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Re: [Xen-devel] dom0 boot failure with 256G

To: Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, <mukesh.rathor@xxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] dom0 boot failure with 256G
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Thu, 05 Jun 2008 08:24:20 +0100
Cc: "Kurt C. Hackel" <kurt.hackel@xxxxxxxxxx>
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On 5/6/08 05:00, "Ian Pratt" <Ian.Pratt@xxxxxxxxxxxxx> wrote:

>>     I've been intensely debugging a dom0 crash right at boot in
>>     pagetable_init() with 256G. We are running 64bit hyp with 32bit
>> dom0.
>>     This on xen 3.1.3, which seems to have fixes from changeset 16548.
> 
> 256GB is more than a 32b dom0 can handle. Presumably it works if you set
> dom0_mem= to something smaller?
> 
> We should probably make the clipping of dom0 memory to something like
> 64GB automatic.

Xen ought to have crashed during dom0 build in that case, being unable to
allocate enough memory of the restricted address width supported by the 32b
dom0 guest. I agree that dom0_mem should be automatically intelligently
clamped. Currently nr_pages is clamped to UINT_MAX (!) for a 32b dom0, which
is still rather a big number.

I'll have to sketch out exactly what that physaddr_bitsize computation is
doing and see if I can make sense of it...

 -- Keir



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