1 files changed, 28 insertions, 9 deletions

diff --git a/sys/dev/xen/timer/timer.c b/sys/dev/xen/timer/timer.c
index 354085bc183a..6c0a140ec762 100644
--- a/sys/dev/xen/timer/timer.c
+++ b/sys/dev/xen/timer/timer.c
@@ -45,6 +45,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/smp.h>
 #include <sys/limits.h>
 #include <sys/clock.h>
+#include <sys/proc.h>
 
 #include <xen/xen-os.h>
 #include <xen/features.h>
@@ -230,22 +231,22 @@ xen_fetch_vcpu_tinfo(struct vcpu_time_info *dst, struct vcpu_time_info *src)
 /**
  * \brief Get the current time, in nanoseconds, since the hypervisor booted.
  *
+ * \param vcpu		vcpu_info structure to fetch the time from.
+ *
  * \note This function returns the current CPU's idea of this value, unless
  *       it happens to be less than another CPU's previously determined value.
  */
 static uint64_t
-xen_fetch_vcpu_time(void)
+xen_fetch_vcpu_time(struct vcpu_info *vcpu)
 {
 	struct vcpu_time_info dst;
 	struct vcpu_time_info *src;
 	uint32_t pre_version;
 	uint64_t now;
 	volatile uint64_t last;
-	struct vcpu_info *vcpu = DPCPU_GET(vcpu_info);
 
 	src = &vcpu->time;
 
-	critical_enter();
 	do {
 		pre_version = xen_fetch_vcpu_tinfo(&dst, src);
 		barrier();
@@ -266,16 +267,24 @@ xen_fetch_vcpu_time(void)
 		}
 	} while (!atomic_cmpset_64(&xen_timer_last_time, last, now));
 
-	critical_exit();
-
 	return (now);
 }
 
 static uint32_t
 xentimer_get_timecount(struct timecounter *tc)
 {
+	uint64_t vcpu_time;
+
+	/*
+	 * We don't disable preemption here because the worst that can
+	 * happen is reading the vcpu_info area of a different CPU than
+	 * the one we are currently running on, but that would also
+	 * return a valid tc (and we avoid the overhead of
+	 * critical_{enter/exit} calls).
+	 */
+	vcpu_time = xen_fetch_vcpu_time(DPCPU_GET(vcpu_info));
 
-	return ((uint32_t)xen_fetch_vcpu_time() & UINT_MAX);
+	return (vcpu_time & UINT32_MAX);
 }
 
 /**
@@ -305,7 +314,10 @@ xen_fetch_wallclock(struct timespec *ts)
 static void
 xen_fetch_uptime(struct timespec *ts)
 {
-	uint64_t uptime = xen_fetch_vcpu_time();
+	uint64_t uptime;
+
+	uptime = xen_fetch_vcpu_time(DPCPU_GET(vcpu_info));
+
 	ts->tv_sec = uptime / NSEC_IN_SEC;
 	ts->tv_nsec = uptime % NSEC_IN_SEC;
 }
@@ -354,7 +366,7 @@ xentimer_intr(void *arg)
 	struct xentimer_softc *sc = (struct xentimer_softc *)arg;
 	struct xentimer_pcpu_data *pcpu = DPCPU_PTR(xentimer_pcpu);
 
-	pcpu->last_processed = xen_fetch_vcpu_time();
+	pcpu->last_processed = xen_fetch_vcpu_time(DPCPU_GET(vcpu_info));
 	if (pcpu->timer != 0 && sc->et.et_active)
 		sc->et.et_event_cb(&sc->et, sc->et.et_arg);
 
@@ -398,7 +410,14 @@ xentimer_et_start(struct eventtimer *et,
 	struct xentimer_softc *sc = et->et_priv;
 	int cpu = PCPU_GET(vcpu_id);
 	struct xentimer_pcpu_data *pcpu = DPCPU_PTR(xentimer_pcpu);
+	struct vcpu_info *vcpu = DPCPU_GET(vcpu_info);
 	uint64_t first_in_ns, next_time;
+#ifdef INVARIANTS
+	struct thread *td = curthread;
+#endif
+
+	KASSERT(td->td_critnest != 0,
+	    ("xentimer_et_start called without preemption disabled"));
 
 	/* See sbttots() for this formula. */
 	first_in_ns = (((first >> 32) * NSEC_IN_SEC) +
@@ -415,7 +434,7 @@ xentimer_et_start(struct eventtimer *et,
 	do {
 		if (++i == 60)
 			panic("can't schedule timer");
-		next_time = xen_fetch_vcpu_time() + first_in_ns;
+		next_time = xen_fetch_vcpu_time(vcpu) + first_in_ns;
 		error = xentimer_vcpu_start_timer(cpu, next_time);
 	} while (error == -ETIME);