[PATCH v2] mm/memtest: add underflow detection for size calculation

[klourencodev@gmail.com]

From: Kevin Lourenco <klourencodev@gmail.com>

The computation: end = start + (size - (start_phys_aligned - start_phys)) / incr
could theoretically underflow if size < offset, leading to a massive
iteration.

Add VM_WARN_ON_ONCE() to detect cases where the region size is smaller
than the alignment offset. While this should never happen in practice
due to memblock guarantees, the warning helps catch potential bugs in
early memory initialization code.

Suggested-by: Mike Rapoport <rppt@kernel.org>
Signed-off-by: Kevin Lourenco <klourencodev@gmail.com>
---
 mm/memtest.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/memtest.c b/mm/memtest.c
index c2c609c39119..bac195e6077a 100644
--- a/mm/memtest.c
+++ b/mm/memtest.c
@@ -46,6 +46,7 @@ static void __init memtest(u64 pattern, phys_addr_t start_phys, phys_addr_t size
 
 	start_phys_aligned = ALIGN(start_phys, incr);
 	start = __va(start_phys_aligned);
+	VM_WARN_ON_ONCE(size < start_phys_aligned - start_phys);
 	end = start + (size - (start_phys_aligned - start_phys)) / incr;
 	start_bad = 0;
 	last_bad = 0;
-- 
2.47.3