On Wed, Feb 24, 2016 at 11:03:08AM -0800, Frank Rowand wrote:

On 2/23/2016 3:58 AM, Mark Rutland wrote:

quoted

Hi,

On Mon, Feb 22, 2016 at 05:58:19PM -0800, David Daney wrote:

quoted

From: Ard Biesheuvel <redacted>

There are two problems with the UEFI stub DT memory node removal
routine:
- it deletes nodes as it traverses the tree, which happens to work
  but is not supported, as deletion invalidates the node iterator;
- deleting memory nodes entirely may discard annotations in the form
  of additional properties on the nodes.

Since the discovery of DT memory nodes occurs strictly before the
UEFI init sequence, we can simply clear the memblock memory table
before parsing the UEFI memory map. This way, it is no longer
necessary to remove the nodes, so we can remove that logic from the
stub as well.

This is a little bit scary, but I guess this works.

My only concern is that when we get kexec, a subsequent kernel must also
have EFI memory map support, or things go bad for the next EFI-aware
kernel after that (as things like the runtime services may have been
corrupted by the kernel in the middle). It's difficult to fix the
general case later.

A different option would be to support status="disabled" for the memory
nodes, and ignore these in early_init_dt_scan_memory. That way a kernel
cannot use memory without first having parsed the EFI memory map, and we
can still get NUMA info from the disabled nodes.

Please do not play games of treating nodes with status="disabled" as
valid nodes.  The mindset should be if it is disabled, it does not exist.

I completely agree with this generally.

The only possible wiggle room is ePAPR's decription of the precise
meaning of the status property being binding-specific (and there may be
some way to later "enable" the node or otehrwise make use of it). As
with above, we'd only be extracting some information in the presence of
a UEFI memory map.

I agree that this is not a great pattern, and we don't necessarily want
that even for "safe" cases like NUMA.

There have been two bugs reported in the last week where code should
have been ignoring disabled nodes and failed to.  An audit of code
scanning all nodes instead of all enabled nodes is now on my todo list.

That would be great!

Mark.