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Force Write Back (FWB) changes how the S2 IOPTE's MemAttr field works. When S2FWB is supported and enabled the IOPTE will force cachable access to IOMMU_CACHE memory when nesting with a S1 and deny cachable access when !IOMMU_CACHE. When using a single stage of translation, a simple S2 domain, it doesn't change things for PCI devices as it is just a different encoding for the existing mapping of the IOMMU protection flags to cachability attributes. For non-PCI it also changes the combining rules when incoming transactions have inconsistent attributes. However, when used with a nested S1, FWB has the effect of preventing the guest from choosing a MemAttr in it's S1 that would cause ordinary DMA to bypass the cache. Consistent with KVM we wish to deny the guest the ability to become incoherent with cached memory the hypervisor believes is cachable so we don't have to flush it. Allow NESTED domains to be created if the SMMU has S2FWB support and use S2FWB for NESTING_PARENTS. This is an additional option to CANWBS. Link: https://patch.msgid.link/r/10-v4-9e99b76f3518+3a8-smmuv3_nesting_jgg@nvidia.com Reviewed-by: Nicolin Chen <nicolinc@nvidia.com> Reviewed-by: Kevin Tian <kevin.tian@intel.com> Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com> Reviewed-by: Donald Dutile <ddutile@redhat.com> Tested-by: Nicolin Chen <nicolinc@nvidia.com> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> |
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| io_uring | ||
| ipc | ||
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| .clang-format | ||
| .cocciconfig | ||
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| .get_maintainer.ignore | ||
| .gitattributes | ||
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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.