x86: Clean up APIC local timer handling.

1. Writing TMICT=0 disables the timer. Use this fact to simplify and
improve reprogram_timer(). In particular, we always write TMICT, and
write zero when we do not need a timer interrupt.

2. In HPET broadcast timer handler, set TMICT=0 when we mask the APIC
local timer. May as well do this early, before entering deep sleep.

3. In HVM-guest APIC emulation, disable the emulated local timer when
the guest sets TMICT=0. Previously we would issue an immediate
one-shot interrupt.

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

1 files changed, 9 insertions, 2 deletions

diff --git a/xen/arch/x86/hvm/vlapic.c b/xen/arch/x86/hvm/vlapic.c
index 6d1d7b9e71..83057f91f5 100644
--- a/xen/arch/x86/hvm/vlapic.c
+++ b/xen/arch/x86/hvm/vlapic.c
@@ -667,10 +667,17 @@ static int vlapic_write(struct vcpu *v, unsigned long address,
 
     case APIC_TMICT:
     {
-        uint64_t period = (uint64_t)APIC_BUS_CYCLE_NS *
-                            (uint32_t)val * vlapic->hw.timer_divisor;
+        uint64_t period;
 
         vlapic_set_reg(vlapic, APIC_TMICT, val);
+        if ( val == 0 )
+        {
+            destroy_periodic_time(&vlapic->pt);
+            break;
+        }
+
+        period = ((uint64_t)APIC_BUS_CYCLE_NS *
+                  (uint32_t)val * vlapic->hw.timer_divisor);
         create_periodic_time(current, &vlapic->pt, period, 
                              vlapic_lvtt_period(vlapic) ? period : 0,
                              vlapic->pt.irq, vlapic_pt_cb,