On 18 March 2016 at 13:56, Matt Fleming [off-list ref] wrote:

On Fri, 18 Mar, at 01:31:59PM, Ard Biesheuvel wrote:

quoted

Typically, the UEFI memory map is more restrictive, since it does not
only describe where the memory lives, but also which parts of it the
firmware has claimed for its own use. So if both memory nodes and the
UEFI memory map are available, we must use the latter anyway, and so
it makes sense to ignore the former. Alternatively, we could sanity
check the memory nodes against the memory map, but it is simpler just
to ignore them.

However, that caused some problems in the past, since discovering the
memory nodes occurs before the EFI entry point is invoked, and so it
was decided that we strip the memory nodes rather than ignore them.

Thanks Ard.

Once you've stripped the memory nodes as represented in memblock,
there's no way for the memory nodes to re-appear in one form or
another after that point, right? The EFI memory map is the sole memory
layout either via memblock or if it's queried directly?

Well, the significance of this patch in this series is that the memory
nodes contain additional properties that describe the NUMA topology,
which the UEFI memory map does not allow us to do. At some point, we
may decide to capture this information in a different way (i.e., a
separate configuration table), but for now, I think this is fine,
especially since stripping nodes is a bit of a blunt tool.