[PATCH] mm, debugfs: workaround undefined behaviour of rounddown_pow_of_two(0)

[Kirill A. Shutemov]

Result of rounddown_pow_of_two(0) is not defined. It can cause a bug if
user will set fault_around_bytes to 0 via debugfs interface.

Let's set fault_around_bytes to PAGE_SIZE if user tries to set it to
something below PAGE_SIZE.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 mm/memory.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index 7e8d8205b610..2d8fa7a7b0ee 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2786,7 +2786,8 @@ static int fault_around_bytes_set(void *data, u64 val)
 {
 	if (val / PAGE_SIZE > PTRS_PER_PTE)
 		return -EINVAL;
-	fault_around_bytes = val;
+	/* rounddown_pow_of_two(0) is not defined */
+	fault_around_bytes = max(val, PAGE_SIZE);
 	return 0;
 }
 DEFINE_SIMPLE_ATTRIBUTE(fault_around_bytes_fops,
-- 
 Kirill A. Shutemov
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