RE: [PATCH v10 2/2] virtio-net: Define Accurate ECN feature in virtio-spec

> From: [email protected] <chia-yu.chang@nokia-bell-
> labs.com>
> 
> From: Chia-Yu Chang <[email protected]>
> 
> This change implements Accurate ECN based on the AccECN specification
> (RFC-to-be 9768):
> 
> https://tools.ietf.org/id/draft-ietf-tcpm-accurate-ecn-34.txt
> 
is this approved IETF draft or there is next version after this?
Suggested link indicates that this draft expires on 11th this month.


> Unlike RFC3168 ECN, Accurate ECN uses the TCP CWR flag as part of the ACE
> field to count new packets with CE marks in the IP-ECN field; however, RFC
> 3168 ECN-aware TSO will clean the TCP CWR flag from the 2nd segment of an
> aggregated segment. Therefore, fallback shall be applied by setting
> NETIF_F_GSO_ACCECN to ensure that the CWR flag should not be changed
> within the aggregated segment (e.g., super-skb in Linux).
> 
It would be to add the link in commit message to NETIF_F_GSO_ACCECN Linux kernel documentation.

> To apply it in virtio-spec, new feature bits for host and guest are added for
> feature negotiation between driver and device. And the translation of the
> Accurate ECN GSO flag between virtio_net_hdr and skb header for
> NETIF_F_GSO_ACCECN is also added to avoid CWR flag corruption due to
> RFC3168 ECN TSO.
> 
> Signed-off-by: Chia-Yu Chang <[email protected]>
> ---
>  device-types/net/description.tex | 54 +++++++++++++++++++++++++-------
>  introduction.tex                 |  3 ++
>  2 files changed, 46 insertions(+), 11 deletions(-)
> 
> diff --git a/device-types/net/description.tex b/device-
> types/net/description.tex
> index 0da8f9f..6761148 100644
> --- a/device-types/net/description.tex
> +++ b/device-types/net/description.tex
> @@ -150,6 +150,15 @@ \subsection{Feature bits}\label{sec:Device Types /
> Network Device / Feature bits
>   when VIRTIO_NET_F_IPSEC is negotiated. When a device offers IPsec feature,
> it SHOULD
>   also offer the VIRTIO_NET_F_OUT_NET_HEADER feature.
> 
> +\item[VIRTIO_NET_F_HOST_ACCECN (71)] Device can receive TSO and follow
> +  the requirements of the ACE field described in
> +  ``Section 3.3.4 . Requirements for TCP Segmentation Offload and Large
> Receive Offload''
> +  of \hyperref[intro:accecn]{[AccECN]}.
> +
> +\item[VIRTIO_NET_F_GUEST_ACCECN (72)] Driver can receive TSO and
> follow
> +  the requirements of the ACE field described in
> +  ``Section 3.3.4 . Requirements for TCP Segmentation Offload and Large
> Receive Offload''
> +  of \hyperref[intro:accecn]{[AccECN]}.
>  \end{description}
> 
>  \subsubsection{Feature bit requirements}\label{sec:Device Types / Network
> Device / Feature bits / Feature bit requirements} @@ -161,6 +170,7 @@
> \subsubsection{Feature bit requirements}\label{sec:Device Types / Network
> Device  \item[VIRTIO_NET_F_GUEST_TSO4] Requires
> VIRTIO_NET_F_GUEST_CSUM.
>  \item[VIRTIO_NET_F_GUEST_TSO6] Requires VIRTIO_NET_F_GUEST_CSUM.
>  \item[VIRTIO_NET_F_GUEST_ECN] Requires VIRTIO_NET_F_GUEST_TSO4 or
> VIRTIO_NET_F_GUEST_TSO6.
> +\item[VIRTIO_NET_F_GUEST_ACCECN] Requires
> VIRTIO_NET_F_GUEST_TSO4 or VIRTIO_NET_F_GUEST_TSO6.
>  \item[VIRTIO_NET_F_GUEST_UFO] Requires VIRTIO_NET_F_GUEST_CSUM.
>  \item[VIRTIO_NET_F_GUEST_USO4] Requires VIRTIO_NET_F_GUEST_CSUM.
>  \item[VIRTIO_NET_F_GUEST_USO6] Requires VIRTIO_NET_F_GUEST_CSUM.
> @@ -171,6 +181,7 @@ \subsubsection{Feature bit
> requirements}\label{sec:Device Types / Network Device
> \item[VIRTIO_NET_F_HOST_TSO4] Requires VIRTIO_NET_F_CSUM.
>  \item[VIRTIO_NET_F_HOST_TSO6] Requires VIRTIO_NET_F_CSUM.
>  \item[VIRTIO_NET_F_HOST_ECN] Requires VIRTIO_NET_F_HOST_TSO4 or
> VIRTIO_NET_F_HOST_TSO6.
> +\item[VIRTIO_NET_F_HOST_ACCECN] Requires VIRTIO_NET_F_HOST_TSO4
> or VIRTIO_NET_F_HOST_TSO6.
