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Tsirkin" To: "Chia-Yu Chang (Nokia)" Cc: "virtio-comment@lists.linux.dev" , "cohuck@redhat.com" , "mvaralar@redhat.com" , "jasowang@redhat.com" , "xuanzhuo@linux.alibaba.com" , "eperezma@redhat.com" , "ij@kernel.org" , "ncardwell@google.com" , "Koen De Schepper (Nokia)" , "g.white" , vidhi_goel , "ingemar.s.johansson@ericsson.com" , "mirja.kuehlewind@ericsson.com" Subject: Re: [PATCH v6 1/2] virtio-net: Fix ECN feature descritpion Message-ID: <20250415132904-mutt-send-email-mst@kernel.org> References: <20250414153425.99726-1-chia-yu.chang@nokia-bell-labs.com> <20250414153425.99726-2-chia-yu.chang@nokia-bell-labs.com> <20250414145806-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: virtio-comment@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: QJd8bUeW5PSypYAfrOgXFWI89BGq_iiEwsd0QHo_jKQ_1744738229 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Tue, Apr 15, 2025 at 01:33:45PM +0000, Chia-Yu Chang (Nokia) wrote: > > -----Original Message----- > > From: Michael S. Tsirkin > > Sent: Monday, April 14, 2025 8:59 PM > > To: Chia-Yu Chang (Nokia) > > Cc: virtio-comment@lists.linux.dev; cohuck@redhat.com; mvaralar@redhat.com; jasowang@redhat.com; xuanzhuo@linux.alibaba.com; eperezma@redhat.com; ij@kernel.org; ncardwell@google.com; Koen De Schepper (Nokia) ; g.white ; vidhi_goel ; ingemar.s.johansson@ericsson.com; mirja.kuehlewind@ericsson.com > > Subject: Re: [PATCH v6 1/2] virtio-net: Fix ECN feature descritpion > > > > > > CAUTION: This is an external email. Please be very careful when clicking links or opening attachments. See the URL nok.it/ext for additional information. > > > > > > > > On Mon, Apr 14, 2025 at 05:34:24PM +0200, chia-yu.chang@nokia-bell-labs.com wrote: > > > From: Chia-Yu Chang > > > > > > Clarify that the VIRTIO_NET_HDR_GSO_ECN gso_type flag does not mean > > > that TCP has IP-ECN set, instead it identifies TCP CWR flag is set and > > > will be cleared from the second segment. This is used to offload TCP > > > CWR flag in a way that is compatible with RFC3168 ECN but is > > > problematic for non-RFC3168 use of CWR flag. > > > > > > Signed-off-by: Chia-Yu Chang > > > --- > > > > > > if this is accepted, we might want to backport this to 1.3 maybe? > > Thanks for feedback. > In my opinion, this fix shall be backported to clarify its relation to RFC3168 ECN. > Shall we make further patch, or you will do the merge once this patch is accepted? > > Best regards, > Chia-Yu For the backport, you will need to open another github issue. > > > > > > > device-types/net/description.tex | 33 +++++++++++++++++--------------- > > > introduction.tex | 3 +++ > > > 2 files changed, 21 insertions(+), 15 deletions(-) > > > > > > diff --git a/device-types/net/description.tex > > > b/device-types/net/description.tex > > > index 1b6b54d..a2c9de8 100644 > > > --- a/device-types/net/description.tex > > > +++ b/device-types/net/description.tex > > > @@ -54,7 +54,9 @@ \subsection{Feature bits}\label{sec:Device Types / > > > Network Device / Feature bits > > > > > > \item[VIRTIO_NET_F_GUEST_TSO6 (8)] Driver can receive TSOv6. > > > > > > -\item[VIRTIO_NET_F_GUEST_ECN (9)] Driver can receive TSO with ECN. > > > +\item[VIRTIO_NET_F_GUEST_ECN (9)] Driver can receive TSO with TCP CWR flag set > > > + and follow the ACE bits handling approach mentioned in > > > + \hyperref[intro:rfc3168]{[RFC3168]}. > > > > > > \item[VIRTIO_NET_F_GUEST_UFO (10)] Driver can receive UFO. > > > > > > @@ -62,7 +64,9 @@ \subsection{Feature bits}\label{sec:Device Types / > > > Network Device / Feature bits > > > > > > \item[VIRTIO_NET_F_HOST_TSO6 (12)] Device can receive TSOv6. > > > > > > -\item[VIRTIO_NET_F_HOST_ECN (13)] Device can receive TSO with ECN. > > > +\item[VIRTIO_NET_F_HOST_ECN (13)] Device can receive TSO with TCP CWR flag set > > > + and follow the ACE bits handling approach mentioend in > > > + \hyperref[intro:rfc3168]{[RFC3168]}. > > > > > > \item[VIRTIO_NET_F_HOST_UFO (14)] Device can receive UFO. > > > > > > @@ -695,8 +699,9 @@ \subsubsection{Packet > > > Transmission}\label{sec:Device Types / Network Device / De > > > > > > \item If the driver negotiated the VIRTIO_NET_F_HOST_ECN feature, > > > the VIRTIO_NET_HDR_GSO_ECN bit in \field{gso_type} > > > - indicates that the TCP packet has the ECN bit set\footnote{This case is not handled by some older hardware, so is called out > > > -specifically in the protocol.