[PATCH RFC 07/35] mm/memremap: reject unreasonable folio/compound page sizes in memremap_pages()

[David Hildenbrand]

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.

Signed-off-by: David Hildenbrand <david at redhat.com>
---
 mm/memremap.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/memremap.c b/mm/memremap.c
index b0ce0d8254bd8..a2d4bb88f64b6 100644
--- a/mm/memremap.c
+++ b/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:
-- 
2.50.1