x86/xen: Disable CPU0 hotplug for Xen PV

jgross1 · Ingo Molnar · commit 999696752db1 · 2018-09-12T21:15:02.000+02:00
Xen PV guests don't allow CPU0 hotplug, so disable it. Signed-off-by: Juergen Gross <jgross@suse.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: boris.ostrovsky@oracle.com Cc: xen-devel@lists.xenproject.org Link: http://lkml.kernel.org/r/20180912174122.24282-1-jgross@suse.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git 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;
 
 	/*