}. > > > + indicates that the TCP packet has TCP CWR flag set and the flag will be handled differently to all segements of > > > + an aggregated segment, as mentioned in \hyperref[intro:rfc3168]{[RFC3168]} > > > + \footnote{This case is not handled by some older hardware, so is called out specifically in the protocol.}. > > > \end{itemize} > > > > > > \item If the driver negotiated the VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO > > > feature and the @@ -788,10 +793,9 @@ \subsubsection{Packet > > > Transmission}\label{sec:Device Types / Network Device / De \field{gso_type} to VIRTIO_NET_HDR_GSO_UDP_L4. > > > > > > The driver SHOULD NOT send to the device TCP packets requiring > > > segmentation offload -which have the Explicit Congestion Notification > > > bit set, unless the -VIRTIO_NET_F_HOST_ECN feature is negotiated, in > > > which case the -driver MUST set the VIRTIO_NET_HDR_GSO_ECN bit in > > > -\field{gso_type}. > > > +which have the TCP CWR flag set and require the flag be handled as > > > +mentioned in \hyperref[intro:rfc3168]{[RFC3168]}, unless the > > > +VIRTIO_NET_F_HOST_ECN feature is negotiated, in which case the driver MUST set the VIRTIO_NET_HDR_GSO_ECN bit in \field{gso_type}. > > > > > > If VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO is negotiated, the driver MAY set > > > VIRTIO_NET_HDR_GSO_UDP_TUNNEL_IPV4 bit or the > > > VIRTIO_NET_HDR_GSO_UDP_TUNNEL_IPV6 bit @@ -1105,9 +1109,9 @@ > > > \subsubsection{Processing of Incoming Packets}\label{sec:Device Types > > > / Network \end{enumerate} > > > > > > Additionally, VIRTIO_NET_F_GUEST_CSUM, TSO4, TSO6, UDP, UDP_TUNNEL > > > -and ECN features enable receive checksum, large receive offload and > > > ECN -support which are the input equivalents of the transmit checksum, > > > -transmit segmentation offloading and ECN features, as described > > > +and ECN features enable receive checksum, large receive offload and > > > +RFC3168 ECN support which are the input equivalents of the transmit > > > +checksum, transmit segmentation offloading and RFC3168 ECN features, > > > +as described > > > in \ref{sec:Device Types / Network Device / Device Operation / > > > Packet Transmission}: > > > \begin{enumerate} > > > @@ -1210,10 +1214,9 @@ \subsubsection{Processing of Incoming > > > Packets}\label{sec:Device Types / Network the VIRTIO_NET_HDR_F_UDP_TUNNEL_CSUM bit in \field{flags}. > > > > > > The device SHOULD NOT send to the driver TCP packets requiring > > > segmentation offload -which have the Explicit Congestion Notification > > > bit set, unless the -VIRTIO_NET_F_GUEST_ECN feature is negotiated, in > > > which case the -device MUST set the VIRTIO_NET_HDR_GSO_ECN bit in > > > -\field{gso_type}. > > > +which have the TCP CWR flag set and require the flag be handled as > > > +mentioned in \hyperref[intro:rfc3168]{[RFC3168]}, unless the > > > +VIRTIO_NET_F_GUEST_ECN feature is negotiated, in which case the device MUST set the VIRTIO_NET_HDR_GSO_ECN bit in \field{gso_type}. > > > > > > If the VIRTIO_NET_F_GUEST_CSUM feature has been negotiated, the > > > device MAY set the VIRTIO_NET_HDR_F_NEEDS_CSUM bit in diff --git > > > a/introduction.tex b/introduction.tex index e60298a..d52622e 100644 > > > --- a/introduction.tex > > > +++ b/introduction.tex > > > @@ -168,6 +168,9 @@ \section{Normative References}\label{sec:Normative References} > > > Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP > > > 14, RFC 8174, DOI 10.17487/RFC8174, May 2017 > > > \newline\url{http://www.ietf.org/rfc/rfc8174.txt}\\ > > > + \phantomsection\label{intro:rfc3168}\textbf{[RFC3168]} & > > > + S. Floyd., ``The Addition of Explicit Congestion Notification (ECN) to IP'', September 2001. > > > + \newline\url{http://www.ietf.org/rfc/rfc3168.txt}\\ > > > \end{longtable} > > > > > > \section{Non-Normative References} > > > -- > > > 2.34.1