Exceptions if mixing Cortex-A76 and Cortex-A55 for KVM vendor kernel 6.1.75

[eselarm]

qemu-system-aarch64 -M virt -cpu host -enable-kvm ...

only works reliably when 1 CPU core ( -smp 1). When a VM has 2 cores, it randomly worked I experienced. If virt-manager pick 2 equal cores, VM UEFI/BIOS/kernel runs OK, but if a Cortex-A76 and Cortex-A55, all sorts of exceptions are shown or just lockup 2x or 1x 100% usage.

 

In order to still be able to use KVM, start qemu-system-aarch64 as follows:

taskset --cpu-list 4-7 qemu-system-aarch64 -M virt -cpu host -enable-kvm -smp 4 ...

or

taskset --cpu-list 0-3 qemu-system-aarch64 -M virt -cpu host -enable-kvm -smp 4 ...

 

Mainline kernel 6.8.x or later does not have this problem. It can transparently use all 8 cores.

 

Userspace is Debian Bookworm based.