consistent VM hang during reboot

[John Nielsen]

On Jun 13, 2014, at 4:23 PM, John Nielsen <lists at jnielsen.net> wrote:

> On Wednesday, May 07, 2014 7:15:43 pm John Nielsen wrote:
>> I am trying to solve a problem with amd64 FreeBSD virtual machines running on a Linux+KVM hypervisor. To be honest I'm not sure if the problem is in FreeBSD or the hypervisor, but I'm trying to rule out the OS first.
>> 
>> The _second_ time FreeBSD boots in a virtual machine with more than one core, the boot hangs just before the kernel would normally print e.g. "SMP: AP CPU #1 Launched!" (The last line on the console is "usbus0: 12Mbps Full Speed USB v1.0", but the problem persists even without USB). The VM will boot fine a first time, but running either "shutdown -r now" OR "reboot" will lead to a hung second boot. Stopping and starting the host qemu-kvm process is the only way to continue.

...

> Following up on the off chance anyone else is interested. I installed -HEAD on a host that was having the problem ("v2" Xeon CPU) and ran a FreeBSD 9 VM under bhyve. The problem did _not_ persist. That's not entirely conclusive but it does point the finger at Qemu a bit more strongly. I have filed a bug with them:
>  https://bugs.launchpad.net/qemu/+bug/1329956

With some help from the Qemu and KVM folks I've finally made some headway. The salient difference between the working and non-working CPUs above seems to be support for APIC virtualization. Loading the intel_kvm module (on the Linux host) with "enable_apicv=N" works around the reboot problem I've been having.

Since this now looks like a Linux KVM bug I won't follow up here any more, but I wanted to wrap up the thread for the archives.

JN