>  \item[VIRTIO_NET_F_HOST_UFO] Requires VIRTIO_NET_F_CSUM.
>  \item[VIRTIO_NET_F_HOST_USO] Requires VIRTIO_NET_F_CSUM.
>  \item[VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO] Requires
> VIRTIO_NET_F_HOST_TSO4, VIRTIO_NET_F_HOST_TSO6 @@ -294,11
> +305,11 @@ \subsection{Device configuration layout}\label{sec:Device Types
> / Network Device  The device MUST NOT modify \field{mtu} once it has been
> set.
> 
>  The device MUST NOT pass received packets that exceed \field{mtu} (plus low
> -level ethernet header length) size with \field{gso_type} NONE or ECN
> +level ethernet header length) size with \field{gso_type} NONE, ECN or
> +ACCECN
>  after VIRTIO_NET_F_MTU has been successfully negotiated.
> 
>  The device MUST forward transmitted packets of up to \field{mtu} (plus low -
> level ethernet header length) size with \field{gso_type} NONE or ECN, and do
> +level ethernet header length) size with \field{gso_type} NONE, ECN or
> +ACCECN, and do
>  so without fragmentation, after VIRTIO_NET_F_MTU has been successfully
> negotiated.
> 
> @@ -348,11 +359,11 @@ \subsection{Device configuration
> layout}\label{sec:Device Types / Network Device
> 
>  If the driver negotiates VIRTIO_NET_F_MTU, it MUST supply enough receive
> buffers to receive at least one receive packet of size \field{mtu} (plus low -level
> ethernet header length) with \field{gso_type} NONE or ECN.
> +level ethernet header length) with \field{gso_type} NONE, ECN or ACCECN.
> 
>  If the driver negotiates VIRTIO_NET_F_MTU, it MUST NOT transmit packets of
> size exceeding the value of \field{mtu} (plus low level ethernet header length) -
> with \field{gso_type} NONE or ECN.
> +with \field{gso_type} NONE, ECN or ACCECN.
> 
>  A driver SHOULD negotiate the VIRTIO_NET_F_STANDBY feature if the device
> offers it.
> 
> @@ -443,7 +454,7 @@ \subsection{Device Initialization}\label{sec:Device
> Types / Network Device / Dev
>     The VIRTIO_NET_F_GUEST_CSUM feature indicates that partially
>    checksummed packets can be received, and if it can do that then
>    the VIRTIO_NET_F_GUEST_TSO4, VIRTIO_NET_F_GUEST_TSO6,
> -  VIRTIO_NET_F_GUEST_UFO, VIRTIO_NET_F_GUEST_ECN,
> VIRTIO_NET_F_GUEST_USO4,
> +  VIRTIO_NET_F_GUEST_UFO, VIRTIO_NET_F_GUEST_ECN,
> + VIRTIO_NET_F_GUEST_ACCECN, VIRTIO_NET_F_GUEST_USO4,
>    VIRTIO_NET_F_GUEST_USO6 VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO
> and
>    VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO_CSUM are the input equivalents
> of
>    the features described above.
> @@ -613,6 +624,7 @@ \subsection{Device Operation}\label{sec:Device
> Types / Network Device / Device O  #define
> VIRTIO_NET_HDR_GSO_UDP_TUNNEL_IPV4 0x20  #define
> VIRTIO_NET_HDR_GSO_UDP_TUNNEL_IPV6 0x40
>  #define VIRTIO_NET_HDR_GSO_ECN      0x80
> +#define VIRTIO_NET_HDR_GSO_ACCECN   0x10
>          u8 gso_type;
>          le16 hdr_len;
>          le16 gso_size;
> @@ -737,6 +749,13 @@ \subsubsection{Packet
> Transmission}\label{sec:Device Types / Network Device / De
>      has the CWR flag set and follows the requirements of the CWR flag
> described in
>      ``Section 6.1.2. The TCP Sender'' of \hyperref[intro:rfc3168]{[RFC3168]}.
>      \footnote{This case is not handled by some older hardware, so is called out
> specifically in the protocol.}.
> +
> +  \item If the driver negotiated the VIRTIO_NET_F_HOST_ACCECN feature,
> +    the VIRTIO_NET_HDR_GSO_ACCECN bit in \field{gso_type} indicates that
> the TCP packet
> +    follows the requirements of the ACE field described in
> +    ``Section 3.3.4 . Requirements for TCP Segmentation Offload and Large
> Receive Offload''
> +    of \hyperref[intro:accecn]{[AccECN]}.
> +    \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 @@ -837,6 +856,12 @@ \subsubsection{Packet
> Transmission}\label{sec:Device Types / Network Device / De  of
> \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}.
