linux-kernel - [PATCH v9 04/18] x86/apic: Initialize APIC ID for Secure AVIC

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Message-ID: <20250811094444.203161-5-Neeraj.Upadhyay@amd.com>
Date: Mon, 11 Aug 2025 15:14:30 +0530
From: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
To: <linux-kernel@...r.kernel.org>
CC: <bp@...en8.de>, <tglx@...utronix.de>, <mingo@...hat.com>,
	<dave.hansen@...ux.intel.com>, <Thomas.Lendacky@....com>, <nikunj@....com>,
	<Santosh.Shukla@....com>, <Vasant.Hegde@....com>,
	<Suravee.Suthikulpanit@....com>, <David.Kaplan@....com>, <x86@...nel.org>,
	<hpa@...or.com>, <peterz@...radead.org>, <seanjc@...gle.com>,
	<pbonzini@...hat.com>, <kvm@...r.kernel.org>,
	<kirill.shutemov@...ux.intel.com>, <huibo.wang@....com>,
	<naveen.rao@....com>, <francescolavra.fl@...il.com>, <tiala@...rosoft.com>
Subject: [PATCH v9 04/18] x86/apic: Initialize APIC ID for Secure AVIC

Initialize the APIC ID in the Secure AVIC APIC backing page with
the APIC_ID msr value read from Hypervisor. CPU topology evaluation
later during boot would catch and report any duplicate APIC ID for
two CPUs.

Reviewed-by: Tianyu Lan <tiala@...rosoft.com>
Signed-off-by: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
---
Changes since v8:
 - Added Tianyu's Reviewed-by.
 - Code cleanup.

 arch/x86/kernel/apic/x2apic_savic.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kernel/apic/x2apic_savic.c b/arch/x86/kernel/apic/x2apic_savic.c
index 86a522685230..55edc6c30ba4 100644
--- a/arch/x86/kernel/apic/x2apic_savic.c
+++ b/arch/x86/kernel/apic/x2apic_savic.c
@@ -141,6 +141,12 @@ static void savic_setup(void)
 	enum es_result res;
 	unsigned long gpa;
 
+	/*
+	 * Before Secure AVIC is enabled, APIC msr reads are intercepted.
+	 * APIC_ID msr read returns the value from the Hypervisor.
+	 */
+	apic_set_reg(ap, APIC_ID, native_apic_msr_read(APIC_ID));
+
 	gpa = __pa(ap);
 
 	/*
-- 
2.34.1