linux-kernel - Re: [PATCH v4 0/4] x86/cpu/topology: Fix the preferred order of initial APIC ID parsing on AMD/Hygon

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Message-ID: <f0ef442b-44ba-465b-86aa-93a810f8e488@amd.com>
Date: Mon, 25 Aug 2025 14:33:17 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Borislav Petkov <bp@...en8.de>
CC: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Dave
 Hansen <dave.hansen@...ux.intel.com>, Sean Christopherson
	<seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, <x86@...nel.org>,
	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>, Tom Lendacky <thomas.lendacky@....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>, Naveen N Rao <naveen@...nel.org>
Subject: Re: [PATCH v4 0/4] x86/cpu/topology: Fix the preferred order of
 initial APIC ID parsing on AMD/Hygon

Hello Boris,

On 8/25/2025 2:19 PM, Borislav Petkov wrote:
> On Mon, Aug 25, 2025 at 07:57:28AM +0000, K Prateek Nayak wrote:
>> This led us down a rabbit hole of XTOPOLOGY vs TOPOEXT support, preferred
> 
> So in order to save people the rabbit hole wandering each time they (or we)
> have to undertake, I think we should document what the whole logic and
> precedences are wrt CPUID leafs and topology. What should be done where and so
> on.
> 
> And those commit messages have a lot of text which explains that and I think
> it would be worth the effort to start holding it down here
> Documentation/arch/x86/topology.rst
> 
> No long texts, no big explanations - just the plain facts and what the current
> strategy is wrt to which CPUID leafs we parse for what in what order and so
> on.
> 
> You could start the AMD side, it doesn't have to be exhaustive - just the
> facts from this rabbit hole trip.
> 
> And then we'll keep extending it and filling out the details so that it is
> right there written down in one place.
> 
> Makes sense?

Ack. I'll start working on it.

-- 
Thanks and Regards,
Prateek