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Subject: Re: [virtio-dev] [PATCH RESEND] virtio-pmem: PMEM device spec
On Wed, Aug 04, 2021 at 03:58:49PM -0700, Taylor Stark wrote: > On Wed, Aug 04, 2021 at 01:33:05PM +0100, Stefan Hajnoczi wrote: > > On Wed, Aug 04, 2021 at 01:11:52PM +0200, David Hildenbrand wrote: > > > On 04.08.21 13:07, Stefan Hajnoczi wrote: > > > > On Wed, Jul 28, 2021 at 05:04:35PM +0200, Pankaj Gupta wrote: > > > > > +\subsection{Device configuration layout}\label{sec:Device Types / PMEM Device / Device configuration layout} > > > > > + > > > > > +\begin{lstlisting} > > > > > +struct virtio_pmem_config { > > > > > + le64 start; > > > > > + le64 size; > > > > > +}; > > > > > +\end{lstlisting} > > > > > + > > > > > +\begin{description} > > > > > +\item[\field{start}] contains the start address from the guest physical address range > > > > > +to be hotplugged into the guest address space using the pmem API. > > > > > + > > > > > +\item[\field{size}] contains the length of this address range. > > > > > +\end{description} > > > > > > > > Please use a Shared Memory Region instead. This is a relatively new > > > > addition to the VIRTIO device model that seems like a good fit for this > > > > device: > > > > https://github.com/oasis-tcs/virtio-spec/blob/master/shared-mem.tex > > > > > > Note that virtio-pmem is already upstream in QEMU and in Linux using this > > > model. There is a proposal to optionally use shared memory for exposing the > > > area, to be unlocked with a feature bit. > > > > Please incorporate the proposal into this patch. A feature bit is a good > > way of handling this case. > > > > Although the difference between configuration space parameters and a > > shared memory region might seem trivial, I think using the shared memory > > region is worthwhile because it makes the memory region a first-class > > concept in the VIRTIO device model that is supported by the driver and > > device emulation infrastructure. > > > > Stefan > > For what it's worth, here's the proposal to add support for shared memory regions: > https://lists.oasis-open.org/archives/virtio-comment/202107/msg00169.html > > The original plan was to have the base spec go in first, and then consider the > proposal. Do you think it's better to include the shared memory region proposal > from the start? Talyor and Pankaj, I hadn't seen Taylor's patch. Since it's small and has already had some review it can probably be merged quickly after the main virtio-pmem spec change. Feel free to keep it as a separate series! Stefan
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