linux-kernel - [tip: x86/apic] x86/apic: Initialize APIC ID for Secure AVIC

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Message-ID: <175680940770.1920.14902722425798051621.tip-bot2@tip-bot2>
Date: Tue, 02 Sep 2025 10:36:47 -0000
From: "tip-bot2 for Neeraj Upadhyay" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Neeraj Upadhyay <Neeraj.Upadhyay@....com>,
 "Borislav Petkov (AMD)" <bp@...en8.de>, Tianyu Lan <tiala@...rosoft.com>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/apic] x86/apic: Initialize APIC ID for Secure AVIC

The following commit has been merged into the x86/apic branch of tip:

Commit-ID:     45e2cef568cdf87cb06c9783b45c8f08d1ab1cec
Gitweb:        https://git.kernel.org/tip/45e2cef568cdf87cb06c9783b45c8f08d1ab1cec
Author:        Neeraj Upadhyay <Neeraj.Upadhyay@....com>
AuthorDate:    Thu, 28 Aug 2025 16:32:41 +05:30
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Mon, 01 Sep 2025 12:21:55 +02:00

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 the hypervisor. CPU topology evaluation later during boot
would catch and report any duplicate APIC ID for two CPUs.

Signed-off-by: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Reviewed-by: Tianyu Lan <tiala@...rosoft.com>
Link: https://lore.kernel.org/20250828110255.208779-2-Neeraj.Upadhyay@amd.com
---
 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 5479605..56c51ea 100644
--- a/arch/x86/kernel/apic/x2apic_savic.c
+++ b/arch/x86/kernel/apic/x2apic_savic.c
@@ -150,6 +150,12 @@ 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);
 
 	/*