> 
> +The driver SHOULD NOT send to the device TCP packets requiring
> +segmentation offload which need to follow the ACE field requirements
> +described in ``Section 3.3.4 . Requirements for TCP Segmentation Offload and
> Large Receive Offload''
> +of \hyperref[intro:accecn]{[AccECN]}, unless the
> +VIRTIO_NET_F_HOST_ACCECN feature is negotiated, in which case the driver
> MUST set the VIRTIO_NET_HDR_GSO_ACCECN 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  in \field{gso_type} according
> to the inner network header protocol type @@ -1171,12 +1196,12 @@
> \subsubsection{Processing of Incoming Packets}\label{sec:Device Types /
> Network
>    value to indicate the outer network header offset in packet.
>  \end{enumerate}
> 
> -Additionally, VIRTIO_NET_F_GUEST_CSUM, TSO4, TSO6, UDP, UDP_TUNNEL
> -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}:
> +Additionally, VIRTIO_NET_F_GUEST_CSUM, TSO4, TSO6, UDP, UDP_TUNNEL,
> ECN
> +and ACCECN features enable receive checksum, large receive offload,
> +RFC3168 ECN and Accurate ECN support which are the input equivalents of
> +the transmit checksum, transmit segmentation offloading, RFC3168 ECN
> +and Accurate ECN features, as described in \ref{sec:Device Types /
> +Network Device / Device Operation / Packet Transmission}:
>  \begin{enumerate}
>  \item If the VIRTIO_NET_F_GUEST_TSO4, TSO6, UFO, USO4 or USO6 options
> were
>    negotiated, then \field{gso_type} MAY be something other than @@ -
> 1286,6 +1311,12 @@ \subsubsection{Processing of Incoming
> Packets}\label{sec:Device Types / Network  if packet contains a valid network
> header. Otherwise, the device MUST not  use \field{outer_nh_offset}.
> 
> +The device SHOULD NOT send to the driver TCP packets requiring
> +segmentation offload which need to follow the ACE field requirements
> +described in ``Section 3.3.4 . Requirements for TCP Segmentation Offload and
> Large Receive Offload''
> +of \hyperref[intro:accecn]{[AccECN]}, unless the
> +VIRTIO_NET_F_GUEST_ACCECN feature is negotiated, in which case the
> device MUST set the VIRTIO_NET_HDR_GSO_ACCECN 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  \field{flags}, if so:
> @@ -2286,6 +2317,7 @@ \subsubsection{Control
> Virtqueue}\label{sec:Device Types / Network Device / Devi  #define
> VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO_CSUM 47
>  #define VIRTIO_NET_F_GUEST_USO4       54
>  #define VIRTIO_NET_F_GUEST_USO6       55
> +#define VIRTIO_NET_F_GUEST_ACCECN     70
> 
>  #define VIRTIO_NET_CTRL_GUEST_OFFLOADS       5
>   #define VIRTIO_NET_CTRL_GUEST_OFFLOADS_SET   0
> diff --git a/introduction.tex b/introduction.tex index 1c4cb33..fabefe4 100644
> --- a/introduction.tex
> +++ b/introduction.tex
> @@ -183,6 +183,9 @@ \section{Normative References}\label{sec:Normative
> References}
>  	\phantomsection\label{intro:rfc3168}\textbf{[RFC3168]} &
>      S. Floyd., ``The Addition of Explicit Congestion Notification (ECN) to IP'',
> September 2001.
> 
> 	\newline\url{https://nam11.safelinks.protection.outlook.com/?url=h
> ttp%3A%2F%2Fwww.ietf.org%2Frfc%2Frfc3168.txt&data=05%7C02%7Cpara
> v%40nvidia.com%7Ccd0d940b2c75467aded808dddb2a55ed%7C43083d15
> 727340c1b7db39efd9ccc17a%7C0%7C0%7C638907697092805411%7CUn
> known%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAw
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> 7C&sdata=q85q1Dlh1v%2Bvf5PUA4D3KlNdTkm6FNhy701It%2BS7648%3D
> &reserved=0}\\
> +        \phantomsection\label{intro:accecn}\textbf{[AccECN]} &
> +    B. Briscoe., ``More Accurate Explicit Congestion Notification (AccECN)
> Feedback in TCP'', March 2025.
> +
> + \newline\url{https://nam11.safelinks.protection.outlook.com/?url=https
> + %3A%2F%2Fwww.ietf.org%2Farchive%2Fid%2Fdraft-ietf-tcpm-accurate-
> ecn-34
> +
> .txt&data=05%7C02%7Cparav%40nvidia.com%7Ccd0d940b2c75467aded80
> 8dddb2a5
> +
> 5ed%7C43083d15727340c1b7db39efd9ccc17a%7C0%7C0%7C6389076970
> 92821586%7C
> +
> Unknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMD
> AwMCIsIlAi
> +
> OiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdat
> a=nFBacE
> + %2BDuwZTbFR6kPuHdJaBt3tWOLzUjrLsYDyRKso%3D&reserved=0}\\
>  \end{longtable}
> 
>  \section{Non-Normative References}
> --
> 2.34.1
>