Issue with Starting VM When Assigning AMD EPYC CPU Model & Query on CPU Auto-scaling Similar to vSphere

[Kuldeep.Roy]

Hello,

I'm facing an issue when trying to assign an AMD EPYC processor model to a virtual machine in Proxmox. The VM fails to start and I receive the following error from QEMU:

kvm: warning: host doesn't support requested feature:
CPUID.07H:EBX.clflushopt [bit 23]
kvm: warning: host doesn't support requested feature:
CPUID.07H:EBX.sha-ni [bit 29]
kvm: warning: host doesn't support requested feature:
CPUID.80000001H:EDX.mmxext [bit 22]
kvm: warning: host doesn't support requested feature:
CPUID.80000001H:EDX.fxsr-opt [bit 25]
kvm: warning: host doesn't support requested feature:
CPUID.80000001H:ECX.cr8legacy [bit 4]
kvm: warning: host doesn't support requested feature:
CPUID.80000001H:ECX.sse4a [bit 6]
kvm: warning: host doesn't support requested feature:
CPUID.80000001H:ECX.misalignsse [bit 7]
kvm: warning: host doesn't support requested feature:
CPUID.80000001H:ECX.osvw [bit 9]
kvm: warning: host doesn't support requested feature:
CPUID.80000001H:ECX.perfctr-core [bit 23]
kvm: warning: host doesn't support requested feature:
CPUID.80000008H:EBX.clzero [bit 0]
kvm: warning: host doesn't support requested feature:
CPUID.80000008H:EBX.xsaveerptr [bit 2]
kvm: warning: host doesn't support requested feature:
CPUID.0DH:EAX.xsavec [bit 1]
kvm: warning: host doesn't support requested feature:
CPUID.0DH:EAX.xgetbv1 [bit 2]
kvm: warning: host doesn't support requested feature:
CPUID.0DH:EAX.xsaves [bit 3]
kvm: Host doesn't support requested features
TASK ERROR: start failed: QEMU exited with code 1

Host Details:​

• Proxmox Version: 8.1.4
• Kernel Version: 6.5.11-8-pve
• CPU: Intel Xeon E5-2696 v4 (88 cores)
• Boot Mode: Legacy BIOS

Problem:​

When I try to assign the AMD EPYC CPU model to the VM, QEMU throws a host doesn't support requested features error, indicating that the required CPU features aren't supported by the host. However, the host CPU is Intel, which is why I suspect these features aren’t compatible with the physical CPU.

Steps Taken:​

• Tried assigning the AMD EPYC processor model directly in the Proxmox VM configuration.
• The VM fails to start and throws the error listed above.

Question:​

• CPU Model Compatibility: Is there any workaround to get AMD EPYC processor models working in Proxmox when the host CPU is Intel? Alternatively, should I be using a different CPU model (e.g., host or kvm64)? Any insights into how to resolve this would be appreciated.
  
  
• CPU Auto-scaling like vSphere: In vSphere, there’s an option to dynamically scale the CPU allocation based on the VM’s demand (auto-scaling), where the VM can request more CPUs if needed, without hitting a hard cap. Does Proxmox have a similar mechanism for CPU auto-scaling, or do the CPU limits need to be manually adjusted for each VM?

 

[BobhWasatch]

PVE won't emulate features that the underlying CPU does not have, it only hides/reveals them from the VM. The use-case is for when you have different CPU's of the same family in a cluster and you want to be able to migrate. If you have an Intel CPU you can't expect that you can pretend it is an AMD one. There is no workaround for this.

As far as auto-scaling, you could look into CPU hot-plugging. I don't know of any other way to dynamically add/remove CPU's. On the other hand, why? CPU's are not hard-assigned to a VM. VM threads are scheduled on CPU's according to need.

 

[alexskysilk]

Is there any workaround to get AMD EPYC processor models working in Proxmox when the host CPU is Intel? Alternatively, should I be using a different CPU model (e.g., host or kvm64)? Any insights into how to resolve this would be appreciated.

@BobhWasatch covered the limits, but before we just close this I do have to wonder WHY you want to do this? If the requirement is to be able to migrate between different types of processor/HAL, you would need to choose a qemu "processor" type that covers the features of both. yes, KVM64 would work but unless you're using really old hardware you'd probably want something that exposes more modern features, eg x86-64-v2-aes or better.

As for cpu scaling, again, the question is why? just assign the maximum possible required cpu to the vm and let the hypervisor manage actual usage. You're allowed to oversubscribe your host