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

["Ning, Hongyu" <hongyu.ning@linux.intel.com>]

On 6/6/2026 10:31 AM, Chen Yu wrote:
> 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@intel.com/.
> 
> 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
> 

Tested-by: Hongyu Ning <hongyu.ning@linux.intel.com>