[RFC PATCH 01/60] hyper_dmabuf: initial working version of hyper_dmabuf drv

[Dongwon Kim]

I forgot to include this brief information about this patch series.

This patch series contains the implementation of a new device driver,
hyper_dmabuf, which provides a method for DMA-BUF sharing across
different OSes running on the same virtual OS platform powered by
a hypervisor.

Detailed information about this driver is described in a high-level doc
added by the second patch of the series.

[RFC PATCH 02/60] hyper_dmabuf: added a doc for hyper_dmabuf sharing

I am attaching 'Overview' section here as a summary.

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Section 1. Overview
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Hyper_DMABUF driver is a Linux device driver running on multiple Virtual
achines (VMs), which expands DMA-BUF sharing capability to the VM environment
where multiple different OS instances need to share same physical data without
data-copy across VMs.

To share a DMA_BUF across VMs, an instance of the Hyper_DMABUF drv on the
exporting VM (so called, “exporter”) imports a local DMA_BUF from the original
producer of the buffer, then re-exports it with an unique ID, hyper_dmabuf_id
for the buffer to the importing VM (so called, “importer”).

Another instance of the Hyper_DMABUF driver on importer registers
a hyper_dmabuf_id together with reference information for the shared physical
pages associated with the DMA_BUF to its database when the export happens.

The actual mapping of the DMA_BUF on the importer’s side is done by
the Hyper_DMABUF driver when user space issues the IOCTL command to access
the shared DMA_BUF. The Hyper_DMABUF driver works as both an importing and
exporting driver as is, that is, no special configuration is required.
Consequently, only a single module per VM is needed to enable cross-VM DMA_BUF
exchange.

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There is a git repository at github.com where this series of patches are all
integrated in Linux kernel tree based on the commit:

        commit ae64f9bd1d3621b5e60d7363bc20afb46aede215
        Author: Linus Torvalds <torvalds at linux-foundation.org>
        Date:   Sun Dec 3 11:01:47 2017 -0500

            Linux 4.15-rc2

https://github.com/downor/linux_hyper_dmabuf.git hyper_dmabuf_integration_v3