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Subject: Re: [PATCH v2 1/3] shared memory: Define shared memory regions
On Fri, 22 Feb 2019 11:54:31 +0000 "Dr. David Alan Gilbert (git)" <dgilbert@redhat.com> 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> > --- > 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.
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