Re: [Xen-devel] [PATCH] x86/boot: re-arrange how/when we do disk I/O

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.06.17 at 17:11, <JBeulich@xxxxxxxx> wrote:
> We place the trampoline no lower than at 256k, so we have ample space
> to read the MBRs of BIOS disks into an aligned buffer right below the
> trampoline (not doing so has been found to be a problem on a buggy BIOS
> coming with a Skull Canyon NUC). To facilitate that move MBR reading
> past EDD info retrieval.
> 
> Also add a wrap check to the EDD info retrieval loop, to match that in
> the MBR reading one.
> 
> Reported-by: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> Tested-by: Paul Durrant <Paul.Durrant@xxxxxxxxxx>

As to 4.9 inclusion, I think I should have mentioned right away
that such a change of course isn't without risk: We're trying to
work around a BIOS bug by relying on other information
coming from the BIOS being correct / usable. Obviously there is
the risk that this regresses with some other BIOS having a bug
elsewhere.

I'm therefore leaning towards suggesting to take this change
only for master right now, and consider pulling it into the 4.9
branch in a couple of weeks time, when the patch has seen at
least a little more testing on a wider set of systems.

Jan


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