Re: [Xen-devel] Multi-vcpu HVM Linux domain hanging during boot

[Gianni Tedesco <gianni.tedesco@xxxxxxxxxx>]

On Fri, 2010-07-02 at 14:40 +0100, George Dunlap wrote:
> I've got an HVM Linux guest, Debian 2.6.18-6-686 kernel, which works
> fine if vcpus=1 but hangs if vcpus=2.
> 
> I'm pretty sure that it worked with vcpus=2 earlier this week, but now
> I seem unable to find a hypervisor/tools/qemu combination within the
> last month that works.
> 
> It hangs just after detecting TSC as a timesource.  It's busy-waiting
> (both cpus pegged).  Vcpu 0 is in a function called
> hrtimer_run_queues, vcpu1 is in a function called do_timer.  Xentrace
> reports that vcpu 1 has an interrupt pending, but that it's not being
> delivered because interrupts are disabled in the vcpu's eflags.
> 
> I've even tried going back to an earlier disk snapshot and booting a
> different kernel (2.6.18-4-686), just to make sure it's not something
> dumb like a corrupt VM image.
> 
> Anyone else had this problem?  Can anyone ATM successfully boot a
> mutli-processor HVM guest of any kind?

I've had very similar problems booting linux HVM guests. I am using
RHEL5.x to reproduce. However in my case EFLAGS has IF flag enabled and
interrupts are being delivered from the 8254 PIT aswell as RESCHED
IPI's. The hangs also happen a lot later, like in early userspace
mounting filesystems. But as for you, this only occurs with SMP.

I take it that in your case the machine doesn't "unhang" if you hit a
key?

Have you tried clocksource=hpet disable_8254_timer on the kernel
commandline? Some tweaking of those params at least alters the timing of
the hangs for me.

Gianni


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