From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-comment-return-585-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id EB889985DBD for ; Fri, 11 Jan 2019 12:27:02 +0000 (UTC) Date: Fri, 11 Jan 2019 12:26:54 +0000 From: "Dr. David Alan Gilbert" Message-ID: <20190111122654.GE2738@work-vm> References: <20190111114200.10026-1-dgilbert@redhat.com> <20190111114200.10026-2-dgilbert@redhat.com> <20190111131540.12a8abca.cohuck@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190111131540.12a8abca.cohuck@redhat.com> Subject: Re: [virtio-comment] [PATCH 1/3] shared memory: Define shared memory regions To: Cornelia Huck Cc: virtio-comment@lists.oasis-open.org, stefanha@redhat.com, Halil Pasic List-ID: * Cornelia Huck (cohuck@redhat.com) wrote: > On Fri, 11 Jan 2019 11:41:58 +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 | 3 +++ > > shared-mem.tex | 25 +++++++++++++++++++++++++ > > 2 files changed, 28 insertions(+) > > create mode 100644 shared-mem.tex > > > > diff --git a/content.tex b/content.tex > > index b101d1b..321a2f4 100644 > > --- a/content.tex > > +++ b/content.tex > > @@ -331,6 +331,9 @@ Virtqueue format, or both. > > \input{split-ring.tex} > > > > \input{packed-ring.tex} > > + > > +\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..6da249c > > --- /dev/null > > +++ b/shared-mem.tex > > @@ -0,0 +1,25 @@ > > +\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. > > + > > +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. > > + > > +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. > > "data structure and mechanism"? Changed; thanks. > > + > > +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. > > + > > Is the intended implementation that the device provides a certain > memory region (in host memory) and exposes it to the driver? Are there > supposed to be any notifications of writes? Or do both simply write to > the region and get whatever updates the other side has made when they > read from the region again? There's no notification; in our case we have two main uses: a) Direct mapping of host files into the guests memory b) Mapping of a version table with quickly updated version numbers for data structures to do quick invalidation > I'm a bit unsure how to implement this for the ccw transport. Maybe a > new pair of ccws to read/write shared memory regions? Without knowing anything about CCW itself, I don't think you'd want to do calls to perform the reads/writes - remember these are entirely emulated devices, and the shared memory regions just correspond to memory regions in the hypervisor; so in most ways they just behave like a region of RAM. If the drivers can't treat them like RAM there's probably no point in using this feature in that environment. > But we'd also > need a mechanism to discover the ids of those shared memory regions, I > think. Yes, I'm assuming you'll need a call to enumerate them. Dave > > Halil, do you have any thoughts? -- 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/