[Xen-devel] [PATCH] x86/hvm: Fix restart of RTC periodic timer with vpt_align=1

[Kouya Shimura <kouya@xxxxxxxxxxxxxx>]

The commit 58afa7ef "x86/hvm: Run the RTC periodic timer on a
consistent time series" aligns the RTC periodic timer to the VM's boot time.
However, it's aligned later again to the system time in create_periodic_time()
with vpt_align=1. The next tick might be skipped.

Signed-off-by: Kouya Shimura <kouya@xxxxxxxxxxxxxx>
Cc: Tim Deegan <tim@xxxxxxx>
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/hvm/rtc.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/rtc.c b/xen/arch/x86/hvm/rtc.c
index d1a6848..cdedefe 100644
--- a/xen/arch/x86/hvm/rtc.c
+++ b/xen/arch/x86/hvm/rtc.c
@@ -130,7 +130,10 @@ static void rtc_timer_update(RTCState *s)
                 s->pt_code = period_code;
                 period = 1 << (period_code - 1); /* period in 32 Khz cycles */
                 period = DIV_ROUND(period * 1000000000ULL, 32768); /* in ns */
-                delta = period - ((NOW() - s->start_time) % period);
+                if ( v->domain->arch.hvm_domain.params[HVM_PARAM_VPT_ALIGN] )
+                    delta = 0;
+                else
+                    delta = period - ((NOW() - s->start_time) % period);
                 create_periodic_time(v, &s->pt, delta, period,
                                      RTC_IRQ, NULL, s);
             }
-- 
1.7.9.5


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