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

Konrad Rzeszutek Wilk
Tue, 12 Nov 2013 12:11:51 -0000

Ian Campbell <Ian.Campbell@citrix.com> wrote:
>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.

CMOS has memory values? That is standard PC spec? Yikes!
>
>> Anyhow why don''t we plumb in the libxl the standard memory
layout and
>> query for that?
>
>What standard memory layout do you mean?

The E820.
>
>> Or use xenstore?
>
>That would put a burden on the BIOS to have a xenstore client.

Hvmloader already uses xenstore.

But I missed the part about this actually being an implementation of a bare
metal ''feature''.

>
>Ian.