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Current AMD IOMMU assumes Host Address Translation (HAT) is always supported, and Linux kernel enables this capability by default. However, in case of emulated and virtualized IOMMU, this might not be the case. For example,current QEMU-emulated AMD vIOMMU does not support host translation for VFIO pass-through device, but the interrupt remapping support is required for x2APIC (i.e. kvm-msi-ext-dest-id is also not supported by the guest OS). This would require the guest kernel to boot with guest kernel option iommu=pt to by-pass the initialization of host (v1) table. The AMD I/O Virtualization Technology (IOMMU) Specification Rev 3.10 [1] introduces a new flag 'HATDis' in the IVHD 11h IOMMU attributes to indicate that HAT is not supported on a particular IOMMU instance. Therefore, modifies the AMD IOMMU driver to detect the new HATDis attributes, and disable host translation and switch to use guest translation if it is available. Otherwise, the driver will disable DMA translation. [1] https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/specifications/48882_IOMMU.pdf Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> Signed-off-by: Ankit Soni <Ankit.Soni@amd.com> Link: https://lore.kernel.org/r/8109b208f87b80e400c2abd24a2e44fcbc0763a5.1749016436.git.Ankit.Soni@amd.com Signed-off-by: Joerg Roedel <joerg.roedel@amd.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.