Re: [Xen-devel] Dom0 crash with old style AMD NUMA detection

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Sep 18, 2012 at 06:50:14PM +0200, Andre Przywara wrote:
> On 09/18/2012 03:44 PM, Konrad Rzeszutek Wilk wrote:
> >On Tue, Sep 18, 2012 at 11:57:33AM +0200, Andre Przywara wrote:
> >>On 09/17/2012 09:14 PM, Konrad Rzeszutek Wilk wrote:
> >>>On Mon, Sep 17, 2012 at 09:29:22AM +0200, Andre Przywara wrote:
> >>>>On 09/14/2012 08:58 PM, Konrad Rzeszutek Wilk wrote:
> >>>>>>>>[    0.000000] Kernel panic - not syncing: Attempted to kill the idle 
> >>>>>>>>task!
> >>>>>>>>(XEN) Domain 0 crashed: 'noreboot' set - not rebooting.
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>The obvious solution would be to explicitly deny northbridge scanning
> >>>>>>>>when running as Dom0, though I am not sure how to implement this 
> >>>>>>>>without
> >>>>>>>>upsetting the other kernel folks about "that crappy Xen thing" again 
> >>>>>>>>;-)
> >>>>>>>
> >>>>>>>Heh.
> >>>>>>>Is there a numa=0 option that could be used to override it to turn it
> >>>>>>>off?
> >>>>>>
> >>>>>>Not compile tested.. but was thinking something like this:
> >>>>>
> >>>>>ping?
> >>>>
> >>>>That looks good to me - at least for the time being.
> >>>
> >>>OK, can I've your Tested-by/Acked-by on it pls?
> >>>
> >>>>I just want to check how this interacts with upcoming Dom0 NUMA
> >>>>support. It wouldn't be too clever if we deliberately disable NUMA
> >>>
> >>>We can always revert this patch in future versions of Linux.
> >>
> >>I don't like this idea. Then we have Linux kernel up to 3.5 working
> >>and say from 3.8 on again, but 3.6 and 3.7 cannot use NUMA. That
> >>would be pretty unfortunate.
> >
> >Huh? v3.5 working? But it never worked? I would say turn off the NUMA
> >detection (keep in mind it still will set up the dummy NUMA stuff)
> >until there are some PV NUMA capability and then we can revert it.
> 
> I was under the impression that somehow the Dom0 NUMA would be made
> compatible, using some of the existing discovery mechanisms. So we
> would enable the hypervisor, and Dom0 would just magically start
> working. I am probably rooted too much in the HVM world ;-)
> 
> >>
> >>I haven't checked back with Dario, but I'd suspect that we use ACPI
> >>for injecting NUMA topology into Dom0. Even if not, a general
> >>"numa=off" for Dom0 is too much of a sledgehammer for me.
> >
> >How would you inject it in Dom0? It s a PV guest so the hypervisor would
> >have to tweak the SRAT/SLIT tables. That is not going to happen
> >in the very short term.. And I don't recall seeing any patches, so
> >the dom0 NUMA support is right now non-existent?
> 
> Right, I just don't wanted to slam the door deliberately. Thinking
> more about this, we probably need some kind of PV enablement in
> Dom0, even if we could somehow use the ACPI tables (and thus the
> ACPI parsing code).
> If this is the case, we could at the same time remove this "force
> numa off" patch.
> 
> I am almost convinced by now.
> Just waiting for Dario's opinion for a few more hours and will send
> my final opinion later today. If you cannot wait, tell me.

Couple of days is OK with me. My deadline is Friday as I would like
to send a git pull to Linus and include this patch if it makes sense.

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