x86/KEXEC: disable hpet legacy broadcasts earlier

On x2apic machines which booted in xapic mode,
hpet_disable_legacy_broadcast() sends an event check IPI to all online
processors.  This leads to a protection fault as the genapic blindly
pokes x2apic MSRs while the local apic is in xapic mode.

One option is to change genapic when we shut down the local apic, but
there are still problems with trying to IPI processors in the online
processor map which are actually sitting in NMI loops

Another option is to have each CPU take itself out of the online CPU
map during the NMI shootdown.

Realistically however, disabling hpet legacy broadcasts earlier in the
kexec path is the easiest fix to the problem.

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

xen/arch/x86/crash.c

@@ -29,6 +29,7 @@
 #include <asm/io_apic.h>
 #include <xen/iommu.h>
 #include <xen/pci.h>
+#include <asm/hpet.h>
 
 static atomic_t waiting_for_crash_ipi;
 static unsigned int crashing_cpu;
@@ -61,6 +62,9 @@ static void nmi_shootdown_cpus(void)
 
     local_irq_disable();
 
+    if ( hpet_broadcast_is_available() )
+        hpet_disable_legacy_broadcast();
+
     crashing_cpu = smp_processor_id();
     local_irq_count(crashing_cpu) = 0;
 

xen/arch/x86/machine_kexec.c

@@ -85,9 +85,6 @@ void machine_kexec(xen_kexec_image_t *image)
         .limit = LAST_RESERVED_GDT_BYTE
     };
 
-    if ( hpet_broadcast_is_available() )
-        hpet_disable_legacy_broadcast();
-
     /* We are about to permenantly jump out of the Xen context into the kexec
      * purgatory code.  We really dont want to be still servicing interupts.
      */