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Dealing with CCS state is significant on LNL+, where we end up clearing the compression state on every page alloc using the blitter for user buffers, including also saving and restoring it when moving between domains, plus we need to alloc extra pages to hold the raw CCS state for the save step. However all compression PAT modes, on platforms like LNL, also require coh_none, meaning that only WC memory can use compression in the first place. With this we can be sneaky and completely ignore CCS for WB buffers, which is likely the common case anyway. This would then skip all blitter moves/clears between sys <-> tt and then also means we can drop the extra CCS pages. This should be safe since there is no way to interact with the compression state (potentially uncleared) without using a PAT enabled index (which is rejected at bind), including if trying to be malicious and copy the raw CCS state from userpace, which should give back all zeroes if the src surface (indirect) is lacking compressed PAT index. Signed-off-by: Matthew Auld <matthew.auld@intel.com> Cc: Satyanarayana K V P <satyanarayana.k.v.p@intel.com> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com> Cc: Matthew Brost <matthew.brost@intel.com> Reviewed-by: José Roberto de Souza <jose.souza@intel.com> Reviewed-by: Satyanarayana K V P <satyanarayana.k.v.p@intel.com> Link: https://lore.kernel.org/r/20250516153810.223530-2-matthew.auld@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 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.