pvclock: detect watchdog reset at pvclock read

Implement reset of kernel watchdogs at pvclock read time. This avoids
adding special code to every watchdog.

This is possible for watchdogs which measure time based on sched_clock() or
ktime_get() variants.

Suggested by Don Zickus.
Acked-by: Don Zickus <dzickus@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

arch/x86/include/asm/pvclock.h

@@ -14,6 +14,8 @@ void pvclock_read_wallclock(struct pvclock_wall_clock *wall,
 			    struct timespec *ts);
 void pvclock_resume(void);
 
+void pvclock_touch_watchdogs(void);
+
 /*
  * Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
  * yielding a 64-bit result.

arch/x86/kernel/kvmclock.c

@@ -139,6 +139,7 @@ bool kvm_check_and_clear_guest_paused(void)
 	src = &hv_clock[cpu].pvti;
 	if ((src->flags & PVCLOCK_GUEST_STOPPED) != 0) {
 		src->flags &= ~PVCLOCK_GUEST_STOPPED;
+		pvclock_touch_watchdogs();
 		ret = true;
 	}
 

arch/x86/kernel/pvclock.c

@@ -43,6 +43,13 @@ unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
 	return pv_tsc_khz;
 }
 
+void pvclock_touch_watchdogs(void)
+{
+	touch_softlockup_watchdog_sync();
+	clocksource_touch_watchdog();
+	rcu_cpu_stall_reset();
+}
+
 static atomic64_t last_value = ATOMIC64_INIT(0);
 
 void pvclock_resume(void)
@@ -74,6 +81,11 @@ cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
 		version = __pvclock_read_cycles(src, &ret, &flags);
 	} while ((src->version & 1) || version != src->version);
 
+	if (unlikely((flags & PVCLOCK_GUEST_STOPPED) != 0)) {
+		src->flags &= ~PVCLOCK_GUEST_STOPPED;
+		pvclock_touch_watchdogs();
+	}
+
 	if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
 		(flags & PVCLOCK_TSC_STABLE_BIT))
 		return ret;