The following reply was made to PR kern/180430; it has been noted by GNATS.

From: Meny Yossefi <me...@mellanox.com>
To: John Baldwin <j...@freebsd.org>, "bug-follo...@freebsd.org"
        <bug-follo...@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:j...@freebsd.org]
 Sent: Friday, July 19, 2013 6:29 PM
 To: bug-follo...@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>&nbsp;</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 packet&#821=
 7;s payload as a whole.<o:p></o:p></span></p>
 <p class=3D"MsoPlainText"><span style=3D"color:#1F497D"><o:p>&nbsp;</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 &#8216;likely=
 &#8217; can be useful here ?<o:p></o:p></span></p>
 <p class=3D"MsoPlainText"><o:p>&nbsp;</o:p></p>
 <p class=3D"MsoPlainText"><span style=3D"color:#1F497D">BTW, I&#8217;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>&nbsp;</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>&nbsp;</o:p></p>
 <p class=3D"MsoPlainText"><o:p>&nbsp;</o:p></p>
 <p class=3D"MsoPlainText">-----Original Message-----<br>
 From: John Baldwin [mailto:j...@freebsd.org] <br>
 Sent: Friday, July 19, 2013 6:29 PM<br>
 To: bug-follo...@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>&nbsp;</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>&nbsp;</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>&nbsp;</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.&nbsp; 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>&nbsp;</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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
 bsp;&nbsp;&nbsp;&nbsp; (revision 253470)<o:p></o:p></p>
 <p class=3D"MsoPlainText">&#43;&#43;&#43; en_tx.c&nbsp;&nbsp;&nbsp;&nbsp;&n=
 bsp;&nbsp;&nbsp; (working copy)<o:p></o:p></p>
 <p class=3D"MsoPlainText">@@ -780,8 &#43;780,12 @@ retry:<o:p></o:p></p>
 <p class=3D"MsoPlainText">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&=
 nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; tx_desc-&gt;ctrl.srcrb_flags =3D cpu_to=
 _be32(MLX4_WQE_CTRL_CQ_UPDATE |<o:p></o:p></p>
 <p class=3D"MsoPlainText">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&=
 nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbs=
 p;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&=
 nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbs=
 p;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&=
 nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbs=
 p;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&=
 nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; MLX4_WQE_=
 CTRL_SOLICITED);<o:p></o:p></p>
 <p class=3D"MsoPlainText">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&=
 nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if (mb-&gt;m_pkthdr.csum_flags &amp; (C=
 SUM_IP|CSUM_TCP|CSUM_UDP)) {<o:p></o:p></p>
 <p class=3D"MsoPlainText">-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb=
 sp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; tx_desc-&gt;ctrl.srcrb_=
 flags |=3D cpu_to_be32(MLX4_WQE_CTRL_IP_CSUM |<o:p></o:p></p>
 <p class=3D"MsoPlainText">-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb=
 sp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb=
 sp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb=
 sp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb=
 sp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=
 &nbsp; MLX4_WQE_CTRL_TCP_UDP_CSUM);<o:p></o:p></p>
 <p class=3D"MsoPlainText">&#43;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
 bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
 ;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if (mb-&gt;m_pkthdr.csum_=
 flags &amp; CSUM_IP)<o:p></o:p></p>
 <p class=3D"MsoPlainText">&#43;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
 bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
 ;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
 bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; tx_d=
 esc-&gt;ctrl.srcrb_flags |=3D<o:p></o:p></p>
 <p class=3D"MsoPlainText">&#43;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
 bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
 ;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
 bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbs=
 p;&nbsp;&nbsp; cpu_to_be32(MLX4_WQE_CTRL_IP_CSUM);<o:p></o:p></p>
 <p class=3D"MsoPlainText">&#43;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
 bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
 ;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if (mb-&gt;m_pkthdr.csum_=
 flags &amp; (CSUM_TCP|CSUM_UDP))<o:p></o:p></p>
 <p class=3D"MsoPlainText">&#43;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
 bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
 ;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
 bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; tx_d=
 esc-&gt;ctrl.srcrb_flags |=3D<o:p></o:p></p>
 <p class=3D"MsoPlainText">&#43;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
 bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
 ;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
 bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbs=
 p;&nbsp;&nbsp; cpu_to_be32(MLX4_WQE_CTRL_TCP_UDP_CSUM);<o:p></o:p></p>
 <p class=3D"MsoPlainText">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&=
 nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbs=
 p;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; priv-&gt;port_stat=
 s.tx_chksum_offload&#43;&#43;;<o:p></o:p></p>
 <p class=3D"MsoPlainText">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&=
 nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; }<o:p></o:p></p>
 <p class=3D"MsoPlainText"><o:p></o:p></p>
 <p class=3D"MsoPlainText"><o:p>&nbsp;</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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