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A "DPA invalidation event" is any scenario where the contents of a DPA (Device Physical Address) is modified in a way that is incoherent with CPU caches, or if the HPA (Host Physical Address) to DPA association changes due to a remapping event. PMEM security events like Unlock and Passphrase Secure Erase already manage caches through LIBNVDIMM, so that leaves HPA to DPA remap events that need cache management by the CXL core. Those only happen when the boot time CXL configuration has changed. That event occurs when userspace attaches an endpoint decoder to a region configuration, and that region is subsequently activated. The implications of not invalidating caches between remap events is that reads from the region at different points in time may return different results due to stale cached data from the previous HPA to DPA mapping. Without a guarantee that the region contents after cxl_region_probe() are written before being read (a layering-violation assumption that cxl_region_probe() can not make) the CXL subsystem needs to ensure that reads that precede writes see consistent results. A CONFIG_CXL_REGION_INVALIDATION_TEST option is added to support debug and unit testing of the CXL implementation in QEMU or other environments where cpu_cache_has_invalidate_memregion() returns false. This may prove too restrictive for QEMU where the HDM decoders are emulated, but in that case the CXL subsystem needs some new mechanism / indication that the HDM decoder is emulated and not a passthrough of real hardware. Reviewed-by: Dave Jiang <dave.jiang@intel.com> Link: https://lore.kernel.org/r/166993222098.1995348.16604163596374520890.stgit@dwillia2-xfh.jf.intel.com Signed-off-by: Dan Williams <dan.j.williams@intel.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 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.