Re: [Xen-devel] debian stretch dom0 + xen 4.9 fails to boot

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.06.17 at 12:36, <Paul.Durrant@xxxxxxxxxx> wrote:
>>  -----Original Message-----
> [snip]
>> >>
>> >> TBH: I really can't see what is wrong with that patch. The only change
>> >> which should be able to break something seems to be the reduction of
>> the
>> >> wakeup stack size to 3kB, but this shouldn't affect booting the system
>> >> at all...
>> >>
>> > Yeah, my next test is going to be increasing the size of the wakeup stack
>> again, but there is really nothing obviously wrong with the patch.
>> 
>> My gut feeling is that there is some path through boot (tickled by these
>> two machines) which is clobbering the wrong piece of memory, which was
>> previously safe and is now not, because of the rearrangements here.
>> 
>> Debugging these machines is very tricky, because they have no serial or
>> IMPI whatsoever.
>> 
> 
> It does appear to be a layout issue. If I modify the code to just set 
> wakeup_stack to wakeup_stack_start + PAGE_SIZE, so it has the full 4k then I 
> still get the problem. However if I then move that code block that includes 
> wakeup.S and move it to the end of trampoline.S so that wakup code and stack 
> are once again located at the end then the problem goes away.

Could you do the following two things:
1) Subtract, say, 4k from trampoline_phys right before setting it
(immediately ahead of trampoline_setup)? Ideally you'd also log
the resulting value (in case it works).
2) Provide the E820 map of that box.
I'm suspecting the BIOS might use an EBDA without recording it in
the low BIOS data area. If it's reported in E820 that would then
likely be the final kick for us to obey to the E820 map when
determining where to put the trampoline.

Jan


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