot options.
If we switch the CPU type to say "host" the Pxe boot option appears. It also works with "Skylake-Server-v4" type.
I'm not sure if there is something I'm missing here?
I'm surprised that I'm seeing this behavior as I thought the boot order options was a function of the BIOS not the CPU type

I attached are some screenshots showing the difference in the boot menu between having CPU type = host vs any of the x86-64 types.
We would like to use the x86-64 type in order for us to migrate between our hosts and clusters of different CPU families easily.

Are other people seeing this?

PVE: 9.1.4 and 9.1.6 ( latest on no subscription repo )

build a VM
BIOS = OVMF (UEFI )
CPU type = choose any of the x86-64-v*

Boot up and enter boot menu. Do you see a selection of Pxe boot options?
Switch CPU type to something else ( host, Skylake-Server-v*, etc ). Do you know see the pxe boot options

 

[deebsr]

So digging into this a bit more it seems that the x86-64-v* CPu types are missing the RDRAND an RDSEED instructions. These are apparently needed for EFI to generate the entropy during the init. Adding the VirtIO RNG to the VM now allows us to boot using PXE while also using the x86-64-v4 CPU type to maintain migration capability.

So why is this being blocked on these CPU types? it would be much cleaner solution to allow us to use the rng being passed from the CPU rather than have to use the host OS and pass that though....
Looking at Vmware EVC modes it seems like they pass the RDRAND and RDSEED instructions with their masking?

To me this seems like a bug? Seems odd to have to request this as a "feature"

 

[deebsr]

So this issue seems to have been around since way back from 8.4 days:
https://forum.proxmox.com/threads/proxmox-ve-8-4-0-unable-to-pxe-boot-under-ovmf.168220/

I'm not convinced that adding he Virtio RNG device is the actual fix to this issue. Rather there needs to be something looked at deeper in how the CPU types that are offered are masking out the CPU instructions that bring in this function ( RDRAND and RDSEED ).