Re: [virtio-comment] [PATCH 1/3] shared memory: Define shared memory regions

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Cornelia Huck (cohuck@redhat.com) wrote:
> On Wed, 16 Jan 2019 20:06:25 +0000
> "Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:
> 
> > So these are all moving this 1/3 forward - has anyone got comments on
> > the transport specific implementations?
> 
> No comment on pci or mmio, but I've hacked something together for ccw.
> Basically, one sense-type ccw for discovery and a control-type ccw for
> activation of the regions (no idea if we really need the latter), both
> available with ccw revision 3.
> 
> No idea whether this will work this way, though...

That sounds (from a shm perspective) reasonable; can I ask why the
'activate' is needed?

Dave

> diff --git a/content.tex b/content.tex
> index 836ee5236939..7f379bca932e 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -2078,6 +2078,8 @@ virtio:
>  #define CCW_CMD_READ_VQ_CONF 0x32
>  #define CCW_CMD_SET_VIRTIO_REV 0x83
>  #define CCW_CMD_READ_STATUS 0x72
> +#define CCW_CMD_GET_REGIONS 0x14
> +#define CCW_CMD_MAP_REGIONS 0x93
>  \end{lstlisting}
>  
>  \subsubsection{Notifications}\label{sec:Virtio Transport Options / Virtio
> @@ -2170,7 +2172,9 @@ The following values are supported:
>  \hline
>  2        & 0      & <empty>   & CCW_CMD_READ_STATUS support \\
>  \hline
> -3-n      &        &           & reserved for later revisions \\
> +3        & 0      & <empty>   & CCW_CMD_GET_REGIONS and CCW_CMD_MAP_REGIONS support \\
> +\hline
> +4-n      &        &           & reserved for later revisions \\
>  \hline
>  \end{tabular}
>  
> @@ -2449,6 +2453,72 @@ command. Some legacy devices will support two-stage queue indicators, though,
>  and a driver will be able to successfully use CCW_CMD_SET_IND_ADAPTER to set
>  them up.
>  
> +\subsubsection{Handling Shared Memory Regions}\label{sec:Virtio Transport Options / Virtio over channel I/O / Device Initialization / Handling Shared Memory Regions}
> +
> +The CCW_CMD_GET_REGIONS command allows the driver to discover shared memory
> +regions provided by the device, if any.
> +
> +The driver provides a pointer to a 4096 byte buffer that is filled out by
> +the device:
> +
> +\begin{lstlisting}
> +  struct shared_regions_info {
> +    be64 num_regions;
> +    struct shared_region_desc regions[];
> +  };
> +\end{lstlisting}
> +
> +The buffer contains 0 or more shared region descriptors, as specified
> +by \field{num_regions}. If the devices does not provide shared regions,
> +\field{num_regions} is 0. Otherwise, the shared region descriptors have
> +the following format:
> +
> +\begin{lstlisting}
> +struct shared_region_desc {
> +        be64 addr;
> +        be64 len;
> +        u8 id;
> +        u8 pad[3];
> +}
> +\end{lstlisting}
> +
> +\field{addr} is the guest-physical address of the region with a length of
> +\field{len}, identified by \field{id}. The contents of \field{pad} are
> +unpredictable, although it is recommended that the device fills in zeroes.
> +
> +To activate or deactivate a shared memory region, the device uses the
> +CCW_CMD_MAP_REGIONS command. It takes the following payload:
> +
> +\begin{lstlisting}
> +struct shared_region_ctrl {
> +        u8 id;
> +        u8 activate;
> +        u8 pad[2];
> +}
> +\end{lstlisting}
> +
> +\field{id} denotes the shared memory region that is the target of the command,
> +while \field{activate} specifies whether the region should be activated (if 1)
> +or deactivated (if 0). When activated, the device makes the guest-physical
> +address of the region available as a shared memory region.
> +
> +\devicenormative{\paragraph}{Handling Shared Memory Regions}{Virtio Transport Options / Virtio over channel I/O / Device Initialization / Handling Shared Memory Regions}
> +
> +The device MUST reject the CCW_CMD_GET_REGIONS and CCW_CMD_MAP_REGIONS
> +commands if not at least revision 3 has been negotiated.
> +
> +The device MUST NOT read from or write to the region before it has been
> +activated by the driver or after it has been deactivated by the driver.
> +
> +If the driver reads from or writes to an address specified to a region that is
> +not activated by the driver, it MUST treat this read or write as a normal
> +read or write operation.
> +
> +\drivernormative{\paragraph}{Handling Shared Memory Regions}{Virtio Transport Options / Virtio over channel I/O / Device Initialization / Handling Shared Memory Regions}
> +
> +The driver MUST NOT treat the guest-physical address of a region as a shared
> +memory region before it has activated it or after it has deactivated it.
> +
>  \subsection{Device Operation}\label{sec:Virtio Transport Options / Virtio over channel I/O / Device Operation}
>  
>  \subsubsection{Host->Guest Notification}\label{sec:Virtio Transport Options / Virtio over channel I/O / Device Operation / Host->Guest Notification}
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

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