Remove single CPU Flag

[Nerion]

Hello,

we give all our VMs the CPU Typ: host
Now we have the problem, that live migration is not working, because not all Hardware Nodes have extactly the same CPU. The Flags of the CPU does not fully match.
So we need to remove the following flags:
-mpx | -sgx | -sha
virtual-address-bits = 48

How can we do that?

CPUs we have:
- Intel(R) Xeon(R) Gold 6442Y
- Intel(R) Xeon(R) Silver 4316
- Intel(R) Xeon(R) Gold 5218R

So to have the same flat set, we need to do the changes described above.

Thanks
Best Regards

Marco

 

[zzz09700]

I guess you shouldn't be giving VMs host CPU type if you want live migration and AFAIK masking out CPU flags only on VMs when using host mode is not possible, you'll probably mask those flags on your host OS.

The qemu man page explicitly says this:
Live migration is unsafe when this mode is used as libvirt / QEMU cannot guarantee a stable CPU is exposed to the guest across hosts.

 

[Nerion]

How can I mask flags on the host OS?

I know best is to use virtual cpus, but which Virtual CPU Typ should I use to match all of these CPU. I didn't found the right one.
x86-64-v4 has too less features

Thanks
Best Regards

Marco

 

[zzz09700]

Try this:
https://qemu-project.gitlab.io/qemu/system/qemu-cpu-models.html

 

[Nerion]

I know this page, but I don't know how this could help me.

 

[leesteken]

I know this page, but I don't know how this could help me.

I have not checked your CPU families in detail, but can't you simply select the highest Icelake-Server CPU-model in Proxmox that matches your lowest CPU type?

 

[zzz09700]

I know this page, but I don't know how this could help me.

In a deployment with amixture of host CPU models between machines, if live migrationcompatibility is required, use the newest CPU model that is compatibleacross all desired hosts.

So you'll want something that goes with Skylake-Server

 

[Nerion]

That's exactly the problem. None of the Icelake-Server virtual CPU Models are working.

 

[leesteken]

That's exactly the problem. None of the Icelake-Server virtual CPU Models are working.

Is Proxmox giving an error message (what error message exactly?) or does it not support the features your software needs?

 

[Nerion]

Wondering that on host with Intel(R) Xeon(R) Gold 6442Y which is a SapphireRapids generation is not working.
Error message:

Virtual CPU: SapphireRapids
kvm: warning: host doesn't support requested feature: CPUID.07H:EBX.hle [bit 4]
kvm: warning: host doesn't support requested feature: CPUID.07H:EBX.rtm [bit 11]
kvm: warning: host doesn't support requested feature: MSR(10AH).taa-no [bit 8]

Virtual CPU: Icelake-Server-v6
kvm: warning: host doesn't support requested feature: MSR(10AH).taa-no [bit 8]

 

[Nerion]

What is Virtual CPU Type: Max?