On Mon, Dec 05, 2016 at 03:42:14PM +0000, Ard Biesheuvel wrote:

On 2 December 2016 at 14:49, James Morse [off-list ref] wrote:

quoted

Patch "arm64: mm: Fix memmap to be initialized for the entire section"
changes pfn_valid() in a way that breaks hibernate. These patches fix
hibernate, and provided struct page's are allocated for nomap pages,
can be applied before [0].

Hibernate core code belives 'valid' to mean "I can access this". It
uses pfn_valid() to test the page if the page is 'valid'.

pfn_valid() needs to be changed so that all struct pages in a numa
node have the same node-id. Currently 'nomap' pages are skipped, and
retain their pre-numa node-ids, which leads to a later BUG_ON().

These patches make hibernate's savable_page() take its escape route
via 'if (PageReserved(page) && pfn_is_nosave(pfn))'.

This makes me feel slightly uneasy. Robert makes a convincing point,
but I wonder if we can expect more fallout from the ambiguity of
pfn_valid(). Now we are not only forced to assign non-existing (as far
as the OS is concerned) pages to the correct NUMA node, we also need
to set certain page flags.

Yes, I really don't know how to proceed here. Playing whack-a-mole with
pfn_valid() users doesn't sounds like an improvement on the current
situation to me.

Robert -- if we leave pfn_valid() as it is, would a point-hack to
memmap_init_zone help, or do you anticipate other problems?

Will