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Subject: [PATCH v3] virtio-net: Add support for correct hdr_len field.
Fixes: https://github.com/oasis-tcs/virtio-spec/issues/57
>-----Original Message-----
>From: virtio-comment@lists.oasis-open.org <virtio-comment@lists.oasis-
>open.org> On Behalf Of Vitaly Mireyno
>Sent: Tuesday, 5 November, 2019 17:26
>To: virtio-comment@lists.oasis-open.org
>Cc: Michael S. Tsirkin <mst@redhat.com>; Jason Wang
><jasowang@redhat.com>
>Subject: [EXT] [virtio-comment] [PATCH v3] virtio-net: Add support for correct
>hdr_len field.
>
>Incorporated more v1 comments
>
>Changes from v2:
> * Added device implementation note for using hdr_len
>
>Signed-off-by: Vitaly Mireyno <vmireyno@marvell.com>
>---
> content.tex | 56 +++++++++++++++++++++++++++++++++++++++++++-----
>-----
> 1 file changed, 46 insertions(+), 10 deletions(-)
>
>diff --git a/content.tex b/content.tex
>index b1ea9b9..5d3f865 100644
>--- a/content.tex
>+++ b/content.tex
>@@ -2811,6 +2811,9 @@ \subsection{Feature bits}\label{sec:Device Types /
>Network Device / Feature bits \item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)]
>Set MAC address through control
> channel.
>
>+\item[VIRTIO_NET_F_GUEST_HDRLEN(59)] Driver can provide the exact
>\field{hdr_len}
>+ value. Device benefits from knowing the exact header length.
>+
> \item[VIRTIO_NET_F_RSC_EXT(61)] Device can process duplicated ACKs
> and report number of coalesced segments and duplicated ACKs
>
>@@ -3095,12 +3098,21 @@ \subsubsection{Packet
>Transmission}\label{sec:Device Types / Network Device / De
> into smaller packets. The other gso fields are set:
>
> \begin{itemize}
>- \item \field{hdr_len} is a hint to the device as to how much of the header
>+ \item If the VIRTIO_NET_F_GUEST_HDRLEN feature has been negotiated,
>+ \field{hdr_len} indicates the header length that needs to be replicated
>+ for each packet. It's a number of bytes from beginning of the packet
>+ to beginning of the transport payload.
>+ Otherwise, if the VIRTIO_NET_F_GUEST_HDRLEN feature has not been
>negotiated,
>+ \field{hdr_len} is a hint to the device as to how much of the
>+ header
> needs to be kept to copy into each packet, usually set to the
> length of the headers, including the transport header\footnote{Due to
>various bugs in implementations, this field is not useful as a guarantee of the
>transport header size.
> }.
>
>+ \begin{note}
>+ Some devices benefit from knowledge of the exact header length.
>+ \end{note}
>+
> \item \field{gso_size} is the maximum size of each packet beyond that
> header (ie. MSS).
>
>@@ -3173,9 +3185,20 @@ \subsubsection{Packet
>Transmission}\label{sec:Device Types / Network Device / De desired MSS.
>
> If one of the VIRTIO_NET_F_HOST_TSO4, TSO6 or UFO options have -been
>negotiated, the driver SHOULD set \field{hdr_len} to a value -not less than the
>length of the headers, including the transport -header.
>+been negotiated:
>+\begin{itemize}
>+\item If the VIRTIO_NET_F_GUEST_HDRLEN feature has been negotiated,
>+ the driver MUST set \field{hdr_len} to a value equal to the length
>+ of the headers, including the transport header.
>+
>+\item If the VIRTIO_NET_F_GUEST_HDRLEN feature has not been
>negotiated,
>+ the driver SHOULD set \field{hdr_len} to a value
>+ not less than the length of the headers, including the transport
>+ header.
>+\end{itemize}
>+
>+The driver SHOULD accept the VIRTIO_NET_F_GUEST_HDRLEN feature if it
>+has been offered, and if it's able to provide the exact header length.
>
> The driver MUST NOT set the VIRTIO_NET_HDR_F_DATA_VALID and
>VIRTIO_NET_HDR_F_RSC_INFO bits in \field{flags}.
>@@ -3187,12 +3210,25 @@ \subsubsection{Packet
>Transmission}\label{sec:Device Types / Network Device / De device MUST
>NOT use the \field{csum_start} and \field{csum_offset}.
>
> If one of the VIRTIO_NET_F_HOST_TSO4, TSO6 or UFO options have -been
>negotiated, the device MAY use \field{hdr_len} only as a hint about the -
>transport header size.
>-The device MUST NOT rely on \field{hdr_len} to be correct.
>-\begin{note}
>-This is due to various bugs in implementations.
>-\end{note}
>+been negotiated:
>+\begin{itemize}
>+\item If the VIRTIO_NET_F_GUEST_HDRLEN feature has been negotiated,
>+ the device MAY use \field{hdr_len} as the transport header size.
>+
>+ \begin{note}
>+ Caution should be taken by the implementation so as to prevent
>+ malicious driver from attacking the device by setting incorrect hdr_len.
>+ \end{note}
>+
>+\item If the VIRTIO_NET_F_GUEST_HDRLEN feature has not been
>negotiated,
>+ the device MAY use \field{hdr_len} only as a hint about the
>+ transport header size.
>+ The device MUST NOT rely on \field{hdr_len} to be correct.
>+
>+ \begin{note}
>+ This is due to various bugs in implementations.
>+ \end{note}
>+\end{itemize}
>
> If VIRTIO_NET_HDR_F_NEEDS_CSUM is not set, the device MUST NOT rely
>on the packet checksum being correct.
>--
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