[PATCH] mm/kasan: use kasan_zero_pud for p4d table

[js1304]

From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>

There is missing optimization in zero_p4d_populate() that can save
some memory when mapping zero shadow. Implement it like as others.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
---
 mm/kasan/kasan_init.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/mm/kasan/kasan_init.c b/mm/kasan/kasan_init.c
index b96a5f7..554e4c0 100644
--- a/mm/kasan/kasan_init.c
+++ b/mm/kasan/kasan_init.c
@@ -118,6 +118,18 @@ static void __init zero_p4d_populate(pgd_t *pgd, unsigned long addr,
 
 	do {
 		next = p4d_addr_end(addr, end);
+		if (IS_ALIGNED(addr, P4D_SIZE) && end - addr >= P4D_SIZE) {
+			pud_t *pud;
+			pmd_t *pmd;
+
+			p4d_populate(&init_mm, p4d, lm_alias(kasan_zero_pud));
+			pud = pud_offset(p4d, addr);
+			pud_populate(&init_mm, pud, lm_alias(kasan_zero_pmd));
+			pmd = pmd_offset(pud, addr);
+			pmd_populate_kernel(&init_mm, pmd,
+						lm_alias(kasan_zero_pte));
+			continue;
+		}
 
 		if (p4d_none(*p4d)) {
 			p4d_populate(&init_mm, p4d,
-- 
2.7.4