Re: [virtio-comment] Re: [PATCH v13] virtio-net: support inner header hash

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Apr 25, 2023 at 04:28:33PM -0400, Parav Pandit wrote:
> 
> 
> On 4/23/2023 3:35 AM, Heng Qi wrote:
> >   \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types / Network Device / Feature bits / Legacy Interface: Feature bits}
> > @@ -198,6 +202,7 @@ \subsection{Device configuration layout}\label{sec:Device Types / Network Device
> >           u8 rss_max_key_size;
> >           le16 rss_max_indirection_table_length;
> >           le32 supported_hash_types;
> > +        le32 supported_tunnel_hash_types;

this needs a comment explaining it only exists with some
feature bits.

> >   };
> In v12 I was asking this to move to above field from the config area to the
> GET command in comment [1] as,
> 
> "With that no need to define two fields at two different places in config
> area and also in cvq."

I think I disagree.
the proposed design is consistent with regular tunneling.

however I feel we should limit this to 1-2 legacy protocols.
with that, we do not really need a new field at all,
they can fit in supported_hash_types.




> I am sorry if that was not clear enough.
> 
> [1] https://lore.kernel.org/virtio-dev/569cbaf9-f1fb-0e1f-a2ef-b1d7cd7dbb1f@nvidia.com/
> 
> >   \subparagraph{Supported/enabled hash types}
> >   \label{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets / Supported/enabled hash types}
> > +This paragraph relies on definitions from \hyperref[intro:IP]{[IP]}, \hyperref[intro:UDP]{[UDP]} and \hyperref[intro:TCP]{[TCP]}.
> >   Hash types applicable for IPv4 packets:
> >   \begin{lstlisting}
> >   #define VIRTIO_NET_HASH_TYPE_IPv4              (1 << 0)
> > @@ -980,6 +993,152 @@ \subsubsection{Processing of Incoming Packets}\label{sec:Device Types / Network
> >   (see \ref{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets / IPv6 packets without extension header}).
> >   \end{itemize}
> > +\paragraph{Inner Header Hash}
> > +\label{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Inner Header Hash}
> > +
> > +If VIRTIO_NET_F_HASH_TUNNEL has been negotiated, the device supports inner header hash and the driver can send
> > +commands VIRTIO_NET_CTRL_TUNNEL_HASH_SET and VIRTIO_NET_CTRL_TUNNEL_HASH_GET for the inner header hash configuration.
> > +
> > +struct virtio_net_hash_tunnel_config {
> Please move field from the config struct to here. Both are RO fields.
> 
> le32 supported_hash_tunnel_types;
> > +    le32 hash_tunnel_types;
> > +};
> > +
> > +#define VIRTIO_NET_CTRL_TUNNEL_HASH 7
> > + #define VIRTIO_NET_CTRL_TUNNEL_HASH_SET 0
> > + #define VIRTIO_NET_CTRL_TUNNEL_HASH_GET 1
> > +
> > +Filed \field{hash_tunnel_types} contains a bitmask of configured hash tunnel types as
> > +defined in \ref{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets / Supported/enabled hash tunnel types}.
> > +
> > +The class VIRTIO_NET_CTRL_TUNNEL_HASH has the following commands:
> > +\begin{itemize}
> > +\item VIRTIO_NET_CTRL_TUNNEL_HASH_SET: set the \field{hash_tunnel_types} to configure the inner header hash calculation for the device.
> > +\item VIRTIO_NET_CTRL_TUNNEL_HASH_GET: get the \field{hash_tunnel_types} from the device.
> > +\end{itemize}
> > +
> > +For the command VIRTIO_NET_CTRL_TUNNEL_HASH_SET, the structure virtio_net_hash_tunnel_config is write-only for the driver.
> > +For the command VIRTIO_NET_CTRL_TUNNEL_HASH_GET, the structure virtio_net_hash_tunnel_config is read-only for the driver.
> > +
> You need to split the structures to two, one for get and one for set in
> above description as get and set contains different fields.
> > +
> > +If VIRTIO_NET_HASH_TUNNEL_TYPE_NONE is set or the encapsulation type is not included in \field{hash_tunnel_types},
> > +the hash of the outer header is calculated for the received encapsulated packet.
> > +
> > +
> > +For scenarios with sufficient external entropy or no internal hashing requirements, inner header hash may not be needed:
> > +A tunnel is often expected to isolate the external network from the internal one. By completely ignoring entropy
> > +in the external header and replacing it with entropy from the internal header, for hash calculations, this expectation
> You wanted to say inner here like rest of the places.
> 
> s/internal header/inner header
> 
> > +The driver MUST NOT set any VIRTIO_NET_HASH_TUNNEL_TYPE_ flags that are not supported by the device.
> Multiple flags so,
> 
> s/flags that are/flags which are/
> 
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