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PCI pass-thru devices in a Hyper-V VM are represented as a VMBus device and as a PCI device. The coherence of the VMbus device is set based on the VMbus node in ACPI, but the PCI device has no ACPI node and defaults to not hardware coherent. This results in extra software coherence management overhead on ARM64 when devices are hardware coherent. Fix this by setting up the PCI host bus so that normal PCI mechanisms will propagate the coherence of the VMbus device to the PCI device. There's no effect on x86/x64 where devices are always hardware coherent. Signed-off-by: Michael Kelley <mikelley@microsoft.com> Acked-by: Boqun Feng <boqun.feng@gmail.com> Acked-by: Robin Murphy <robin.murphy@arm.com> Link: https://lore.kernel.org/r/1648138492-2191-3-git-send-email-mikelley@microsoft.com Signed-off-by: Wei Liu <wei.liu@kernel.org>
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 Restructured Text 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.