kern/180430: [ofed] [patch] Bad UDP checksum calc for fragmented packets
Meny Yossefi
menyy at mellanox.com
Mon Jul 22 14:20:02 UTC 2013
The following reply was made to PR kern/180430; it has been noted by GNATS.
From: Meny Yossefi <menyy at mellanox.com>
To: John Baldwin <jhb at freebsd.org>, "bug-followup at freebsd.org"
<bug-followup at freebsd.org>
Cc:
Subject: RE: kern/180430: [ofed] [patch] Bad UDP checksum calc for
fragmented packets
Date: Mon, 22 Jul 2013 14:11:51 +0000
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Hi John,
The problem is that the HW will only calculate csum for parts of the payloa=
d, one fragment at a time,
while the receiver side, in our case the tcp/ip stack, will expect to valid=
ate the packet's payload as a whole.
I agree with the change you offered, though one thing bothers me.
This change will add two conditions to the send flow which will probably ha=
ve an effect on performance.
Maybe 'likely' can be useful here ?
BTW, I'm not entirely sure, but I think the CSUM_IP flag is always set, so =
maybe the first condition is not necessary.
What do you think ?
-Meny
-----Original Message-----
From: John Baldwin [mailto:jhb at freebsd.org]
Sent: Friday, July 19, 2013 6:29 PM
To: bug-followup at freebsd.org; Meny Yossefi
Subject: Re: kern/180430: [ofed] [patch] Bad UDP checksum calc for fragment=
ed packets
Oops, my previous reply didn't make it to the PR itself.
Is the problem that the hardware checksum overwrites arbitrary data in the =
packet (at the location where the UDP header would be)?
Also, I've looked at other drivers, and they all look at the CSUM_* flags t=
o determine the right settings. IP fragments will not have CSUM_UDP or CSU=
M_TCP set, so I think the more correct fix is this:
Index: en_tx.c
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
--- en_tx.c (revision 253470)
+++ en_tx.c (working copy)
@@ -780,8 +780,12 @@ retry:
tx_desc->ctrl.srcrb_flags =3D cpu_to_be32(MLX4_WQE_CTRL_CQ_U=
PDATE |
=
MLX4_WQE_CTRL_SOLICITED);
if (mb->m_pkthdr.csum_flags & (CSUM_IP|CSUM_TCP|CSUM_UDP)) {
- tx_desc->ctrl.srcrb_flags |=3D cpu_to_be32(M=
LX4_WQE_CTRL_IP_CSUM |
- =
MLX4_WQE_CTRL_TCP_UDP_CSUM);
+ if (mb->m_pkthdr.csum_flags & CSUM_IP)
+ tx_desc->ctrl.srcrb_flags |=
=3D
+ cpu_to_be32(MLX4_WQE_CTRL=
_IP_CSUM);
+ if (mb->m_pkthdr.csum_flags & (CSUM_TCP|CSUM_=
UDP))
+ tx_desc->ctrl.srcrb_flags |=
=3D
+ cpu_to_be32(MLX4_WQE_CTRL=
_TCP_UDP_CSUM);
priv->port_stats.tx_chksum_offload++;
}
--
John Baldwin
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<p class=3D"MsoPlainText"><span style=3D"color:#1F497D">Hi John, <o:p></o:p=
></span></p>
<p class=3D"MsoPlainText"><span style=3D"color:#1F497D"><o:p> </o:p></=
span></p>
<p class=3D"MsoPlainText"><span style=3D"color:#1F497D">The problem is that=
the HW will only calculate csum for parts of the payload, one fragment at =
a time,
<o:p></o:p></span></p>
<p class=3D"MsoPlainText"><span style=3D"color:#1F497D">while the receiver =
side, in our case the tcp/ip stack, will expect to validate the packet̵=
7;s payload as a whole.<o:p></o:p></span></p>
<p class=3D"MsoPlainText"><span style=3D"color:#1F497D"><o:p> </o:p></=
span></p>
<p class=3D"MsoPlainText"><span style=3D"color:#1F497D">I agree with the ch=
ange you offered, though one thing bothers me.<o:p></o:p></span></p>
<p class=3D"MsoPlainText"><span style=3D"color:#1F497D">This change will ad=
d two conditions to the send flow which will probably have an effect on per=
formance.<o:p></o:p></span></p>
<p class=3D"MsoPlainText"><span style=3D"color:#1F497D">Maybe ‘likely=
’ can be useful here ?<o:p></o:p></span></p>
<p class=3D"MsoPlainText"><o:p> </o:p></p>
<p class=3D"MsoPlainText"><span style=3D"color:#1F497D">BTW, I’m not =
entirely sure, but I think the CSUM_IP flag is always set, so maybe the fir=
st condition is not necessary.
