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

[Greg Kurz]

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
(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
(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