>>> On 12.06.17 at 10:14, <Paul.Durrant@citrix.com> wrote:
> Looking at the code in arch/x86/boot/edd.c in Linux, it sector aligns the 
> buffer into which it reads the MBR and the sector size is pulled from the EDD 
> which means, I believe, that the MBR read on the skull canyon would be 4k 
> aligned.
> 
> What do you think it best to do for Xen 4.9? Hardcoding a 4k alignment is 
> clearly easy and would work around this BIOS issue but, as you say, it does 
> grow the image. Reverting Juergen's patch also works round the issue, but 
> that is more by luck. Re-working the code is preferable, but I guess it's too 
> late to introduce such code-churn in 4.9.

Reverting Jürgen's code is out of question with all the information
you've gathered by now. I think re-working the EDD code slightly
is the best option. Would you mind giving the attached patch a
try? This still slightly grows the trampoline due to a few more
instructions being needed, but should still be far better than
embedding a whole 4k buffer (and then later finding a BIOS/disk
combination which wants even more). Note that I've left a tiny
bit of debugging code in there.

Jan