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Leon Romanovsky 37f0c7a8df block-dma: properly take MMIO path 
In commit eadaa8b255 ("dma-mapping: introduce new DMA attribute to
indicate MMIO memory"), DMA_ATTR_MMIO attribute was added to describe
MMIO addresses, which require to avoid any memory cache flushing, as
an outcome of the discussion pointed in Link tag below.

In case of PCI_P2PDMA_MAP_THRU_HOST_BRIDGE transfer, blk-mq-dm logic
treated this as regular page and relied on "struct page" DMA flow.
That flow performs CPU cache flushing, which shouldn't be done here,
and doesn't set IOMMU_MMIO flag in DMA-IOMMU case.

As a solution, let's encode peer-to-peer transaction type in NVMe IOD
flags variable and provide it to blk-mq-dma API.

Link: https://lore.kernel.org/all/f912c446-1ae9-4390-9c11-00dce7bf0fd3@arm.com/
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
History 2025-11-14 05:09:56 -07:00
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README 

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.