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This function is used to establish the "private interconnect" between the
VFIO DMABUF exporter and the iommufd DMABUF importer. This is intended to
be a temporary API until the core DMABUF interface is improved to natively
support a private interconnect and revocable negotiation.
This function should only be called by iommufd when trying to map a
DMABUF. For now iommufd will only support VFIO DMABUFs.
The following improvements are needed in the DMABUF API to generically
support more exporters with iommufd/kvm type importers that cannot use the
DMA API:
1) Revoke semantics. VFIO needs to be able to prevent access to the MMIO
during FLR, and so it will use dma_buf_move_notify() to prevent
access. iommmufd does not support fault handling so it cannot
implement the full move_notify. Instead if revoke is negotiated the
exporter promises not to use move_notify() unless the importer can
experiance failures. iommufd will unmap the dmabuf from the iommu page
tables while it is revoked.
2) Private interconnect negotiation. iommufd will only be able to map
a "private interconnect" that provides a phys_addr_t and a
struct p2pdma_provider * to describe the memory. It cannot use a DMA
mapped scatterlist since it is directly calling iommu_map().
3) NULL device during dma_buf_dynamic_attach(). Since iommufd doesn't use
the DMA API it doesn't have a DMAable struct device to pass here.
Link: https://patch.msgid.link/r/1-v2-b2c110338e3f+5c2-iommufd_dmabuf_jgg@nvidia.com
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Tested-by: Shuai Xue <xueshuai@linux.alibaba.com>
Acked-by: Alex Williamson <alex@shazbot.org>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.