[PATCH v3 0/6] Introduce MMIO-based CMT access for Enhanced RDT

[Chen Yu]

Intel Enhanced Resource Director Technology (ERDT) extends the existing
RDT framework with two major capabilities:

  1. MMIO-based access to monitoring and allocation registers, replacing
     the legacy MSR-based interface.
  2. Region-aware RDT for fine-grained control over different tiers of
     memory (e.g., CXL.mem, DDR).

This is described in the Intel RDT Architecture Specification:
https://cdrdv2-public.intel.com/789566/356688-intel-rdt-arch-spec.pdf

This patch set focuses on the first part: enabling MMIO-based access for
Cache Monitoring Technology (CMT), while CAT/MBM/MBA are still using MSR.
The platform advertises the MMIO register layout through the ACPI ERDT
(Enhanced Resource Director Technology) table, which contains sub-tables
describing per-domain register regions for monitoring and allocation.

With ERDT, L3 cache occupancy counters are read via MMIO rather than
MSR, allowing the reads to be performed from any CPU without requiring
cross-CPU IPIs. This series parses the relevant ACPI sub-tables (RMDD,
CMRC), prepares the resctrl monitor infrastructure for MMIO-based reads,
and adds initial support for reading L3 occupancy via the CMRC interface.

kselftest of CMT and L3_CAT has passed with minor adjustment at
https://lore.kernel.org/lkml/20260523101715.3964456-1-yu.c.chen@xxxxxxxxx/.

Changes from V2 to V3:
- Wrap __resctrl_arch_late_init() to avoid the goto logic. (Thomas Gleixner)
- Make the variables in struct erdt_domain_info tabular format (Thomas Gleixner)
- Remove tail comments (Thomas Gleixner)
- Make the name of erdt_enabled() and variable in it consistent and
  comprehensible. (Thomas Gleixner)
- Use topo_lookup_cpuid() to search the CPU id according to the x2apic id
  (Thomas Gleixner)
- Fix kernel doc comment format (Thomas Gleixner)
- Use brackets for multiple lines "if" case. (Thomas Gleixner)
- Let the parameter for cacd_init() to fully utilize 100 characters.
  (Thomas Gleixner)
- Variables are reordered in reverse fir-tree.(Thomas Gleixner)
- Added a named constant and use it in the rmdd->flags check.
  (Thomas Gleixner)
- Introduce helper functions to make the code readable when iterating
  the RMDD tables. (Thomas Gleixner)
- Make the macros tabular format. (Thomas Gleixner)

Changes from V1 to V2:
- Add #include <linux/cleanup.h> to follow the "include-what-you-use" best
  practice (Tony Luck)
- Fix 3 issues reported by:
  https://sashiko.dev/#/patchset/cover.1779872016.git.yu.c.chen%40intel.com
  Remove the variable of cacd in struct erdt_domain_info as it will
  never be used after initialization.
  Invoke erdt_exit() to avoid resource leak if rdt_alloc_capable and
  rdt_mon_capable are both false.
  Adjust the comments suggested by sashiko.

Anil S Keshavamurthy (1):
  x86/resctrl: Parse ACPI ERDT table and map RMDD domains by L3 cache ID

Chen Yu (4):
  x86/resctrl: Parse ACPI CMRC table
  x86/resctrl: Rename prev_msr to prev_mon_val
  x86/resctrl: Refactor the monitor read function
  x86/resctrl: Add support for L3 occupancy monitoring via RMID MMIO
    read

Tony Luck (1):
  fs/resctrl: Do not invoke smp_processor_id() in preemptible context

 arch/x86/Kconfig                       |   4 +-
 arch/x86/include/asm/apic.h            |   1 +
 arch/x86/include/asm/resctrl.h         |   4 +
 arch/x86/kernel/cpu/resctrl/Makefile   |   1 +
 arch/x86/kernel/cpu/resctrl/core.c     |  16 +-
 arch/x86/kernel/cpu/resctrl/erdt.c     | 433 +++++++++++++++++++++++++
 arch/x86/kernel/cpu/resctrl/internal.h |  11 +-
 arch/x86/kernel/cpu/resctrl/monitor.c  |  64 ++--
 arch/x86/kernel/cpu/topology.c         |   2 +-
 fs/resctrl/monitor.c                   |  41 ++-
 10 files changed, 535 insertions(+), 42 deletions(-)
 create mode 100644 arch/x86/kernel/cpu/resctrl/erdt.c

-- 
2.25.1