Bug 2203186

Summary:	glibc: Fix cache size detection for hypervisors or older AMD hardware
Product:	Red Hat Enterprise Linux 9	Reporter:	Carlos O'Donell <codonell>
Component:	glibc	Assignee:	Florian Weimer <fweimer>
Status:	MODIFIED ---	QA Contact:	Sergey Kolosov <skolosov>
Severity:	urgent	Docs Contact:
Priority:	unspecified
Version:	9.3	CC:	ashankar, codonell, dj, fweimer, mcermak, pfrankli, sipoyare
Target Milestone:	rc	Keywords:	Bugfix, Regression, Triaged
Target Release:	---
Hardware:	x86_64
OS:	Linux
Whiteboard:
Fixed In Version:	glibc-2.34-80.el9	Doc Type:	No Doc Update
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:
Bug Blocks:	2166709, 2166710

Description Carlos O'Donell 2023-05-11 13:10:10 UTC

The current -67 glibc build uses the upstream cache size detection code which is incorrect under certain hypervisors and older AMD hardware.

We need to do one of two things:
- Revert the current cache size detection code.
- Backport an upstream correction that supports the old cpuid mechanism and the new cpuid mechanism.

Comment 5 Carlos O'Donell 2023-07-14 21:26:05 UTC

We will be reverting the current AMD cacheline changes until we have a solution that works for old and new CPUs.

Comment 10 Carlos O'Donell 2023-08-14 14:28:26 UTC

Upstream commit:

commit dcad5c8578130dec7f35fd5b0885304b59f9f543
Author: Sajan Karumanchi <sajan.karumanchi>
Date:   Tue Aug 1 15:20:55 2023 +0000

    x86: Fix for cache computation on AMD legacy cpus.
    
    Some legacy AMD CPUs and hypervisors have the _cpuid_ '0x8000_001D'
    set to Zero, thus resulting in zeroed-out computed cache values.
    This patch reintroduces the old way of cache computation as a
    fail-safe option to handle these exceptions.
    Fixed 'level4_cache_size' value through handle_amd().
    
    Reviewed-by: Premachandra Mallappa <premachandra.mallappa>
    Tested-by: Florian Weimer <fweimer>

Committed to c9s:

commit 3a04eb2e1826da207b64a254af3d17e30a27db11
Author: Florian Weimer <fweimer>
Date:   Fri Aug 11 17:54:52 2023 +0200

    Fix AMD cache size computation for hypervisors, old CPUs (#2166710)
    
    Missing spec file update.
    
    Related: #2166710