Re: [tboot-devel] When !is_kernel_linux(), tboot memory is set to E820_UNUSABLE

[Konrad R. W. <ko...@da...>]

>>
>> Only Unusable AddressRange is forbidden to be used by OS. So we set tboot
>> memory as E820_UNUSABLE for both Linux kernel&  Xen cases in the beginning.
>> But in Linux case, we then found some issues so we had to reset the type to
>> RESERVED to fix that issue.
>>
>> That is all I can recall now.
>
> Ok, well we are running into a problem too with our dom0 Linux. It is
> trying to map that range at 0x800000 even though it is clearly marked as
> E820_UNUSABLE in the memory map that it is provided. This seems
> completely wrong and Xen mm code crashes when this occurs. So we wanted
> to understand all aspects of this in trying to figure this out. Thanks
> for the explanation. If you could remember what issue you saw in Linux
> that caused you to switch to using reserved that might prove helpful.


It could be a bug in the Linux arch/x86/xen/setup.c code that parses the E820
provided by Xen. There is code in there to mark 'balloon' memory as
E820_UNUSABLE
and it might be squashing the tboot E820_UNUSABLE along with its own
region of E820_RAM that it has marked as E820_UNUSABLE.

What version of Linux kernel are you running and what does the earlyprintk=xen
(on the Linux line) give you?