Re: [PATCH] virtio-net: introduce admin control virtqueue

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

On Fri, Jan 22, 2021 at 04:23:25PM +0800, Jason Wang wrote:
> When implementing multiple (sub)functions virtio device like SRIOV or
> sub-function. We're suffering from several issues:
> 
> - There's no management interface for management function (PF) to
>   configure features, attributes for a (sub)function
> - Per (sub)function control virtqueue could be too expensive as the
>   number of (sub)functions could be very large
> - Virtualize per (sub)function control virtqueue could be very
>   challenge as we need the support of DMA isolation at queue level
> 
> So this patch introduces the feature of VIRTIO_NET_CTRL_ADMIN_VQ. This
> allows the device to implement a single admin control virtqueue to
> manage per (sub)function features and attributes.
> 
> The idea is simple, a new function id is introduced on top of the
> exist virtio_net_ctrl structure. This id is transport or device
> specific to uniquely identify a (sub)function.
> 
> With this, we get a way of using management function (PF) to configure
> per (sub)function features and attributes. And since the admin control
> virtqueue belongs to management function (PF), the DMA is naturally
> isolated at (sub)function level instead of the queue level for per
> (sub)function control vq.
> 
> Signed-off-by: Jason Wang <jasowang@redhat.com>

Let's specify how this works at least for PCI? What about sub-functions
under VF level? How are these specified?

> ---
>  content.tex | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
> 
> diff --git a/content.tex b/content.tex
> index 620c0e2..98592a4 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -2940,6 +2940,9 @@ \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_ADMIN_CTRL_VQ(56)] Admin control channel is
> +    available.
> +
>  \item[VIRTIO_NET_F_HASH_REPORT(57)] Device can report per-packet hash
>      value and a type of calculated hash.
>  
> @@ -3864,6 +3867,26 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi
>  do except issue a diagnostic if \field{ack} is not
>  VIRTIO_NET_OK.
>  
> +\subsubsection{Admin Control Virtqueue}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue}
> +
> +When VIRTIO_NET_F_ADMIN_CTRL_VQ is negotiated, the driver can use the
> +control virtqueue to manipulate features of individual function where

manipulate features? You don't mean feature bits, do you?

> +the control virtqueues is not easily implemented in each function.
> +
> +All commands are of the following form:
> +
> +\begin{lstlisting}
> +struct virtio_net_admin_ctrl {
> +        u32 function_id;
> +        struct virtio_net_ctrl ctrl;
> +};
> +
> +\end{lstlisting}
> +
> +The \field{function_id} is an unique transport or device specific
> +identifier for a function. E.g for the case of PCI SRIOV, it's the id
> +of PCI function.
> +
>  \paragraph{Packet Receive Filtering}\label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Packet Receive Filtering}
>  \label{sec:Device Types / Network Device / Device Operation / Control Virtqueue / Setting Promiscuous Mode}%old label for latexdiff
>  
> -- 
> 2.25.1