[tip:x86/urgent] x86/xen: Disable CPU0 hotplug for Xen PV

[tip-bot for Juergen Gross]

Commit-ID:  999696752db1099aba595aac4f8d881f8c7cf4e6
Gitweb:     https://git.kernel.org/tip/999696752db1099aba595aac4f8d881f8c7cf4e6
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Wed, 12 Sep 2018 19:41:22 +0200
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 12 Sep 2018 21:15:02 +0200

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@xxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: boris.ostrovsky@xxxxxxxxxx
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20180912174122.24282-1-jgross@xxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 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;
 
 	/*