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

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 12 June 2017 11:41
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: Julien Grall (julien.grall@xxxxxxx) <julien.grall@xxxxxxx>; Andrew
> Cooper <Andrew.Cooper3@xxxxxxxxxx>; xen-devel(xen-
> devel@xxxxxxxxxxxxxxxxxxxx) <xen-devel@xxxxxxxxxxxxxxxxxxxx>; 'Boris
> Ostrovsky' <boris.ostrovsky@xxxxxxxxxx>; Juergen Gross
> <jgross@xxxxxxxx>
> Subject: RE: [Xen-devel] debian stretch dom0 + xen 4.9 fails to boot
> 
> >>> On 12.06.17 at 10:14, <Paul.Durrant@xxxxxxxxxx> 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.
> 

Sure, I'll give that a go now.

  Paul

> Jan
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