> Could it be address space randomisation having an effect?
Not sure, since I explicitly disabled kaslr. I appended nokaslr in the GRUB command line. With kaslr enabled it's not possible to access any of the virtual address in the kernel space.
The thing is removing --enable-kvm -cpu host makes it possible to break on e.g. start_kernel() when running with -S option. While adding --enable-kvm -cpu produces "Cannot access address" errors when trying to break only on init function like start_kernel() (also run with -S option) . But it's still completely fine to break on, e.g. sys_read or any other syscall entry point.