From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mails.dpdk.org (mails.dpdk.org [217.70.189.124]) by inbox.dpdk.org (Postfix) with ESMTP id ECA4AA034C for ; Tue, 21 Jun 2022 11:35:12 +0200 (CEST) Received: from [217.70.189.124] (localhost [127.0.0.1]) by mails.dpdk.org (Postfix) with ESMTP id E7D30427E9; Tue, 21 Jun 2022 11:35:12 +0200 (CEST) Received: from smartserver.smartsharesystems.com (smartserver.smartsharesystems.com [77.243.40.215]) by mails.dpdk.org (Postfix) with ESMTP id DC2EA40151; Tue, 21 Jun 2022 11:35:09 +0200 (CEST) Content-class: urn:content-classes:message MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Subject: RE: [PATCH] net: fix checksum with unaligned buffer X-MimeOLE: Produced By Microsoft Exchange V6.5 Date: Tue, 21 Jun 2022 11:35:07 +0200 Message-ID: <98CBD80474FA8B44BF855DF32C47DC35D87148@smartserver.smartshare.dk> In-Reply-To: X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: [PATCH] net: fix checksum with unaligned buffer Thread-Index: AdiFSDAjLePhqVOxTS+NZiVf2zItKwAB4TGQ References: <98CBD80474FA8B44BF855DF32C47DC35D87139@smartserver.smartshare.dk> <20220617084505.62071-1-mb@smartsharesystems.com> <98CBD80474FA8B44BF855DF32C47DC35D8713A@smartserver.smartshare.dk> <98CBD80474FA8B44BF855DF32C47DC35D87141@smartserver.smartshare.dk> <98CBD80474FA8B44BF855DF32C47DC35D87145@smartserver.smartshare.dk> From: =?iso-8859-1?Q?Morten_Br=F8rup?= To: "Emil Berg" Cc: "Bruce Richardson" , "Stephen Hemminger" , , , , , X-BeenThere: stable@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: patches for DPDK stable branches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: stable-bounces@dpdk.org > From: Bruce Richardson [mailto:bruce.richardson@intel.com] > Sent: Tuesday, 21 June 2022 10.23 >=20 > On Tue, Jun 21, 2022 at 10:05:15AM +0200, Morten Br=F8rup wrote: > > +TO: @Bruce and @Stephen: You signed off on the 16 bit alignment > requirement. We need background info on this. > > > > > From: Emil Berg [mailto:emil.berg@ericsson.com] > > > Sent: Tuesday, 21 June 2022 09.17 > > > > > > > From: Morten Br=F8rup > > > > Sent: den 20 juni 2022 12:58 > > > > > > > > > From: Emil Berg [mailto:emil.berg@ericsson.com] > > > > > Sent: Monday, 20 June 2022 12.38 > > > > > > > > > > > From: Morten Br=F8rup > > > > > > Sent: den 17 juni 2022 11:07 > > > > > > > > > > > > > From: Morten Br=F8rup [mailto:mb@smartsharesystems.com] > > > > > > > Sent: Friday, 17 June 2022 10.45 > > > > > > > > > > > > > > With this patch, the checksum can be calculated on an > unligned > > > > > > > part > > > > > of > > > > > > > a packet buffer. > > > > > > > I.e. the buf parameter is no longer required to be 16 bit > > > aligned. > > > > > > > > > > > > > > The DPDK invariant that packet buffers must be 16 bit > aligned > > > > > remains > > > > > > > unchanged. > > > > > > > This invariant also defines how to calculate the 16 bit > > > checksum > > > > > > > on > > > > > an > > > > > > > unaligned part of a packet buffer. > > > > > > > > > > > > > > Bugzilla ID: 1035 > > > > > > > Cc: stable@dpdk.org > > > > > > > > > > > > > > Signed-off-by: Morten Br=F8rup > > > > > > > --- > > > > > > > lib/net/rte_ip.h | 17 +++++++++++++++-- > > > > > > > 1 file changed, 15 insertions(+), 2 deletions(-) > > > > > > > > > > > > > > diff --git a/lib/net/rte_ip.h b/lib/net/rte_ip.h index > > > > > > > b502481670..8e301d9c26 100644 > > > > > > > --- a/lib/net/rte_ip.h > > > > > > > +++ b/lib/net/rte_ip.h > > > > > > > @@ -162,9 +162,22 @@ __rte_raw_cksum(const void *buf, > size_t > > > len, > > > > > > > uint32_t sum) { > > > > > > > /* extend strict-aliasing rules */ > > > > > > > typedef uint16_t __attribute__((__may_alias__)) > u16_p; > > > > > > > - const u16_p *u16_buf =3D (const u16_p *)buf; > > > > > > > - const u16_p *end =3D u16_buf + len / sizeof(*u16_buf); > > > > > > > + const u16_p *u16_buf; > > > > > > > + const u16_p *end; > > > > > > > + > > > > > > > + /* if buffer is unaligned, keeping it byte order > > > independent */ > > > > > > > + if (unlikely((uintptr_t)buf & 1)) { > > > > > > > + uint16_t first =3D 0; > > > > > > > + if (unlikely(len =3D=3D 0)) > > > > > > > + return 0; > > > > > > > + ((unsigned char *)&first)[1] =3D *(const unsigned > > > > > > char *)buf; > > > > > > > + sum +=3D first; > > > > > > > + buf =3D (const void *)((uintptr_t)buf + 1); > > > > > > > + len--; > > > > > > > + } > > > > > > > > > > > > > > + u16_buf =3D (const u16_p *)buf; > > > > > > > + end =3D u16_buf + len / sizeof(*u16_buf); > > > > > > > for (; u16_buf !