linux-kernel - [PATCH] x86/xen: mark boot CPU of PV guest in MSR_IA32

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Message-ID: <20241007104201.15607-1-jgross@suse.com>
Date: Mon,  7 Oct 2024 12:42:01 +0200
From: Juergen Gross <jgross@...e.com>
To: linux-kernel@...r.kernel.org,
	x86@...nel.org
Cc: Juergen Gross <jgross@...e.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	xen-devel@...ts.xenproject.org,
	Niels Dettenbach <nd@...dicat.com>
Subject: [PATCH] x86/xen: mark boot CPU of PV guest in MSR_IA32_APICBASE

Recent topology checks of the x86 boot code uncovered the need for
PV guests to have the boot cpu marked in the APICBASE MSR.

Fixes: 9d22c96316ac ("x86/topology: Handle bogus ACPI tables correctly")
Reported-by: Niels Dettenbach <nd@...dicat.com>
Signed-off-by: Juergen Gross <jgross@...e.com>
---
 arch/x86/xen/enlighten_pv.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 2c12ae42dc8b..d6818c6cafda 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1032,6 +1032,10 @@ static u64 xen_do_read_msr(unsigned int msr, int *err)
 	switch (msr) {
 	case MSR_IA32_APICBASE:
 		val &= ~X2APIC_ENABLE;
+		if (smp_processor_id() == 0)
+			val |= MSR_IA32_APICBASE_BSP;
+		else
+			val &= ~MSR_IA32_APICBASE_BSP;
 		break;
 	}
 	return val;
-- 
2.43.0