[SeaBIOS] 1TB Guest changes to receive phys bits >=40

[Paolo Bonzini]

On 11/06/2018 15:21, Christian Ehrhardt wrote:
> Hi,
> I was asked about x86 Guests of >1TB in size. And while some discussions
> where around qemu/libvirt and host-phys-bits [1] I realized that in
> Seabios I need exactly what is already in CentOS/RHEL [2] to get the
> phys-bits passed on.
> 
> The change [2] itself is rather old, so I wondered if I'm missing that
> this was implemented in a totally different way. Do I have to switch/set
> options these days instead of using that patch?

That patch is not needed anymore.  It is only there to support old
machine types.  In newer versions of QEMU, QEMU builds the e820 memory
map for SeaBIOS, and that is enough to support >=1TB guests nicely.

Paolo

> But I saw that it is still applied even to rather recent versions.
> 
> So the question become why the change is not upstream yet?
> Was it maybe discussed in the past and Nack'ed for some reason?
> I didn't find the discussion if that is the case and would appreciate
> the pointer.
> 
> We are closing in to make 1TB more common rather quickly, so I wonder if
> really nothing would speak against it - would it be reasonable to
> consider committing that upstream to Seabios these days?
> 
> [1]: https://bugs.launchpad.net/ubuntu/+source/qemu/+bug/1769053
> [2]: https://git.centos.org/blob/rpms!seabios.git/14f0fd75785bc5f1468fa84fbd3a1627f3433032/SOURCES!0002-allow-1TB-of-RAM.patch
> 
> P.S. Subscribing people acking the original patch as they might have old
> context to provide on this.
> 
> -- 
> Christian Ehrhardt
> Software Engineer, Ubuntu Server
> Canonical Ltd