[3.16.y-ckt stable] Patch "IB/mlx4: Fix WQE LSO segment calculation" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    IB/mlx4: Fix WQE LSO segment calculation

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt11.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

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>From 630aa3681bba39b7cd4245ab5f80089e06562da0 Mon Sep 17 00:00:00 2001
From: Erez Shitrit <erezsh at mellanox.com>
Date: Thu, 2 Apr 2015 13:39:05 +0300
Subject: IB/mlx4: Fix WQE LSO segment calculation

commit ca9b590caa17bcbbea119594992666e96cde9c2f upstream.

The current code decreases from the mss size (which is the gso_size
from the kernel skb) the size of the packet headers.

It shouldn't do that because the mss that comes from the stack
(e.g IPoIB) includes only the tcp payload without the headers.

The result is indication to the HW that each packet that the HW sends
is smaller than what it could be, and too many packets will be sent
for big messages.

An easy way to demonstrate one more aspect of the problem is by
configuring the ipoib mtu to be less than 2*hlen (2*56) and then
run app sending big TCP messages. This will tell the HW to send packets
with giant (negative value which under unsigned arithmetics becomes
a huge positive one) length and the QP moves to SQE state.

Fixes: b832be1e4007 ('IB/mlx4: Add IPoIB LSO support')
Reported-by: Matthew Finlay <matt at mellanox.com>
Signed-off-by: Erez Shitrit <erezsh at mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz at mellanox.com>
Signed-off-by: Doug Ledford <dledford at redhat.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/infiniband/hw/mlx4/qp.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/infiniband/hw/mlx4/qp.c b/drivers/infiniband/hw/mlx4/qp.c
index 67780452f0cf..6914462e4b5b 100644
--- a/drivers/infiniband/hw/mlx4/qp.c
+++ b/drivers/infiniband/hw/mlx4/qp.c
@@ -2535,8 +2535,7 @@ static int build_lso_seg(struct mlx4_wqe_lso_seg *wqe, struct ib_send_wr *wr,

 	memcpy(wqe->header, wr->wr.ud.header, wr->wr.ud.hlen);

-	*lso_hdr_sz  = cpu_to_be32((wr->wr.ud.mss - wr->wr.ud.hlen) << 16 |
-				   wr->wr.ud.hlen);
+	*lso_hdr_sz  = cpu_to_be32(wr->wr.ud.mss << 16 | wr->wr.ud.hlen);
 	*lso_seg_len = halign;
 	return 0;
 }