RE: [PATCH V2 4/6] virtio-pci: implement VIRTIO_F_QUEUE_STATE

[Parav Pandit <parav@nvidia.com>]

> From: Zhu Lingshan <lingshan.zhu@intel.com>
> Sent: Friday, November 3, 2023 4:05 PM
> 
> This patch adds two new le16 fields to common configuration structure to
> support VIRTIO_F_QUEUE_STATE in PCI transport layer.
> 
> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> ---
>  transport-pci.tex | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/transport-pci.tex b/transport-pci.tex index a5c6719..3161519 100644
> --- a/transport-pci.tex
> +++ b/transport-pci.tex
> @@ -325,6 +325,10 @@ \subsubsection{Common configuration structure
> layout}\label{sec:Virtio Transport
>          /* About the administration virtqueue. */
>          le16 admin_queue_index;         /* read-only for driver */
>          le16 admin_queue_num;         /* read-only for driver */
> +
> +	/* Virtqueue state */
> +        le16 queue_avail_state;         /* read-write */
> +        le16 queue_used_state;          /* read-write */
This tiny interface for 128 virtio net queues through register read writes, does not work effectively.
There are inflight out of order descriptors for block also.
Hence toy registers like this do not work.

Series [1] is comprehensive that covers it even if you consider non-passtrhough device migration model.
Where you can suspend individual queues using new admin command and get them in the device context state.

[1] https://lists.oasis-open.org/archives/virtio-comment/202310/msg00472.html

>  };
>  \end{lstlisting}
> 
> @@ -428,6 +432,17 @@ \subsubsection{Common configuration structure
> layout}\label{sec:Virtio Transport
>  	The value 0 indicates no supported administration virtqueues.
>  	This field is valid only if VIRTIO_F_ADMIN_VQ has been
>  	negotiated.
> +
> +\item[\field{queue_avail_state}]
> +        This field is valid only if VIRTIO_F_QUEUE_STATE has been
> +        negotiated. The driver sets and gets the available state of
> +        the virtqueue here (see \ref{sec:Virtqueues / Virtqueue State}).
> +
> +\item[\field{queue_used_state}]
> +        This field is valid only if VIRTIO_F_QUEUE_STATE has been
> +        negotiated. The driver sets and gets the used state of the
> +        virtqueue here (see \ref{sec:Virtqueues / Virtqueue State}).
> +
>  \end{description}
> 
>  \devicenormative{\paragraph}{Common configuration structure layout}{Virtio
> Transport Options / Virtio Over PCI Bus / PCI Device Layout / Common
> configuration structure layout} @@ -488,6 +503,9 @@ \subsubsection{Common
> configuration structure layout}\label{sec:Virtio Transport  present either a value
> of 0 or a power of 2 in  \field{queue_size}.
> 
> +If VIRTIO_F_QUEUE_STATE has not been negotiated, the device MUST ignore
> +any accesses to \field{queue_avail_state} and \field{queue_used_state}.
> +
>  If VIRTIO_F_ADMIN_VQ has been negotiated, the value
> \field{admin_queue_index} MUST be equal to, or bigger than
> \field{num_queues}; also, \field{admin_queue_num} MUST be
> --
> 2.35.3