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

[tip-bot2 for Neeraj Upadhyay]

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@xxxxxxx>
AuthorDate:    Thu, 28 Aug 2025 16:32:41 +05:30
Committer:     Borislav Petkov (AMD) <bp@xxxxxxxxx>
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@xxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Reviewed-by: Tianyu Lan <tiala@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/20250828110255.208779-2-Neeraj.Upadhyay@xxxxxxx
---
 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);
 
 	/*