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MPAM platforms retrieve the cache-id property from the ACPI PPTT table. The cache-id field is 32 bits wide. Under resctrl, the cache-id becomes the domain-id, and is packed into the mon_data_bits union bitfield. The width of cache-id in this field is 14 bits. Expanding the union would break 32bit x86 platforms as this union is stored as the kernfs kn->priv pointer. This saved allocating memory for the priv data storage. The firmware on MPAM platforms have used the PPTT cache-id field to expose the interconnect's id for the cache, which is sparse and uses more than 14 bits. Use of this id is to enable PCIe direct cache injection hints. Using this feature with VFIO means the value provided by the ACPI table should be exposed to user-space. To support cache-id values greater than 14 bits, convert the mon_data_bits union to a structure. These are shared between control and monitor groups, and are allocated on first use. The list of allocated struct mon_data is free'd when the filesystem is umount()ed. Co-developed-by: Tony Luck <tony.luck@intel.com> Signed-off-by: Tony Luck <tony.luck@intel.com> Signed-off-by: James Morse <james.morse@arm.com> Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de> Reviewed-by: Reinette Chatre <reinette.chatre@intel.com> Reviewed-by: Fenghua Yu <fenghuay@nvidia.com> Tested-by: Fenghua Yu <fenghuay@nvidia.com> Tested-by: Babu Moger <babu.moger@amd.com> Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com> Tested-by: Tony Luck <tony.luck@intel.com> Link: https://lore.kernel.org/20250515165855.31452-13-james.morse@arm.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.