Re: Core dump happened when starting a VM on arm64 server

[Andrew Jones]

On Thu, Jun 11, 2020 at 04:46:45PM +0800, Haibo Xu wrote:
> Hi,
> 
> I met a qemu core dump issue when starting a VM with cpu feature
> "pmu=on" on an arm server.
> The commands to start the machine is:
> 
>   ./qemu-system-aarch64 \
>            -cpu host,pmu=on -M virt,accel=kvm,gic-version=3 -nographic
> -m 2048M \
>            -kernel ./Image \
>            -initrd /boot/initrd.img-5.6.0-rc2+ \
>            -append "root=/dev/vda rw console=ttyAMA0" -nodefaults -serial 
> stdio\
>            -drive if=none,file=./xenial.rootfs.ext4,id=hd0,format=raw \
>            -device virtio-blk-device,drive=hd0
> 
> 
> And here is the stack dump:
> 
>  Core was generated by `./qemu-system-aarch64 -cpu host,pmu=on -M
> virt,accel=kvm,gic-version=3 -nograph'.
>  Program terminated with signal SIGSEGV, Segmentation fault.
>  #0  kvm_ioctl (s=0x0, type=type@entry=44547) at

s=0x0 means cpu->kvm_state is NULL

> The root cause is in the arm_get_pmu() operation which was introduced
> in ae502508f83.

Actually the root cause is d70c996df23f ("target/arm/kvm: Use
CPUState::kvm_state in kvm_arm_pmu_supported()"). ae502508f83 used
the machine kvm_state, not the cpu kvm_state, and that allows pmu=on
to work. d70c996df23f changed that saying that "KVMState is already
accessible via CPUState::kvm_state, use it.", but I'm not sure why,
since kvm_init_vcpu() doesn't run until the vcpu thread is created.

Philippe?

Thanks,
drew