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IOMMU Extended Feature Register (EFR) is used to communicate the supported features for each IOMMU to the IOMMU driver. This is normally read from the PCI MMIO register offset 0x30, and used by the iommu_feature() helper function. However, there are certain scenarios where the information is needed prior to PCI initialization, and the iommu_feature() function is used prematurely w/o warning. This has caused incorrect initialization of IOMMU. This is the case for the commit6d39bdee23("iommu/amd: Enforce 4k mapping for certain IOMMU data structures") Since, the EFR is also available in the IVHD header, and is available to the driver prior to PCI initialization. Therefore, default to using the IVHD EFR instead. Fixes:6d39bdee23("iommu/amd: Enforce 4k mapping for certain IOMMU data structures") Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> Tested-by: Brijesh Singh <brijesh.singh@amd.com> Reviewed-by: Robert Richter <rrichter@amd.com> Link: https://lore.kernel.org/r/20210120135002.2682-1-suravee.suthikulpanit@amd.com Signed-off-by: Joerg Roedel <jroedel@suse.de>
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.