kho: make sure preservations do not span multiple NUMA nodes

The KHO restoration machinery is not capable of dealing with preservations
that span multiple NUMA nodes.  kho_preserve_folio() guarantees the
preservation will only span one NUMA node since folios can't span multiple
nodes.

This leaves kho_preserve_pages().  While semantically kho_preserve_pages()
only deals with 0-order pages, so all preservations should be single page
only, in practice it combines preservations to higher orders for
efficiency.  This can result in a preservation spanning multiple nodes. 
Break up the preservations into a smaller order if that happens.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Pratyush Yadav (Google) <[email protected]>
Suggested-by: Pasha Tatashin <[email protected]>
Reviewed-by: Samiullah Khawaja <[email protected]>
Reviewed-by: Mike Rapoport (Microsoft) <[email protected]>
Cc: Alexander Graf <[email protected]>
Cc: Pasha Tatashin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

kernel/liveupdate/kexec_handover.c

@@ -870,9 +870,17 @@ int kho_preserve_pages(struct page *page, unsigned long nr_pages)
 	}
 
 	while (pfn < end_pfn) {
-		const unsigned int order =
+		unsigned int order =
 			min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn));
 
+		/*
+		 * Make sure all the pages in a single preservation are in the
+		 * same NUMA node. The restore machinery can not cope with a
+		 * preservation spanning multiple NUMA nodes.
+		 */
+		while (pfn_to_nid(pfn) != pfn_to_nid(pfn + (1UL << order) - 1))
+			order--;
+
 		err = kho_radix_add_page(tree, pfn, order);
 		if (err) {
 			failed_pfn = pfn;