Bug#606964: linux-image-2.6.32-5-xen-amd64: Xen fails to boot dom0 kernel on system with, lots of RAM

[Ian Campbell <ijc@hellion.org.uk>]

On Wed, 2010-12-22 at 07:20 +0100, Rik Theys wrote:
> Hi,
> 
> On 12/14/2010 02:41 PM, Ian Campbell wrote:
> >> When adding dom0_mem=2G to the boot line, the system boots OK.
> >
> > I expect it will work ok with everything up to and including
> > dom0_mem=32G?
> 
> It does.

Thanks.

> > It depends a bit on your usecase but it is often best recommended to use
> > dom0_mem= anyway, since you are most often going to balloon dom0 down
> > significantly anyway to make room for guest domains.
> 
> I agree and I was planning to use the dom0_mem parameter. But I did 
> expect the system to actually boot. Maybe it should be mentioned 
> somewhere that the dom0_mem _must_ be set on systems with >32GB memory?

Yes, I should at least mention it in the wiki or something.

I was wondering about clamping something in the kernel to correspond to
CONFIG_XEN_MAX_DOMAIN_MEMORY and avoid the issue but you say the crash
is after "x VCPUS" and before "Scrubbing Free RAM" so I'm surprised the
dom0 kernel has run at this point and hence changing it would not help.
The hypervisor doesn't know about this guest configuration item so there
isn't much which can be done there.

To try and confirm what is going on is there any chance you could you
collect a serial console log with verbose debugging enabled by using the
command line parameters described in "Are there more debugging options I
could enable to troubleshoot booting problems?" of
http://wiki.xensource.com/xenwiki/XenParavirtOps (without the
recommended dom0_mem).

The primary options of interest in this case are "loglvl=all
guest_loglvl=all sync_console console_to_ring" on the hypervisor plus
"com1=115200,8n1 console=com1" to enable serial logging and
"console=hvc0 earlyprintk=xen nomodeset initcall_debug debug
loglevel=10" on the kernel.

Assuming that shows that the domain 0 kernel did actually get a chance
to run and crash I'll take a look at what else needs to be clamped to
have it just work.

Thanks,
Ian.
-- 
Ian Campbell
Current Noise: Suffocation - Demise Of The Clone

Conscience doth make cowards of us all.
		-- Shakespeare