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Subject: [PATCH v2 1/3] shared memory: Define shared memory regions
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. + +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 and mechanism. + +Memory consistency rules vary depending on the region and the +device. Devices MUST define the required behaviour for each +region. + +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. + -- 2.20.1
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