Re: [virtio-comment] [PATCH v4 1/1] virtio-pmem: Support describing pmem as shared memory region

[Cornelia Huck <cohuck@redhat.com>]

On Fri, Nov 05 2021, tstark@linux.microsoft.com wrote:

> From: Taylor Stark <tstark@microsoft.com>
>
> Update the virtio-pmem spec to add support for describing the pmem region as a
> shared memory window. This is required to support virtio-pmem in Hyper-V, since
> Hyper-V only allows PCI devices to operate on memory ranges defined via BARs.
> When using the virtio PCI transport, shared memory regions are described via
> PCI BARs.
>
> Signed-off-by: Taylor Stark <tstark@microsoft.com>
> ---
>  conformance.tex | 14 ++++++++++++--
>  virtio-pmem.tex | 34 +++++++++++++++++++++++++++++-----
>  2 files changed, 41 insertions(+), 7 deletions(-)

(...)

> @@ -41,17 +44,38 @@ \subsection{Device configuration layout}\label{sec:Device Types / PMEM Device /
>  \item[\field{size}] contains the length of this address range.
>  \end{description}

I wonder whether we should also amend the description of the config
space fields to "contains (...), if VIRTIO_PMEM_F_SHMEM_REGION has not
been negotiated". But maybe that is not really needed.

>  
> +\subsection{Device Initialization}\label{sec:Device Types / PMEM Device / Device Initialization}
> +
> +The device indicates the guest physical address to the driver in one of two ways:
>  \begin{enumerate}
> -\item Driver vpmem start is read from \field{start}.
> -\item Driver vpmem end is read from \field{size}.
> +\item As a guest absolute address, using virtio_pmem_config.
> +\item As a shared memory region.
>  \end{enumerate}

Otherwise, looks good to me.