Re: [patch V3 00/40] x86/cpu: Rework the topology evaluation

From: Juergen Gross
Date: Wed Aug 02 2023 - 07:56:49 EST

On 02.08.23 12:20, Thomas Gleixner wrote:

This is the follow up to V2:

which addresses the review feedback and some fallout reported on and


This reworks the way how topology information is evaluated via CPUID
in preparation for a larger topology management overhaul to address
shortcomings of the current code vs. hybrid systems and systems which make
use of the extended topology domains in leaf 0x1f. Aside of that it's an
overdue spring cleaning to get rid of accumulated layers of duct tape and

What changed vs. V2:

- Decoded and fixed the fallout vs. XEN/PV reported by Juergen. Thanks to
Juergen for the remote hand debugging sessions!

That's addressed in the first two new patches in this series. Summary:
XEN/PV booted by pure chance since the addition of SMT control 5 years

- Fixed the off by one in the AMD parser which was debugged by Michael

- Addressed review comments from various people

As discussed in:

this series unfortunately brings the Hyper-V BIOS inconsistency into
effect, which results in a slight performance impact. The L3 association
which "worked" so far by exploiting the inconsistency of the Linux topology
code is not longer supportable as we really need to get the actual short
comings of our topology management addressed in a consistent way.

The series is based on V3 of the APIC cleanup series:

and also available on top of that from git:

git:// topo-cpuid-v3



For Xen PV (dom0 and unprivileged guest):

Tested-by: Juergen Gross <jgross@xxxxxxxx>


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