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

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Paul Durrant
> Sent: 12 June 2017 13:06
> To: 'Jan Beulich' <JBeulich@xxxxxxxx>
> 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
> 
> > -----Original Message-----
> > From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> > Sent: 12 June 2017 12:12
> > 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 12:53, <Paul.Durrant@xxxxxxxxxx> wrote:
> > >>  -----Original Message-----
> > > [snip]
> > >> > >
> > >> > > 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.
> > >>
> > >
> > > That worked fine:
> > >
> > > (XEN) MBR[80] @ 85e0 (86000)
> >
> > But that's contrary to your earlier findings: Didn't you say simply
> > avoiding a 4k-boundary wasn't enough? And it certainly tells us
> > that this isn't a 4k drive (or at least the BIOS doesn't surface 4k
> > sectors) - I was really expecting a larger gap between the two
> > logged values.
> >
> 
> I'll go dump out the edd and double check what it is saying.
> 

I dumped a bit of the info:

(XEN) device 0x80 version 0x30
(XEN) number_of_sectors = 0x1dcf32b0
(XEN) sectors_per_track = 0x3f
(XEN) bytes_per_sector = 0x200

So it is indeed advertising a 512 byte sector. It is an SSD though so it'll be 
something much bigger underneath.

  Paul

> My findings indicated that the problem seemed to be doing a read that
> spanned a 4k boundary caused a problem, so using 0x85e00 would be safe.
> The anomaly was that simply aligning the edd_info buffer and a 512 byte
> boundary and continuing to use that for reading did not work.
> 
> > > so you can add my Tested-by to that.
> >
> > I.e. I'm not sure about this, as I'm still uncertain whether some
> > corruption didn't again occur. Of course APs coming up properly
> > would already be a relatively good sign (as now the permanent
> > part of the trampoline would be the predestined area for
> > corruption to occur in).
> >
> 
> None of my findings ever indicated memory corruption (although there, of
> course, may have been some that I happened to miss), but rather
> misbehaviour of the int13 handler itself - either locking up, having odd
> effects (e.g. black screen), or both.
> 
>   Paul
> 
> > Jan
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