[PATCH 2/2] kho: drop restriction on maximum page order

[Pratyush Yadav <pratyush@kernel.org>]

KHO currently restricts the maximum order of a restored page to the
maximum order supported by the buddy allocator. While this works fine
for much of the data passed across kexec, it is possible to have pages
larger than MAX_PAGE_ORDER.

For one, it is possible to get a larger order when using
kho_preserve_pages() if the number of pages is large enough, since it
tries to combine multiple aligned 0-order preservations into one higher
order preservation.

For another, upcoming support for hugepages can have gigantic hugepages
being preserved over KHO.

There is no real reason for this limit. The KHO preservation machinery
can handle any page order. Remove this artificial restriction on max
page order.

Signed-off-by: Pratyush Yadav <pratyush@kernel.org>
Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---

Notes:
    This patch was first sent with this RFC series [0]. I am sending it
    separately since it is an independent patch that is useful even without
    hugepage preservation. No changes since the RFC.
    
    [0] https://lore.kernel.org/linux-mm/20251206230222.853493-1-pratyush@kernel.org/T/#u

 kernel/liveupdate/kexec_handover.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index bc9bd18294ee..1038e41ff9f9 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -253,7 +253,7 @@ static struct page *kho_restore_page(phys_addr_t phys, bool is_folio)
 	 * check also implicitly makes sure phys is order-aligned since for
 	 * non-order-aligned phys addresses, magic will never be set.
 	 */
-	if (WARN_ON_ONCE(info.magic != KHO_PAGE_MAGIC || info.order > MAX_PAGE_ORDER))
+	if (WARN_ON_ONCE(info.magic != KHO_PAGE_MAGIC))
 		return NULL;
 	nr_pages = (1 << info.order);
 
-- 
2.53.0.473.g4a7958ca14-goog