From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-comment-return-642-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Date: Fri, 22 Feb 2019 13:48:39 +0100 From: Cornelia Huck Message-ID: <20190222134839.7e0ef3e7.cohuck@redhat.com> In-Reply-To: <20190222115433.7160-2-dgilbert@redhat.com> References: <20190222115433.7160-1-dgilbert@redhat.com> <20190222115433.7160-2-dgilbert@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: [virtio-comment] Re: [PATCH v2 1/3] shared memory: Define shared memory regions To: "Dr. David Alan Gilbert (git)" Cc: virtio-comment@lists.oasis-open.org, virtio-dev@lists.oasis-open.org, stefanha@redhat.com List-ID: On Fri, 22 Feb 2019 11:54:31 +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 > --- > content.tex | 2 ++ > shared-mem.tex | 33 +++++++++++++++++++++++++++++++++ > 2 files changed, 35 insertions(+) > create mode 100644 shared-mem.tex > > diff --git a/content.tex b/content.tex > index 836ee52..3dd504c 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..85b0c55 > --- /dev/null > +++ b/shared-mem.tex > @@ -0,0 +1,33 @@ > +\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. > + > +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. This explanation looks good to me. > + > +Shared memory regions MUST NOT be used to control the operation > +of the device, nor to stream data; those should still be performed > +using virtqueues. The 'MUST NOT' makes it look like a normative statement; however, this is more like design advice? > + > +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. > + > +Memory consistency rules vary depending on the region and the > +device. Devices MUST define the required behaviour for each > +region. Same here. > + > +The guest physical address and the host virtual address MUST NOT > +be used to identify structures within the memory regions; all > +addressing MUST be relative to the start of a particular region. > + For that high-level overview, I'm not sure if any normative statements are needed/wanted, or whether those should be confined to the individual transport or device type definitions... The text on its own looks good to me. 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/