linux-kernel - Re: [PATCH v4 1/4] x86/cpu/topology: Use initial APIC ID from XTOPOLOGY leaf on AMD/HYGON

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Message-ID: <aa5cb79b-914a-474c-9015-e36d54149cf8@amd.com>
Date: Mon, 25 Aug 2025 13:47:54 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Thomas Gleixner <tglx@...utronix.de>, 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>,
	<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>, 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>,
	<stable@...r.kernel.org>
Subject: Re: [PATCH v4 1/4] x86/cpu/topology: Use initial APIC ID from
 XTOPOLOGY leaf on AMD/HYGON

On 8/25/2025 1:27 PM, K Prateek Nayak wrote:
> AMD64 Architecture Programmer's Manual Volume 2: System Programming Pub.
> 24593 Rev. 3.42 [2] Section 16.12 "x2APIC_ID" mentions the Extended
> Enumeration leaf 0x8000001e (which was later superseded by the extended

The above should have been CPUID leaf 0xb (Fn0000_000B_EDX[31:0]) and
not 0x8000001e. Sorry for the oversight.

> leaf 0x80000026) provides the full x2APIC ID under all circumstances
> unlike the one reported by CPUID leaf 0x8000001e EAX which depends on
> the mode in which APIC is configured.
-- 
Thanks and Regards,
Prateek