=3D end; ++u16_buf) > > > > > > > sum +=3D *u16_buf; > > > > > > > > > > > > > > -- > > > > > > > 2.17.1 > > > > > > > > > > > > @Emil, can you please test this patch with an unaligned > buffer on > > > > > your > > > > > > application to confirm that it produces the expected result. > > > > > > > > > > Hi! > > > > > > > > > > I tested the patch. It doesn't seem to produce the same > results. I > > > > > think the problem is that it always starts summing from an = even > > > > > address, the sum should always start from the first byte > according > > > to > > > > > the checksum specification. Can I instead propose something > Mattias > > > > > R=F6nnblom sent me? > > > > > > > > I assume that it produces the same result when the "buf" > parameter is > > > > aligned? > > > > > > > > And when the "buf" parameter is unaligned, I don't expect it to > > > produce the > > > > same results as the simple algorithm! > > > > > > > > This was the whole point of the patch: I expect the overall > packet > > > buffer to > > > > be 16 bit aligned, and the checksum to be a partial checksum of > such > > > a 16 bit > > > > aligned packet buffer. When calling this function, I assume that > the > > > "buf" and > > > > "len" parameters point to a part of such a packet buffer. If > these > > > > expectations are correct, the simple algorithm will produce > incorrect > > > results > > > > when "buf" is unaligned. > > > > > > > > I was asking you to test if the checksum on the packet is = correct > > > when your > > > > application modifies an unaligned part of the packet and uses > this > > > function to > > > > update the checksum. > > > > > > > > > > Now I understand your use case. Your use case seems to be about > partial > > > checksums, of which some partial checksums may start on unaligned > > > addresses in an otherwise aligned packet. > > > > > > Our use case is about calculating the full checksum on a nested > packet. > > > That nested packet may start on unaligned addresses. > > > > > > The difference is basically if we want to sum over aligned > addresses or > > > not, handling the heading and trailing bytes appropriately. > > > > > > Your method does not work in our case since we want to treat the > first > > > two bytes as the first word in our case. But I do understand that > both > > > methods are useful. > > > > Yes, that certainly are two different use cases, requiring two > different ways of calculating the 16 bit checksum. > > > > > > > > Note that your method breaks the API. Previously (assuming no > crashing > > > due to low optimization levels, more accepting hardware, or a > different > > > compiler (version)) the current method would calculate the = checksum > > > assuming the first two bytes is the first word. > > > > > > > Depending on the point of view, my patch either fixes a bug (where > the checksum was calculated incorrectly when the buf pointer was > unaligned) or breaks the API (by calculating the differently when the > buffer is unaligned). > > > > I cannot say with certainty which one is correct, but perhaps some = of > the people with a deeper DPDK track record can... > > > > @Bruce and @Stephen, in 2019 you signed off on a patch [1] > introducing a 16 bit alignment requirement to the Ethernet address > structure. > > > > It is my understanding that DPDK has an invariant requiring packets > to be 16 bit aligned, which that patch supports. Is this invariant > documented anywhere, or am I completely wrong? If I'm wrong, then the > alignment requirement introduced in that patch needs to be removed, as > well as any similar alignment requirements elsewhere in DPDK. >=20 > I don't believe it is explicitly documented as a global invariant, but > I > think it should be unless there is a definite case where we need to > allow > packets to be completely unaligned. Across all packet headers we = looked > at, > there was no tunneling protocol where the resulting packet was left > unaligned. >=20 > That said, if there are real use cases where we need to allow packets > to > start at an unaligned address, then I agree with you that we need to > roll > back the patch and work to ensure everything works with unaligned > addresses. >=20 > /Bruce > @Emil, can you please describe or refer to which tunneling protocol you = are using, where the nested packet can be unaligned? I am asking to determine if your use case is exotic (maybe some Ericsson = proprietary protocol), or more generic (rooted in some standard = protocol). This information affects the DPDK community's opinion about = how it should be supported by DPDK. If possible, please provide more details about the tunneling protocol = and nested packets... E.g. do the nested packets also contain Layer 2 = (Ethernet, VLAN, etc.) headers, or only Layer 3 (IP) or Layer 4 (TCP, = UDP, etc.)? And how about ARP packets and Layer 2 control protocol = packets (STP, LACP, etc.)? > > > > [1] > = http://git.dpdk.org/dpdk/commit/lib/librte_net/rte_ether.h?id=3Dda5350ef2= > 9afd35c1adabe76f60832f3092269ad > > > > @Emil, we should wait for a conclusion about the alignment invariant > before we proceed. > > > > If there is no such invariant, my patch is wrong, and we need to > provide a v2 of the patch, which will then fit your use case. > > If there is such an invariant, my patch is correct, and another > function must be added for your use case. > >