[Bug 2049793] Re: [MTL] x86: Fix Cache info sysfs is not populated

This bug is awaiting verification that the linux-aws/6.8.0-1009.9 kernel
in -proposed solves the problem. Please test the kernel and update this
bug with the results. If the problem is solved, change the tag
'verification-needed-noble-linux-aws' to 'verification-done-noble-linux-
aws'. If the problem still exists, change the tag 'verification-needed-
noble-linux-aws' to 'verification-failed-noble-linux-aws'.


If verification is not done by 5 working days from today, this fix will
be dropped from the source code, and this bug will be closed.


See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how
to enable and use -proposed. Thank you!


** Tags added: kernel-spammed-noble-linux-aws-v2 verification-needed-noble-linux-aws

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https://bugs.launchpad.net/bugs/2049793

Title:
[MTL] x86: Fix Cache info sysfs is not populated

Status in intel:
New
Status in linux package in Ubuntu:
Fix Released
Status in linux source package in Noble:
Fix Released

Bug description:
[SRU Justification]

[Impact]

The interface /sys/devices/system/cpu/cpuX/cache is broken (not populated) if
CPUs have different numbers of subleaves in CPUID 4. This is the case of Intel
Meteor Lake.

[Fix]

https://lore.kernel.org/all/20231212222519.12834-1-ricardo.neri-calderon@linux.intel.com/
Reviewed, but probably will only land in v6.9.

[Test Case]

Check existence of cpu cache info:

$ ls /sys/devices/system/cpu/cpu0/cache/
index0 index1 index2 index3 uevent

[Where problems could occur]

This populates sysfs entries that should have been available, not
something new or alters existing interface.

[Other Info]

While this is targets v6.8 for Intel LPMD (Low Power Model Daemon)'s
use, only Noble and Unstable will be nominated for fix.

========== original bug report ==========

[Description]
  The interface /sys/devices/system/cpu/cpu*/cache is empty. In Meteorlake, not all CPUs have the same number of subleaves in the CPUID 4 leaf. The compute die CPUs have 3 subleaves whereas the CPUs in the SoC die have 2. This problem happens because Linux assumes that all CPUs have the same number of subleaves.

[Hardware Information]
  Architecture:
    Intel / AMD (x86_64)
  Platform(s):
    Meteor Lake
  Date HW is expected at Canonical:

  Component(s):
    x86

[Software Information]
  Target Version:
    24.04
  Target Kernel:
    6.8
  Commit IDs:
    TBD
  External Links:
    https://lore.kernel.org/all/20231212222519.12834-5-ricardo.neri-calderon@linux.intel.com/

[Business Justification]

[Testing guidance]

[External ID]
  LFE-6901

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