From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Subject: Re: 2.6.32.27 dom0 + latest xen staging boot failure
Date: Fri, 11 Feb 2011 14:51:23 +0000
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To: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Keir Fraser <keir@xen.org>, Stefano Stabellini <Stefano.Stabellini@eu.citrix.com>, "Kay,
	Allen M" <allen.m.kay@intel.com>, xen-devel <xen-devel@lists.xensource.com>, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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On Fri, 11 Feb 2011, Jeremy Fitzhardinge wrote:
> On 02/10/2011 05:03 PM, Kay, Allen M wrote:
> > Konrad/Stefano,
> >
> > Getting back to the xen/dom0 boot failure on my Sandybridge SDP I reported a few weeks ago.
> >
> > I finally got around to narrow down the problem the call to xen_add_extra_mem() in arch/x86/xen/setup.c/xen_memory_setup().  This call increase the top of E820 memory in dom0 beyond what is actually available.
> >
> > Before xen_add_extra_mem() is called, the last entry of dom0 e820 table is:
> >
> >     0000000100000000 - 000000016b45a000 (usable)
> >
> > After xen_add_extra_mem() is called, the last entry of dom0 e820 table becomes:
> >
> >     0000000100000000 - 000000023a6f4000 (usable)
> >
> > This pushes the top of RAM beyond what was reported by Xen's e820 table, which is:
> >
> > (XEN)  0000000100000000 - 00000001de600000 (usable)
> >
> > AFAICT, the failure is caused by dom0 accessing non-existent physical memory.  The failure went away after I removed the call to xen_add_extra_mem().
> 
> That "extra memory" stuff is reserving some physical address space for
> ballooning.  It should be completely unused (and unbacked by any pages)
> until the balloon driver populates it; it is reserved memory in the
> meantime.
> 
> How is that memory getting referenced in your case?
> 

In particular it would be very interesting to know what the RIP of the
crash resolves to.