mm/hugetlb: defer vmemmap population for bootmem hugepages

Currently, the vmemmap for bootmem-allocated gigantic pages is populated
early in hugetlb_vmemmap_init_early().  However, the zone information is
only available after zones are initialized.  If it is later discovered
that a page spans multiple zones, the HVO mapping must be undone and
replaced with a normal mapping using vmemmap_undo_hvo().

Defer the actual vmemmap population to hugetlb_vmemmap_init_late().  At
this stage, zones are already initialized, so it can be checked if the
page is valid for HVO before deciding how to populate the vmemmap.

This allows us to remove vmemmap_undo_hvo() and the complex logic required
to rollback HVO mappings.

In hugetlb_vmemmap_init_late(), if HVO population fails or if the zones
are invalid, fall back to a normal vmemmap population.

Postponing population until hugetlb_vmemmap_init_late() also makes zone
information available from within vmemmap_populate_hvo().

Link: https://lkml.kernel.org/r/20260227194302.274384-10-kas@kernel.org
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Baoquan He <bhe@redhat.com>
Cc: Christoph Lameter <cl@gentwo.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Frank van der Linden <fvdl@google.com>
Cc: Harry Yoo <harry.yoo@oracle.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 0 insertions, 2 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 4e999c21d89a..d7e53532a109 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4481,8 +4481,6 @@ int vmemmap_populate(unsigned long start, unsigned long end, int node,
 		struct vmem_altmap *altmap);
 int vmemmap_populate_hvo(unsigned long start, unsigned long end, int node,
 			 unsigned long headsize);
-int vmemmap_undo_hvo(unsigned long start, unsigned long end, int node,
-		     unsigned long headsize);
 void vmemmap_wrprotect_hvo(unsigned long start, unsigned long end, int node,
 			  unsigned long headsize);
 void vmemmap_populate_print_last(void);