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From:   John Hubbard <jhubbard@nvidia.com>
To:     Marcin Wojtas <mw@semihalf.com>,
        Russell King <linux@armlinux.org.uk>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>
CC:     "David S . Miller" <davem@davemloft.net>, <netdev@vger.kernel.org>,
        <bpf@vger.kernel.org>, <linux-s390@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        John Hubbard <jhubbard@nvidia.com>,
        "Sven Auhagen" <sven.auhagen@voleatech.de>,
        Matteo Croce <mcroce@microsoft.com>
Subject: [PATCH] net: mvvp2: fix short frame size on s390
Date:   Thu, 5 Aug 2021 23:53:30 -0700
Message-ID: <20210806065330.23000-1-jhubbard@nvidia.com>
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On s390, the following build warning occurs:

drivers/net/ethernet/marvell/mvpp2/mvpp2.h:844:2: warning: overflow in
conversion from 'long unsigned int' to 'int' changes value from
'18446744073709551584' to '-32' [-Woverflow]
844 |  ((total_size) - MVPP2_SKB_HEADROOM - MVPP2_SKB_SHINFO_SIZE)

This happens because MVPP2_SKB_SHINFO_SIZE, which is 320 bytes (which is
already 64-byte aligned) on some architectures, actually gets ALIGN'd up
to 512 bytes in the s390 case.

So then, when this is invoked:

    MVPP2_RX_MAX_PKT_SIZE(MVPP2_BM_SHORT_FRAME_SIZE)

...that turns into:

     704 - 224 - 512 == -32

...which is not a good frame size to end up with! The warning above is a
bit lucky: it notices a signed/unsigned bad behavior here, which leads
to the real problem of a frame that is too short for its contents.

Increase MVPP2_BM_SHORT_FRAME_SIZE by 32 (from 704 to 736), which is
just exactly big enough. (The other values can't readily be changed
without causing a lot of other problems.)

Fixes: 07dd0a7aae7f ("mvpp2: add basic XDP support")
Cc: Sven Auhagen <sven.auhagen@voleatech.de>
Cc: Matteo Croce <mcroce@microsoft.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---

Hi,

This patch is based on today's linux.git (commit 902e7f373fff).

thanks,
John Hubbard
NVIDIA


 drivers/net/ethernet/marvell/mvpp2/mvpp2.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2.h b/drivers/net/ethernet/marvell/mvpp2/mvpp2.h
index b9fbc9f000f2..cf8acabb90ac 100644
--- a/drivers/net/ethernet/marvell/mvpp2/mvpp2.h
+++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2.h
@@ -938,7 +938,7 @@ enum mvpp22_ptp_packet_format {
 #define MVPP2_BM_COOKIE_POOL_OFFS	8
 #define MVPP2_BM_COOKIE_CPU_OFFS	24
 
-#define MVPP2_BM_SHORT_FRAME_SIZE	704	/* frame size 128 */
+#define MVPP2_BM_SHORT_FRAME_SIZE	736	/* frame size 128 */
 #define MVPP2_BM_LONG_FRAME_SIZE	2240	/* frame size 1664 */
 #define MVPP2_BM_JUMBO_FRAME_SIZE	10432	/* frame size 9856 */
 /* BM short pool packet size
-- 
2.32.0