x86/pvclock: Zero last_value on resume

If the guest domain has been suspend/resumed or migrated, then the
system clock backing the pvclock clocksource may revert to a smaller
value (ie, can be non-monotonic across the migration/save-restore).

Make sure we zero last_value in that case so that the domain
continues to see clock updates.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 8 insertions, 0 deletions

diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index 7f7e577a0e39..31d84acc1512 100644
--- a/arch/x86/include/asm/pvclock.h
+++ b/arch/x86/include/asm/pvclock.h
@@ -11,6 +11,7 @@ unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src);
 void pvclock_read_wallclock(struct pvclock_wall_clock *wall,
                             struct pvclock_vcpu_time_info *vcpu,
                             struct timespec *ts);
+void pvclock_resume(void);
 
 /*
  * Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
index 008b91eefa18..42eb3300dfc6 100644
--- a/arch/x86/kernel/pvclock.c
+++ b/arch/x86/kernel/pvclock.c
@@ -83,6 +83,11 @@ unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
 
 static atomic64_t last_value = ATOMIC64_INIT(0);
 
+void pvclock_resume(void)
+{
+        atomic64_set(&last_value, 0);
+}
+
 cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
 {
         struct pvclock_shadow_time shadow;
diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index b2bb5aa3b054..5da5e53fb94c 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -426,6 +426,8 @@ void xen_timer_resume(void)
 {
         int cpu;
 
+        pvclock_resume();
+
         if (xen_clockevent != &xen_vcpuop_clockevent)
                 return;