linux-kernel - [RFC PATCH v6 18/32] x86/apic: Initialize APIC ID for Secure AVIC

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Message-ID: <20250514071803.209166-19-Neeraj.Upadhyay@amd.com>
Date: Wed, 14 May 2025 12:47:49 +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: [RFC PATCH v6 18/32] 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.

Signed-off-by: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
---
Changes since v5:

 - Use common apic_set_reg().

 arch/x86/kernel/apic/x2apic_savic.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/x86/kernel/apic/x2apic_savic.c b/arch/x86/kernel/apic/x2apic_savic.c
index 186e69a5e169..618643e7242f 100644
--- a/arch/x86/kernel/apic/x2apic_savic.c
+++ b/arch/x86/kernel/apic/x2apic_savic.c
@@ -131,6 +131,18 @@ static void savic_write(u32 reg, u32 data)
 	}
 }
 
+static void init_apic_page(struct apic_page *ap)
+{
+	u32 apic_id;
+
+	/*
+	 * Before Secure AVIC is enabled, APIC msr reads are intercepted.
+	 * APIC_ID msr read returns the value from the Hypervisor.
+	 */
+	apic_id = native_apic_msr_read(APIC_ID);
+	apic_set_reg(ap, APIC_ID, apic_id);
+}
+
 static void savic_setup(void)
 {
 	void *backing_page;
@@ -138,6 +150,7 @@ static void savic_setup(void)
 	unsigned long gpa;
 
 	backing_page = this_cpu_ptr(apic_page);
+	init_apic_page(backing_page);
 	gpa = __pa(backing_page);
 
 	/*
-- 
2.34.1