Re: [Xen-devel] Kernel panic with tboot E820_UNUSABLE region

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.05.13 at 19:16, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
> On 14/05/13 18:02, Konrad Rzeszutek Wilk wrote:
>> David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
>> 
>>> On 14/05/13 15:46, Jan Beulich wrote:
>>>>>>> On 14.05.13 at 16:33, Aurelien Chartier
>>> <aurelien.chartier@xxxxxxxxxx> 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
>> 
>> But option b) seems the proper one.
> 
> Well...  The pfns currently overlapping the machine's UNUSABLE region
> are usable RAM and nothing else is the kernel will want to access any
> machine address within this region (and evidently can't, even if it
> wanted to!).
> 
> If it helps, think of it as dom0 taking the pseudo-physical memory map
> and putting holes in it to corresponding to interesting bits of the
> machine memory map.  UNUSABLE regions aren't interesting so we don't
> make holes for them.

But then they must not be 1:1 mapped.

Jan


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