From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Vrabel <david.vrabel@citrix.com>
Subject: Re: Kernel panic with tboot E820_UNUSABLE region
Date: Tue, 14 May 2013 17:49:32 +0100
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To: Jan Beulich <JBeulich@suse.com>
Cc: "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>, Aurelien Chartier <aurelien.chartier@citrix.com>, David Vrabel <david.vrabel@citrix.com>, Ross Philipson <Ross.Philipson@citrix.com>, "konrad.wilk@oracle.com" <konrad.wilk@oracle.com>
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On 14/05/13 15:46, Jan Beulich wrote:
>>>> On 14.05.13 at 16:33, Aurelien Chartier <aurelien.chartier@citrix.com> wrote:
> 
> With
> 
>> (XEN)  0000000000100000 - 0000000000800000 (usable)
>> (XEN)  0000000000800000 - 0000000000975000 (unusable)
>> (XEN)  0000000000975000 - 0000000020000000 (usable)
>> ...
>> The region 0000000000975000 - 0000000020000000 has been set to unusable
>> by tboot.
> 
> ... you certainly mean the range 800000-975000.
> 
>> Calls to update_va_mapping show the following error messages (with mfn
>> going from 800 to 974):
>>
>> (XEN) mm.c:911:d0 Error getting mfn 800 (pfn 5555555555555555) from L1
>> entry 0000000000800463 for l1e_owner=0, pg_owner=0
> 
> Yes, the kernel has no business mapping that region, and the
> hypervisor rightly refuses the attempt.

Ok, so this is Xen checking the new PTE supplied in the
update_va_mapping hypercall and saying no.

I think there are two things the kernel can do here.

a) Change the type of UNUSABLE regions to RAM.

b) Release pages overlapping UNUSABLE regions, destroy their mapping and
clear/invalidate the region in the p2m.

Option a) is probably the easiest.

David