x86: Clean up vpt-align patch.

Also disable by default if not specified in domain config. Otherwise
the feature would be incorrectly enabled for old saved domain images.

Signed-off-by: Keir Fraser <keir.fraser@citrix.com>

1 files changed, 11 insertions, 5 deletions

diff --git a/xen/arch/x86/hvm/vpt.c b/xen/arch/x86/hvm/vpt.c
index 33f2400a0e..fe4ec99129 100644
--- a/xen/arch/x86/hvm/vpt.c
+++ b/xen/arch/x86/hvm/vpt.c
@@ -384,17 +384,23 @@ void create_periodic_time(
     pt->period_cycles = (u64)period;
     pt->one_shot = !period;
     pt->scheduled = NOW() + delta;
-    /*
-     * Offset LAPIC ticks from other timer ticks. Otherwise guests which use
-     * LAPIC ticks for process accounting can see long sequences of process
-     * ticks incorrectly accounted to interrupt processing.
-     */
+
     if ( !pt->one_shot )
     {
         if ( v->domain->arch.hvm_domain.params[HVM_PARAM_VPT_ALIGN] )
+        {
             pt->scheduled = align_timer(pt->scheduled, pt->period);
+        }
         else if ( pt->source == PTSRC_lapic )
+        {
+            /*
+             * Offset LAPIC ticks from other timer ticks. Otherwise guests
+             * which use LAPIC ticks for process accounting can see long
+             * sequences of process ticks incorrectly accounted to interrupt
+             * processing (seen with RHEL3 guest).
+             */
             pt->scheduled += delta >> 1;
+        }
     }
 
     pt->cb = cb;