From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-comment-return-751-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Date: Wed, 19 Jun 2019 17:06:04 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20190619160603.GD2844@work-vm> References: <20190320120740.8514-1-dgilbert@redhat.com> <20190320120740.8514-2-dgilbert@redhat.com> <20190617142554-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190617142554-mutt-send-email-mst@kernel.org> Subject: Re: [virtio-comment] [PATCH v4 1/3] shared memory: Define shared memory regions To: "Michael S. Tsirkin" Cc: virtio-dev@lists.oasis-open.org, virtio-comment@lists.oasis-open.org, stefanha@redha.com, cohuck@redhat.com List-ID: * Michael S. Tsirkin (mst@redhat.com) wrote: > On Wed, Mar 20, 2019 at 12:07:38PM +0000, Dr. David Alan Gilbert (git) wrote: > > From: "Dr. David Alan Gilbert" > > > > Define the requirements and idea behind shared memory regions. > > > > Signed-off-by: Dr. David Alan Gilbert > > Reviewed-by: Stefan Hajnoczi > > --- > > 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 Done. > > + > > +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 It means the memory can be allocated by another library in the host and then passed into the guest; the alternative is where the guest gives a pointer into the guests own RAM. > > + > > +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. Done. > > + > > +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? I'm trying to find a way to say that people shouldn't side-step virtio queues by putting everything in a big blob of shared memory. Better wording welcome. Dave > > > + > > -- > > 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/ -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK 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/