kho: drop restriction on maximum page order

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.

Link: https://lkml.kernel.org/r/20260309123410.382308-2-pratyush@kernel.org
Signed-off-by: Pratyush Yadav <pratyush@kernel.org>
Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Samiullah Khawaja <skhawaja@google.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 3586490f7487cadbb5f16e3186dd87c12e417fa4..532f455c5d4f4a312a1921dbe2259ea6d0874c29 100644 (file)
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -411,7 +411,7 @@ 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);