Re: [Qemu-devel] i386/kvm: QEMU crash when doing 'info cpus' after CPU hotplug

[Greg Kurz <groug@kaod.org>]

On Tue, 10 Oct 2017 14:40:58 +0200
Igor Mammedov <imammedo@redhat.com> wrote:

> On Mon, 9 Oct 2017 19:19:15 +0200
> Greg Kurz <groug@kaod.org> wrote:
> 
> > Hi x86 folks,
> > 
> > While trying to reproduce on x86 an issue we're currently hitting on ppc,
> > I got this:
> > 
> > $ ./x86_64-softmmu/qemu-system-x86_64 -snapshot -no-shutdown -nographic -machine q35,accel=kvm -smp 1,maxcpus=2 -serial mon:stdio -drive file=$HOME/images/fedora26-x86_64.qcow2,if=virtio
> > QEMU 2.10.50 monitor - type 'help' for more information
> > (qemu) device_add host-x86_64-cpu,socket-id=1,core-id=0,thread-id=0,id=foo  
> cpu type here doesn't match currently in use one,

Oh, I didn't realize that...

> I've just sent patch that adds check
> 

I'll test it ASAP.

> valid cpu type and other mandatory for hotplug properties
> one could find out with HMP command:
>   info hotpluggable-cpus
> or its QMP equivalent
> 

Sure, I'll do that to see if I hit the issue I was initially trying to
reproduce.

> > (qemu) info cpus
> > error: failed to get MSR 0x38d
> > qemu-system-x86_64: /home/greg/Work/qemu/qemu-devel/target/i386/kvm.c:2121: kvm_get_msrs: Assertion `ret == cpu->kvm_msr_buf->nmsrs' failed.
> > Aborted (core dumped)
> > 
> > Same happens with a pc machine.
> > 
> > But it doesn't happen if I use cpu-add instead of device_add:
> > 
> > (qemu) cpu-add 1  
> that one works because of it plugs the same cpu type
> 
> PS:
> we probably should obsolete cpu-add in couple releases as the last user (s390)
> just gained support for device_add cpu, so it won't confuse people.
> 

Good idea indeed.

Thanks for the clarification.

> > (qemu) [    8.335221] CPU1 has been hot-added
> > (qemu) info cpus
> > * CPU #0: pc=0xffffffffb08986e6 (halted) thread_id=23964
> >   CPU #1: pc=0x00000000fffffff0 thread_id=24001
> > 
> > This is with the QEMU master branch SHA1 530049bc1dcc24c.
> > 
> > Cheers,
> > 
> > --
> > Greg
> >   
>