KEXEC BUG: nmi_shootdown_cpus doesn't look after the interrupt flag

nmi_shootdown_cpus is part of the kexec path, coming from a panic, and
as such can be called both with interrupts enabled or disabled. We
really dont want to accidentally set IF.

Therefore, use save/restore in preference to disable/enable.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

diff -r a6f5c3a474e3 xen/arch/x86/crash.c
--- a/xen/arch/x86/crash.c	Wed Jun 15 11:47:12 2011 +0100
+++ b/xen/arch/x86/crash.c	Wed Jun 15 11:57:12 2011 +0100
@@ -57,7 +57,7 @@ static void nmi_shootdown_cpus(void)
 {
     unsigned long msecs;
 
-    local_irq_disable();
+    BUG_ON(local_irq_is_enabled());
 
     crashing_cpu = smp_processor_id();
     local_irq_count(crashing_cpu) = 0;
@@ -79,14 +79,14 @@ static void nmi_shootdown_cpus(void)
 
     __stop_this_cpu();
     disable_IO_APIC();
-
-    local_irq_enable();
 }
 
 void machine_crash_shutdown(void)
 {
     crash_xen_info_t *info;
 
+    local_irq_disable();
+
     nmi_shootdown_cpus();
 
     info = kexec_crash_save_info();