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List:       freebsd-hackers
Subject:    Re: consistent VM hang during reboot
From:       John Nielsen <lists () jnielsen ! net>
Date:       2014-06-17 16:59:14
Message-ID: 7D960087-1839-4295-AEE3-5D8F60D9D710 () jnielsen ! net
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On Jun 13, 2014, at 4:23 PM, John Nielsen <lists@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

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