[PATCH 0/7] x86/topology: Improve CPUID.1F handling

Zhang Rui
2022-08-12T16:38:02Z

On Intel AlderLake-N platforms where there are Ecores only, the Ecore
Module topology is enumerated via CPUID.1F Module level, which has not
been supported by Linux kernel yet.

This exposes two issues in current CPUID.1F handling code.
1. Linux interprets the Module id bits as package id and erroneously
reports a multi module system as a multi-package system.
2. Linux excludes the unknown Module id bits from the core_id, and results
in duplicate core_id’s shown in a package after the first issue solved.

Plus that, a third problem is observed on Intel Hybrid ADL-S/P platforms.
The return value of CPUID.1F SMT level EBX (number of siblings) differs on
Pcore CPUs and Ecore CPUs, and results in inconsistent smp_num_siblings
value based on the Pcore/Ecore CPU enumeration order. This could bring
some potential issues although we have not observed any functionalities
issues so far.

Patch 1/7 and 2/7 fix the first two issues. And at the same time, it
reveals a reality that the core_id could be sparse on platforms with
CPUID.1F support.
Patch 3/7 improves coretemp driver code to be able to handle sparse core
id, which is the only driver that uses core_id as array index and run on
platforms with CPUID.1F support.

Patch 4/7 to 7/7 propose a fix for the third problem and update the
related Documents.

The patch series have been tested on Intel ICL/CLX servers, SKL/KBL/ADL
clients.

thanks,
-rui