Re: [Xen-devel] [V3 PATCH 9/9] pvh dom0: add opt_dom0pvh to setup.c

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Wed, 27 Nov 2013 15:00:43 +0000
George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:

> On 11/27/2013 02:27 AM, Mukesh Rathor wrote:
> > Add opt_dom0pvh. Note, pvh dom0 is disabled until the fixme in
> > domain_build.c is resolved. The fixme is added by patch title:
> > "PVH dom0: construct_dom0 changes"
> 
> So it's been asked before but I haven't seen an answer yet: What
> exactly is the problem here, and when might it be fixed?

The problem would happen if an mmio space sits above the highest
e820 address. Ie, the e820 didn't report it. FWIW, PV linux would not
boot as dom0 in those cases anyways, as it doesn't support anything
not in the e820 at present. Konrad is looking into it.

As for the hardware, I've not found any where it would happen. Here's 
Jan's response where this was discussed previously:

-------
> For testing purposes, do you have reference for hardware? I don't see 
> any here with such configuration.  

Nothing specific, but I know that SR-IOV virtual functions easily
cause kernels to run out of MMIO space below 4G (namely when
the hole is only around 1Gb or even less), and Intel must have
knowledge of graphics cards having so huge a frame buffer that
it can only be mapped above 4G.

Jan
-------

IMO, this is a pre-existing condition, that is not specific to
PVH only, as such a case would not work for linux PV dom0 either.

thanks,
Mukesh

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