mm/memremap: reject unreasonable folio/compound page sizes in memremap_pages()

Let's reject unreasonable folio sizes early, where we can still fail. 
We'll add sanity checks to prepare_compound_head/prepare_compound_page
next.

Is there a way to configure a system such that unreasonable folio sizes
would be possible?  It would already be rather questionable.

If so, we'd probably want to bail out earlier, where we can avoid a WARN
and just report a proper error message that indicates where something went
wrong such that we messed up.

Link: https://lkml.kernel.org/r/20250901150359.867252-8-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: davidhildenbrand

mm/memremap.c

@@ -275,6 +275,9 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
 
 	if (WARN_ONCE(!nr_range, "nr_range must be specified\n"))
 		return ERR_PTR(-EINVAL);
+	if (WARN_ONCE(pgmap->vmemmap_shift > MAX_FOLIO_ORDER,
+		      "requested folio size unsupported\n"))
+		return ERR_PTR(-EINVAL);
 
 	switch (pgmap->type) {
 	case MEMORY_DEVICE_PRIVATE: