VMXNET3 BUG

ESXi VM – The CPU has been disabled by the guest operating system

For some weeks now, a couple of my virtual machines on ESXi would stop working out of nowhere. They were completely unresponsive (including via the ESXi VM Console). Nothing would help, except a shutdown / start of the VM. Just to find out later that, randomly, the VM would become unresponsive again.

The only human readable information about these failures was in the ESXi host Events and was saying something like this (among other things):

 The CPU has been disabled by the guest operating system

One other thing which I should mention is that all my VM encountering this issue where Linux based, mainly Ubuntu 20.04 as OS distribution.

Not much to work with, but I gave it a try and searching for the error did point me to this VMware KB: https://kb.vmware.com/s/article/2000542

The KB is clearly accurate, just that it didn’t help me at all to resolve my problem. The troubleshooting process explain in the KB lead me to a dead end.

Other web resources (for the above error) pointed to articles which explained a procedure for VMware Workstation / Player. Not my case, since I’m using ESXi.

More research done, which took a while – that’s why I’m writing this article, hopefully others with this problem will find it easier – pointed to a BUG. Seems this BUG is a particular case between my VM Linux kernel and the version of the ESXi I’m using currently.

I’ve arrived to this VMware KB https://kb.vmware.com/s/article/2151480 which was a game changer. In my case this KB was hard to find, because the title – Linux VM fails with the error “kernel BUG at drivers/net/vmxnet3/vmxnet3_drv.c:1413!” (2151480) – is completely different than the error I was seeing and which I used searching the web.

Skipping the long output at the beginning of the KB, I saw something interesting in lower part of the page:

This issue occurs due to a bug in VMXNET3 vNIC backend which is part of the vmkernel. This issue occurs if the following conditions are met:

    Linux VM is running kernel >= 4.8
    HW version of VM is >=13
    ESXi version is 6.5

All the above fits my scenario, VMXNET3 as vNIC, Kernel 5.4, VM HW version 13 and ESXi 6.5

Like in most of BUG cases, the obvious solution is upgrade. Same here:

This issue is resolved in VMware ESXi 6.5 U1

Just that I cannot upgrade now for various reasons.

So, I’ve decide to look into the workarounds.

Second workaround on the page seems to be more simple and I don’t even have to restart the VM:

ethtool -G ethX rx-mini 0

Of course replace the ethX with your interface name.

Worked like a charm without any visible side-effects.

The other workaround is also doable, but I didn’t want to modify the .vmx file

Power off the virtual machine
         
Edit the vmx file and add the below parameter:
vmxnet3.rev.30 = FALSE
         
Power on the virtual machine

Now I’m just curious if I would encounter the same issues using another vNIC adapter type, like E1000 or E1000E instead of VMXNET3. Maybe I’ll give it a try…

Published by

Calin

Calin is a network engineer, with more than 15 years of experience in designing, installing, troubleshooting, and maintaining large enterprise WAN and LAN networks.

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