linux-kernel - Re: [PATCH v5 1/4] x86/cpu/topology: Always try cpu_parse_topology

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Message-ID: <87o6rirrvc.ffs@tglx>
Date: Wed, 10 Sep 2025 22:10:15 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: K Prateek Nayak <kprateek.nayak@....com>, Ingo Molnar
 <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen
 <dave.hansen@...ux.intel.com>, Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Jonathan Corbet <corbet@....net>,
 x86@...nel.org
Cc: Naveen rao <naveen.rao@....com>, Sairaj Kodilkar <sarunkod@....com>, "H.
 Peter Anvin" <hpa@...or.com>, "Peter Zijlstra (Intel)"
 <peterz@...radead.org>, "Xin Li (Intel)" <xin@...or.com>, Pawan Gupta
 <pawan.kumar.gupta@...ux.intel.com>, linux-kernel@...r.kernel.org,
 kvm@...r.kernel.org, Mario Limonciello <mario.limonciello@....com>,
 "Gautham R. Shenoy" <gautham.shenoy@....com>, Babu Moger
 <babu.moger@....com>, Suravee Suthikulpanit
 <suravee.suthikulpanit@....com>, K Prateek Nayak <kprateek.nayak@....com>,
 stable@...r.kernel.org, Naveen N
 Rao <naveen@...nel.org>
Subject: Re: [PATCH v5 1/4] x86/cpu/topology: Always try
 cpu_parse_topology_ext() on AMD/Hygon

On Mon, Sep 01 2025 at 17:04, K. Prateek Nayak wrote:
> Unconditionally call cpu_parse_topology_ext() on AMD and Hygon
> processors to first parse the topology using the XTOPOLOGY leaves
> (0x80000026 / 0xb) before using the TOPOEXT leaf (0x8000001e).
>
> While at it, break down the single large comment in parse_topology_amd()
> to better highlight the purpose of each CPUID leaf.
>
> Cc: stable@...r.kernel.org # Only v6.9 and above; Depends on x86 topology rewrite
> Link: https://lore.kernel.org/lkml/1529686927-7665-1-git-send-email-suravee.suthikulpanit@amd.com/ [1]
> Link: https://lore.kernel.org/lkml/20080818181435.523309000@linux-os.sc.intel.com/ [2]
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537 [3]
> Suggested-by: Naveen N Rao (AMD) <naveen@...nel.org>
> Fixes: 3986a0a805e6 ("x86/CPU/AMD: Derive CPU topology from CPUID function 0xB when available")
> Signed-off-by: K Prateek Nayak <kprateek.nayak@....com>
> ---
> Changelog v4..v5:
>
> o Made a note on only targeting versions >= v6.9 for stable backports
>   since the fix depends on the x86 topology rewrite. (Boris)

Shouldn't that be backported? I think so, so leave that v6.9 and above
comment out. The stable folks will notice that it does not apply to pre
6.9 kernels and send you a nice email asking you to provide a solution
for pre 6.9 stable kernels.

Thanks,

        tglx