Re: [Qemu-devel] [RfC PATCH] e820: pass high memory too.

[Gerd Hoffmann <kraxel@redhat.com>]

On Fr, 2013-10-11 at 13:20 +0200, Igor Mammedov wrote:
> On Thu, 10 Oct 2013 14:54:29 +0200
> Gerd Hoffmann <kraxel@redhat.com> wrote:
> 
> > We have a fw_cfg entry to pass e820 entries from qemu to the firmware.
> > Today it's used to pass reservations only.  This patch makes qemu pass
> > entries for RAM too.
> > 
> > This allows to pass RAM sizes larger than 1TB to the firmware and it
> > will also allow to pass non-contignous memory ramges should we decide
> > to implement that some day, say for our virtual numa nodes.
> > 
> > Obviously this needs some extra care to not break existing firware.
> > 
> > SeaBIOS loads the entries and happily adds them without looking at the
> > type.  Which is problematic for memory below 4g as this will overwrite
> > reservations added for bios memory etc.  For memory above 4g it works
> > just fine, seabios will merge the entry derived from cmos with the one
> > loaded from fw_cfg.
> It will make amount of available memory in e820 table more than described
> in smbios and could break MS's SMBIOS HCT test.

Happens only in case the installed amount of memory is larger than 1TB
(which is the maximum the cmos can describe).  Such a setup doesn't work
correctly without the patch anyway, so it isn't a regression IMHO.  And
with an additional patch on the seabios side we can fix the smbios info
even for the >1TB case.

>  Perhaps related smbios info
> also should be picked up from QEMU.

Worth investigating, but lets concentrate on the acpi table merge first.

cheers,
  Gerd