linux-kernel - [PATCH] x86/xen: disable cpu0 hotplug for xen pv

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Message-Id: <20180912174122.24282-1-jgross@suse.com>
Date:   Wed, 12 Sep 2018 19:41:22 +0200
From:   Juergen Gross <jgross@...e.com>
To:     linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        x86@...nel.org
Cc:     boris.ostrovsky@...cle.com, hpa@...or.com, tglx@...utronix.de,
        mingo@...hat.com, Juergen Gross <jgross@...e.com>
Subject: [PATCH] x86/xen: disable cpu0 hotplug for xen pv

Xen pv guests don't allow cpu0 hotplug, so disable it.

Signed-off-by: Juergen Gross <jgross@...e.com>
---
 arch/x86/kernel/topology.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/topology.c b/arch/x86/kernel/topology.c
index 12cbe2b88c0f..738bf42b0218 100644
--- a/arch/x86/kernel/topology.c
+++ b/arch/x86/kernel/topology.c
@@ -111,8 +111,10 @@ int arch_register_cpu(int num)
 	/*
 	 * Currently CPU0 is only hotpluggable on Intel platforms. Other
 	 * vendors can add hotplug support later.
+	 * Xen PV guests don't support CPU0 hotplug at all.
 	 */
-	if (c->x86_vendor != X86_VENDOR_INTEL)
+	if (c->x86_vendor != X86_VENDOR_INTEL ||
+	    boot_cpu_has(X86_FEATURE_XENPV))
 		cpu0_hotpluggable = 0;
 
 	/*
-- 
2.16.4