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Re: [Xen-devel] [PATCH] hvmloader: write extra memory in CMOS

On Tue, Nov 12, 2013 at 12:30:52PM +0000, Jan Beulich wrote:
> >>> On 12.11.13 at 13:11, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> 
> >>> wrote:
> > Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> >>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!
> That's the first time I hear about this - there are a couple of more
> or less standard locations in CMOS where some of the memory
> gets reported, but all are at most two bytes wide and (having at
> best 64k granularity) don't allow expressing memory beyond 4Gb.
> Now, if there is a standard for the locations used here, fine with
> me (but it should be referenced in the commit message then). But
> if this is custom, then I wonder (a) how compatible such an
> extension is going to be and (b) why it needs to be restricted to
> 3 bytes (allowing to cover only up to 1Tb).

It's not custom.

AFAICT Boches reads this, seabios reads this (when not running on Xen)
and OVMF reads this as well.


However in some CMOS maps I found those bytes are marked as reserved.
That's why I say "Some BIOSes" in comment.



> Jan

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