Re: [PATCH] hvmloader: write extra memory in CMOS

Ian Campbell
Tue, 12 Nov 2013 12:00:24 -0000

On Tue, 2013-11-12 at 06:52 -0500, Konrad Rzeszutek Wilk
wrote:
> Wei Liu <wei.liu2@citrix.com> wrote:
> >Some firmware, such as OVMF relies on this value to get the size of
> >extra memory above 4GB.
> >
> >Seabios in Xen doesn''t need this as it gets e820 directly from
Xen.
> >Rombios doesn''t read this value.
>
> I was looking at this some time ago for the GPU. I think a better way
> is to take advantage that the e820 can be retrieved from the
> hypervisor (used to be only for PV - but with thr PVH patches it works
> on HVM too). There is code from Gordan that also takes advantage of
> e820_hole.

I think that is orthogonal to Wei''s fix here.

As it stands for HVM guests the e820 map is determined by hvmloader, so
it makes sense for it to populate standard CMOS locations with the
values they should have.

> Anyhow why don''t we plumb in the libxl the standard memory layout
and
> query for that?

What standard memory layout do you mean?

> Or use xenstore?

That would put a burden on the BIOS to have a xenstore client.

Ian.