Re: [RFC] bpf: change bpf syacall to use u64 temp variables

This patch change map_lookup_elem() and map_update_elem() function
to use u64 temp variable if the key_size or value_size is less than
u64, we don't need use kmalloc() for these small variables.

Signed-off-by: yalin wang <redacted>
---
 kernel/bpf/syscall.c | 30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index f640e5f..c82d7bf 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c

@@ -189,7 +189,8 @@ static int map_lookup_elem(union bpf_attr *attr)
 	void __user *uvalue = u64_to_ptr(attr->value);
 	int ufd = attr->map_fd;
 	struct bpf_map *map;
-	void *key, *value, *ptr;
+	u64 key_buf, value_buf;
+	void *key = &key_buf, *value = &value_buf, *ptr;
 	struct fd f;
 	int err;
 

@@ -202,7 +203,8 @@ static int map_lookup_elem(union bpf_attr *attr)
 		return PTR_ERR(map);
 
 	err = -ENOMEM;
-	key = kmalloc(map->key_size, GFP_USER);
+	if (map->key_size > sizeof(u64))
+		key = kmalloc(map->key_size, GFP_USER);