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/20260309123410.382308-1-pratyush@kernel.org
Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
Suggested-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Samiullah Khawaja <skhawaja@google.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 747a35107c84273f53ae2bd3a00895fdbdd8fc99..3586490f7487cadbb5f16e3186dd87c12e417fa4 100644 (file)
--- a/kernel/liveupdate/kexec_handover.c
+++ b/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;