linux-kernel - [PATCH 4.17 057/101] s390/qeth: avoid using is_multicast_ether_addr

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Date:   Fri, 20 Jul 2018 14:14:03 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Julian Wiedmann <jwi@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.17 057/101] s390/qeth: avoid using is_multicast_ether_addr_64bits on (u8 *)[6]

4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

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

[ Upstream commit 9d0a58fb9747afd27d490c02a97889a1b59f6be4 ]

*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@...ux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@...ux.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@...ux.ibm.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/s390/net/qeth_l2_main.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/s390/net/qeth_l2_main.c
+++ b/drivers/s390/net/qeth_l2_main.c
@@ -141,7 +141,7 @@ static int qeth_l2_send_setmac(struct qe
 
 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;
 
@@ -158,7 +158,7 @@ static int qeth_l2_write_mac(struct qeth
 
 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;