[PATCH net 3/5] s390/qeth: avoid using is_multicast_ether_addr_64bits on (u8 *)[6]

Julian Wiedmann
2018-06-29T17:45:52Z

From: Vasily Gorbik <gor@linux.ibm.com>

*ether_addr*_64bits functions have been introduced to optimize
performance critical paths, which access 6-byte ethernet address as u64
value to get "nice" assembly. A harmless hack works nicely on ethernet
addresses shoved into a structure or a larger buffer, until busted by
Kasan on smth like plain (u8 *)[6].

qeth_l2_set_mac_address calls qeth_l2_remove_mac passing
u8 old_addr[ETH_ALEN] as an argument.

Adding/removing macs for an ethernet adapter is not that performance
critical. Moreover is_multicast_ether_addr_64bits itself on s390 is not
faster than is_multicast_ether_addr:

is_multicast_ether_addr(%r2) -> %r2
llc %r2,0(%r2)
risbg %r2,%r2,63,191,0

is_multicast_ether_addr_64bits(%r2) -> %r2
llgc %r2,0(%r2)
risbg %r2,%r2,63,191,0

So, let's just use is_multicast_ether_addr instead of
is_multicast_ether_addr_64bits.

Fixes: bcacfcbc82b4 ("s390/qeth: fix MAC address update sequence")
Reviewed-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
---
drivers/s390/net/qeth_l2_main.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/net/qeth_l2_main.c b/drivers/s390/net/qeth_l2_main.c
index 7daf125dae76..5464515b71f1 100644
--- a/drivers/s390/net/qeth_l2_main.c
+++ b/drivers/s390/net/qeth_l2_main.c
@@ -140,7 +140,7 @@ static int qeth_l2_send_setmac(struct qeth_card *card, __u8 *mac)

static int qeth_l2_write_mac(struct qeth_card *card, u8 *mac)
{
- enum qeth_ipa_cmds cmd = is_multicast_ether_addr_64bits(mac) ?
+ enum qeth_ipa_cmds cmd = is_multicast_ether_addr(mac) ?
IPA_CMD_SETGMAC : IPA_CMD_SETVMAC;
int rc;

@@ -157,7 +157,7 @@ static int qeth_l2_write_mac(struct qeth_card *card, u8 *mac)

static int qeth_l2_remove_mac(struct qeth_card *card, u8 *mac)
{
- enum qeth_ipa_cmds cmd = is_multicast_ether_addr_64bits(mac) ?
+ enum qeth_ipa_cmds cmd = is_multicast_ether_addr(mac) ?
IPA_CMD_DELGMAC : IPA_CMD_DELVMAC;
int rc;

--
2.16.4