[SOLVED] Kernel panic installing rocky or almalinux

Proximate

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Feb 13, 2022
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Solved by using CPU 'host' option during guest creation.


I'm not sure if this is actually a proxmox issue but I'm posting to see if anyone else has found a way to get past this.
The installer runs but then I get a kernel panic on install.
I've tried on several nodes, all running 7.2. The reason I don't think it's proxmox is because the exact same thing happens trying to install almalinux.
The post is mainly looking for others that may have solved this issue so that I can get back to installing.

Thanks.

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The root cause of this issue is the compilation of RHEL 9 and it's derivatives to use the x86-64-v2 instruction set https://developers.redhat.com/blog/...ground_of_the_x86_64_microarchitecture_levels

More info at https://forums.rockylinux.org/t/el9-will-require-x86-64-v2-support/5311

In summary, it is NOT a Proxmox/QEMU issue. It's a CPU issue.

Please mark this thread as SOLVED.
The choice of CPU type for the Proxmox VM does matter, though.
The "kvm64" default does not work while eg "host" works fine on modern hardware. I'm not sure what exactly the lowest working option is.
 
So what is the answer since 'host' does allow it to install? Does it mean some guest limitations or something not so obvious initially?
It may not be a proxmox issue specifically but an answer could help someone else trying to install these operating systems.

I've installed it and it seems to be running fine so far.
 
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So what is the answer since 'host' does allow it to install? Does it mean some guest limitations or something not so obvious initially?

CPU-type host is recommended for best performance and all CPU-feature-flags inside the VM anyway; unless you need live-migration between different platforms and/or perhaps even different generations.

[0] https://pve.proxmox.com/pve-docs/chapter-qm.html#qm_cpu (CPU Type)
 
So what is the answer since 'host' does allow it to install? Does it mean some guest limitations or something not so obvious initially?
It may not be a proxmox issue specifically but an answer could help someone else trying to install these operating systems.

I've installed it and it seems to be running fine so far.
It means that the CPU, as seen by EL9 (what is exposed to the guest in the VM scenario), must support the x86-64-v2 feature set.

Ie, the host CPU must support it, but also the CPU type setting on the VM must not hide any of the v2 features (which for example the "kvm64" setting does).
 
From the link shared;

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This has a downside though. If you want to do a live migration of VMs between
different hosts, your VM might end up on a new system with a different CPU type.
If the CPU flags passed to the guest are missing, the qemu process will stop.
To remedy this Qemu has also its own CPU type kvm64, that Proxmox VE uses by
defaults. kvm64 is a Pentium 4 look a like CPU type, which has a reduced CPU
flags set, but is guaranteed to work everywhere.

In short, if you care about live migration and moving VMs between nodes, leave
the kvm64 default. If you don’t care about live migration or have a homogeneous
cluster where all nodes have the same CPU, set the CPU type to host, as in theory
this will give your guests maximum performance.

Wondering why it's not possible to force the same CPU setting on live migration. Is this something being thought about or is it impossible.
Is it only 'host' that affects live migration or picking any non default?

It also mentions 'maximum performance' if your CPUs are the same across hosts but doesn't say if that means live migration will or has a better chance to work?

Oddly, live migration was something I wanted to test next at some point.
 
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If the nodes in your cluster have the same CPU family type, live migration should work with the VM CPU type set to 'host'.

For example, I can live migrate between a R720 and R820 because they both have Sandy Bridge CPUs.
 
Thanks all for the direction.
I managed to get going after changing the CPU type to 'host' when creating the VM (Rocky Linux 9). Not getting that panic error anymore.
 
Well this is an Issue.

Are we expecting "AlmaLinux/Rocky Linux/Red Hat Linux" to fix this by requesting them to recompile it and repackage the ISO?
Is there something that the Proxmox Team can do regarding updating KVM64?
 
Well this is an Issue.

Are we expecting "AlmaLinux/Rocky Linux/Red Hat Linux" to fix this by requesting them to recompile it and repackage the ISO?
Is there something that the Proxmox Team can do regarding updating KVM64?
We should definitely not expect RHEL and their derivates to change their hardware requirements.
I also don't really expect Proxmox to change the definition of "kvm64" (as that would break other things).

But I think it would be good if Proxmox added:
* a setting for which CPU level to use for any newly created VMs
* a "kvm64-2" or similar new generic level that corresponds to the "x86-64-v2" requirements (maybe one of the existing levels is already good for this, idk)

But as noted earlier in the thread, for now, if you don't need to be able to migrate VMs within a cluster, you can even pick "host", which exposes the full feature set of the host CPU. Or otherwise any other level that fulfills the RHEL9 system requirements and is compatible with the CPUs of all your cluster nodes.
 
Thanks for the update @fabian

Is this suggesting that when I change the CPU to "nahelem", that I do not have AES flag enabled when I run the VM?
I hope the Proxmox developers could create a patch soon. Most of the enterprises that I've worked with that do Software Development run on the Red Hat Family as opposed to Debian and Ubuntu.

By the way, where does Debian / Ubuntu sit in regards to 'microarchitecture' topic?

Cheers!
 

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