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Subject: Re: [virtio-comment] [PATCH v4 1/3] shared memory: Define shared memory regions
On Wed, Mar 20, 2019 at 12:07:38PM +0000, Dr. David Alan Gilbert (git) wrote: > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com> > > Define the requirements and idea behind shared memory regions. > > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com> > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> > --- > conformance.tex | 1 + > content.tex | 2 ++ > shared-mem.tex | 40 ++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 43 insertions(+) > create mode 100644 shared-mem.tex > > diff --git a/conformance.tex b/conformance.tex > index ad7e82e..f6c0d50 100644 > --- a/conformance.tex > +++ b/conformance.tex > @@ -195,6 +195,7 @@ A device MUST conform to the following normative statements: > \item \ref{devicenormative:Basic Facilities of a Virtio Device / Virtqueues / Used Buffer Notification Suppression} > \item \ref{devicenormative:Basic Facilities of a Virtio Device / Virtqueues / The Virtqueue Used Ring} > \item \ref{devicenormative:Basic Facilities of a Virtio Device / Virtqueues / Available Buffer Notification Suppression} > +\item \ref{devicenormative:Basic Facilities of a Virtio Device / Shared Memory Regions} > \item \ref{devicenormative:Reserved Feature Bits} > \end{itemize} > > diff --git a/content.tex b/content.tex > index ede0ef6..8cd1a38 100644 > --- a/content.tex > +++ b/content.tex > @@ -371,6 +371,8 @@ making any more buffers available. When VIRTIO_F_NOTIFICATION_DATA > has been negotiated, these notifications would then have > identical \field{next_off} and \field{next_wrap} values. > > +\input{shared-mem.tex} > + > \chapter{General Initialization And Device Operation}\label{sec:General Initialization And Device Operation} > > We start with an overview of device initialization, then expand on the > diff --git a/shared-mem.tex b/shared-mem.tex > new file mode 100644 > index 0000000..6dc506a > --- /dev/null > +++ b/shared-mem.tex > @@ -0,0 +1,40 @@ > +\section{Shared Memory Regions}\label{sec:Basic Facilities of a Virtio Device / Shared Memory Regions} > + > +Shared memory regions are an additional facility > +available to devices that need a region of memory that's > +continuously shared between the host and the guest, rather > +than passed between them in the way virtqueue elements are. Please rewrite host->device, guest->driver > + > +Example uses include shared caches and version pools for versioned > +data structures. > + > +The region is chosen by the host and presented to the guest, as > +such it is useful in situations where the memory is accessed on > +the host by other libraries that can't safely access guest RAM. I'm not sure what does above mean in context of virtio. Is this an example? So maybe: For example, with device being part of a hypervisor and driver being part of a VM guest etc etc > + > +A device may have multiple shared memory regions associated with > +it. Each region has a \field{shmid} to identify it, the meaning > +of which is device-specific. > + > +Enumeration and location of shared memory regions is performed > +using a transport-specific data structure and mechanism. Let's just say in a transport-specific way. > + > +Memory consistency rules vary depending on the region and the > +device and they will be specified as required by each device. > + > +\subsection{Addressing within regions}\label{sec:Basic Facilities of a Virtio Device / Shared Memory Regions / Addressing within regions } > + > +References into shared memory regions are represented as offsets from > +the beginning of the region instead of absolute memory addresses. > +Offsets are used both for references between structures stored > +within shared memory and for requests placed in virtqueues that > +refer to shared memory. > +The \field{shmid} may be explicit or may be inferred from the > +context of the reference. > + > +\devicenormative{\subsection}{Shared Memory Regions}{Basic Facilities of a Virtio > +Device / Shared Memory Regions} > +Shared memory regions MUST NOT expose shared memory regions which > +are used to control the operation of the device, nor to stream > +data. regions must not expose regions. confused. typo? Also, what does stream data mean? > + > -- > 2.20.1 > > > This publicly archived list offers a means to provide input to the > OASIS Virtual I/O Device (VIRTIO) TC. > > In order to verify user consent to the Feedback License terms and > to minimize spam in the list archive, subscription is required > before posting. > > Subscribe: virtio-comment-subscribe@lists.oasis-open.org > Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org > List help: virtio-comment-help@lists.oasis-open.org > List archive: https://lists.oasis-open.org/archives/virtio-comment/ > Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf > List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists > Committee: https://www.oasis-open.org/committees/virtio/ > Join OASIS: https://www.oasis-open.org/join/
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