3.0-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Stefano Stabellini <[email protected]>

commit 3c05c4bed4ccce3f22f6d7899b308faae24ad198 upstream.

Fix regression for HVM case on older (<4.1.1) hypervisors caused by

  commit 99bbb3a84a99cd04ab16b998b20f01a72cfa9f4f
  Author: Stefano Stabellini <[email protected]>
  Date:   Thu Dec 2 17:55:10 2010 +0000

    xen: PV on HVM: support PV spinlocks and IPIs

This change replaced the SMP operations with event based handlers without
taking into account that this only works when the hypervisor supports
callback vectors. This causes unexplainable hangs early on boot for
HVM guests with more than one CPU.

BugLink: http://bugs.launchpad.net/bugs/791850

Signed-off-by: Stefan Bader <[email protected]>
Signed-off-by: Stefano Stabellini <[email protected]>
Tested-and-Reported-by: Stefan Bader <[email protected]>
Signed-off-by: Konrad Rzeszutek Wilk <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

---
 arch/x86/xen/smp.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -521,8 +521,6 @@ static void __init xen_hvm_smp_prepare_c
        native_smp_prepare_cpus(max_cpus);
        WARN_ON(xen_smp_intr_init(0));
 
-       if (!xen_have_vector_callback)
-               return;
        xen_init_lock_cpu(0);
        xen_init_spinlocks();
 }
@@ -546,6 +544,8 @@ static void xen_hvm_cpu_die(unsigned int
 
 void __init xen_hvm_smp_init(void)
 {
+       if (!xen_have_vector_callback)
+               return;
        smp_ops.smp_prepare_cpus = xen_hvm_smp_prepare_cpus;
        smp_ops.smp_send_reschedule = xen_smp_send_reschedule;
        smp_ops.cpu_up = xen_hvm_cpu_up;


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