From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Jan Beulich" <JBeulich@novell.com>
Subject: Re: Xen PANIC in MCE interrupt context : can
	global variable dom0 be NULL ?
Date: Tue, 16 Feb 2010 09:05:33 +0000
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References: <4B795809.5070304@lsi.com>
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To: Yunhong Jiang <yunhong.jiang@intel.com>, Ashwin Pankaj <ashwin.pankaj@lsi.com>
Cc: Xen-devel@lists.xensource.com
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>>> Ashwin Pankaj <ashwin.pankaj@lsi.com> 15.02.10 15:19 >>>
>  After some digging, probable culprit seems to be smp_cmci_interrupt
>
>> if (bs.errcnt && mctc !=3D NULL) {
>>         if (guest_enabled_event(dom0->vcpu[0],=20
>> <------------------------------------ here
>>                      VIRQ_MCA)) {
>>             mctelem_commit(mctc);
>>             printk(KERN_DEBUG "CMCI: send CMCI to DOM0 through =
virq\n");
>>             send_guest_global_virq(dom0, VIRQ_MCA);
>>         } else {
>>             x86_mcinfo_dump(mctelem_dataptr(mctc));
>>             mctelem_dismiss(mctc);
>>        }
>
>
>Looks like dom0 is NULL here ( vcpu[0] offset is 0x468). Is this =
possible?

Yes, your call trace confirms this.

>Other functions like mce_softirq() perform a NULL check on dom0 before=20
>accessing it's members ....

The majority of uses doesn't seem to do that check, yet it is essential
if CMCIs occur during boot of Xen. Even more, it should not only be
dom0 that is checked against NULL, but also dom0->vcpu (or
dom0->max_vcpus) and dom0->vcpu[0].

Jan