[PATCH v3 0/2] CXL: Apply SRAT defined PXM to entire CFMWS window

[alison . schofield]

From: Alison Schofield <alison.schofield@xxxxxxxxx>

Changes in v3:
- Define CFMWS and add CXL Spec link in cover letter (Peter, Jonathan)
- s/HPA/physical address in Patch 1 (Peter)
- Remove overkill comment in Patch 1 (Dan)
- Simplify cmp_memblk() in Patch 1 (Dan)

v2: https://lore.kernel.org/linux-cxl/cover.1686712819.git.alison.schofield@xxxxxxxxx/

----
Cover Letter:

The CXL subsystem requires the creation of NUMA nodes for CFMWS
Windows[1] not described in the SRAT. The existing implementation
only addresses windows that the SRAT describes completely or not
at all. This work addresses the case of partially described CFMWS
Windows by extending proximity domains in a portion of a CFMWS
window to the entire window.

Introduce a NUMA helper, numa_fill_memblks(), to fill gaps in a
numa_meminfo memblk address range. Update the CFMWS parsing in the
ACPI driver to use numa_fill_memblks() to extend SRAT defined
proximity domains to entire CXL windows.

An RFC of this patchset was previously posted for CXL folks review
here[2]. The RFC feedback led to the implementation here, extending
existing memblks (Dan). Also, both Jonathan and Dan influenced the
changelog comments in the ACPI patch, with regards to setting
expectations on this evolving heuristic.

Repeating here to set reviewer expectations:
*Note that this heuristic will evolve when CFMWS Windows present a
wider range of characteristics. The extension of the proximity domain,
implemented here, is likely a step in developing a more sophisticated
performance profile in the future.

[1] CFMWS is defined in CXL Spec 3.0 Section 9.17.1.3 :
https://www.computeexpresslink.org/spec-landing

A CXL Fixed Memory Window is a region of Host Physical Address (HPA)
Space which routes accesses to CXL Host bridges. The 'S', of CFMWS,
stand for the structure that describes the window, hence it's common
name, CFMWS.

[2] https://lore.kernel.org/linux-cxl/cover.1683742429.git.alison.schofield@xxxxxxxxx/

Alison Schofield (2):
  x86/numa: Introduce numa_fill_memblks()
  ACPI: NUMA: Apply SRAT proximity domain to entire CFMWS window

 arch/x86/include/asm/sparsemem.h |  2 +
 arch/x86/mm/numa.c               | 81 ++++++++++++++++++++++++++++++++
 drivers/acpi/numa/srat.c         | 11 +++--
 include/linux/numa.h             |  7 +++
 4 files changed, 98 insertions(+), 3 deletions(-)


base-commit: 214a71b53bc7cb30f6b8d43089037e9fe7f3ae1f
-- 
2.37.3