Re: [virtio-dev] [PATCH v3 2/2] virtio: pci support virtqueue reset

[Cornelia Huck <cohuck@redhat.com>]

On Mon, Sep 27 2021, Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:

> PCI support virtqueue reset.
>
> virtio_pci_common_cfg add "queue_reset" to support virtqueue reset.
> The driver uses this to selectively reset the queue.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> ---
>  content.tex | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
>
> diff --git a/content.tex b/content.tex
> index 603b1f1..35228dc 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -896,6 +896,7 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
>          le64 queue_driver;              /* read-write */
>          le64 queue_device;              /* read-write */
>          le16 queue_notify_data;         /* read-only for driver */
> +        le16 queue_reset;               /* read-write */
>  };
>  \end{lstlisting}
>  
> @@ -975,6 +976,12 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
>          may benefit from providing another value, for example an internal virtqueue
>          identifier, or an internal offset related to the virtqueue number.
>          \end{note}
> +
> +\item[\field{queue_reset}]
> +        The driver uses this to selectively reset the queue.
> +        This field exists only if VIRTIO_F_RING_RESET has been
> +        negotiated. (see \ref{sec:Virtqueues / Virtqueue Reset}).
> +
>  \end{description}
>  
>  \devicenormative{\paragraph}{Common configuration structure layout}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Common configuration structure layout}
> @@ -1016,6 +1023,14 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
>  
>  The device MUST present a 0 in \field{queue_enable} on reset.
>  
> +The device MUST present a 0 in \field{queue_reset} after the virtqueue is
> +enabled with \field{queue_enable}. The device MUST reset the queue when 1 is
> +written to \field{queue_reset}, and present a 1 in \field{queue_reset} until the
> +queue is enabled with \field{queue_enable}. (see \ref{sec:Virtqueues / Virtqueue Reset}).

"present a 1 in \field{queue_reset} after the queue has been reset,
until the driver re-enables the queue via \field{queue_enable}"

?

I suppose queue_reset is reset to 0 when the whole device is reset?

> +
> +The device MUST present a 0 in \field{queue_enable} after the virtqueue is reset
> +with \field{queue_reset}. (see \ref{sec:Virtqueues / Virtqueue Reset}).

"after the driver has reset the virtqueue via \field{queue_reset}" ?

This section should probably also refer to the feature bit at least once?

> +
>  The device MUST present a 0 in \field{queue_size} if the virtqueue
>  corresponding to the current \field{queue_select} is unavailable.
>  
> @@ -1040,6 +1055,12 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
>  
>  The driver MUST NOT write a 0 to \field{queue_enable}.
>  
> +If the VIRTIO_F_RING_RESET feature bit is negotiated, the driver can stop using
> +the queue by writing a 1 to \field{queue_reset} and MUST read the value back to
> +ensure synchronization. Then optionally re-enable the queue by writing a 1 to
> +\field{queue_enable} after configuring the other virtqueue fields. (see
> +\ref{sec:Virtqueues / Virtqueue Reset}).

"If VIRTIO_F_RING_RESET has been negotiated, after the driver writes 1 to
\field{queue_reset} to reset the queue, it MUST verify that the queue
has been reset by reading back \field{queue_reset} and ensuring that it
is 1. The driver MAY re-enable the queue by writing a 1 to
\field{queue_enable} after ensuring that the other virtqueue fields have
been set up correctly."

?

> +
>  \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability}
>  
>  The notification location is found using the VIRTIO_PCI_CAP_NOTIFY_CFG

MMIO can probably use a similar mechanism.

For CCW, maybe we can add a payload to the existing RESET command if the
feature has been negotiated; the queue can be re-enabled by the normal
READ_VQ_CONF/SET_VQ procedure. I have not yet thought that through.


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