<o:p></o:p></span></p>
<p class=3D"MsoPlainText"><span style=3D"color:#1F497D">What do you think ?=
<o:p></o:p></span></p>
<p class=3D"MsoPlainText"><o:p> </o:p></p>
<p class=3D"MsoPlainText"><span style=3D"color:#1F497D">-Meny <o:p></o:p></=
span></p>
<p class=3D"MsoPlainText"><o:p> </o:p></p>
<p class=3D"MsoPlainText"><o:p> </o:p></p>
<p class=3D"MsoPlainText">-----Original Message-----<br>
From: John Baldwin [mailto:jhb at freebsd.org] <br>
Sent: Friday, July 19, 2013 6:29 PM<br>
To: bug-followup at freebsd.org; Meny Yossefi<br>
Subject: Re: kern/180430: [ofed] [patch] Bad UDP checksum calc for fragment=
ed packets</p>
<p class=3D"MsoPlainText"><o:p> </o:p></p>
<p class=3D"MsoPlainText">Oops, my previous reply didn't make it to the PR =
itself.<o:p></o:p></p>
<p class=3D"MsoPlainText"><o:p> </o:p></p>
<p class=3D"MsoPlainText">Is the problem that the hardware checksum overwri=
tes arbitrary data in the packet (at the location where the UDP header woul=
d be)?<o:p></o:p></p>
<p class=3D"MsoPlainText"><o:p> </o:p></p>
<p class=3D"MsoPlainText">Also, I've looked at other drivers, and they all =
look at the CSUM_* flags to determine the right settings. IP fragment=
s will not have CSUM_UDP or CSUM_TCP set, so I think the more correct fix i=
s this:<o:p></o:p></p>
<p class=3D"MsoPlainText"><o:p> </o:p></p>
<p class=3D"MsoPlainText">Index: en_tx.c<o:p></o:p></p>
<p class=3D"MsoPlainText">=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D<o:p></o:p></p>
<p class=3D"MsoPlainText">--- en_tx.c &n=
bsp; (revision 253470)<o:p></o:p></p>
<p class=3D"MsoPlainText">+++ en_tx.c &n=
bsp; (working copy)<o:p></o:p></p>
<p class=3D"MsoPlainText">@@ -780,8 +780,12 @@ retry:<o:p></o:p></p>
<p class=3D"MsoPlainText"> &=
nbsp; tx_desc->ctrl.srcrb_flags =3D cpu_to=
_be32(MLX4_WQE_CTRL_CQ_UPDATE |<o:p></o:p></p>
<p class=3D"MsoPlainText"> &=
nbsp; &nbs=
p; &=
nbsp; &nbs=
p; &=
nbsp; &nbs=
p; &=
nbsp; MLX4_WQE_=
CTRL_SOLICITED);<o:p></o:p></p>
<p class=3D"MsoPlainText"> &=
nbsp; if (mb->m_pkthdr.csum_flags & (C=
SUM_IP|CSUM_TCP|CSUM_UDP)) {<o:p></o:p></p>
<p class=3D"MsoPlainText">- =
&nb=
sp; tx_desc->ctrl.srcrb_=
flags |=3D cpu_to_be32(MLX4_WQE_CTRL_IP_CSUM |<o:p></o:p></p>
<p class=3D"MsoPlainText">- =
&nb=
sp; =
&nb=
sp; =
&nb=
sp; =
&nb=
sp; =
MLX4_WQE_CTRL_TCP_UDP_CSUM);<o:p></o:p></p>
<p class=3D"MsoPlainText">+ &n=
bsp;  =
; if (mb->m_pkthdr.csum_=
flags & CSUM_IP)<o:p></o:p></p>
<p class=3D"MsoPlainText">+ &n=
bsp;  =
; &n=
bsp; tx_d=
esc->ctrl.srcrb_flags |=3D<o:p></o:p></p>
<p class=3D"MsoPlainText">+ &n=
bsp;  =
; &n=
bsp; &nbs=
p; cpu_to_be32(MLX4_WQE_CTRL_IP_CSUM);<o:p></o:p></p>
<p class=3D"MsoPlainText">+ &n=
bsp;  =
; if (mb->m_pkthdr.csum_=
flags & (CSUM_TCP|CSUM_UDP))<o:p></o:p></p>
<p class=3D"MsoPlainText">+ &n=
bsp;  =
; &n=
bsp; tx_d=
esc->ctrl.srcrb_flags |=3D<o:p></o:p></p>
<p class=3D"MsoPlainText">+ &n=
bsp;  =
; &n=
bsp; &nbs=
p; cpu_to_be32(MLX4_WQE_CTRL_TCP_UDP_CSUM);<o:p></o:p></p>
<p class=3D"MsoPlainText"> &=
nbsp; &nbs=
p; priv->port_stat=
s.tx_chksum_offload++;<o:p></o:p></p>
<p class=3D"MsoPlainText"> &=
nbsp; }<o:p></o:p></p>
<p class=3D"MsoPlainText"><o:p></o:p></p>
<p class=3D"MsoPlainText"><o:p> </o:p></p>
<p class=3D"MsoPlainText">--<o:p></o:p></p>
<p class=3D"MsoPlainText">John Baldwin<o:p></o:p></p>
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