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

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 6/17/20 10:23 AM, Philippe Mathieu-Daudé wrote:
> On 6/11/20 11:14 AM, Andrew Jones wrote:
>> 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?
> 
> Sorry for some reason I missed this email. I'll look at this today.

Quick reproducer:

$ qemu-system-aarch64 -cpu host,pmu=on -M virt,accel=kvm,gic-version=3
Segmentation fault (core dumped)

Eduardo, I thought we had a 'machine' qtest testing for various
combination of properties, but I can't find it, do you remember?
Or maybe it was Thomas? Or Markus? =)

> 
>>
>> Thanks,
>> drew
>>
>