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Subject: Re: [PATCH v3 1/3] shared memory: Define shared memory regions
On Mon, 4 Mar 2019 13:25:29 +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> > --- > conformance.tex | 1 + > content.tex | 2 ++ > shared-mem.tex | 40 ++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 43 insertions(+) > create mode 100644 shared-mem.tex > (...) > diff --git a/shared-mem.tex b/shared-mem.tex > new file mode 100644 > index 0000000..86b0050 > --- /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. > + > +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. > + > +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 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 } > + > +Commands sent over the virtqueues may refer to data within the > +shared memory regions, for example a command may be used by a > +driver to cause a device to add or remove a mapping within > +a region. When referring to data, the addresses will normally be > +offsets within a particular region rather than absolute host or > +guest addresses. The \field{shmid} may be explicit or may be > +inferred from the command type. It's probably reasonable to frame it like that instead of making it a normative statement. Maybe "the addresses are expected to be offsets"? It would feel odd if most devices handled it like that and then an oddball device came along... > + > +\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. > + Otherwise, looks good to me.
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