Re: [Xen-devel] HVM SMP linux guest hangs in cpu_idle() with EFLAGS.IF = 1

[Gianni Tedesco <gianni.tedesco@xxxxxxxxxx>]

On Thu, 2010-07-08 at 11:03 +0100, George Dunlap wrote:
> If both cpus are idling with EFLAGS.IF=1, this would imply that the
> kernel thinks it's waiting on a device, yes?  One thing you could do
> is to track the interaction between the guest and the devices, and see
> if you can figure out what it's waiting for and why the thing it's
> waiting for isn't happening.  You can use xentrace + xenalyze
> (http://xenbits.xensource.com/ext/xenalyze.hg) to see all the PIO,
> MMIO, and interrupts delivered to the guest.
> 
> Unfortunately this would mean understanding at some level the
> interface the device presents, which may involve a lot of going
> through driver code / going through QEMU, which doesn't sound fun. :-/
>  Maybe someone else will have some suggestions...

Hmm, yeah, usually that's a headache to do for one device never mind the
whole system...

> I ended up with a similar-looking problem during boot with a stock
> 2.6.18.8 kernel, after hacking up a work-around to allow it to get
> past the timer synchronization stage.  It might be easier to track
> down if you have a failure mode that's quicker to reproduce and a
> guest kernel that's easier to modify.  (But of course there's always
> the possibility that it's a different bug with similar symptoms...)

Well this reproduces relatively quick but because it's a vendor kernel +
custom initrd it's a bit harder to modify components. Just re-building
the original turns out to be a pain.

I think for now my time is probably best spent trying to minimise the
code required to reproduce the thing and hopefully, in turn, minimise
the amount of PIO + MMIO + IRQ traces to go through.

Argh :)


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